Simple method for measuring the azimuthal anchoring strength of nematic liquid crystals

Fonseca, João F. B. D.; Galerne, Y.

doi:10.1063/1.1415344

Cited by 23 publications

(39 citation statements)

References 8 publications

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“…Image processing is then used to determine the mean luminosity of the LC in each image and this data can be plotted as a function of analyzer position (Figure 10B). The magnitude of light transmitted through the twisted LC film can be fit to a function of the form 14, 45 …”

Section: Quantitation Of the Orientations Of Lcs At Planar Interfacesmentioning

confidence: 99%

Introduction to Optical Methods for Characterizing Liquid Crystals at Interfaces

et al. 2013

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This Instructional Review describes methods and underlying principles that can be used to characterize both the orientations assumed spontaneously by liquid crystals (LCs) at interfaces and the strength with which the LCs are held in those orientations (so-called anchoring energies). The application of these methods to several different classes of LC interfaces is described, including solid and aqueous interfaces as well as planar and non-planar interfaces (such as those that define a LC-in-water emulsion droplet). These methods, which enable fundamental studies of the ordering of LCs at polymeric, chemically-functionalized and biomolecular interfaces, are described in this article at a level that can be easily understood by a non-expert reader such as an undergraduate or graduate student. We focus on optical methods because they are based on instrumentation that is found widely in research and teaching laboratories.

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Section: Quantitation Of the Orientations Of Lcs At Planar Interfacesmentioning

confidence: 99%

Introduction to Optical Methods for Characterizing Liquid Crystals at Interfaces

et al. 2013

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“…A variety of methods exist to measure the anchoring energies of LC on surfaces 43. One approach exploits the elastic nature of LCs, as illustrated in Figure 2D, and provides measurement of the azimuthal anchoring energy 19, 23-25.…”

Section: Section 1: Anchoring Of Liquid Crystals On Chemically Functimentioning

confidence: 99%

Recent Advances in Colloidal and Interfacial Phenomena Involving Liquid Crystals

2010

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This article describes recent advances in several areas of research involving the interfacial ordering of liquid crystals (LCs). The first advance revolves around the ordering of LCs at bio/ chemically functionalized surfaces. Whereas the majority of past studies of surface-induced ordering of LCs have involved surfaces of solids that present a limited diversity of chemical functional groups (surfaces at which van der Waals forces dominate surface-induced ordering), recent studies have moved to investigate the ordering of LCs on chemically complex surfaces. For example, surfaces decorated with biomolecules (e.g. oligopeptides and proteins) and transition metal ions have been investigated, leading to an understanding of the roles that metal-ligand coordination interactions, electrical double-layers, acid-base interactions, and hydrogen bonding can have on the interfacial ordering of LCs. The opportunity to create chemically-responsive LCs capable of undergoing ordering transitions in the presence of targeted molecular events (e.g., ligand exchange around a metal center) has emerged from these fundamental studies. A second advance has focused on investigations of the ordering of LCs at interfaces with immiscible isotropic fluids, particularly water. In contrast to prior studies of surface-induced ordering of LCs on solid surfaces, LC-aqueous interfaces are deformable and molecules at these interfaces exhibit high levels of mobility and thus can reorganize in response to changes in interfacial environment. A range of fundamental investigations involving these LC-aqueous interfaces have revealed that (i) the spatial and temporal characteristics of assemblies formed from biomolecular interactions can be reported by surface-driven ordering transitions in the LCs, (ii) the interfacial phase behaviour of molecules and colloids can be coupled to (and manipulated via) the ordering (and nematic elasticity) of LCs, and (iii) confinement of LCs leads to unanticipated size-dependent ordering (particularly in the context of LC emulsion droplets). The third and final advance addressed in this article involves interactions between colloids mediated by LCs. Recent experiments involving microparticles deposited at the LC-aqueous interface have revealed that LC-mediated interactions can drive interfacial assemblies of particles through reversible ordering transitions (e.g., from one-dimensional chains to two-dimensional arrays with local hexagonal symmetry). In addition, recent single nanoparticle measurements suggest that the ordering of LCs about nanoparticles differs substantially from micrometer-sized particles and that the interactions between nanoparticles mediated by the LCs are far weaker than predicted by theory (sufficiently weak that the interactions are reversible and thus enable self-assembly). Finally, LC-mediated interactions between colloidal particles have also been shown to lead to the formation of colloidin-LC gels that possess mechanical properties relevant to the design of materials to interface with li...

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“…In our studies, we paired two surfaces, an analytic surface with anchoring energy W az and a reference surface with sufficiently high anchoring energy that there was negligible deviation of the LC orientation from the easy axis of the reference surface. For optical cells with a known LC film thickness (d) and twist elastic constant (K 22 ), the anchoring energy of the analytic surface can be calculated using the so-called torque-balance model (29) as:

W_{a z} = \frac{2 K_{22} Ψ}{d sin (2 ϕ)}

…”

Section: Introductionmentioning

confidence: 99%

Design of Surfaces for Liquid Crystal-Based Bioanalytical Assays

Lowe

Ozer

Bai

et al. 2010

ACS Appl. Mater. Interfaces

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Surface-induced ordering of liquid crystals (LCs) offers the basis of a label-free analytical technique for the detection of surface-bound biomolecules. The orientation-dependent energy of interaction of a LC with a surface (anchoring energy of LC), in particular, is both sensitive to the presence of surface-bound molecules and easily quantified. Herein we report a study that analyzes a simple model of twisted nematic LC systems and thereby identifies surfaces with LC anchoring energies in the range of 0.5 μJ/m 2 to 2.0 μJ/m 2 to be optimal for use with LC-based analytical methods. Guided by these predictions, we demonstrate that analytic surfaces possessing anchoring energies within this range can be fabricated with a high level of precision (< 0.1 μJ/m 2 ) through formation of monolayers of organothiols (with ω-functional groups corresponding to oligoethyleneglycols and amines) on gold films deposited by physical vapor deposition at oblique angles of incidence. Finally, by using the human epidermal growth factor receptor (EGFR) as a model protein analyte, we have characterized the influence of the anchoring energies of the surfaces on the response of the LC to the presence of surface-bound EGFR. These results, when combined with 32 P-radiolabeling of the EGFR to independently quantify the surface concentration of EGFR, permit identification of surfaces that allow use of LCs to report surface densities of EGFR of 70-90 pg/mm 2 . Overall, the results reported in this paper guide the design of surfaces for use in LC-based analytical systems.

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Simple method for measuring the azimuthal anchoring strength of nematic liquid crystals

Cited by 23 publications

References 8 publications

Introduction to Optical Methods for Characterizing Liquid Crystals at Interfaces

Introduction to Optical Methods for Characterizing Liquid Crystals at Interfaces

Recent Advances in Colloidal and Interfacial Phenomena Involving Liquid Crystals

Design of Surfaces for Liquid Crystal-Based Bioanalytical Assays

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