Effect of mold treatment by solvent on PDMS molding into nanoholes

Abstract

Polydimethylsiloxane (PDMS) is the most popular and versatile material for soft lithography due to its flexibility and easy fabrication by molding process. However, for nanoscale patterns, it is challenging to fill uncured PDMS into the holes or trenches on the master mold that is coated with a silane anti-adhesion layer needed for clean demolding. PDMS filling was previously found to be facilitated by diluting it with toluene or hexane, which was attributed to the great reduction of viscosity for diluted PDMS. Here, we suggest that the reason behind the improved filling for diluted PDMS is that the diluent solvent increases in situ the surface energy of the silane-treated mold and thus the wetting of PDMS to the mold surface. We treated the master mold surface (that was already coated with a silane anti-adhesion monolayer) with toluene or hexane, and found that the filling by undiluted PMDS into the nanoscale holes on the master mold was improved despite the high viscosity of the undiluted PDMS. A simple estimation based on capillary filing into a channel also gives a filling time on the millisecond scale, which implies that the viscosity of PMDS should not be the limiting factor. We achieved a hole filling down to sub-200-nm diameter that is smaller than those of the previous studies using regular Sylgard PDMS (not hard PDMS, Dow Corning Corporation, Midland, MI, USA). However, we are not able to explain using a simple argument based on wetting property why smaller, e.g., sub-100-nm holes, cannot be filled, for which we suggested a few possible factors for its explanation.

Patterning of worm‐like soft polydimethylsiloxane structures using a TiO2 nanotubular array

“…In sample 2, 3, and 4, the nanotubes were filled by toluene to the base of the tubes (Wenzel state) after soaking the nanotubular template in toluene for 10 min, which may ultimately enhance the surface wetting of the tube by PDMS. 19 However, only microroughness observed on diluted PDMS sample 2 and 3 (Figure 4(b,c) Figure 4(c,d)) indicating deeper infiltration of 33.33 vol% PDMS. Without stirring, toluene in nanotubes (from toluene soaking process) may not mixed well with PDMS at 25 C and hold the PDMS mixture on top of the tube, in which external energy was needed to overcome the energy barrier of Cassie-Baxter state.…”

“…Low curing temperature (40-80 C) is usually used for natural mold yielding relatively low elastic modulus of PDMS even after a longer curing time. For high curing temperature, synthetic materials such as micro/nanofabricated silicon 18,19 , SU-8 epoxy, 20 CuO nanowire 21 porous nickel oxide, 22 and alumina nanotubes array [23][24][25] can be utilized.…”

“…An accurate replica of soft PDMS with high aspect ratio and good quality using a pores smaller than 150 nm is still challenging task. 19 A higher fidelity of PDMS at a smaller diameter (≈100 nm) was achieved on the silicon template, with composites of two different PDMS layers. 30 A stiffer polymer consisting of vinyl and hydrosilane end-linked polymers (hard PDMS, h-PDMS) was used as the first layer, which improved the quality of the replica due to its lower viscosity.…”

Investigation of cavitation-induced damage on PDMS films

“…The S a calculation gives an optimal description of the surface roughness due to the fact that in the derivation, impurities or foreign objects adhered to the surface have a minimal effect on the nal value. 25 The average S a value for all the control surfaces was calculated to be 22.0 nm. This value is noticeably different from the experimental samples, which had an average S a value of 28.8 nm.…”

Double sided solvent-imprint lithography (DSSIL) on glassy thermoplastic luminescent surfaces using a soft stamp

“…Alternatively one can lower the surface temperature of the mold by dipping it in a solvent [16]. Solvents (including low volatile solvents) were not used here because the Young's Modulus of cured diluted PDMS is appreciably lower than cured undiluted PDMS [16]. The PDMS copy of the holographic grating film demonstrated a sinusoidal period of 1050 nm and a height of 187 nm.…”