Modification of Surface Properties of Colloidal Suspensions of NixOy-SiO2 Mixed Oxides with Different Ni Contents by the Adsorption Layers of Poly(Vinyl Alcohol)

Journal of Cluster Science - The adsorption and electrokinetic properties of hybrid silica materials composed of nickel and silicon oxides (NixOy-SiO2), characterized by different contents of...     

Vinyl Acetate Copolymers in Die Pressing of Alumina

The studies on the application of the emulsions of poly(vinyl acetate-co-allyl ether)s containing nonionic hydrophilic poly(oxyethylene) fragments as binders in the die pressing of alumina is presented. It was found that introduction of hydrophilic fragments into molecules of a typical water dispersible polymer led to better polymer affinity to the ceramic powders. It was also shown that low molecular mass of such copolymers should be relatively low ca 1500 g mol^–1 to increase the density and thickening uniformity of the samples before and after sintering. The resultant sinters indicated exceptionally high mechanical strength (bending strength ca 500 MPa). This revised version was published online in August 2006 with corrections to the Cover Date.     

Potentials of mean force for hydrophobic interactions between hydrocarbons in water solution: dependence on temperature,solute shape,and solute size

We carried out molecular dynamics (MD) simulations with the AMBER force field for four pairs of spherical dimers of different size (neopentane, bicyclooctane, adamantane, and fullerene‐C₆₀) using the TIP3P model of water as solvent. For comparison, we performed MD simulations for a linear molecule of n‐pentane at the same conditions. To assess the entropy contribution to the Gibbs free energy, MD simulations were run at three different temperatures of 273 K, 323 K, and 348 K, respectively, using umbrella‐sampling/the WHAM method. The stability of dimers is described by a potential of mean force (PMF). The shape of PMF curves for hydrophobic interactions is characteristic, and entails a contact minimum, a solvent‐separated minimum, and a desolvation maximum. The depth and position of the contact minimum for each pair change with the size of the nonpolar particle, and are consequently shifted to a larger distance for larger molecules. Additionally, the Lennard–Jones contribution to the PMF increases simultaneously with an increase in particle size. For a linear dimer, the contact minimum is shifted to a shorter distance than it is for spherical systems with the same number of carbon atoms. The contact minima on PMF curves increase with temperature, suggesting that the association entropy is positive. Dimensionless PMF curves showed a low dependency (near contact minima regions) on temperature, as the association entropy is low. Copyright © 2014 John Wiley & Sons, Ltd.     

Temperature effect on adsorption properties of silica-polyacrylic acid interface

The temperature influence (15–35 °C) on the adsorption mechanism and conformation of nonionic polymers (polyethylene glycol (PEG), polyethylene oxide (PEO) and polyvinyl alcohol (PVA)) on the zirconium dioxide surface was examined. The applied techniques (spectrophotometry, viscosimetry, potentiometric titration and microelectrophoresis) allowed characterization of the changes in structure and thickness of polymer adsorption layers with the increasing temperature. The rise of temperature favours more stretched conformation of polymer chains on the ZrO₂ surface, which results in higher adsorption and thicker adsorption layer. Moreover, these conformational changes of adsorbed macromolecules affect the electric (solid surface charge density) and electrokinetic (zeta potential) properties of the zirconia–polymer interface. The obtained data indicate that the polyvinyl alcohol adsorption has a greater influence on zirconia properties in comparison to that of PEG and PEO. It is due to the presence of acetate groups in the PVA macromolecules (degree of hydrolysis 97.5%), which undergo dissociation.     

Studies of temperature influence on adsorption behaviour of nonionic polymers at the zirconia–solution interface

The temperature influence (15–35 °C) on the adsorption mechanism and conformation of nonionic polymers (polyethylene glycol (PEG), polyethylene oxide (PEO) and polyvinyl alcohol (PVA)) on the zirconium dioxide surface was examined. The applied techniques (spectrophotometry, viscosimetry, potentiometric titration and microelectrophoresis) allowed characterization of the changes in structure and thickness of polymer adsorption layers with the increasing temperature. The rise of temperature favours more stretched conformation of polymer chains on the ZrO₂ surface, which results in higher adsorption and thicker adsorption layer. Moreover, these conformational changes of adsorbed macromolecules affect the electric (solid surface charge density) and electrokinetic (zeta potential) properties of the zirconia–polymer interface. The obtained data indicate that the polyvinyl alcohol adsorption has a greater influence on zirconia properties in comparison to that of PEG and PEO. It is due to the presence of acetate groups in the PVA macromolecules (degree of hydrolysis 97.5%), which undergo dissociation.     

Diagonalization in Double Frames

We consider structures of the form (Φ, Ψ, R), where Φ and Ψ are non-empty sets and R í Y×F{R\subseteq \Psi\times \Phi} is a relation whose domain is Ψ. In particular, by using a special kind of a diagonal argument, we prove that if Φ is a denumerable recursive set, Ψ is a denumerable r.e. set, and R is an r.e. relation, then there exists an infinite family of infinite recursive subsets of Φ which are not R-images of elements of Ψ. The proof is a very elementary one, without any reference even to e.g. the S_n^m{S_{n}^{m}}-theorem. Some consequences of the main result are also discussed.     

Reactions of Lithium Salts of Triphosphanes tBu2P–PLi–PtBu2 and tBu2P–PLi–P(NEt2)2 with Metal Complexes [(R3P)2MCl2] (M = Ni,Pd, Pt,R3P = Et3P,pTol3P,Ph2EtP,iPr3P)

tBu₂P–PLi–PtBu₂ · 2THF reacts with [(R₃P)₂MCl₂] (M = Pt, Pd, Ni; R₃P = Et₃P, pTol₃P, Ph₂EtP, iPr₃P) to yield isomers of [(1,2‐η‐tBu₂P=P–PtBu₂)M(PR₃)Cl], in which the tBu₂P–P–PtBu₂ ligand adopts the arrangement of a side‐on bonded 1,1‐di‐tert‐butyl‐2‐(di‐tert‐butylphosphanyl)diphosphenium cation. tBu₂P–PLi–P(NEt₂)₂ · 2THF reacts with [(R₃P)₂MCl₂] but does not form complexes with a tBu₂P–P–P(NEt₂)₂ moiety, however, splitting of a P–P(NEt₂)₂ bond of the parent triphosphane takes place.     

A Study of the Lipophilicity of Amide Derivatives of α-(1,2,3,4-Tetrahydroisoquinolin-2-yl)-γ-hydroxybutyric Acid by Use of RP-TLC and Calculation

JPC – Journal of Planar Chromatography – Modern TLC - Evaluation of the lipophilicity of derivatives of N-benzylamides and N-phenylethylamides of...