Dynamic contact angle on a reconstructive polymer surface by segregation

Abstract

We report the peculiar time evolution of the contact angle of water on reconstructive polymer surface. Surface reconstruction is driven by segregation of amphiphilic diblock copolymer to the water interface of the elastomer, in which amphiphilic diblock copolymer is mixed. In other words, the brush of hydrophilic block is spontaneously formed at the elastomer/water interface and can be called dynamic polymer brush. The contact angle measurement of water droplet was carried out as a function of time after a droplet was placed on the surface. The contact angles stay the same value for certain induction period before decrease monotonically with time. We also proposed a simple model to explain the experimental results quantitatively. The model is based on two hypotheses: water droplet starts to spread only after a depletion layer of the hydrophilic block at the air interface is dissolved, and segregated block copolymer brush begins to repel one another.