Critical mixtures of aqueous solutions of polymers can be separated into two or more immiscible phases. Particulate materials are distributed in such phase systems generally between one bulk phase and the interface between bulk phases. The distribution is described by a simple partition law and is quantitatively determined by temperature, interfacial tensions, the electromotic potential difference between phases and the nature of the particle surface. The effects on transfacial potential differences of varying polymer, NaCl and sodium phosphate concentrations in dextran/polyethylene glycol systems were studied: increase of polyethylene glycol concentration increased the potential; addition of up to 40 mM NaCl progressively reduced the potential to zero: very small (less than 10 mM) concentrations of sodium phosphate buffer increased the potential, but further increase caused a fall in potential, which was less marked than that caused by equivalent concentrations of NaCl. The partition properties of a variety of cells, native or modified by treatment with trypsin, neuraminidase or maleic anhydride, were studied. In systems containing greater than 40 mM NaCl no difference in partition patterns for modifications of each cell type was observed. In systems containing no NaCl the partition pattern was highly dependent on the nature of the modification. From the behaviour of such models, polymer-electrolyte phase systems suitable for study of cell surface modification involving change, or no change, in net surface have been identified.
