Circularly polarized light was previously employed to stimulate the reversible and reconfigurable writing of scattering states in cholesteric liquid crystal (CLC) cells constructed with a photosensitive layer. Such dynamic photodriven responses have utility in remotely triggering changes in optical constructs responsive to optical stimulus and applications where complex spatial patterning is required. Writing of scattering regions required the handedness of incoming radiation to match the handedness of the CLC and the reflection bandwidth of the CLC to envelop the wavelength of the incoming radiation. In this paper, the mechanism of transforming the CLC into a light scattering state via the influence of light on the photosensitive alignment layer is detailed. Specifically, the effects of: (i) the polarization state of light on the photosensitive alignment layer; (ii) the exposure time; and (iii) the incidence angle of radiation on domain formation are reported. The photogenerated light-scattering domains are shown to be similar in appearance between crossed polarizers to a defect structure that occurs at a CLC/air interface ( i.e., a free CLC surface). This observation provides strong indication that exposure of the photosensitive alignment layer to the circularly polarized light of appropriate wavelength and handedness generates an out-of-plane orientation leading to a periodic distortion of the original planar structure.
References
[1]
Collings, P.J. Liquid Crystals: Nature’s Delicate Phase of Matter, 2nd ed.; Princeton University Press: Princeton, NJ, USA, 2002; pp. 9–10.
[2]
Belyakov, V.A.; Dmitrienko, V.E. Optics of Chiral Liquid Crystals, 1st ed.; Routledge: Harwood, NY, USA, 1989.
[3]
St. John, W.D.; Fritz, W.J.; Lu, Z.J.; Yang, D.-K. Bragg reflection form cholesteric liquid crystals. Phys. Rev. E 1995, 51, 1191–1198, doi:10.1103/PhysRevE.51.1191.
[4]
Sharma, V.; Crne, M.; Park, J.O.; Srinivasarao, M. Structural Origin of Circularly Polarized Iridescence in Jeweled Beetles. Science 2009, 325, 449–110, doi:10.1126/science.1172051.
[5]
Vignolini, S.; Rudall, P.J.; Rowland, A.V.; Reed, A.; Moyroud, E.; Faden, R.B.; Baumberg, J.J.; Glover, B.J.; Steiner, U. Pointillist structural color in Pollia fruit. Proc. Natl. Acad. Sci. USA 2012, 109, 15712–15715, doi:10.1073/pnas.1210105109.
[6]
Fan, B.; Vartak, S.; Eakin, J.N.; Faris, S.M. Surface anchoring effects on spectral broadening of cholesteric liquid crystal films. J. Appl. Phys. 2008, 104, 023108:1–023108:5.
[7]
Chigrinov, V.G.; Kozenkov, V.M.; Kwok, H.-S. Photoalignment of Liquid Crystalline Materials: Physics and Applications, 1st ed.; John Wiley and Sons Ltd.: West Sussex, UK, 2008; p. 5.
[8]
Ichimura, K. Photoalignment of Liquid-Crystal Systems. Chem. Rev. 2000, 100, 1847–1873, doi:10.1021/cr980079e.
[9]
Yaroshchuk, O.; Reznikov, Y. Photoalignment of liquid crystals: Basics and current trends. J. Mater. Chem. 2012, 22, 286–300, doi:10.1039/c1jm13485j.
Schadt, M.; Schmitt, K.; Kozinkov, V.; Chigrinov, V. Surface-induced parallel alignment of liquid crystals by linearly polymerized photopolymer. J. Appl. Phys. 1992, 31, 2155–2164.
Helfrich, W. Deformation of Cholesteric Liquid Crystals with Low Threshold Voltage. Appl. Phys. Lett. 1970, 17, 531–532, doi:10.1063/1.1653297.
[24]
Gerritsma, C.J.; van Zanten, P. Periodic Perturbations in the Cholesteric Plane Texture. Phys. Lett. A 1971, 37, 47–48, doi:10.1016/0375-9601(71)90325-2.
[25]
Hervet, H.; Hurault, J.P.; Rondelez, F. Static one-dimensional distortions in cholesteric liquid crystals. Phys. Rev. A 1973, 8, 3055–3064, doi:10.1103/PhysRevA.8.3055.
[26]
Senyuk, B.I.; Smalyukh, I.I.; Lavrentovich, O.D. Undulations of lamellar liquid crystals with finite surface anchoring near and well above the threshold. Phys. Rev. E 2006, 74, 011712:1–011712:13.
[27]
Saupe, A. Disclinations and properties of the directorfield in nematic and cholesteric liquid crystals. Mol. Cryst. Liq. Cryst. 1973, 21, 211–238, doi:10.1080/15421407308083320.
Meister, R.; Dumoulin, H.; Halle, M.-A.; Pieranski, P. Structure of the cholesteric focal conic domains at the free surface. Phys. Rev. E 1996, 54, 3771–3782, doi:10.1103/PhysRevE.54.3771.
[30]
Meister, R.; Dumoulin, H.; Halle, M.-A.; Pieranski, P. The Anchoring of a Cholesteric Liquid Crystal at the Free Surface. J. Phys. II Fr. 1996, 6, 827–844.
[31]
Yager, K.G.; Barrett, C.J. Azobenzene Polymers for Photonic Applications. In Smart Light-Responsive Materials, 1st; Zhao, Y., Ikeda, T., Eds.; John Wiley and Sons, Inc.: Hoboken, NJ, USA, 2009; pp. 1–46.
[32]
Markave, E.; Gustina, D.; Matixova, G.; Kaula, I.; Muzikante, I.; Rutkis, M.; Gerca, L. Reversible trans/cis photoisomerization in Langmuir-Blodgett multilayers from polyfunctional azobenzenes. Supramol. Sci. 1997, 4, 369–374, doi:10.1016/S0968-5677(97)00018-7.
[33]
Menzel, H.; Weichart, B.; Schmidt, A.; Paul, S.; Knoll, W.; Stumpe, J.; Fischer, T. Small-angle X-ray scattering and ultraviolet-visible spectroscopy studies on the structure and structural changes in Langmuir-Blodgett films of polyglutamates with azobenzene moieties tethered by alkyl spacers of different length. Langmuir 1994, 10, 1926–1933, doi:10.1021/la00018a052.
[34]
Cojocariu, C.; Rochon, R. Light-induced motions in azobenzene-containing polymers. Pure Appl. Chem. 2004, 76, 1479–1497, doi:10.1351/pac200476071479.
[35]
Ruslim, C.; Ichimura, K. Photocontrolled Alignment of Chiral Nematic Liquid Crystals. Adv. Mater. 2001, 13, 641–644, doi:10.1002/1521-4095(200105)13:9<641::AID-ADMA641>3.0.CO;2-B.
Serak, S.; Tabiryan, N. Microwatt Power Optically Controlled Spatial Solitons in Azobenzene Liquid Crystals. Proc. SPIE 2006, 6332, 63320Y:1–63320Y:13.