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Phase Separation of Hydrophilic Monomer/Surfactant Aqueous Solution Studied by a Combined Light Scattering and Interference Approach

Polymerization-induced phase separation behavior of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS)/sodium dodecylsulfonate (SDS) aqueous solution was investigated by using a combined small angle light scattering (SALS) and laser light interference (LI) system. Compared with the conventional SALS technique that has been widely used in studying the phase separation kinetics and mechanism of multicomponent polymer blends or solution, the present combined SALS and LI system can additionally provide valuable information on polymerization kinetics prior to the onset of phase separation. It was found that the 1 mol.L -1 AMPS aqueous solution in the presence of 0.2 mol.L -1 SDS underwent apparent phase separation when polymerization conversion approached 82%. The phase separation rate is so rapid that it takes only 90 s for scattering intensity to reach the maximum. The early stage phase separation follows the spinodal decomposition (SD) mechanism that can be described by the classic linear theory sponsored by Cahn and Hilliard. At late stage of phase separation, however, an observable shift of characteristic vector q m to larger values take place, which may result from the secondary phase separation in the monomer-rich phase that leads to a deceased average domain size in sample solution. On the other hand, the integral scattering intensity decreased apparently at late stage of phase separation due to the decreased refractive index difference between the monomer-rich and polymer-rich phases as result of the continued polymerization in the monomer-rich phase.