Phase characterization using SANS

A number of multidimensional analyses have been developed that provide powerful methods for characterizing these polymers. Linking a liquid chromatogram to a pyrolysis gas chromatograph [l 9] can determine the breadth of the composition distribution, as the method fractionates the SAN copolymer before pyrolysis. This information is useful for determining the source of variation in SAN copolymer properties. Composition drift towards high acrylonitrile-containing fractions can lead to undesirable yellow color, and excessively broad composition drift can cause opacity and brittleness in the material due to phase separation... 

Drugs. Farkas et al. " have used a combination of polarizing microscopy, SANS, and transmission electron microscopy to characterize the liquid crystalline phases produced by the non-ionic surfactants, Syn-peronic A7 (PEG7-C13.15), alone and in the presence of two chlorhexidine species, chlorhexidine base, and its diacetate salt. Polarizing microscopy and electron microscopy were used to examine the nature of the liquid crystals formed, while SANS was used to determine their interlayer spacing. For the SANS studies. 

First, different data sets (away from and at binodal) must be scaled to the identical temperature and concentrations. This is possible for a few blends with (assumed) identical interaction parameter but characterized by different chain lengths (Na, Nb) and hence different phase diagrams. This method is used for isotopic polystyrene mixtures. If the parameter ySANs((t)) is linear with 1/T for each concentration < > then %SANS(=const, T) can be reasonably extrapolated to regions at or inside coexistence curve. We use this solution for olefinic blends composed of random copolymers E EE. Here the self-same mixtures are used in both bulk SANS samples and in profiled thin films. 

The most used techniques for characterizing the internal nanostructures of aqueous dispersions of LLC phases are the small angle X-ray (SAXS) and neutron (SANS) scattering techniques. Figure 2 (left) shows the typical SAXS patterns for the fully hydrated non-dispersed V2, H2, and L2 bulk phases (black lines) and their corresponding nanostructured aqueous dispersions (red lines) [83]. It is evident from the SAXS patterns in Figure 2 (left) that the internal nanostructures are preserved upon dispersing the bulk phases in excess water, as the same characteristic X-ray diffraction peaks are observed for the dispersed and the non-dispersed phases. 

Using FRES and others techniques, Wang and Composto investigated wetting and phase separation in polymer blend films composed of deuterated poly(methyl methacrylate) (d-PMMA) and poly(styrene-raw-acrylonitrile) (h-SAN) at the critical concentration [176-180]. This blend is characterized by a lower critical solution temperature (LCST) behavior with Tlcst 160 °C and 0d-PMMA 0.5 [180]. In this... 

SANS measurements on blends of PVME/PS have been reported in a number of studies [187-192]. PS/PVME is a widely studied blend, at least partly due to the lest behavior well-documented by various characterization methods. The results show miscibility in the region classified as single phase by more conventional methods. The difference in the lest temperature ( 40 °C) of deuterated PS/PVME versus PS/PVME blends was noted, yielding a relatively small effect, thus justifying the use of deuterated polymers to model hydrogenated polymer blends [187,192]. Additional SANS studies include PMMA/PVF2 [187], PS/P(nBMA) [189], PB(different vinyl contents)/PS [193],polyaniline/PA6 [194] and chlorinated PE/PMMA [195] blends as well as citations noted in Table 5.1. 

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