Joseph J. Wysocki

Interaction Between UV Radiation and Cholesteric Liquid Crystals

Abstract Mixtures of cholesteryl iodide and cholesteryl bromide with cholesteryl nonanoafce were exposed to UV radiation and the resultant color shifts were measured as a function of exposure and composition. The formation of images by this process will be described, and the presiding mechanism will be briefly discussed.

Light Scattering Properties of Cholesteric Liquid Crystal Films

Abstract It has been observed that cholesteric liquid crystal films exist in two states both of which exhibit characteristic brilliant colors. A transition between the two states can be caused by a variety of disturbances including mechanical perturbation and electrophoretic action.1 Optical scattering data indicate that the fundamental dispersive cause in both the undisturbed state and the disturbed state is the existence of regions of local order characterized by optically anisotropic layers stacked in a helical fashion. Intensity studies indicate that the angular distribution of helical axes is not isotropic in either state. In the undisturbed state the helical axes lie predominantly in the plane of the surface whereas in the disturbed state the helical axes are predominantly normal to the surface. This is confirmed by microscopic observations which show in the undisturbed state regions (with the dimensions of microns) of large birefringence and no optical activity. The disturbed state exhibits one uni...

Continued Kinetic Study of the Cholesteric-Nematic Transition in a Liquid Crystal Film

Abstract Liquid crystals react to electric fields in strange, exciting ways. For example, when the field is sufficiently intense, a helicoidal cholesteric system transforms into a linear nematic form(1) As a result of previous experimental and theoretical work, steady state phenomenological aspects of the transformation and its dependence on material parameters are now well understood. (2,3 A study was initiated to extend observations further by considering kinetic aspects of the transition; that is, the transient behavior provoked by application of voltage as the material transforms to the nematic state, the transformation transient, and the behavior observeb when the field is removed and the sample resumes its cholesteric form, the relaxation transient.(4,5)

The Effective Rotary Power of the Fatty Esters of Cholesterol

The pitch of two component mixtures of certain cholesteric liquid crystals is a strong function of chemical composition. We have found that over a wide range of materials the pitch of a mixture can be accurately represented by a weighted average of ingredients. If an effective rotary power,which we define as the inverse of pitch, is assigned to each constituent, the resultant pitch is just the inverse of the net effective rotary power of the mixture. In particular, if components with opposite intrinsic screw sense are mixed, there will exist one composition corresponding to no net rotation or infinite pitch. This technique was used to measure the effective rotary power of the fatty esters of cholesterol. Each ester was studied in mixtures with cholesteryl chloride. The results indicate a strong dependence on composition, with effective rotary power decreasing with decreasing aliphatic chain length. This technique provides a direct comparison of all esters at a common temperature. This is not possible in single component systems since there is no common cholesteric temperature and the strong pitch temperature dependence complicates studies. Although neither ingredient is liquid crystal at room temperature, the mixtures are liquid crystals over a wide compositional range and a modest extrapolation provides the single component data.

Spatial-frequency response of gamma ruticons

An experimental study of the response of gamma-ruticons to sinusoidal excitation was performed. The parameters investigated were mirror thickness, photoconductor/elastomer thickness ratio, and applied voltage. Overall frequency response and limiting behavior at high and low frequencies were determined. The frequency dependence of the deformation follows generally the theory of Kermisch, allowing mirror tension to be deduced from the high-frequency data. The shear modulus could not be obtained from low-frequency data because of the onset of viscous flow, which was not treated in the theory.

Switching response of surface stabilized ferroelectric liquid crystal in a full-wave plate geometry

Abstract The optical transmission and response to an electric field of a surface stabilized ferroelectric liquid crystal (SSFLC) is frequently described for simplicity by a model which amounts to a rotation of a uniaxial crystal about the smectic layer normal. This model, though quite useful under most circumstances, neglects some interesting properties of the SSFLC. We have measured the optical properties of an SSFLC cell in the quiescent state and found it to deviate from the uniform birefringent slab model. When the thickness of the cell corresponds to a full-wave plate, an applied square-wave voltage reveals deviations in the form of scattering during the switching transitions.

Response time and contrast ratio of ferroelectric liquid crystal cells

The response time and contrast ratio of ferroelectric liquid crystals with positive and negative dielectric anisotropy were examined. The behavior observed after an isotropic anneal depended on the application of a high field. Before application, anomalous regions were observed which vanished after the application of a high field. Contrast ratio changes were observed, caused by the generation and annihilation of defects. Surfaces and structural changes appear to be involved in both the response-time and contrast-ratio behavior.<<ETX>>

Imagewise Deformation and Color Change of Liquid Crystals in Electric Fields

Liquid crystals can be used in deformation imaging. In addition, unique color changes can be produced in suitable cholesteric liquid crystals. This paper describes two processes involving imagewise deformation and color change of liquid crystal films. The first process is due to electrophoretic action in electric fields and the second to uv induced effects. The anomalous optical properties of liquid crystals are discussed in terms of a physical model which also provides a basis for understanding the mechanism responsible for the color change associated with deformations.