Preparation of γ-APS monolayer with complete coverage via contact printing

A monolayer film of 3-aminopropyltriethoxysilane (γ-APS) was prepared by contact printing with featureless PDMS stamp. First, γ-APS ink solutions in dry toluene were prepared in a dry nitrogen-filled glove box and immediately used for spin coating onto a PDMS stamp, followed by printing on a silicon wafer. Next, water contact angles and film thicknesses were measured as a function of ink concentration (5–100 mM) and printing time (1–60 min) after printing, as well as after aging in toluene for 24 h. In addition, surface coverage, topology, RMS roughness and surface amine density were also evaluated, while the chemical structure of γ-APS monolayer was analyzed by FT-IR/ATR. Optimum conditions for γ-APS monolayer with complete coverage were determined to be ink concentration of 20 mM and printing time of 30 min, which resulted in a water contact angle of 93°, film thickness of 0.78 nm and surface amine density of 7.6 molecules/nm2.

Graphical abstractSurface coverage of γ-APS molecules on Si wafer via microcontact printing at the concentration of 20 mM.Figure optionsDownload full-size imageDownload as PowerPoint slide