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Effect of photooxidation on the surface properties of polystyrene

The effect of UV irradiation on the surface properties of polystyrene was studied. It was established that an increase in the exposure dose significantly improves the water wettability of polystyrene; that is, its surface undergoes hydrophilization under the action of photooxidation. It was found that a partial relaxation (rearrangement) of the surface of the photooxidized polymer to the initial low-energy state takes place at the annealing temperatures which are appreciably below the glass transition temperature T g of block polystyrene. An analogous effect was observed when evacuation of the photooxidized samples was carried out even at room temperature. Hence, already at the early stages of photooxidation, rather low-molecular-mass polar products of degradation are formed on the surface layer of polystyrene. These products plasticize the surface layer and markedly decrease its T g . This conclusion is supported by the data of atomic force microscopy, which suggest that, after sufficiently prolonged UV irradiation, the surface layer of polystyrene behaves as a high-viscous liquid in contact with the edge of a microscope.