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Abstract
Associative polymers, which are made of water-soluble polyethylene oxide (PEO) backbones with hydrophobic ends, were used to study the thermodynamics and kinetics of polymer adsorption on polystyrene (PS) latex particles in aqueous solution. Light scattering was the technique used in the study.
The thermodynamics of the study deals with a first order phase transition predicted by S. Alexander in 1977. We have provided the first experimental evidence for this transition, involving a configurational change of polymers on surfaces from a "pancake" phase at a low surface coverage, to a "brush" phase at a high surface coverage. The transition is triggered by the competitive adsorption between backbones and hydrophobes. The nature of the transition appears to be first order by the isotherm study.
On the kinetics part of the study we focused on the exchange kinetics of polymer brushes and free chains in solution. The relaxation of brushes due to the invasion of free chains can be characterized by a non-exponential function. Possible expulsion mechanisms of polymer brushes from interfaces are discussed.
A special feature for associative polymers, the bridging effect, is also discussed. We studied the bridging effect of associative polymers from two aspects: the onset bridging flocculation and the bridging induced chain transfer. The study of the onset bridging flocculation revealed that unless the system's entropy loss from binding particles together is balanced by the adsorption energy of polymer chains, particles stay in a singlet form. A relevant issue to the bridging flocculation is the bridging induced chain transfer between brush surface and bare surface. In this case particles in solution favor the singlet form because the energy gained by adsorbing chains on two surfaces is not great enough to balance the entropy loss. Equilibrium and non-equilibrium cases were distinguished in the study of bridging induced chain transfer.
