I am making PDMS flexible microfluidics and would like to deposit SiO2 onto the microchannels to make them hydrophilic for longer (since plasma treatments only last a few hours at best). I've heard of many surface modification strategies but like the idea of glass on PDMS, but am worried about the quality of the film and how that relates to the contact angle made. Any insights would be greatly helpful! This is a project for autonomous sweat induction, thus the need for hydrophilicity.
The problem with PDMS is, that it keeps changing its surface, through internal rearranging of bonds. That's why you loose hydrophilicity after a couple of hours (that and through airborne hydrocarbon contaminants). Depositing SiO2 on PDMS is possible but the adhesion is bad. There is no affinity of the polar SiO2 to the non-polar PDMS. It might work if you first treat the PDM with oxygen plasma to create OH-groups on the PDMS surface, immediately followed by SiO2 deposition so that you get a chemical bond through the OH groups, which then will be more difficult to rearrange internally, since they are stuck to the SiO2 layer.
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