Bioinspired dry adhesive: Poly(dimethylsiloxane) grafted with poly(2-ethylhexyl acrylate) brushes

• Poly(dimethylsiloxane) was grafted successfully with poly(2-ethylhexyl acrylate) brushes.
• A significant improvement in adhesion in brush grafted PDMS samples was observed as compared with un-grafted ones.
• Adhesion strength can be tailored by altering molecular weight of the grafted chains.
• A detailed nano-mechanical characterization revealed interesting mechanical effects on the grafted PDMS samples.

In this report we demonstrate that modification of poly(dimethylsiloxane) (PDMS) surfaces with polymer brushes offers a promising route towards materials with improved, bioinspired dry adhesive surfaces. To that end, poly(2-ethylhexyl acrylate) brushes were grafted from PDMS surfaces by surface-initiated atom transfer radical polymerization (SI-ATRP) and also on silicon wafers in the presence of a structurally similar sacrificial initiator. Attenuated Total Reflection-Fourier Transformed Infrared spectroscopy (ATR-FTIR), Nuclear Magnetic Resonance Spectroscopy (NMR), Gel Permeation Chromatography (GPC) and ellipsometric studies confirmed the presence and regular growth of polymer chains both in solution and on PDMS and silicon surfaces respectively. Adhesion of the modified PDMS surfaces was tested using Hysitron TI-950 Triboindenter at indentation depths of 50–500 nm and retraction rates of 5–50 nm/s. Finally, micro-fabricated pillars (diameter = 18 μm) were grafted with the polymer brushes. All samples showed a significant increase in adhesion after grafting. Micro patterned PDMS surface has also shown a marked increase in adhesion after grafting of the polymer brushes as compared to non-grafted PDMS.

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