Jan Jadżyn

Bio: Jan Jadżyn is an academic researcher from Polish Academy of Sciences. The author has contributed to research in topic(s): Liquid crystal & Dielectric. The author has an hindex of 25, co-authored 234 publication(s) receiving 2453 citation(s). Previous affiliations of Jan Jadżyn include Katholieke Universiteit Leuven.

Structural changes in the 6CHBT liquid crystal doped with spherical, rodlike, and chainlike magnetic particles.

Abstract: In this work the 4-(trans- 4'-n -hexylcyclohexyl)-isothiocyanatobenzene (6CHBT) liquid crystal was doped with differently shaped magnetite nanoparticles. The structural changes were observed by capacitance measurements and showed significant influence of the shape and size of the magnetic particles on the magnetic Freedericksz transition. For the volume concentration phi= 2 x 10(-4) of the magnetic particles, the critical magnetic field was established for the pure liquid crystal, and for liquid crystals doped with spherical, chainlike, and rodlike magnetic particles. The influence of the magnetic field depends on the type of anchoring, which is characterized by the density of anchoring energy and by the initial orientation between the liquid crystal molecules and the magnetic moment of the magnetic particles. The experimental results indicated soft anchoring in the case of spherical magnetic particles and rigid anchoring in the case of rodlike and chainlike magnetic particles, with parallel initial orientation between the magnetic moments of the magnetic particles and director.

Excess molar volumes of binary mixtures of diols and water

Abstract: Volumes d'exces des melanges eau-butaneiols-1,2, -1,3 et -1,4, propanediol-1,3 et pentanediol-1,5

Capacitance changes in ferronematic liquid crystals induced by low magnetic fields.

Abstract: The response in capacitance to low external magnetic fields (up to 0.1 T) of suspensions of spherical magnetic nanoparticles, single-wall carbon nanotubes (SWCNT), SWCNT functionalized with carboxyl group (SWCNT-COOH), and SWCNT functionalized with Fe${}_{3}$O${}_{4}$ nanoparticles in a nematic liquid crystal has been studied experimentally. The volume concentration of nanoparticles was ${\ensuremath{\phi}}_{1}={10}^{\ensuremath{-}4}$ and ${\ensuremath{\phi}}_{2}={10}^{\ensuremath{-}3}$. Independent of the type and the volume concentration of the nanoparticles, a linear response to low magnetic fields (far below the magnetic Fr\'eederiksz transition threshold) has been observed, which is not present in the undoped nematic.

The restaurant at the end of the random walk: recent developments in the description of anomalous transport by fractional dynamics

Abstract: Fractional dynamics has experienced a firm upswing during the past few years, having been forged into a mature framework in the theory of stochastic processes. A large number of research papers developing fractional dynamics further, or applying it to various systems have appeared since our first review article on the fractional Fokker–Planck equation (Metzler R and Klafter J 2000a, Phys. Rep. 339 1–77). It therefore appears timely to put these new works in a cohesive perspective. In this review we cover both the theoretical modelling of sub- and superdiffusive processes, placing emphasis on superdiffusion, and the discussion of applications such as the correct formulation of boundary value problems to obtain the first passage time density function. We also discuss extensively the occurrence of anomalous dynamics in various fields ranging from nanoscale over biological to geophysical and environmental systems.

A Medicinal Chemist’s Guide to Molecular Interactions

Abstract: Molecular recognition in biological systems relies on the existence of specific attractive interactions between two partner molecules. Structure-based drug design seeks to identify and optimize such interactions between ligands and their host molecules, typically proteins, given their three-dimensional structures. This optimization process requires knowledge about interaction geometries and approximate affinity contributions of attractive interactions that can be gleaned from crystal structure and associated affinity data. Here we compile and review the literature on molecular interactions as it pertains to medicinal chemistry through a combination of careful statistical analysis of the large body of publicly available X-ray structure data and experimental and theoretical studies of specific model systems. We attempt to extract key messages of practical value and complement references with our own searches of the CSDa,(1) and PDB databases.(2) The focus is on direct contacts between ligand and protein functional groups, and we restrict ourselves to those interactions that are most frequent in medicinal chemistry applications. Examples from supramolecular chemistry and quantum mechanical or molecular mechanics calculations are cited where they illustrate a specific point. The application of automated design processes is not covered nor is design of physicochemical properties of molecules such as permeability or solubility. Throughout this article, we wish to raise the readers’ awareness that formulating rules for molecular interactions is only possible within certain boundaries. The combination of 3D structure analysis with binding free energies does not yield a complete understanding of the energetic contributions of individual interactions. The reasons for this are widely known but not always fully appreciated. While it would be desirable to associate observed interactions with energy terms, we have to accept that molecular interactions behave in a highly nonadditive fashion.3,4 The same interaction may be worth different amounts of free energy in different contexts, and it is very hard to find an objective frame of reference for an interaction, since any change of a molecular structure will have multiple effects. One can easily fall victim to confirmation bias, focusing on what one has observed before and building causal relationships on too few observations. In reality, the multiplicity of interactions present in a single protein−ligand complex is a compromise of attractive and repulsive interactions that is almost impossible to deconvolute. By focusing on observed interactions, one neglects a large part of the thermodynamic cycle represented by a binding free energy: solvation processes, long-range interactions, conformational changes. Also, crystal structure coordinates give misleadingly static views of interactions. In reality a macromolecular complex is not characterized by a single structure but by an ensemble of structures. Changes in the degrees of freedom of both partners during the binding event have a large impact on binding free energy. The text is organized in the following way. The first section treats general aspects of molecular design: enthalpic and entropic components of binding free energy, flexibility, solvation, and the treatment of individual water molecules, as well as repulsive interactions. The second half of the article is devoted to specific types of interactions, beginning with hydrogen bonds, moving on to weaker polar interactions, and ending with lipophilic interactions between aliphatic and aromatic systems. We show many examples of structure−activity relationships; these are meant as helpful illustrations but individually can never confirm a rule.

Supercooled dynamics of glass-forming liquids and polymers under hydrostatic pressure

Abstract: An intriguing problem in condensed matter physics is understanding the glass transition, in particular the dynamics in the equilibrium liquid close to vitrification Recent advances have been made by using hydrostatic pressure as an experimental variable These results are reviewed, with an emphasis in the insight provided into the mechanisms underlying the relaxation properties of glass-forming liquids and polymers

A new era for liquid crystal research: Applications of liquid crystals in soft matter nano-, bio- and microtechnology

Abstract: Liquid crystals constitute a fascinating class of soft condensed matter characterized by the counterintuitive combination of fluidity and long-range order. Today they are best known for their exceptionally successful application in flat panel displays, but they actually exhibit a plethora of unique and attractive properties that offer tremendous potential for fundamental science as well as innovative applications well beyond the realm of displays. Today this full breadth of the liquid crystalline state of matter is becoming increasingly recognized and numerous new and exciting lines of research are being opened up. We review this exciting development, focusing primarily on the physics aspects of the new research thrusts, in which liquid crystals – thermotropic as well as lyotropic – often meet other types of soft matter, such as polymers and colloidal nano- or microparticle dispersions. Because the field is of large interest also for researchers without a liquid crystal background we begin with a concise introduction to the liquid crystalline state of matter and the key concepts of the research field. We then discuss a selection of promising new directions, starting with liquid crystals for organic electronics, followed by nanotemplating and nanoparticle organization using liquid crystals, liquid crystal colloids (where the liquid crystal can constitute either the continuous phase or the disperse phase, as droplets or shells) and their potential in e.g. photonics and metamaterials, liquid crystal-functionalized polymer fibers, liquid crystal elastomer actuators, ending with a brief overview of activities focusing on liquid crystals in biology, food science and pharmacology.

Confinement effects on freezing and melting

Abstract: A review of experimental work on freezing and melting in confinement is presented. A range of systems, from metal oxide gels to porous glasses to novel nanoporous materials, is discussed. Features such as melting-point depression, hysteresis between freezing and melting, modifications to bulk solid structure and solid-solid transitions are reviewed for substances such as helium, organic fluids, water and metals. Recent work with well characterized assemblies of cylindrical pores like MCM-41 and graphitic microfibres with slit pores has suggested that the macroscopic picture of melting and freezing breaks down in pores of molecular dimensions. Applications of the surface force apparatus to the study of freezing and melting phenomena in confinement are discussed in some detail. This instrument is unique in allowing the study of conditions in a single pore, without the complications of pore blockage and connectivity effects. The results have confirmed the classical picture of melting-point depression in larger pores, and allowed the direct observation of capillary condensation of solid from vapour. Other results include the measurement of solvation forces across apparently fluid films below the bulk melting point and a solid-like response to shear of films above the bulk melting point. These somewhat contradictory findings highlight the difficulty of using bulk concepts to define the phase state of a substance confined to nanoscale pores.