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Adsorption Studies of Block Copolymers

Jabir Ali Shar

Jabir Ali Shar (previous student, left the group in 1998)

Pluronics and Reverse Pluronics are a series of ABA and BAB type block copolymers composed of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) and poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) blocks respectively.

Generally, the A blocks in the former case and B blocks in the latter case are of the same length. The poly(ethylene oxide), PEO, blocks are hydrophilic, whereas poly(propylene oxide), PPO, blocks are hydrophobic in nature. Due to the dual nature of copolymers of this type, they are used in wide range of applications as stabilisers, emulsifiers and flocculating agents for colloidal dispersions. The conformation of the copolymers in the adsorbed state determines their ability to influence the stability of the dispersed phase. In colloid science, the adsorption of copolymers is of great industrial importance.

Adsorption studies of a series of copolymers of different concentrations in aqueous solutions were investigated on polystyrene latex and silica substrates. It has been shown that the amount of adsorption increases with increase in overall copolymer molecular weight and PEO block mass. It is apparent from the plots of adsorbed amount, * (mg/m2), versus polymer equilibrium concentration that for all the systems studied so far, adsorption initially increases with copolymer concentration up to a certain value after which it acquires a plateau level. In general, we found higher adsorbed amounts and hydrodynamic layer thickness for the Reverse Pluronics than the corresponding Pluronics of equivalent mass. This we attribute to surface-aggregation of the hydrophobic polymers at the adsorbing particle surface.

This project is funded by the Government of Pakistan