Dependence Of Specific Viscosity Research Articles

Rheological, Surface Tension and Conductivity Insights on the Electrospinnability of Poly(lactic-co-glycolic acid)-hyaluronic Acid Solutions and Their Correlations with the Nanofiber Morphological Characteristics.

In this study, solutions were prepared with fixed concentrations of hyaluronic acid (HA) but varied concentrations of poly (lactic-co-glycolic acid) (PLGA) to emphasize the effects of PLGA concentration and HA addition on solution properties and to further evaluate their electrospinning performance. The dependence of specific viscosity on PLGA concentration was studied to determine the concentration regimes and evaluate the critical concentration (Ce) for successful fiber generation. The Ce of PLGA solutions is 12.07% compared to 10.09% for PLGA-HA solutions. Blending with HA results in a lower concentration dependence and better consistency to the theoretical scaling mechanisms due to the additional topological constrains, which thus result in more chain entanglements. Solutions in semi-dilute entangled regimes show the crossover of complex moduli, verifying the stable and reliable entanglement network. Higher concentrations and HA addition both led to lower crossover frequencies and, thus, a longer relaxation time. The effects of a higher PLGA concentration and HA addition on the surface tension were not evident. However, the HA addition significantly improved the solution conductivity up to three times in the pure PLGA solutions due to its polyelectrolyte nature. Defect-free and uniform nanofibers were generated from 35% to 40% of the PLGA-HA solutions, yet fibers with bead-on-string structures were produced from all studied pure PLGA solutions. Such solution characteristics and parametric correlations can provide predictive insights on tailoring the morphological characteristics of nanofibers for specific applications.

Rheological properties of non-modified and n-alkyl surface-modified colloidal silica sols

Surface-modified silicas have been prepared from Aerosil 200 and various n-alkylchlorosilanes. The flow behavior of aqueous sols of these silicas was investigated as a function of n-alkyl chain length ( C) and surface coverage (θ) with the chemisorbed species, as well as the polarity of the continuum. Flow behavior and specific viscosity were found to be strongly dependent upon all three factors. Increasing C or θ produced changes from Newtonian to pseudoplastic flow at much lower volume fractions of dispersed phase than seen with nonmodified silica. The dependence of specific viscosity upon volume fraction was directly proportional to θ, although a somewhat different relationship to C was observed. The addition of propan-2-ol in general reduced the specific viscosity and changed the flow pseudoplastic to Newtonian. The sols with the longest chemisorbed chains showed, however, an increase in specific viscosity at low alkanol concentrations. These results were compared with those obtained for sols of nonmodified silica and are considered in terms of the silica/continuum interactions which control the extent to which the highly aggregated silica particles may be broken up during the dispersion process.

Purification and Properties of a Tropomyosin-containing Protein Fraction That Sensitizes Reconstituted Actomyosin to Calcium-binding Agents

Abstract A protein fraction that confers 1,2-bis-(2-dicarboxymethylaminoethoxy)ethane (EGTA) sensitivity on reconstituted actomyosin made with highly purified actin and myosin has been prepared from actin extracted from the acetone-dried muscle powder at 25–37°. This protein fraction had effects upon reconstituted actomyosin that, in the absence of Ca++-binding agents, resembled those of tropomyosin made by classical methods in that the Mg++-activated adenosine triphosphatase activity was inhibited during the clearing phase and enhanced after superprecipitation. Unlike tropomyosin made by classical methods, this protein fraction potentiated an inhibitory action of EGTA upon the Mg++-activated ATPase activity of reconstituted actomyosin. In the presence of Mg++ and the protein fraction, EGTA appeared to prevent activation of myosin ATPase by actin. The EGTA-sensitizing protein fraction, which sedimented as a single symmetrical peak in the ultracentrifuge, had a sedimentation coefficient of 2.66 S, a value similar to that of tropomyosin. The dependence of specific viscosity upon ionic strength was similar for both. However, the intrinsic viscosity of the protein fraction was less than that of tropomyosin, and amino acid analyses revealed several significant differences between the two. The relatively high contents of proline and phenylalanine found in the EGTA-sensitizing protein fraction indicate that a previously undescribed protein was present in addition to tropomyosin. It is possible that this additional protein material was responsible for sensitization of actomyosin to Ca++-binding agents, but the possibility remains that this action was produced by a native form of tropomyosin.