Effect of pH on colloidal properties of native ovalbumin aqueous systems

The effect of pH on the molecular shape and dispersed state of native ovalbumin molecules in 20 mM phosphate and acetic acid buffer solutions has been studied using small-angle x-ray scattering (SAXS) and a rheological method The degree of association of the OA molecule at the 0.5% colloid system increases slightly with decreasing pH, i.e., 2.10 at pH 7.0, and 2.88 at pH 4.0, and the radius of the OA molecule decreases slightly with decreasing pH, i.e., 24.5 Å at pH 7.0, and 22.0 Å at pH 4.0.The OA colloid shows apparent yield stress and rigidity which are due to a certain ordered arrangement of the molecules. The yield stress and the rigidity increase abruptly at a pH value near to an isoelectric point (ca. pH 4.4). In the dilute system this increment is attributed to the change in the ordered arrangement or in the interparticle interaction, and not to the change in the association state of the OA molecules. The values of the yield stress and the rigidity remain almost constant over a wide concentration range and this feature (an auto-controlled mechanism) is kept over a certain range of pH.     

Morphology and mechanical properties of ultrahigh molecular weight polypropylene prepared by gelation/crystallization at various temperatures

Films of ultrahigh molecular weight (5.4×10⁶) polypropylene were produced by gelation/crystallization at various temperatures from dilute decalin solutions according to the method of Smith and Lemstra. The temperatures chosen were 20°, 30°, 50°, and 60°C. With increasing the temperature, the long period and crystallinity of the resultant gel film increased. By contrast, when the films were stretched up to 50 } 60 times, the increases in Young's modulus and crystallinity become more significant, as the temperature of the gelation/crystallization became lower. This interesting phenomenon is thought to be due to the dependence of the number of entanglements on the temperatures concerning gelation/crystallization and evaporation of solvent from the gel to form a film.     

Effect of plasticizer concentration on the hysteresis,tear strength and stress-relaxation characteristics of black-loaded rubber vulcanizate

The effect of plasticizer concentration on the stress softening, tear strength and stress relaxation of black loaded bromobutyl rubber vulcanizate has been investigated. The stress softening in the rubber vulcanizate, an energy dissipative process at higher strain, may be explained primarily by changes that take place in the rubber phase of the filled vulcanizate. Increased plasticizer concentration leads to decrease in the equilibrium hysteresis. A quantitative relationship between energy density and hysteresis has been derived, which is applicable at and below the elongation at break. Increase in plasticizer concentration results in decrease in the effective diameter of the tip of the tear, which in turn decreases the tear strength. Rate of relaxation decreases with increase in the plasticizer concentration in the carbon-black-filled vulcanizate.     

Dielectric relaxation in polymeric solids Part 1. A new model for the interpretation of the shape of the dielectric relaxation function

A model is proposed which explains the shape of the dielectric relaxation function at the glass transition of polymers. The model is based on the idea that the molecular mobility at the glass transition is controlled by intra- and intermolecular interaction. In addition, a specific model for the local chain dynamics in amorphous polymer systems is used. According to the scaling hypothesis of molecular dynamics the model relates the high frequency dependence of the dielectric loss curve to the local chain dynamics and the low frequency dependence to the intermolecular correlation.     

Dielectric relaxation in polymer solids Part 2: Application of the new model to polyurethane systems

Measurements of the complex permittivity of crosslinked polyurethanes at different temperatures in the frequency range 1–10⁵ Hz are discussed with respect to shape of relaxation curves. Using a new model (published in preceding paper) the shape parameters are related to small and large scale interaction.     

Effect of surface charge on adsorption of bovine serum albumin 2. Interaction of protein molecules with an anionic monolayer,as studied by ellipsometry,radiotracer and surface tension measurements

The adsorption of bovine serum albumin (BSA) onto an anionic monolayer of sodium docosylsulfate (SDocS) spread at the air/water interface was studied by ellipsometry. The adsorption behavior of BSA was estimated from the observed changes in phase differences and in the ratio of reflection coefficients. The dynamic process of BSA adsorption was measured after the injection of BSA solution into the aqueous substrate of SDocS monolayer. The gentle stirring of the substrate solution for 10 min was found to be enough to make the solution homogeneous without damaging the monolayer. The adsorption characteristics of BSA onto a negatively charged surface was compared with that onto a positively charged surface previously reported.The amount of adsorption depended on time and showed a maximum with an initial rapid rise, followed by gradual decrease toward the ultimate equilibrium value. The amount and time of the maximum adsorption depended on the concentration of BSA added to the aqueous substrate.Separate radiotracer measurement, using³⁵S-labeled SDocS monolayer, which is insoluble by itself, revealed that SDocS is solubilized into the bulk solution when BSA is added to the aqueous substrate.