Polydimethylsiloxane (PDMS) elastomer is a silicone-based organic polymer. Recently, it has attracted the attention of many researchers as a basic substrate of an e-skin for flexible and wearable personal health monitoring devices. The wide range of applications of PDMS is attributed to its flexibility, stretchability, biocompatibility, transparency, inexpensiveness, and ease to manufacture at an industrial scale. PDMS elastomer also can be used to make stamps for contact printing electronic circuits on polymer surfaces like Polyethylene terephthalate (PET). Microcontact printing is a type of soft lithography process wherein an elastomeric stamp is used to transfer the ink deposited on the sub-micron scale surface patterns onto a flexible substrate. Recently, the integration of microcontact printing into a roll-to-roll (R2R) system enables the mass manufacturing of flexible electronics. In the R2R print system, the PDMS stamp is compressed between the impression roller and print roller to get the desired print, thus compression properties of the PDMS play an important role in print quality.&nbsp;The Elastic modulus of PDMS mostly depends on the mixing ratio of base and curing agent, curing temperature and duration, and aspect ratio of the sample. For example, the commercially available PDMS kit, “Sylgard 184” from the Dow Corning Corporation, has two parts of liquid, i.e., base and curing agent. It is mixed in the ratio 10:1 i.e., base: curing agent. After thoroughly mixing the two liquids, it is cured forming a flexible elastomer. Considering the impacts of the various parameters on the modulus of PDMS, many researchers have discussed the elastic modulus in tensile loading conditions, however, very few of them have discussed the compressive modulus. In this project, The compressive modulus of PDMS is studied for samples molded in various diameters and thicknesses as well as length to diameter ratios (L/D), blank PDMS samples without any patterns, and PDMS with sub-micron scale patterns.We investigate the compressive modulus of PDMS as follows. We first make the PDMS mixture and fill this mixture into various molds to achieve desired thicknesses and diameters as designed. Second, the mixture is cured at 700C for 2 hours and the cured PDMS sample is removed from the mold. Third, we load the sample into the Instron universal testing machine 3345 for compression testing. Fourth, we perform a compression test and plotted the stress and strain curve for each sample. Finally, the compressive modulus is calculated from the graph of different samples of different diameters, thicknesses, L/D ratios, blanks, and patterned PDMS.&nbsp;When we increase the diameter, we notice a decrease in the elastic modulus. When we increase the height, the modulus decreases. A lower modulus means the material is more flexible. In many cases when the PDMS increases in either diameter or thickness, the flexibility will also increase as the modulus decreases.This investigation will offer fundamental knowledge for the design and control of PDMS stamps for R2R microcontact printing processes, and hence improve the print process control and production of flexible wearable devices.

Analyzing PDMS Stamps for Contact Printing

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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