Hybrid structure of pH-responsive hydrogel and carbon nanotube array with superwettability

Abstract

We report an all-dry fabrication method of the hybrid structure of pH-responsive hydrogel and carbon nanotube arrays using initiated chemical vapor deposition (iCVD). Vertically aligned carbon nanotube (VACNT) arrays with low site density were coated by a vapor-deposited poly(methacrylic acid-co-ethylene glycol diacrylate) hydrogel with complete retention of the aligned structure and precise control of the coating thickness on each nanotube. The hydrogel coating imparted pH-responsiveness to the nanotube arrays and significantly enhanced the surface wettability. With an ultrathin 50 nm hydrogel coating, the hybrid hydrogel–VACNT array structure exhibited superwettability in neutral buffer solutions, which was attributed to the synergistic effect of the structure porosity and the ionization of the pH-responsive hydrogel. Under the acidic condition, the wettability depended on the coating thickness, and the apparent contact angle of the hybrid structure was in agreement with the calculated results from the Cassie–Baxter model.