Fabrication of Surface Energy Gradients Using Self-Assembled Monolayer Surfaces Prepared by Photodegradation

Abstract

A new technique, direct photodegradation of self-assembled monolayers (SAM), to obtain surface energy gradients on Si substrates was demonstrated. The gradient surface, with hydrophobic to hydrophilic gradients, was prepared by two steps: Firstly, a homogeneous fluoroalkylsilane SAM film was deposited by a chemical vapor deposition on a Si substrate. Secondly, a controlled photodegradation technique was directly applied to the homogeneous FAS-SAM surface. The surface energy gradient was then obtained due to the different intensity of photoirradiation in the different positions along the photodegraded path on the SAM surfaces. The resulting surface displayed a gradient of wettability (with the contact angle of water changing from 55° to 18°) over a distance of 4.2 mm. The water droplet was driven by surface energy gradient and spontaneously moved from the hydrophobic to hydrophilic surface. During the moving process, the water droplet accelerated firstly and then decelerated. The peak velocity was about 23.3 mm/s. The velocity is dependent on the gradient of the surface energy.

Rapid, ultraviolet-induced, reversibly switchable wettability of superhydrophobic/superhydrophilic surfaces

“…However, the reason of the faster transition process has not explained. Due to the high energy of UV illumination and the photocatalysis effect of TiO 2 , the –CF 2− , –CF 3 groups of the modified trimethoxy(alkyl)silane might become photodegraded and the end of the trimethoxy(alkyl)silane would change into –OH groups without reversibility [31–32]. It can then be assumed that the degradation of trimethoxy(alkyl)silane could reduce the transition time from superhydrophobic to superhydrophilic for surfaces modified with TiO 2 nanoparticles and trimethoxy(alkyl)silane.…”

Electrochemical Fabrication of Surface Chemical Gradients in Thiol Self-Assembled Monolayers with Tailored Work-Functions

“…Several methods have been proposed for the fabrication of chemical gradients on a solid substrate. They include chemical vapor deposition, − solution controlled deposition, − contact printing, − photoirradiation, − photodegration, , thermal treatment, and others. Many of these techniques are based on the surface modification/deposition of a self-assembled monolayers (SAMs) adsorbed on a substrate. , Usually these methods include an initially controlled gradual immersion (or extraction) of the surface into (from) a solution containing the molecules able to form the SAM.…”

“…8,9 Several methods have been proposed for the fabrication of chemical gradients on a solid substrate. They include chemical vapor deposition, 10−13 solution controlled deposition, 14−17 contact printing, 18−20 photoirradiation, 21−23 photodegration, 24,25 thermal treatment, 26 and others. Many of these techniques are based on the surface modification/deposition of a self-assembled monolayers (SAMs) adsorbed on a substrate.…”