Surface Wettability Control Of Elastic Molds And Their Applications In Soft Lithographic Fabrication Of Ceramic Micro-structures

Air plasma and near-infrared light sensitive poly?dimethylsiloxane??PDMS?@Fe₃O₄ molds and moisture-sensitive PDMS@poly?3-sulfopropyl methacrylate potassium salt??PSPMK?molds were prepared by improved thermal curing and surface-initiated atom transfer radical polymerization respectively.The microchannel green parts were fabricated using the two molds by transfer micro-molding from an alumina aqueous suspension with solids loading of 75 wt%.The structure,composition,surface wettability and morphology of the two molds and alumina micro-structures were investigated by infrared spectrometer,X-ray photoelectron spectroscopy,contact angle measuring instrument,optical microscopy,scanning electron microscopy,nano-indentation and atomic force microscopy etc.The control mechanisms of the surface wettability of the two kinds of molds used in soft lithographic fabrication were studied.The main contents and results are as follows:1.Defect-free,free-standing alumina micro-structures green parts can be obtained from both the air plasma and near-infrared light sensitive PDMS@Fe₃O₄molds.The micro-structures of the green parts have a lateral feature size of 99.5±0.7?m,an aspect ratio of 1.3,and a surface roughness?R_a?of 14.7 nm.The micro-structures of the alumina green parts obtained by PDMS@Fe₃O₄ mold have higher structural integrity than that obtained by the PDMS@Fe₃O₄ mold without any treatment and air plasma treatment.This is related to the generation of hydrophilic hydroxyl functional groups on the surface of the PDMS@Fe₃O₄ mold after air plasma treatment and the photothermal effect of Fe₃O₄ nanoparticles in near-infrared light which accelerates the hydrophobic recovery of the mold surface.They are beneficial to the flow of the aqueous alumina suspension into the microchannels and demolding.2.Defect-free,free-standing alumina micro-structures green parts can be obtained from PDMS@PSPMK molds.The micro-structures of the green parts have a lateral feature size of 99.6±1.3?m,an aspect ratio of 1.3,and a surface roughness?R_a?of 19.2 nm.After sintering at 1600?,defect-free alumina micro-part with a relative density of 96%,a hardness of 1958 HV and a roughness of 21.4 nm was attained.This is related to the hydration-dehydration reversible process of the PSPMK brushes.During the molding process,the PSPMK brushes are fully hydrated and show a stretched conformation at the high moisture content of the aqueous suspension,which enables the suspension fill the micro-channels of the PDMS@PSPMK mold completely.During the drying process,the PSPMK brushes are gradually dehydrated and show a collapsed conformation while the suspension loses moisture,which makes demolding easier after complete drying.In addition,the service life of the PDMS@PSPMK mold is significantly improved.It can be reused about 10 times for the high-precision fabrication of free-standing ceramic micro-parts.