Concurrent effect of microporosity and chemical structure on the equilibrium sorption properties of cellulose-based hydrogels

Polyelectrolite hydrogels are crosslinked polymers which display high sorption capacity in water and water solutions. They are widely used in the marked of personal hygiene products, as well as in other biomedical and industrial applications. In the most industrial application they are not biodegradable and prepared starting from acrylamide.In this work, the chemical-physical analysis of a novel class of natural polymers-based microporous superabsorbent hydrogels has been presented. The main focus is the definition of the relationship between material's chemical-physical structure and its equilibrium sorption properties.The effect of the variation of the degree of crosslinking, the polyelectrolyte nature of the backbone and the hydrogel microporosity on its swelling properties has been analysed, and a good agreement with the theoretical statements has been displayed.The effect of the ionic strength and the pH of the external solution in contact with the hydrogel on its equilibrium sorption properties has also been assessed, and an high sensitivity to these variations was detected for all the tested chemical compositions and physical structures.This work have to be considered part of the efforts towards the reduction of the environmental impact of the large scale consumption industrial polymer based products.     

Oxygen content of the fixative is important in the interpretation of the ultrastructure of ischaemic myocardium

Isolated rat hearts were subjected to 15, 45, or 60 minutes of global ischaemia and then fixed by perfusion at 37°C with glutaraldehyde containing various amounts of oxygen. This either had been bubbled with 100% oxygen (PO₂ 620 mm Hg) or with 100% nitrogen (PO₂ 40 mm Hg) immediately before use, or it had been routinely prepared and stored exposed to atmospheric oxygen (PO₂ 245 mm Hg). The ultrastructure of myocytes and endothelial cells subjected to 15 minutes of ischaemia was not affected by the treatment of the fixative. However, when the tissue subjected to longer periods of ischaemia was fixed with routinely prepared or oxygen-bubbled glutaraldehyde, ultrastructural changes characteristic of reoxygenation damage were uniformly evident in both the microvasculature and myocytes. These qualitatively distinct changes included mitochondrial swelling, cell swelling, endothelial bleb formation, and narrowing of capillary lumina. These abnormalities were not observed in tissue fixed with nitrogen-bubbled glutaraldehyde. These findings indicate that deliberate steps should be taken to reduce or eliminate dissolved oxygen from the fixatives used to study ischaemic tissues. Otherwise artefactual reoxygenation damage in vitro may occur and make valid ultrastructural interpretation difficult or impossible.     

Water uptake of water-borne paint resin films as studied by impedance spectroscopy and gravimetry

Impedance spectroscopy and gravimetry were employed to characterize alkyd-acrylate and styrene-acrylate water-borne resin film properties during wetting-through (i.e. during water uptake).     

Sorption of solvents in plastics and solvent desorption and retention

The experiments reported here have studied the following systems within the temperature range 25–50°C: sorption and desorption of solvents on LDPE, OPP, PS, rigid PVC, OPA, PETP and regenerated cellulose with methanol, ethanol, n-propanol, and ethyl acetate. With reference to these, the theory presented indicates the most important aspects related to the tests, refers to identification data on similar problems and enumerates the possibilities of interaction. The application of equation 1 and the reported measuring method allows the determination of diffusion coefficients within a vapour-saturated atmosphere system. As the gravimetric method also allows the determination of solubilities (α_L, the solubility coefficient), the permeation behaviour in the Fick range is calculable from The equation used by the author can be related to other equations from the technical literature, such as for the range Q_(t)Q∞>0.4, or where for the range <0.4 The agreement can be considered as good. The D values provide a calculation base within the scope of the outlined problem definition. The taste limits for solvents in water reveal which solvents could, as residual solvents, become critical. These values—connected with sorption/desorption identification values, evaporation numbers etc. —indicate where there is a risk and those cases where sufficient drying, or even the use of more adequate solvents is essential.     

PVA/UiO-66复合薄膜的制备及性能表征

采用溶剂热法合成出了金属有机骨架材料UiO-66,并通过流延法制备出了一系列PVA/UiO-66复合膜。通过红外光谱仪(FTIR)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)、接触角、溶胀度、拉伸强度和透光性等表征方法,详细研究了UiO-66含量对复合膜各种物性的影响。结果表明,PVA在经富马酸交联后,耐水溶胀性和拉伸性能都得到了显著改善。随着UiO-66负载量的提高,复合膜的溶胀度、拉伸强度和透光性能逐渐降低,而水接触角和甘油接触角逐渐增大。     

聚乙烯对油田加热集输工艺的适用性

为明确非金属复合管聚乙烯内衬在油田加热输送工艺的适用性,借助反应釜、扫描电镜研究4731B聚乙烯挂片在温度50℃、压力0.1、4、6 MPa、采出原油与采出水介质中168 h内的渗透行为。研究发现,采出原油、采出水均可渗透进入聚乙烯使其溶胀、增重,采出原油引起的增重率大于采出水,最大为4.52%;聚乙烯表面产生裂纹,介质沿裂纹局部渗透,最大渗透深度达166.7μm;介质渗透使聚乙烯力学性能降低;采出原油引起的溶胀随压力增大而减小,采出水引起的溶胀在压力4 MPa时最严重;光氧老化对聚乙烯力学性能的影响显著高于介质渗透。结果表明,加热输送条件下,聚乙烯耐油田介质性能虽满足ISO 23936-1-2009要求,但裂纹现象与高裂纹扩展速率易导致非金属复合管泄漏失效。     

PH敏感性水凝胶的分子热力学模型

本工作是在非离子凝胶的分子热力学模型基础，引入Ｄｏｎｎａｎ平衡项和大分子离子链的静电排斥项对凝胶自由能的贡献，建立了一个新的离子凝胶的分子热力学模型。该模型在解释离子凝胶的ＰＨ敏感性及其各种影响因素，以及预测ＰＨ溶胀曲线方面都取得了较好的效果。     

Moisture absorption into ultrathin hydrophilic polymer films on different substrate surfaces

Moisture absorption into ultrathin poly(vinyl pyrrolidone) (PVP) films with varying thickness was examined using X-ray reflectivity (XR) and quartz crystal microbalance (QCM) measurements. Two different surfaces were used for the substrate: a hydrophilic silicon oxide (SiO_x) and a hydrophobic hexamethyldisilazane (HMDS) treated silicon oxide surface. The total equilibrium moisture absorption (solubility) was insensitive to the surface treatment in the thickest films (≈150 nm). However, strong reductions in the equilibrium uptake with decreasing PVP film thickness were observed on the HMDS surfaces, while the SiO_x surface exhibited thickness independent equilibrium absorption. The decreased absorption with decreasing film thickness is attributed a depletion layer of water near the polymer/HMDS interface, arising from hydrophobic interactions between the surface and water. The diffusivity of water decreased when the film thickness was less than 60 nm, independent of the surface treatment. Changes in the properties of ultrathin polymer films occur even in plasticized films containing nearly 50% water.     

Unusual swelling behavior of polymer-clay nanocomposite hydrogels

The swelling behavior and the elastic properties of nanocomposite hydrogels have been investigated. The hydrogels were prepared by free-radical polymerization of the monomers acrylamide (AAm), N,N-dimethylacrylamide (DMA), and N-isopropylacrylamide (NIPA) in aqueous clay suspensions at 21 °C. Laponite with a radius of gyration in distilled water of 20 nm was used as clay particles in the hydrogel preparation. The reactions with AAm monomer were carried out in the presence of the chemical crosslinker N,N′-methylenebis(acrylamide) (BAAm). It was found that the volume of nanocomposite hydrogels immersed in water rapidly increases and attains a maximum value after about one day. Surprisingly, further increase in the swelling time results in the deswelling of the gels until they reach a limiting swelling ratio after about 5 days. This unusual swelling behavior is observable only when the clay concentration in the hydrogel is above the overlap threshold c^∗. Swelling measurements combined with the elasticity tests show that the effective crosslink density first decreases, but then increases with increasing time of swelling of the hydrogels. The results were explained in terms of the rearrangements of the highly entangled polymer chains and clay particles during the gel volume change.     

Errors associated with swelling in the analysis of polymer-solvent diffusion measurements

Sorption curves are generated from a mathematical model which includes the influence of the polymer swelling for unsteady-state sorption of a vapor or liquid by a polymer. To investigate the simultaneous effects of the specific volumes of the polymer-penetrant pair and the difference between the final and initial equilibrium concentrations on the sorption curves, statistical experimental design approach is used. Simulation results obtained from the numerical solution of model equations are utilized to estimate the error that would occur if one simply evaluates the diffusion coefficient using the traditional formulas derived from the analytical solution of the sorption equation. An empirical expression is developed that describes the effects of the difference between the final and initial equilibrium concentrations and the specific volumes of the polymer and the penetrant on the magnitude of error in diffusivity associated with the use of one of these traditional formulas so called the initial slope method. The predictive ability of the regression model is tested by performing additional simulations not used in the regression analysis.