Langmuir films of flexible polymers transferred to aqueous/liquid crystal interfaces induce uniform azimuthal alignment of the liquid crystal

Abstract

We reported recently that amphiphilic polymers can be assembled at interfaces created between aqueous phases and thermotropic liquid crystals (LCs) in ways that (i) couple the organization of the polymer to the order of the LC and (ii) respond to changes in the properties of aqueous phases that can be characterized as changes in the optical appearance of the LC. This investigation sought to characterize the behavior of aqueous-LC interfaces decorated with uniaxially compressed thin films of polymers transferred by Langmuir-Schaefer (LS) transfer. Here, we report physicochemical characterization of interfaces created between aqueous phases and the thermotropic LC 4-cyano-4'-pentylbiphenyl (5CB) decorated with Langmuir films of a novel amphiphilic polymer (polymer 1), synthesized by the addition of hydrophobic and hydrophilic side chains to poly(2-vinyl-4,4'-dimethylazlactone). Initial characterization of this system resulted in the unexpected observation of uniform azimuthal alignment of 5CB after LS transfer of the polymer films to aqueous-5CB interfaces. This paper describes characterization of Langmuir films of polymer 1 hosted at aqueous-5CB interfaces as well as the results of our investigations into the origins of the uniform ordering of the LC observed upon LS transfer. Our results, when combined, support the conclusion that uniform azimuthal alignment of 5CB is the result of long-range ordering of polymer chains in the Langmuir films (in a preferred direction orthogonal to the direction of compression) that is generated during uniaxial compression of the films prior to LS transfer. Although past studies of Langmuir films of polymers at aqueous-air interfaces have demonstrated that in-plane alignment of Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.Supporting Information Available. Additional figures and other data showing: (i) surface pressure recorded during repeated compression and expansion of a Langmuir film of polymer 1, (ii) a fluorescent micrograph of a film of 5CB after Langmuir-Schafer transfer of polymer 1 TMR to the aqueous-5CB interface, (iii) a representative AFM image of a film of polymer 1 transferred to an OTScoated Si substrate, (iv) polarized light micrographs of a LC film after transfer of polymer 1 at an angle ~ 45° relative to the aqueous-air interface, (v) fractional transmittance of polarized light through polymer 1-laden LC interfaces transferred at various angles relative to the direction of compression, (vi) representative π-A isotherms of Langmuir films of PMMA and PVS, (vii) polarized FT-IR spectra of PMMA films on CaF 2 substra...

Biosensor utilizing a liquid crystal/water interface functionalized with poly(4-cyanobiphenyl-4′-oxyundecylacrylate-b-((2-dimethyl amino) ethyl methacrylate))

“…Because of their high sensitivity and rapid response with respect to orientation, small-molecule LCs are an attractive medium for detecting chemical/biochemical events occurring at an interface as a result of optical changes that can be viewed with the aid of a polarized optical microscopy [28][29][30][31]. An optical change can occur as a result of a change in orientation of the LCs from vertical to parallel alignments at the water/LC interface upon adsorption of biomaterials [32].…”

Liquid Crystalline Materials for Biological Applications

“…16, 17, 19, 40, 56, 57, 59-61 Here we note that in biological membranes, many functions of the membrane result from the ability of the proteins and lipids comprising the membrane to reorganize in a manner that is dependent on interactions of these species within the membrane. 70, 71 In synthetic systems, it has been observed that interfaces at which lipids exhibit mobility can be used to form organized assemblies of proteins, including protein crystals.…”

“…The first approach involves the spontaneous adsorption of lipid from an aqueous dispersion onto the LC interface, 15, 16, 18, 23, 59 and the second involves the transfer of a Langmuir monolayer of lipid prepared at the surface of water onto the LC-aqueous interface using the Langmuir-Schaefer technique. 55, 60, 61 Below we review each of these methods for functionalization of LC interfaces, and then illustrate the utility of these tailored LC interfaces for reporting protein binding events.…”

Beyond displays: The recent progress of liquid crystals for bio/chemical detections

“…Over incubation for 2 h, a monolayer of L-DLPC was laden at LC-aqueous interface and resulted in a complete anchoring transition from planar to homeotropic alignment ( Figure 5(d)). Aside from lipids [29,30], it has been shown that amphiphilic molecules, such as surfactants [31][32][33][34][35][36][37] and polymers [38][39][40][41] at these interfaces are strongly coupled to the ordering of the LCs, and the presence and organization of these molecules can be reported through changes in the optical appearance of the LCs. It was noted that LCs are fluid-like and possess mobility, combined with liquid crystallinity, assembling biological amphiphiles at the LC-aqueous interface promises a possibility for mimicking cell membrane, which is mobile and composed of a large amount of lipids in liquid crystalline phase.…”