Dr. Hemang Shah 💡

In this paper we describe methods to control liquid crystal (LC) alignment using plasma discharge on ferroelectric fluoropolymers. Two different plasma modification techniques were investigated: corona discharge and RF plasma in Ar gas. Corona discharge is a proven technique known to reorient the dipoles in poly (vinylidene fluoride) and its copolymers resulting in a strong remnant polarization. The polarization was patterned resulting in preferential LC alignment in selected regions. RF plasma… Show more

In this paper we describe methods to control liquid crystal (LC) alignment using plasma discharge on ferroelectric fluoropolymers. Two different plasma modification techniques were investigated: corona discharge and RF plasma in Ar gas. Corona discharge is a proven technique known to reorient the dipoles in poly (vinylidene fluoride) and its copolymers resulting in a strong remnant polarization. The polarization was patterned resulting in preferential LC alignment in selected regions. RF plasma in Ar gas defluorinates the polymer surface leading to planar alignment of positive dielectric anisotropy LCs. The defluorination of the alignment layer also causes low voltage switching of the LC. Show less

A nematic-to-isotropic transition has been observed in suspensions of carbon nanotubes(CNTs) and a cyanobiphenyl-based liquid crystal(LC) confined within an indium tin oxide glass sandwich cell. Upon the application of electric field,CNTs rotate out of plane short-circuiting the electrodes and producing a current flow through the CNTs. The resulting Joule heating leads to a local increase in temperature of the LC-CNT medium. Hence, starting from a metastable nematic phase, a complete transition… Show more

A nematic-to-isotropic transition has been observed in suspensions of carbon nanotubes(CNTs) and a cyanobiphenyl-based liquid crystal(LC) confined within an indium tin oxide glass sandwich cell. Upon the application of electric field,CNTs rotate out of plane short-circuiting the electrodes and producing a current flow through the CNTs. The resulting Joule heating leads to a local increase in temperature of the LC-CNT medium. Hence, starting from a metastable nematic phase, a complete transition to the isotropic phase is observed. On removal of the electric field, the transition is reversed with the LC-CNT medium returning to the nematic phase Show less

The development of voltage-controlled visible-wavelength progression in displays and optical data storage devices using ferroelectric polymers and liquid crystals is described. Ferroelectric polymers are materials that have a ready distribution of dipoles which can be oriented by manipulating material composition and external fields. Utilizing the charge polarization distribution, their performance as an alignment layer for inducing liquid-crystal alignment is presented. The switching response… Show more

The development of voltage-controlled visible-wavelength progression in displays and optical data storage devices using ferroelectric polymers and liquid crystals is described. Ferroelectric polymers are materials that have a ready distribution of dipoles which can be oriented by manipulating material composition and external fields. Utilizing the charge polarization distribution, their performance as an alignment layer for inducing liquid-crystal alignment is presented. The switching response of the devices was tailored by changing the material composition through copolymers and nanoclay doping. Show less

This letter investigates the unexplored phenomenon of the wetting of liquid crystals inside carbon nanopipes. Carbon nanopipes are similar to carbon nanotubes but are open ended with straight walls. Using environmental scanning electron microscopy, the authors have observed liquid crystal menisci inside the nanopipes. Raman spectroscopy was used to confirm the presence of liquid crystals confined in the nanopipes and verify the physical interaction between the two materials. In addition… Show more

This letter investigates the unexplored phenomenon of the wetting of liquid crystals inside carbon nanopipes. Carbon nanopipes are similar to carbon nanotubes but are open ended with straight walls. Using environmental scanning electron microscopy, the authors have observed liquid crystal menisci inside the nanopipes. Raman spectroscopy was used to confirm the presence of liquid crystals confined in the nanopipes and verify the physical interaction between the two materials. In addition, observations from reflection polarized optical microscopy experiments suggest the use of liquid crystals inside carbon nanotubes to develop electro-optic switches. Show less

We have studied patterned substrates to identify liquid crystal alignment. The Polarized Optical Microscope (POM) was used to observe the alignment variations. Image analysis algorithms were developed to enhance the alignment information for POM images. The algorithms were developed to correlate the grayscale intensities in the image to the alignment variations. The resulting resolution of alignment variations is higher than the physical dimensions of the patterns. Using the technique, for 500… Show more

We have studied patterned substrates to identify liquid crystal alignment. The Polarized Optical Microscope (POM) was used to observe the alignment variations. Image analysis algorithms were developed to enhance the alignment information for POM images. The algorithms were developed to correlate the grayscale intensities in the image to the alignment variations. The resulting resolution of alignment variations is higher than the physical dimensions of the patterns. Using the technique, for 500 nm wide grooves, the alignment variations were observed every 166 nm. Thus, a resolution improvement factor of three is obtained. Show less

This work studies the influence of ferroelectric polyvinylidene fluoride (PVDF) on the alignment of liquid crystal (LC) 5CB. The chemical structure of PVDF (CH2 – CF2) leads to a dipole moment between the CH and the CF bonds. The dipoles typically order randomly such that there is no bulk polarization from the substrate. The ferroelectric phase will be obtained by poling the films to result in a uniform orientation of dipoles. LC alignment on a ferroelectric film will follow the polarization… Show more

This work studies the influence of ferroelectric polyvinylidene fluoride (PVDF) on the alignment of liquid crystal (LC) 5CB. The chemical structure of PVDF (CH2 – CF2) leads to a dipole moment between the CH and the CF bonds. The dipoles typically order randomly such that there is no bulk polarization from the substrate. The ferroelectric phase will be obtained by poling the films to result in a uniform orientation of dipoles. LC alignment on a ferroelectric film will follow the polarization vector of the charge distribution. Thus, alignment on different polarization domains will be discussed. The effect of electric fields on the LCs aligned on PVDF films will be presented. Homopolymers of PVDF and its copolymers with Trifluoro Ethylene P(VDF-TrFE) and Hexa Fluoro Propylene P(VDF-HFP) are the substrate materials. The LC alignment on films varying in molecular weight, copolymer ratio, thickness, and exposure to LASER irradiation will be characterized. Show less

The nature of the liquid crystal (LC) alignment in devices is a crucial parameter in the operating efficiency of these devices and there are numerous methods to induce LC alignment. Nanopatterned substrates of polymers including PMMA and PTFE are known to influence the LC alignment due to the confinement. Nanopatterned polymer substrates created using the NanoIndenter have dimensions 500nm x 500nm x 100nm. Following this procedure, the LC alignment is studied after its deposition these… Show more

The nature of the liquid crystal (LC) alignment in devices is a crucial parameter in the operating efficiency of these devices and there are numerous methods to induce LC alignment. Nanopatterned substrates of polymers including PMMA and PTFE are known to influence the LC alignment due to the confinement. Nanopatterned polymer substrates created using the NanoIndenter have dimensions 500nm x 500nm x 100nm. Following this procedure, the LC alignment is studied after its deposition these nanopatterned surfaces. The LC alignment variation is observed using a Polarizing Optical Microscope (POM). The POM images will be analyzed to map the pixel values to LC alignment in different patterns like grid structures and grooves. Also, finite difference modeling is used to study the theoretical nature of the LC alignment. The Simulated Annealing algorithm is used to minimize the energy of the LC on the patterned surface. Various boundary conditions like anchoring on the side and top walls and surface anchoring strengths will be applied to observe the nature of the resulting alignment. Modeling results of the LC alignment, when performed on different patterns like square grids, triangular and sawtooth shaped substrates shall be compared with the experimental results. Show less

A crucial factor governing the electrical as well as optical efficiency of liquid crystal (LC) based devices is the alignment of the LC on the substrate. This surface alignment propagates to the bulk LC, and is responsible for many of the optical properties responsible for device performance. Conventionally, alignment has been influenced by rubbing the substrate or by chemical treatment. However, the exact nature of the alignment remains an unanswered question. In this paper, nano-patterned… Show more

A crucial factor governing the electrical as well as optical efficiency of liquid crystal (LC) based devices is the alignment of the LC on the substrate. This surface alignment propagates to the bulk LC, and is responsible for many of the optical properties responsible for device performance. Conventionally, alignment has been influenced by rubbing the substrate or by chemical treatment. However, the exact nature of the alignment remains an unanswered question. In this paper, nano-patterned polymer structures coupled with image analysis techniques are used to probe the alignment of LCs on assorted non-smooth surfaces. The nano-patterned structures provide varying confinement configurations which affect the LC alignment. The morphologies reported in this paper are rectangular grids and parallel grooves (rectangular and triangular) with multiple side-wall orientations, produced on PMMA and urethane resins. All results are compared to conventional rubbed morphologies on polyimide. Pattern generation was achieved using an MTS Nano-Indenter and characterizing was by Atomic Force Microscope. Polarizing Optical Microscopy was used to track the alignment changes of LC in the patterns after deposition. Image analysis will be used to classify the alignment orientation to within one degree. Show less

Holographically-formed Polymer Dispersed Liquid Crystals (H-PDLCs) are electro-optic devices containing alternating planar layers of polymer and liquid crystal droplets. Here, we investigate the effects of patterned polymer layers on the liquid crystal alignment. Three types of polymers were investigated: urethane resin, Poly Tetra Fluoro Ethylene (PTFE) and Poly Methyl Methacrylate (PMMA). Nanopatterns of the form of square grids were formed on the polymer using the MTS Nano-Indenter in the… Show more

Holographically-formed Polymer Dispersed Liquid Crystals (H-PDLCs) are electro-optic devices containing alternating planar layers of polymer and liquid crystal droplets. Here, we investigate the effects of patterned polymer layers on the liquid crystal alignment. Three types of polymers were investigated: urethane resin, Poly Tetra Fluoro Ethylene (PTFE) and Poly Methyl Methacrylate (PMMA). Nanopatterns of the form of square grids were formed on the polymer using the MTS Nano-Indenter in the scratch mode. Liquid crystal deposition on these structures showed unique alignment effects at the polymer interface. The polymers were examined under the Atomic Force Microscope and alignment of the liquid crystals was observed by Polarizing Optical Microscopy. Show less