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Liquid Crystals and Other Partially Disordered Molecular Systems
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Liquid Crystals and Other Partially Disordered Molecular Systems

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Optical and Photonic Materials".

Deadline for manuscript submissions: 20 March 2025 | Viewed by 5782

Special Issue Editor

Dr. Dorota Dardas

E-Mail Website
Guest Editor
Institute of Molecular Physics, Polish Academy of Sciences, 60-179 Poznań, Poland
Interests: liquid crystals; ferroelectricity; electro-optic; elasticity; viscosity; composites; nanomaterials; soft matter

Special Issue Information

Dear Colleagues,

Liquid crystals are materials that possess both the characteristics of liquids and solids due to their partially ordered molecular structure. The molecules in liquid crystals exhibit some degree of alignment while maintaining a certain level of disorder. This unique arrangement gives rise to intriguing physical properties that differ from ordinary liquids or solids.

Liquid crystals have diverse physical properties that make them suitable for various applications. One of their most well-known applications is liquid crystal displays (LCDs), which utilize the optical properties of liquid crystals to produce visual representations. The alignment of liquid crystal molecules can be controlled by applying electric fields, allowing for the manipulation of light transmission through the display.

Apart from LCDs, liquid crystals also find applications in other fields, such as electro-optical devices, photonics, and sensors. Liquid crystals can self-assemble into organized structures, and their properties can be modified by adding different compounds or varying the temperature. By incorporating liquid crystals into polymer matrices, interesting hybrid materials called polymer-dispersed liquid crystals can be obtained, which have unique optical and mechanical properties.

Non-trivial properties are exhibited by liquid crystals doped with micro- and nanoparticles, composite materials, hybrid materials, and complex molecular systems.

In addition to liquid crystals, there are other molecular systems that exhibit partial disorder, such as liquid crystal polymers, block copolymers, and colloidal suspensions. These partially disordered materials have attracted attention due to their potential for achieving desired properties through manipulation of molecular arrangement.

In conclusion, liquid crystals and other partially disordered molecular systems possess intriguing properties that make them valuable in various applications. Understanding the nature and behavior of these materials is essential for their further development and utilization in fields ranging from electronics to materials science.

Dr. Dorota Dardas
Guest Editor

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Keywords

  • liquid crystals
  • LCDs
  • electro-optical devices
  • photonics
  • molecular systems
  • block copolymers

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Published Papers (8 papers)

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Research

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13 pages, 6609 KiB  
Article
Increase in Auxeticity Due to the Presence of a Disordered Crystalline Phase of Hard Dumbbells Within the Nanolayer–Nanochannel Inclusion Introduced to the f.c.c. Hard Sphere Crystal
by Jakub W. Narojczyk
Materials 2024, 17(22), 5558; https://doi.org/10.3390/ma17225558 - 14 Nov 2024
Viewed by 357
Abstract
To obtain materials or metamaterials with desired elastic properties that are tailor-made for a particular application, it is necessary to design a new material or composite (which may be cumbersome) or to modify the structure of existing materials in order to change their [...] Read more.
To obtain materials or metamaterials with desired elastic properties that are tailor-made for a particular application, it is necessary to design a new material or composite (which may be cumbersome) or to modify the structure of existing materials in order to change their properties in the desired direction. The latter approach, although also not easy, seems favourable with respect to parameters like costs and time-to-market. Despite the fact that elastic properties are one of the oldest studied physical parameters of matter, our understanding of the processes at the microstructural level, that are behind these properties, is still far from being complete. The present work, with the help of Monte Carlo computer simulations, aims to broaden this knowledge. The previously studied model crystal of hard spheres, containing a combined nanolayer and nanochannel inclusions, is revisited. This periodic model crystal has been extended to include a degree of disorder in the form of degenerate crystalline phase by introducing a degenerate crystalline phase within its structure. The inclusion has been transformed (without changes to its shape, size, or orientation) by randomly connecting the neighbouring spheres into di-atomic molecules (dumbbells). The impact of this modification on elastic properties has been investigated with the help of the Parrinello–Rahman approach in the isothermal–isobaric ensemble (NpT). It has been shown, that the presence of the degenerate crystalline phase of hard dumbbells in the system leads to a significant decrease in the Poisson’s ratio in [110]-direction (ν=−0.235) and an overall enhancement of the auxetic properties. Full article
(This article belongs to the Special Issue Liquid Crystals and Other Partially Disordered Molecular Systems)
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19 pages, 7079 KiB  
Article
Molecular Dynamics, Dielectric Properties, and Textures of Protonated and Selectively Deuterated 4′-Pentyl-4-biphenylcarbonitrile Liquid Crystal
by Jadwiga Tritt-Goc, Magdalena Knapkiewicz, Piotr Harmata, Jakub Herman and Michał Bielejewski
Materials 2024, 17(20), 5106; https://doi.org/10.3390/ma17205106 - 19 Oct 2024
Viewed by 718
Abstract
Using liquid crystals in near-infrared applications suffers from effects related to processes like parasitic absorption and high sensitivity to UV-light exposure. One way of managing these disadvantages is to use deuterated systems. The combined 1H and 2H nuclear magnetic resonance relaxometry [...] Read more.
Using liquid crystals in near-infrared applications suffers from effects related to processes like parasitic absorption and high sensitivity to UV-light exposure. One way of managing these disadvantages is to use deuterated systems. The combined 1H and 2H nuclear magnetic resonance relaxometry method (FFC NMR), dielectric spectroscopy (DS), optical microscopy (POM), and differential scanning calorimetry (DSC) approach was applied to investigate the influence of selective deuteration on the molecular dynamics, thermal properties, self-organization, and electric-field responsiveness to a 4′-pentyl-4-biphenylcarbonitrile (5CB) liquid crystal. The NMR relaxation dispersion (NMRD) profiles were analyzed using theoretical models for the description of dynamics processes in different mesophases. Obtained optical textures of selectively deuterated 5CB showed the occurrence of the domain structure close to the I/N phase transition. The dielectric measurements showed a substantial difference in switching fields between fully protonated/deuterated 5CB and selectively deuterated molecules. The DSC thermograms showed a more complex phase transition sequence for partially deuterated 5CB with respect to fully protonated/deuterated molecules. Full article
(This article belongs to the Special Issue Liquid Crystals and Other Partially Disordered Molecular Systems)
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15 pages, 5539 KiB  
Article
Synthesis and Properties of Highly Tilted Antiferroelectric Liquid Crystalline (R) Enantiomers
by Magdalena Urbańska, Monika Zając, Michał Czerwiński, Przemysław Morawiak, Alexej Bubnov and Aleksandra Deptuch
Materials 2024, 17(20), 4967; https://doi.org/10.3390/ma17204967 - 11 Oct 2024
Viewed by 474
Abstract
This work reports the synthesis method and various properties of four rod-like antiferroelectric (R) laterally substituted enantiomers, with or without fluorine atoms used as substituents in the benzene ring. The influence of fluorine substitution on the mesophase temperature range was determined. [...] Read more.
This work reports the synthesis method and various properties of four rod-like antiferroelectric (R) laterally substituted enantiomers, with or without fluorine atoms used as substituents in the benzene ring. The influence of fluorine substitution on the mesophase temperature range was determined. The synthesized compounds are three-ring rod-like smectics with a chiral center based on (R)-(−)-2-octanol. Their chemical and optical purity was checked using high-performance liquid chromatography (HPLC). Two newly synthesized enantiomers and three previously reported (R) enantiomers were used to formulate two antiferroelectric mixtures. The mesomorphic behavior was characterized by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction (XRD). The helical pitch and tilt angle measurements were done using the selective light reflection phenomenon and the electro-optical method, respectively. All the enantiomers exhibit a wide temperature range of the antiferroelectric phase, with a high tilt angle. Furthermore, the enantiomer with lateral fluorine substitution in the ortho position has a very long helical pitch (more than 2.0 µm), relatively low enthalpy of melting point, and a tilt angle close to 45 degrees. The designed (R) enantiomers can be useful for formulating eutectic mixtures for further use in various devices, including photonics and optoelectronics. Full article
(This article belongs to the Special Issue Liquid Crystals and Other Partially Disordered Molecular Systems)
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10 pages, 909 KiB  
Article
Strong Impact of Particle Size Polydispersity on the Thermal Conductivity of Yukawa Crystals
by Konstantin V. Tretiakov and Krzysztof Hyżorek
Materials 2024, 17(20), 4955; https://doi.org/10.3390/ma17204955 - 10 Oct 2024
Viewed by 497
Abstract
Control of thermal transport in colloidal crystals plays an important role in modern technologies. A deeper understanding of the governing heat transport processes in various systems, such as polydisperse colloidal crystals, is required. This study shows how strongly the particle size polydispersity of [...] Read more.
Control of thermal transport in colloidal crystals plays an important role in modern technologies. A deeper understanding of the governing heat transport processes in various systems, such as polydisperse colloidal crystals, is required. This study shows how strongly the particle size polydispersity of a model colloidal crystal influences the thermal conductivity. The thermal conductivity of model colloidal crystals has been calculated using molecular dynamics simulations. The model crystals created by particles interacting through Yukawa (screened-Coulomb) interaction are assumed to have a face-centered cubic structure. The influence of the Debye screening length, contact potential, and particle size polydispersity on the thermal conductivity of Yukawa crystals was investigated. It was found that an increase in particle size polydispersity causes a strong—almost fivefold—decrease in the thermal conductivity of Yukawa crystals. In addition, the obtained results showed that the effect of the particle size polydispersity on reducing the thermal conductivity of Yukawa crystals is stronger than changes in values of the Debye screening length or the contact potential. Full article
(This article belongs to the Special Issue Liquid Crystals and Other Partially Disordered Molecular Systems)
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13 pages, 5439 KiB  
Article
Miscibility Studies of Bismesogen CBnCB Forming Nematic Twist-Bend Phase with Cyanobiphenyls nCB
by Marzena Tykarska, Barbara Klucznik, Jerzy Dziaduszek and Stanisław Jóźwiak
Materials 2024, 17(17), 4256; https://doi.org/10.3390/ma17174256 - 28 Aug 2024
Viewed by 568
Abstract
This work aims to determine how the nematic twist-bend phase (NTB) of bismesogens containing two rigid parts of cyanobiphenyls connected with a linking chain containing n = 7, 9, and 11 methylene groups behaves in mixtures with structurally similar cyanobiphenyls nCB, [...] Read more.
This work aims to determine how the nematic twist-bend phase (NTB) of bismesogens containing two rigid parts of cyanobiphenyls connected with a linking chain containing n = 7, 9, and 11 methylene groups behaves in mixtures with structurally similar cyanobiphenyls nCB, n = 4–12, 14. The whole phase diagrams are presented for the CB7CB-nCB system. For the other systems, CB9CB-nCB and CB11CB-nCB, only curves corresponding to NTB-N phase transition are presented. Based on the temperature-concentration range of the existence of NTB phase, it was established that an increase in the alkyl chain length of CBnCB causes an increase in the stability of the NTB phase. But surprisingly, an increase in the alkyl chain length of nCB compounds does not change the slope of the NTB-N equilibrium line on phase diagrams. It is slightly bigger when the nCB compound has the same length of alkyl chain as the length of the linking group of a bismesogen. XRD studies were carried out for two mixtures. Full article
(This article belongs to the Special Issue Liquid Crystals and Other Partially Disordered Molecular Systems)
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13 pages, 1980 KiB  
Article
Plasmid DNA Complexes in Powder Form Studied by Spectroscopic and Diffraction Methods
by Aleksandra Radko, Sebastian Lalik, Natalia Górska, Aleksandra Deptuch, Jolanta Świergiel and Monika Marzec
Materials 2024, 17(14), 3530; https://doi.org/10.3390/ma17143530 - 17 Jul 2024
Viewed by 698
Abstract
Currently, new functional materials are being created with a strong emphasis on their ecological aspect. Materials and devices based on DNA biopolymers, being environmentally friendly, are therefore very interesting from the point of view of applications. In this paper, we present the results [...] Read more.
Currently, new functional materials are being created with a strong emphasis on their ecological aspect. Materials and devices based on DNA biopolymers, being environmentally friendly, are therefore very interesting from the point of view of applications. In this paper, we present the results of research on complexes in the powder form based on plasmid DNA (pDNA) and three surfactants with aliphatic chains containing 16 carbon atoms (cetyltrimethylammonium chloride, benzyldimethylhexadecylammonium chloride and hexadecylpyridinium chloride). The X-ray diffraction results indicate a local hexagonal packing of DNA helices in plasmid DNA complexes, resembling the packing for corresponding complexes based on linear DNA. Based on the Fourier-transform infrared spectroscopy results, the DNA conformation in all three complexes was determined as predominantly of A-type. The two relaxation processes revealed by dielectric spectroscopy for all the studied complexes are connected with two different contributions to total conductivity (crystallite part and grain boundaries). The crystallite part (grain interior) was interpreted as an oscillation of the polar surfactant head groups and is dependent on the conformation of the surfactant chain. The influence of the DNA type on the properties of the complexes is discussed, taking into account our previous results for complexes based on linear DNA. We showed that the type of DNA has an impact on the properties of the complexes, which has not been demonstrated so far. It was also found that the layer of pDNA–surfactant complexes can be used as a layer with variable specific electric conductivity by selecting the frequency, which is interesting from an application point of view. Full article
(This article belongs to the Special Issue Liquid Crystals and Other Partially Disordered Molecular Systems)
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21 pages, 12831 KiB  
Article
Dielectric Modes in Antiferroelectric and Ferroelectric Liquid Crystals in a Pure Enantiomeric Version and a Racemic Mixture
by Paweł Perkowski and Magdalena Urbańska
Materials 2024, 17(13), 3335; https://doi.org/10.3390/ma17133335 - 5 Jul 2024
Viewed by 783
Abstract
The dielectric properties of synclinic (ferroelectric SmC*) and anticlinic (antiferroelectric SmCA*) smectic liquid crystals composed of molecules of one chiral version (S) are presented and compared with properties of racemic mixture (R, S), showing SmC and SmCA phases. The racemic [...] Read more.
The dielectric properties of synclinic (ferroelectric SmC*) and anticlinic (antiferroelectric SmCA*) smectic liquid crystals composed of molecules of one chiral version (S) are presented and compared with properties of racemic mixture (R, S), showing SmC and SmCA phases. The racemic mixture completely loses its ferroelectric and antiferroelectric properties. Surprisingly, only one dielectric mode observed in the antiferroelectric SmCA* phase disappeared in the dielectric response of the racemic SmCA phase. Additionally, we observed that in the SmC phase, seen in the racemic mixture, the weak dielectric mode (named the X mode) is detected, which seems to be the continuation of the PL mode existing in the racemic SmCA. Moreover, this mode in the racemic SmC has nothing to do with the Goldstone mode, typical for the SmC* phase. This paper describes in detail the real and imaginary parts of dielectric permittivity in smectic phases for the enantiomer and racemate with and without a DC field, compares the properties of the X and PL modes, and discusses the full scheme of dielectric modes in enantiomer and racemate. Full article
(This article belongs to the Special Issue Liquid Crystals and Other Partially Disordered Molecular Systems)
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22 pages, 3912 KiB  
Review
Survey of Applicable Methods for Determining Viscoelastic Effects in Ferroelectric and Antiferroelectric Chiral Liquid Crystals
by Dorota Dardas
Materials 2024, 17(16), 3993; https://doi.org/10.3390/ma17163993 - 11 Aug 2024
Viewed by 1088
Abstract
Viscosity, elasticity, and viscoelastic properties are one of the most fundamental properties of liquid crystalline materials; the main problem in determining these properties is the multitude of physical parameters needed to determine the values of elasticity and viscosity constants. In this paper, a [...] Read more.
Viscosity, elasticity, and viscoelastic properties are one of the most fundamental properties of liquid crystalline materials; the main problem in determining these properties is the multitude of physical parameters needed to determine the values of elasticity and viscosity constants. In this paper, a number of different measurement methods for the complete characterization of viscoelastic properties for smectic liquid crystalline materials and their mixtures are analyzed, both theoretically and experimentally. The way in which viscoelastic material constants are determined depends mainly on the application/purpose of the materials under study. The subject of this work was to review the methods used to determine viscoelastic effects in ferroelectric and antiferroelectric chiral liquid crystals, their mixtures, composite materials, and even in dielectric systems, which would bear the hallmark of a universal method allowing the application of sufficiently low electric fields. In the case of chiral liquid crystals with ferroelectric and antiferroelectric phases and their subphases, the following assumption applies: fulfilment of Hooke’s law (in the case of elastic coefficients) and preservation of laminar flow (in the case of viscosity coefficients). Full article
(This article belongs to the Special Issue Liquid Crystals and Other Partially Disordered Molecular Systems)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Theoretical Insights into Twist-Bend Nematic Liquid Crystals: Infrared Spectra Analysis of Naphthalene-Based Dimers
Authors: Barbara Loska 1, Yuki Arakawa 2 and Katarzyna Merkel 1,*
Affiliation: 1 Institute of Materials Engineering, Faculty of Science and Technology, University of Silesia in Katowice, ul. 75 Pułku Piechoty, Chorzów, 41-500, Poland; [email protected] (B.L) 2 Department of Applied Chemistry and Life Science, Graduate School of Engineering, Toyohashi University of Technology, Toyohashi 441-8580, Japan; [email protected] (Y.A.)
Abstract: In this study, we employed Density Functional Theory (DFT), a standard method in quantum chemistry, to investigate the structural intricacies of a naphthalene-based thioether-linked liquid crystal dimers. The theoretical analysis included the calculation of the molecular bend angle, a crucial factor influencing the formation of the Twist-Bend Nematic (TB) phase, as well as other molecular parameters such as transition dipole moments, bond lengths, and bond energies. These calculations allowed for determining the probable conformations and the computation of their vibrational spectra, which are essential for interpreting experimental spectra. Connecting these insights, we identified stable conformations and observed differences in the spectra between the twist-bend and nematic phases. The combined DFT calculations and infrared absorbance measurements allowed us to investigate the structure and intermolecular interactions of molecules in the nematic and twist-bend phases of the dimers. Notably, significant changes in average absorbance were detected in the experimental spectra in the nematic twist-bend phase. During the transition from the nematic phase to the TB phase, a clear decrease in absorbance for longitudinal dipoles and an increase for transverse dipoles were observed. This phenomenon suggests that longitudinal dipoles are antiparallel, while transverse dipoles are parallel. To verify the influence of nearest-neighbour interactions, DFT calculations were conducted on a system comprising several neighbouring molecules.

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