The predictive and correlative capabilities of two recent versions of the free‐volume theory for self‐diffusion in polymer–solvent systems are examined by comparisons with experimental data. Neither the Vrentas–Duda free‐volume theory nor the Paul version generally provides satisfactory predictions for the temperature and concentration variations of solvent self‐diffusion coefficients. However, the Vrentas–Duda theory does provide good correlations of solvent self‐diffusion data, and, furthermore, this theory can provide good predictions if a small amount of solvent self‐diffusion data is used to help estimate the parameters of the theory. New diffusivity and equilibrium data were collected for the toluene‐PVAc system to provide a broader database for evaluation of the self‐diffusion theories.
SynopsisVapor sorption data were obtained for the ethylbenzene-poly(ethy1 methacrylate) system at 120OC. Successive step-change sorption experiments carried out at two-film thicknesses indicate the presence of maxima in the sorption curves. The fractional amount of overshoot decreased as the final pressure or weight fraction of the experiment increased and as the sample thickness increased. It is proposed that the maxima in the sorption curves are caused by structural rearrangements produced by relaxation of polymer chains.
Light-
and humidity-responsive chiral nematic photonic crystal
(PC) films containing cellulose nanocrystals (CNCs) were fabricated.
A photoactive polymer with hydrophilic groups, poly-(3,3′-benzophenone-4,4′-dicarboxylic
acid dicarboxylate polyethylene glycol) ester, was coassembled with
CNCs to form flexible iridescent films with a tunable chiral nematic
order. In the coassembly process, the intermolecular hydrogen bonds
of CNCs were weakened, which facilitated the fine regulation of the
chiral PC nanostructure. The PC films displayed sensitive responses
to both light and humidity. With increasing humidity from 30 to 100%,
the chiral nematic helix pitch increased from 328 to 422 nm. The color
of the PC films changed from blue to green, yellow, orange, and dark
red with increasing relative humidity. Over 15 min of light irradiation,
the absorption intensity of the films increased gradually. The light
and humidity responses of the films were reversible. The films maintained
their variable cholesteric liquid crystal texture and helical lamellar
structure after light irradiation at different humidities. These PC
films are expected to be useful in intelligent coatings and 3D printing.
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