Geoffrey R. Luckhurst

Bio: Geoffrey R. Luckhurst is an academic researcher from University of Southampton. The author has contributed to research in topics: Liquid crystal & Biaxial nematic. The author has an hindex of 60, co-authored 253 publications receiving 11989 citations. Previous affiliations of Geoffrey R. Luckhurst include Osaka Sangyo University.

Phase behavior and properties of the liquid-crystal dimer 1′′,7′′-bis(4-cyanobiphenyl-4′-yl) heptane: A twist-bend nematic liquid crystal

Abstract: The liquid-crystal dimer 1'',7''-bis(4-cyanobiphenyl-4'-yl)heptane (CB7CB) exhibits two liquid-crystalline mesophases on cooling from the isotropic phase. The high-temperature phase is nematic; the identification and characterization of the other liquid-crystal phase is reported in this paper. It is concluded that the low-temperature mesophase of CB7CB is a new type of uniaxial nematic phase having a nonuniform director distribution composed of twist-bend deformations. The techniques of small-angle x-ray scattering, modulated differential scanning calorimetry, and dielectric spectroscopy have been applied to establish the nature of the nematic-nematic phase transition and the structural features of the twist-bend nematic phase. In addition, magnetic resonance studies (electron-spin resonance and (2)H nuclear magnetic resonance) have been used to investigate the orientational order and director distribution in the liquid-crystalline phases of CB7CB. The synthesis of a specifically deuterated sample of CB7CB is reported, and measurements showed a bifurcation of the quadrupolar splitting on entering the low-temperature mesophase from the high-temperature nematic phase. This splitting could be interpreted in terms of the chirality of the twist-bend structure of the director. Calculations using an atomistic model and the surface interaction potential with Monte Carlo sampling have been carried out to determine the conformational distribution and predict dielectric and elastic properties in the nematic phase. The former are in agreement with experimental measurements, while the latter are consistent with the formation of a twist-bend nematic phase.

Non-symmetric dimeric liquid crystals The preparation and properties of the α-(4-cyanobiphenyl-4′-yloxy)-ω-(4-n-alkylanilinebenzylidene-4′-oxy)alkanes

Abstract: Six series of a family of non-symmetric dimers, the α-(4-cyanobiphenyl-4′-yloxy)-ω-(4-n-alkylanilinebenzylidene-4′-oxy)alkanes, have been prepared. In three of the series, the number of methylene groups in the flexible alkyl spacer has been varied from 3 to 12 while the terminal alkyl chain is held constant at either 2, 6 or 10. In the remaining series, the effect of increasing the terminal chain length has been studied by holding the spacer length constant at 3, 4 or 5 methylene units while varying the length of the terminal chain from 0 to 10 carbon atoms. The phase behaviour and transitional properties of these series have been investigated using optical microscopy and differential scanning calorimetry, while the structures of the mesophases have been studied using X-ray diffraction on both powder and aligned samples. This study has revealed novel phase behaviour involving intercalated smectic phases stabilized by the mixed mesogenic group interaction. We have identified the first examples of ...

The Molecular Dynamics of Liquid Crystals

Abstract: 1. A Comparative Survey of the Physical Techniques Used in Studies of Molecular Dynamics.- 1. Introduction.- 2. Molecular Motion in Liquid Crystals.- 3. Spectroscopy in Studies of Molecular Motion.- 4. Applications of Spectroscopy to the Study of Rotational Motion.- 5. Applications to Studies of Translational Diffusion.- 2. On the Description of Ordering in Liquid Crystals.- 1. Introduction.- 2. General Approach.- 3. Purely Positional Order.- 4. Orientational Order.- 5. Positional-Orientational Order in Uniaxial Phases.- 6. Rotameric Molecules.- 3. Diffusion Models for Molecular Motion in Uniaxial Mesophases.- 1. Diffusion Equations.- 2. Solution of the Diffusion Equation.- 3. Diffusion Across Potential Barriers.- 4. Dynamics of Chain Molecules.- 5. Diffusive Coupling with the Solvent.- 4. ESR and Liquid Crystals: Statistical Mechanics and Generalised Smoluchowski Equations.- 1. Introduction.- 2. Rotational and Translational Motion in Ordered Fluids.- 3. Symmetries of the Liquid-Crystalline Potential.- 4. Relative Translational Diffusion: The Pair Correlation Function.- 5. Fluctuating Torques and Slowly Relaxing Local Structures.- 5. Techniques and Applications of Langevin Dynamics Simulations.- 1. Introduction.- 2. Hydrodynamics.- 3. Algorithms and Errors.- 4. Barrier Crossing.- 5. Rotation.- 6. Application to Lipid Bilayers.- 7. Limitations and Extensions of Langevin Dynamics.- 8. Appendix.- 6. An Introduction to the Molecular Dynamics Method and to Orientational Dynamics in Liquid Crystals.- 1. Introduction.- 2. Equations of Motion.- 3. Integration of the Equations of Motion.- 4. Calculation of Static and Dynamic Properties.- 5. General Properties of Orientational Correlation Functions.- 6. Evaluation of Correlation Functions by Molecular Dynamics.- 7. Appendix.- 7. Nuclear Spin Relaxation Formalism for Liquid Crystals.- 1. Introduction.- 2. Spin Dynamics: Density Matrix Description of Relaxation.- 3. Molecular Dynamics.- 4. Cooperative Motion.- 5. Illustrative Experiments.- 6. Summarising Remarks.- 8. Nuclear Spin Relaxation and Molecular Motion in Liquid Crystals.- 1. Introduction.- 2. Experiments and Methods.- 3. Density Operator Theory.- 4. Conclusions.- 9. The Effects of Director Fluctuations on Nuclear Spin Relaxation.- 1. Introduction.- 2. Historical Background.- 3. Theory.- 4. Experiments.- 5. Conclusions.- 10. Nuclear Spin Relaxation Mechanisms in Liquid Crystals Studied By Field Cycling NMR.- 1. Introduction.- 2. Principles and Techniques of Field Cycling NMR.- 3.T1 Relaxation Dispersion in Nematic Mesophases.- 4.T1 Relaxation Dispersion in Smectic Mesophases.- 5. DeuteronT1 Relaxation Dispersion in Methyl Deuteriated MBBA.- 11. Probe Studies of Liquid Crystals.- 1. Introduction.- 2. Orientational Order.- 3. Tools for Molecular Ordering.- 4. Solute-Solvent Interactions.- 5. Interesting Complications.- 6. Conclusions.- 12. ESR and Molecular Motions in Liquid Crystals: Motional Narrowing.- 1. The ESR Spin Hamiltonian: g and A Tensors.- 2. Effective Spin Hamiltonian and Order Parameters.- 3. Spectral Densities and Linewidths.- 4. Rotational Dynamics in Liquid-Crystalline Phases.- 5. Translational Motion in Liquid Crystals.- 13. Thermodynamics of Liquid Crystals and the Relation to Molecular Dynamics: ESR Studies.- 1. Introduction.- 2. Smectic A-Nematic Tricritical Point and Crossover Behaviour.- 3. Universality in Nematic Ordering.- 4. Lipid-Cholesterol Mixtures.- 5. Dynamics: Thermotropics.- 6. Dynamics: Lyotropics.- 14. ESR Studies of Molecular Dynamics at Phase Transitions in Liquid Crystals.- 1. Introduction.- 2. Models of Collective Dynamics: Director Fluctuations.- 3. The Nematic-Isotropic Phase Transition.- 4. The Smectic A-Nematic Phase Transition.- 5. The Dynamic Cluster Model.- 6. Fast versus Slow Collective Motions.- 7. Treatment of Data.- 15. ESR and Slow Motions in Liquid Crystals.- 1. Introduction.- 2. ESR Lineshapes: The Stochastic Liouville Equation.- 3. Methods of Solution: Lanczos and Conjugate Gradient Methods.- 4. Relation to Mori's Method in Statistical Mechanics.- 5. Ordering and Thermodynamics: Behaviour of Large versus Small Probes.- 6. Dynamics in I, N, SA and NR Phases.- 7. Rotational Dynamics in Lyotropics: Lipid Multilayers.- 8. Experimental Techniques: Lineshapes in One and Two Dimensions.- 9. On Fitting the Data.- 16. Raman and IR Fluctuation Spectroscopy of Liquid Crystals.- 1. Introduction.- 2. Determination of Correlation Functions from IR and Raman Lineshapes.- 3. Fluctuation Raman and IR Spectroscopy in Liquid Crystals.- 4. Experimental Results.- 5. Conclusions.- 17. Dielectric Relaxation Behaviour of Liquid Crystals.- 1. Introduction.- 2. Phenomenological Aspects of Dielectric Relaxation.- 3. Measurement of Dielectric Permittivity.- 4. Molecular Aspects of the Dielectric Permittivity.- 5. Experimental Results.- 6. Conclusions.- 18. Neutron Scattering From Liquid Crystals.- 1. Introduction to the Neutron.- 2. Types of Neutron Scattering Experiments.- 3. Coherent and Incoherent Scattering.- 4. Examples of Neutron Diffraction from Liquid Crystals.- 5. Inelastic and Quasi-Elastic Scattering.- 6. Model Incoherent Scattering Laws.- 7. Experiments and Examples of Results.- 19. Molecular Order and Motion in Liquid Crystal Polymers Studied By Pulsed Dynamic NMR.- 1. Introduction.- 2. Experiments and Methods.- 3. Results and Discussion.- 4. Conclusions.- 20. Aggregates of Amphiphiles in Lyotropic Liquid Crystals.- 1. Aggregation of Amphiphiles.- 2. Structure and Aggregates.- 3. Within the Aggregates.- 21. Orientation and Frequency Dependent NMR Relaxation Studies of Bilayer Membranes: Characterisation of the Lipid Motions.- 1. Introduction.- 2. Experiments and Methods.- 3. Results and Discussion.- 4. Conclusions.- 22. Molecular Dynamics in Liquid-Crystalline Systems Studied By Fluorescence Depolarisation Techniques.- 1. Introduction.- 2. Principles of Fluorescence Spectroscopy.- 3. Instrumentation for Fluorescence Spectroscopy.- 4. Principles of Fluorescence Polarisation.- 5. Data Analysis.- 6. Order and Dynamics of DPH and TMA-DPH Molecules in Lipid Bilayer Configurations.- 23. Spectroscopic Studies on Structure and Dynamics of Lyotropic Liquid Crystals: Cubic and Reversed Hexagonal Phases and Lipid Vesicles.- 1. Introduction.- 2. Phase Equilibria and Structural Polymorphism.- 3. Theoretical Aspects on Lipid Self-Assembly.- 4. Nuclear Magnetic Resonance.- 5. Electron Spin Resonance.- 6. Time-Resolved Fluorescence Spectroscopy.- 7. Fluorescence Anisotropy.

A molecular field theory for uniaxial nematic liquid crystals formed by non-cylindrically symmetric molecules

Abstract: Most molecular theories of nematic liquid crystals assume that the constituent molecules are cylindrically symmetric. However, although this may be a useful approximation the molecules of real nematogens are of lower symmetry; here we develop a theory for an ensemble of such particles based on a general expansion of the pairwise intermolecular potential together with the molecular field approximation. The dependence of the orientational properties of the uniaxial mesophase on the deviation from molecular cylindrical symmetry is calculated from the series expansion of the pseudopotential. In these calculations the number of arbitrary parameters in the orientational pseudo-potential is reduced by assuming that the anisotropic intermolecular potential originates solely from dispersion forces. The theoretical predictions for the values of the ordering matrix and the entropy change at the nematic-isotropic transition are found to be in good agreement with those observed for 4,4′-dimethoxyazoxybenzene. In addit...

Constant pressure molecular dynamics simulation: The Langevin piston method

Abstract: A new method for performing molecular dynamics simulations under constant pressure is presented. In the method, which is based on the extended system formalism introduced by Andersen, the deterministic equations of motion for the piston degree of freedom are replaced by a Langevin equation; a suitable choice of collision frequency then eliminates the unphysical ‘‘ringing’’ of the volume associated with the piston mass. In this way it is similar to the ‘‘weak coupling algorithm’’ developed by Berendsen and co‐workers to perform molecular dynamics simulation without piston mass effects. It is shown, however, that the weak coupling algorithm induces artifacts into the simulation which can be quite severe for inhomogeneous systems such as aqueous biopolymers or liquid/liquid interfaces.

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Dendron-Mediated Self-Assembly, Disassembly, and Self-Organization of Complex Systems

Abstract: Dendron-mediated self-assembly, disassembly, and self-organization of complex systems have been investigated. The most ideal building blocks would need to display shape persistence in solution and in the solid state, since only this feature provides access to the use of complementary methods of structural analysis. Most supramolecular dendrimers are chiral even when they are constructed from nonchiral building blocks and are equipped with mechanisms that amplify chirality. This poses additional challenges associated with the understanding of the structural origin of chirality in different supramolecular structures through combinations of structural analysis methods. While many supramolecular structures assembled from dendrimers and dendrons resemble some of the related morphologies generated from block-copolymers, they are much more complex and are not determined by the volume ratio between the dissimilar parts of the molecule.

Discotic Liquid Crystals: From Tailor-Made Synthesis to Plastic Electronics

Abstract: Most associate liquid crystals with their everyday use in laptop computers, mobile phones, digital cameras, and other electronic devices. However, in contrast to their rodlike (calamitic) counterparts, first described in 1907 by Vorlander, disklike (discotic, columnar) liquid crystals, which were discovered in 1977 by Chandrasekhar et al., offer further applications as a result of their orientation in the columnar mesophase, making them ideal candidates for molecular wires in various optical and electronic devices such as photocopiers, laser printers, photovoltaic cells, light-emitting diodes, field-effect transistors, and holographic data storage. Beginning with an overview of the various mesophases and characterization methods, this Review will focus on the major classes of columnar mesogens rather than presenting a library of columnar liquid crystals. Emphasis will be given to efficient synthetic procedures, and relevant mesomorphic and physical properties. Finally, some applications and perspectives in materials science and molecular electronics will be discussed.

Mitsunobu and Related Reactions: Advances and Applications

Abstract: 10. Patented Literature 2616 10.1. Esterification 2616 10.2. Ether Formation 2619 10.2.1. Etherification without Cyclization 2619 10.2.2. Etherification with Cyclization 2624 10.3. N-Alkylation 2625 10.4. Other Reactions 2627 11. Summary and Outlook 2628 12. Note Added in Proof 2628 13. Abbreviations Used in This Review 2629 14. Acknowledgments 2629 15. Supporting Information Available 2630 16. References 2630