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Micelle Formation in Polymer / Copolymer Blends

In this project a blend of amphiphilic block copolymer (a copolymer with a hydrophilic and a hydrophobic block) and hydrophobic homopolymer was analyzed. The goal was to predict the critical micelle concentration (CMC) as a function of temperature, polymer length and copolymer composition.

Similar to surfactants dissolved in e.g. water, the block copolymers A-b-B can self-assemble into micelles with the homopolymer hA acting as a solvent. To reduce the unfavorable interaction with hA the hydrophilic blocks accumulate in the micelle core whereas the hydrophobic blocks stick out to build the corona.

To form micelles a certain minimum surfactant or block copolymer concentration is needed. For low copolymer concentrations the polymer / copolymer blend builds a uniform mixture. If the copolymer concentration is increased, at a certain concentration the number of micelles rises abruptly. This is the critical micelle concentration (CMC).

Assuming spherical micelles, we used a scaling ansatz (e.g. de Gennes 1978, Leibler etal. 1983) to compute the free energy of the coploymer / homopolymer blend as a function of temperature, number of micelles and so on. The equilibrium configuration of the system, and thus the CMC, was then determined as the minimum of the free energy.

Project contact

Thomas Haller

Dr. Flavio De Lorenzi

Project partner

Geberit Schweiz