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Molecular ejection transition in liquid crystal columns self-assembled from wedge-shaped minidendrons

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Abstract

Fan-shaped molecules with aromatic head-groups and two or more flexible pendant chains often self-assemble into columns that form columnar liquid crystals by packing on a 2d lattice. Such dendrons or minidendrons are essential building blocks in a large number of synthetic self-assembled systems and organic device materials. Here we report a new type of phase transition that occurs between two hexagonal columnar phases, Colh1 and Colh2, of Na-salt of 3,4,5-tris-dodecyloxy benzoic acid. Interestingly, the transition does not change the symmetry, which is p6mm in both phases, but on heating it involves a quantised drop in the number of molecules 〈n〉 in the cross-section of a column. The drop is from 4 to 3.5, with a further continuous decrease toward 〈n〉 = 3 as temperature increases further above Tc. The finding is based on evidence from X-ray diffraction. Using a transfer matrix formulation for the interactions within a column, with small additional mean field terms, we describe quantitatively the observed changes in terms of intermolecular forces responsible for the formation of supramolecular columns. The driving force behind temperature-induced molecular ejection from the columns is the increase in conformational disorder and the consequent lateral expansion of the alkyl chains. The asymmetry of the transition is due to the local order between 4-molecule discs giving extra stability to purely 〈n〉 = 4 columns.

Graphical abstract: Molecular ejection transition in liquid crystal columns self-assembled from wedge-shaped minidendrons

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Publication details

The article was received on 10 Sep 2018, accepted on 31 Oct 2018 and first published on 02 Nov 2018


Article type: Paper
DOI: 10.1039/C8SM01851K
Citation: Soft Matter, 2018, Advance Article
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    Molecular ejection transition in liquid crystal columns self-assembled from wedge-shaped minidendrons

    W. S. Fall, M. Yen, X. Zeng, L. Cseh, Y. Liu, G. A. Gehring and G. Ungar, Soft Matter, 2018, Advance Article , DOI: 10.1039/C8SM01851K

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