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The interplay between spatial and heliconical orientational order in twist-bend nematic materials (2021)
Journal Article
Saha, R., Feng, C., Welch, C., Mehl, G. H., Feng, J., Zhu, C., …Jakli, A. (2021). The interplay between spatial and heliconical orientational order in twist-bend nematic materials. Physical chemistry chemical physics : PCCP, https://doi.org/10.1039/d0cp06633h

The helical pitch formed by organic molecules, such as the a-helix of proteins, usually requires hydrogen bonding between chiral units and long-range positional order. It was recently found that certain liquid crystal oligomers can have a twist-bend... Read More about The interplay between spatial and heliconical orientational order in twist-bend nematic materials.

Molecular biaxiality determines the helical structure - Infrared measurements of the molecular order in the nematic twist-bend phase of difluoro terphenyl dimers (2021)
Journal Article
Merkel, K., Loska, B., Welch, C., Mehl, G. H., & Kocot, A. (in press). Molecular biaxiality determines the helical structure - Infrared measurements of the molecular order in the nematic twist-bend phase of difluoro terphenyl dimers. Physical chemistry chemical physics : PCCP, https://doi.org/10.1039/d1cp00187f

Fourier-transform infrared polarized spectroscopy was employed, to obtain the three components of the infrared absorbance for a series of bent-shaped dimers containing double fluorinated terphenyl core (DTC5Cn, n = 5, 7, 9, 11). The data were used to... Read More about Molecular biaxiality determines the helical structure - Infrared measurements of the molecular order in the nematic twist-bend phase of difluoro terphenyl dimers.

The role of intermolecular interactions in stabilizing the structure of the nematic twist-bend phase (2021)
Journal Article
Merkel, K., Loska, B., Welch, C., Mehl, G. H., & Kocot, A. (2021). The role of intermolecular interactions in stabilizing the structure of the nematic twist-bend phase. RSC advances, 11(5), 2917-2925. https://doi.org/10.1039/d0ra10481g

The understanding of the relationship between molecular structure and the formation of the nematic twist-bend phase is still at an early stage of development. This is mainly related to molecular geometry, while the correlation between the nematic twi... Read More about The role of intermolecular interactions in stabilizing the structure of the nematic twist-bend phase.

Two helices from one chiral centre – self organization of disc shaped chiral nanoparticles (2020)
Journal Article
Mehl, G. H., Yu, H., Qu, W., & Liu, F. (2020). Two helices from one chiral centre – self organization of disc shaped chiral nanoparticles. Chemical science, https://doi.org/10.1039/d0sc05100d

Gold nanoparticles (AuNPs) have been prepared and surfacefunctionalized with a mixture of 1-hexanethiol co-ligands and chiral discogen ligands separated from a disulfide function via a flexible spacer. Polarized optical microscopy together with di... Read More about Two helices from one chiral centre – self organization of disc shaped chiral nanoparticles.

A Compact Full 2π Flexoelectro‐Optic Liquid Crystal Phase Modulator (2020)
Journal Article
Fells, J. A., Wang, X., Fells, J. A. J., Shi, Y., Ali, T., Welch, C., …Elston, S. J. (2020). A Compact Full 2π Flexoelectro‐Optic Liquid Crystal Phase Modulator. Advanced Materials Technologies, 5(12), https://doi.org/10.1002/admt.202000589

Wavefront shaping, which is often achieved using liquid crystal (LC) spatial light modulators, is particularly important for a wide range of applications including laser microfabrication and micromanipulation, microscopy, and quantum optics. In this... Read More about A Compact Full 2π Flexoelectro‐Optic Liquid Crystal Phase Modulator.

Chirality enhancement in macro-chiral liquid crystal nanoparticles (2020)
Journal Article
Yu, H., Welch, C., Qu, W., Schubert, C. J., Liu, F., Siligardi, G., & Mehl, G. H. (2020). Chirality enhancement in macro-chiral liquid crystal nanoparticles. Materials Horizons, 7(11), 3021-3027. https://doi.org/10.1039/d0mh01274b

The amplification of molecular chirality by metal nanoparticles (NPs) is an important and rapidly evolving field in nanomaterial research with wide applications in smart materials, catalysis, and solvent-solute interactions. Here we present the resul... Read More about Chirality enhancement in macro-chiral liquid crystal nanoparticles.

Millisecond optical phase modulation using multipass configurations with liquid-crystal devices (2020)
Journal Article
Jin, Y., Elston, S. J., Fells, J. A., Booth, M. J., Welch, C., Mehl, G. H., & Morris, S. M. (2020). Millisecond optical phase modulation using multipass configurations with liquid-crystal devices. Physical Review Applied, 14(2), https://doi.org/10.1103/PhysRevApplied.14.024007

We present two configurations for analog 0 to 2π optical phase modulation using liquid crystals (LCs), each of which achieve switching times that are 1 ms or less. One configuration is based on the switching behavior of a so-called nematic pi cell, a... Read More about Millisecond optical phase modulation using multipass configurations with liquid-crystal devices.

Self-Assembly and Temperature-Driven Chirality Inversion of Cholesteryl-Based Block Copolymers (2020)
Journal Article
Krishnasamy, V., Qu, W., Chen, C., Huo, H., Ramanagul, K., Gothandapani, V., …Liu, F. (2020). Self-Assembly and Temperature-Driven Chirality Inversion of Cholesteryl-Based Block Copolymers. Macromolecules, 53(11), 4193-4203. https://doi.org/10.1021/acs.macromol.9b02264

Block copolymers (BCPs), comprising a poly(methyl methacrylate) (PMMA) block and a poly(cholesteryloxyhexyl methacrylate) (PChMA) block, were synthesized via reversible addition–fragmentation chain transfer polymerization. The self-assembly of the li... Read More about Self-Assembly and Temperature-Driven Chirality Inversion of Cholesteryl-Based Block Copolymers.

Transmissive flexoelectro-optic liquid crystal optical phase modulator with 2 π modulation (2020)
Journal Article
Wang, X., Fells, J. A. J., Ali, T., Lin, J. D., Welch, C., Mehl, G. H., …Elston, S. J. (2020). Transmissive flexoelectro-optic liquid crystal optical phase modulator with 2 π modulation. AIP Advances, 10(5), https://doi.org/10.1063/5.0009630

© 2020 Author(s). In this paper, we demonstrate analog phase modulation in a transmissive configuration using the flexoelectro-optic effect in short-pitch chiral nematic liquid crystal (LC) devices. Two different modes are considered, both of which a... Read More about Transmissive flexoelectro-optic liquid crystal optical phase modulator with 2 π modulation.

Temperature dependence of bend elastic constant in oblique helicoidal cholesterics (2020)
Journal Article
Iadlovska, O. S., Babakhanova, G., Mehl, G. H., Welch, C., Cruickshank, E., Strachan, G. J., …Shiyanovskii, S. V. (2020). Temperature dependence of bend elastic constant in oblique helicoidal cholesterics. Physical Review Research, 2(1), https://doi.org/10.1103/physrevresearch.2.013248

Elastic moduli of liquid crystals, known as Frank constants, are of quintessential importance for understanding fundamental properties of these materials and for the design of their applications. Although there are many methods to measure the Frank... Read More about Temperature dependence of bend elastic constant in oblique helicoidal cholesterics.

Analog modulation by the flexoelectric effect in liquid crystals (2020)
Journal Article
Yip, W. C., Welch, C., Mehl, G. H., & Wilkinson, T. D. (2020). Analog modulation by the flexoelectric effect in liquid crystals. Applied optics, 59(9), 2668-2673. https://doi.org/10.1364/AO.386096

We have solved the long-standing problems of stability and hysteresis, and we are able to obtain the homogeneous uniform lying helix structure in polymer-free cholesteric liquid crystals. This is instrumental for the present work to demonstrate the a... Read More about Analog modulation by the flexoelectric effect in liquid crystals.

Probing molecular ordering in the nematic phases of para-linked bimesogen dimers through NMR studies of flexible prochiral solutes (2020)
Journal Article
Heist, L. M., Samulski, E. T., Welch, C., Ahmed, Z., Mehl, G. H., Vanakaras, A. G., & Photinos, D. J. (2020). Probing molecular ordering in the nematic phases of para-linked bimesogen dimers through NMR studies of flexible prochiral solutes. Liquid crystals, 1-16. https://doi.org/10.1080/02678292.2019.1711214

The quadrupolar splittings of perdeuteriated n-decane dissolved in nematic phases formed by mesogenic dimers of the CBnCB series, for n = 7,9,10,11, are measured throughout the entire temperature range of these phases. These results are reported toge... Read More about Probing molecular ordering in the nematic phases of para-linked bimesogen dimers through NMR studies of flexible prochiral solutes.

Macroscopic chirality of twist-bend nematic phase in bent dimers confirmed by circular dichroism (2019)
Journal Article
Stevenson, W. D., Zeng, X., Welch, C., Thakur, A. K., Ungar, G., & Mehl, G. H. (2020). Macroscopic chirality of twist-bend nematic phase in bent dimers confirmed by circular dichroism. Journal of Materials Chemistry C, 8(3), 1041-1047. https://doi.org/10.1039/c9tc05061b

Many achiral bent molecules and some polymers with such repeat units exhibit a liquid crystal phase transition between a conventional nematic (N), and a second nematic (Nx) with periodically modulated orientation. Theory predicts several possible str... Read More about Macroscopic chirality of twist-bend nematic phase in bent dimers confirmed by circular dichroism.

A cholesteric liquid crystal device having stable uniform lying helix structure (2019)
Journal Article
Yip, W. C., Welch, C., Mehl, G. H., & Wilkinson, T. D. (2020). A cholesteric liquid crystal device having stable uniform lying helix structure. Journal of Molecular Liquids, 299, https://doi.org/10.1016/j.molliq.2019.112141

A cholesteric liquid crystal device having the uniform lying helix (ULH) structure shows stable and reversible characteristics and it has been demonstrated for the analogue modulation in 10 micro-second response time at room temperature. The device c... Read More about A cholesteric liquid crystal device having stable uniform lying helix structure.

Soft modes of the dielectric response in the twist-bend nematic phase and identification of the transition to nematic splay bend phase in the CBC7CB dimer (2019)
Journal Article
Merkel, K., Kocot, A., Mehl, G. H., & Welch, C. (2019). Soft modes of the dielectric response in the twist-bend nematic phase and identification of the transition to nematic splay bend phase in the CBC7CB dimer. Physical chemistry chemical physics : PCCP, https://doi.org/10.1039/c9cp04952e

The dielectric spectra of the twist–bend nematic phase (NTB) of (the bent-shaped) achiral liquid-crystal dimer 1”-,7”-bis(4-cyanobiphenyl-4’-yl) heptane (CB7CB) are studied for the determination of the different relaxation modes. Two molecular proces... Read More about Soft modes of the dielectric response in the twist-bend nematic phase and identification of the transition to nematic splay bend phase in the CBC7CB dimer.

Dielectric response of electric-field distortions of the twist-bend nematic phase for LC dimers (2019)
Journal Article
Merkel, K., Welch, C., Ahmed, Z., Piecek, W., & Mehl, G. H. (2019). Dielectric response of electric-field distortions of the twist-bend nematic phase for LC dimers. The Journal of chemical physics, 151(11), 114908. https://doi.org/10.1063/1.5114824

Wide band dielectric spectroscopy of bent-shaped achiral liquid-crystal dimers 1′′-n′′-bis(4-cyanobiphenyl-4′-yl) n-alkanes (CBnCB n = 7, 9, 11) has been investigated in a frequency range 0.1 Hz–100 MHz using planar-aligned cells of sample thicknesse... Read More about Dielectric response of electric-field distortions of the twist-bend nematic phase for LC dimers.

Oligomeric odd-even effect in liquid crystals (2019)
Journal Article
Gleeson, J., Jákli, A., Saha, R., Babakhanova, G., Parsouzi, Z., Rajabi, M., …Jakli, A. (2019). Oligomeric odd-even effect in liquid crystals. Materials Horizons, 6(9), 1905-1912. https://doi.org/10.1039/c9mh00428a

Odd-even effects, oscillations in properties of materials comprised of an odd or even number of connected repeating units, are well-known phenomena in materials science. In organic materials, they are usually associated with the number of methylene... Read More about Oligomeric odd-even effect in liquid crystals.

Pretransitional behavior of viscoelastic parameters at the nematic to twist-bend nematic phase transition in flexible: N -mers (2019)
Journal Article
Parsouzi, Z., Babakhanova, G., Rajabi, M., Saha, R., Gyawali, P., Turiv, T., …Sprunt, S. (2019). Pretransitional behavior of viscoelastic parameters at the nematic to twist-bend nematic phase transition in flexible: N -mers. Physical chemistry chemical physics : PCCP, 21(24), 13078-13089. https://doi.org/10.1039/c9cp00984a

© 2019 the Owner Societies. We report dynamic light scattering measurements of the orientational (Frank) elastic constants and associated viscosities among a homologous series of a liquid crystalline dimer, trimer, and tetramer exhibiting a uniaxial... Read More about Pretransitional behavior of viscoelastic parameters at the nematic to twist-bend nematic phase transition in flexible: N -mers.

Dynamic response of large tilt-angle flexoelectro-optic liquid crystal modulators (2019)
Journal Article
Fells, J. A. J., Welch, C., Yip, W. C., Elston, S. J., Booth, M. J., Mehl, G. H., …Morris, S. M. (2019). Dynamic response of large tilt-angle flexoelectro-optic liquid crystal modulators. Optics express, 27(11), 15184-15193. https://doi.org/10.1364/oe.27.015184

We present here the first time-resolved tilt-angle and retardance measurements for large-tilt (>45°) flexoelectro-optic liquid crystal modulators. These devices have potential for next generation fast switching (>1 kHz), 0-2π analog phase spatial lig... Read More about Dynamic response of large tilt-angle flexoelectro-optic liquid crystal modulators.

Fast and low loss flexoelectro-optic liquid crystal phase modulear with a chiral nematic reflector (2019)
Journal Article
Wang, X., Fells, J. A., Yip, W. C., Ali, T., Lin, J., Welch, C., …Elston, S. J. (2019). Fast and low loss flexoelectro-optic liquid crystal phase modulear with a chiral nematic reflector. Scientific reports, 9, https://doi.org/10.1038/s41598-019-42831-5

In this paper, we demonstrate a flexoelectro-optic liquid crystal phase-only device that uses a chiral nematic reflector to achieve full 2 pi  phase modulation. This configuration is found to be very tolerant to imperfections in the chiral nematic r... Read More about Fast and low loss flexoelectro-optic liquid crystal phase modulear with a chiral nematic reflector.