Shouren Ge

Confinement-induced super strong PS/MWNT composite nanofibers

Shear Modulation Force Microscopy (SMFM) together with the Atomic Force Microscopy (AFM) based three-point bending technique were used to measure the mechanical properties of electrospun polymers and polymer nanocomposite fibers. Both techniques showed that the moduli of the fibers increased significantly with decreasing fiber diameter. We attributed this enhancement to the orientation of polymer chains which occurs during the electrospinning process. We then predicted, and confirmed experimentally, that the phenomenon scales with Rg rather than with the absolute fiber diameter and can propagate radially for large distances (~20Rg) into the fiber interior. The inclusion of nanotubes into the fibers further enhanced the orientation by introducing additional surfaces. The additional increase in modulus (more than an order of magnitude) could then be explained by the same model and scaled on a universal curve.

Use of functionalized WS2 nanotubes to produce new polystyrene/polymethylmethacrylate nanocomposites

Multiwall WS2 nanotubes of 40 ‐ 50 nm diameter were functionalized with n-octadecyl phosphonic acid by sonication in toluene and blended with mixtures of polystyrene (PS) and polymethylmethacrylate (PMMA) to form new nanocomposite (NC) materials. The surface and domain structures were studied by atomic force microscopy (AFM), scanning transmission X-ray microscopy (STXM) and transmission electron microscopy (TEM) for various levels of loading of nanotubes up to 20 wt%. Phase-separated domain size and surface roughness of the nanocomposite films were found to be dramatically reduced relative to the pure homopolymer blend and good dispersal of the nanotubes in the blend matrix was attained. q 2003 Published by Elsevier Science Ltd.

Surface characterization of cross-linked elastomers by shear modulation force microscopy

Abstract Brominated poly(isobutylene- co -4-methylstyrene) (BIMS) is a synthetic terpolymer which can be stoichiometrically cross-linked by N , N ′-dicinnamylidene-1,6-hexanediamine (DIAK). The degree of cross-links on bulk samples was determined by measuring the low frequency shear modulus with parallel plate method. The surface modulus of the same samples was measured using a new method, shear modulation force microscopy (SMFM). The moduli of the bulk sample and the surface were found to have the same scaling with the cross-link density, and good agreement with rubber elasticity theory was obtained in both cases. The SMFM was then used to monitor the cross-linking process, as a function of DIAK concentration and curing time, in thin films where standard rheological methods cannot be applied. The results show that in all cases the cross-linking reaction at the surface reaches saturation in less than 10 min as compared to at least 1 h in the bulk samples.

Nanostructure Formation in Spin Cast Polystyrene Films

The dependence of spin-cast polystyrene film thickness on silicon substrates is examined as a function of concentration (in toluene) and molecular weight. For uniform films ranging in thickness from 100 A to 1 µm, thickness follows a power law dependence on concentration, with the power varying from 1.25 at low molecular weights, to greater than 2 at the highest molecular weights examined. For very dilute concentrations, atomic force microscopy reveals that the films break up into a uniform distribution of voids or islands with submicron dimensions, as has been observed previously. The apparent film thickness (at molecular weight 690 000), is determined by secondary ion mass spectrometry, and is found to vary linearly with concentration for film thicknesses below ∼30 A, the thickness at which the film begins to break up. At this molecular weight, X-ray reflectivity results indicate that the limiting thickness of the remnant polymer regions is ∼30 A. Effects of annealing are also investigated. © 2000 Society of Chemical Industry