Depolarized dynamic light scattering was used to measure the
translational and rotational
diffusion of tobacco mosaic virus, TMV, in aqueous solutions of dextran
(M ∼505 000). TMV is an
electrically charged, nucleoprotein assembly with the shape of a stiff,
rigid rod. Dextran is an uncharged,
flexible carbohydrate polymer. The TMV was held at a fixed, dilute
concentration (0.5 mg/mL), while
the concentration of dextran spanned both dilute and semidilute regimes
(0−14.5% by weight). There
was no evidence of phase separation or strong aggregation of the TMV
particles in the presence of the
dextran. The TMV particles dominated the depolarized scattering at
all dextran concentrations. The
angular variation of the decay rates of the autocorrelation functions
always followed the form expected
for symmetric top molecules in the absence of
translational−rotational coupling. Nevertheless,
translational and rotational motions are almost surely coupled in most
dextran-containing solutions.
The apparent translational and rotational diffusion rates
decreased with added dextran, but not exactly
according to the rise in macroscopic solution viscosity. A
transition occurred at about 6.5% dextran.
Beyond this concentration, pronounced failures of the continuum
(Stokes−Einstein) relation between
diffusion and viscosity were found. Translational diffusion
continued more rapidly than expected on the
basis of the macroscopic viscosity, while rotational diffusion fell
sharply below expectation. The quotient
D
r/D
t of rotational and
translational diffusion, which presumably cancels effects due to
viscosity, also
dropped suddenly above the transition point. These findings are
consistent with a sudden onset of
topological constraints to rotational motion of the TMV, without onset
of severe constraints to translational
motion. Temperature dependent studies showed that either the
solution or the solvent viscosity can
describe translation and rotation fairly well, at least at
concentrations below the transition. Energies of
activation for translational and rotational diffusion of TMV were
similar and not strongly dependent on
dextran concentration in this regime.
Graphical abstractHighlights► Vacuum-evaporated polyethylene (PE) is a highly stable and trap-free dielectric. ► PE supports low-hysteresis transport in C60 and pentacene. ► PE additionally allows ambipolar transistor operation of 6,6′-dibromoindigo with balanced mobilities of ∼0.3 cm2/Vs. ► This work shows that high-quality gate dielectrics consisting of polymeric materials can be vacuum-processed.
Polypropylene(PP)/carbon black(CB) composites at different compositions were prepared via melt blending of PP with CB. The effect of CB content on mechanical and electrical properties was studied. Test samples were prepared by injection molding and compression molding techniques. The effect of processing type on mechanical and electrical properties was also investigated. Composites become semi-conductive by addition of 2 wt% CB. The relation between mechanical and electrical properties was discussed. The influence of CB content on morphology and crystallinity was also studied.
ABSTRACT:The synthesis was performed by the electropolymerization of thiophene on a poly(dimethylsiloxane) (PDMS)-coated platinum electrode at 2.2 V with tetrabutylammoniumtetrafloroborate (TBAFB) as a supporting electrolyte and with acetonitrile as a solvent. The characterization of the PDMS-polythiophene (Pth) composites was carried out with cyclic voltammetry, Fourier transform infrared (FTIR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis, and conductivity measurements. The observed conductivities of the PDMS composites were 2.2-5.2 S/cm. The conductivity of Pth did not change appreciably with the addition of up to 30% insulating PDMS, but its processability improved. FTIR, SEM, and DSC studies showed the existence of a strong interaction, rather than physical adhesion, between PDMS and Pth. Highly flexible and foldable PDMSPth composites were obtained.
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