Field-flow fractionation and hydrodynamic chromatography on a microfluidic chip.

We present gravitational field-flow fractionation and hydrodynamic chromatography of colloids eluting through 18 μm microchannels. Using video microscopy and mesoscopic simulations, we investigate the average retention ratio of colloids with both a large specific weight and neutral buoyancy. We consider the entire range of colloid sizes, including particles that barely fit in the microchannel and nanoscopic particles.

Analysis of a simple method for the reduction of phonon peak broadening in surface Brillouin light scattering.

We present an investigation of the effect of the collecting lens aperture on the line shape of phonon peaks observed in surface Brillouin light scattering (SBLS) from surfaces of opaque materials and transparent thin films. In general, the broadening that is due to the aperture is asymmetric and can be as large as 60% of the peak frequency shift in the case of a f/1.4 aperture with an angle of incidence theta(i) = 30 degrees.

Molecular weight dependence of reductions in the glass transition temperature of thin, freely standing polymer films.

We have used transmission ellipsometry to perform a comprehensive study of the glass transition temperature T(g) of freely standing polystyrene films. Six molecular weights M(w), ranging from 575 x 10(3) to 9100 x 10(3), were used in the study. For each M(w) value, large reductions in T(g) (as much as 80 degrees C below the bulk value) were observed as the film thickness h was decreased.