We review the current state of knowledge of phase separation and phase equilibria in porous materials. Our emphasis is on fundamental studies of simple fluids (composed of small, neutral molecules) and well-characterized materials. While theoretical and molecular simulation studies are stressed, we also survey experimental investigations that are fundamental in nature. Following a brief survey of the most useful theoretical and simulation methods, we describe the nature of gas‐liquid (capillary condensation), layering, liquid‐liquid and freezing/melting transitions. In each case studies for simple pore geometries, and also more complex ones where available, are discussed. While a reasonably good understanding is available for phase equilibria of pure adsorbates in simple pore geometries, there is a need to extend the models to more complex pore geometries that include effects of chemical and geometrical heterogeneity and connectivity. In addition, with the exception of liquid‐liquid equilibria, little work has been done so far on phase separation for mixtures in porous media.

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Phase separation in confined systems

Advanced Mathematical Methods for Scientists and Engineers

Aspects of Scientific Explanation: and Other Essays in the Philosophy of Science

We present a review of experimental, theoretical, and molecular simulation studies of confinement effects on freezing and melting We consider both simple and more complex adsorbates that are confined in various environments (slit or cylindrical pores and also disordered porous materials) The most commonly used molecular simulation, theoretical and experimental methods are first presented We also provide a brief description of the most widely used porous materials The current state of knowledge on the effects of confinement on structure and freezing temperature, and the appearance of new surface-driven and confinement-driven phases are then discussed We also address how confinement affects the glass transition

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Effects of confinement on freezing and melting.

With the maturation of the information display field, liquid-crystal materials research is undergoing a modern-day renaissance. Devices and configurations based on liquid-crystal materials are being developed for spectroscopy, imaging and microscopy, leading to new techniques for optically probing biological systems. Biosensors fabricated with liquid-crystal materials can allow label-free observations of biological phenomena. Liquid-crystal polymers are starting to be used in biomimicking colour-producing structures, lenses and muscle-like actuators. New areas of application in the realms of biology and medicine are stimulating innovation in basic and applied research into these materials.

Liquid-crystal materials find a new order in biomedical applications.

The core structure of a laboratory-made dust devil-like vortex and its condensed matter analogs

We studied numerically external stimuli enforced annihilation of a pair of daughter nematic topological defect (TD) assemblies bearing a relatively strong topological charge |m|=3/2. A Landau- de Gennes phenomenological approach in terms of tensor nematic order parameter was used in an effectively two-dimensional Cartesian coordinate system, where spatial variations along the z-axis were neglected. A pair of {m=3/2,m=−3/2} was enforced by an appropriate surface anchoring field, mimicking an experimental sample realization using the atomic force microscope (AFM) scribing method. Furthermore, defects were confined within a rectangular boundary that imposes strong tangential anchoring. This setup enabled complex and counter-intuitive annihilation processes on varying relevant parameters. We present two qualitatively different annihilation paths, where we either gradually reduced the relative surface anchoring field importance or increased an external in-plane spatially homogeneous electric field E. The creation and depinning of additional defect pairs {12,−12} mediated the annihilation in such a geometry. Furthermore, we illustrate the absorption of TDs by sharp edges of the confining boundary, accompanied by m=±1/4↔∓1/4 winding reversal of edge singularities, and also E-driven zero-dimensional to one-dimensional defect core transformation.

https://www.mdpi.com/2073-4352/10/8/673/pdf

Annihilation of Highly-Charged Topological Defects

We have simulated lattice models of homogenous and randomly perturbed systems exhibiting continuous symmetry breaking, concentrating on domain sizes and configuration character. The system consists of rod-like objects within a cubic lattice interacting via a Lebwohl–Lasher-type interaction at temperature T, but including impurities at concentration p imposing a random anisotropy field-type disorder, coupled with anchoring strength W to neighboring host director molecules. An example of such systems represents nematic LC or nanotubes. We study molecular domain patterns as a function of p, W, T, and sample history. Histories are defined either by a temperature-quenched history (TQH), a field-quenched history (FQH) or from an annealed history (AH). Finite size-scaling is used to determine the nature of the orientational ordering correlations. We distinguish three different kinds of phase. Short ranged order (SRO) implies exponential decay of orientational correlations. Quasi-long-range order (QLRO) sustains ...

Domain Patterns in Homogeneous and Random Perturbed Nematic Liquid Crystals: A Simulation Study

In this article, we theoretically and numerically study the chirality and saddle-splay elastic constant ( K 24 ) -enabled stability of multiple twist-like nematic liquid crystal (LC) structures in cylindrical confinement. We focus on the so-called radially z-twisted (RZT) and radially twisted (RT) configurations, which simultaneously exhibit twists in different spatial directions. We express the free energies of the structures in terms of dimensionless wave vectors, which characterise the structures and play the roles of order parameters. The impact of different confinement anchoring conditions is explored. A simple Landau-type analysis provides an insight into how different model parameters influence the stability of structures. We determine conditions for which the structures are stable in chiral and also nonchiral LCs. In particular, we find that the RZT structure could exhibit macroscopic chirality inversion upon varying the relevant parameters. This phenomenon could be exploited for the measurement of K 24 .

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Multiple Twisted Chiral Nematic Structures in Cylindrical Confinement

We have observed that a single groove made by an atomic force microscope (AFM) tip in a polyimide layer strongly aligns nematic liquid crystals locally and have used this phenomenon for studying twist nematic lines. We have measured the intensity profile of light transmitted across a single line and the azimuthal surface energy as a function of the spatial separation of grooves. From these measurements, we have determined the azimuthal surface anchoring energy of the AFM structured and of the untreated polyimide. We find that the twist coherence length, which determines the width of TN lines, is approximately proportional to the cell thickness, while the surface anchoring energy can change it for a factor of 2 at maximum.

http://samo.kralj.fnm.uni-mb.si/clanki/a3c4.pdf

Samo Kralj

Papers

The core structure of a laboratory-made dust devil-like vortex and its condensed matter analogs

Annihilation of Highly-Charged Topological Defects

Domain Patterns in Homogeneous and Random Perturbed Nematic Liquid Crystals: A Simulation Study

Multiple Twisted Chiral Nematic Structures in Cylindrical Confinement

Observation of twist nematic liquid-crystal lines