Liquid crystals (LCs) are a phase of matter within which the constituent molecules exhibit long-range orientational order and high levels of mobility.  Changes in boundary conditions, such as adsorption of synthetic surfactants (e.g., dodecyltrimethylammonium bromide, DTAB) that alter constraints on the interfacial orientational ordering of LCs, can trigger mesoscale optical responses in LCs that reflect competing contributions to the free energies of these complex systems. In this paper, we report the use of reactive surfactants, which integrate triggerable Michael acceptor (TMAc) functionalities as components of head groups, to trigger ordering transitions in LCs.  The head-groups of the surfactants are cleaved in response to the presence of nucleophiles.  We have characterized the adsorption of these surfactants from aqueous dispersions onto LC-aqueous interfaces and the reordering of the LC that accompanies the formation of interfacial surfactant assemblies.  Subsequent addition of nucleophiles to the aqueous phase (e.g., thiols or amines) is observed to lead to a complex spatial and temporal response of the LC that is dependent on the choice of nucleophile. In particular, we observed that select nucleophiles generated a re-entrant reordering of the LC in which the same LC orientational state was encountered multiple times during the reaction.  These results and others will be discussed in the context of the use of LCs to probe interfacial reactions.   The results also hint at new designs of responsive soft matter.

Dynamic and programmable response of liquid crystals to surface reactions

ACS Fall 2021

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