The stability of silica sols has been studied in the presence of adsorbing (hydroxyethyl cellulose) and nonadsorbing (sodium carboxymethyl cellulose and sodium polystyrene sulphonate) polymers. The state of aggregation has been monitored by turbidity measurements and for the adsorbing polymer, flocculation due to polymer bridging was observed at low polymer additions while at higher polymer concentrations flocculation induced by a depletion mechanism was observed for all samples studied. The critical polymer concentrations required to induce depletion flocculation were 0.2, 0.1 and 0.05% for hydroxyethyl cellulose (HEC), sodium carboxymethyl cellulose (CMC) and sodium polystyrene sulphonate (PSS), respectively. Varying the charge density of the CMC had no apparent effect on the critical polymer concentration required to induce flocculation.The pair potentials of the particles for the various systems have been calculated incorporating contributions from van dor Waals, electrostatic, steric (for HEC) and depletion forces and the depth of the secondary minima in the energy curves have been used as an index for the onset of flocculation. A critical value for this minima of 5 k , Tfor the onset of flocculation was established from stability measurements determined using simple elec-Paper 0/05516F;

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The interaction between uncharged polymer and nonionic surfactants is usually weak or nonexistent, except for the association between polyacids and ethoxylated nonionic surfactants. In this paper we have studied the interaction between poly(acrylic acid) and an ethoxylated nonyl phenol ether. Below pH 3 an insoluble complex forms, which redissolves on addition of excess surfactant. While the amount of surfactant required to form the maximum amount of precipitate or redissolve the complex is linearly dependent on polymer concentration, that required for the onset of precipitation is not. Despite the polydisperse nature of the ethoxylate chain, little fractionation of the surfactant after precipitation was observed. The nonionic surfactant was preferentially partitioned into water rather than dodecane, except where the polymer/surfactant complex formed; in this case the complex dissolved mainly in the dodecane, forming a gel containing the oil. The origins of the effect of solution conditions and polymer characteristics on complex formation are discussed.

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