Multi‐Scale Responses of Liquid Crystals Triggered by Interfacial Assemblies of Cleavable Homopolymers

Kim, Young‐Ki; Huang, Yongfeng; Tsuei, Michael; Wang, Xin; Gianneschi, Nathan C.; Abbott, Nicholas L.

doi:10.1002/cphc.201800106

Cited by 18 publications

(18 citation statements)

References 91 publications

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“…Previous work on “bolaform” amphiphiles of the Me 3 N + (CH 2 ) n [Fe] type have established that for shorter chain homologues both the trimethylammonium and the ferrocene lie close to the surface of the water, but for longer chains an extended conformation is observed in which only the trimethylammonium is close to the water surface . For such amphiphiles their ability to induce planar anchoring of LCs has been attributed to this particular conformation of the amphiphile , rather than to inhibition of interdigitation . However, for example, in the case of DFPC such an arrangement should lead to a surface area per molecule of the order of ca.…”

Section: Results and Discussionmentioning

confidence: 99%

“…In the resultant “phase space” the order in which the phospholipid components need to be arranged is that qualitatively expected in terms of ease of interpenetration of the LC molecules into a fluid “normal” phospholipid monolayer. This is probably not the only factor involved, , but it seems to be the major influence. The order seen for the LC component is less easy to understand, but our studies suggest that for these droplets, at least, the intrinsic surface rather than the intrinsic bulk properties is the most important.…”

Section: Discussionmentioning

confidence: 99%

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Control of Director Fields in Phospholipid-Coated Liquid Crystal Droplets

et al. 2020

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In liquid crystal (LC) droplets, small changes in surface anchoring energy can produce large changes in the director field which result in readily detectable optical effects. This makes them attractive for use as biosensors. Coating LC droplets with a phospholipid monolayer provides a bridge between the hydrophobic world of LCs and the water-based world of biology and makes it possible to incorporate naturally occurring biosensor systems. However, phospholipids promote strong perpendicular (homeotropic) anchoring that can inhibit switching of the director field. We show that the tendency for phospholipid layers to promote perpendicular anchoring can be suppressed by using synthetic phospholipids in which the acyl chains are terminated with bulky tert-butyl or ferrocenyl groups; the larger these end-group(s), the less likely the system is to be perpendicular/radial. Additionally, the droplet director field is found to be dependent on the nature of the LC, particularly its intrinsic surface properties, but not (apparently) on the sign of the dielectric anisotropy, the proximity to the melting/isotropic phase transition, the surface tension (in air), or the values of the Frank elastic constants.

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Section: Results and Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Control of Director Fields in Phospholipid-Coated Liquid Crystal Droplets

et al. 2020

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“…The small magnitude of the interfacial anchoring energy of a LC means that subtle interactions at a LC interface (e.g., caused by adsorption of a surfactant) can cause changes in the orientations of LCs. In this context, LCs have been used to report a wide range of molecular/microscopic events at interfaces, such as supramolecular clustering of amphiphiles, photoisomerization, , enzymatic reactions, formation of DNA complexes, directed assembly of oligopeptides, and interfacial interactions of ions. , In most past reports, however, the optical responses of LCs to these molecular stimuli have been studied in the absence of flow (see below for additional comments). Here, we move to study flow-induced organizations of amphiphiles at LC interfaces.…”

Section: Introductionmentioning

confidence: 99%

Using Liquid Crystals for In Situ Optical Mapping of Interfacial Mobility and Surfactant Concentrations at Flowing Aqueous–Oil Interfaces

2021

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Flow-induced states of fluid interfaces decorated with amphiphiles underlie phenomena such as emulsification, foaming, and spreading. While past studies have shown that interfacial mass transfer, the kinetics of surfactant adsorption and desorption, interfacial mobility, and surfactant reorganization regulate the dynamic properties of surfactant−laden interfaces, few simple methods permit simultaneous monitoring of this interplay. Here, we explore the optical responses of micrometer-thick films of oils (4-cyano-4′-pentylbiphenyl, 5CB) with a liquid crystalline order in contact with flowing aqueous phases of soluble [e.g., sodium dodecyl sulfate (SDS)] or insoluble (e.g., 1,2-dilauroyl-snglycero-3-phosphocholine) amphiphiles. We observe the onset of flow of 0.5 mM SDS solutions within a millifluidic channel (area-average velocity of 200 mm/s) to transform a liquid crystal (LC) film with an alignment along the interface normal into a bright birefringent state (average LC tilt angle of 30°), consistent with an initially mobile interface that shears and thus tilts the LC along the flow direction. Subsequently, we observed the LC film to evolve to a steady state (over ∼10 s) with position-dependent optical retardance controlled by gradients in surfactant concentration and thus Marangoni stresses. For 0.5 mM SDS solutions, by using particle tracking and a simple hydrodynamic model, we reveal that the dominant role of the flow-induced interfacial surfactant concentration gradient is to change the mobility of the interface (and thus shear rate of LC) and not to change the easy axis (equilibrium orientation) or anchoring energy (orientation-dependent interfacial energy) of the LC. At lower surfactant concentrations (0.015 mM SDS), however, we show that the LC directly maps flow-induced interfacial surfactant concentration gradients via a change in the local easy axis of the LC. When combined with additional measurements obtained with simple salts and insoluble amphiphiles, these results hint that LC oils may offer the basis of general and facile methods that permit mapping of both interfacial mobilities and surfactant distributions at flowing interfaces.

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“…Responsive materials undergo changes in structure and properties as a consequence of their interactions with their environment, including via electrical and magnetic fields, 1,2 mechanical shear, 3,4 changes in pH, 5−8 UV irradiation, 9−13 exchange of heat, 14−16 and electrolyte composition. 17,18 This growing class of materials is enabling many potential applications, such as the basis of sensors 3,[6][7][8]12,17 and actuators, 2,8−11 and for achieving controlled release of active chemical agents. 4,5,[13][14][15]18 Liquid crystals (LCs), in particular, offer substantial opportunities for the design of responsive materials due to their ability to amplify molecular-level stimuli into the optical scale.…”

Section: ■ Introductionmentioning

confidence: 99%

Oligomers as Triggers for Responsive Liquid Crystals

et al. 2018

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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 to 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.

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Multi‐Scale Responses of Liquid Crystals Triggered by Interfacial Assemblies of Cleavable Homopolymers

Cited by 18 publications

References 91 publications

Control of Director Fields in Phospholipid-Coated Liquid Crystal Droplets

Control of Director Fields in Phospholipid-Coated Liquid Crystal Droplets

Using Liquid Crystals for In Situ Optical Mapping of Interfacial Mobility and Surfactant Concentrations at Flowing Aqueous–Oil Interfaces

Oligomers as Triggers for Responsive Liquid Crystals

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