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See detailMicrofluidic Wet Spinning of Core-Sheath Elastomer-Liquid Crystal Fibers
Honaker, Lawrence William UL; Vats, Shameek UL; Anyfantakis, Emmanouil UL et al

Scientific Conference (2019, March 29)

Liquid crystals encapsulated in fibers have a wide variety of applications in sensing. In order to produce these, several methods have been explored. Electrospinning is among the better-known techniques ... [more ▼]

Liquid crystals encapsulated in fibers have a wide variety of applications in sensing. In order to produce these, several methods have been explored. Electrospinning is among the better-known techniques with considerable successes. Only a limited range of polymers, though, has been used for electrospinning with liquid crystal cores, and the process of electrospinning has many obstacles to its utility at an industrial scale. On the other hand, wet-spinning techniques are better suited for industrial applications and are widely used in textile manufacturing, but are not commonly used for coaxial fiber production, especially with the large experimental scales that are difficult to replicate in a standard liquid crystal research laboratory. We therefore propose a method for wet-spinning coaxial core-sheath liquid crystal-filled elastomer fibers using a microfluidic set-up. Based on the flow-focusing method used for the production of liquid crystal shells and emulsions, this technique generates coaxial filaments by pumping a core-sheath flow of a liquid crystal surrounded by a rubbery polymer solution into a co-flowing coagulation bath. The coagulation bath is tuned to quickly extract the elastic polymer solution solvent, leaving behind a dry, continuous fiber. We have employed this method to produce fibers of polybutadiene and polyisoprene containing a core of a liquid crystal, such as 4-cyano-4'-pentylbiphenyl (5CB). Investigations into the choice of polymer solution, i.e. both the polymer and solvents used, will be presented in addition to discussion on parameters affecting the contiguity of the core. [less ▲]

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See detailConference report on the 45th German liquid crystal conference
Honaker, Lawrence William UL

in Liquid Crystals Today (2018), 27(3), 77-79

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See detailMicrofluidic Tensiometry Technique for the Characterization of the Interfacial Tension between Immiscible Liquids.
Honaker, Lawrence William UL; Lagerwall, Jan UL; Jampani, Venkata UL

in Langmuir (2018)

The interfacial tension between two immiscible fluids is of critical importance for understanding many natural phenomena as well as in industrial production processes; however, it can be challenging to ... [more ▼]

The interfacial tension between two immiscible fluids is of critical importance for understanding many natural phenomena as well as in industrial production processes; however, it can be challenging to measure this parameter with high accuracy. Most commonly used techniques have significant shortcomings because of their reliance on other data such as density or viscosity. To overcome these issues, we devise a technique that works with very small sample quantities and does not require any data about either fluid, based on micropipette aspiration techniques. The method facilitates the generation of a droplet of one fluid inside of the other, followed by immediate in situ aspiration of the droplet into a constricted channel. A modified Young-Laplace equation is then used to relate the pressure needed to produce a given deformation of the droplet's radius to the interfacial tension. We demonstrate this technique on different systems with interfacial tensions ranging from sub-millinewton per meter to several hundred millinewton per meter, thus over 4 orders of magnitude, obtaining precise results in agreement with the literature solely from experimental observations of the droplet deformation. [less ▲]

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See detailThermotropic Liquid Crystal-Assisted Chemical and Biological Sensors
Popov, Nicolai; Honaker, Lawrence William UL; Popova, Maia et al

in Materials (2017), 11(20),

In this review article, we analyze recent progress in the application of liquid crystal-assisted advanced functional materials for sensing biological and chemical analytes. Multiple research groups ... [more ▼]

In this review article, we analyze recent progress in the application of liquid crystal-assisted advanced functional materials for sensing biological and chemical analytes. Multiple research groups demonstrate substantial interest in liquid crystal (LC) sensing platforms, generating an increasing number of scientific articles. We review trends in implementing LC sensing techniques and identify common problems related to the stability and reliability of the sensing materials as well as to experimental set-ups. Finally, we suggest possible means of bridging scientific findings to viable and attractive LC sensor platforms. [less ▲]

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See detailChiral Nematic Liquid Crystal Microlenses
Popov, Piotr; Honaker, Lawrence William UL; Mirheydari, Mona et al

in Scientific Reports (2017)

Nematic liquid crystals (NLCs) of achiral molecules and racemic mixtures of chiral ones form flat films and show uniform textures between circular polarizers when suspended in sub-millimeter size grids ... [more ▼]

Nematic liquid crystals (NLCs) of achiral molecules and racemic mixtures of chiral ones form flat films and show uniform textures between circular polarizers when suspended in sub-millimeter size grids and immersed in water. On addition of chiral dopants to the liquid crystal, the films exhibit optical textures with concentric ring patterns and radial variation of the birefringence color. Both are related to a biconvex shape of the chiral liquid crystal film; the rings are due to interference. The curvature radii of the biconvex lens array are in the range of a few millimeters. This curvature leads to a radial variation of the optical axis along the plane of the film. Such a Pancharatnam-type phase lens dominates the imaging and explains the measured focal length of about one millimeter. To our knowledge, these are the first spontaneously formed Pancharatnam devices. The unwinding of the helical structure at the grid walls drives the lens shape. The relation between the lens curvature and material properties such as helical pitch, the twist elastic constant, and the interfacial tensions, is derived. This simple, novel method for spontaneously forming microlens arrays can also be used for various sensors. [less ▲]

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See detailA Liquid Crystal Biosensor for Specific Detection of Antigens
Popov, Piotr; Honaker, Lawrence William UL; Kooijman, Edgar E. et al

in Sensing and Bio-Sensing Research (2016), 8

Following the principle of the enzyme-linked immunosorbent assay (ELISA) pathogen detection method, we demonstrate specific sensing of goat Immunoglobulin G (IgG) by a nematic liquid crystal material ... [more ▼]

Following the principle of the enzyme-linked immunosorbent assay (ELISA) pathogen detection method, we demonstrate specific sensing of goat Immunoglobulin G (IgG) by a nematic liquid crystal material. Sensing occurs via the visually-striking realignment of a pre-fabricated liquid crystal film, suspended in grids and coated with biotinylated lipids followed by biotinylated anti-goat IgG. Realignment occurs when the targeted goat IgG is added to the cell, but not when rat or rabbit serum IgG is added to the same surface. In principle, this method can be generalized to provide an inexpensive, fast and sensitive prefabricated sensor for any pathogen. [less ▲]

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