(626i) Responsive Monolayer Films for Environmentally Adaptative Surfaces

Monolayer films can be used to create tailored surfaces with a wide range of interfacial properties by modifying the outer chemical composition, which affects interactions with the surrounding environment.¹ This tailored chemical composition enables the design of coatings that respond dynamically to various stimuli, such as changes in pH, temperature, and solvent exposure, creating surfaces with intelligent adaptability.² The goal of our project is to combine experiments and molecular simulations to design and assemble surfaces that dynamically minimize their interfacial free energy in different environments. Developing such smart surfaces would thus enable the development of materials with numerous potential applications, including self-cleaning and anti-fouling surfaces.³ In this work, we investigate the surface properties of silane monolayers with diverse interfacial molecular compositions and assembly characteristics. These monolayers feature a chemically heterogeneous surface composition consisting of hydrophilic and hydrophobic moieties that can reorient towards or away from the surface upon changes in the environment to minimize surface free energy. We have used molecular simulations to guide the design of highly switchable molecular compositions, and we have fabricated some of the more promising monolayer systems on the surface of silicon through a series of high-yield surface reactions. The synthesis and functionalization of these monolayers have been validated using FTIR spectroscopy, ellipsometry, and water contact angle measurements. To study the effect of chemical composition on surface properties, we measured contact angles under different conditions and determined the surface free energies. Furthermore, we have used mixed monolayers of both functionalized and shorter, non-responsive (back-filling) adsorbates to examine the steric hindrance effects on these surface properties. Overall, our integrated approach of simulations and experiments presents a methodology for developing and studying adaptative surface materials that provide rapid molecular reorientation of interfacial groups for responding to environmental changes.

(1) Laibinis, P. E.; Bain, C. D.; Nuzzo, R. G.; Whitesides, G. M. Structure and Wetting Properties of ω-Alkoxy-n-Alkanethiolate Monolayers on Gold and Silver. J. Phys. Chem. 1995, 99 (19), 7663–7676. https://doi.org/10.1021/j100019a054.

(2) Nandivada, H.; Ross, A. M.; Lahann, J. Stimuli-Responsive Monolayers for Biotechnology. Progress in Polymer Science 2010, 35 (1), 141–154. https://doi.org/10.1016/j.progpolymsci.2009.11.001.

(3) Choi, Y.; Tran, H.-V.; Lee, T. R. Self-Assembled Monolayer Coatings on Gold and Silica Surfaces for Antifouling Applications: A Review. Coatings 2022, 12 (10), 1462. https://doi.org/10.3390/coatings12101462.