Polymer mixtures, crystallization distributions

Statistical mechanics was originally formulated to describe the properties of systems of identical particles such as atoms or small molecules. However, many materials of industrial and commercial importance do not fit neatly into this framework. For example, the particles in a colloidal suspension are never strictly identical to one another, but have a range of radii (and possibly surface charges, shapes, etc.). This dependence of the particle properties on one or more continuous parameters is known as polydispersity. One can regard a polydisperse fluid as a mixture of an infinite number of distinct particle species. If we label each species according to the value of its polydisperse attribute, a, the state of a polydisperse system entails specification of a density distribution p(a), rather than a finite number of density variables. It is usual to identify two distinct types of polydispersity variable and fixed. Variable polydispersity pertains to systems such as ionic micelles or oil-water emulsions, where the degree of polydispersity (as measured by the form of p(a)) can change under the influence of external factors. A more common situation is fixed polydispersity, appropriate for the description of systems such as colloidal dispersions, liquid crystals, and polymers. Here the form of p(cr) is determined by the synthesis of the fluid. 

Several approaches towards the synthesis of hierarchical meso- and macro-porous materials have been described. For instance, a mixture that comprised a block co-polymer and polymer latex spheres was utilized to obtain large pore silicas with a bimodal pore size distribution [84]. Rather than pre-organizing latex spheres into an ordered structure they were instead mixed with block-copolymer precursor sols and the resulting structures were disordered. A similar approach that utilized a latex colloidal crystal template was used to assemble a macroporous crystal with amesoporous silica framework [67]. 

This accessory was used to image, in situ, the phase separation of a homogeneous LCST PS/PVME (50/50 w/w) polymer blend. A homogeneous mixture was cast directly onto the diamond, which was the ATR crystal used for the measurements. The resultant FTIR images are presented in Fig. 10.8 (Section 3.2), showing the distribution of both PS and PVME, before and after exposure to 60 bar of CO2. Following exposure to CO2 it can be seen that phase separation occurs, resulting in domains of ca. 200 pm [135]. 

The type and quality of solvents can influence the MALDI analysis of polymer samples. For example, the dryness and purity of tetrahydrofuran (THF) used to prepare polymer samples play a central role in the success of detecting high-molecular mass polymers [29]. The solvent system used can affect analyte incorporation and distribution in matrix crystals. As has been shown in MALDI biopolymer analysis, analyte distribution in matrix crystals can significantly affect the signal reproducibility, detection sensitivity, and relative intensities of individual components in a mixture [40]. However, unlike biopolymer analysis-where a... 

The polymer film may have resulted from cross-linking of the anionic units via calcium ions. Outside the region of the polymer film there was a mixture of calcite and vaterite crystals, as in the control experiment indicating that the surface film was influencing the surface crystallisation. The SEM image shows calcite crystals with roughened faces, the crystals on the surface of the polymer film displayed a relatively narrow distribution of shape and size as compared to the blank experiment. 

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