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Non-equilibrium ordering of liquid crystalline (LC) films driven by external gradients in surfactant concentration

Cornell Affiliated Author(s)

Author

S. Maiti
S. Roh
Itai Cohen
N.L. Abbott

Abstract

Hypothesis: Gradients in the concentration of amphiphiles play an important role in many non-equilibrium processes involving complex fluids. Here we explore if non-equilibrium interfacial behaviors of thermotropic (oily) liquid crystals (LCs) can amplify microscopic gradients in surfactant concentration into macroscopic optical signals. Experiments: We use a milli-fluidic system to generate gradients in aqueous sodium dodecyl sulfate (SDS) concentration and optically quantify the dynamic ordering of micrometer-thick nematic LC films that contact the gradients. Findings: We find that the reordering of the LCs is dominated by interfacial shearing by Marangoni flows, thus providing simple methods for rapid mapping of interfacial velocities from a single optical image and investigating the effects of confinement of surfactant-driven interfacial flows. Additionally, we establish that surface advection and surfactant desorption are the two key processes that regulate the interfacial flows, revealing that the dynamic response of the LC can provide rapid and potentially high throughput approaches to measurement of non-equilibrium interfacial properties of amphiphiles. We also observe flow-induced assemblies of microparticles to form at the LC interface, hinting at new non-equilibrium approaches to microparticle assembly. We conclude that dynamic states adopted by LCs in the presence of surfactant concentration gradients provide new opportunities for engineering complex fluids beyond equilibrium. © 2022

Date Published

Journal

Journal of Colloid and Interface Science

Volume

637

Number of Pages

134-146,

URL

https://www.scopus.com/inward/record.uri?eid=2-s2.0-85146625132&doi=10.1016%2fj.jcis.2022.12.124&partnerID=40&md5=78463e6d62910134f3b1018a07f09c31

DOI

10.1016/j.jcis.2022.12.124

Group (Lab)

Itai Cohen Group

Funding Source

CBET-1803409
EFMA1935252
NNCI-2025233
W911NF-15-1-0568
W911NF-17-1-0575

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