Thomas P. Rieker

Director and layer structure of SSFLC cells

Abstract X-ray scattering and optical studies reveal two key features of Surface Stabilized Ferroelectric Liquid Crystal (SSFLC) cell structure: (1) The temperature dependence of the layer thickness is an important effect in determining both the layer and director-polarization structure; and (2) There exists in some SSFLC cells an internal FLC—FLC interface, where surface stabilization of the director-polarization field occurs in addition to that at the FLC—substrate interface.

Small-angle X-ray scattering of a new series of organic aerogels

Abstract During the last decade, several new precursors have been proposed for the synthesis of organic aerogels. In a large majority of cases, the sol–gel reaction is base catalyzed and water is used as the solvent. Because of the poor solubility of liquid CO 2 in water, a time consuming two-step exchange is necessary (exchange of water by acetone followed by exchange of acetone by liquid CO 2 ). To eliminate this step, a new process with the solvent acetone was developed. Also in order to reduce gelation time, acid catalysis is used. The aim of the present work is to compare the solid and the porous texture of resorcinol–formaldehyde (RF) aerogels prepared by the conventional method (in water and base catalysis) to that of samples prepared by the new method (in acetone and acid catalysis), all other parameters (mass ratio, catalyst concentration R/C, supercritical extraction, pyrolysis conditions) remaining the same. Determination of pore size distribution (PSD) in different series of organic and pyrolyzed aerogels by thermoporometry and characterization of the solid structure by small-angle X-ray scattering (SAXS) measurements over a wide range of length are reported. The main difference between the two series of aerogels lies in the aggregation of the primary particles: the new series prepared in acetone and acid catalysis displays fractal scaling over more than a decade in length, while the conventional one does not. It is also shown that thermoporometry yields reliable information for both series of aerogels.

Morphology and mechanical property relationship in linear low-density polyethylene blown films

Linear low-density polyethylene (LLDPE) blown films fabricated under two different processing conditions, namely a non-stalk bubble configuration and a stalk bubble configuration, were investigated. Morphological characterization was performed using small-angle X-ray scattering, transmission electron microscopy, infrared dichroism, and differential scanning calorimetry. The findings on crystal orientation characteristics of the films suggest that modification on the widely accepted row orientation model of Keller and Machin may be needed. In comparison to the conventional non-stalk bubble geometry for LLDPE film blowing, the stalk bubble configuration can produce a more randomly orientated lamellar texture, resulting in less anisotropy in mechanical properties and a higher dart impact resistance. A good correlation between mechanical properties and morphological features was found.

Surfactant-templated silica aerogels

By combining the molecular silica precursor tetramethoxysilane (TMOS) with an alkaline, micellar, water: methanol solution, we form surfactant-templated silica gel (STSG) monoliths. The wet monoliths can be exchanged with ethanol and then supercritically extracted with carbon dioxide to produce surfactant-templated silica aerogels (STSAs). STSAs represent a new class of aerogels that are composed of aggregated submicron porous particles that have tunable intraparticle nanoporosity. STSAs catalyzed with NH4OH experience no measurable shrinkage upon extraction and have bulk densities less than ~0.15 g/cc. The STSAs can then be calcined to remove the remainder of the surfactant. The calcination process leads to minimal shrinkage (<8%), high surface area (~700 m2/g), uncracked monoliths with hierarchical inter- and intraparticle porosities, and bulk densities less than 0.08 g/cc. We use XRD, SAXS, SEM. 29Si NMR. and N2 Sorption to characterize the structure and porosity of these novel aerogels.

Dual crystalline texture in HDPE blown films and its implication on mechanical properties

The morphological features of a series of high-density polyethylene (HDPE) blown films were studied using transmission electron microscopy, small-angle X-ray scattering and infrared dichroism. An orthogonally-oriented, dual crystalline texture was found in these HDPE films. This structure appears to consist of two superimposed row-oriented textures. In one row-oriented texture, the lamellae are stacked along the machine direction; while in the other, the lamellae are stacked along the transverse direction. The lamellar populations in the two textures are greatly affected by the neck height of the film blowing process. The mechanical properties of the films correlate well with the observed dual crystalline texture.

Layer and director structure in surface stabilized ferroelectric liquid crystal cells with non-planar boundary conditions

Abstract High resolution X-ray scattering studies of thin smectic C* (SC) samples prepared between solid plates coated with obliquely evaporated silicon monoxide to favor surface director orientation tilted out of the surface plane, reveal a local layer structure which is dependent on the evaporation directions on the plates. Samples with the evaporation directions antiparallel exhibit uniformly tilted layers. Those with parallel evaporation directions exhibit a zig-zag defect free chevron structure of tilted layers.

The University of New Mexico/Sandia National Laboratories small-angle scattering laboratory

The University of New Mexico/Sandia National Laboratories small-angle scattering laboratory provides a wide q-range, 3×10−4 A−1<q<0.7 A−1, for the structural analysis of materials on length scales from a few angstrom to ∼0.1 μm. The wide q-range is accomplished by combining data from a Bonse-Hart spectrometer (3×10−4 A−1<q<3×10−2 A−1) and a 5 m pinhole (3×10−3 A−1<q<0.7 A−1) instrument. Automation of the data acquisition systems along with a variety of sample environments and sample changers yields flexible, high throughput instruments.

The Layer and Director Structures of Ferroelectric Liquid Crystals

Liquid Crystals are a fascinating state of matter which have long been studied for their rich and diverse physical properties1,2. These materials have become of interest in a variety of applications, mainly due to their large optical anisotropy which is easily manipulated by applied fields and surface interactions. Twisted nematic (TN) devices have proved to be phenomenally useful and as a result, their response to applied fields and surface interactions is well understood.

Chevron layer structures in surface stabilized ferroelectric liquid crystal (SSFLC) cells filled with a material which exhibits the chiral nematic to smectic C* phase transition

In this paper we report on the layer structure in Surface Stabilized Ferroelectric Liquid Crystal (SSFLC) electro-optic cells, adopted by a compound which exhibit the smectic C* (SC*) to chiral nematic (N*) phase transition. This class of compounds is unique in that the SC* layers form directly from the N* phase. These materials demonstrate a large tilt (/Theta/) of the director (/cflx n/) from the layer normal (/cflx z//prime/) immediately upon cooling into the SC* phase. Recent high resolution x-ray experiments have demonstrated the presence of a chevron layer structure of tilted layers in compounds which exhibit the smectic A (SA) to SC* and the N*-SC* phase transitions, and also in a compound which has a very broad smectic A Phase. Chevron formation in smectic samples is a result of the layers anchoring normal or nearly normal to the bounding plates and subsequent layer contraction in the absence of dislocations. Patel and Goodby have demonstrated that compounds which exhibit the N*-SC* phase transition in the SSFLC geometry can be aligned by the application of an electric field across a cell with a buffed polymer surface treatment. With this method two domains of smectic layers form at large angles to the buffing direction normal. This is a consequence of the system simultaneously satisfying the imposed alignment direction, the large director tilt angle /Theta/, surface stabilization and the alignment of the polarization (P) along E. 9 refs., 5 figs.

Proximity effect for scrolling spatial light modulator applications of surface‐stabilized ferroelectric liquid‐crystal switching

We demonstrate a ‘‘proximity effect’’ in a linear pixel array of bistable electro‐optic surface‐stabilized ferroelectric liquid‐crystal (SSFLC) light valves, in which the switching threshold for a given pixel depends on the states of neighboring pixels. This effect should allow operation of SSFLC spatial light modulators as electro‐optic shift registers.