"Freezable" and "unfreezable" water in waxy corn starch were characterized by thermal analysis, and the mobility in those states was characterized by solid state (2)H and (1)H NMR. Water was found to be isotropically mobile for samples over a range of water contents (6.3-47% by total weight) at room temperature. Mobility increased with increasing water content and temperature. According to (1)H and (2)H NMR data, a large fraction of "unfreezable" (DSC) was relatively mobile comparable to a liquid state even down to -32 degrees C. Some anisotropically immobile D(2)O at low temperatures exhibited a solid state Pake pattern in (2)H NMR spectra, which was similar to that of frozen D(2)O (ice) with a 144 kHz splitting. The decreasing fraction of mobile water with decreasing temperature suggested that only some of the so-called "unfreezable" water could be progressively immobilized as temperature decreased. However, much of the water (>50% of water present) remained very high in mobility, regardless of the relatively rigid starch molecules in the glassy solid state.

The water sorption of several starch samples and resistant starch (RS) samples were analyzed using an equilibrium solution‐gel structure model and the results were compared to various sorption theories. It is found that the water sorption relations to water activity in starch in the high water content region could be properly described by the equilibrium two‐phase structural model. The results suggested that favorable starch‐starch interaction determined the formation of starch gel in water. The gel structure had a high molecular modulus of 108 Pa and thus had limited water sorption capability. Part of the starch also exhibited the solution properties with water due to chain ends and defects of the gel structure. Despite the unfavorable starch‐water interaction, starch‐water solution might be formed due to the predominant contributions from the entropy of mixing. The solution phase was responsible for the rapid increase of water sorption at high water activity. It was also demonstrated that the starch could maintain a maximum dynamic unfreezable water up to ≈ 36%, which was consistent with the DSC measurements. © 1996 John Wiley & Sons, Inc.

SYNOPSISProton spin magnetization relaxation in the rotating frame is a simple exponential for poly ( 2,6-dimethylphenylene ether) ( P P O ) (23K) /polystyrene (PS ) (9K) blends of various compositions; these blends are truly homogeneous a t the spin-diffusion distance scale of a few nanometers. Blends of PPO with high molecular weight PS exhibit nonexponential decays for the PS component but exponential decays for the PPO component, indicating compositional fluctuation for PS. In some blends, the relaxations are nonexponential for both components. Three factors have been identified to promote microheterogeneity of nanometer dimensions: high polymer molecular weight, increase of temperature, and preparation of blend using solvent that induces crystallization of PPO such as toluene.

Solid‐state NMR relaxation has been used to explore the distribution of components in poly(phenylene oxide) (PPO) high impact polystyrene (HIPS) and PPO/poly(styrene‐b‐butadiene‐b‐styrene) (SBS) blends. The nuclear relaxation of PPO in the former system is single exponential for all compositions, but the relaxation of PS in the blend is simple exponential only when the PPO content is low but is otherwise nonexponential. The nuclear magnetization decay curves were analyzed in terms of statistical compositional fluctuation at the scale of spin diffusion distances of several nm. Distribution functions for nuclear relaxation and for blend composition have been derived. Extraction of low molecular weight occluded PS from HIPS resulted in blends having reduced homogeneity. Addition of low molecular weight PS enhanced homogeneity in both the PPO/HIPS and PPO/SBS blends. © 1994 John Wiley & Sons, Inc.