Journal of Polymer Science Part B: Polymer Physics

The temperature dependence of the viscoelastic properties of thin polystyrene (PS) films is monitored via the indentation of an atomic force microscope tip into films prepared on native silicon oxide, H-terminated silicon, and PS brushes. For film/brush combinations with Mw above the critical value for the occurrence of molecular entanglement or for films with the same Mw values on H-terminated silicon, the Tg of thin films becomes comparable with the bulk value. Data are discussed in terms of residual solvent presence, interfacial free volume, and molecular entanglement.

The structure of the polymer network and water are important factors governing the chemical and physical properties of gel materials. In this manuscript, the effects of crosslinker density on the properties of poly-N,N-dimethylacrylamide hydrogels are investigated. Mechanical strength of the gel increases with increasing crosslinker density. Differential scanning calorimetry results show that the thickness of the bound water increases as the crosslinker density increases. These results suggest that the bound water plays an important role in strengthening the hydrogel.

An improvement in the mechanical and gas barrier properties of elastomeric nanocomposites would be invaluable for applications such as packaging. Here, nanocomposites are prepared from a styrene-butadiene rubber (SBR) matrix and synthetic lamellar nanofillers. A novel nanofiller surface treatment, allowing further use of a coupling agent, is proposed. A significant improvement of the filler dispersion state is obtained, resulting in highly enhanced mechanical and gas barrier properties; the key factors behind the improvements are also identified.

The effects of graphene and carbon nanotube (CNT)-based fillers on the shear properties of a thermoset epoxy were investigated. In brief, 10 wt % of one of the epoxy-functionalized CNTs was found to increase the shear storage modulus, G′, by 136% and the corresponding loss modulus, G″, by almost 400%. A hybrid system of the functionalized CNT and graphite (pictured) was also studied and was found to increase G′ and G″ up to 51 and 181%, respectively.

Nanostructured amorphous samples of poly(vinyl acetate), poly(methyl methacrylate), and their blends were produced by forming crystalline inclusion compounds (ICs) with urea (U) and γ-cyclodextrin (γ-CD), followed by careful host removal. Also, non-stoichiometric γ-CD-IC samples of each were formed. All nanostructured samples exhibited Tgs elevated above those of as-received and solution-cast samples, and several conclusions were reached concerning how the degrees of constraint experienced by each affect their chain mobilities and resultant T_gs.