Amphiphilic fluorinated block-copolymer coating for the preparation of hydrophobic porous materials

A new approach to the preparation of hydrophobic porous polymers has been proposed. Three series of porous polymers which pores equally well-absorbed as water and organic liquids (benzene and iso-octane) were synthesized by visible light polymerization from compositions based on three different dimethacrylic esters with n-butanol. Three block copolymers based on N-vinylpyrrolidone and 2,2,3,3-tetrafluoropropyl methacrylate, differing in the length of the poly-(2,2,3,3-tetrafluoropropyl methacrylate) block, were synthesized for the purpose of hydrophobization of such porous polymers. A distinctive feature of synthesized block copolymers is that they are soluble only in methanol. It has been found that the treatment of porous polymers only with 2 wt.% of block copolymer methanol solution leads to a decrease water uptake by an order of magnitude, and the absorption of organic liquids does not change. In the course of the study it was possible to obtain a hydrophobic porous polymer sample that has water contact angle θ?=?121^° and a low value of the polar component of the surface Gibbs energy (\( {\gamma}_s^p=0.2 \) mJ·m^?2). The fundamental possibility of using such material for purification of organic liquids from water is shown.

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Hydrophobicity of Thin Films of Compounds of Low‐Electronegativity Metals

Hydrophobic materials capable of withstanding harsh conditions are required for various applications. Here, we show that oxides and nitrides of various low‐electronegativity metals are hydrophobic hard ceramics. We attribute their hydrophobicity to low Lewis acidity of the low‐electronegativity cations implying a low ability of the cations on the surface to form coordinate bonds with water oxygen anions. Furthermore, we observe a systematically stronger hydrophobic behavior of nitrides compared with the corresponding oxides, which we attribute to nitrogen being a poorer Lewis base than oxygen due to a reduced number of lone pairs of electrons, implying a lower ability of nitrogen anions on the surface to form hydrogen bonds with water hydrogen cations. Most of the oxides and nitrides investigated exhibit high values of hardness. Therefore, oxides and nitrides of low‐electronegativity metals should find application as hydrophobic materials in harsh conditions.     

Influence of temperature and permeate recovery on energy consumption of a reverse osmosis system

A model permits analysis of the influence of temperature on permeate recovery and energy consumption. The proposed model is based on the following assumptions: (1) membrane morphology is temperature-independent; (2) membrane rejection and other transport characteristics of membranes are position-independent; (3) specific water permeability of membranes was based on exponential dependence of viscosity vs. temperature; (4) temperature-dependence depembrane rejection is assumed to be linear. This allows for analyzing the influence of channel geometry, feed concentration, flow rate and temperature on permeate recovery and energy consumption. Calculated data are included. The solutionpresented can be segmented andbuilt into systems for comprehensive techno-economic evaluation of the RO-based process where temperature-dependence of process characteristics has to be considered.     

Dielectric study of side-chain liquid crystalline polyazomethine/fullerene C<Subscript>60</Subscript> nanocomposite

For side-chain liquid crystalline polyazomethine/fullerene C₆₀ nanocomposite (C₆₀ loading is 0.25 wt%), both real and imaginary components of the dielectric permittivity were investigated in wide regions of temperature and frequency. Analysis of frequency dependent permittivity allowed finding three relaxations (α, β ₁ and β ₂) in the nanocomposite. They were attributed to specific modes of molecular mobility. β-relaxations were described with the Arrhenius equation, whereas α-relaxation was described with the Vogel-Fulcher-Tammann equation. Anti-plasticization effect of the C₆₀ doping was shown to be manifested as an increase of the glass transition temperature of the nanocomposite as compared with that of the neat polymer.     

Complex Formation of Divalent Cations with Carboxylic Acid Resins as a Factor Determining Different Stationary States of Their Swelling

Three samples of carboxylic acid gel-type cross-linked polyelectrolytes were examined by registering the extent and kinetics of their volume change depending on the temperature, concentration, and nature of external electrolyte solutions, as well as the initial state (ionic form, water content) of the bead. It is found that in some systems the swelling of the bead (as a result of lowering the temperature) proceeds much more slowly than the preceding shrinking (as a result of the increase of temperature). Moreover, the initial volume of the bead is not restored, and a new stationary state of swelling is established. By means of optical dilatometry, it is found that in the systems in which the differences in the stationary states of swelling are found, the beads display plasto-elastic properties, whereas in the absence of such differences the beads show elastic properties. It is found that different stationary states of swelling are also established when the beads of copolymer of methacrylic acid cross-linked with divinylbenzene in Na⁺ form in the dry state and in the NaCl solution-swollen state are placed into a solution of a divalent cation salt. The difference in the stationary states of swelling reaches 12% in 4 N NiCl₂ solution. The substantial differences in the swelling behavior and viscoelastic properties of the resins in their Na⁺, Mg²⁺, Ca²⁺, and Ni²⁺ forms are interpreted in terms of formation of different kinds of complexes of functional groups of the polymer with Ca²⁺ and Ni²⁺ ions.     

Domain Wall Motion Across Various Grain Boundaries in Ferroelectric Thin Films

Domain wall movement at and near engineered 10°, 15°, and 24° tilt and 10° and 30° twist grain boundaries was measured by band excitation piezoresponse force microscopy for Pb(Zr,Ti)O₃ films with Zr/Ti ratio of 45/55 and 52/48. A minimum in nonlinear response was observed at the grain boundary for the highest angle twist and tilt grain boundaries, while a maximum in nonlinear response was observed at the 10° tilt grain boundaries. The observed nonlinear response was correlated with the domain configurations imaged in cross section by transmission electron microscopy.     

Thermomechanical surface instability at the origin of surface fissure patterns on heated circular MDF samples

When a flat sample of medium density fibreboard (MDF) is exposed to radiant heat in an inert atmosphere, primary crack patterns suddenly start to appear over the entire surface before pyrolysis and any charring occurs. Contrary to common belief that crack formation is due to drying and shrinkage, it was demonstrated for square samples that this results from thermomechanical instability. In the present paper, new experimental data are presented for circular samples of the same MDF material. The sample was exposed to radiant heating at 20 or 50 kW/m², and completely different crack patterns with independent eigenmodes were observed at the two heat fluxes. We show that the two patterns can be reproduced with a full 3‐D thermomechanical surface instability model of a hot layer adhered to an elastic colder foundation in an axisymmetric domain. Analytical and numerical solutions of a simplified 2‐D formulation of the same problem provide excellent qualitative agreement between observed and calculated patterns. Previous data for square samples, together with the results reported in the present paper for circular samples, confirm the validity of the model for qualitative predictions and indicate that further refinements can be made to improve its quantitative predictive capability.     

A limit load solution for a highly weld strength undermatched tensile panel with an arbitrary crack

A new plane strain upper bound solution for highly undermatched welded tensile panels with a crack is proposed. A distinguished feature of this solution is that the crack is arbitrarily located within the weld and its shape is also arbitrary, though some restrictions do apply. The latter are explained in detail such that the class of structures for which the solution is applicable is precisely specified. The solution is given in a very simple closed form.     

Modelling of pharmaceutical tablet swelling and dissolution using discrete element method

This work presents a novel use of the Discrete Element Method (DEM) combined with inter-particle mass transfer in order to simulate polymer swelling and dissolution. Each particle can absorb water and swell, pushing on its neighbours and causing an overall expansion. Once the disentanglement threshold is reached, the polymer dissolves and the particle reduces in size. This paper applies DEM to simulate the radial swelling and dissolution of cylindrical tablets. The method was validated against exact numerical solution of the same system to assess the accuracy of the DEM simulations for different DEM particle sizes. Parametric studies were done to assess the impact of physical parameters – namely the concentration-dependent diffusion coefficient of water through the polymer, the dissolution rate constant of the polymer and the disentanglement threshold of the polymer – on the radial expansion of the tablet. It was found that different settings of the concentration-dependent water diffusion coefficient function could produce similar radial expansion curves but with different internal concentration profiles. Increasing the dissolution rate constant or decreasing the disentanglement threshold of the polymer caused a reduction in the maximum radius of tablet. Lastly, ATR-FTIR spectroscopic imaging was used to obtain chemical images of a pure hydroxy-propyl methylcellulose (HPMC) tablet swelling and dissolving. The model was optimised to match both the HPMC tablet radius and the concentration profiles over time.     

SDP-based approximation of stabilising solutions for periodic matrix Riccati differential equations

Numerically finding stabilising feedback control laws for linear systems of periodic differential equations is a nontrivial task with no known reliable solutions. The most successful method requires solving matrix differential Riccati equations with periodic coefficients. All previously proposed techniques for solving such equations involve numerical integration of unstable differential equations and consequently fail whenever the period is too large or the coefficients vary too much. Here, a new method for numerical computation of stabilising solutions for matrix differential Riccati equations with periodic coefficients is proposed. Our approach does not involve numerical solution of any differential equations. The approximation for a stabilising solution is found in the form of a trigonometric polynomial, matrix coefficients of which are found solving a specially constructed finite-dimensional semidefinite programming (SDP) problem. This problem is obtained using maximality property of the stabilising solution of the Riccati equation for the associated Riccati inequality and sampling technique. Our previously published numerical comparisons with other methods shows that for a class of problems only this technique provides a working solution. Asymptotic convergence of the computed approximations to the stabilising solution is proved below under the assumption that certain combinations of the key parameters are sufficiently large. Although the rate of convergence is not analysed, it appeared to be exponential in our numerical studies.