Abstract

Control over the surface morphology of solids as well as manufacturing of functional biomimetic surfaces with special responsive properties, also known as "smart surfaces", have attracted intense scientific research effort. The recent surge of interest in these responsive systems stems from the widespread number of applications ranging from environmental cleanup to molecular sensors and micro/nano fluidic devices. We report here a methodology for the development of multifunctional responsive surfaces via ablating Si wafers with femtosecond laser pulses and subsequently coating them with different types of functional coatings [1]. The initial laser structured surfaces exhibit controlled dual-scale roughness at both the micro- and the nano-scale, which mimics the hierarchical morphology of responsive surfaces found in nature. Depending on the conformal coating deposited onto these surfaces, the following functionalities and reversible responsive properties are attained: a) pH responsiveness (Fig. la): when a polymer brush is "grafted from" these surfaces based on a pH-sensitive polymer, these artificially structured surfaces can alter their behaviour from super-hydrophilic (after immersion in a low pH buffer) to super-hydrophobic and water repellent (following immersion to a high pH buffer), (b) Photo-responsiveness (Fig. lb): when photo-responsive azobenzene molecules are grafted onto the surface, a dynamic optical control of the wetting properties is obtained and the surface can be switched from super-hydrophilic (after irradiation with UV light) to hydrophobic (following irradiation with visible light), (c) Electro-responsiveness (Fig. lc): when a conformal oxide layer is thermally grown, a dynamic electrical control of the wettability can be achieved by means of electrowetting and (d) Chemo-responsiveness (Fig. 1d): when the surface is electrochemically etched to form a porous Si layer selective sensitivity to organic solvents is obtained.

© 2009 IEEE