Interfacial tension measurement of reconstructive interfaces

New fabrication method of polymer brushes, “dynamic polymer brush”, was developed recently. In the system where amphiphilic diblock copolymers are added to hydrophobic elastomer, they avoid the elastomer surface in air, but, upon contact with water, spontaneously segregate to the elastomer/water interface and form highly dense polymer brush to lower the interfacial tension. This system is one of many reconstructive surfaces, which change the interfacial structures upon contact with water and hence direct evaluation of interfacial tension is difficult with conventional contact angle measurement. To measure interfacial tension of reconstructive interface, we developed a novel method using elastomer thin films floating on water. Thin films on water was observed by Brewster imaging and their size change was analyzed using the force balance of surface tensions, interfacial tension and elastic force of thin film. The interfacial tension between water and reconstructive elastomer directly measured by this method drastically decreases down to zero due to the dense PEG brushes appeared at elastomer/water interface.