Effect of Annealing on Improved Hydrophobicity of Vapor Phase Deposited Self-Assembled Monolayers

Abstract

The hydrolytic stability and the effect of annealing on the improved aging properties of self-assembled monolayer (SAM) hydrophobic coatings have been investigated. Surfaces coated with hydrophobic SAM coatings give higher flow rate and are of wide interest to researchers in the area of microfluidics. Hydrophobic SAM of fluorooctyltrichlorosilane (FOTS) was deposited on silicon by using a vapor phase technique. The aging of the hydrophobic property was examined by using contact angle measurements. It has been found that while such a monolayer suffers from a loss of hydrophobicity with time, annealing can partially recover the hydrophobicity. The mechanism of aging was investigated through Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), which revealed very little chemical change in annealed monolayers. Surface roughness and morphological changes due to hydrolytic attack was studied by atomic force microscopy (AFM). A spontaneous formation of silane mounds on the surface of the monolayers was found. These mounds have been irreversibly transformed from initially uniform hydrophobic surface layers. It is highly probable that the compliance of these mounds can reasonably allow hydrophilic microcapillaries to be located around the mounds. Interestingly, the density of these mounds decreases when the monolayer samples are annealed, with no significant chemical change. This novel finding explains the observed recovery of hydrophobicity of the monolayers as primarily a morphological effect that originates from the densification of the monolayers upon annealing.

Design Optimization of Perfluorinated Liquid‐Infused Surfaces for Blood‐Contacting Applications

“…While the size of the aggregates varied across the sample as seen in Figure 2C–F (also Figure S3, Supporting Information), surface coverage was reproducible as indicated by the high static contact angle and low sliding angles (Figure 2A,B). The formation of similar morphologies has previously been seen in other CVD studies, [ 14,18 ] being described as polymerized clusters of self‐assembling monomers. [ 14 ] Aggregate formation during CVD was suggested to proceed by oligomerization using surface‐bound water as a co‐monomer via a step‐growth polymerization mechanism.…”

“…[ 14b ] Such features are common in the silanization process when extensive oligomerization occurs in the presence of moisture and humidity. [ 11a,f,14a ] As seen in Table 2 , prior to rinsing of the layers, LPD TP‐layers displayed a high fluorine content of 56% (for samples produced at 30% RH, with the highest contact angle), similar to the fluorine content (53–54%) of TP layers prepared in a previous study using LPD. [ 6 ] However, a wash by ultrasonication in pure PFD for 1 min led to a decrease in fluorine concentration to 17%, which has also been observed before.…”

Chemical Funneling of Colloidal Gold Nanoparticles on Printed Arrays of End-Grafted Polymers for Plasmonic Applications

“…The roughness of the deposited FAS film shows a noticeable increase with thermal annealing (Figure a,b). This texture is the result of formation and growth of FAS islands during the annealing process, as observed in previous studies. − The oligomers of FAS likely dewet during the thermal annealing process. The implication here is that there are unreacted Si–OH groups between mounds of FAS molecules that are available for PEGs to react with (see schematics in Figure d and Figure S3).…”

Droplet evaporation characteristics on transparent heaters with different wettabilities

“…In the hydrophilic case, oxygen plasma (O 2 ) treatment was performed on the heater surface using an O 2 plasma generation system (LF PlasmaSTAR 100, JNE Corp.) with a power of 20 W, O 2 ow rate of 20 sccm, and chamber pressure of 200 mTorr, for 30 s. In contrast, the hydrophobic surfaces were obtained by selfassembled monolayer (SAM) treatment on the heater surface. 17,18 In this process, the heater surface was exposed to 1H,1H,2H,2H-peruorooctyltrichlorosilane for 30 min at 85 C in a vacuum desiccator.…”