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In this work the formation of modulated structures in chiral liquid crystals is studied. For different chiral nematics that at low temperature form the usual (with twist in one direction) cholesteric phase, we found that at high temperature in the vicinity of the phase transition into isotropic liquid a universal sequence of structural transformations is observed. Planar cholesteric transforms at short helical pitch into the three-dimensional phases with cubic symmetry (Blue Phases), in two-dimensional structure at intermediate helical pitch and in one-dimensional structure in the plane of the sample at large pitch. The structures possess periodic orientational and translational order on scales much larger than molecular scale. Optical measurements were made on ordered structures obtained near the transition temperature to the isotropic phase. Possible reasons of formation of the structures are discussed on the basis of existing experimental data and theoretical considerations.

An Erratum to this paper has been published: https://doi.org/10.1134/S0021364022340045

A new mechanism of thinning of smectic nanofilms is discovered, differing from that previously described in experimental and theoretical works. The size and shape of a meniscus change at a temperature above the temperature of the Smectic-A–isotropic liquid bulk phase transition. Near the temperature of instability of nanofilms, the boundary of the meniscus penetrates deeper into a nanofilm and the thickness of the meniscus becomes about and smaller than the thickness of the nanofilm. A thinner region of the film that is formed in the meniscus near the boundary with the film induces the thinning of the entire nanofilm.

In this work we report on observations of new twisted (cholesteric-like) structures in liquid-crystalline dispersion particles with a hexagonal packing of double-stranded (ds) DNA molecules. Heating up to 80 °C of the DNA dispersion formed in a aqueous-salt solution with a high osmotic pressure (concentration) of poly(ethylene glycol) induces the formation of a new, optically active, spirally twisted structure of these molecules ("re-entrant" cholesteric structure (rest-A structure)). Cooling of this dispersion up to 22 °C is accompanied by the formation of an additional "re-entrant" cholesteric structure (rest-B). Modification of particles of the ds DNA dispersion (with rest-B structure) by replacing Na+ cations by multi-charged Gd3+ cations results in the third " re-entrant" structure (rest-C) despite a high density packing of ds nucleic acid molecules.

Time-dependent concentrations of n-mers P(n, t) have been found by numerically solving rate equations for a system containing a finite number N of monomers from 32 to 1024 at the initial point of time t = 0, where chain growth is limited, n ≤ N, and the total mass of the phases is conserved before and after the gel point. It has been shown that the property of dynamic self-similarity of clusters with different values of N suggests that Ps(n, N, t > T0) = P(n, N, T0) in the sol and Pg(n, N, t > T0) = P(n, N, T0) − Ps(n, N, t) in the gel. The increase in the gel mass is due to the polycondensation flux from the sol resulting in the formation of loose clusters followed by aging, when the gel transforms into a dense globule with an average length of 〈n〉 ~ N and a loose shell 〈n〉 ~ N1/2. The times of these transformations have been found.

In this paper, a simple example to illustrate what is basically known from the Gauss’ times interplay between geometry and mechanics in thin shells is presented. Specifically, the eigen-mode spectrum in spontaneously curved (i.e., up-down asymmetric) extensible polymerized or elastic membranes is studied. It is found that in the spontaneously curved crystalline membrane, the flexural mode is coupled to the acoustic longitudinal mode, even in the harmonic approximation. If the coupling (proportional to the membrane spontaneous curvature) is strong enough, the coupled modes dispersions acquire the imaginary part, i.e., effective damping. The damping is not related to the entropy production (dissipation); it comes from the redistribution of the energy between the modes. The curvature-induced mode coupling makes the flexural mode more rigid, and the acoustic mode becomes softer. As it concerns the transverse acoustical mode, it remains uncoupled in the harmonic approximation, keeping its standard dispersion law. We anticipate that the basic ideas inspiring this study can be applied to a large variety of interesting systems, ranging from still fashionable graphene films, both in the freely suspended and on a substrate states, to the not yet fully understood lipid membranes in the so-called gel and rippled phases.

A very important and influential idea of the so-called combined topological defects was proposed for the first time in cosmology (see, for example, the fundamental work [1]) to describe the emergence of various topological defects in the early stages of the evolution of the universe. This idea was later developed in detail theoretically and confirmed by sophisticated experiments in superfluid helium-3 carried out by a group of researchers from the Low Temperature Laboratory in Helsinki, the Kapitsa Institute for Physical Problems and the Landau Institute for Theoretical Physics, Russian Academy of Sciences. In the present publication, which is motivated precisely by these studies, the possibility of such combined defects is illustrated using a much less exotic example of liquid crystals.

Information about properties of liquid-crystalline dispersions of DNA molecules formed as a result of their phase exclusion is systematized. The influence of temperature and osmotic pressure on the structure of these dispersions has been elucidated in the framework of the concept of ‘quasinematic’ layers of orientationally ordered DNA molecules in dispersion particles. A new hexagonal → ‘re-entrant’ cholesteric packing phase transition of DNA molecules discovered by the authors is described, taking into account the generalized Lindemann criterion. The multiplicity of the ‘re-entrant’ phases and their structure are shown to depend on the characteristics of DNA and water-polymer solutions.

Reasons behind a higher photoelectric quantum yield in donor–acceptor organic solar cells (D-A--OSCs) than in one-component OSCs have been considered: (1) the appearance of an intense charge-transfer (CT) vibronic band in the absorption spectrum; (2) a change in the spectrum of CT states, in which the molecular exciton (ME) zone is located above the lowest charge-transfer state (LCTS); and (3) a longer lifetime of the LCTS as compared to the ME. Cause 1 makes it possible to select the optimal OCS absorption spectrum corresponding to the solar spectrum, and causes 2 and 3 eliminate the need for fast charge separation in the LCTS, for which the rate by ionization in the bulk heterojunction field is sufficient.

Polycondensation of bifunctional organosilicon monomers as a chain unbranched process includes initiation (hydrolysis of nonreactive end groups), propagation (sequential addition of monomers and bimolecular aggregation of n-mers), and termination (cyclization and entanglement of end groups in a nonreactive environment). Kinetic models of these steps with a minimum number of rate constants have been proposed. It has been shown that the chain propagation pathways involving different end groups are mixed and the competition of the chain growth and termination processes determines the molecular mass distribution of oligomers and their fractal packing in nanoscale aggregates.

In free-standing smectic films islands (regions of larger thickness than the film) can be considered as two-dimensional analogues of liquid droplets in a three-dimensional medium. The dynamics of droplet coalescence is an important but up to now incompletely solved problem in non-equilibrium mechanics. Here, we report on our investigations of island coalescence with the film meniscus. This phenomenon is analogous to the coalescence of a 3D droplet with a flat liquid surface. We found that the time evolution of island dimension is described by universal power-law dependencies for different stages of coalescence. Limited agreement with existing theory was found. In particular, in the final stage of coalescence the domain dynamics differs from theoretical predictions.

Chain transfer causes recurrence cycles—restoring the concentration of primary radicals in next generations and the subsequent repeated growth of macroradicals. The chain growth in the absence of chain transfer corresponds to movement along the chain-length coordinate of the first-generation wave packet, and packets with a time lag depending on the chain length of previously formed macroradicals appear in the recurrence cycles. The superposition of lagged packets is compared with the Loschmidt echo arising in quantum systems due to transitions between the initial state and the reservoir. A method is proposed for separating the concentrations of first-generation macroradicals and echoes, and the echo age (mean time lag) depending on the chain length has been found.

Small (but still containing many atoms) quantum systems (traditionally termed nano-systems) are dramatically different from their macroscopic or genuine microscopic (atomic) cousins. Microscopic molecular systems (with a few atoms) obey a regular quantum dynamics (described by time dependent Schrodinger equation), whereas in macroscopic systems with continuous energy spectra, one can expect, also regular, although typically relaxation, dynamic behavior. The topic of our paper is in-between these limits. System behavior becomes non-trivial and manifests a sort of transitions between regular and chaotic dynamics. We show that such dynamic transitions occur when the Loschmidt echo time of life exceeds the typical recurrence cycle period. We illustrate this behavior in the frame work of a few versions of the exactly solvable quantum problem, proposed long ago by Zwanzig. It is based on the study of time evolution of the initially prepared vibrational state coupled to a reservoir with dense spectrum of its vibrational states. In the simplest version of the Zwanzig model, the reservoir has an equidistant spectrum, and the system - reservoir coupling matrix elements are independent of the reservoir states. We generalize the model to include into consideration the coupling of the initially prepared single state to system phonon excitations. The coupling results to temperature dependent broadening and decay of the echo components. Another generalization is to replace a single level by two states coupled to the Zwanzig reservoir. We anticipate that the basic ideas inspiring our work can be applied to a large variety of interesting for the applications nano-systems (e.g., dissipative free propagation of excitations along molecular chains, or as a model for exchange reactions)., 46 pages, 9 figures

The idea proposed and implemented by Landau and Khalatnikov to describe the dispersion and absorption of sound in superfluid helium is applied to smectic liquid crystals. The order parameter Φ that describes the phase transition between an orthogonal smectic SmA and a tilted smectic SmC is a two-component complex scalar and in this sense resembles the order parameter of superfluid helium. The interaction of the sound waves propagating in a system with the order parameter Φ leads to a periodic modulation of the system’s physical characteristics and parameters (in particular, its temperature). However, the order parameter cannot follow the temperature oscillations induced by a sound wave due to the presence of spatial order parameter correlations (long-range ones near the phase transition). It is this delay that leads to a sound-frequency-dependent dynamic specific heat. In this paper, we calculate this dynamic specific heat for the SmA–SmC phase transition for the so-called de Vries smectics (SmdV), with a highly developed short-range order. In turn, we analyze the dependence of the dynamic specific heat on frequency and temperature and find the dispersion and absorption of sound near the SmdV–SmC phase transition.

In smectic nanofilms, the coalescence of islands (areas thicker than the smectic nanofilm) of different thicknesses and radial dimensions is studied. The initial stage of coalescence (fusion of islands) has a dislocation nature and is associated with changes in the energy of dislocation loops. The second stage of coalescence with the collapse of one of the islands occurs with the increase in the size of the other island. The estimates obtained show that the change in the energy of dislocation loops and the interaction of the surfaces of the smectic nanofilm play the decisive role at this stage. An unexpected effect of displacement of the center of mass of two islands in the process of their coalescence is also discovered. The effect is related to the collective dynamics of the material flows of the islands and the smectic nanofilm.

Numerical and analytical solutions of kinetic equations and the relevant equations for the moments of distribution of macroradicals and oligomers during radical chain polymerization are presented. It has been shown that the initial chain growth occurs in the ballistic mode involving first-generation primary radicals. The chain transfer in which a macroradical, reacting with a solvent, forms an oligomer and the primary radical of the next generation, causes a transition from the ballistic to the diffusion mode in which distributions of chains of different generations are mixed. Time-dependent distributions have been found for chain propagation and transfer rate constants independent of chain length.

The CD spectra of dispersion particles with the “re-entrant” packing of ds DNA have been compared to the CD spectra of particles with the cholesteric ordering of these molecules. The intercalation of daunomycin (DAU) between base pairs of DNA leads to an appearance of new additional band in the CD spectra. The linking of DNA in the single particles by (DAU-copper) nanobridges transforms the “liquid-like” structures of the both particles into the “rigid” state. These effects prove the existence of the cholesteric structure in “re-entrant” DNA phase.

A theoretical model is proposed that describes the experimentally observed phase diagram of colloidal dispersions of disk-shaped polydisperse particles. In the framework of the phenomenological theory of phase transitions, it is shown that if disk-shaped particles have polydispersity comparable in thickness and disk diameter, then the following sequence of phase transitions should be expected with increasing volume fraction of ϕ particles: an isotropic liquid (I); a nematic liquid crystal (N), in which the director n sets the preferred orientation of the disk normal; and the discotic (columnar) phase (C), in which the disklike molecules aggregate into liquid columns, and the latter form a two-dimensional hexagonal crystal consisting of liquid columns. However, when the particles forming the colloidal dispersion do not have any polydispersity in thickness (but the polydispersity in the particle diameter is preserved), another sequence of phase transitions takes place, in which the columnar phase is replaced by a smectic liquid crystal (S); that is, particles form a system of equidistant liquid layers. This work proposes and discusses the mechanisms of this behavior and new predictions that follow from this consideration.

The recent discovery of the ferroelectric nematic phase ${N}_{F}$ resurrects a question about the stability of the uniform ${N}_{F}$ state with respect to the formation of either a standard for the solid ferroelectric domain structure or for the often occurring liquid crystal space modulation of the polarization vector $\mathbf{P}$ (and naturally coupled to $\mathbf{P}$ nematic director $\mathbf{n}$). In this work, within Landau mean-field theory, we investigate the linear stability of the minimal model admitting the conventional paraelectric nematic $N$ and ${N}_{F}$ phases. Our minimal model (in addition to the standard terms of the expansion over the $\mathbf{P}$ and director gradients) includes the standard for liquid crystals, the director flexoelectric coupling term ($f$), and, often overlooked in the literature (although similar by its symmetry to the director flexoelectric coupling), the flexodipolar coupling ($\ensuremath{\beta}$). We find that in the easy-plane anisotropy case (when the configuration with $\mathbf{P}$ orthogonal to $\mathbf{n}$ is energetically favorable), the uniform ${N}_{F}$ state loses its stability with respect to one-dimensional (1D) or two-dimensional (2D) modulation. If $f\ensuremath{\ne}0$, the 2D modulation threshold (${\ensuremath{\beta}}_{c2}$ value) is always higher than its 1D counterpart value ${\ensuremath{\beta}}_{c1}$. There is no instability at all if one neglects the flexodipolar coupling ($\ensuremath{\beta}=0$). In the easy-axis case (when $\mathbf{n}$ prefers to align along $\mathbf{P}$), both instability (1D and 2D) thresholds are the same, and the instability can occur even at $\ensuremath{\beta}=0$. We speculate that the phases with 1D or 2D modulations can be identified as discussed in the literature [see M. P. Rosseto and J. V. Selinger, Phys. Rev. E 101, 052707 (2020)] for single-splay or double-splay nematics.

The dispersions were obtained as a result of phase exclusion of the DNA molecules from aqueous-salt-PEG-containing solutions. The CD spectra have shown cholesteric and hexagonal packing of the DNA in single dispersion particles at room temperature. The phase transition of the hexagonal → the “re-entrant” cholesteric packing of DNA takes place at elevated temperature. The texture of the “re-entrant” phase does not demonstrate attributes of DNA cholesteric phase. Alternative reasons of such discrepancy are discussed in the presented Letter.

It has been shown that in addition to the conventional mechanism of photovoltaic effect in organic solar cells (OSCs), which is the ionization of molecular excitons on impurities, a new mechanism is possible in nanoscale cells, namely, tunneling autoionization in a strong electric field of the pn junction. Its quantum yield for molecular excitons and charge-transfer excitons becomes higher than for ionization on impurities with a cell length of less than 20–25 or 60–80 lattice periods (~10 and ~25 nm), respectively. The possibility of creating cascades of series-connected OSCs with a quantum yield close to 1 on the basis of the new mechanism is discussed.

The eigenvalues and the eigenfunctions of molecular excitons, charge-transfer excitons, and electron–hole pairs have been found in the approximation of electron and hole transfer between the lowest unoccupied and highest occupied orbitals in a rigid molecular chain of identical photosensitive molecules, the recognized model of organic solar cells. It has been shown that as the Coulomb binding energy decreases, the wave functions become superposition of functions of the increasing number of sites and the decay time, determined by electron or hole transitions, is shorter that the transfer time of the exciton as a whole, so that energy transfer and charge transfer become interrelated processes.

The mechanisms of formation and coherent transport of free and bound electron excited states in organic solar cells are considered. In the model of a photocell (one-dimensional chain of photosensitive molecules in a uniform electric field of the p–n junction), the energy eigenvalues and the eigenfunctions of molecular excitons, charge-transfer excitons (CTE), and electron–hole pairs are determined. It is assumed that processes of transport between adjacent sites dominate in the case of the Coulomb interaction between the electron and the hole constituting a CTE. With decreasing Coulomb coupling energy, the CTE wavefunctions become superpositions of localized functions of the increasing number of sites. The decay time determined by independent transitions of the electron and the hole in this case becomes shorter than the transport time of the CTE as a whole. It is shown that autoionization of molecular excitons and small-radius CTEs in a strong electric field of a nanosize chain induces the mixing of states of these excitons as well as of electron–hole pairs, which substantially increases the quantum yield of the photoeffect.

In this paper we report on observations of unusual linear defects forming spontaneously in polar free-standing smectic-C* films near the temperatures of thinning transitions. At high temperature a periodic structure of defects becomes the ground state of the system. We found that the defects are characterized by continuous rotation of the molecular orientation with a change of the sense of the rotation across the defects. We develop a simple theoretical model that describes the observed behavior. The structure of the defects is governed by the competition between two-dimensional quadratic and linear orientational elasticity. The proposed model explains the origin of the linear defects, the periodic structure and their transformation with temperature and chirality of the liquid crystal.

The character of packing of double-stranded DNA molecules in particles of liquid-crystal dispersions formed as a result of the phase exclusion of DNA molecules from aqueous salt polyethylene glycol solutions has been estimated by comparing the circular dichroism (CD) spectra of these dispersions recorded at different osmotic pressures and temperatures. It is shown that the first cycle of heating of dispersion particles with hexagonally packed double-stranded DNA molecules leads to the occurrence of abnormal optical activity of these particles, which manifests itself in the form of a strong negative CD band, characteristic of DNA cholesterics. Moreover, subsequent cooling is accompanied by a further increase in the abnormal optical activity, which indicates the existence of the “hexagonal → cholesteric packing” phase transition, controlled by both the osmotic pressure of the solution and its temperature. The result obtained can be described in terms of “quasi-nematic” layers composed of orientationally ordered DNA molecules in the structure of dispersion particles. There are two possible ways of packing for these layers, which determine their hexagonal or cholesteric spatial structure. The second heating → cooling cycle confirms these results and is indicative of possible differences in the packing of double-stranded DNA molecules in the hexagonal phase, which depend on the osmotic pressure of the solution.

A macroscopic counterpart to the microscopic mechanism of the straightening dimer mesogens conformations, proposed recently by S.M. Saliti, M.G. Tamba, S.N. Sprunt, C. Welch, G.H. Mehl, A. Jakli, and J.T. Gleeson [Phys. Rev. Lett. 116, 217801 (2016)] to explain their experimental observation of the unprecedentedly large shift of the nematic–isotropic transition temperature is discussed. The proposed interpretation is based on singular longitudinal fluctuations of the nematic order parameter. Since these fluctuations are governed by the Goldstone director fluctuations, they exist only in the nematic state. External magnetic field suppresses the singular longitudinal fluctuations of the order parameter (similarly as is the case for the transverse director fluctuations, although with a different scaling over the magnetic field). The reduction of the fluctuations changes the equilibrium value of the magnitude of the order parameter in the nematic state. Therefore, it leads to additional (with respect to the mean field contribution) fluctuation shift of the nematic–isotropic transition temperature. Our mechanism works for any nematic liquid crystals, however the magnitude of the fluctuation shift increases with decrease in the Frank elastic moduli. Since some of these moduli supposed to be anomalously small for so-called bent-core or dimer nematic liquid crystals, just these liquid crystals are promising candidates for the observation of the predicted fluctuation shift of the phase transition temperature.

In this research, we observe and rationalize theoretically the transition from hexagonal to cholesteric packing of double-stranded (ds) DNA in dispersion particles. The samples were obtained by phase exclusion of linear ds DNA molecules from water-salt solutions of poly(ethylene glycol)—PEG—with concentrations ranging from 120 mg ml−1 to 300 mg ml−1. In the range of PEG concentrations from 120 mg ml−1 to 220 mg ml−1 at room temperature, we find ds DNA molecule packing, typical of classical cholesterics. The corresponding parameters for dispersion particles obtained at concentrations greater than 220 mg ml−1 indicate hexagonal packing of the ds DNA molecules. However, slightly counter-intuitively, the cholesteric-like packing reappears upon the heating of dispersions with hexagonal packing of ds DNA molecules. This transition occurs when the PEG concentration is larger than 220 mg ml−1. The obtained new cholesteric structure differs from the classical cholesterics observed in the PEG concentration range 120–220 mg ml−1 (hence, the term ‘re-entrant’). Our conclusions are based on the measurements of circular dichroism spectra, X-ray scattering curves and textures of liquid-crystalline phases. We propose a qualitative (similar to the Lindemann criterion for melting of conventional crystals) explanation of this phenomenon in terms of partial melting of so-called quasinematic layers formed by the DNA molecules. The quasinematic layers change their spatial orientation as a result of the competition between the osmotic pressure of the solvent (favoring dense, unidirectional alignment of ds DNA molecules) and twist Frank orientation energy of adjacent layers (favoring cholesteric-like molecular packing).

In this review, we compare the circular dichroism (CD) spectra of liquid-crystalline dispersion (LCD) particles formed in PEG-containing aqueous-salt solutions with the purpose of determining the packing of ds DNA molecules in these particles. Depending on the osmotic pressure of the solution, the phase exclusion of ds DNA molecules at room temperature results in the formation of LCD particles with the cholesteric or the hexagonal packing of molecules. The heating of dispersion particles with the hexagonal packing of the ds DNA molecules results in a new phase transition, accompanied by an appearance of a new optically active phase of ds DNA molecules. Our results are rationalized by way of a concept of orientationally ordered “quasinematic„ layers formed by ds DNA molecules, with a parallel alignment in the hexagonal structure. These layers can adopt a twisted configuration with a temperature increase; and as a result of this process, a new, helicoidal structure of dispersion particle is formed (termed as the “re-entrant„ cholesteric phase). To prove the cholesteric pattern of ds DNA molecules in this phase, the “liquid-like„ state of the dispersion particles was transformed into its “rigid„ counterpart.

We explain theoretical peculiarities of the smectic-A-hexatic-B equilibrium phase coexistence in a finite-temperature range recently observed experimentally in free-standing smectic films [I. A. Zaluzhnyy et al., Phys. Rev. E 98, 052703 (2018)2470-004510.1103/PhysRevE.98.052703]. We quantitatively describe this unexpected phenomenon within Landau phase transitions theory assuming that the film state is close to a tricritical point. We found that the surface hexatic order diminishes the phase coexistence range as the film thickness decreases, shrinking it to zero at some minimal film thickness L_{c}, of the order of a few hexatic correlation length. We established universal laws for the temperature width of the phase coexistence range in terms of the reduced variables. Our theory is in agreement with the existing experimental data.

The circular dichroism spectra of liquid-crystalline dispersions obtained by phase exclusion of linear double-stranded DNA molecules from aqueous saline solutions of polyethylene glycol (120 ≤ C PEG ≤ 300 mg/mL) have been investigated. The formation of liquid-crystalline dispersions at polyethylene glycol concentrations ranging from 120 to 200 mg/mL was accompanied by the emergence of an abnormal negative band in the spectrum of circular dichroism; this is indicative of cholesteric packing of the double stranded DNA molecules in the particles of the dispersion. Liquid-crystalline dispersions formed at PEG concentrations higher than 220 mg/mL and room temperature did not show any abnormal bands in the circular dichroism spectra; this is indicative of hexagonal packing of double-stranded DNA molecules in the particles of the dispersions. Heating of optically inactive liquid crystal dispersions induced a transition of the dispersions into a different state accompanied by the emergence of an abnormal negative band in the spectrum of circular dichroism. This transition is considered within the concept of the transformation of a hexagonal packing of DNA molecules into a cholesteric packing. A qualitative mechanism of such a transition is proposed that is formulated in the terms of the “quasinematic” layers of double-stranded DNA molecules that change their spatial orientation under the competing influences of the osmotic pressure of the solvent, orientational elasticity of the cholesteric packing, and thermal fluctuations.

Motivated by new experimental observations we generalize the Landau-like approach to include the direct phase transition between isotropic liquid ( I) and heliconical nematic liquid crystal ( NTB) structure. We show that depending on the Landau expansion coefficients, our model allows either direct I–NTB transition, or the sequence of the phases I–N–NTB with the classical nematic liquid crystal ( N) sandwiched between the isotropic liquid and heliconical nematic liquid crystal. Which of these two situations is realized depends on how strong is the first order phase transition from the isotropic liquid. If it is strong enough the system undergoes I–N–NTB sequence, and for the very weak first order phase transition I–NTB transformation occurs. Furthermore in the latter case the NTB structure can be biaxial heliconical nematic liquid crystal.

Physical review / E 98(5), 052703 (2018). doi:10.1103/PhysRevE.98.052703, Experimental and theoretical studies of a smectic-A–hexatic-B transition in freely suspended films of thickness 2 –10 $μm$ of the n-pentyl-4′−n-pentanoyloxy-biphenyl-4-carboxylate (54COOBC) compound are presented. X-ray investigations revealed a discontinuous first-order transition into the hexatic phase. The temperature region of two-phase coexistence near the phase transition point diminishes with decreasing film thickness. The width of this temperature region as a function of the film thickness was derived on the basis of a Landau mean-field theory in the vicinity of a tricritical point (TCP). Close to TCP the surface hexatic-B order penetrates anomalously deep into the film interior., Published by APS, Woodbury, NY

The answer to a question on the organization of molecules in a cholesteric phase is well enough proved in case of low molecular mass compounds. However, in case of double-stranded nucleic acids molecules the unequivocal answer to such question is a subject of discussions. In this work an attempt to generalize the well known literary data on the structure of the cholesteric phase formed by double-stranded DNA molecules was undertaken. Besides the experimental results of authors describing the packing of these molecules in the cholesteric liquid-crystalline dispersion particles are added to these data. Comparison of the results obtained offers the possibility to come out with an assumption of high probability of the existence of both the short-range positional and long-range orientational order in arrangement of double-stranded DNA molecules in a liquid-crystalline phase, and in the particles of dispersions of this phase generated under certain conditions. The occurrence of the orientational order, i.e. rotation of 'quasinematic' layers of double-stranded DNA molecules by a small angle, defines the formation of spatially twisted (cholesteric) structure with characteristic for it physical and chemical properties.

It has been shown that a meniscus of microinclusions in freely suspended smectic films can be significantly different from a meniscus near a flat surface. Measurements have been performed in smectic A films into which glycerol drops have been dispersed. The formation of the meniscus near a glycerol drop is accompanied by an increase in the size of the meniscus and by an increase in the corresponding material flow to the central part of the meniscus with the parallel dissolution of glycerol in the film. Structural instability associated with different curvatures of the surfaces of the meniscus of microinclusions, together with hydrodynamic instability associated with the motion of the material, can result in the transformation of particles with the meniscus to other structures.

Textures created by point topological defects in defects in polar smectic films have been studied. Such defects have been created by the dynamic method (substance from a very thin film does not have time to approach its edges and thicker islands with a topological defect are controllably formed). Topological defects have been studied in smectic islands with a thickness of six to eight molecular layers in a film with a thickness of two molecular layers. Competition between two-dimensional orientational elasticity in islands and the orientation of the director at the boundary of smectic islands results in different configurations of the field of the c-director created by a topological defect. A transition between configurations occurs at a change in the dimension of islands and depends on the dipole polarization of a liquid crystal. The comparison of the numerical calculations of the structure of topological defects with experimental data has allowed determining the dependence of the anisotropy of the two-dimensional orientational elasticity on the polarization of smectic films.

This review focuses on physicochemical and nanotechnological approaches to the design of 'rigid' particles based on double-stranded DNA molecules. The physicochemical methods imply cross-linking of adjacent DNA molecules ordered in quasinematic layers of liquid-crystalline dispersion particles by synthetic nanobridges consisting of alternating molecules of an antibiotic (daunomycin) and divalent copper ions, as well as cross-linking of these molecules as a result of their salting-out in quasinematic layers of liquid-crystalline dispersion particles under the action of lanthanide cations. The nanotechnological approach is based on the insertion of gold nanoparticles into the free space between double-stranded DNA molecules that form quasinematic layers of liquid-crystalline dispersion particles. This gives rise to extended clusters of gold nanoparticles and is accompanied by an enhancement of the interaction between the DNA molecules through gold nanoparticles and by a decrease in the solubility of dispersion particles. These approaches produce integrated 'rigid' DNA-containing spatial structures, which are incompatible with the initial aqueous polymeric solutions and have unique properties. The bibliography includes 116 references.

This paper explores a novel way of charge separation (autoionization) of molecular excitons, by quantum tunneling through a p-n nanojunction. This mechanism can dominate the standard one (i.e., when Frenkel exciton is ionized at donor or acceptor impurity sites) for very short, nanosized, p-n junction, where the junction electric field can be strong for relatively small (on the order of 1 V) voltage drop. Within a simple one-dimensional model for the depletion region of the p-n junction (donor and acceptor reservoirs connected by a short molecular wire) we compute the quantum yield Yb for the tunneling exciton autoionization in the “bulk” of the depletion region. For modern organic photosensitive materials with p-n junction size on the order of 10–20 nm, Yb could be close to 1. Such a high efficiency of the charge separation (one of the main factor entering figure of merit, indicating how good are photovoltaic conversion cells) makes this new mechanism potentially very perspective for the applications.

E M Lifshitz's theory of fluctuation molecular forces (Zh. Eksp. Teor. Fiz., Vol. 29, p. 94, 1955 [Sov. Phys. JETP, Vol. 2, 73, 1956]) and related problems are introduced from a historical perspective. Applications of the theory to soft matter physics are discussed, together with some new predictions (for example, the stability of smectic or cholesteric liquid crystal films).

In this paper we propose and explore a method of analysis of the scattering experimental data for uniform liquid-like systems. In our pragmatic approach we are not trying to introduce by hands an artificial small parameter to work out a perturbation theory with respect to the known results e.g., for hard spheres or sticky-hard spheres (all the more that in the agreement with the notorious Landau statement, there is no any physical small parameter for liquids). Instead of it guided by the experimental data we are solving the the Ornstein-Zernike equation with a trial (variational) form of the inter-particle interaction potential. To find all needed correlation functions this variational input is iterated numerically to satisfy the Ornstein-Zernike equation supplemented by a closure relation. We illustrate by a number of model and real experimental examples of the X-ray and neutron scattering data how the approach works., Comment: 9 pages, 5 figures

The present study is the application of a two-state model formerly developed by Bicout and Zaccai [ Bicout , D. J. and Zaccai , G. Biophys. J. 2001 , 80 ( 3 ), 1115 - 1123 ] to describe the dynamical transition exhibited in the atomic mean square displacements of biological samples in terms of dynamic and thermodynamic parameters. Data were obtained by elastic incoherent neutron scattering on 1,2-dimyristoyl-sn-glycero-3-phosphocholine lipid membranes in various hydration states and on one partially per-deuterated lipid membrane. Fitting the data with the model allowed investigating which parts of lipid molecules were mainly involved in the dynamical transition, heads, tails, or both. Clear differences were found between the fully protonated and partially deuterated membranes. These findings shed light on the question of what is the degree of dynamical cooperativity of the atoms during the transition. Whereas the level of hydration does not significantly affect it, as the dry, the intermediate dry, and fully hydrated membranes all undergo a rather broad transition, the transition of the lipid tails is much sharper and sets in at much lower temperature than that of the heads. Therefore, the dynamical cooperativity appears high among the particles in the tails. Moreover, the transition of the lipid tails has to be completed first before the one of the head groups starts.

Two different approaches to the creation of "rigid" (gel-like) DNA particles (or DNA nanoconstructions) are considered. The physicochemical approach is based on the formation of nanobridges between double-stranded DNA molecules ordered in quasinematic layers of cholesteric liquid-crystalline dispersion (CLCD) particles or their salting-out. This approach represents by itself a "chemical gelation" of DNA molecules realized inside the nanometric DNA particles. The formed "rigid" DNA particles have unique physicochemical properties. The nanotechnological approach is based on induction of "physical gelation" as a result of the formation of Au-clusters in the "free" space between double-stranded DNA molecules ordered in CLCD particles. This approach results in the formation of a new "rigid" DNA material. Its dis- tinctive peculiarity, in contrast to the chemically bonded "rigid" DNA particles, consists in a very weak binding affinity to the nuclear membrane filter used for atomic force microscopy. This opens up a possibility for easy manipulations with CLCD particles doped with gold nanoparticles.