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Stetsyshyn Y, Raczkowska J, Budkowski A, Awsiuk K, Kostruba A, Nastyshyn S, Harhay K, Lychkovskyy E, Ohar H, Nastishin Y. Cholesterol-Based Grafted Polymer Brushes as Alignment Coating with Temperature-Tuned Anchoring for Nematic Liquid Crystals. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:11029-11038. [PMID: 27689751 DOI: 10.1021/acs.langmuir.6b02946] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Novel alignment coating with temperature-tuned anchoring for nematic liquid crystals (NLCs) was successfully fabricated in three step process, involving polymerization of poly(cholesteryl methacrylate) (PChMa) from oligoproxide grafted to the glass surface premodified with 3-aminopropyltriethoxysilane. Molecular composition, thickness, wettability of the PChMa coating and its alignment action for a NLC were examined with time of flight-secondary ion mass spectrometry, ellipsometry, contact angle measurements, polarization optical microscopy and commercially produced PolScope technique allowing for mapping of the optic axis and optical retardance within the microscope field view. We find that the PChMa coating provides a specific monotonous increase (decrease) in the tilt angle of the NLC director with respect to the substrates normal upon heating (cooling) referred to as anchoring tuning.
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Affiliation(s)
- Yurij Stetsyshyn
- Lviv Polytechnic National University , S. Bandery 12, 79013 Lviv, Ukraine
| | - Joanna Raczkowska
- Smoluchowski Institute of Physics, JagiellonianUniversity , Łojasiewicza 11, 30-348 Kraków, Poland
| | - Andrzej Budkowski
- Smoluchowski Institute of Physics, JagiellonianUniversity , Łojasiewicza 11, 30-348 Kraków, Poland
| | - Kamil Awsiuk
- Smoluchowski Institute of Physics, JagiellonianUniversity , Łojasiewicza 11, 30-348 Kraków, Poland
| | - Andriy Kostruba
- Lviv Academy of Commerce , Samtshuk 9, Lviv 79005 Ukraine
- Vlokh Institute of Physical Optics , 23 Dragomanov st., Lviv 79011, Ukraine
| | | | - Khrystyna Harhay
- Lviv Polytechnic National University , S. Bandery 12, 79013 Lviv, Ukraine
| | - Edward Lychkovskyy
- Lviv Danylo Halytsky National Medical University , Pekarska 69, 79010 Lviv, Ukraine
| | - Halyna Ohar
- Lviv Polytechnic National University , S. Bandery 12, 79013 Lviv, Ukraine
| | - Yuriy Nastishin
- Vlokh Institute of Physical Optics , 23 Dragomanov st., Lviv 79011, Ukraine
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Meyer C, Nastishin Y, Kleman M. Helical defects in smectic-A and smectic-A∗ phases. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 82:031704. [PMID: 21230088 DOI: 10.1103/physreve.82.031704] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2010] [Indexed: 05/30/2023]
Abstract
There are two categories of helical line defects in Sm-A phases: screw dislocations of small Burgers vectors and double helices (DHs), whose macroscopic configuration constitutes a mode of splitting of screw dislocations of giant Burgers vectors. Their counterparts in Sm-A∗'s (Sm-A's with chiral molecules) show a number of differences with the former and are investigated theoretically on the basis of recent observations [C. Meyer, Liq. Cryst. 37, 1047 (2010)]. The first part of the paper is a short review of the main features of helical defects in Sm-A's proper. In Sm-A∗'s, small Burgers vector screw dislocations with the same chirality as the high-temperature N∗ phase are favored over the opposite ones, a result that is related to the defect core singularity. This is also true for the macroscopic DH∗ s for a more subtle reason; we advance that the DH∗ nucleation at the N∗→Sm-A∗ transition stems from a peculiar texture of the cybotactic groups, akin in the ideal case to a set of two twisted χ disclinations in the N∗ phase, linked by a stacking fault of continuous disclinations. This stacking fault vanishes in the Sm-A∗ phase, and one recovers a DH∗ much similar to a DH but with the appropriate chirality. Cases that differ from ideality are described: they involve small Burgers vector screw dislocations and can be evoked to explain the numerous observed distorted double helices (the Darboux condition is not obeyed) and twisted ribbons. The case when the N∗→Sm-A∗ transition is type II (presence of a twist grain boundary phase in between) is briefly discussed.
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Affiliation(s)
- Claire Meyer
- Laboratoire de Physique des Systèmes Complexes, Université de Picardie Jules Verne, 33 rue Saint-Leu, 80039 Amiens, France.
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Sun X, Garetz BA, Moreira MF, Palffy-Muhoray P. Nonphotochemical laser-induced nucleation of nematic phase and alignment of nematic director from a supercooled thermotropic liquid crystal. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 79:021701. [PMID: 19391759 DOI: 10.1103/physreve.79.021701] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2008] [Indexed: 05/27/2023]
Abstract
A nonphotochemical laser-induced phase transition was studied in a supercooled 4;{'}-n -pentyl-4-cyanobiphenyl (5CB, also referred to as PCB and K15) liquid crystal, using linearly polarized 45 ps light pulses at a wavelength of 532 nm. The laser induced nucleation from the metastable supercooled isotropic phase to the nematic phase during slow cooling (0.001 degrees C/min) and high light intensity (3.9 MW/cm{2}) . The resulting nematic director tended to be aligned along the direction of the plane of polarization of the light. At the intensities used, there is no observable laser-induced realignment of the director once the sample is in the nematic phase, nor any permanent laser-induced ordering when the sample is illuminated only in the stable isotropic phase during slow cooling. These experimental results are consistent with a mechanism based on optical Kerr alignment.
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Affiliation(s)
- Xiaoying Sun
- Department of Chemical and Biological Sciences, Polytechnic Institute of New York University, Brooklyn, New York 11201, USA
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Fernández-Nieves A, Link DR, Márquez M, Weitz DA. Topological changes in bipolar nematic droplets under flow. PHYSICAL REVIEW LETTERS 2007; 98:087801. [PMID: 17359128 DOI: 10.1103/physrevlett.98.087801] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2006] [Revised: 11/22/2006] [Indexed: 05/14/2023]
Abstract
Bipolar liquid crystal drops moving inside microchannels exhibit periodic director field transformations due to induced circulating flows inside them. These modifications are characterized by changes in the type of point surface disclinations; they periodically change from splay to bend disclinations, implying the drop changes between bipolar and escaped concentric configurations. Upon stopping the flow, this structure does not relax to the lower energy bipolar configuration; we argue this is due to drop flattening inside the channels.
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Affiliation(s)
- A Fernández-Nieves
- Department of Physics and HSEAS, Harvard University, Cambridge, MA 02138, USA
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