Challenges in Characterizing Small Particles: Exploring Particles from the Nano- to Microscale: A Workshop Summary (2012)

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Poster Abstracts

MEASUREMENTS OF NEUTRAL NUCLEATING MOLECULAR CLUSTERS IN THE ATMOSPHERE

J. Zhao,¹ F. L. Eisele,¹ J. N. Smith,^1,2 M. Chen,³ J. Jiang,³ M. Titcombe,³ C. Kuang,⁴ and P. H. McMurry³

¹Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO 80301

²Department of Physics and Mathematics, University of Eastern Finland, P.O. Box 70211 Kuopio, Finland

³University of Minnesota, Department of Mechanical Engineering, Minneapolis, MN 55455

⁴Department of Atmospheric Science, Brookhaven National Laboratory, Upton, NY 11973-5000

Atmospheric nanoparticles produced by nucleation can subsequently grow to cloud condensation nuclei (CCN) within one or two days and hence affect cloud formation, precipitation, and atmospheric radiation budgets. As an intermediate stage between molecules and nanoparticles, neutral molecular clusters are believed to play an important role in processes that lead to boundary layer nucleation. Therefore, knowledge of chemical composition, concentrations, thermodynamic properties, and evolution of neutral molecular clusters is essential to better elucidate the nucleation mechanism and to reduce the uncertainty in nucleation rates used in global climate models.

Here we present field measurements from a recently developed chemical ionization mass spectrometer (the Cluster-CIMS) designed to measure atmospheric neutral clusters (Zhao et al., 2010). The sensitivity of the Cluster-CIMS was significantly improved by using a unique conical octopole device in the first vacuum stage for transmitting and focusing ions, which was further confirmed by ion trajectory simulations using SIMION. The Cluster-CIMS was well calibrated with an electrospray coupled to a high-resolution differential mobility analyzer (ES-HDMA). The calibration showed that the Cluster-CIMS has a relatively flat sensitivity in the mass range of 190-400 amu, covering the masses of sulfuric acid clusters containing 2-4 H₂SO₄. The ion cluster formation in the atmospheric-pressure inlet was controlled by two processes: neutral ionization and ion-induced clustering (IIC), which can be differentiated from the time independency of the intensity ratio between the cluster and monomer ions. Two methods were employed to separate neutral clusters from the ion-induced clustering. The concentrations and distribution of the neutral nucleating clusters containing up to 4 H₂SO₄ are estimated from the above methods at three measurement sites (NCAR foothill laboratory, Manitou Forest Observatory, and Atlanta). Typically, the molecular cluster concentrations are well correlated with the concentrations of nanoparticles measured simultaneously during the nucleation event periods. The Cluster-CIMS was employed to measure clusters containing both sulfuric acid and amines in summer 2010 at NCAR foothill laboratory. Correlation between these clusters and nanoparticles measured by several particle counters will be presented.

Zhao, J., F. L. Eisele, M. Titcombe, C. Kuang and P. H. McMurry. 2010. Chemical ionization mass spectrometric measurements of atmospheric neutral clusters using the Cluster CIMS. Journal of Geophysical Research 115, D08205, doi:10.1029/2009JD012606.

EXPLORING PARTICLES FROM THE NANO- TO MICROSCALES ELECTRON MICROSCOPIC ANALYSES ON ENGINEERED AND INCIDENTAL NANOPARTICLES IN BIOSOLID PRODUCTS

B. Kim,¹ C.-S. Park,² M. Murayama,^2,3 and M. F. Hochella, Jr.^1,3

¹The Center for NanoBioEarth, Department of Geosciences, Virginia Tech, Blacksburg, VA 24061

²Department of Materials Science and Engineering, Virginia Tech, Blacksburg, VA 24061

³Institute for Critical Technology and Applied Science, Virginia Tech, Blacksburg, VA 24061

With the dramatic growth of nanotechnology, the production and use of engineered nanoparticles has been rapidly increasing for the past few years. Engineered nanoparticles that are produced and/or incorporated into consumer products will enter the environment after and/or during the term of use, which in turn has raised concerns about their potentially adverse impact on the environment. However, there has been little success with identifying nanosized engineered and incidental particles from complex heterogeneous environmental samples, limiting our understanding of their environmental fate and influence. Lack of such studies is in part due to technical challenges in discovering and monitoring the environmental occurrence of engineered and incidental nanoparticles present at trace levels. In order to overcome this problem, we looked at a “bottleneck” for engineered nanoparticles in the form of a large metropolitan wastewater treatment facility. There, nanoparticles from consumer products may concentrate especially at the end stage of treatment processes where biosolids (sludges) are generated. We looked for the presence of nanosized particles in this complex organic material using analytical high-resolution transmission electron microscopy. We found nanoparticulate silver sulfides, presumably derived from silver nanoparticles and/or ionic Ag that were reacting with reduced S species in the sedimentation processes during wastewater treatment, as well as a variety of titanium oxide nanoparticles. For both materials, their size, morphology, elemental compositions, and degree of crystallinity and aggregation state were studied in detail. The results of our work clearly show a great degree of nanoparticle heterogeneity and complexity in biosolid products. We believe that this study will help us evaluate further risks when nanoparticle-bearing biosolid products enter the soil environment through agricultural land applications.

IN SITU STUDIES OF EQUILIBRIUM AND NON-EQUILIBRIUM SMALL-PARTICLE DYNAMICS OVER EXTENDED LENGTH AND TIME SCALES USING ULTRASMALL-ANGLE X-RAY SCATTERING/X-RAY PHOTON CORRELATION SPECTROSCOPY (USAXS/XPCS)

J. Allen,¹ F. Zhang,¹ L. E. Levine,¹ J. Ilavsky,² A. R. Sandy,² and G. G. Long1,²

¹Material Measurement Lab., NIST, Gaithersburg, MD. Email: Andrew.allen@nist.gov

²X-ray Science Div., APS, Argonne National Lab., Argonne, IL. Email: ilavsky@aps.anl.gov

Both scattering and imaging techniques successfully characterize the microstructures of advanced materials, including small particle systems and suspensions. Yet the dynamics of these materials, especially responses to abrupt changes in environment, largely remain elusive. X-ray photon correlation spectroscopy (XPCS) has emerged as a technique offering unprecedented sensitivity to equilibrium and nonequilibrium dynamics within material systems, including small particles. However, existing XPCS facilities are limited to microstructure length scales smaller than 50 nanometers, eliminating large classes of materials of technological importance. Recently, we have developed combined ultrasmall-angle x-ray scattering/x-ray photon correlation spectroscopy (USAXS/XPCS) to probe the slow equilibrium and nonequilibrium dynamics of optically opaque materials with features in a size range from 100 nm to several micrometers, i.e., between those of dynamical light scattering and conventional XPCS. Two examples illustrate the in situ capability of USAXS-XPCS: the equilibrium dynamics of colloidal particle dispersions at various volume concentrations as a function of temperature; and the nonequilibrium dynamics of the small particle configuration within a polymer composite, for which USAXS/XPCS reveals incipient dynamical changes not observable by other techniques.

CHARACTERIZATION OF MICRO-PARTICLE ADHESION IN PHARMACEUTICAL ENGINEERING

N. Zarate,¹ D. Balachandran,¹ J. Litster,¹ and S. Beaudoin¹

¹School of Chemical Engineering, Purdue University, West Lafayette, IN 47906

The understanding of interaction forces that arise when particles and surfaces come into close contact continues to be a significant focus of research. It can benefit many areas of study particularly in the pharmaceutical, chemical, and mineral industries involving solid processing. The work presented investigates capillary condensation effect on adhesion forces between particles and surfaces as it is exposed to different levels of relative humidity. Direct force measurements between molecularly smooth surfaces seem to match accurately with conventional models, but with real particles and surfaces the forces display extreme discrepancies due to their natural heterogeneity such as roughness and uneven liquid condensate layers.

The investigations on the microscale interactions are developed for nonideal surfaces to give more significant insight on the macroscale than ideal surfaces. The results have confirmed liquid condensation is present on the surface area of tooling surface on the microscale through a phase imaging technique. This was the first time it was applied in the context of pharmaceutical manufacturing, which can facilitate the design of surfaces during processing. The traditional approach for designing processing and particle interactions heavily relied on the behavior of large amounts of particles and indirect measurements of the adhesion forces of the surface. The understanding of the interactions between single particles and tooling surfaces can provide useful information through several characterization techniques such as atom force microscopy (AFM) and scanning electron microscopy (SEM).

IMAGING SMALL PARTICLES IN CELLS USING SOFT X-RAY TOMOGRAPHY

M. Uchida,^1,3 E. Hanssen,² C. Knoechel,^1,3 G. McDermott,^1,3 M. Le Gros,^3,4 L. Tilley,⁵ and C. Larabell1^3,4

¹Department of Anatomy, University of California San Francisco, San Francisco, CA 94143, USA

²Electron Microscopy Unit Bio21, Molecular Science and Biotechnology Institute, University of Melbourne, Melbourne, VIC 3010, Australia

³National Center for X-ray Tomography, Lawrence Berkeley Laboratory, Berkeley, CA 94720, USA

⁴Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA

⁵Department of Biochemistry and Center of Excellence for Coherent X-ray Science, La Trobe University, Melbourne, VIC 3086, Australia

Soft x-ray tomography (SXT) is a new tool for imaging whole, hydrated biological specimens up to 15 microns thick with a spatial resolution better than 50 nm. In SXT, cells are imaged using photons between the K shell absorption edges of carbon (284 eV, λ = 4.4 nm) and oxygen (543 eV, λ = 2.3 nm). These photons readily penetrate the aqueous environment while encountering significant absorption from carbon- and nitrogen-containing organic material. In this energy range, referred to as the “water window,” organic material absorbs approximately an order of magnitude more strongly than water, producing quantitative, high-contrast images of intact, fully hydrated cells without the need to use contrast-enhancing agents. The high penetrating power, coupled with a near absence of reflection at the interface of dissimilar materials, makes x-rays an ideal probe for studying cellular morphology. These unique imaging properties also make x-ray a powerful tool for determining the precise position of small particles with respect to cellular structures.

CHARACTERIZING MOLECULAR CONJUGATION AND AGGREGATION OF NANOSCALE PARTICLES USING COMPLEMENTARY PHYSICAL MEASUREMENT METHODS

D.-H. Tsai,¹ T.-J. Cho,¹ F. DelRio,¹ R. I. MacCuspie,¹ M. R. Zachariah,^1,2 and V. A. Hackley¹

¹Materials Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899

²Departments of Mechanical Engineering & Chemistry, University of Maryland, College Park, MD 20742

We present results based on complementary physical characterization methods performed under both fluid-based and aerosolized conditions in order to interrogate the molecular conjugation and colloidal stability of nanoscale particles. From the change in hydrodynamic and aerosol particle size, we can probe the formation of molecular coatings and particle aggregates. For the purpose of characterizing nanoscale gold-based platforms for cancer therapeutics, citrate-stabilized gold nanoparticles (Au-NPs) conjugated by thiolated polyethylene glycol (SH-PEG) are used as a model system. Dynamic light scattering and asymmetric-flow field flow fractionation are used to characterize particle populations under relevant fluid conditions. For comparison, atomic force microscopy and electrospray differential mobility analysis offer static imaging and dry aerosol characterization, respectively. Combining information derived from these physical-based methods, we can then analyze the molecular conformation of SH-PEG on the Au-NP surface, calculate the surface coverage of SH-PEG, and estimate the degree of aggregation and shelf life of Au-NP based products in dispersed form.

CHEMICAL IMAGING ACTIVITIES ASSOCIATED WITH NANOPARTICLES AT PACIFIC NORTHWEST NATIONAL LABORATORY

S. Thevuthasan,¹ L. Terminello,¹ and E Hui¹

¹Pacific Northwest National Laboratory, Richland, WA 99354, Theva@pnl.gov

Chemical analysis and identification through direct imaging is a powerful means to develop an atomistic understanding of scientific issues associated with knowledge gaps and problems in energy, environment, and national security. For example, identification of mechanisms associated with transformations requires the direct observation of the reactions to develop the atom-by-atom model of the structural and chemical changes. Recently we introduced a laboratory-wide chemical imaging initiative to develop the suite of tools needed for such a transformation. Central to this initiative will be development of an in situ tool suite with nanometer resolution and element specificity that will allow researchers to couple the molecular-level chemical and structural information to large-scale scientific challenges. In particular, we will develop (a) synchrotron light-source-based capabilities coupled with laboratory-based imaging capabilities for three-dimensional tomographic, structural, and element-specific interrogation at the molecular level, (b) coupled optical, electron, ion, mass, and scanning probe microscopies to understand chemical, material, and biological transformations and mechanisms, and (c) integrative hardware and software applications for real-time image reconstruction, feature extraction, and information integration. Brief descriptions of these activities will be presented along with the detailed descriptions of two to three projects related to nanoparticle characterization.

IMPORTANCE OF SYNERGISM IN ATMOSPHERIC SECONDARY ORGANIC AEROSOL FORMATION: CASE STUDY OF α-PINENE OXIDATION BY NO₃ RADICALS

V. Perraud,¹ E. A. Bruns,¹ M. J. Ezell,¹ S. N. Johnson,¹ Y. Yu,² M. L. Alexander,³ A. Zelenyuk,³ D. Imre,⁴ and B. J. Finlayson-Pitts¹

¹Department of Chemistry, University of California, Irvine, CA 92697

²Currently at California Air Resources Board, 9528 Telstar Avenue, El Monte, CA 91731

³Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352

⁴Irme Consulting, 181 McIntosh Ct., Richland, WA 99352

Secondary organic aerosols (SOAs) formed from the gas-phase oxidation of volatile organic compounds (VOCs) are a major component of atmospheric particles. Biogenic VOCs have been long known as SOA sources via oxidation by O₃, OH radicals, and NO₃ radicals. While these reactions are usually studied separately in laboratory controlled experiments, in the atmosphere, reaction of VOC with one specific oxidant rarely occur in isolation. We report here the oxidation of a-pinene, a well-documented biogenic emission, by NO₃ radicals with varying contributions from the O₃ reaction, where the O₃ + NO₂ reaction is the source of NO₃ radicals. Experiments were carried out in air using a newly developed large stainless steel flow tube. Particle concentration and chemical composition were measured simultaneously using scanning mobility and aerodynamic particle sizers, two aerosol mass spectrometers, and two integrative sampling techniques (impaction on either ZnSe discs with subsequent analysis by Fourier transform infrared spectroscopy or on quartz-fiber filters followed by liquid chromatography with UV-vis detection). Even small contributions by the ozone chemistry had significant impacts on particle formation and growth, as well as on composition. The synergism between O₃ and NO₃ chemistry is discussed.

HARD SHELL GAS-FILLED CONTRAST ENHANCEMENT PARTICLES FOR COLOR DOPPLER ULTRASOUND IMAGING OF TUMORS

H. P. Martinez,¹ Y. Kono,² S. L. Blair,³ R. F. Mattrey,² A. C. Kummel,¹ and W. C. Trogler¹

¹University of California San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0358; martinez@ucsd.edu, wtrogler@ucsd.edu

²University of California San Diego, Medical Center, Dickson St., San Diego, CA 92103

³University of California San Diego, Moores Cancer Center, 3855 Health Sciences Dr., La Jolla, CA 92093

Hollow hard shell particles of 200 nm and 2 micron diameter with a 10-nm-thick porous silica shell have been synthesized using polystyrene templates and a sol-gel process. The template insures than the hollow particles are monodispersed, while the charged silica surface insures that they remain suspended in solution for weeks. When filled with perfluorocarbon gas, the particles behave as an efficient contrast agent for color Doppler ultrasound imaging in human breast tissue. The silica shell provides unique properties compared to conventional soft shell particles employed as ultrasound contrast agents: uniform size control, strong adsorption to tissue and cells immobilizing particles at the tissue injection site, a long imaging lifetime, and a silica surface that can be easily modified with biotargeting ligands or small molecules to adjust the surface charge and polarity.

CARDIOVASCULAR HEALTH EFFECTS OF PM2.5 AND NICKEL NANOPARTICLE

E. N. Liberda,¹ A. J. Madrid,¹ Q. Qu,¹ and L. C. Chen¹

¹New York University, Department of Environmental Medicine, School of Medicine; eric.liberda@nyumc.org

It is well documented that exposure to ambient fine particulate matter (PM2.5) creates increased risks for cardiovascular disorders (CVD) in humans. However, the mechanism(s) and component(s) responsible for PM2.5-associated CVD are not known. Our recent animal studies suggest that nickel (Ni) plays critical roles in PM2.5-associated CVD. To test this hypothesis, we identified two areas, Jinchange and Zhangye, in China with comparable PM2.5 but different Ni exposures for which to investigate a variety of cardiovascular markers including reparative endothelial progenitor cells (EPCs). Ambient PM2.5 with high Ni content induced elevated systemic inflammatory markers and reduced EPCs. Additionally, we have shown that both low and high concentrations of inhaled Ni nanoparticles cause reduced numbers of bone marrow EPCs of mice as well as reduced functions of these cells and may be a mechanism by which CVDs occur. Taken together, the results of the mouse exposure bolster the findings from the human study and point toward a common cardiovascular maintenance cell population that may be adversely affected by Ni on or in PM2.5.

EFFICIENT CHARACTERIZATION OF NANOPARTICLES THROUGH AN INTELLIGENT COMBINATION OF ANALYTICAL TECHNIQUES

S. V. N. T. Kuchibhatla,¹ S. Thevuthasan,¹ A. S. Karakoti^1,2 P. Adusumilli,² T. Prosa,³ R. Ulfig,³ V. Shutthanandan,¹ C. M. Wang,¹ P. Yang,¹ and S. Seal⁴

¹EMSL, Pacific Northwest National Laboratory, Richland, WA 99354

²Northwestern University, Evanston, IL 60208

³Cameca Instruments Inc., Madison, WI 53711

⁴NSTC and AMPAC, University of Central Florida, Orlando, FL 32826; Satya@pnl.gov

“There is plenty of room at the bottom”—the statement of the legendary Feynman has been realized within a decade by the researchers across the globe. The advent of “nanoparticles” and the realization of their potential applications in defense, energy, environment and health made the need for their synthesis and characterization quite essential. However, the inherently complex nature of various nanoparticles made their detailed characterization significantly intricate. Here we present two specific examples: (1) nanoparticles embedded in a matrix and (2) functionalized nanoparticles. The efforts by the team of scientists from EMSL, to utilize the combination of high-resolution analytical electron microscopy and laser-assisted 3D-atom probe tomography for the three-dimensional chemical imaging of embedded Au-nanoparticles in MgO single crystal, will be presented. Also, in order to understand the functionalized cerium oxide (ceria) nanoparticles, we are using a combination of experimental, surface analysis using electron and optical spectroscopies, and theoretical analysis of the materials system. Nonlinear optical spectroscopy techniques such as SHG, SFG along with XPS, TEM, UV-Vis, and atomistic modeling are being utilized to obtain a molecular-scale visualization of the functional group conformation on the nanoparticles, surface chemistry, and its influence on the functionality of the nanoparticles.

SIZE DISTRIBUTION MEASUREMENTS OF NEWLY FORMED 1-6 NANOMETER ATMOSPHERIC AEROSOLS

C. Kuang,¹ P. McMurry,² and J. Wang³

¹Atmospheric Science Division, Brookhaven National Laboratory, Building 815E, Upton, NY 11973; ckuang@bnl.gov

²Department of Mechanical Engineering, University of Minnesota, 111 Church St. SE, Minneapolis, MN 55455; mcmurry@me.umn.edu

³Atmospheric Science Division, Brookhaven National Laboratory, Building 815E, Upton, NY 11973; jian@bnl.gov

Atmospheric aerosols influence climate and climate change on local to global scales by affecting the atmospheric radiation balance directly by scattering and absorbing incoming solar radiation and indirectly as cloud condensation nuclei. New particle formation (NPF) by photochemical reactions of gas-phase precursors greatly increases the number concentrations of atmospheric aerosols, and therefore their impact on climate. Although methods for measuring sizes and concentrations N of newly formed particles of diameter greater than 3 nm are well established, measurements of nanoparticles and neutral molecular clusters smaller than this are needed to constrain nucleation rates and to better understand nucleation mechanisms. A new instrument for “bridging the gap” in measurements from neutral molecular clusters to nanoparticles has been developed and was continuously deployed in an intensive measurement campaign at Boulder, CO, in September 2010. Size distribution measurements down to 1 nm are achieved with an electrical mobility spectrometer using diethylene glycol as working fluid (50% activation efficiency at 1.2 nm). Under conditions of rapid NPF, N (Dp < 5 nm) can exceed N (Dp > 5 nm) by more than 100 fold, greatly influencing the dynamics of the evolving aerosol.

NEW PARTICLE FORMATION FROM METHANESULFONIC ACID IN AIR

M. L. Dawson,¹ V. Perraud,¹ M. J. Ezell,¹ L. M. Wingen,¹ and B. J. Finlayson-Pitts¹

¹Department of Chemistry, University of California, Irvine, CA 92697-2025

Identifying precursors and determining rates of formation for new particles in the atmosphere is an essential step in quantifying the effects of particulate matter on human health and climate change. Sulfuric acid is well known to play an important role in new particle formation, and much work has been done to characterize its role as a particle precursor, with recent studies suggesting the involvement of both ammonia and organic amines. Methanesulfonic acid (MSA) is widespread in the atmosphere as is formed alongside sulfuric acid in the oxidation of organosulfur compounds such as dimethyl sulfide and methyl mercaptan. However much less is known about its impact on new particle formation. We report here preliminary results from laboratory studies of new particle formation and growth from the gas phase reaction of MSA with organic amines. These studies are performed using a unique flow tube system equipped with an electrical aerosol analyzer and an scanning mobility particle sizer (SMPS), which are used to measure particle size distributions as a function of time and reactant concentration at 295 K in 1 atm of air. The implications for the role of MSA in new particle formation and growth will be discussed.

INHALED NICKEL NANOPARTICLES ENHANCES PROGRESSION OF ATHEROSCLEROSIS, REDUCES VASCULAR REACTIVITY, AND ALTERS GENE ACTIVITY IN BRAIN IN A MURINE MODEL

A. K. Cuevas,¹ E. N. Liberda,¹ P. A. Gillespie,¹ G. Kang,¹ and L.-C. Chen1

¹Department of Environmental Medicine, New York University School of Medicine, 57 Old Forge Road, Tuxedo, NY 10987; amj316@nyu.edu, eric.liberda@nyumc.edu, gillespie.patricia@gmail.com, gsk227@nyu.edu, lung-chi.chen@nyumc.org

There is evidence that once deposition of inhaled nanoparticles (NPs) occurs, the particles can bypass clearance mechanisms and target secondary organs, such as, the cardiovascular system and the brain. Utilizing a whole-body exposure system, ApoE-/- or C57BL/6 male mice were exposed to either nickel hydroxide NPs (NHNP; 100, 150, or 900 μg/m³) or filtered air (FA) for time periods ranging from 1 d to 5 m (5 h/d; 5 d/w). At 24-hr post exposure, tension studies were conducted to evaluate vascular function in response to a vasoconstrictors and -dilators in the carotid artery. Results indicated that arteries from NHNP mice showed statistically significant differences in contractile and relaxation responses compared to those from FA mice. Oxidative stress and inflammation in the pulmonary and extrapulmonary system indicated damage, and the degree of plaque formation was determined in the ascending aorta. In addition, three brain regions were collected (olfactory bulb, midbrain, and cerebellum) for gene expression analyses. These results suggest that both short- and long-term exposure to inhaled NHNPs can induce oxidative stress and inflammation in both pulmonary and extrapulmonary organs that can accelerate atherosclerosis in ApoE-/- mice as well as alter vascular function and brain gene expression in C57BL/6 mice.

PHYSICOCHEMICAL PROPERTY MEASUREMENTS: KEY TO ENABLING RISK AND FATE ASSESSMENT FOR ENGINEERED NANOMATERIALS

T.-J. Cho,¹ J. S. Taurozzi,¹ D.-H. Tsai,¹ R. I. McCuspie,¹ A. J. Allen,¹ and V. A. Hackley¹

¹National Institute of Standards and Technology, Nanoparticle Measurements and Standards Project, Gaithersburg, MD 20899

The National Institute of Standards and Technology is actively working to address the need for physicochemical property measurements applicable to engineered nanomaterials (ENMs) by developing, standardizing, and validating transferable measurement methods, protocols, and certified reference materials. Another important component of this effort is the interrogation of structure-property relationships derived from critically evaluated experimental results. Research activities include the following: development of nanoscale reference materials for instrument and method validation, laboratory qualification, and benchmarking, and to support interlaboratory comparisons; studies to develop standardized dispersion protocols for ENMs in biological and environmental test media, and to evaluate current practices; research to assess the physicochemical stability of nanoscale Ag and Au in biological and environmental matrices; measurements to characterize and quantify the amount, conformation, and distribution of surface-bound molecular species; evaluation of methods for detection and characterization of aggregates formed in ENM dispersions; and application of synchrotron X-ray and neutron scattering methods to study ENM formation, interactions, and functionalization.

USING MASS SPECTROMETRY TO CHARACTERIZE AIRBORNE PARTICLES

E. A. Bruns,¹ V. Perraud,¹ M. L. Alexander,² A. Zelenyuk,² M. J. Ezell,¹ S. N. Johnson,¹ J. Greaves,¹ D. Imre,³ and B. J. Finlayson-Pitts¹

¹Department of Chemistry, University of California, Irvine, CA 92697-2025

²Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352

³Imre Consulting, Richland, WA 99352

Airborne particles affect health, reduce visibility, and impact climate by scattering light and altering cloud properties, and complete particle characterization is essential to understand these impacts. Secondary organic aerosols (SOAs) are a significant constituent of atmospheric particles and are formed from the condensation of semi-volatile oxidation products. The partitioning of these semi-volatile compounds between the gas phase and particles makes characterization particularly challenging. Traditional analysis techniques involve filter-based sampling and extraction, which can introduce artifacts. In the past decade, real-time particle mass spectrometry has emerged as a powerful technique that overcomes these artifacts. However, their response to organic nitrates, which are present in SOAs, is unknown. Ambient ionization mass spectrometry has also emerged as a promising technique for particulate analysis because little or no sample preparation is needed and Fourier transform infrared (FTIR) spectra of the same sample can be obtained. We report here results from the analysis of laboratory-generated SOAs from the oxidation of several terpenes, including á-pinene, using high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS), atmospheric solids analysis probe mass spectrometry (ASAP-MS), and FTIR. The ability of HR-ToF-AMS, a real-time technique, to analyze organic nitrates will be explored, as will the applicability of ASAP-MS, an ambient ionization technique, to particulate analysis.

CHARACTERIZATION OF HIDDEN NANOPARTICLES-POLYMER INTERFACE IN COMPOSITES

M. Zhao,¹ B. Ming,¹ A. E. Vladar,¹ X. Gu,¹ and T. Nguyen¹

¹National Institute of Standards and Technology, Gaithersburg, MD 20899, mzhao@nist.gov

The interface of nanoparticles-polymer plays an important role in properties and applications of nanocomposites. However, few analytical techniques are suitable for characterizing this interface due to its small length scale and hidden natures. In this work, the hidden nanoparticles-polymer interface in composites is studied by scanning probe microscopy (SPM) and scanning electron microscopy (SEM). Specifically, electric force microscopy (EFM), a special type of SPM based on long-range electrostatic interactions, and poly-transparent SEM (PT-SEM), a newly developed SEM technique for subsurface imaging, were applied in this study. The high-imaging of nanoparticles-polymer interface such as zinc oxide-polyurethane, titanium oxide-epoxy, carbon nanotube-epoxy, and carbon nanotube-polyimide was demonstrated. The effect of experimental parameters of EFM and PT-SEM on interface imaging was also discussed. In particular, EFM and PT-SEM are nondestructive techniques for the nanoscale characterization of hidden interface in both thin film and bulk samples without any sample preparations. Hence, EFM and PT-SEM will be powerful tools not only for the characterization of hidden interface in nanocomposites, but also for a broad range of other nanotechnology applications.

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