Graphene-Augmented Polymer Stabilization: Drastically Reduced and Temperature-Independent Threshold and Improved Contrast Liquid Crystal Device.

Polymers reinforced with nanofillers, especially graphene in recent times, have continued to attract attention to realize novel materials that are cheap and also have better properties. At a different level, encapsulating liquid crystals (LCs) in polymer networks not only adds mechanical strength, but could also result in device-based refractive index mismatch. Here, we describe a novel strategy combining the best of both these concepts to create graphene-incorporated polymer-stabilized LC (PSLC) devices. The presence of graphene associated with the virtual surface of the polymer network besides introducing distinct morphological changes to the polymer architecture as seen by electron microscopy brings out several advantages for the PSLC characteristics, which include 7-fold lowered critical voltage, its temperature invariance, and enhanced contrast ratio between field-off scattering/field-on transparent states. The results bring to fore the importance of working at very-dilute-concentration limits of the filler nanoparticles in augmenting the desired properties. These observations open up a new vista for polymer-graphene composites in the area of device engineering, including substrate-free smart windows.

Carbon Nanotube Reinforced Polymer-Stabilized Liquid Crystal Device: Lowered and Thermally Invariant Threshold with Accelerated Dynamics.

Polymer-stabilized liquid crystal (PSLC) devices comprise a polymer matrix in an otherwise continuous phase of liquid crystal. The fibrils of the polymer provide, even in the bulk, virtual surfaces with finite anchoring energy resulting in attractive electro-optic properties. Here, we describe a novel variation of the PSLC device fabricated by reinforcing the polymer matrix with polymer-capped single-walled carbon nanotubes (CNTs). The most important outcome of this strengthening of the polymer strands is that the threshold voltage associated with the electro-optic switching becomes essentially temperature independent in marked contrast to the significant thermal variation seen in the absence of the nanotubes. The reinforcement reduces the magnitude of the threshold voltage, and notably accelerates the switching dynamics and the effective splay elasticity. Each of these attributes is quite attractive from the device operation point of view, especially the circuit design of the required drivers. The amelioration is caused by the polymer decorating CNTs being structurally identical to that of the matrix. The resulting good compatibility between CNTs and the matrix prevents the CNTs from drifting away from the matrix polymer, a lacuna in previous attempts to have CNTs in PSLC systems. The difference in the morphology, perhaps the primary cause for the effects seen, is noted in the electron microscopy images of the films.