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A thermodynamic scaling law for the relaxation times of complex liquids as a function of temperature and volume has been proposed in the literature: τ(T,V) = ƒ(TVγ), where γ is a material-dependent constant. We test this scaling for six materials, linear polystyrene, star polystyrene, two polycyanurate networks, poly(vinyl acetate), and poly(vinyl chloride), and compare the thermodynamic scaling to T - Tg scaling, where τ = ƒ(T - Tg). The thermodynamic scaling law successfully reduces the data for all of the samples; however, polymers with similar structures but different glass transition (Tg) and pressure-volume-temperature (PVT) behavior, i.e., the two polycyanurates, cannot be superposed unless the scaling law is normalized by TgVgγ. On the other hand, the T - Tg scaling successfully reduced data for all polymers, including those having similar microstructures. In addition, the T - Tg scaling is easier to implement since it does not require knowledge of the PVT behavior of the material. The relationship between TgVgγ/TVγ and T - Tg scaling is clarified and is found to be weakly dependent on pressure. [ABSTRACT FROM AUTHOR]

High aspect ratio multi-walled carbon nanotubes (MWCNTs) having an average length of 4.23 μm and an average diameter of 9.5 nm have been melt mixed with immiscible polystyrene/poly(methyl methacrylate) (PS/PMMA) blends in mass ratio 80:20 and 20:80, respectively. The carbon nanotubes (CNTs) reside in the PMMA phase, and length analysis after melt mixing indicates that when PMMA was the minor phase (20 wt%), little or no CNT breaking occurred during mixing. On the other hand, when PMMA was the major phase (80 wt%), the average length of the CNTs was reduced to 2.78 μm, approximately 70% of their original length. Mixing the CNTs with neat PMMA under the same mixing conditions resulted in a reduction in CNT length to 1.02 μm, only 24% of the original length. Electrical conductivity results show that less CNT breakage leads to a reduction by a factor of 2.5 in the electrical percolation threshold in the 20:80 PMMA/PS blend polymer, which is much larger than a simple volume fraction argument would suggest. This article shows for the first time that relatively long MWCNTs break less in polymer blends than in the neat polymer with concomitant reductions in percolation threshold. [ABSTRACT FROM AUTHOR]

ABSTRACT Two multi-walled carbon nanotubes (MWCNTs) having relatively high aspect ratios of 313 and 474 with approximately the same diameter were melt mixed with polycarbonate (PC) in a twin-screw conical micro compounder. The effects of aspect ratio on the electrical, mechanical, and thermal properties of the PC/MWCNT composites were investigated. Electrical conductivities and storage moduli of the filled samples are found to be independent of the starting aspect ratio for these high aspect ratio tubes; although the conductivities and storage moduli are still significantly higher than values of composites made with nanotubes having more commercially common aspect ratios of ∼100. Transmission electron microscopy results suggest that melt-mixing reduces these longer nanotubes to the same length, but still approximately two times longer than the length of commercially common aspect ratio tubes after melt-mixing. Molecular weight measurements show that during melt-mixing the longer nanotubes significantly degrade the molecular weight of the polymer as compared to very similar nanotubes with aspect ratio ∼100. Because of the molecular weight reduction glass transition temperatures predictably show a large decrease with increasing nanotube concentration. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 73-83 [ABSTRACT FROM AUTHOR]