Characterization of Polymer-Dispersed Liquid Crystal Systems by FT-IR Microspectroscopy

1995 ◽  
Vol 49 (3) ◽  
pp. 267-272 ◽  
Author(s):  
Sudarsana R. Challa ◽  
Shi-Qing Wang ◽  
Jack L. Koenig
Keyword(s):  
Liquid Crystal ◽  
Power Laws ◽  
Butyl Methacrylate ◽  
Valuable Insight ◽  
Infrared Microspectroscopy ◽  
Polymer Dispersed Liquid Crystal ◽  
Spatially Resolved ◽  
The Matrix ◽  
Polymer Dispersed ◽  
Ft Ir

Infrared microspectroscopy was used to generate functional group images of liquid crystal (E7) droplets dispersed in poly( n-butyl methacrylate) (PBMA). The spatial concentration fluctuations that occur within the system were studied as a function of time. This approach is possible because spectral information can be obtained by focusing on regions on the order of tens of micrometers. The peak intensities were used as a measure of concentration of the components. The amount of liquid crystal dissolved in the polymer matrix determines the extent to which the polymer is plasticized, which in turn affects the shape and size of the droplets. The growth of the domains at any temperature is also determined by whether the system is maintained above or below the glass transition temperature of the matrix. It is observed that the growth of the droplets follows temporal power laws. The spatially resolved spectroscopic images provide valuable insight into the phase separation process and the formation of microdroplets of E7 in PBMA.

Influence of the Polymer Matrix on the Bipolar and Radial Droplet Configurations within PDLC Films Examined by Infrared Spectroscopy

1993 ◽  
Vol 47 (5) ◽  
pp. 598-605 ◽  
Author(s):  
Coleen A. McFarland ◽  
Jack L. Koenig ◽  
John L. West
Keyword(s):  
Infrared Spectroscopy ◽  
Liquid Crystal ◽  
Polymer Matrix ◽  
Butyl Methacrylate ◽  
Droplet Growth ◽  
Thermally Induced ◽  
Polymer Dispersed Liquid Crystal ◽  
Polymer Dispersed ◽  
Ft Ir ◽  
Configuration Changes

The influence of the polymer matrix on the liquid crystal droplet configuration within a polymer-dispersed liquid crystal (PDLC) film is studied with the use of infrared spectroscopy. With a change of the polymer from poly( n-butyl methacrylate) to poly(isobutyl methacrylate) with the use of E7 liquid crystal, the droplet configuration changes from bipolar to radial. For both of these PDLC systems with 80:20, 70:30, and 60:40 E7/polymer compositions, the LC droplets grow in diameter with time. The spectroscopic data monitoring the droplet growth are described exponentially. A transition temperature is observed as both types of PDLCs cool, forming droplets by the thermally induced phase-separation technique. The TN-I, transition for the E7/PBMA PDLC appears at 46°C and for the E7/PIBMA PDLC appears at 51°C. Index Headings: FT-IR spectroscopy; Polymer-dispersed liquid crystals (PDLC).

Determination of Solubility Limits of Photocured PDLC Systems Using Infrared Microspectroscopy

1997 ◽  
Vol 51 (1) ◽  
pp. 10-16 ◽  
Author(s):  
Sudarsana R. Challa ◽  
Shi-Qing Wang ◽  
Jack L. Koenig
Keyword(s):  
Liquid Crystal ◽  
Low Molecular Weight ◽  
Contact Method ◽  
Concentration Gradients ◽  
Uv Curable ◽  
Infrared Microspectroscopy ◽  
Polymer Dispersed Liquid Crystal ◽  
The Matrix ◽  
Polymer Dispersed

Infrared microspectroscopy is used to determine the solubility limits of a UV-curable polymer-dispersed liquid crystal (PDLC) system comprised of a low-molecular-weight liquid crystal (E7) and a photocurable monomer (NOA65). The LC is allowed to diffuse into the monomer by the contact method, and then the sample is subjected to curing. The morphology of the system after polymerizaton exhibits several distinct spatial regions, and the associated concentration gradients are measured. At an irradiation temperature of 30 °C, the concentration of LC in the matrix is found to be 27 ± 3%, and at a temperature of 100 °C, it is 65 ± 3%.

Holographic Polymer Dispersed Liquid Crystals: Effect of Partial Matrix Fluorination on Electro-Optical and Morphological Properties

2001 ◽  
Vol 709 ◽  
Author(s):  
Michael D. Schulte ◽  
Stephen J. Clarson ◽  
Lalgudi V. Natarajan ◽  
C. Allan Guymon ◽  
Timothy J. Bunning
Keyword(s):  
Liquid Crystal ◽  
Low Voltage ◽  
Morphological Properties ◽  
Acrylate Monomer ◽  
Polymer Dispersed Liquid Crystal ◽  
Morphological Studies ◽  
Polymer Dispersed Liquid Crystals ◽  
The Matrix ◽  
Polymer Dispersed ◽  
Morphological Differences

ABSTRACTHolographic polymer dispersed liquid crystal (H-PDLC) films with partially fluorinated matrices were investigated. Electro-optical and morphological studies revealed that fluorinated composites were substantially different from non-fluorinated analogues. The addition of a fluorinated monofunctional acrylate monomer to a pentaacrylate-derived polymer matrix resulted in improved diffraction efficiency. These findings suggest that the partial fluorination of the host polymer decreases the compatibility between the matrix and liquid crystal phase. Morphological differences between fluorinated films and non-fluorinated control specimens were verified using low-voltage, high-resolution scanning electron microscopy (LVHRSEM).

In Situ Diffusion and Miscibility Studies of Thermoplastic PDLC Systems by FT-IR Microspectroscopy

1997 ◽  
Vol 51 (3) ◽  
pp. 297-303 ◽  
Author(s):  
Sudarsana R. Challa ◽  
Shi-Qing Wang ◽  
Jack L. Koenig
Keyword(s):  
Liquid Crystal ◽  
Phase Diagrams ◽  
Butyl Methacrylate ◽  
Contact Method ◽  
Polymer Dispersed Liquid Crystal ◽  
Polymer Dispersed ◽  
Ir Microspectroscopy ◽  
In Situ Diffusion ◽  
Miscibility Studies

Infrared microspectroscopy was used to study the interaction of liquid crystal (E7) with poly( n-butyl methacrylate) (PBMA). A novel experimental technique is introduced to conduct in situ diffusion and miscibility studies of polymer-dispersed liquid crystal (PDLC) systems. The amount of liquid crystal dissolved in the polymer matrix is determined by using the IR microspectroscope, which is a powerful tool for characterizing domains on the order of tens of micrometers. Quantitative phase diagrams are constructed for the PBMA and E7 mixture. It is observed that the diffusion of E7 into PBMA follows Fick's second law of diffusion with a diffusion coefficient of (1.3 ± 0.2) × 10−7 cm2/s at 61 °C. The intensities of the peaks in the IR spectrum were used as a measure of the concentration of the components. The combination of IR microspectroscopy with the contact method is proven to be a powerful technique for the quantitative elucidation of phase diagrams.

Analysis of Polymer-Dispersed Liquid Crystals by Infrared Spectroscopy

1993 ◽  
Vol 47 (3) ◽  
pp. 321-329 ◽  
Author(s):  
Coleen A. McFarland ◽  
Jack L. Koenig ◽  
John L. West
Keyword(s):  
Liquid Crystal ◽  
Polymer Matrix ◽  
Infrared Region ◽  
Field Analysis ◽  
Visual Images ◽  
Polymer Dispersed Liquid Crystal ◽  
Polymer Dispersed Liquid Crystals ◽  
Polymer Dispersed ◽  
Ft Ir ◽  
Electric Field Analysis

FT-IR microspectroscopy is used to compare the polymer and liquid crystal droplet regions within polymer-dispersed liquid crystal (PDLC) films. Thermoplastic polymer matrix PDLCs contain a higher amount of liquid crystal within the polymer regions than do thermoset polymer matrix films. IR functional group images of a droplet show characteristic textures corresponding to the visual images of the same droplet. The textures in the IR images change with IR polarization and with an applied electric field. Analysis by conventional IR spectroscopy shows that the C=N and the pentyl CH2 groups require an equivalent voltage to switch in the IR region. However, the phenyl C=C group does not exhibit changes under the same voltage conditions. Hysteresis also is seen in the infrared region as a function of voltage and temperature.

Molecular Orientation in Polymer-Dispersed Liquid Crystals Using Time-Resolved FT-IR

1993 ◽  
Vol 47 (9) ◽  
pp. 1367-1369 ◽  
Author(s):  
Sachiko Kohri ◽  
Junji Kobayashi ◽  
Shin Tahata ◽  
Shuichi Kita ◽  
Isamu Karino ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Central Region ◽  
Time Resolution ◽  
Molecular Orientation ◽  
Time Resolved ◽  
Polymer Dispersed Liquid Crystal ◽  
Polymer Dispersed Liquid Crystals ◽  
Polymer Dispersed ◽  
Ft Ir ◽  
Reorientation Dynamics

Molecular orientation of nematic microdroplets in polymer-dispersed liquid crystal (PDLC) films has been investigated by time-resolved FT-IR (TR/FT-IR) in the presence of an applied electric field. Two kinds (fast and slow) of reorientation processes are found, and these may be attributed to reorientation of liquid crystal molecules at the surface and the central region of droplets. In addition, an induction time has been observed before the onset of the actual reorientation. It is suggested that there are no essential differences between rigid and flexible molecular segments with respect to reorientation dynamics of at least 1 ms time resolution. TR and micro-FT-IR techniques have been combined in order to study the reorientation dynamics of the different regions of droplets.

scholarly journals Polymer Dispersed Cholesteric Liquid Crystals With a Toroidal Director Configuration under an Electric Field

Polymers ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 732
Author(s):  
Anna P. Gardymova ◽  
Mikhail N. Krakhalev ◽  
Victor Ya. Zyryanov ◽  
Alexandra A. Gruzdenko ◽  
Andrey A. Alekseev ◽  
...  
Keyword(s):  
Optical Properties ◽  
Liquid Crystal ◽  
Electric Field ◽  
Point Defects ◽  
Structural Response ◽  
Optical Filters ◽  
Response Curves ◽  
Polymer Dispersed Liquid Crystal ◽  
Dichroic Dye ◽  
Polymer Dispersed

The electro-optical properties of polymer dispersed liquid crystal (PDLC) films are highly dependent on the features of the contained liquid crystal (LC) droplets. Cholesteric LC droplets with homeotropic boundaries can form several topologically different orientational structures, including ones with single and more point defects, layer-like, and axisymmetric twisted toroidal structures. These structures are very sensitive to an applied electric field. In this work, we have demonstrated experimentally and by computer simulations that twisted toroidal droplets reveal strong structural response to the electric field. In turn, this leads to vivid changes in the optical texture in crossed polarizers. The response of droplets of different sizes were found to be equivalent in terms of dimensionless parameters. In addition, the explanation of this phenomenon showed a comparison of theoretical and experimental structural response curves aids to determine the shape of the droplet. Finally, we demonstrated that the addition of a dichroic dye allows such films to be used as optical filters with adjustable color even without polarizers.

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