Title: Oligomers as Triggers for Responsive Liquid Crystals

Abstract

We report an investigation of the influence of aqueous solutions of amphiphilic oligomers on the ordering of micrometer-thick films of thermotropic liquid crystals (LCs), thus addressing the gap in knowledge arising from previous studies of the interactions of monomeric and polymeric amphiphiles with LCs. Specifically, we synthesized amphiphilic oligomers (with decyl hydrophobic and pentaethylene glycol hydrophilic domains) in monomer, dimer, and trimer forms, and incubated aqueous solutions of the oligomers against nematic films of 4'-pentyl-4-biphenylcarbonitrile (5CB). All amphiphilic oligomers caused sequential surface-driven orientational (planar to homeotropic) and then bulk phase transitions (nematic to isotropic) with dynamics depending strongly on the degree of oligomerization. The dynamics of the orientational transitions accelerated from monomer to trimer, consistent with the effects of an increase in adsorption free energy. The mechanism underlying the orientational transition, however, involved a decrease in anchoring energy and not change in the easy axis of the LC. In contrast, the rate of the phase transition induced by absorption of oligomers into the LC decreased from monomer to trimer, suggesting that constraints on configurational degrees of freedom influence the absorption free energies of the oligomers. Interestingly, the oligomer-induced transition from the nematic to isotropic phase of 5CB was observed tomore » nucleate at the aqueous-5CB interface, consistent with surface-induced disorder underlying the above-reported decrease in anchoring energy caused by the oligomers. Finally, we provided proof-of-concept experiments of the triggering of LCs using a trimeric amphiphile that is photocleaved by UV illumination into monomeric fragments. Overall, our results provide insight into the rational design of oligomers that can be used as triggers to create responsive LCs.« less

Authors:

Kim, Young-Ki  ^[1];

• Search DOE PAGES for author "Kim, Young-Ki"
• Search DOE PAGES for ORCID "0000-0002-4420-3489"

Raghupathi, Krishna R. ^[2]; Pendery, Joel S. ^[1]; Khomein, Piyachai ^[2]; Sridhar, Uma ^[2]; de Pablo, Juan J.  ^[3];

• Search DOE PAGES for author "de Pablo, Juan J."
• Search DOE PAGES for ORCID "0000-0002-3526-516X"

Thayumanavan, S.  ^[2];

• Search DOE PAGES for author "Thayumanavan, S."
• Search DOE PAGES for ORCID "0000-0002-6475-6726"

Abbott, Nicholas L.  ^[1]

• Search DOE PAGES for author "Abbott, Nicholas L."
• Search DOE PAGES for ORCID "0000-0002-9653-0326"

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+ Show Author Affiliations

1. Univ. of Wisconsin, Madison, WI (United States). Dept. of Chemical and Biological Engineering
2. Univ. of Massachusetts, Amherst, MA (United States). Dept. of Chemistry
3. Univ. of Chicago, IL (United States). Inst. for Molecular Engineering

Publication Date:

Fri Jul 27 00:00:00 EDT 2018

Research Org.:

Argonne National Lab. (ANL), Argonne, IL (United States)

Sponsoring Org.:

Army Research Office (ARO); University of Wisconsin - Madison - Materials Research Science and Engineering Center (MRSEC); National Science Foundation (NSF)

OSTI Identifier:

1498505

Grant/Contract Number:  

AC02-06CH11357

Resource Type:

Accepted Manuscript

Journal Name:

Langmuir

Additional Journal Information:

Journal Volume: 34; Journal Issue: 34; Journal ID: ISSN 0743-7463

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 59 BASIC BIOLOGICAL SCIENCES