Effects of a non-adsorbing polymer on colloid stability : force measurements between mica surfaces immersed in dextran solution

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Abstract
The forces between two cylindrically curved mica surfaces have been measured in aqueous dextran solution in the presence of NaCl. At various NaCl concentrations (10-4, 10-3, 10-2 M) we observe an additional attractive contribution to DLVO forces when dextran is added to the aqueous solution. The most striking consequence of this effect is that the jumps into primary minimum contact occur at larger distances and at weaker forces than with pure electrolyte solution; moreover in some cases where hydration forces prevent the jump in primary minimum contact (NaCl 10-2 M), the addition of dextran produces this jump. In all cases the primary minimum contact takes place at zero distance which proves that no adsorbed dextran is trapped between the two mica surfaces. These experimental results are analysed and compared with the recent theories of polymer depletion effect on colloid stability