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We have conducted a study of the phase compositions of a ternary solution containing dextran/polyethylene glycol (PEG)/water using UV–visible spectrometry to study the equilibrium behaviour and confocal microscopy to study the dynamic behaviour observed when the system undergoes phase separation driven by the loss of water. Such a study of phase compositions using confocal microscopy is a new development of the technique. In the static experiments, we find a cloud curve, which lies above the coexistence curve on the PEG rich side of the phase diagram, this is found to be in qualitative agreement with calculations of the phase behaviour for a model polydisperse system. In the dynamic experiments, we are able to measure the phase composition using confocal microscopy in the late stages of separation. Here, the compositions lie well inside the coexistence curve at lower drying rates but converge with it at higher drying rates. This is linked to a change in phase morphology: at low rates, a droplet morphology is observed throughout the process whilst at high drying rates a gross phase separation into two layers is observed to occur even at the earliest times probed by the experiment.

The ingress of water from various solutions into dense starch and sucrose:starch plaques has been observed over a range of temperatures using stray field nuclear magnetic resonance imaging. Profiles of water content as a function of depth from the surface and sorption time have been analysed to obtain mutual diffusion coefficients. This has been done using the Boltzmann transform and by measuring the front position as a function of time which produces an average mutual diffusion coefficient. This average diffusion coefficient can be fit with an Arrenhius expression with an activation energy of 56 ^ 4 kJ mol 21 . It was found that the average diffusion coefficients for 30:70 and 50:50 sucrose:starch mixtures could be calculated using a weighted mean of the average diffusion coefficients for pure sucrose and pure starch. Although the diffusion coefficients for amorphous and crystalline sucrose are quite different, this has a minor effect on the calculated diffusion coefficients for the range of crystallinities observed in the sucrose:starch mixtures. q 2001 Elsevier Science Ltd. All rights reserved.

Mixtures of deuterated polyethylene oxide with hydrogenous polymethyl methacrylate and hydrogenous polyethylene oxide with deuterated polymethyl methacrylate have been investigated using small angle neutron scattering. The range of temperatures used was 423–473 K and the volume fraction of polyethylene oxide in the mixtures varied from ca. 0.1 to ca. 0.27. Values of the effective interaction parameter ( χ eff ) were obtained using the incompressible random phase approximation. Both temperature dependence and composition dependence were noted in the values of χ eff . The temperature dependence observed was compared with that predicted by equation of state theory. A notable feature of the composition dependence of χ eff was the change in behaviour as temperature increased. Changes in the excess volume of mixing have been cited as a possible source of this behaviour, but the currently available data do not allow us to confirm this. Using the relation between χ eff and a composition independent interaction parameter proposed from Monte Carlo simulations, approximate values of the composition independent interaction parameter have been obtained.

Mixtures of high-molecular-weight hydrogenous, syndiotactic poly(methyl methacrylate) with two lower-molecular-weight deutero poly(methyl methacrylate)s have been investigated over a range of temperatures and compositions using small-angle neutron scattering. Effective interaction parameters have been obtained which have been used to estimate the Flory-Huggins interaction parameter. Spinodal temperatures have been defined from the temperature dependence of these effective interaction parameters and other parameters of the mixtures. The conclusion is that these isotopic mixtures are incompatible at ambient temperatures and have an upper critical solution temperature. The influence of local stereochemistry on the polymer configuration is evident in the scattering cross-section variation with scattering vector. This variation is compared with the scattering obtained from Monte Carlo rotational isomeric state calculations.