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Special Issue "Liquid Crystal Thin Films: Structures and Applications"

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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Chemical and Molecular Sciences".

Deadline for manuscript submissions: 20 September 2023 | Viewed by 7219

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Special Issue Editor

Dr. Mohamed Amine Gharbi

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Guest Editor

Department of Physics, University of Massachusetts Boston, Boston, MA 02125, USA
Interests: active soft matter; liquid crystals; directed self-assembly; interfacial phenomena; functional nanomaterials; biomaterials

Special Issue Information

Dear Colleagues,

Soft materials, in particular liquid crystals, assemble and reconfigure in response to external constraints. They provide a model system for fundamental physics questions and the development of novel applications. Investigating the properties of liquid crystal films can lead to the development of new means to control the assembly of colloidal objects, including functional nanomaterials, biomaterials, and active matter. A better understanding of how these films behave when confined under particular conditions will provide a fascinating tool for the creation of a new generation of advanced materials that may respond to external conditions.

This issue highlights the properties of liquid crystal films and emphasizes their role in the development of novel applications. We are inviting submissions exploring the latest advances in studying the properties of liquid crystal films, including bulk and surface properties that can lead to potential applications in the future. In particular, we encourage the submission of papers investigating a broad range of liquid crystal mesophases. Reviews that succinctly analyze recent progress in the field will also be considered.

Dr. Mohamed Amine Gharbi
Guest Editor

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Keywords

confinement
thin films
interfaces
directed assembly
liquid crystal devices

Published Papers (5 papers)

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Research

Open AccessArticle

Geometric Confinement of 3D Smectic Liquid Crystal Foams

and

Appl. Sci. 2023, 13(6), 3414; https://doi.org/10.3390/app13063414 - 08 Mar 2023

Viewed by 642

Abstract

Due to their long history and extensive applications within modern society, foams have always been a popular topic of study. These systems are present everywhere in our life. They are also valuable in many industrial applications. For this reason, it is essential to continue investigating their properties and develop new materials to fabricate them. In this paper, we demonstrate a new way to create 3D foams by using an ordered viscoelastic material, the smectic liquid crystal (LC). Because of their lamellar structure, which is similar to soap, and their tunable properties that can be controlled via geometric confinement and external fields, smectic LCs are suitable for the fabrication of bubbles and foams. In this work, we present a compelling study of the parameters that influence the fabrication of LC foams in 3D. Particularly, we analyze the effects of the airflow rate and the geometry of confining boundaries on the assembly of their cells. We also compare our results to foams made with sodium dodecyl sulfate (SDS) and discuss the difference between their behaviors. Finally, we discuss how LC elasticity can substantially affect the stability and organization of foams. This work paves the way to exploiting new materials to fabricate foams with better monodispersity, uniformity, and controlled ordering that are useful in a wide range of industrial applications for which the tuning of properties is required. This includes the fields of oil recovery, decontamination, architecture, and design. Full article

(This article belongs to the Special Issue Liquid Crystal Thin Films: Structures and Applications)

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Open AccessCommunication

Phase Shifting Enhancement of a Substrate-Integrated Waveguide Phase Shifter Based on Liquid Crystal

and

Appl. Sci. 2023, 13(4), 2504; https://doi.org/10.3390/app13042504 - 15 Feb 2023

Viewed by 687

Abstract

A novel technique to enhance the phase shifting range of a liquid crystal (LC)-based, substrate-integrated waveguide (SIW) phase shifter by inserting inductive posts (IPs) is presented for the first time. The IPs inserted in the LC-based SIW phase shifter produce a phase advance based on the relative permittivity of the LC, resulting in an additional differential phase shift. At 28 GHz, the proposed structure with IPs achieves a ratio of maximum differential phase shift (

∆ ϕ_{m a x}

) to maximum insertion loss

{(I L}_{m a x})

(FoM1) = 52.82

° / d B

and ratio of maximum differential phase shift to length (FoM2) = 2.62

° / m m

. Compared with conventional LC-based SIW phase shifters that lack an IP and use the same amount of LC, the FoM1 increased by 16% and the FoM2 increased by 55%. In addition, compared to the typical structure that uses additional LCs instead of IPs, the FoM1 decreased by 7%, and FoM2 increased by 21%. Therefore, inserting IPs into the LC-based SIW phase shifter can reduce the dimensions of the phase shifter and the amount of LCs required to achieve the desired differential phase shift. We believe this work can contribute to the design of compact and efficient SIW phase shifters for future telecommunication systems. Full article

(This article belongs to the Special Issue Liquid Crystal Thin Films: Structures and Applications)

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Open AccessFeature PaperArticle

Orientation of Liquid Crystalline Molecules on PDMS Surfaces and within PDMS Microfluidic Systems

and

Katarzyna A. Rutkowska

Appl. Sci. 2021, 11(24), 11593; https://doi.org/10.3390/app112411593 - 07 Dec 2021

Cited by 2 | Viewed by 1358

Abstract

The unique components of PDMS-based microfluidic systems are those combined with liquid crystalline materials. Their functionality, especially when it comes to optical applications, highly depends on the LC molecular arrangement. This work summarizes experimental investigations on the orientation of molecules within LC:PDMS structures according to the manufacturing technologies. The availability of high-quality molds to pattern PDMS is a significant barrier to the creation of advanced microfluidic systems. The possibility of using inexpensive molds in the rapid and reproducible fabrication process has been particularly examined as an alternative to photolithography. Different geometries, including an innovative approach for the electrical control of the molecular arrangement within PDMS microchannels, are presented. These studies are critical for novel optofluidic systems, introducing further research on LC:PDMS waveguiding structures. Full article

(This article belongs to the Special Issue Liquid Crystal Thin Films: Structures and Applications)

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Open AccessArticle

Comment on the Determination of the Polar Anchoring Energy by Capacitance Measurements in Nematic Liquid Crystals

Patrick Oswald

Appl. Sci. 2021, 11(16), 7387; https://doi.org/10.3390/app11167387 - 11 Aug 2021

Cited by 1 | Viewed by 1207

Abstract

Capacitance measurements have been extensively used to measure the anchoring extrapolation length L at a nematic–substrate interface. These measurements are extremely delicate because the value found for L often critically depends on the sample thickness and the voltage range chosen to perform the measurements. Several reasons have been proposed to explain this observation, such as the presence of inhomogeneities in the director distribution on the bounding plates or the variation with the electric field of the dielectric constants. In this paper, I propose a new method to measure L that takes into account this second effect. This method is more general than the one proposed in Murauski et al. Phys. Rev. E 71, 061707 (2005) because it does not assume that the anchoring angle is small and that the anchoring energy is of the Rapini–Papoular form. This method is applied to a cell of 8CB that is treated for planar unidirectional anchoring by photoalignment with the azobenzene dye Brilliant Yellow. The role of flexoelectric effects and the shape of the anchoring potential are discussed. Full article

(This article belongs to the Special Issue Liquid Crystal Thin Films: Structures and Applications)

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Open AccessArticle

Environmentally Stable Chiral-Nematic Liquid-Crystal Elastomers with Mechano-Optical Properties

and

Appl. Sci. 2021, 11(11), 5037; https://doi.org/10.3390/app11115037 - 29 May 2021

Cited by 5 | Viewed by 2139

Abstract

Chiral-nematic liquid crystal (N* LC) elastomers exhibit mechano-optical responsive behavior. However, practical sensor applications have been limited by the intrinsic sensitivity of N* LC elastomers to environmental conditions, such as temperature. Although densely cross-linked LC network polymers exhibit high thermal stability, they are not proper for the mechanical sensor due to high glass transition temperatures and low flexibility. To overcome these issues, we focused on enhancing thermal stability by introducing noncovalent cross-linking sites via intermolecular interactions between LC molecules bonded to the polymer network. N* LC elastomers with a cyanobiphenyl derivative as a side-chain mesogen exhibited mechano-optical responsive behavior, with a hypsochromic shift of the reflection peak wavelength under an applied tensile strain and quick shape and color recovery owing to high elasticity. Notably, the N* LC elastomers showed high resistance to harsh environments, including high temperatures and various solvents. Interactions, such as π–π stacking and dipole–dipole interactions, between the cyanobiphenyl units can act as weak cross-links, thus improving the thermal stability of the LC phase without affecting the mechano-optical response. Thus, these N* LC elastomers have great potential for the realization of practical mechano-optical sensors. Full article

(This article belongs to the Special Issue Liquid Crystal Thin Films: Structures and Applications)

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