Demixing of Aqueous Polymer Two-Phase Systems in Low Gravity

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Abstract
When polymers such as dextran and poly(ethy1ene glycol) are mixed in aqueous solution, biphasic systems often form. On Earth the emulsion formed by mixing the phases rapidly demixes because of phase density differences. Biological materials can be purified by selcctive partitioning between the phases. In the case of cells and other particulates thc efficiency of these separations appears to be compromised by the demixing process. To modify this process and to evaluate the potential of two-phase partitioning in space, experiments on the effects of gravity on phase emulsion demixing were undertaken. The behavior of phase systems possessing phase density differences and systems with essentially identical phase densities was studied at one-g and during low-g parabolic aircraft maneuvers. Results indicate that demixing can occur rather rapidly in space, although more slowly than on Earth. We have examined the demixing process from a theoretical standpoint by applying the theory of Ostwald ripening. This theory predicts demixing rates many ordcrs of magnitude lower than observed. Other possible demixing mechanisms are considered.