Modulating Wettability of Layered Materials by Controlling Headgroup Dynamics and Alkyl Chain Conformations
Evolution to the next generation of organic photovoltaics and computer processors requires the capability to pattern organic and inorganic materials consistently at interfaces with feature sizes as small as 5-7 nm. A particular challenge is to generate interfaces that display chemical patterns consisting of two or more very different constituents at such scales. Biology routinely orders orthogonal chemical patterns at this scale, as is observed in the structure of the cellular membrane. Phospholipids have also been observed to form repeating striped phases on layered materials, e.g. graphene, molybdenum disulfide (MoS2), and highly oriented pyrolytic graphite (HOPG). Research performed in the Claridge lab has shown that modifications of the lipid structure can impact how these monolayer films interact with the environment. Starting with 10,12-pentacosadiynoic acid as an initial template, a family of fatty acids and phospholipids were synthesized, then their behavior characterized. Using a combination of contact angle titrations and molecular dynamics simulations, we demonstrated that headgroup dynamics and tail‒substrate interactions can be altered by changing the position of the internal diyne or the length of the fatty acid, thereby modulating wettability of the 2D material. Molecules with short chain segments proximal to the carboxylic acid head undergo significant dynamics after polymerization, allowing the headgroups to interact more readily with solvents and increasing hydrophilicity. For specific terminal alkyl segment lengths, we instead observed a decrease in hydrophilicity of the monolayer post-polymerization, suggesting chain-length specific differences in the polymerization. Together, these observations enable us to selectively control the surface chemistry of the 2D material to create desired interactions with the environment. The final section of this research focused on modifying diyne phospholipid headgroups, for instance to attach a catechol moiety, which then can interact with inorganic species to form ordered arrays of inorganic nanocrystals at the interface.
Claridge, Purdue University.
Materials science|Inorganic chemistry|Organic chemistry
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