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Nonequilibrium poly(N-isopropylacrylamide) (PNIPAM) chains are generated by temperature-induced conformational transitions in the densely interfacial PNIPAM layer at high adsorbed amounts in aqueous solution. The interleaving chains relax in a spatially heterogeneous space of adsorbed layer which is filled with the domains via the hydrogen bonding and hydrophobic interactions. The relaxation dynamics of interleaving chains is changed from the weekly stretched exponential behaviour at the lower adsorbed amount to the strongly stretched exponential behaviour at the higher adsorbed amount. The kinetic constraints for the relaxation dynamics depend on the segment density of the adsorbed layer which is controlled by the temperature. The stretched exponential relaxation is related to an ensemble of relaxations confined in the domains with different physical origins for the heterogeneous dynamics. The range of energy barriers for the relaxation is estimated from the stretched exponent based on the random first order transition theory. [ABSTRACT FROM AUTHOR]

The effect of two colorant particles with different surface geometries on the stability of shear-induced precursors in isotactic polypropylene was studied after the cessation of shear flow at 140 °C. In the absence of particles, the shear-induced precursors survived for at least 100 s after the shear flow ended. The presence of particles was found to stabilize lower molecular weight chains assisting in the formation of additional shear-induced precursors. The precursors thus formed in the samples containing particles contained two oriented clusters with different molecular weights. Incorporation of lower molecular weight chains in the precursors led to increased dissolution rates of the shear-induced precursors. Particle surface geometry was found to influence precursor dissolution, with planar particles stabilizing the shear-induced precursors to a much greater extent than curved particles. The particles investigated thus act like structural probes to follow quantitatively the dissolution process of precursors after shear and importantly to infer the formation of precursors during shear. [ABSTRACT FROM AUTHOR]

Sheared isotactic polypropylene (iPP) forms a special crystalline assembly called branched shish kebab. The effects of two colorants, Cu-phthalocyanine and ultramarine blue, on the branched shish-kebab structure have been investigated by using synchrotron wide-angle x-ray scattering. The effects of the colorants on the morphological distributions of iPP are well constructed through the shear field or temperature gradient, including crystallinity, molecular orientation, fraction of lamellae, and thickness of crystalline lamellae. It is found that the Cu-phthalocyanine can significantly affect the morphological development of sheared iPP but the ultramarine blue cannot. In the presence of Cu-phthalocyanine, the degree of crystallinity is increased, the molecular orientation is enhanced, the more a*-axis-oriented components form, and the crystalline lamellae are thickened. [ABSTRACT FROM AUTHOR]

We present a new correlation function in the form of γ(r)=r(Df-D) exp(-r/a0)cos(br) to describe the essential features of aggregate structure. The scattered intensity distribution corresponding to this correlation function was obtained. Compared with existing models, the new scattering formula can predict a scattering peak in a finite wavevector and control the scattered intensity decay in larger wave vectors. The experimental scattering patterns obtained from polydimethylsiloxane/paraffin liquid mixtures were tested well by the new model. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Zeolite W membranes were grown on their seed pellets prepared via a straightforward vacuum filtration method followed by crystallization, rendering them self-supported. Herein, the feasible application of self-supported zeolite W membranes for CO2/CH4 separation with astonishing CO2/CH4 selectivity was demonstrated. [ABSTRACT FROM AUTHOR]

Theeffect of sodium dodecyl sulfate (SDS) on the poly(N-isopropylacrylamide) (PNIPAM) tethered to nanoparticles was experimentallyinvestigated using dynamic light scattering below the lower criticalsolution temperature. A mean-field analytical model was used to calculatethe parameters of interfacial PNIPAM–SDS complexes. Particularly,the magnitude of SDS adsorption energy obtained decreases with decreasingexcluded volume parameter, implying that the partially collapsed PNIPAMbrush virtually favors the adsorption of SDS onto the PNIPAM chains.A self-consistent field theory (SCFT) model was used to get a detailedquantitative description of monomer density distribution. By loweringthe solvent quality, a number of phenomena related to the noncontinuityof monomer density are revealed. These phenomena are either referredto as the vertical phase separation or as its precursor, which canbe delayed and eventually eliminated as the SDS coverage is increased.The distribution of free chain ends was calculated using the SCFTmodel. Increasing the SDS coverage gives rise to a broader and moreasymmetric distribution of free chain ends, accompanied by a considerableexpansion of the dead zone (below which the free chain ends do notexist), but lowering the solvent quality has opposite influences.The relative thickness of the dead zone can be scaled to a mastercurve, regardless of SDS coverage. [ABSTRACT FROM AUTHOR]

Removal of CO 2 by membrane technologies is one promising approach as compared to other CO 2 capture technologies due to advantages such as simpler operation, higher reliability, lower capital and operating cost, higher energy efficiency, and a cleaner process. In the field of CO 2 gas separation, inorganic membranes have been attracting a lot of attention. Three classes of microporous membrane family, i.e. microporous silica membranes, microporous carbon membranes and zeolite membranes, have been widely studied due to their potential in separating CO 2 gas molecules, contributed by their distribution of selective micropores which are almost identical to the required molecular sizes for diffusing CO 2 gas. This paper review various methods to fabricate the above three types of microporous membranes, at the same time, looking at other researchers employing these methods to fabricate microporous membranes for CO 2 separation. [ABSTRACT FROM AUTHOR]