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Adsorption from binary liquid solutions into mesoporous silica: a capacitance isotherm on 5CB nematogen/cyclohexane mixtures
Publikationstyp
Journal Article
Date Issued
2021
Sprache
English
Author(s)
Institut
Journal
Volume
119
Issue
15-16
Article Number
e1909160
Citation
Molecular Physics 119 (15-16): e1909160 (2021)
Publisher DOI
Scopus ID
We present a capacitance method to measure the adsorption of rod-like nematogens (4-cyano- (Formula presented.) -pentylbiphenyl, 5CB) from a binary liquid 5CB/cyclohexane solution into a monolithic mesoporous silica membrane traversed by tubular pores with radii of 5.4 nm at room temperature. The resulting adsorption isotherm is reminiscent of classical type II isotherms of gas adsorption in mesoporous media. Its analysis by a model for adsorption from binary solutions, as inspired by the Brunauer–Emmett–Teller (BET) approach for gas adsorption on solid surfaces, indicates that the first adsorbed monolayer consists of flat-lying (homogeneously anchored) 5CB molecules at the pore walls. An underestimation of the adsorbed 5CB amount by the adsorption model compared to the measured isotherm for high 5CB concentrations hint towards a capillary filling transition in the mesopores similar to capillary condensation, i.e. film-growth at the pore walls is replaced by filling of the pore centres by the liquid crystal. The experimental method and thermodynamic analysis presented here can easily be adapted to other binary liquid solutions and thus allows a controlled filling of mesoporous materials with non-volatile molecular systems.
Subjects
Adsorption
binary solution
capacitance
isotherm
liquid crystal
Funding(s)