Hello Gabriel Silveira ,

You state that you want to modify surface roughness in PDMS, but do you want to reduce or increase the surface roughness? What properties of the surface chemistry are you wishing to retain? It may be simple to reinstate certain properties/functionalities with a post-etch procedure.

What type of oxygen plasma system do you have? Is it RIE? ICP-RIE? A high-power oxygen plasma treatment should work - with optimisation of the parameters required depending on which outcome you require.

For a wet etch technique, how about tetrabutylammonium fluoride (TBAF) and N-methylpyrrolidinone (NMP) at (1:6, vol.); etch rate around 6 µm.min-1. Reference: Article Polydimethyl siloxane wet etching for three dimensional fabr...

I attach another article discussing the etch rate of PDMS in relation to the TBAF concentration.

I would imagine that the curing process of the PDMS and the way that it is cast will have a significant affect on the surface roughness. Hopefully other RG members may provide suggestions as unfortunately I have never verified this relation. Attached is an interesting article where a magnetic field is used in combination with MWCNTs and magnetic cobalt ferrites during the curing process to alter the surface roughness.

Jules

Dear Gabriel

I have modified the surface of polydimethylsiloxane by corona treatment. I recommend you to study attached paper which may help you.

Generally, for improvement of printability, wettability and adhesion property of the fabricated membrane, the corona treatment method is used for surface modification technology in packaging processes. The treatment acts by generating a visible electrical discharge from an electrode over the polymeric surface at low voltage (10–40 kV) and high frequency (1–4 kHz). The corona discharge causes partial ionization of the surrounding atmosphere and produces excited species (free radicals, ions or electrons). These chemical species are able to react and oxidize the molecules exposed to the polymeric surface. In fact, corona treatment can produce physical effects by coating nanoparticles while creating additional pores on the membrane surface. In addition, the creation of extra chemical bonds may change the chemical nature of the surface.

https://doi.org/10.1007/s11837-018-3158-8

Best regards

Gabriel,

One possibility is to form the PDMS over a rough surface or to use nano/microparticles to imprint the desired roughness during PDMS solidification.

Hello Jules Lloyd Hammond ,

Thank you for your help and recommendations.

I can't change the surface chemistry of PDMS in order to evaluate only the effect of physical properties in my system, especially roughness. Perhaps, plasma treatment doesn't seem to be the right treatment for my purpose.

I'm looking for a post-cure treatment of PDMS arrays that would modify the roughness without greatly modifying the surface chemistry.

It would be really great if I could do something after the curing process since I already did it to all samples.

Gabriel Silveira : Hi Gabriel, Have you found a solution to change the physical properties of your cured PDMS substrate?

I need the same things.

Thanks