(538d) Dynamic Molecular Switching for Environmentally Adaptive Surfaces

Monolayer films provide a means to modify interactions of surfaces with their environment (e.g., water-[1] and oil-repellent [2] surfaces, lubricating films [3], biological implants [4], and adhesives [5]) that can be tuned by changing the chemistry of the film. While efforts have been made to create films that are able to adapt to different environment conditions [6,7], oftentimes such films are slow to respond or require external stimuli to change. Here we perform molecular dynamics simulations of amorphous silica surfaces functionalized with short chain (6-18 carbons) alkylsilane chains, focusing on the modification of terminal functional groups in the outer 0.5 nm of the film. In particular, we focus on terminal groups composed of both hydrophobic and hydrophilic groups. We hypothesize such terminal groups can achieve dynamic switching response through reorientation of the individual hydrophobic/hydrophilic groups to minimize surface energy in response to contrasting environments. We perform screening on combinations of chemistry of the competing groups, chain surface density, chain length, and presence of secondary chains (backfills) [8] to identify systems and conditions where dynamic switching occurs in response to changing solvent. Using the MoSDeF software packages [9, 10] and the Signac [11] workflow manager, approximately 10,000 of these surfaces have been evaluated. The solvent penetration, terminal group positions, chain ordering, degree of hydrogen bonding, and contact angles are calculated to distinguish which configurations show optimal switching in prevalent environments, such as organic and polar solvents.

References:

1. Nosonovsky, M.; Bhushan, B. "Superhydrophobic Surfaces and Emerging Applications: Non-Adhesion, Energy, Green Engineering," Current Opinion in Colloid & Interface Science 2009, 14, 270-280.
2. Tuteja, A.; Choi, W.; Ma, M.; Mabry, J.; Mazzella, S.; Rutledge, G. C.; McKinley, G.; Cohen, R. E. "Designing Superoleophobic Surfaces," Science 2007, 318, 1618-1622.
3. Raviv, U.; Klein, J. "Fluidity of Bound Hydration Layers.," Science 2002, 297, 1540.
4. Sigal, G. B.; Mrksich, M.; Whitesides, G. M. "Effect of Surface Wettability on the Adsorption of Proteins and Detergents," J. Am. Chem. Soc. 1998, 120, 3464-3473.
5. Liu, X.; Liang, Y.; Zhou, F.; Liu, W. "Extreme Wettability and Tunable Adhesion: Biomimicking Beyond Nature?," Soft Matter 2012, 8, 2070-2086.
6. Angew Chem “One-Step Modification of Superhydrophobic Surfaces by a Mussel-Inspired Polymer Coating” Int Ed Engl. 2010 December 3; 49(49): 9401–9404. doi:10.1002/anie.201004693.
7. Bo He and Junghoon Lee, "Dynamic wettability switching by surface roughness effect," The Sixteenth Annual International Conference on Micro Electro Mechanical Systems, 2003. MEMS-03 Kyoto. IEEE, Kyoto, Japan, 2003, pp. 120-123, doi: 10.1109/MEMSYS.2003.1189702.
8. Holger Merlitz, Gui-Li He, Chen-Xu Wu, and Jens-Uwe Sommer, “Nanoscale Brushes: How to Build a Smart Surface Coating” Phys. Rev. Lett. 102, 115702, doi: https://doi-org.proxy.library.vanderbilt.edu/10.1103/PhysRevLett.102.115702
9. “MoSDeF” [Online]. Available: https://mosdef.org.
10. Thompson, M.; Gilmer, J.; Matsumoto, R;.; Quach, C.; Shamaprasad, P.; Yang, A.; Iacovella, C.; McCabe, C.; and Cummings P., (2020) Towards molecular simulations that are transparent, reproducible, usable by others, and extensible (TRUE), Molecular Physics, 118:9-10.
11. “Signac Framework” [Online]. Available: https://signac.io.