IASTA-2010

G–O–1

Synthesis of Solid Lipid Nanoparticles in a Low Temperature Aerosol Reactor (LoTAR)

Amol A. Pawar and Chandra Venkataraman

Department of Chemical Engineering, Indian Institute of Technology Bombay

Powai, Mumbai, Maharashtra - 400076, India

Background and motivation

In the last two decades, nanoparticles, including drug particles, polymeric particles, and solid lipid nanoparticles have been developed for systemic, oral, pulmonary and transdermal delivery [1]. They contain a therapeutic agent dispersed in or conjugated on the surface. Advantages include enhancement of dissolution, sustained/controlled release, drug targeting (cellular/tissue) and improved stability of therapeutic agents, especially proteins, peptides and nucleic acids. Polymeric nanoparticles are reported to high cytotoxicity, while solid lipid nanoparticles (SLN) have lower cytotoxicity since their constituents naturally occur in the human body[1]. Particle properties of importance are size and size distribution, degree of crystallinity and morphology (core-shell or dispersed). Current methods of SLN synthesis, like high pressure/shear homogenization or solvent evaporation, need extensive post processing steps and exhibit limitations in size control, drug loading capability and dose reproducibility [2].

Aerosol synthesis offers a single step continuous process to produce nanoparticles. Gas- phase high-temperature aerosol reactors have seen broad application to inorganic nanomaterial synthesis. Droplet-phase aerosol synthesis has been recently attempted for drug nanoparticle synthesis [3] and can be explored for synthesis of lipid nanoparticles, which are thermolabile. Changes in the particle size and morphology with temperature and precursor have been studied for pure drug and biopolymer systems [4]. In this work, we investigate the control of SLN properties through synthesis in a low temperature aerosol reactor (our designation, LoTAR). We investigate control of aerosol processing parameters, like evaporation rate of the precursor solvent, for the control of particle size and crystallinity.

Experimental methods

The LoTAR (Figure 1) comprised of a collision-type air jet atomizer (Model 3076, TSI Inc. Particle Instruments, St. Paul, USA), aerosol reactor (internal diameter 30 mm and length 800 mm), aerosol diluter (internal diameter 70 mm and length 250 mm) and a cascade impactor (Micro-orifice uniform deposit impactor, MOUDI 110, MSP) for aerosol collection. The upstream pressure of the atomizer was 35 psig and the precursor solution was fed with syringe pump at 0.6ml/min. The resulting atomized droplets were suspended in a nitrogen flow through the reactor, wherein the solvent evaporated to yield nanoparticles. After the evaporation stage, aerosol was diluted with zero-particle air, to

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bring down the total particle number concentration, within the operating limits of the characterization instruments.

Figure 1. Schematic of low temperature atmospheric pressure aerosol reactor for synthesis of solid lipid nanoparticles

Mobility diameter measurement was made using a scanning mobility particle sizer (SMPS, Model 3936, TSI Inc. Particle Instruments, St. Paul, USA) with a differential mobility analyzer (Long DMA, Model 3081, TSI Inc. Particle Instruments, St. Paul, USA) and a condensation particle counter (CPC, Model 3775, TSI Inc. Particle Instruments, St. Paul, USA). Crystalline state was determined by X-ray diffraction (XRD, Model X’Pert PRO, PANalytical, Almelo, The Netherlands) and differential scanning calorimetry (DSC, Model 2000, DuPont USA), on particles collected by impaction (MOUDI, Model 110, MSP Corporation, Minnesota, USA). Morphology of particles, collected by interception, was examined by electron microscopy (TEM, Model Philips CM200, FEI Company, Eindhoven, The Netherlands).

Results and discussion

The evaporation rate of solvent is believed to govern particle size and morphology, with the formation of small, dense particles at lower evaporation rates and larger, porous or hollow particles at higher evaporation rates [5]. Further, evaporation rate has the potential to influence crystal structure, with less ordered structures which could encapsulate more drug, forming at higher evaporation rates. To study the effect of evaporation rates on SLN size and morphology, stearic acid SLN were synthesized in the LoTAR using a choice of precursor solvents, with different physical properties. Solvent vapor pressure which directly affects evaporation rate, was varied from low (cyclohexane, Ps=16229Pa) to high (chloroform and dichloromethane, Ps=31964Pa and 69572Pa, respectively) values.

SLN synthesized at low evaporation rate (cyclohexane) were of smaller sizes, in terms of lower mean mobility diameter (86 ± 3 nm) measured by the SMPS. At higher evaporations rates (chloroform and dichloromethane), SLN of larger sizes (104 ± 12 nm and 98 ± 5 nm mobility diameter, respectively) were synthesized (Figure 2). The size distributions were polydisperse (with geometric standard deviation, GSD, of 1.7-1.9), resulting from the polydisperse droplet size distributions generated by the atomizer. The

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difference in SLN size was statistically significant at the 95% confidence level (P<0.05, by one-way analysis of variance, Tukey test).

Mobility diameter (nm)

Figure 2. Measured number particle size distribution curves for lipid nanoparticles synthesized in the LoTAR. Each value reported is the MEAN ± STDEV of three experiments

The kinetics of supersaturation, which increases with evaporation rate, is believed to significantly affect both nucleation and crystal growth processes. At higher evaporation rates solute molecules do not get sufficient time to arrange themselves in a crystalline lattice and thus, exhibit small order intra- and inter-crystal arrangement or amorphous properties [6]. To determine the crystalline state of lipids in SLN, X-ray diffraction patterns and melting enthalpies of the SLN were measured and analyzed vis-à-vis those of bulk stearic acid. Bulk stearic acid was found to have a monoclinic crystalline structure of the C-form similar to the standard diffractogram provided by International center for diffraction data (ICDD, reference code: 00-038-1923). SLN synthesized at lower evaporation rates (using cyclohexane and chloroform solvents) had mixed crystalline and amorphous states, with lower crystalline behavior than the bulk compound. SLN synthesized at the highest evaporation rate (dichloromethane solvent) showed complete loss of crystallinity (noisy diffractogram with no crystalline peaks).

Changes in the crystallinity of SLN were further supported by measurement of melting enthalpies of the SLN and bulk stearic acid. Melting enthalpy is the amount of thermal energy which must be absorbed or evolved for 1 mole of a substance to change states from a solid to a liquid or vice versa. It varies with bond strength among the molecules and their relative ordering. For a crystalline substance, where molecules are arranged in an order favoring thermodynamic stability, melting enthalpy is higher than for an amorphous substance whose ordering is relatively thermodynamically unstable. A higher melting enthalpy of SLN synthesized at low evaporation rates (198.9J/g), close to that of bulk stearic acid (199.1 J/g), indicated crystalline stearic acid and persistence of crystal structure. In contrast, SLN synthesized at higher evaporation rates, had lower melting enthalpies (191.1 J/g and 80.30 J/g), corroborating a less well-ordered or more amorphous structure.

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Studies of the influence of evaporation on the morphology of particles [6, 7] indicate increases in nucleation rate and numbers of crystals formed, with increasing evaporation rate, eventually resulting in hollow, non-spheriodal particles. The morphology of the SLN was examined using TEM imaging. Small, spherical SLN, with uniform surface morphology were obtained at lower evaporation rates (cyclohexane). However, larger asymmetric SLN were observed using fast evaporating solvents (chloroform and dichloromethane). The study demonstrates proof-of-concept of the control of nanoparticle size and properties through aerosol processing in a LoTAR. Manipulation of gas temperature or pressure could offer potential for still greater control on particle properties.

References

1.Wissing, S. A., Kayser, O. and Muller, R. H. (2004). Solid lipid nanoparticles for parenteral drug delivery. Advanced Drug Delivery Reviews 56 (9), 1257-1272.

2.Schubert, M. A. and Muller-Goymann, C. C. (2003). Solvent injection as a new approach for manufacturing lipid nanoparticles - Evaluation of the method and process parameters. European Journal of Pharmaceutics and Biopharmaceutics 55 (1), 125-131.

3.Date, A. A. and Patravale, V. B. (2004). Current strategies for engineering drug nanoparticles Current Opinion in Colloids & Interface Science 9 222-235.

4.Eerikainen, H., Watanabe, W., Kauppinen, E. I. and Ahonen, P. P. (2003). Aerosol flow reactor method for synthesis of drug nanoparticles. Eur. J. Pharm. Biopharm. 55 357-360.

5.Jayanthi, G. V., Zhang, S. C. and Messing, G. L. (1993). Modeling of solid particle formation during solution aerosol thermolysis. Aerosol Science and Technology 19:478-490.

6.Wilson, L. J. and Suddath, F. L. (1992). Control of solvent evaporation in hen egg white lysozyme crystallization. Journal of Crystal Growth 116:414-420.

7.Leong, K. H. (1987). Morphological control of particles generated from the evaporation of solution drops: Theoretical considerations. J. Aerosol Sci. 18:511-524.

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G–O–2

NanoCheck- a Tool for Size Range Expansion of Optical Particle Counters

Lothar Keck, Xiaoai Guo, Roland Hagler, Markus Pesch and Hans Grimm

GRIMM Aerosol Technik GmbH & Co.KG, Dorfstrasse 9, D-83404 Ainring, Germany

Introduction

Handling of engineered nanostructured material imposes the risk that nanoparticles are released in airborne state, and such nanoparticles might be harmful to health when inhaled by the employees. Thus monitoring of nanoparticle concentrations is required to exclude any risk for the workers, moreover such monitoring can amend the acceptance of nanotechnology. The monitoring of airborne Nanoparticles should preferably cover not only the total number concentration, but also the particle size.

A well established tool for measuring nanoparticles is the Scanning Mobility Particle Sizer (SMPS), and these instruments provide a complete size distribution even for low number concentrations. SMPS systems feature however only a limited time resolution, moreover they are rather expensive, large and elaborate to operate. Hence, SMPS systems are less suitable for the routinely real-time monitoring of nanoparticles.

Optical systems, based on the detection of scattered light from individual particles, are very common for measuring particle concentrations, mainly due to their simple operation, the small size and the fast response time. Since the intensity of scatter light decreases with the sixth power of the particle size, optical particle counters systems can however not detect particles below about 100 nm.

We have developed a simple portable instrument, the “Nanocheck”, intended for fast and easy assessment of nanoparticle exposure risks. An additional requirement was that the instrument should be usable along the way with a well established optical GRIMM aerosol spectrometers, which cover the size range from 250 nm - 32 m. Thus the combination of optical spectrometer and Nanocheck records not only size and concentration of nanoparticles, but also mass concentrations.

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the ratio Itot/ I measured by the Nanocheck increases with increasing particle size because the fraction of particles, which is removed by the condenser, decreases for larger particles. With this diameter inferred from the calibration, the total number concentration can then be calculated from the product of Ntot and Dmean that was calculated from Itot.

Validation and field tests

The instrument was compared with a conventional SMPS system as a reverence. The detection limit of the Nanocheck system is a function of the mean particle size and amounts to 500 particles/ccm for typical size distributions. Figure 4 shows a comparison of total number concentrations measured by SMPS and Nanocheck. Good agreement both for total number concentration and mean particle size was observed. Practical tests were performed with the instrument being operated downstream of a GRIMM optical aerosol spectrometer. The instrument worked reliably both for indoor measurements, and also for outdoor nanoparticle monitoring where the system was installed in a compact weather housing with air conditioning and integrated drier.

Figure 4. Comparison of total number concentration (left) and mean particle diameter (right) measured by Nanocheck and by SMPS system

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G–O–3

Characterization of Electro-hydrodynamic Atomization (EHDA) System in Relation to Liquid Flow Rate

and Charge Neutralization

Sanjay Singh, Arshad Khan, B. K. Sapra and Y. S. Mayya

Health Safety & Environment Group

Bhabha Atomic Research Center, Mumbai-85, India

Introduction

Electro-hydrodynamic atomization (EHDA) is a new technique used for generating well defined droplets with sizes ranging from micrometers to nanometres. EHDA refers to the process where a liquid jet emerging from a nozzle, maintained at a high voltage, breaks in to droplets under the influence of electrostatic force. Depending on the field strength, the liquid properties (conductivity, viscosity, dielectric constant) and liquid flow rate, various modes of spraying are observed (Cloupeau et.al, 1990). The particles produced in the cone jet-mode are most appropriate for various applications. The particles carry very high charge, sometimes up to the Rayleigh limits when they emerge into air space. The charge is often used for focussing particles for specific applications such as thin film coating, studies related to neutralization of generated test aerosols. Other applications are in aerosol technology, pharmaceutical and medical industry, material science for the production of powders and generation of metallic nano-particles etc. Occurrence of high charge and high concentration of particles make them eminently suitable for studying electrical aerosol effects. The parameters which control the dispersion process include voltage to the capillary, liquid flow rate and liquid physical properties like, electrical conductivity, surface tension, viscosity and dielectric constant etc. Several studies have been carried out so far to establish the relationship between the process variables; however, not much experimental data is available to adopt these relationships in a robust form. The present study illustrates experimental observations of dependence of these process variables on particle generation.

Experimental Set-up

The schematic of the prototype EHDA system designed and fabricated is as shown in Fig.1 consisting three compartments. First compartment consists of a metal capillary (OD 1.5 mm and ID 0.5 mm) placed vertically to which a positive DC voltage in the range of 2- 8 KV is applied. A circular brass electrode of diameter 160 mm, placed at a distance of approx. 10 mm from the capillary tip, serves as the guard plate for this system and is maintained at a positive DC potential. The flow of the liquid (ethylene glycol) is controlled using a syringe pump (plenum make). The ambient particles are deterred from entering the chamber by flow of Carbon-dioxide gas at 2 litre min-1. The second compartment consists of Am-241 radioactive source to neutralize highly charged droplets produced. The third compartment is for particle sampling, using GRIMM Scanning Mobility Particle

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Sizer (SMPS- 9.8 nm to 875 nm in about 44 channels) and Optical Particle Counter (OPC- 0.3 to 20 m in 15 size channels). Spray generated by the EHDA system is shown in Fig 2.

Results and Discussions

Neutralization of droplets

The droplets produced by EHDA carry a high electric charge, very often close to the Rayleigh charge limit (Hartman et al. 2000). This results in an increased electrical mobility of the droplets. The strong electric filed in the vicinity of the outlet of counter-electrode plate results in substantial droplet deposition. This reduces the output of the EHDA. In addition to this, droplets undergo Rayleigh disintegration, which happens when the mutual repulsion of electric charges exceeds the confining force of surface tension. This increases poly-dispersity of the droplet size distribution. To avoid these processes, the droplets have to be completely neutralized. In the present set-up, Am-241 source is used as a neutralizer. It gives out alpha particles of energy 5.5 MeV which ionise the gas in the neutralization chamber, thereby neutralizing the charge on the electrosprayed droplets. The negative ions thereby produced, quickly move towards the guard plate maintained at positive potential thus leading to a residence time dependent neutralization rate in the chamber. The ions produced at a distance of 75 mm

from the guard plate (at bottom) have longer residence time than those produced at a distance of 30 mm from the guard plate (middle). This will lead to source position dependence neutralization rate of the droplets. This dependency can be seen in Fig.3.

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Scaling law relating droplet size with liquid Flow Rate

The liquid flow rate in the capilary is the dominant parameter controlling the droplet size of the electrospray. The electrospray stytem was operated at the onset voltage condition defined as the minimum voltage required for operation of EHDA in cone-jet mode. Fig.4 shows the droplet size distribution for varying liquid flow rates of Ethylene-Glycol at the conductivity value of 12.7 mho/cm. Fig.5 shows the correlation of the droplet size with liquid flow rate. A power law relationship can be seen from the fitted curve. This dependency is in accordance with the measurement by Ganan-Calvo et.al(1997), Harman et. al (1999, 2000). An exponent of 0.29 was found in the measurement for Ethylene glycol at conductivity value of 12.7 mho/cm . The slope of 0.29 is close to that of 0.33 (Dp ~ (Q/K)1/3 by Da-Ren Chen, 1995) and 0.5 (Dp ~ Q1/2 by Ganon-Calvo, 1997). Similar results were obtained when the conductiy value was raised to 27 mho/cm..

Conclusions

A prototype EHDA system designed and developed in the laboratory is characterised for the droplet size generation characteristics as a

function of liquid flow rate and the neutralization condition. It is seen that size distribution characteristics and out-put of the EHDA depend on the position of the neutralizer. Also, droplet size was correlated with the liquid flow rate and a power law relationship is observed. Further studies are being conducted in the laboratory to study the exponent of the power law of various liquid with varying physio-chemical nature.

Acknowledgement

The authors are greatful to Dr. D.N Sharma, Head, RSSD, BARC for his constant support and encouragement during the study.

References

Cloupeau, M. and Prunet-Foch, B. (1990), Electrostatic spraying of liquids: Main functioning modes, J. Electrostatics 23, 165-184.

Ganan-Calvo A.M., Davila, J. and Barrero, A. (1997) J. Aerosol Sci., 28 (2) 249-275.

Hartman R.P.A., Brunner, D.J., Camelot, D.M.A., Marijnissen, J.C.M. and Scarlett, B. (1999) J. Aerosol Sci., 30(7) 823-849.

Hartman R.P.A., Brunner, D.J., Camelot, D.M.A., Marijnissen, J.C.M. and Scarlett, B. (2000) J. Aerosol Sci., 31(1) 65-95.

Chen D.R., David Y.H. Pui and Stanley L. Kaufman (1995) J. Aerosol Sci., 26(6) 963-977.

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G–O–4

Nanoparticle Aerosol Generation from Liposome Suspensions

Saptarshi Chattopadhyay1,2, Chandra Venkataraman1

and Pratim Biswas2

1Department of Chemical Engineering, Indian Institute of Technology,Bombay 400076, India.

2Aerosol and Air Quality Research Laboratory, Department of Energy, Environmental, & Chemical Engineering, Washington University in St. Louis, St. Louis, MO 63130, USA

Background and motivation

Aerosol delivery is a non-invasive mechanism explored for systemic drugs, like antibacterial ciprofloxacin (Wong et al., 2003) and various anti-cancer drugs (Giovanella et al., 2008), encapsulated in nanometer size matrices for controlled release. Liposomes, self assembled structures made of phospholipids, are used as drug delivery matrices as they can be easily engineered to nanometer sizes to enhance bioavailability and ensure sustained drug release. Key concerns related to aerosol delivery are aerosol stability, consistent dosage, bioavailability, drug encapsulation, convenience and the cost

of treatment.

Here, we study liposomes synthesized from phospholipids like dipalmitoyl phosphatidylcholine, the primary constituent of the lung surfactant. Aerosol generation, from suspensions of nanometer size liposomes, using conventional atomization techniques generates polydisperse micron sized aerosol of 1-5 m (Kleemann et al., 2007). Despite their great potential in drug delivery, studies of liposome aerosol suffer from an intrinsic limitation because the process of loading liposomes into droplets is purely random. Liposome distribution in the droplets can be calculated by Poisson statistics (Hogan et al., 2006). This work addresses the air jet atomization of liposomal suspensions and understanding of the resulting particle size distribution after droplet evaporation, significant for aerosol drug delivery.

Experimental approach and schematic

The scientific objective of this work is to study the distribution of liposomes in polydispersed micron size droplets generated by an air jet atomizer (TSI Inc., Model #3076). The calculated number of liposomes inclusive in a droplet is compared with measured dry particles size distribution based on mobility diameter by scanning mobility particle sizer. Further, imaging using electron microscope was used before and after atomization to understand the effect of drying and atomization on the liposomes.

Results and discussions

The suspensions contain mono-dispersed liposomes of 160-nm hydrodynamic diameter stabilized by high surface charge. The liposomes were synthesized in 1 mg mL-1 of buffer salts required for stability of the liposome suspension. The liposome before atomization

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were observed under the transmission electron microscope have spherical morphology (Figure 1-a,1-b) where the bilayer structure shows the lattice fringes (Figure 1, inset) representing the underlying crystal lattice of the lipids (Mulet et al. 2009).

Figure 1. HR-TEM images of liposome (1,2) before atomization with the crystalline arrangement of the lipid molecules in the bilayer (inset) and (3,4) air jet nebulized liposome

The maximum diameter droplet generated by the atomizer was 3 m which is selected for calculating the average number of liposome in a droplet by the Poisson distribution function (Figure 2a). As the lipid mass concentration is successively increased the calculation shows that the probability of droplets without liposome decreases.

The dissolved buffer salts have impact on the aerosol size distribution as they leave a residual particle on droplet evaporation. At low lipid mass concentration, a sizable fraction of the residual particles generated from droplets without liposome were dominant in the aerosol size distribution over the small liposome mode around 100 nm. A mode of 55 nm (Figure 2b) was measured by atomizing the buffer medium without liposomes (lipid mass concentration 0 mg/mL).

At high lipid mass concentration the probability of more than one liposome per drop also increases with larger measured geometric mean diameter (Figure 2b). At high lipid mass concentration of 1 and 0.5 mg/ml, there are greater chances of multiple liposome in one drop. This corroborates the TEM images of the liposome collected after atomization (Figure 1-c,1-d). The derived geometric mean diameter for high lipid mass concentration is ~130 nm and low lipid mass concentration is ~100 nm. Lipid mass concentration of 1 and 0.5 mg/ml is observed to have greater chances of multiple liposomes from probability

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calculation which leads to larger geometric mean diameter rather than increasing the aerosol number concentration.

Figure 2. Graphs with different lipid mass concentration a) calculated distribution of liposome in a 3 ìm droplet by Poisson distribution and b) measured size distribution of aerosols

Conclusions

We observed that air jet atomization of liposome suspensions produce nanometer size particles in the aerosol and their measured size is consistent with calculated number of liposome per droplet from Poisson distribution function. The liposomes result in soft nanoparticles which change morphology upon drying and atomization. This study includes investigation of multiple liposomes in one droplet and the effect of phosphate buffer on the dry particle size generated.

References

1.Wong, J.P., H.Yang, K.L.Blasetti, G. Schnell, J. Conley, L.N.Schofield (2003), J. Controlled Release, 92, 265-273.

2.Giovanella, B.C., J.V.Knight, J.C. Waldrep, N. Koshkina, B. Gilbert, C.W.Wellen, US Patent 7,341,739 B2, issued Mar. 11, 2008.

3.Kleemann,E., T. Schmehl, T. Gessler, U. Bakowsky,T. Kissel, W. Seeger (2007), Pharm. Res., 24(2), 277- 287.

4.Hogan,C. J. Jr., E.M. Kettleson, B.Ramaswami, D.R. Chen, and Pratim Biswas (2006), Anal. Chem.,78, 844-852.

5.Chattopadhyay, S., L.B.Modesto-Lopez, C. Venkataraman, P.Biswas (2009), Proceedings of the 28th Annual Conference of the American Association of Aerosol Research, Minneapolis, Oct 26-30.

6.Mulet, X., Gong, X., Waddington, L. J., and Drummond, C. J. (2009). Acs Nano, 3(9), 2789-2797.

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G–O–5

Synthesis of Solid Nanoparticles with Hydrophilic Cores in a Low Temperature Aerosol Reactor (LoTAR)

Amol A. Pawar, Tandeep Singh Chadha, Chandra Venkataraman and Anurag Mehra

Department of Chemical Engineering, Indian Institute of Technology Bombay

Powai, Mumbai, Maharashtra - 400076, India

Background and Motivation

In the last two decades, nanoparticles, including drug particles, polymeric particles, and solid lipid nanoparticles have been developed for systemic, oral, pulmonary and transdermal delivery [1]. They contain a therapeutic agent dispersed in or conjugated on the surface. Advantages include enhancement of dissolution, sustained/controlled release, drug targeting (cellular/tissue) and improved stability of therapeutic agents, especially proteins, peptides and nucleic acids. Polymeric nanoparticles are reported to high cytotoxicity, while solid lipid nanoparticles (SLN) have lower cytotoxicity since their constituents naturally occur in the human body[1]. The use of SLN matrices to hold a combination of hydrophilic and hydrophobic drugs has recently been explored for anti- tubercular applications by the emulsion solvent diffusion method. However, these SLN were found to have low encapsulation efficiency and uneven release for the hydrophilic drugs [2].

Aerosol synthesis offers a single step continuous process to produce nanoparticles. Gas- phase high-temperature aerosol reactors have seen broad application to inorganic nanomaterial synthesis. Droplet-phase aerosol synthesis has been recently attempted for drug nanoparticle synthesis [3] and can be explored for synthesis of lipid nanoparticles, which are thermolabile. Changes in the particle size and morphology with temperature and precursor have been studied for pure drug and biopolymer systems [4]. The use of water in oil (w/o) emulsions as precursors could address encapsulation of both hydrophilic as well as lipophillic drugs in SLN. In the present work, we investigate the synthesis of SLN with hydrophilic cores in a low temperature aerosol reactor (LoTAR) using w/o emulsions as precursors. The effect of concentration of model hydrophilic core (sucrose), in the dispersed phase, on SLN properties (size and sucrose encapsulation) will be investigated.

Experimental methods

The LoTAR (Figure 1) comprised of a collision-type air jet atomizer (Model 3076, TSI Inc. Particle Instruments, St. Paul, USA), aerosol reactor (internal diameter 30 mm and length 800 mm), aerosol diluter (internal diameter 70 mm and length 250 mm) and a cascade impactor (Micro-orifice uniform deposit impactor, MOUDI 110, MSP) for aerosol collection. The upstream pressure of the atomizer was 35 psig and the w/o precursor

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emulsion was fed with syringe pump at 0.6ml/min. The resulting atomized droplets were suspended in a nitrogen flow through the reactor, wherein the solvent evaporated to yield nanoparticles. After the evaporation stage, aerosol was diluted with zero-particle air, to bring down the total particle number concentration, within the operating limits of the characterization instruments.

Figure 1. Schematic of low temperature atmospheric pressure aerosol reactor for synthesis of solid lipid nanoparticles containing hydrophilic cores

A w/o precursor emulsion, for synthesis of SLN with hydrophilic cores, was prepared by dispersing an aqueous sucrose solution (containing sucrose and Sorbitan mono-oleate ethoxylate, TWEEN 80) in the stearic acid cyclohexane solution (containing stearic acid and Sorbitan mono-oleate, SPAN 80). This emulsion was stirred at 1200 rpm for 10 minutes followed by sonication at 40MHz, for 5 minutes. The microphase size was measured by optical microscopy.

Mobility diameter measurement was made using a scanning mobility particle sizer (SMPS, Model 3936, TSI Inc. Particle Instruments, St. Paul, USA) with a differential mobility analyzer (Long DMA, Model 3081, TSI Inc. Particle Instruments, St. Paul, USA) and a condensation particle counter (CPC, Model 3775, TSI Inc. Particle Instruments, St. Paul, USA). The amount of sucrose encapsulated was measured by Dinitrosalicylic

Figure 2. Optical Microscope image of the w/o emulsion (a) Bright field (b) Fluorescent mode

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colorimetric method assay, on particles collected by impaction (MOUDI, Model 110, MSP Corporation, Minnesota, USA).

Preliminary Results

The w/o emulsion containing a solution of 0.1mg/mL stearic acid in cyclohexane as the continuous phase, 5% dispersed aqueous phase and 2% Span 80 as the emulsifier was observed to be turbid. Dye solubility test was used to observe the stability of the emulsion for 24hrs. The emulsion was found to be stable during this period. Optical Microscopy image (Fig. 2) of the emulsion shows that the average size of the dispersed phase droplets is approximately 10μm.

The SLN formed after atomizing the w/o emulsion were found to have a geometric mean diameter of 99nm and a geometric standard deviation of 1.85 (Fig. 3).

Diameter (nm)

Figure 3. Mobility diameter based number distribution of stearic acid –SLN synthesized in a LoTAR, using a water-in-cyclohexane emulsion

The preliminary results demonstrate formation of stable w/o emulsion and SLN of 99nm geometric mean diameter. The paper will further investigate the relative distribution of hydrophilic and lipophilic constituents (i.e. sucrose and stearic acid) in size resolved particles 56nm to 2 um collected using the MOUDI cascade impactor. We will discuss attempts to control sizes of two-component nanoparticles through control of concentration of the hydrophilic and lipophilic constituents in the emulsion. Implications will be discussed for the encapsulation of multiple drugs in single nanoparticles.

References

1.Wissing, S. A., Kayser, O. and Muller, R. H. (2004). Solid lipid nanoparticles for parenteral drug delivery. Advanced Drug Delivery Reviews 56 (9), 1257-1272.

2.Pandey, R. and Khuller, G.K. (2005). Solid lipid particle-based inhalable sustained drug delivery system against experimental tuberculosis. Tuberculosis 85, 227-234.

3.Date, A. A. and Patravale, V. B. (2004). Current strategies for engineering drug nanoparticles Current Opinion in Colloids & Interface Science 9 222-235.

4.Eerikainen, H., Watanabe, W., Kauppinen, E. I. and Ahonen, P. P. (2003). Aerosol flow reactor method for synthesis of drug nanoparticles. Eur. J. Pharm. Biopharm. 55 357-360.

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G–O–6

Design, Development and Field Evaluation of a PM2.5 Sampler

Tarun Gupta* and Jaiprakash

Department of Civil Engineering, Indian Institute of Technology, Kanpur

*Corresponding Author : Email : tarun@iitk.ac.in

Introduction

There is an increased anxiety over the undesirable health effects of air pollution, especially in urban areas, where many sources of air pollutants are concentrated. Aerosol particles in particular have received much interest because of epidemiological and experimental evidence of their health impact. Mass concentration of particulate matter (PM) has shown to correlate with sensitive health effects and measurable functional changes in the cardiovascular and respiratory system (Pope et al. 2002). Studies conducted by Donaldson and McNee (1998) and Ferin et al. (1991) showed that, for the same amount of PM mass deposited in the lung, toxicity tends to increase as particle size decreases. This may be attributed to the increased surface per unit mass or to the ability of finer particles to penetrate the lung tissues (Harrison and Yin 2000; Schwartz et al. 1996).

Impactors are used for sampling and separation of air borne particulate matter because of their sharp separation, high collection abilities and relatively simple design. These are simple devices, consisting of air flowing around an impaction substrate subjected to sudden change in airflow direction. Particle with sufficient inertia will slip across the air streamline and impact on the impaction surface (Hinds 1999). Impactors have been in existence for more than 100 y. However, there has been a constant and specific need felt for development of new impactors for different applications.

Materials and Methods

The sampler is fabricated from the metal aluminum because this metal is corrosion resistant, light weight; there is no problem of static charge and easy to machine as per design specifications. The main impactor consists of one round impactor nozzle, which is conical in shape, one spacer and impaction substrate plate. Impaction substrate unit is the plate which holds the vacuum grease as an impaction substrate. Impaction substrate is the most important factor in the operation of impactor because the application of adhesive vacuum grease as substrate prevents the errors caused by particles bounce. Thus, to minimize the bounce off and breakup losses of large particles a smooth impaction substrate was created from vacuum grade silicon grease, using a razor blade. The pictures shown below depict the fully assembled impactor and internal parts of the impactor (Gupta et al., 2009)

The impactor nozzles of diameter in the range of 4.5 mm to 7.0 mm were designed. The nozzles were tested with flow rate of 15 lpm, for the dry aerosol conditions, using the

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dry aerosol generation system. The instrument used to measure the performance of the impactor was Aerodynamic Particle Sizer (APS), which runs at the flow rate of 5 lpm.

Figure 1. PM2.5 air sampler and its internal components

The difference in particle concentration was then calculated for the upstream and downstream flows to determine the efficiency of the impactor nozzle. The efficiency of various nozzles so obtained was plotted against the aerodynamic diameter of particles (in μm) to determine the cut-point of the impactor nozzle and also evaluated the shape of the efficiency curve.

For the field evaluation co-located sampling with an EPA approved sampler has been carried out during the month of Nov, 2009 inside the IIT Kanpur. The sampler was placed on the roof a building around 12 m high. The sampling period was 10 h day. During the sampling days maximum temperature was 25°C and minimum was 15°C and max and min relative humidity were 60% and 76% respectively. The sampling was carried out using a single stage impactor type sampler developed in IIT Kanpur itself and co-located Sampler (Thermal Anderson Model –GEM-2360BL1 for PM2.5). Flow rate maintained through the sampler was 15 LPM using a vacuum pump and a Rota meter. Filter papers used for the sampling of co-located sampler were glass fiber filter papers size (8"× 10") of Whatman and Quartz Filter. Similarly, for the tested impactor, samples were collected on Quartz filters of 47 mm diameter. All the filters were pre-conditioned at 25°C and 60% relative humidity before sampling and post-conditioned after sampling at same condition. After completion of sampling, all the collected filters will be analyzed gravimetrically using a microbalance (Mettler, Toledo) range between 0.001 mg to 2 g. Before weighing the filters will be conditioned in a room with controlled temperature (25oC ±1oC) and relative humidity (50% ±5%) and permit the filter to equilibrate for at least 8 h. About 5% of the filters will be kept as blank. After the sampling filters were immediately transferred to sealed plastic boxes and kept in refrigerator till further chemical analysis.

Particles collected on Quartz filters and Glass fiber filters will be analyzed for major elements – As, Ca, Cd, Co, Cr, Cu, Fe, Mg, Ni, Pb, Se, V, Zn and anions –F-, Cl-, NO3-, SO4-2, PO4-3. For chemical analysis each collected filter will be cut into two equal halves using a clean scissor. One half will be used for elemental analysis using ICP-OES (Inductively coupled plasma – optical emission spectrometer, Thermo Fischer, iCAP6300, Duo) and another half will be used for anion analysis using Ion Chromatography (compact IC 761, Metrohm).

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Result and Discussion

Following results will be presented in the proposed platform presentation:

1. Collection efficiency curve for PM2.5 with dry aerosol generation using (APS) from nozzle with diameter 5.0 mm.

2.Parametric Investigation for finding PM2.5 cut point.

3.Average ambient concentration of PM2.5 from Impactor and co-located sampler.

4.Correlation between average ambient concentrations of both samplers.

5.Concentration of chemical constituents including trace metals and anions.

6.Correlation between concentrations of chemical constituents from both samplers.

References

Donaldson, K. and MacNee, W. (1998) The mechanism of lung injury caused by PM10. Environmental Science and Technology, 10, 21–32.

Ferin, J., Oberdorster, G., Soderholm, S. C., and Gelein, R.(1991) Pulmonary tissue access of ultrafine particles.

Journal of Aerosol Medicine, 4, 57–68.

Gupta T., Chakraborty A., Ujinwal KK. Development and use of a sampler for collection and chemical characterization of submicron ambient aerosol in the Kanpur region. Aerosol and Air Quality Research, 2009 (submitted).

Harrison, R. M., & Yin, J. (2000) Particulate matter in the atmosphere: Which particle properties are important for its effects on health? Science of the Total Environment, 249, 85–101.

Hinds, W.C., Aerosol Technology, John Willey and Sons Inc., New York (1999).

Pope, C. A., Burnett, R. T., Thun, M. J., Calle, E. E., Krewski, D., Ito, K., et al. (2002) Lung cancer, cardiopulmonary mortality, and long-term exposure to fine particulate air pollution. Journal of the American Medical Association, 287, 1132–1141.

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G–O–7

Detection and Identification of Bioaerosols By using Surface Enhanced Raman Spectroscopy

V. M. Harpale*a and S.D. Ralegankar *

*Department of Physics, Ahmednagar College,

Ahmednagar -414001, (M.S.), India

*aCorresponding Author E-mail:- vm_harpale@rediffmail.com

Introduction

Bioaerosols are airborne particles which are either alive, carrying living organisms or released by them (Ariya & Amyot, 2004). The presence of bioaerosols in the troposphere and even in the stratosphere has long been established by variety of aerobiological research (Morris, C.E. et al., 2008) which is focused on current issues related to health hazards. The international concern over terrorism and specifically, bioterrorism has significantly increased the interest in the detection and chemical identification of bioaerosols. The conventional methods for identification for bioaerosols are largely limited to observation of bioaerosols with optical or scanning electron microscopes. Alternate approach to the characterization of bioaerosols is the fluorescence spectroscopy. Since, amino acids such as tryptophan are common to many bioaerosols and strongly fluoresce, the fluorescence spectra of various bioaerosols do not differ greatly. Also, conventional off-line methods of detecting bioaerosols by removing them from surface (or filter) upon which they have been deposited and analyzing them by various techniques do not provide rapid identification and response. In this paper, we report on a new approach (SERS technique) to detection and characterization of bioaerosols that permit real time or near real time identification of bioaerosols particles of relatively low cost, and with compact instrument.

SERS (Surface Enhance Raman Spectroscopy) Technique

Spontaneous Raman effect is so weak that when fluorescence occurs, obscure the Raman spectrum. However, Resonance Raman requires a tunable laser source to probe the various absorption bands in the biomaterials. Surface enhanced Raman spectroscopy (SERS) suppresses fluorescence and greatly increases the Raman signal. Therefore, SERS appears to be suitable probe for determining the chemical composition of bioaerosols especially when the detection of small amount of material is required. It appears that SERS has a number of advantages over other methods of bioaerosol detection because it can be incorporated into a real time and potentially portable detection system for micro amount of biomaterial (bio-aerosols).

Surface Enhanced Raman Spectroscopy (SERS) is a Raman Spectroscopy (RS) which provides greatly enhanced Raman signal from Raman active analyte molecules that have been adsorbed onto certain specially prepared metal surfaces. Increase in the intensity of

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Raman have been regularly observed in the order of 104 – 106 and can be as high as 108 and 1014 for some systems (Kneipp katrin et al.1999, Moskovits , M., 1985). The importance of SERS is that, it is both surface selective and highly sensitive where RS is neither. SERS selectivity of surface signal results from the presence of surface enhancement (SE) mechanism only at the surface. Thus, the surface signal overwhelms the bulk signal.

In SERS experiment (fig.1) the molecules are attached to the metallic nano-structure which is section of a cluster formed by aggregation of metal colloids. The surface enhanced stokes Raman signal ISERS is proportional to the following quantities,

Figure 1. Schematic of Surface enhanced Raman Scattering

1)Raman cross-section of the adsorbed molecule = (s)Rads

2)The excitation laser Intensities = I ( L)

And 3) The number of molecules which are involved in the SERS process = N

ISERS is expressed as,

ISERS = N. I ( L) | A ( L) |2 | A( S) |2 (s)Rads

Where,

A ( L) = Field enhancement factors at laser frequency A ( S) = Field enhancement factors at stokes frequency

The field enhancement factors arise from enhanced local optical fields at the place of the molecule near by the metal surface due to excitation of electromagnetic resonances.

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Experimental

Objective is to develop the new cost effective portable instrument where Raman spectrometer can be interfaced with SERS probe. The combination of these technology enables the construction of a field portable Raman sensor. The experimental arrangement consists of passing of laser beam through an optical glass cuvette (dimension 1cm X 1cm X 4.5cm) containing a colloidal suspension of silver or gold metals. The system is shown in (fig.2).

Figure 2. The schematic of system used for bioaerosols sampling and chemical characterization by SERS

Light scattered is passed through monochromator with grove density 1800 groves / mm and spectrum is recorded with recording system. Initially, the bio-analyte is simply added to colloid using nebulizer designed to obtain appropriate spectral window, laser irradiance and optimum ratio of the concentration of micro-organisms to the colloid concentrations. The silver colloid solution with silver concentration as 0.0002Molar is appropriate to create surface substrate for SERS effect. The proper technique (Keir, K., Sadler et al., 2002) is used to prepare the colloidal solution. In this technique, an aqueous solution of silver nitrate (9ml, 0.0002M) is added drop wise with continuous stirring to aqueous sodium borohydride solution (75ml, 0.0012M) via conical flask in an ice bath.

RAMAN SHIFT (cm–1)

Figure 3. Comparison of enhancement measurement of pyridine with normal Raman spectrum (a) SERS Spectrum (b) Normal Raman Spectrum

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Results and Discussion

The studies carried out (Sengupta, A et al., 2005) with pyridine is reported here. The results show that concentration ratio of pyridine to Ag colloid significantly affect the enhancement (Fig.3)

The enhancement is observed at maximum ratio of pyridine to Ag colloid solution. Upper spectrum is for 10-9 M pyridine solution in silver colloid solution (As a 2X 10-4 M) and lower curve is for a 1M pyridine solution in the absence of colloid. The enhancement (~109) is observed at SERS peak at 1069cm-1 with as compared to Raman peak at 1050 cm-1 in the normal spectrum (1M). The enhanced Raman spectrum with silver colloid show some new structure as well as some shifting in Raman frequency peaks.

Conclusions

It is demonstrated that bioaerosols under experiment can be characterized by SERS. The method is relatively simple and fast compared with conventional methods. It is not possible to characterize the bioaerosols with respect to their size distribution, number density and other aerosol properties. It is also clear that sensitivity and detection limits depends on the ratio of number density of aerosols ( bacteria, bio-molecules) to the number density of colloidal particles as well as the size and surface properties of the colloidal particles.

References

1)Ariya P.A. & M.Amyot (2004), New direction: The role of bioaerosols in atmospheric chemistry and physics, Atmospheric Environment, 38 (8), 1231-1232.

2)Kneipp Katrin et al ( 1999), Ultra Sensitive Chemical Analysis by Raman Spectroscopy, Chem. Rev. 99, 2957-2975.

3)Keir, R. Sadler D. et al (2002), Preparation of stable, reproducible silver colloids for use as surface enhanced Raman scattering substrate, Applied Spectroscopy, 56, 551-559.

4)Morris C.E. et al (2008), Microbiology and atmospheric processes: an upcoming era of research on bio-meterology, Biogeosciences Discuss 5, 191-212.

5)Moskovits, Martin. (1985), Surface Enhance Raman Spectroscopy, Rev. Mod. Phy. 57(3), 783 -826.

6)Sengupta A and Laucks M.L. et al (2005), Bioaerosol Characterization by Surface Enhanced Raman Spectroscopy (SERS) , Journal of Aerosol Science, 36, 651-664.

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G–O–8

Development of Multi-Channel Hand Held Sun Photometer

*Anil. A Kulkarni, M. Suresh Kumar and Jaydeep Krishna

Society for Applied Microwave Electronics and Engineering

Research, Powai, IIT Campus, Mumbai

*Corresponding author: anilk@sameer.gov.in

Key Words : Sun photometer, Aerosol optical thickness, columnar water vapor.

Sunphotometry is a passive remote sensing technique used to measure the intensity of the sunlight through the atmosphere. Such measurement, made in several narrow bands of the solar spectrum, provide information on the properties of aerosols and important trace gases that can be used in climate modeling and air pollution monitoring.

This paper describes development of indigenous Multi-channel Handheld sun photometer for measuring AOT, Columnar Water Vapor (CWV) and columnar ozone content (Ozone). Filter photo detectors, which were used in place of traditional interference filters, have significant potential advantages, including, durability, long-term optical stability and low cost. The bandwidth of the Filter photo detectors is ~10nm (AOT, CWV) and ~2nm (Ozone). The optical collimators and electronics of the instrument were carefully designed to optimize pointing accuracy, stray light rejection,

thermal and long-term optical stability, signal-to-noise ratio and data analysis. An internal microcomputer automatically calculates the AOT based on measurements at 880 nm wavelengths, CWV using outputs of 880, 940 nm and ozone using 305, 312, 320 nm detectors. The geographic coordinates of the observation site, universal time can be entered manually or by a Global Positioning System (GPS) receiver (optional). A built-in pressure transducer automatically measures atmospheric pressure. The instrument can record up to 9000 scans of the raw and processed data.

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G–O–9

Control of Packing Fraction of Nano-particles in Micrometric Grain by Spray Drying of a Nanoparticle Sol

J. Bahadur1*, D. Sen1, S. Mazumder1, Bhaskar Paul2, Arshad Khan3, B.K. Sapra3 and Y.S. Mayya2

1Solid State Physics Division, 2Materials Processing Division, 3Radiological Physics and Advisory Division, Bhabha Atomic Research centre,Trombay,400085, Mumbai, India

ABSTRACT : Hierarchically structured micrometric mesoporous silica spheres are synthesized by evaporation induced self assembly of silica colloids under slow drying condition. Scanning electron microscopy, dynamic light scattering have been performed to see the morphology of the dried grain. The particle-particle correlation inside grain has been investigated by small- angle neutron scattering. In a slow drying regime the droplets shrink isotropically leading to spherical dried grains. The packing of the nano-particle during drying is an important issue. It has been observed for the first time that the packing of the nano-particles vis-à-vis particle- particle correlation inside the grain varies with colloidal concentration. The packing of the nano-particle for low colloidal concentration is uniform throughout the grain but at higher concentration of the colloid dried grain possesses core shell type structure. The packing of nano- particle is different at shell and at core of dried grain for higher colloidal concentration. The average packing fraction of the nano-particle decreases with increasing colloidal concentration. These observations have been attributed to modification in viscosity of the colloidal dispersion and hence variation of Peclet number during drying.

Introduction

Self assembly is generally regarded as the most promising means for designing and controlling the bottom up assembly of nanometer-scale objects into structures such as sheets, tubes, wires, and shells needed as scaffolds and structures for catalysis, hydrogen storage, nanoelectronic devices, and drug delivery. A process fabricating the nanoparticles to larger sub-micrometric solid particles is of potential interest for a variety of practical applications especially in fabricating nano devices. Spray drying [1] is an established method by atomizing colloidal nanoparticles suspensions to obtain droplets, and then converting the droplets into solid spherical particles to give nanostructured powder. These porous materials are of interest for catalysis, chromatography and controlled release of drugs, biotechnologies and as fillers with low dielectric constant, pigments and hosts for optically active compounds.

As colloidal dispersions dry from liquid to solid states, they manifest a variety of mechanical behavior that are of both fundamental and practical interest [1-3]. Control of morphological properties of dried grain is crucial for the design of new functional materials [2]. In spray drying method, morphology of the spray dried materials may be either spherical or crumpled shape. The kinetics of drying may drive suspensions far from equilibrium leading to dramatic changes in morphology as solvent evaporates. The quantitative measure of the strength of drying is represented by Peclet number Pe. This is defined as the ratio of R2 and Dt, where R is the radius of the droplets, D is the diffusion

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coefficient of the colloidal particles in the droplet and t is the drying time. If Pe>>1, the drying is said to be fast, and there is a formation of non-spherical or crumpled grain during drying. However, if Pe<< 1, the drying process is regarded as slow process and the droplets shrink isotropically throughout the drying process resulting into spherical grain [1-3]. Now, a question arises regarding packing of nano-particles vis-à-vis particle-particle correlation in dried grain in a non-buckling regime. The most widely studied packings are those composed of uniform-sized spheres. Ordered structures include rhombohedral packings and cubic packings, which bracket the range of attainable solid volume fraction at max = 0.7405 and min = 0.5326 respectively. Disordered packings exhibit a much smaller range of solid volume fraction values. A key parameter of interest is the random- close-packed porosity limit, which has been investigated using experiments, theory, and numerical simulations. No generalized theory has provided an exact value, but the well- accepted limit is max = 0.64. Generally, real packings fall into the fairly narrow density range = 0.60 – 0.64 as long as the spheres are nearly uniform in size.

In the present work, packing of nano-particles has been studied under slow drying regime as a function of colloid concentration. Scanning electron microscopy (SEM) has been carried out to probe the overall morphology of the self-assembled dried grain. Small angle neutron scattering (SANS) technique have been used to characterize the packing fraction of the silica nano-particles.

Experimental

Spray drying : Initial colloidal dispersion was 40% Silica (Visa Chemical, Mumbai, India). This dispersion was diluted with pure water (Milli-Q, Millipore) to make 20%, 10%, and 5% and 2.5% dispersions, and finally these diluted dispersions were used for spray drying. Spray drying of silica colloidal dispersions was carried out using an indigenously developed spray drier [4]. The instrument consists of cylindrical drying chamber of ~10 cm in diameter and of 100 cm in length. The droplets were generated using an ultrasonic nebulizer at the bottom of the spray dryer. The feed was kept at ~ 60 ml/hr. The temperature of the oven was kept at 160 oC. The aspiration value was kept at 40 liter/ min. The dried sub-micrometric powders for different colloidal silica dispersion were collected at the end of the drying chamber using a wire mesh filter. The powder collected from the wire mesh, for 2.5%, 5%, 10% and 20% colloid dispersions were denoted as Sp-2.5, Sp-5, Sp-10 and Sp-20, respectively.

Mesoscopic characterization

The dried grains were characterized using SEM, SANS and DLS. SEM micrographs were obtained using CAM Scan (UK) instrument (Model 2300CT/100). SEM micrographs for spray dried grains of Sp-2.5, Sp-5, Sp-10 and Sp-20 have been depicted in Fig.1.

SANS experiments have been carried out on the specimens obtained after drying e.g. sp-2.5, sp-5, sp-10 and sp-20.

Data analysis

The Peclet number Pe for the present indigenously developed spray dryer has been calculated for the present experimental condition as follows: The velocity (vg) of the carrier gas inside the tube may be calculated from the ratio of the gas flow rate (40 liter/

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Figure 1. SEM micrograph of dried grain obtained from spray drying of (a) 2.5% silica colloids (sp-2.5) and

(b) 5% silica colloids (sp-5) (c) 10% silica colloids (sp-5) and (d) 20% silica colloids (sp-20)

min) to the cross section of the drying chamber (~10 cm in diameter). The value of vg comes out to be ~8.5 cm/sec. If it is assumed that the droplets get fully dried at the end of the drying chamber, which is ~100 cm long, then the drying time (t) is calculated to be ~11 sec. Such a drying time normally

corresponds to a slow drying regime. Let us calculate the Peclet number (Pe=R2/Dt) for such a situation. D may be calculated from Einstein- Stokes relation, D=KBT/6p, where KB is Boltzmann constant, is the viscosity and r represents the radius of the particles in the droplet. For T= 40 oC (at the initial stage of drying where the droplets are entering the drying chamber), r = 6 nm (as for the present silica colloids) and = 6.53 x 10-4 Pa s (assuming viscosity of pure water at 313 K), D comes out to be

5.849 x 10-11 m2/s. From the SEM Figure 2. SANS profiles in Porod plot indicating two level micrographs, it is evident that the structures

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sizes of the dried grains are always less than 2-3 microns. Assuming the initial droplet size (R) as 5 micron, Pe for the above condition is calculated to be 0.05 which is much less than unity. Thus, it is evident that the present spray drying of colloidal silica has been carried out in a slow drying regime. From SEM micrographs of the samples sp-2.5, sp-5, sp-10 and sp-20 show the morphology of the dried grain. The excellent spherical self assembled dried grain is observed for all the samples, indicating evaporation driven self- assembly of the silica colloid dispersion falls into non-buckling regime i.e. slow spray drying regime. SANS profiles for the sample sp-2.5, sp-5, sp-10 and sp-20 have been depicted in Figs.3a, 3b. The scattered profiles have been represented in porod plot i.e. I (q) x q4 vs. q (Fig.2). The two constant levels in Porod plot are indicating two level structures in the dried grain.

Table Fitting parameters obtained from SANS analysis

Conclusions

The spray drying of silica colloid with varying silica concentration has been carried out under slow drying regime. The nice spherical dried grains have been achieved for all the colloidal concentrations from the SEM micrographs indicating. The scattering results show different packing fraction of the silica nano-particle in dried grain for different concentration of the colloids. These results were attributed to the modified colloid properties due to increased colloidal concentration leading to slight increase in Peclet number. It has been observed that average packing fraction of the silica nano-particle reduces with increasing colloidal concentration.

References

1.Sen, D., Spalla, O., Belloni, L., Charpentier, T. and Thill, A. Langmuir 2006, 22, 3798.

2.Sen, D., Spalla, O., Spalla, T., Haltebourg, P. and Thill, T. Langmuir 2007, 23, 4296.

3.Sen, D., Mazumder, S., Melo, J. S., Arshad Khan, Bhattyacharya, S. and D’Souza, S. F. Langmuir 2009, 25 (12), 6690.

3.Khan Arshad, Sen, D., Spara B. K. and Mazumder S. “Proceedings of the 54th DAE Solid State Physics Symposium” 2009 page 445.

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G–O–10

Aerosol Measurement Techniques: Needs of Standards and Measurement Protocols to Better Constrain the Climate Effects

Shankar G. Aggarwal* and Prabhat K. Gupta

Chemical Metrology Section, National Physical Laboratory,

Dr. K.S. Krishnan Road, New Delhi -110 012

*E-mail: aggarwalsg@nplindia.org

Aerosols are short-lived as compared to greenhouse gases, their impact is more regional, and the extent of their cooling and heating effects on earth’s system is still quite uncertain. Black/brown aerosol particles absorb the radiation in the UV-visible regions, and thus heat the atmosphere and consequently cool the surface. This absorption effect reduces evaporation rates, convection, humidity and cloud formation on regional and global scales. Instead, this effect is not been included in the climate model, and currently a major gap in climate understanding. This is one of the possible reasons that the uncertainty in total anthropogenic radiative forcing (greenhouse gases + aerosols) is dominated by the uncertainty in aerosol radiative forcing. On the other hand, in the climate model, aerosol composition, optical and physical data are required as the inputs, therefore a small error in the aerosol measurements can further enhance the complexity in understanding their impact on climate. The measurement data are largely influenced by the instrumentation and measurement protocol. For example, black carbon (BC) is a major component of aerosol particles, which significantly governs the nature of net effect of aerosols, however up to 50% variation in BC concentration is reported depending on the measurement protocol adopted. Therefore, a standard measurement protocol is needed to better constrain the aerosol effects in the long-term studies.

For chemical and physical characterization of aerosol particles, recently, several on-line techniques have been introduced in the aerosol research field. Apart from the importance of instrument and method used in the measurement, it is recognized that the calibration and validation of instrument performance using aerosol certified reference material is also a key to get reliable and comparable data especially in long-term observation of aerosol characterization studies related to climate change issues.

In India, aerosol research is recently paid much attention. As we are initiating climate change program, we need to construct and standardized the measurement protocols for aerosol research, so that the data obtained in any regions, and by any institutes could be confidently compared. Although the National Institute of Standard and Technology (NIST), USA provides some aerosol standard reference materials (SRMs) for aerosol research, they are not enough in types (also very expensive, need a lot of time to get them). Research on the development of aerosol standard reference material is deliberately required for the country needs. The focus of this talk will be to review the recent measurement techniques, performance results and highlight the importance of aerosol metrology issues in aerosol studies.

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G–P–1

Open Path Fourier Transform Infrared Spectrometer – A Tool to Measure the Optical Properties of an Atmospheric Column

S. K. Mishra1 and D R Nakra1

National Physical Laboratory,

New Delhi, India

Introduction

An atmospheric column comprising of clouds, gases and aerosols extends from the Earth’s surface to the top of the atmosphere. The assumption of homogeneous distribution of columnar aerosol in terms of its concentration, chemical composition leads to the uncertainty in the aerosol optical properties which are estimated using retrieval algorithms such as AERONET [Dubovik and King, 2000]. The aerosol nature, type and its concentration govern the physical properties of the aerosol and all these governing parameters have been found to be very region specific [Kalashnikova and Sokolik, 2004]. So for the better retrieval, spatiotemporal variation of the aerosol concentration/characteristics is required. For, simplicity and at primary level, the experimental observations can be performed at a given place. This will provide the concentration variation at real time with varying vertical grid. However, the same could be done using insitu aircraft observations but such operations are very expensive and tedious. So, alternatively the vertical profiling of aerosol could be achieved using ground based observations by Open Path- Fourier Transform Infrared Spectrometer (OP-FTIR) which measures the optical properties/ concentrations of the columnar constituents at a varying vertical grid [Grant et al., 1992; Marshall et al., 1994]. At present scenario the numerical estimation of the optical properties is limited due to lack of information on region specific dust morphology and mineralogy. This will constrain the optical model for its estimation. In such situation, OP-FTIR may be a boon for the optical properties measurement.

Instrument’s Technical Specifications

IFS 125 HR is a high resolution (0.0035 cm-1) Fourier Transform-Infrared Spectrometer with a spectral range of 4,800 to 620 cm-1. The detectors used in the instrument for selecting the concerned wavelength range are Mercury Cadmium Telluride detector (MCT) with a wave-number spread 12,000 to 420 cm-1 and the Indium Antimonide detector (InSb) ranges from 9,600 to 1,850 cm-1. Beam Splitter used in the instrument is KBr window in Mid Infrared Range; 4,800 to 450 cm-1 and CaF2 window in Near Infrared Range; 14,000 to 1,850 cm-1.

The combination of the above components is decided based on the experimental need. Component’s selection and operation is solely based on OPUS spectroscopic software.

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Results and discussions

The atmospheric column over Delhi comprises of pollution (due to industries, vehicles etc.) and mineral dust (from Thar Desert, Rajasthan) with their stratified layers. The pure mineral dust is polluted in the vicinity of the pollution and makes a complicated dust system where pollutants are attached with the pure dust externally or internally. The optical modeling by accounting such a complicated dust system (in terms of morphology and mineralogy) for the numerical estimation of optical properties of the polluted dust, is very difficult. Exact information of the optical properties of such a system is very important as these are held responsible for governing any perturbation in the radiation budget over a region. In Delhi, the perturbation due to pollution leads the change in dust optical properties which in tern effect the radiation budget. The perturbation in radiative forcing may lead to effect the local weather or on a broader scale the normal monsoon cycle. Thus, it is imperative to measure the optical properties of the polluted dust over Delhi for better radiative forcing estimation. Keeping this in mind, the columnar optical properties are measured using ground based OP-FTIR at NPL, New Delhi campus. The optical properties of the aerosol will be quantified using this data. Thus measured aerosol optical properties will help to understand the radiative signature of whole atmospheric column. The absorbance spectrum of the atmospheric column taken by the OP-FTIR in the NPL, Delhi has been shown in Figure 1.

Figure 1. The absorbance spectrum of sun radiation passed through the atmospheric column

The results pertaining to the spectral variation of the optical properties (such as absorption and extinction coefficients) of the columnar constituents will be discussed.

References

Dubovik, O., and King, M. D. (2000), A flexible inversion algorithm for retrieval of aerosol optical properties from sun and sky radiance measurements, J. Geophys. Res., 105 (D16), 20,673-20,696.

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Grant,W.B., Kagan, R.H. and McClenny,W.A.(1992), Optical Remote Measurement of Toxic Gases, J Air Waste Man Assoc., 42(1),18–30.

Kalashnikova, O. V. and I. N. Sokolik (2004), Modeling the radiative properties of nonspherical soil-derived mineral aerosols, J. Quant. Spectrosc. Radiat. Transfer, 87,137-166.

Marshall, T.L., Chaf. n, C.T., Hammaker, R.M. and Fateley,W.G. (1994), An Introduction to Open-Path FT-IR Atmospheric Monitoring., Environ Sci Technol, 28(5), 224A.

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