Water-driven surface wrinkling of poly(2-hydroxyethyl methacrylate) after ultraviolet irradiation

Engineering surface structures/textures have opened new avenues for various applications in lab-on-chip, flexible electronics, photonics, and so forth. In this work, we demonstrate the possibility of water-driven surface wrinkles of poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogel after ultraviolet (UV) irradiation in air and uptake of deionized (DI) water. Surface patterns form after the UV-irradiated pHEMA disks are taken out of DI water. We perform the Fast-Fourier-Transform analysis and calculate the characteristic wavelengths of the surface patterns. The characteristic wavelength is dependent on the combinational effect of the UV-irradiation dose, the immersion temperature, and the immersion time (initial and total immersion times). Increasing the UV-irradiation dose, the immersion temperature, and the initial immersion time increases the characteristic wavelengths of the surface patterns.