Experimental characterizations of the response of nematic liquid crystal droplets upon adsorption of nanoparticles from aqueous media

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2021-9-08

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Şengül, Selin

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Nematic liquid crystal (LC) droplets have been widely used for the detection of molecular species. In this study, we investigated the response of micrometer sized nematic LC droplets against the adsorption of nanoparticles from aqueous media. In the first part of this study, we synthesized ~100 nm-in-diameter silica nanoparticles and modified their surfaces to mediate either planar or homeotropic LC anchoring and a pH-dependent charge. Secondly, we carried out the adsorption of nanoparticles to the LC-aqueous interface and investigated the response of LC droplets upon adsorption. We showed surface functionality- and concentration-dependent configurations of the droplets consistent with the change in the surface anchoring and the formation of local heterogeneities upon adsorption of the nanoparticles to LC-aqueous interfaces. According to our results, the adsorption of nanoparticles modified with dimethyloctadecyl [3-(trimethoxysilyl) propyl] ammonium chloride (DMOAP, homeotropic) exhibit a transition from bipolar to radial, whereas the adsorption of -COOH-terminated counterparts (planar) did not cause a configuration transition. By manipulating the electrostatic interactions, we controlled the adsorption of the nanoparticles to the LC-aqueous interfaces, providing access to the physicochemical properties of the nanoparticles. We demonstrated a temporal change in the droplet configurations caused by the adsorption of the nanoparticles functionalized with -COOH/DMOAP mixed monolayers. These results provide a basis for studies in applications for the detection of nano-sized species, for sensing applications that combine nanoparticles with LCs, and for the synthesis of anisotropic composite particles with complex structures.

Subject Keywords

Liquid crystals, Nanoparticles, Adsorption, Response, Emulsions

URI

https://hdl.handle.net/11511/93198

Collections

Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

S. Şengül, “Experimental characterizations of the response of nematic liquid crystal droplets upon adsorption of nanoparticles from aqueous media,” M.S. - Master of Science, Middle East Technical University, 2021.