Diphylleia grayi-Inspired Hydrochromic Adhesive PDMS Film Using Nano Sphere Lithography

Many living things in nature have the ability to change their colors, and this has inspired the development of bio mimetic technology, such as flexible information display devices, color control applications, and energy-free applications. Inspired by the ability of <i>Diphylleia grayi</i> to become transparent on rainy days, we developed a hypochromic adhesive PDMS film. We produced a <i>Diphiylleia grayi-</i>inspired PDMS film by forming a nanocavity structure on the surface of a PDMS (Polydimethylsiloxane) film based on Mie theory. The formation of nanocavities on the PDMS surface induced scattering, reducing the surface transmittance, and leading to transparency in wet state. Nanocavity structures were fabricated using polystyrene (PS)-based nanosphere lithography (NSL) and PDMS transfer methods. Nanosphere lithography using polystyrene beads is suitable for forming various cavities because the process makes it easy to adjust the diameter via reactive-ion etching (RIE). Scattering-induced PDMS films were optimized using polystyrene beads of various sizes (0.2, 0.4, 0.6, 1.0, and 2.0 μm). The greatest contrast between wet and dry states was shown in the 1.0 μm cavity structured PDMS film (44.93% (ΔTD) T = 59.11-14.18%) and 54.88% (ΔH = 69.42-14.54%)). The optimized film with 1.0 μm nano-pores suggests the possibility of application to various water-changing applications that require color change, such as smart windows, camouflage, and transparent umbrellas for rainy weather. To improve the wettability of the PDMS surface, polyvinyl alcohol (PVA) was used to modify the surface. The PDMS film surface was measured with a scanning electron microscope (SEM). The scattering effect of the nano-cavity structure was measured by UV-visible spectroscopy, and the haze value was measured using a hazemeter.