Standard state of soil dispersions for rheological measurements.

The structural degradation of land is increasing all over the world; hence any effort to characterize it effectively is of great practical importance. By rheology we were able to compare the stability and resilience of structured soils containing the same clay minerals. The shear resistance of soil dispersions can be measured over a limited range of solid to water ratios. A precise methodology for theological characterization of soil dispersions which contain as much water as they can hold in equilibrium, introduced here as standard state, was developed within a European specific targeted research project (acronym: INDEX-GOCE-CT-2003-505450) to determine parameters indicating structural degradation of European soils. We also aimed to find a measuring method for non specialists to follow structural changes in soils. Based on the entire INDEX sample pool, it was shown that soils with particles smaller than 1 mm can be measured in a reproducible way. First the water content of dispersions in a standard state (WCSDinStS) containing the maximum occluded water had to be determined, which itself is a characteristic of soil quality. Then the method for preparation of dispersions was standardized at 25 + 0.1 degrees C and 1 bar, and the theological measurements were performed with a stress controlled rheometer using plate-to-plate and vane sensors. The flow character of all concentrated soil dispersions was viscoplastic and showed thixotropy, with two exceptions. Rheological parameters, i.e., initial stress, thixotropic hysteresis area, extrapolated (Bingham) yield value, plastic viscosity and absolute yield stress, of soil dispersions were determined. They changed in parallel, and were related to the particle adhesion, sensitivity to mechanical effects, and the strength of the physical network built up during the gradual aggregation of particles in soil dispersions. It was shown that the fragile networks of particles are thixotropic, so that external forces above the measurable limits destroy them, but they recover on standing for a longer time period. In the present paper, the development of a precise methodology for structural characterization of several clayey systems is described in detail showing only some examples from the thousands of rheological measurements, and in the end a useful comparison with field test measurements is shown

Competitive processes associated to the interaction of a cavitand derivative with caffeic acid

The interaction of caffeic acid and a newly synthesised cavitand derivative was investigated by UV– vis and fluorescence spectroscopy in tetrahydrofuran–water matrix. The temperature dependence of the equilibrium constants was determined first, then the thermodynamic parameters were calculated using the van’t Hoff equation. Absorption measurements highlighted entropy-controlled formation of cavitand–caffeic acid complexes with 1:2 stoichiometry. It was proved by fluorescence measurements that caffeic acid dimerisation is followed by the formation of cavitand–caffeic acid complexes with 1:2 stoichiometry. It was also shown that both the caffeic acid dimerisation and the formation of 1:2 complexes are controlled by the entropy gain. PL signal is preferred to use for analytical application in this particular case

The effect of temperature, pH, and ionic strength on color stability of red wine

The temperature and pH dependence of the color stability of a Hungarian red wine (Portugieser variety from Villány, Southern Transdanubia, Hungary) was investigated. Results show that both color intensity and pH were decreased by increasing temperature due to the dissociation of several phenolic OH groups. However, wine color intensity was increased upon addition of HCl even in the presence of additional potassium ions. This leads to the conclusion that added potassium ions change the pH dependence, while the addition of calcium ions resulted in moderated change on the pH dependence of color intensity. Comparing the color changes induced by the temperature or the pH highlights that the change in color intensity is a result of complex processes and its temperature dependence cannot be described solely as the decrease of pH at elevated temperatures

The Effect of the PVA/Chitosan/Citric Acid Ratio on the Hydrophilicity of Electrospun Nanofiber Meshes

In this study, scaffolds were prepared via an electrospinning method for application in oral cavities. The hydrophilicity of the fiber mesh is of paramount importance, as it promotes cell spreading; however, the most commonly used polyvinyl alcohol (PVA) and other hydrophilic fiber meshes immediately disintegrate in aqueous media. In contrast, the excessive hydrophobicity of the scaffolds already inhibits cells adhesion on the surface. Therefore, the hydrophilicity of the fiber meshes needed to be optimized. Scaffolds with different polyvinyl alcohol (PVA)/chitosan/citric acid ratios were prepared. The addition of chitosan and the heat initiated cross-linkage of the polymers via citric acid enhanced the scaffolds’ hydrophobicity. The optimization of this property could be followed by contact angle measurements, and the increased number of cross-linkages were also supported by IR spectroscopy results. The fibers’ physical parameters were monitored via low-vacuum scanning electron microscopy (SEM) and atomic force microscopy (AFM). As biocompatibility is essential for dental applications, Alamar Blue assay was used to prove that meshes do not have any negative effects on dental pulp stem cells. Our results showed that the optimization of the fiber nets was successful, as they will not disintegrate in intraoral cavities during dental applications

Degree of Conversion and BisGMA, TEGDMA, UDMA Elution from Flowable Bulk Fill Composites

The degree of conversion (DC) and the released bisphenol A diglycidyl ether dimethacrylate (BisGMA), triethylene glycol dimethacrylate (TEGDMA) and urethane dimethacrylate (UDMA) monomers of bulk-fill composites compared to that of conventional flowable ones were assessed using micro-Raman spectroscopy and high performance liquid chromatography (HPLC). Four millimeter-thick samples were prepared from SureFil SDR Flow (SDR), X-tra Base (XB), Filtek Bulk Fill (FBF) and two and four millimeter samples from Filtek Ultimate Flow (FUF). They were measured with micro-Raman spectroscopy to determine the DC% of the top and the bottom surfaces. The amount of released monomers in 75% ethanol extraction media was measured with HPLC. The differences between the top and bottom DC% were significant for each material. The mean DC values were in the following order for the bottom surfaces: SDR_4mm_20s > FUF_2mm_20s > XB_4mm_20s > FBF_4mm_20s > XB_4mm_10s > FBF_4mm_10s > FUF_4mm_20s. The highest rate in the amount of released BisGMA and TEGDMA was found from the 4 mm-thick conventional flowable FUF. Among bulk-fills, FBF showed a twenty times higher amount of eluted UDMA and twice more BisGMA; meanwhile, SDR released a significantly higher amount of TEGDMA. SDR bulk-fill showed significantly higher DC%; meanwhile XB, FBF did not reach the same level DC, as that of the 2 mm-thick conventional composite at the bottom surface. Conventional flowable composites showed a higher rate of monomer elution compared to the bulk-fills, except FBF, which showed a high amount of UDMA release