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Special Issue "Experimental and Theoretical Studies of Liquid Crystalline Materials: Where Do We Stand after 120 Years?"

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A special issue of International Journal of Molecular Sciences (ISSN 1422-0067). This special issue belongs to the section "Material Sciences and Nanotechnology".

Deadline for manuscript submissions: closed (25 September 2013)

Special Issue Editor

Guest Editor
Prof. Dr. Martin Schoen (Website)

Stranski Lab for Physical and Theoretical Chemistry, Berlin Institute of Technology, 17. Juni 135, Berlin 10623, Germany
Interests: statistical physics; computer simulation; classical density functional theory; soft matter; phase behavior and transport; self-assembly; fluids at interfaces

Special Issue Information

Dear Colleagues,

Since their discovery 120 years ago by the Viennese chemist Reinitzer and his colleague Lehmann the liquid-crystalline state, often referred to as the ``fourth state of matter'', has received a lot of attention because of its fascinating physical properties.  The unique properties of liquid-crystalline materials prompted numerous important technological developments. Perhaps the most traditional ones are in the area of display technology where one utilizes the fact that liquid crystals can form ordered structures if exposed to suitable external fields. Depending on whether these fields are switched off or on the liquid-crystalline material may be transparent to visible light or not. More recently the range of potential applications of liquid crystals has considerably broadened. It is nowadays possible to use liquid crystals as sensors in the recognition and detection of biomaterials. In tribology liquid crystals have been employed as lubricants to reduce friction coefficients, wear rates, and contact temperature of sliding surfaces. Other applications include photonic and organic electronic devices. Even in food industry liquid crystals are used to stabilize dispersions and. Particularly interesting issues in contemporary liquid-crystal research include biaxial nematics, the issue of chirality, or the structure and dynamics of liquid-crystal phases formed by molecules of unusual shapes and geometries.

Prof. Dr. Martin Schoen
Guest Editor

Submission

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Keywords

  • structure and dynamics
  • defect topologies
  • symmetry of ordered phases
  • surfaces and external fields
  • novel liquid-crystal molecules and their characterization
  • molecular simulation
  • mesoscale description
  • devices
  • nonequilibrium phenomena

Published Papers (16 papers)

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Research

Jump to: Review

Open AccessArticle Liquid Crystalline Assembly of Coil-Rod-Coil Molecules with Lateral Methyl Groups into 3-D Hexagonal and Tetragonal Assemblies
Int. J. Mol. Sci. 2014, 15(4), 5634-5648; doi:10.3390/ijms15045634
Received: 16 October 2013 / Revised: 3 March 2014 / Accepted: 11 March 2014 / Published: 2 April 2014
Cited by 3 | PDF Full-text (875 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In this paper, we report the synthesis and self-assembly behavior of coil-rod-coil molecules, consisting of three biphenyls linked through a vinylene unit as a conjugated rod segment and poly(ethylene oxide) (PEO) with a degree of polymerization (DP) of 7, 12 and 17, [...] Read more.
In this paper, we report the synthesis and self-assembly behavior of coil-rod-coil molecules, consisting of three biphenyls linked through a vinylene unit as a conjugated rod segment and poly(ethylene oxide) (PEO) with a degree of polymerization (DP) of 7, 12 and 17, incorporating lateral methyl groups between the rod and coil segments as the coil segment. Self-organized investigation of these molecules by means of differential scanning calorimetry (DSC), thermal polarized optical microscopy (POM) and X-ray diffraction (XRD) reveals that the lateral methyl groups attached to the surface of rod and coil segments, dramatically influence the self-assembling behavior in the liquid-crystalline mesophase. Molecule 1 with a relatively short PEO coil length (DP = 7) self-assembles into rectangular and oblique 2-dimensional columnar assemblies, whereas molecules 2 and 3 with DP of 12 and 17 respectively, spontaneously self-organize into unusual 3-dimensional hexagonal close-packed or body-centered tetragonal assemblies. Full article
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Open AccessArticle Dynamics of Order Reconstruction in a Nanoconfined Nematic Liquid Crystal with a Topological Defect
Int. J. Mol. Sci. 2013, 14(12), 24135-24153; doi:10.3390/ijms141224135
Received: 26 September 2013 / Revised: 26 November 2013 / Accepted: 27 November 2013 / Published: 12 December 2013
Cited by 12 | PDF Full-text (2863 KB) | HTML Full-text | XML Full-text
Abstract
At the wall in a hybrid nematic cell with strong anchoring, the nematic director is parallel to one wall and perpendicular to the other. Within the Landau-de Gennes theory, we have investigated the dynamics of s = ±1/2 wedge disclinations in such [...] Read more.
At the wall in a hybrid nematic cell with strong anchoring, the nematic director is parallel to one wall and perpendicular to the other. Within the Landau-de Gennes theory, we have investigated the dynamics of s = ±1/2 wedge disclinations in such a cell, using the two-dimensional finite-difference iterative method. Our results show that with the cell gap decreasing, the core of the defect explodes, and the biaxiality propagates inside the cell. At a critical value of dc* (where ξ is the characteristic length for order-parameter changes), the exchange solution is stable, while the defect core solution becomes metastable. Comparing to the case with no initial disclination, the value at which the exchange solution becomes stable increases relatively. At a critical separation of dc ≈ 6ξ, the system undergoes a structural transition, and the defect core merges into a biaxial layer with large biaxiality. For weak anchoring boundary conditions, a similar structural transition takes place at a relative lower critical value. Because of the weakened frustration, the asymmetric boundary conditions repel the defect to the weak anchoring boundary and have a relatively lower critical value of da, where the shape of the defect deforms. Further, the response time between two very close cell gaps is about tens of microseconds, and the response becomes slower as the defect explodes. Full article
Open AccessArticle A Histone-Like Protein Induces Plasmid DNA to Form Liquid Crystals in Vitro and Gene Compaction in Vivo
Int. J. Mol. Sci. 2013, 14(12), 23842-23857; doi:10.3390/ijms141223842
Received: 30 October 2013 / Revised: 17 November 2013 / Accepted: 21 November 2013 / Published: 6 December 2013
Cited by 2 | PDF Full-text (2350 KB) | HTML Full-text | XML Full-text
Abstract
The liquid crystalline state is a universal phenomenon involving the formation of an ordered structure via a self-assembly process that has attracted attention from numerous scientists. In this study, the dinoflagellate histone-like protein HCcp3 is shown to induce super-coiled pUC18 plasmid DNA [...] Read more.
The liquid crystalline state is a universal phenomenon involving the formation of an ordered structure via a self-assembly process that has attracted attention from numerous scientists. In this study, the dinoflagellate histone-like protein HCcp3 is shown to induce super-coiled pUC18 plasmid DNA to enter a liquid crystalline state in vitro, and the role of HCcp3 in gene condensation in vivo is also presented. The plasmid DNA (pDNA)-HCcp3 complex formed birefringent spherical particles with a semi-crystalline selected area electronic diffraction (SAED) pattern. Circular dichroism (CD) titrations of pDNA and HCcp3 were performed. Without HCcp3, pUC18 showed the characteristic B conformation. As the HCcp3 concentration increased, the 273 nm band sharply shifted to 282 nm. When the HCcp3 concentration became high, the base pair (bp)/dimer ratio fell below 42/1, and the CD spectra of the pDNA-HCcp3 complexes became similar to that of dehydrated A-form DNA. Microscopy results showed that HCcp3 compacted the super-coiled gene into a condensed state and that inclusion bodies were formed. Our results indicated that HCcp3 has significant roles in gene condensation both in vitro and in histone-less eukaryotes in vivo. The present study indicates that HCcp3 has great potential for applications in non-viral gene delivery systems, where HCcp3 may compact genetic material to form liquid crystals. Full article
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Open AccessArticle Synthesis of 1,4-Bis(phenylethynyl)benzenes and Their Application as Blue Phase Liquid Crystal Composition
Int. J. Mol. Sci. 2013, 14(12), 23257-23273; doi:10.3390/ijms141223257
Received: 14 September 2013 / Revised: 16 October 2013 / Accepted: 11 November 2013 / Published: 25 November 2013
Cited by 2 | PDF Full-text (610 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A number of 1,4-bis(phenylethynyl)benzene derivatives (BPEBs) and their analogues with different numbers of side-substitute fluorine atoms on benzene rings, and alkyl chains, ethoxyl groups, fluorine atoms and trifluoromethyl groups as the end groups have been synthesized. The effects of the different substituents [...] Read more.
A number of 1,4-bis(phenylethynyl)benzene derivatives (BPEBs) and their analogues with different numbers of side-substitute fluorine atoms on benzene rings, and alkyl chains, ethoxyl groups, fluorine atoms and trifluoromethyl groups as the end groups have been synthesized. The effects of the different substituents on their properties such as thermal behavior of melting point and clearing point, the temperature of nematic phase, optical anisotropy and dielectric anisotropy have been well investigated, and it has been found that some BPEBs have a wide range of the nematic phase temperature with high optical anisotropy (Δn) and acceptable dielectric anisotropy (Δε), which have been applied as the crucial compositions to constitute a liquid crystal mixture having the properties of Δε = 29.0 and Δn = 0.283 at 25 °C. With the addition of the chiral dopant to the obtained liquid crystal mixture, blue phase liquid crystal with a blue phase temperature range of 8 °C has been achieved. Full article
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Open AccessArticle Tuning Fluidic Resistance via Liquid Crystal Microfluidics
Int. J. Mol. Sci. 2013, 14(11), 22826-22844; doi:10.3390/ijms141122826
Received: 26 September 2013 / Revised: 4 November 2013 / Accepted: 8 November 2013 / Published: 19 November 2013
Cited by 4 | PDF Full-text (2808 KB) | HTML Full-text | XML Full-text
Abstract
Flow of molecularly ordered fluids, like liquid crystals, is inherently coupled with the average local orientation of the molecules, or the director. The anisotropic coupling—typically absent in isotropic fluids—bestows unique functionalities to the flowing matrix. In this work, we harness this anisotropy [...] Read more.
Flow of molecularly ordered fluids, like liquid crystals, is inherently coupled with the average local orientation of the molecules, or the director. The anisotropic coupling—typically absent in isotropic fluids—bestows unique functionalities to the flowing matrix. In this work, we harness this anisotropy to pattern different pathways to tunable fluidic resistance within microfluidic devices. We use a nematic liquid crystalline material flowing in microchannels to demonstrate passive and active modulation of the flow resistance. While appropriate surface anchoring conditions—which imprint distinct fluidic resistances within microchannels under similar hydrodynamic parameters—act as passive cues, an external field, e.g., temperature, is used to actively modulate the flow resistance in the microfluidic device. We apply this simple concept to fabricate basic fluidic circuits, which can be hierarchically extended to create complex resistance networks, without any additional design or morphological patterning of the microchannels. Full article
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Open AccessArticle Synthesis and Characterization of Ferroelectric Liquid Crystalline Organosiloxanes Containing 4-(4-undecanyloxy bi-phenyl-1-carboxyloxy)phenyl (2S,3S)-2-chloro-3-methylvalerate and 4-(4-undecanyloxybenzoyloxy)biphenyl (2S,3S)-2-chloro-3-methylvalerate
Int. J. Mol. Sci. 2013, 14(11), 21306-21318; doi:10.3390/ijms141121306
Received: 16 August 2013 / Revised: 29 September 2013 / Accepted: 30 September 2013 / Published: 25 October 2013
Cited by 2 | PDF Full-text (455 KB) | HTML Full-text | XML Full-text
Abstract
A series of new organosiloxane ferroelectric liquid crystalline (FLC) materials have been synthesized, and their mesomorphic and physical properties have been characterized. Four new disiloxanes and trisiloxanes, containing biphenyl 4-hydroxybenzoate and phenyl 4-hydroxybiphenylcarboxylate as mesogenic units and eleven methylene unit as spacers [...] Read more.
A series of new organosiloxane ferroelectric liquid crystalline (FLC) materials have been synthesized, and their mesomorphic and physical properties have been characterized. Four new disiloxanes and trisiloxanes, containing biphenyl 4-hydroxybenzoate and phenyl 4-hydroxybiphenylcarboxylate as mesogenic units and eleven methylene unit as spacers and (2S,3S)-2-chloro-3-methylvalerate unit as chiral end groups. The molecule, using three phenyl ring as a mesogenic unit, formulates much wider liquid crystalline phase temperature ranges than that of a two phenyl ring unit. The phenyl arrangement differences of mesogenic unit result in the greater differences of the liquid crystal phase formation. The siloxane molecule induction is helpful to the more regular smectic phase formation and smectic phase stabilization, such as chiral SC (SC*) and SB phases. The siloxane molecule is helpful to reduce the phase transition temperature and broaden the liquid crystal temperature range of the SC* phase and, simultaneously, it will not induce chain crystallization phenomenon and dilute the Ps value. The synthesis and characterization of the new FLCs materials, which exhibit a room temperature SC* phase and higher spontaneous polarization are presented. Full article
Open AccessArticle Enhanced Solar Cell Conversion Efficiency Using Birefringent Liquid Crystal Polymer Homeotropic Films from Reactive Mesogens
Int. J. Mol. Sci. 2013, 14(11), 21319-21327; doi:10.3390/ijms141121319
Received: 12 September 2013 / Revised: 12 October 2013 / Accepted: 17 October 2013 / Published: 25 October 2013
PDF Full-text (621 KB) | HTML Full-text | XML Full-text
Abstract
Novel birefringent liquid crystal polymer homeotropic films have been coated on semiconductor solar cells to improve the effective incident sunlight angles. The liquid crystal polymer precursor, based on reactive mesogens, is fluidic and flows like liquid. It would distribute uniformly on the [...] Read more.
Novel birefringent liquid crystal polymer homeotropic films have been coated on semiconductor solar cells to improve the effective incident sunlight angles. The liquid crystal polymer precursor, based on reactive mesogens, is fluidic and flows like liquid. It would distribute uniformly on the solar cell sample surface by any traditional coating technique. The birefringence for light, due to the liquid crystal retardation properties, manipulated the optical length and the deflection of incident light, thus allowed an increase in the energy conversion efficiency. The expensive sunlight tracking systems could be avoided. The processing parameters can be tuned such as different mesogen concentrations and plate speeds of spin-coating. The results showed that the solar cell conversion efficiency was improved from 14.56% to 14.85% at an incident sunlight angle of 15°. It was further improved from 13.40% to 13.81% when the angle was 30°. The interesting angular dependency on solar cell efficiency enhancement has been evaluated. Full article
Open AccessArticle The Influence of Silica Nanoparticles on Ionic Liquid Behavior: A Clear Difference between Adsorption and Confinement
Int. J. Mol. Sci. 2013, 14(10), 21045-21052; doi:10.3390/ijms141021045
Received: 12 August 2013 / Revised: 26 September 2013 / Accepted: 29 September 2013 / Published: 18 October 2013
Cited by 3 | PDF Full-text (293 KB) | HTML Full-text | XML Full-text
Abstract
The phase behaviors of ionic liquids (ILs) confined in nanospace and adsorbed on outer surface of nanoparticles are expected to be different from those of the bulk. Anomalous phase behaviors of room temperature ionic liquid tributylhexadecylphosphonium bromide (P44416Br) confined in [...] Read more.
The phase behaviors of ionic liquids (ILs) confined in nanospace and adsorbed on outer surface of nanoparticles are expected to be different from those of the bulk. Anomalous phase behaviors of room temperature ionic liquid tributylhexadecylphosphonium bromide (P44416Br) confined in ordered mesoporous silica nanoparticles with average pore size 3.7 nm and adsorbed on outer surface of the same silica nanoparticles were reported. It was revealed that the melting points (Tm) of confined and adsorbed ILs depressed significantly in comparison with the bulk one. The Tm depressions for confined and adsorbed ILs are 8 °C and 14 °C, respectively. For comparison with the phase behavior of confined P44416Br, 1-butyl-3-methylimidazolium bromide (BmimBr) was entrapped within silica nanopores, we observed an enhancement of 50 °C in Tm under otherwise similar conditions. The XRD analysis indicates the formation of crystalline-like phase under confinement, in contrast to the amorphous phase in adsorbed IL. It was confirmed that the behavior of IL has clear difference. Moreover, the complex π-π stacking and H-bonding do not exist in the newly proposed phosphonium-based IL in comparison with the widely studied imidazolium-based IL. The opposite change in melting point of P44416Br@SiO2 and BmimBr@SiO2 indicates that the cationic species plays an important role in the variation of melting point. Full article
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Open AccessArticle Thermal Properties and Crystallite Morphology of Nylon 66 Modified with a Novel Biphenyl Aromatic Liquid Crystalline Epoxy Resin
Int. J. Mol. Sci. 2013, 14(10), 20682-20691; doi:10.3390/ijms141020682
Received: 19 August 2013 / Revised: 23 September 2013 / Accepted: 30 September 2013 / Published: 15 October 2013
Cited by 2 | PDF Full-text (435 KB) | HTML Full-text | XML Full-text
Abstract
In order to improve the thermal properties of important engineering plastics, a novel kind of liquid crystalline epoxy resin (LCER), 3,3',5,5' -Tetramethylbiphenyl-4,4' -diyl bis(4-(oxiran-2-ylmethoxy)benzoate) (M1) was introduced to blend with nylon 66 (M2) at high temperature. The effects of [...] Read more.
In order to improve the thermal properties of important engineering plastics, a novel kind of liquid crystalline epoxy resin (LCER), 3,3',5,5' -Tetramethylbiphenyl-4,4' -diyl bis(4-(oxiran-2-ylmethoxy)benzoate) (M1) was introduced to blend with nylon 66 (M2) at high temperature. The effects of M1 on chemical modification and crystallite morphology of M2 were investigated by rheometry, thermo gravimetric analysis (TGA), dynamic differential scanning calorimetry (DSC) and polarized optical microscopy (POM). TGA results showed that the initial decomposition temperature of M2 increased by about 8 °C by adding 7% wt M1, indicating the improvement of thermal stability. DSC results illustrated that the melting point of composites decreased by 12 °C compared to M2 as the content of M1 increased, showing the improvement of processing property. POM measurements confirmed that dimension of nylon-66 spherulites and crystallization region decreased because of the addition of liquid crystalline epoxy M1. Full article
Open AccessArticle Synthesis and Thermotropic Studies of a New Series of Teraryl Liquid Crystals 2-(4'-Alkoxybiphen-4-yl)-5-Cyanopyridines
Int. J. Mol. Sci. 2013, 14(9), 18809-18823; doi:10.3390/ijms140918809
Received: 13 August 2013 / Revised: 30 August 2013 / Accepted: 6 September 2013 / Published: 12 September 2013
Cited by 2 | PDF Full-text (585 KB) | HTML Full-text | XML Full-text
Abstract
A new series of teraryl 2-(4'-alkoxybiphen-4-yl)-5-cyanopyridines (nO-PPPyCN, n = 2–8) compounds, bearing a cyanopyridine terminus, were synthesized using a short 2-step reaction with overall yields between 33% and 69%. Spectral analyses were in accord with the expected structures. Thermotropic behavior [...] Read more.
A new series of teraryl 2-(4'-alkoxybiphen-4-yl)-5-cyanopyridines (nO-PPPyCN, n = 2–8) compounds, bearing a cyanopyridine terminus, were synthesized using a short 2-step reaction with overall yields between 33% and 69%. Spectral analyses were in accord with the expected structures. Thermotropic behavior of the teraryl compounds was investigated using polarised optical microscopy and differential scanning calorimetry. All compounds exhibited both enantiotropic nematic and smectic A phases, with an additional enantiotropic smectic C phase when n = 7 and 8. Polymesomorphism appears to be a common behavior in this series of linear liquid crystal compounds. Full article
Open AccessArticle Nanoconfinement-Induced Structures in Chiral Liquid Crystals
Int. J. Mol. Sci. 2013, 14(9), 17584-17607; doi:10.3390/ijms140917584
Received: 11 July 2013 / Revised: 8 August 2013 / Accepted: 16 August 2013 / Published: 28 August 2013
Cited by 5 | PDF Full-text (14929 KB) | HTML Full-text | XML Full-text
Abstract
We employ Monte Carlo simulations in a specialized isothermal-isobaric and in the grand canonical ensemble to study structure formation in chiral liquid crystals as a function of molecular chirality. Our model potential consists of a simple Lennard-Jones potential, where the attractive contribution [...] Read more.
We employ Monte Carlo simulations in a specialized isothermal-isobaric and in the grand canonical ensemble to study structure formation in chiral liquid crystals as a function of molecular chirality. Our model potential consists of a simple Lennard-Jones potential, where the attractive contribution has been modified to represent the orientation dependence of the interaction between a pair of chiral liquid-crystal molecules. The liquid crystal is confined between a pair of planar and atomically smooth substrates onto which molecules are anchored in a hybrid fashion. Hybrid anchoring allows for the formation of helical structures in the direction perpendicular to the substrate plane without exposing the helix to spurious strains. At low chirality, we observe a cholesteric phase, which is transformed into a blue phase at higher chirality. More specifically, by studying the unit cell and the spatial arrangement of disclination lines, this blue phase can be established as blue phase II. If the distance between the confining substrates and molecular chirality are chosen properly, we see a third structure, which may be thought of as a hybrid, exhibiting mixed features of a cholesteric and a blue phase. Full article
Open AccessArticle Liquid Crystal Phase Behaviour of Attractive Disc-Like Particles
Int. J. Mol. Sci. 2013, 14(8), 16414-16442; doi:10.3390/ijms140816414
Received: 25 June 2013 / Revised: 24 July 2013 / Accepted: 25 July 2013 / Published: 8 August 2013
Cited by 5 | PDF Full-text (980 KB) | HTML Full-text | XML Full-text
Abstract
We employ a generalized van der Waals-Onsager perturbation theory to construct a free energy functional capable of describing the thermodynamic properties and orientational order of the isotropic and nematic phases of attractive disc particles. The model mesogen is a hard (purely repulsive) [...] Read more.
We employ a generalized van der Waals-Onsager perturbation theory to construct a free energy functional capable of describing the thermodynamic properties and orientational order of the isotropic and nematic phases of attractive disc particles. The model mesogen is a hard (purely repulsive) cylindrical disc particle decorated with an anisotropic square-well attractive potential placed at the centre of mass. Even for isotropic attractive interactions, the resulting overall inter-particle potential is anisotropic, due to the orientation-dependent excluded volume of the underlying hard core. An algebraic equation of state for attractive disc particles is developed by adopting the Onsager trial function to characterize the orientational order in the nematic phase. The theory is then used to represent the fluid-phase behaviour (vapour-liquid, isotropic-nematic, and nematic-nematic) of the oblate attractive particles for varying values of the molecular aspect ratio and parameters of the attractive potential. When compared to the phase diagram of their athermal analogues, it is seen that the addition of an attractive interaction facilitates the formation of orientationally-ordered phases. Most interestingly, for certain aspect ratios, a coexistence between two anisotropic nematic phases is exhibited by the attractive disc-like fluids. Full article
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Open AccessArticle Domain Structures in Nematic Liquid Crystals on a Polycarbonate Surface
Int. J. Mol. Sci. 2013, 14(8), 16303-16320; doi:10.3390/ijms140816303
Received: 5 June 2013 / Revised: 12 July 2013 / Accepted: 18 July 2013 / Published: 7 August 2013
Cited by 4 | PDF Full-text (6529 KB) | HTML Full-text | XML Full-text
Abstract
Alignment of nematic liquid crystals on polycarbonate films obtained with the use of solvents with different solvations is studied. Domain structures occurring during the growth on the polymer surface against the background of the initial thread-like or schlieren texture are demonstrated. It [...] Read more.
Alignment of nematic liquid crystals on polycarbonate films obtained with the use of solvents with different solvations is studied. Domain structures occurring during the growth on the polymer surface against the background of the initial thread-like or schlieren texture are demonstrated. It is established by optical methods that the domains are stable formations visualizing the polymer surface structures. In nematic droplets, the temperature-induced transition from the domain structure with two extinction bands to the structure with four bands is observed. This transition is shown to be caused by reorientation of the nematic director in the liquid crystal volume from the planar alignment to the homeotropic state with the pronounced radial configuration of nematic molecules on the surface. The observed textures are compared with different combinations of the volume LC orientations and the radial distribution of the director field and the disclination lines at the polycarbonate surface. Full article

Review

Jump to: Research

Open AccessReview Nematicons and Their Electro-Optic Control: Light Localization and Signal Readdressing via Reorientation in Liquid Crystals
Int. J. Mol. Sci. 2013, 14(10), 19932-19950; doi:10.3390/ijms141019932
Received: 30 August 2013 / Revised: 16 September 2013 / Accepted: 22 September 2013 / Published: 8 October 2013
Cited by 1 | PDF Full-text (4099 KB) | HTML Full-text | XML Full-text
Abstract
Liquid crystals in the nematic phase exhibit substantial reorientation when the molecules are driven by electric fields of any frequencies. Exploiting such a response at optical frequencies, self-focusing supports transverse localization of light and the propagation of self-confined beams and waveguides, namely [...] Read more.
Liquid crystals in the nematic phase exhibit substantial reorientation when the molecules are driven by electric fields of any frequencies. Exploiting such a response at optical frequencies, self-focusing supports transverse localization of light and the propagation of self-confined beams and waveguides, namely “nematicons”. Nematicons can guide other light signals and interact with inhomogeneities and other beams. Moreover, they can be effectively deviated by using the electro-optic response of the medium, leading to several strategies for voltage-controlled reconfiguration of light-induced guided-wave circuits and signal readdressing. Hereby, we outline the main features of nematicons and review the outstanding progress achieved in the last twelve years on beam self-trapping and electro-optic readdressing. Full article
Open AccessReview Single Molecule Studies on Dynamics in Liquid Crystals
Int. J. Mol. Sci. 2013, 14(10), 19506-19525; doi:10.3390/ijms141019506
Received: 15 August 2013 / Revised: 11 September 2013 / Accepted: 12 September 2013 / Published: 26 September 2013
Cited by 5 | PDF Full-text (2724 KB) | HTML Full-text | XML Full-text
Abstract
Single molecule (SM) methods are able to resolve structure related dynamics of guest molecules in liquid crystals (LC). Highly diluted small dye molecules on the one hand explore structure formation and LC dynamics, on the other hand they report about a distortion [...] Read more.
Single molecule (SM) methods are able to resolve structure related dynamics of guest molecules in liquid crystals (LC). Highly diluted small dye molecules on the one hand explore structure formation and LC dynamics, on the other hand they report about a distortion caused by the guest molecules. The anisotropic structure of LC materials is used to retrieve specific conformation related properties of larger guest molecules like conjugated polymers. This in particular sheds light on organization mechanisms within biological cells, where large molecules are found in nematic LC surroundings. This review gives a short overview related to the application of highly sensitive SM detection schemes in LC. Full article
Open AccessReview Self-Organizing Cyclolinear Organosilicon Polymers in Bulk and on the Surface of Water
Int. J. Mol. Sci. 2013, 14(9), 18215-18238; doi:10.3390/ijms140918215
Received: 17 June 2013 / Revised: 18 July 2013 / Accepted: 18 July 2013 / Published: 5 September 2013
Cited by 1 | PDF Full-text (668 KB) | HTML Full-text | XML Full-text
Abstract
yclolinear organocarbosiloxane polymers with varying content and location of (CH2)n groups in the monomer unit were synthesized by reactions of heterofunctional polycondensation and polyaddition of difunctional organocyclosiloxanes and organocyclocarbosiloxanes. Their bulk properties were studied by differential scanning calorimetry and [...] Read more.
yclolinear organocarbosiloxane polymers with varying content and location of (CH2)n groups in the monomer unit were synthesized by reactions of heterofunctional polycondensation and polyaddition of difunctional organocyclosiloxanes and organocyclocarbosiloxanes. Their bulk properties were studied by differential scanning calorimetry and X-ray structural analysis. It was shown that on introduction of CH2 groups into the methylcyclohexasiloxane unit, the polymer retains the ability to self-organize with formation of a mesomorphic state in a wide temperature range, while on introduction of (CH2)2 fragments in a cyclotetrasiloxane unit or in a bridge connecting two methylcyclotetra(hexa)siloxane units it does not. Comparison of the X-ray data of dihydroxy derivatives of decamethylcyclohexasiloxane and decamethyl-5-carbocyclohexasiloxane with packing of cyclolinear organosilicon polymers in bulk shows that the polymer inherits the layered type of crystalline structure typical for monomers. Langmuir films of cyclolinear polymethylcarbosiloxanes with different design of monomer units were studied as well. It was revealed that all polymers form monomolecular films at the air/water interface, excluding those having longer hydrophobic fragment than hydrophilic ones. The ability to form multilayers depends on the surroundings of Si atom in the bridge between the cycles. Full article

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