| Silanes are used for surface modification to improve dispersion, bind biomaterials, improve adhesion, etc. Their use in improving adhesion in new composite materials is critical, and for these systems there is a growing call for both increased adhesion performance and resistance to water penetration. This work proposes a strategy for both enhanced adhesion and reduced water penetration in such systems by using two silanes in a patterned array, where one is an adhesion promoter and the other a water repellant. The focus here is on adhesion enhancement across oxide-polymer interfaces. The first goal is to investigate methods of making chemically heterogeneous silane surfaces including solution deposition and micro-contact printing. The properties of the deposited layer are characterized with atomic force microscopy in pulsed force mode. The research shows that solution deposition of the adhesion promoter followed by micro-contact printing of the second silane gives the most reproducible results.; The second goal of this research is to determine the adhesive force between polymers and heterogeneous patterned and homogeneous surfaces. Results obtained show that the mechanical force required to peel apart a sample depends critically on the feature size, shape and fractional coverage. With the proper feature dimensions, heterogeneous surfaces have been shown to produce up to 80% greater adhesion than those of homogeneous surfaces. The research investigates feature sizes from 5mum to 10mm. In homogeneous peel tests, cracks initiate and then propagate across the sample, whereas in peel tests of heterogeneous surfaces, cracks initiate and are subsequently arrested. In the latter case, re-initiation of the crack requires additional force causing relative increases in practical adhesion, even though there is a reduction in the fractional coverage of the adhesion promoter. In addition to increases in adhesion, heterogeneous surfaces have been shown to reduce water penetration. Comparing wet and dry adhesion with adhesives and primers commonly used in industry, results show that due to exposure to moisture, adhesion is reduced 46% in the homogeneous samples but only 20% in the heterogeneous samples. This has implications for the use of heterogeneous patterned silane surfaces for commercial composites, which are routinely exposed to moisture. |
