Thermal molecular motion of poly(methyl methacrylate) at various interfaces

Thermal molecular motion of poly(methyl methacrylate) (PMMA) at various interfaces, gases and liquids, was discussed. The α _a- and β-relaxation processes were clearly observed even at the air interface. Both relaxation temperatures at the air interface were lower than the corresponding ones in the bulk. In addition, the extent to which the peak temperature for the surface relaxation processes fell below that of the bulk strongly depended on the stereoregularity of the films. Then, thermal molecular motion of PMMA was analyzed at gaseous carbon dioxide (CO ₂) interface. It was more enhanced than that at gaseous nitrogen interface because CO ₂ molecules were sorbed in the interfacial region, which played as plasticizing agents. Finally, mechanical properties of PMMA were also studied at interfaces with liquids such as water, hexane and methanol. The modulus decreased closer to the outermost region of the film. The extent to which the modulus decreased in the interfacial region was consistent with the amount of liquid sorbed into the film. Therefore, it can be claimed that interfacial molecular motion of polymers can be regulated on the basis of the aggregation states.