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Featured researches published by David Dunmur.


Liquid Crystals | 2016

Distinctive dielectric properties of nematic liquid crystal dimers

Nerea Sebastián; Beatriz Robles-Hernández; S. Diez-Berart; J. Salud; Geoffrey R. Luckhurst; David Dunmur; David López; M. R. De La Fuente

ABSTRACT We provide an overview of the effect of the molecular structure on the dielectric properties of dimers exhibiting nematic and twist-bend nematic phases with special focus on how the conformational distribution changes are reflected by the dielectric behaviour. Nematic dimers show distinctive dielectric properties which differ from those of archetypical nematic liquid crystals, as for example, unusual temperature dependence of the static permittivity or dielectric spectra characterised by two low-frequency relaxation processes with correlated strengths. The interpretation of such characteristic behaviour requires that account is taken of the effect of molecular flexibility on the energetically favoured molecular shapes. The anisotropic nematic interactions greatly influence the conformational distribution. Dielectric behaviour can be used to track those conformational changes due to dependence of the averaged molecular dipole moment on the averaged molecular shape. Results for a number of dimers are compared and analysed on the basis of the influence of details of the molecular structure, using a recently developed theory for the dielectric properties of dimers. GRAPHICAL ABSTRACT


Physical Review E | 2016

Molecular dynamics of a binary mixture of twist-bend nematic liquid crystal dimers studied by dielectric spectroscopy.

Beatriz Robles Hernández; Nerea Sebastian Ugarteche; Josep Salud Puig; Sergio Díez Berart; David Dunmur; Geoffrey R. Luckhurst; David Orencio López Pérez; Maria Rosario de la Fuente Lavin

We report a comprehensive dielectric characterization of a liquid crystalline binary mixture composed of the symmetric mesogenic dimer CB7CB and the nonsymmetric mesogenic dimer FFO9OCB. In addition to the high-temperature nematic phase, such a binary mixture shows a twist-bend nematic phase at room temperature which readily vitrifies on slow cooling. Changes in the conformational distribution of the dimers are reflected in the dielectric permittivity and successfully analyzed by means of an appropriate theoretical model. It is shown that the dielectric spectra of the mixture reflect the different molecular dipole properties of the components, resembling in the present case the characteristic dielectric spectra of nonsymmetric dimers. Comparison of the nematic and twist-bend nematic phases reveals that molecular dynamics are similar despite the difference in the molecular environment.


Liquid Crystals Today | 2016

The International Liquid Crystal Society 1990–2015

David Dunmur; Heinz Kitzerow

ABSTRACT The International Liquid Crystal Society has now been in existence for 25 years. It has established itself as an organisation that promotes and supports liquid crystal science around the world. This article chronicles the foundation of the Society, and gives a brief account of the history of international conferences on liquid crystals.


Liquid Crystals Today | 2013

125 years of liquid crystals

David Dunmur

As founding editor of Liquid Crystals Today, it is a great pleasure to contribute an article to mark the 125th anniversary of the birth of our subject. On 3 May 1888, Friederich Reinitzer presented his paper on ‘Understanding Cholesteryls’ at the monthly meeting of the Chemistry Society of Vienna, and this traditionally marks the beginning of liquid crystal science. Despite the title of his paper, Reinitzer did not understand cholesteryls, and in some respects we still do not fully understand them today. But Friederich Reinitzer was not too proud to seek help, and he consulted a young microscopist and crystallographer Otto Lehmann to help, and, as we say, the rest is history (Figure 1). Tim Sluckin and I have chronicled the story in our two books [1,2], but of course there have been a number of other excellent accounts on various aspects of the history of liquid crystals, and these are listed in the references [3–7]. For practitioners of science, what matters are the facts, observations and measurements and then interpretation through theory. Actually, this is only half the story, and the results of what we like to call research have to be recorded and communicated to other scientists. The public also needs to be made aware of our work if it is to be used for the benefit of humankind. In matters of communication, not only the message but also the messenger counts. Can he be trusted, and does the message deserve our collective attention or even action? Let the facts speak for themselves we cry, but this is rarely enough. The acceptance of what the professionals might regard as scientific truths requires more than just the facts. The integrity of the work and its proponents must be established, and then as far as possible the processes of investigation must be explained. This is the work of journalists, a description that includes scientific commentators and, indeed, scientists when they write commentaries and reviews on the results of scientific study. Amongst this group of communicators we obviously include historians of science, and it is they who should examine the probity of scientists, the work and how various interactions result in durable and honest additions to knowledge (Figure 2). In this brief celebration of 125 years of liquid crystal science, I could not possibly give even a potted history of the subject. Obviously it has matured, but more importantly it has been accepted by the scientific world and increasingly the public. Liquid crystals are no longer a bizarre backwater of knowledge but figure strongly in the mainstream of physics, chemistry and materials science. It was not always like this, and the coming of age of liquid crystals has happened relatively recently, even within the past few decades (Figure 3). Liquid Crystals Today is the newsletter of the International Liquid Crystal Society (ILCC), which itself will soon be celebrating 25 years of existence. One might ask why is there a society for liquid crystals? There are no similar societies for gases or solids or liquids. What is special about liquid crystals? As liquid crystal scientists, we enthuse about our subject, but enthusiasm alone does not guarantee interest and acceptance. The early records chronicle the difficulties of persuading others of the importance of liquid crystal science and its applications. Nowhere was this more true than within the scientific community, which did not immediately grasp the significance of a new state of matter. The practising scientists had to operate on the fringes of their subjects, and support for their science and acceptance of the work through publications and conferences was a constant challenge. Disregard of their work by other scientists eventually resulted in liquid crystal scientists coming together in National Societies and then the International Society which spawned conferences, seminars and discussions devoted to liquid crystals. At last there were forums for like-minded scientists to meet and discuss and, most importantly, exchange ideas. In parallel with this was the launch of specialist journals such asMolecular Crystals and Liquid Crystals and Liquid Crystals, so that research could be readily published and was accessible to a specialist readership (Figure 4).


Physical Review E | 2011

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

Mirko Cestari; S. Diez−Berart; David Dunmur; Alberta Ferrarini; M. R. De La Fuente; D. J. B. Jackson; David López; Geoffrey R. Luckhurst; M. A. Perez Jubindo; Robert M. Richardson; J. Salud; Bakir A. Timimi; Herbert Zimmermann


Physical Review E | 2015

Twist, tilt, and orientational order at the nematic to twist-bend nematic phase transition of 1 '',9 ''-bis(4-cyanobiphenyl-4 '-yl) nonane: A dielectric, H-2 NMR, and calorimetric study

Beatriz Robles Hernández; Nerea Sebastian Ugarteche; M. Rosario de la Fuente; David Orencio López Pérez; Sergio Díez Berart; Josep Salud Puig; M. Blanca Ros; David Dunmur; Geoffrey R. Luckhurst; Bakir A. Timimi


Physical Chemistry Chemical Physics | 2016

Miscibility studies of two twist-bend nematic liquid crystal dimers with different average molecular curvatures. A comparison between experimental data and predictions of a Landau mean-field theory for the NTB–N phase transition

David López; Beatriz Robles-Hernández; J. Salud; M. R. De La Fuente; Nerea Sebastián; S. Diez-Berart; X. Jaen; David Dunmur; Geoffrey R. Luckhurst


Journal of Chemical Physics | 2012

Disentangling molecular motions involved in the glass transition of a twist-bend nematic liquid crystal through dielectric studies.

David López; Nerea Sebastián; M. R. De La Fuente; J. C. Martínez-García; J. Salud; M. A. Pérez-Jubindo; S. Diez-Berart; David Dunmur; Geoffrey R. Luckhurst


Journal of Physical Chemistry B | 2010

Cylindrical sub-micrometer confinement results for the odd-symmetric dimer alpha,omega-bis[(4-cyanobiphenyl)-4'-yloxy]undecane (BCB.O11).

M. R. De La Fuente; David López; M. A. Pérez-Jubindo; David Dunmur; S. Diez-Berart; J. Salud


Handbook of Liquid Crystals | 2014

Elastic and Flexoelectric Properties

David Dunmur

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David López

Polytechnic University of Catalonia

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J. Salud

Polytechnic University of Catalonia

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M. R. De La Fuente

University of the Basque Country

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S. Diez-Berart

Polytechnic University of Catalonia

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Nerea Sebastián

Otto-von-Guericke University Magdeburg

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Bakir A. Timimi

University of Southampton

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Beatriz Robles-Hernández

University of the Basque Country

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M. A. Pérez-Jubindo

University of the Basque Country

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