Tunable wrinkle and crease surface morphologies from photoinitiated polymerization of furfuryl alcohol

Addition of a small fraction of hydrophobic photoacid generator (PAG) to furfuryl alcohol provides a facile route to generate wrinkle topology by acid-catalyzed polymerization that is induced by ultraviolet (UV) light. Here, we describe how the primary characteristic parameters, wavelength and amplitude, of these periodic wrinkles can be tuned through control of the thickness of this furfuryl alcohol-PAG solution prior to UV exposure and the environmental humidity. As the initial coating thickness is increased, the wavelength remains unchanged at fixed temperature and PAG concentration, but the amplitude of the wrinkles increases exponentially with increased coating thickness. A wrinkle to crease transition is observed in some cases as the thickness of the solution coating is increased; this behavior is dependent on the PAG selection. Conversely, variation in relative humidity does not significantly impact the amplitude of the wrinkles, but there is a step change in the wavelength of the wrinkles near approximately 45% relative humidity with a factor of 3 decrease in the wavelength at high humidity. Through this knowledge, we have been able to fabrication wrinkles with an aspect ratio greater than 0.7 in a single step by UV exposure. These simple processing parameters to independently control wavelength and amplitude provide a facile route to systematically examine the role of aspect ratio of wrinkles on physical properties.