Instructional Review: An Introduction to Optical Methods for Characterizing Liquid Crystals at Interfaces.

Langmuir (Impact Factor: 4.46). 01/2013; 29(10). DOI: 10.1021/la304679f
Source: PubMed


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.

7 Reads
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report the use of flow cytometry to identify the internal ordering (director configurations) of micrometer-sized droplets of thermotropic liquid crystals (LCs) dispersed in aqueous solutions of adsorbates (surfactants and phospholipids). We reveal that changes in the configurations of the LC droplets induced by the adsorbates generate distinct changes in light scattering plots (side versus forward scattering). Specifically, when compared to bipolar droplets, radial droplets generate a narrower distribution of side scattering intensities (SSC, large angle light scattering) for a given intensity of forward scattering (FSC, small angle light scattering). This difference is shown to arise from the rotational symmetry of a radial LC droplet which is absent for the bipolar configuration of the LC droplet. In addition, the scatter plots for radial droplets possess a characteristic "S-shape", with two or more SSC intensities observed for each intensity of FSC. The origin of the experimentally observed S-shape is investigated via calculation of form factors and established to be due to size-dependent interference effects that differ for the forward and side scattered light. Finally, by analyzing emulsions comprised of mixtures of bipolar and radial droplets at rates of up to 10,000 droplets per second, we demonstrate that flow cytometry permits precise determination of the percentage of radial droplets within the mixture with a coefficient of determination of 0.98 (as validated by optical microscopy). Overall, the results presented in this paper demonstrate that flow cytometry provides a promising approach for high throughput quantification of the internal configurations of LC emulsion microdroplets. Because large numbers of droplets can be characterized, it enables statistically robust analyses of LC droplets. The methodology also appears promising for quantification of chemical and biological assays based on adsorbate-induced ordering transitions within LC droplets.
    Analytical Chemistry 09/2013; 85(21). DOI:10.1021/ac4021193 · 5.64 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Micrometer-sized, periodic protein lines printed on a solid surface cause interference color which is invisible to the naked eye. However, the interference color can be amplified by using a thin layer of liquid crystal (LC) covered on the surface to form a phase diffraction grating. Strong interference color can thus be observed under ambient light. By using the LC-amplified interference color, we demonstrate naked-eye detection of a model protein—immunoglobulin G (IgG). Limit of detection can reach 20 μg/ml of IgG without using any instrumentation. This detection method is potentially useful for the development of low-cost and portable biosensors.
    Applied Physics Letters 12/2013; 103(24):243701-243701-3. DOI:10.1063/1.4844835 · 3.30 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: I'm stuck on you: Droplet-based liquid crystal (LC) chemical sensors can be immobilized on living cells. The decorated cells can report in real time on the presence of toxins in surrounding culture media. The approach provides new principles for the design of droplet-based LC sensors as well as methods for the local detection and reporting of chemical agents that are difficult to achieve in cellular environments using free-floating LC droplets.
    Angewandte Chemie International Edition 12/2013; 52(52). DOI:10.1002/anie.201306630 · 11.26 Impact Factor
Show more