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

Abstract

Holographic 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).

Monomer Functionality Effects in the Formation of Thiol−Ene Holographic Polymer Dispersed Liquid Crystals

“…Since the original report of their development in 1993, research of holographic polymer dispersed liquid crystal (HPDLC) has taken numerous approaches to enhancing electrooptic performance. Predominately, researchers have focused on adjusting the prepolymer formulation by varying monomer functionality 14,15 or adding components such as monofunctional reactive diluent, ,,, surfactant, , and fluorinated monomer − and characterized the corresponding impact of these changes on electrooptic performance and polymer/LC morphology. In acrylate-based HPDLCs, fast polymerization kinetics and high monomer functionality are known to be critical for the development of HPDLCs with polymer/LC morphology that yields high diffraction efficiency (DE) and sufficient baseline transmission. − This work examines the influence of these two critical factors, polymerization kinetics and monomer functionality, on the formation and performance of thiol−ene-based HPDLCs.…”

Holographic Polymer‐Dispersed Liquid Crystals: Materials, Formation, and Applications

“…Another way to reduce the driving voltage is to modify the monomers. The experimental results have shown the partial fluorination of the polymer matrix has significant effects on the morphology and electro-optical performance of H-PDLC [92,93]. The morphology of the fluorinated transmission gratings displayed an enhanced phase separation as manifested in a significant increase in nematic domain size and the LC volume fraction, as shown in Figures 41 and 42.…”

“…In addition, adding a small portion of surfactant to the prepolymer/LC syrup also helps to reduce the threshold voltage [88][89][90][91]. Fluorination of the polymer matrix also has significant effects on decreasing the driving voltage of H-PDLC [92,93]. In the following, the effects of surfactants and polymer fluorination will be discussed.…”

“…How to reduce the driving voltage is the key for H-PDLC applications. As a matter of fact, many factors affect the driving voltage of H-PDLCs, such as the ratios of components in the material formulation, morphologies of gratings, adding a small amount of surfactant [88,90,91] or high dielectric anisotropy material [87], and fluorination of polymer matrix [92,93]. Many researchers studied the morphology effect on the driving voltages [71,81,146].…”

Tunable polymer/liquid crystal composite devices

“…that the surface area of interaction between the polymer matrix and LC droplets is strongly enlarged, and hence the anchoring energy of the LC droplets is greatly 93 Partial fluorination of the host polymer matrix is also beneficial to decrease the driving voltage. 39,94 However, the response time also increases due to the fluorination. In addition, adding a small portion of surfactant to the prepolymer/LC mixture also helps to reduce the threshold voltage.…”