Impermeable and Elastic Polydimethylsiloxane Film by Parylene-Caulking for Inflatable Soft Devices

Moldable polymers, such as polydimethylsiloxane (PDMS), are widely used for microstructures. Various PDMS microstructures have been developed by molding and applied to microfluidic devices. In addition to the moldability of PDMS, its elasticity, optical transparency, gas permeability, and biocompatibility facilitate its utilization in diverse applications. However, the permeability of PDMS makes it unsuitable in cases that require sealing. For instance, inflatable soft devices, including pneumatic balloon actuators, require their constituent material to exhibit both elastic and impermeable features to utilize driving pressure effectively. In this context, this paper presents the poly-para-xylylene (parylene)-caulking of PDMS without losing elasticity of PDMS. Parylene-caulked PDMS is obtained by etching coated parylene on PDMS. In the context of the previous study on parylene-caulked PDMS and similar works published recently, updated surface analysis results, and prepolymer ratio dependences are reported in this paper. Surface analysis is performed based on Fourier transform infrared spectrometry and time-of-flight secondary ion mass spectrometry is used to examine the presence of parylene on and inside the PDMS superficial layer. Parylene-caulked PDMS is attractive for inflatable soft actuators. This study believes that these results will potentially contribute to a wide range of applications that require gas impermeability.