Wetting between Cassie-Baxter and Wenzel regimes: a cellular model approach.

The cellular model with periodic boundary conditions was proposed for the study of liquid-solid interface properties of solid surfaces decorated by a regular pattern. The solid surface was represented by a mosaic of truncated pyramids of two different slopes of side walls equivalent to a surface covered with triangular grooves of different dihedral angles. On the basis of the computations performed for a single elementary cell, the components of the interfacial energies and the apparent contact angles have been found for different Young contact angles and different tilting angles of the pyramid walls. It was found that at certain sets of angles, the wetting takes place with the partial coverage of the pyramid sidewalls-in between the Cassie-Baxter and Wenzel regimes. The influence of the line tension on the studied surface wettability was also examined.

The Longitudinal Superdiffusive Motion of Block Copolymer in a Tight Nanopore.

The structure and dynamic properties of polymer chains in a confined environment were studied by means of the Monte Carlo method. The studied chains were represented by coarse-grained models and embedded into a simple 3D cubic lattice. The chains stood for two-block linear copolymers of different energy of bead-bead interactions. Their behavior was studied in a nanotube formed by four impenetrable surfaces. The long-time unidirectional motion of the chain in the tight nanopore was found to be correlated with the orientation of both parts of the copolymer along the length of the nanopore. A possible mechanism of the anomalous diffusion was proposed on the basis of thermodynamics of the system, more precisely on the free energy barrier of the swapping of positions of both parts of the chain and the impulse of temporary forces induced by variation of the chain conformation. The mean bead and the mass center autocorrelation functions were examined. While the former function behaves classically, the latter indicates the period of time of superdiffusive motion similar to the ballistic motion with the autocorrelation function scaling with the exponent t5/3. A distribution of periods of time of chain diffusion between swapping events was found and discussed. The influence of the nanotube width and the chain length on the polymer diffusivity was studied.

Elucidating the structure of the graphitic carbon nitride nanomaterials via X-ray photoelectron spectroscopy and X-ray powder diffraction techniques.

By using the most popular method of thermal condensation of dicyandiamide in a semi-closed system, graphitic carbon nitrides (gCNs) were synthesized at 500, 550, and 600 °C. The resulting materials were comprehensively analyzed via X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRD)techniques. We show that the use of routine analytical methods provides an insight into the structure of the carbon nitride materials. The analysis of geometric linear structures and fully condensed structure of polymeric carbon nitrides was performed and the ranges within which the contents of different nitrogen species (pyridine, amine, imine and quaternary nitrogen) can change were determined. This analysis, in combination with quantitative XPS studies, permits to state that the carbon nitride structure prepared by the thermal condensation of dicyandiamide is closer to the structure in which poly(aminoimino)heptazine subunits are linked into chains rather than the structure involving fully-condensed polyheptazine network. The XRD analysis proved that the 3D crystal structure of carbon nitride is described more correctly by the orthorhombic cell and space group P21212 applied to condensed chains of poly(aminoimino)heptazine (melon) and not by the hexagonal cell with the space group P6m2.

The capillary bistable switch constrained by pinning/wetting angles as a sensor of pressure.

A droplet deposited onto an orifice in the flat smooth plate can remain in a bistable state. Such system -a droplet and a flat surface- behaves as a bistable capillary switch, which can be used for threshold detection of some system's properties, e.g., the difference in the pressure on both sides of the plate. The droplet morphology changes abruptly at a certain value of the pressure difference and shows hysteresis. The specific behavior of the system is a result of the geometrical constraints defining the curvature of the liquid droplet at both sides of the surface. These constraints can be represented either by pinning angles at both sides of the plate or by the pinning angle at one side and the contact angle at the other. The dependence of details of the droplet morphology and energy on the difference in pressure at both sides of the plate is calculated by means of the semi-analytical model and Surface Evolver simulations.

Electrostatic/entropic macromolecule manipulation in nanochannel. Swapping of macromolecule locations.

Evolution of a polyion and an electrically uncharged macromolecule in confined environment, represented by a tight nanopore, induced by external electric field, is investigated. The motion of the uncharged macromolecule is forced by the polyion. In suitably selected conditions, the collision between macromolecules, compression of the uncharged macromolecule, and finally the swap of positions of macromolecules in the nanochannel are observed by means of the nonequilibrium Monte Carlo method on the lattice. The exemplary trajectories of macromolecules, their geometry, and energetics are analyzed. The dependence of the time of swapping on the number of macromolecule beads is described by scaling laws. Graphical abstract .

The interfacial energy in the Cassie-Baxter regime on the pyramid decorated solid surface.

The wettability of the solid surface covered with a pattern of pyramids is studied in categories of behavior of a single liquid droplet settled onto such a surface. The Cassie-Baxter regime of wetting is assumed. The cellular model of liquid-solid interface has been proposed. On the basis of the calculations for a single elemental cell with applied periodic boundary conditions, the components of the interfacial energy have been obtained. The dependence of the interfacial energy and hypothetical pseudo-contact angle on the hydrostatic pressure is discussed. The influence of the line tension on the wettability of the surface, expressed in terms of the apparent contact angle is shown.

Morphological Transitions of Droplets Wetting a Series of Triangular Grooves.

Morphology and thermodynamics of a microdroplet deposited on a grooved inhomogeneous surface with triangular cross section of the grooves were studied by computer simulations with the use of Surface Evolver program. With increasing volume of the droplet, it initially spreads along the series of grooves assuming the filament-like morphology. After reaching a certain volume, the surface wetted by the droplet is reduced and the droplet assumes the bulge morphology or spreads over the surface bordering on the groove initially occupied (it can be either a neighboring groove or a flat surface). The character of the process is determined by the geometry of the edge of the inhomogeneity studied. The effect described also depends on the number of grooves G and the Young contact angle θY. The change in the shape of the droplet becomes more pronounced with decreasing θY and G. Above a certain number of grooves, in the range of contact angles studied (e.g., G > 6 if θY = 70° and G > 4 if θY = 75°), no morphological transition of the droplet was observed.

Droplet on a regularly patterned solid. Wenzel's regime and meso-scale roughness.

The applicability of Wenzel's equation to describe a liquid droplet settled on the solid surface regularly patterned with rectangular prisms was examined by means of simulations of the droplet/surface system morphology and energetics. The droplet deposited on the meso-scale surface roughness (i.e. the droplet size was larger than the size of heterogeneities by about an order of magnitude) was considered. Several different approaches to the estimation of the contact angle were employed. The discrepancies between the results of simulated experimental measurements and the predictions based on the Wenzel equation were analyzed and discussed. The influence of three-phase contact line effects on the droplet morphology and the existence of metastable states was shown.

Monte Carlo simulations of a polymer chain conformation. The effectiveness of local moves algorithms and estimation of entropy.

A linear chain on a simple cubic lattice was simulated by the Metropolis Monte Carlo method using a combination of local and non-local chain modifications. Kink-jump, crankshaft, reptation and end-segment moves were used for local changes of the chain conformation, while for non-local chain rearrangements the "cut-and-paste" algorithm was employed. The statistics of local micromodifications was examined. An approximate method for estimating the conformational entropy of a polymer chain, based on the efficiency of the kink-jump motion respecting chain continuity and excluded volume constraints, was proposed. The method was tested by calculating the conformational entropy of the undisturbed chain, the chain under tension and in different solvent conditions (athermal, theta and poor) and also of the chain confined in a slit. The results of these test calculations are qualitatively consistent with expectations. Moreover, the obtained values of the conformational entropy of self avoiding chain with ends fixed over different separations, agree very well with the available literature data.

Conformational entropy of a polymer chain grafted to rough surfaces.

A polymer molecule (represented by a statistical chain) end-grafted to a topologically rough surface was studied by static MC simulations. A modified self-avoiding walk on a cubic lattice was used to model the polymer in an athermal solution. Different statistical models of surface roughness were applied. Conformational entropies of chains attached to uncorrelated Gaussian, Brownian, and fractional Brownian surfaces were calculated. Results were compared with the predictions of a simple analytical model of a macromolecule end-grafted to a fractal surface.

Polonium (²¹°Po), uranium (²³4U, ²³8U) isotopes and trace metals in mosses from Sobieszewo Island, northern Poland.

The activity of polonium (210)Po and uranium (234)U, (238)U radionuclides, as well as trace metals in mosses, collected from Sobieszewo Island area (northern Poland), were determined using the alpha spectrometry, AAS (atomic absorption spectrometry) and OES-ICP (atomic emission spectrometry with inductively coupled plasma). The concentrations of mercury (directly from the solid sample) were determined by the cold vapor technique of CV AAS. The obtained results revealed that the concentrations of (210)Po, (234)U, and (238)U in the two analyzed kinds of mosses: schrebers big red stem moss (Pleurozium schreberi) and broom moss (Dicranum scoparium) were similar. The higher polonium concentrations were found in broom moss (Dicranum scoparium), but uranium concentrations were relatively low for both species of analyzed mosses. Among the analyzed trace metals the highest concentration in mosses was recorded for iron, while the lowest for nickel, cadmium and mercury. The obtained studies showed that the sources of polonium and uranium isotopes, as well as trace metals in analyzed mosses are air city contaminations transported from Gdansk and from existing in the vicinity the phosphogypsum waste heap in Wislinka (near Gdansk).

Synthesis, structure and biological evaluation of novel bicyclic nitroimidazole derivatives.

A new series of 3-hydroxy-8-nitroimidazo[5,1-b]-1,4,5,6-tetrahydropyrimidine systems, being potential tuberculostatic agents, were synthesized. These products are close structural analogs of the basic structure of the known antitubercular bicyclic nitroimidazooxazine PA-824. The structures of the products obtained were confirmed by X-ray methods on the example of 3-hydroxy-8-nitro-1-phenylaminoimidazo[5,1-b]-1,4,5,6-tetrahydropyrimidine. Evaluation of these products for their anti-tuberculosis effects revealed interesting structure-activity relationships.