Modelling the surface free energy parameters of polyurethane coats—part 2. Waterborne coats obtained from cationomer polyurethanes

Polyurethane cationomer coats were synthesised on the basis of typical diisocyanates, properly selected polyether polyols, HO-tertiary amines and HCOOH as quaternisation reagents. The values of their surface free energy (SFE) parameters were obtained by the van Oss-Good method, with the use of the contact angle values which had been found by the goniometric method. Based on the obtained findings, empirical models were developed which made it possible to anticipate the effects of the raw material types on the SFE values of the produced coats. The possibility was noted to adjust the SFE values within 25–50 mJ/m² by selecting carefully suitable parent substances. The principal consequences for the formation of improved hydrophobicity coats, applicable inter alia specialised protective coatings, were found to come not only from diisocyanate and polyol types but also from the alkylammonium cation structure which results from the use of different tertiary amines. The fundamental SFE lowering effect was noted when tertiary amines with 0–15 % of the 2,2,3,3-tetrafluoro-1,4-butanediol as a fluorinated chain extender was incorporated into polymer chains.     

Poly(HEMA-co-NBMI) Monolithic Cryogel Columns for IgG Adsorption

Supermacroporous poly(2-hydroxyethyl methacrylate-co-1,5-naphthalene bismaleimide) [poly(HEMA-co-NBMI)] monolithic cryogel column was prepared by free radical cryo-copolymerization of HEMA with NBMI as a hydrophobic functional comonomer and N,N′-methylene-bisacrylamide as cross-linker directly in a plastic syringe for adsorption of albumin. The monolithic cryogel contained a continuous polymeric matrix which has interconnected pores of 10–100 μm size. Poly(HEMA-co-NBMI) cryogel was characterized by swelling studies, FTIR and scanning electron microscopy. The equilibrium swelling degree of the poly(HEMA-co-NBMI) cryogel was 10.5 g of H₂O/g dry cryogel. Poly(HEMA-co-NBMI) cryogel was used in the adsorption/desorption of IgG from aqueous solutions. The maximum amount of IgG adsorption from aqueous solution in phosphate buffer was 98.20 mg/g polymer at pH 7.0. The nonspecific adsorption of IgG onto plain poly(HEMA) cryogel was very low (2.79 g/g polymer). It was observed that IgG could be repeatedly adsorbed and desorbed with the poly(HEMA-co-NBMI) cryogel without significant loss of adsorption capacity.     

Hypercube subgraphs with minimal detours

Define a minimal detour subgraph of the n-dimensional cube to be a spanning subgraph G of Q_n having the property that for vertices x, y of Q_n, distances are related by d_G(x, y) ≤ d_Qn(x, y) + 2. Let f(n) be the minimum number of edges of such a subgraph of Q_n. After preliminary work on distances in subgraphs of product graphs, we show that The subgraphs we construct to establish this bound have the property that the longest distances are the same as in Q_n, and thus the diameter does not increase. We establish a lower bound for f(n), show that vertices of high degree must be distributed throughout a minimal detour subgraph of Q_n, and end with conjectures and questions. © 1996 John Wiley & Sons, Inc.     

Evolution of Physicochemical Parameters during the Thermal-Based Production of Água-mel,a Traditional Portuguese Honey-Related Food Product

The purpose of this work was to investigate the physicochemical changes occurring during the thermal-based production of água-mel, a traditional Portuguese honey-related food product. The refractive index, color parameters (hue angle, H°; chroma, C*), and the content of total reducing sugars, glucose, fructose, total brown pigments, and 5-hydroxymethylfurfural were monitored along the entire production process, and their evolution was kinetically modelled. Thermal processing caused a gradual decrease in sugars, which was accompanied by the formation of brown pigments and 5-hydroxymethylfurfural, increased concentration of soluble solids as evaluated through refractive index measurements, as well as the appearance of darker colors. In particular, a zero-order kinetic model could explain the changes in H° and reducing sugars, while the evolution of refractive index, brown pigments, 5-hydroxymethylfurfural, C*, fructose, and glucose were best fitted using a first-order kinetics model.     

Enantioselective crossed intramolecular [2+2] photocycloaddition reactions mediated by a chiral chelating Lewis acid

In intramolecular [2+2] photocycloaddition reactions, the two tethered olefins can approach each other in a straight or in a crossed fashion. Despite the fact that the latter reaction mode leads to intriguing, otherwise inaccessible bridged skeletons, there has so far not been any enantioselective variants thereof. This study concerned the crossed [2+2]-photocycloaddition of 2-(alkenyloxy)cyclohex-2-enones to bridged cyclobutanes. It was found that the reaction could be performed with high enantioselectivity (80–94% ee) under visible light conditions when employing a chiral rhodium Lewis acid as a catalyst (2 mol%).

An enantioselective crossed [2+2] photocycloaddition is presented which proceeds under visible light irradiation in the presence of a chiral Lewis acidic metal complex. Chelation of two oxygen atoms to the metal centre accounts for the observed enantioface differentiation.     

Crystal Structure and Computational Study of 5-Ethyl-4-(4-Methoxyphenethyl)-4,5-Dihydro-3H-1,2,4-Triazol-3-One and 4-(4-Methoxyphenethyl)-5-Propyl-4,5-Dihydro-3H-1,2,4-Triazol-3-One

Crystallography Reports - Molecular structures of compounds 5-ethyl-4-(4-methoxyphenethyl)-4,5-dihydro-3H-1,2,4-triazol-3-one, (C13H17N3O2) (I) and...     

Crystal structure and computational studies of (E)-1-(benzo[b]thiophen-3-yl)-N-(4-ethoxyphenyl)methanimine

Crystallography Reports - The title compound, C17H15NOS, crystallizes in the orthorhombic sp. gr. Pca21. Two molecules in the asymmetric unit have similar structure. Crystal structure contains weak...     

Growth of hexagonal quantum dots under preferential evaporation

We perform numerical simulations of hexagonal quantum dots of AlGaN semiconductors. We show that the competition between surface mass diffusion and evaporation rules the morphology of the quantum dots. The system displays three different behaviors: presence of separated islands without a wetting layer, islands dissolving into the wetting layer, or islands that do not evolve. The first behavior is of special interest because its optoelectrical properties are significantly improved in comparison with quantum dots with a wetting layer.