Structural transitions in holographic polymer-dispersed liquid crystals

Area of Science:

• Materials Science
• Condensed Matter Physics
• Optics

Background:

• Holographic polymer-dispersed liquid crystals (HPDLCs) are crucial for optical applications.
• Understanding the nematic director field dynamics is key to controlling HPDLC properties.
• Prepolymer formulation affects the phase separation and resulting liquid crystal (LC) domain structure.

Purpose of the Study:

• To investigate the structural and dynamic properties of the nematic director field in HPDLC transmission gratings.
• To analyze samples prepared with visible (VIS) light and UV light curable prepolymer mixtures.
• To identify critical phenomena associated with external electric fields and temperature variations.

Main Methods:

• Dynamic light scattering (DLS) was employed to probe director fluctuations.
• HPDLC transmission gratings were fabricated using two distinct prepolymer formulations.
• Analysis included characterization of phase-separated droplet morphology and viscoelastic properties for VIS samples.

Main Results:

• A critical slowing down of thermal director fluctuations was observed in both VIS and UV samples near critical electric fields and temperatures.
• This slowing down signifies a second-order structural transition of the nematic director field.
• For VIS samples, droplet size, shape, viscoelastic parameters, and surface anchoring parameters were determined, showing deviations from pure LC values.

Conclusions:

• The nematic director field in HPDLC gratings exhibits critical behavior indicative of a second-order phase transition.
• The curing method (VIS vs. UV) influences the resulting LC domain structure and properties.
• The viscoelastic properties of the LC material within the droplets differ significantly from the bulk LC, highlighting the impact of confinement and phase separation.