Bionanoparticles as candidate reference materials for mobility analysis of nanoparticles.

We propose bionanoparticles as a candidate reference material for determining the mobility of nanoparticles over the range of 6 × 10(-8)-5 × 10(-6) m(2)V(-1)s(-1). Using an electrospray differential mobility analyzer (ES-DMA), we measured the empirical distribution of several bionanoparticles. All of them show monomodal distributions that are more than two times narrower than the currently used calibration particles for mobility larger than 6 × 10(-8) m(2)V(-1)s(-1) (diameters less than 60 nm). We also present a numerical method to calculate corrected distributions of bionanoparticles by separating the contribution of the diffusive transfer function. The corrected distribution is about 20% narrower than the empirical distributions. Even with the correction, the reduced width of the mobility distribution is about a factor of 2 larger than the diffusive transfer function. The additional broadening could result from the nonuniform conformation of bionanoparticles and from the presence of volatile impurities or solvent adducts. The mobilities of these investigated bionanoparticle are stable over a range of buffer concentration and molarity, with no evidence of temporal degradation over several weeks.

Re-Analysis of the Uncertainty of the 0.895 µm Diameter (NIST SRM(®) 1690) and the 0.269 µm Diameter (NIST SRM(®) 1691) Sphere Standards.

The uncertainties of the mean diameters of the nominal 1.0 µm SRM(®) 1690 polystyrene spheres and of the nominal 0.3 µm SRM(®) 1691 polystyrene spheres are recomputed using the current NIST Guidelines for computing uncertainty. The revised expanded uncertainty (approximately 95 % confidence level) for SRM(®) 1690 polystyrene spheres is equal to 0.005 µm compared to previous value of 0.008 µm. The revised expanded uncertainty for SRM(®) 1691 is equal to 0.004 µm compared to the previous value of 0.007 µm. The major cause of the reduction in the uncertainty for the 1.0 µm spheres is from a decrease in the recomputed uncertainty of the refractive index of the polystyrene spheres. The 1.0 µm spheres were used in calibrating the electron microscope used to size the 0.3 µm spheres, and the reduction in the uncertainty of 1.0 µm SRM(®) uncertainty was the biggest factor in the decrease in the uncertainty of the 0.3 µm spheres.

In Situ Burning of Oil Spills.

For more than a decade NIST conducted research to understand, measure and predict the important features of burning oil on water. Results of that research have been included in nationally recognized guidelines for approval of intentional burning. NIST measurements and predictions have played a major role in establishing in situ burning as a primary oil spill response method. Data are given for pool fire burning rates, smoke yield, smoke particulate size distribution, smoke aging, and polycyclic aromatic hydrocarbon content of the smoke for crude and fuel oil fires with effective diameters up to 17.2 m. New user-friendly software, ALOFT, was developed to quantify the large-scale features and trajectory of wind blown smoke plumes in the atmosphere and estimate the ground level smoke particulate concentrations. Predictions using the model were tested successfully against data from large-scale tests. ALOFT software is being used by oil spill response teams to help assess the potential impact of intentional burning.

Polarized light-scattering measurements of dielectric spheres upon a silicon surface.

The polarization of light scattered into directions out of the plane of incidence by polystyrene latex spheres upon a silicon substrate was measured for p -polarized incident light. The experimental data show good agreement with theoretical predictions for three sizes of spheres. These results demonstrate that the polarization of light scattered by particles can be used to determine the size of particulate contaminants on silicon wafers. Theoretical models, based on successive degrees of approximation, indicate that the mean distance of a particle from the surface is the primary determinant of the scattered light polarization for small out-of-plane scattering angles.

Development of a One-Micrometer-Diameter Particle Size Standard Reference Material.

The average diameter of the first micrometer particle size standard (Standard Reference Material 1690), an aqueous suspension of monosized polystyrene spheres with a nominal 1 µm diameter, was accurately determined by three independent techniques. In one technique the intensity of light scattered by a diluted suspension of polystyrene spheres was measured as a function of scattering angle, using a He-Ne laser polarized in the vertical direction. The second technique consisted of measuring as a function of angle the intensity of light scattered from individual polystyrene spheres suspended in air, using a He-Cd laser with light polarized parallel and perpendicular to the scattering plane. The measurement of row length by optical microscopy for polystyrene spheres arranged in close-packed, two-dimensional hexagonal arrays was the basis of the third technique. The measurement errors for each technique were quantitatively assessed. For the light scattering experiments, this required simulation with numerical experiments. The average diameter determined by each technique agreed within 0.5% with the most accurate value being 0.895±0.007 µm based on light scattering by an aqueous suspension. Transmission electron microscopy, flow through electrical sensing zone counter measurements, and optical microscopy were also used to obtain more detailed information on the size distribution including the standard deviation (0.0095 µm), fraction of off-size particles, and the fraction of agglomerated doublets (1.5%).