Surface protonated amine gradients have been prepared on silicon wafers via programmed controlled rate infusion (CRI) with varying degrees of hydrophobicity. The silicon wafers were first spin coated from sols containing tetramethoxysilane (TMOS) and either phenyltrimethoxysilane (PTMOS), dimethyldimethoxysilane (DMDMOS) or octyltrimethoxysilane (OTMOS, C8). Amine gradients were then prepared from 3-aminopropyltriethoxysilane (APTEOS) via CRI followed by protonation of the amine functionalities by exposure to the vapor of concentrated HCl acid. The gradients were then characterized by X-ray photoelectron spectroscopy (XPS) and static and Wilhelmy plate dynamic contact angle measurements. It was found that the overall extent of N modification depended on the characteristics of the base layer used for gradient formation: the higher the hydrophobicity the lower the extent of modification. The wettability and water contact angle (CA) hysteresis varied along the length of the gradient depending on the base layer characteristics. The greatest CA change across the length of the gradient was observed on the gradient formed on the C8-derived base layer. In contrast to uniformly modified substrates, Wilhelmy plate CA analysis gave S-shaped CA-distance curves on immersion and emersion (Figure 1). A detailed analysis of the unique S-shaped curves of the gradients will be discussed in the presentation.

Influence of the base layers on the real time dynamic water contact angle

254th National Meeting (2017)

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