Holographically Formed Polymer Dispersed Liquid Crystal Research Articles

Integrating the NAE Grand Challenges and Holographically-formed Polymer Dispersed Liquid Crystal Thin Films (H-PDLC) into the Kenyan High School Curriculum.

ABSTRACTAccess to cutting-edge technologies in materials science and engineering within K-12 education is a great struggle in developing countries. In this work, a problem-based, hands on set of seven modules for integrating Holographically-formed Polymer Dispersed Liquid Crystal (H-PDLC) Bragg Grating thin films into the Kenyan secondary physics, chemistry and mathematics curriculum is proposed. Through funding provided by the National Science Foundation, a pilot study of the integration of these modules, using the National Academy of Engineering’s (NAE) Grand Challenges for Engineering as a contextual vessel, is carried out. The efficacy of these curriculum-integrated modules in communicating real world materials science and engineering challenges is examined using qualitative and quantitative means. A method for expanding the use of this experience with other graduate students is proposed.

Lineshape and morphology study of structures formed using a reconfigurable photomasking element

The proposed application of holographically formed polymer dispersed liquid-crystal (H-PDLC) thin films is a real-time dynamically reconfigurable mask for the resist exposure step in the photolithographic process. An adaptable photomask has advantages over traditional binary masks that include multiple fabrication patterns using a single mask, reduction in realignment error between different masks, real-time correction and adjustment of fabricated structures, and the ability to alter the mask pattern during exposure. H-PDLC films, or thin periodic nanostructures of alternating layers of polymer and liquid crystal, have unique electro-optic properties, including the ability to modulate a particular wavelength as a function of bias applied to the film. Structures formed using the H-PDLC photomask device have been compared to similar structures formed with a static photomask using an optical profilometer. Features studied were decreasing lines with a maximum width of 121 µm to a minimum width of 84 µm. Edge width between structures formed using the H-PDLC mask and static photomask differ by <5%. Additionally, morphology studies have been performed on developed regions of glass and resist formed using a static and an H-PDLC mask to demonstrate that no structural defects exist due to formation under an H-PDLC grating.

Gap Material Study for Holographically Formed Polymer Dispersed Liquid Crystal Composite Film Stacks

We present a comparison of materials for adhering layers of holographically formed polymer dispersed liquid crystal (H-PDLC) films layered in stacks fabricated on common substrates. The results of this study are used in applications that rely on maximization of transmitted light through the layers of H-PDLC. Data is presented by comparing a simulated transmission envelope modeled on the individual H-PDLC cells with the actual stacked transmission spectrum. Additionally, data is presented on the quality of the wavefront of H-PDLC transmission spectrum individually and layered using air and index matching layers.

Liquid crystal polymer composite films for reconfigurable photomasking applications

We show proof of concept of a real-time reconfigurable photomask fabricated from holographically formed polymer-dispersed liquid crystal (H-PDLC) reflection gratings on etched indium tin oxide patterned electrodes. H-PDLC films were formed using a thiolene based polymer to have a reflection wavelength that modulates 440nm, the peak sensitivity wavelength of Shipley 1800 series positive photoresist. A working prototype of this adaptable photomask device is shown by comparing patterns formed using the H-PDLC mask and similar patterns formed using a static contact photomask showing that H-PDLC films have the ability to modulate 440nm light and control the exposure dose of photoresist.

Holographically formed polymer dispersed liquid crystal films for transmission mode spectrometer applications

We show proof of concept of a transmission-mode wavelength filtering device consisting of layered holographically formed polymer dispersed liquid crystal (H-PDLC) cells. H-PDLC cells were fabricated from a thiolene based polymer composite to have transmission notches in the near-IR wavelength range. Wavelength filtering was achieved by stacking four H-PDLC cells with transmission notches spaced at 10 nm intervals. Results show a broad transmission notch spanning the spectral width of the constituent cells. With bias applied to an individual cell within the stack, the transmission notch of the cell inverts and the overall transmission envelope changes shape. Using a transmitted energy sensing device and a lineshape mapping algorithm, spectral content can be determined to a resolution of 0.1 nm for narrow banded signals. Applications for this switchable wavelength filtering device include serial detection of spectral content for telecom data signals or chemical and biological sample identification through absorption or emission spectroscopy.

P-28: A Novel Medical Diagnostic Tool for Non-Invasively Measuring Hemoglobin Utilizing Switchable H-PDLC Display Technology

We present results on a novel medical diagnostic tool using holographically formed polymer dispersed liquid crystal (H-PDLC) display cells. Anemia can be diagnosed through inspection of the palpebral conjunctiva. While qualitative inspection is insensitive, spectroscopically characterizing the conjunctiva significantly improves diagnoses. Spectral differences of the conjunctiva with changing hemoglobin concentration are given; along with changing CIE chromaticity coordinates. The ability of an H-PDLC stack to model these changes is explored, followed by experimental data showing representative responses of ten-micron H-PDLC stacks.

Polarization-selective switching in holographically formed polymer dispersed liquid crystals

We have developed an optical stack of holographically formed polymer dispersed liquid-crystal (H-PDLC) devices that is fully operational with nonpolarized light sources. The device consists of two H-PDLC transmission gratings separated by a passive polarization rotator that can output a diffracted s-polarized, p-polarized, or s- and p-polarized beam simultaneously.

P‐81: In‐Situ Spectroscopy of Holographically formed Polymer Dispersed Liquid Crystal Materials for High Performance Reflective Display Applications

AbstractWe investigate the in‐situ formation dynamics of holographically formed polymer dispersed liquid crystal (H‐PDLC) reflective display pre‐polymer mixtures in an effort to quantify polymer shrinkage during fabrication. Understanding how to control shrinkage will allow for better optimization of the performance of reflective displays.

Advances in Holographic Polymer Dispersed Liquid Crystal Technology

ABSTRACTWe discuss recent advances in reflective holographically-formed polymer dispersed liquid crystal materials in the context of their suitability for reflective display applications. A dual-domain phenomenon resulting in a broadened reflection peak is presented. A simple phenomenological model is developed to explain this unusual effect The effect of monomer functionality on the reflectance characteristics of these materials is also discussed. Monomers of effective functionality ∼4.5 yield the brightest holograms, however, the data suggests that these systems are currently far from optimal.