Akihiro Koike

Dynamic viscoelasticity of end-linking α,ω-dimethyl silyl poly(propylene oxide) solutions near the gel point

Dynamic viscoelasticity of α,ω-dimethyl silyl poly(propylene oxide) solutions was studied through the gelation process with end-linking. The gel point was determined as the reaction time, t = tc, at which the storage and the loss shear moduli, G′(ω) and G″(ω), respectively, both became proportional to ωn over the whole ω range measured, where ω is the angular frequency and n is a constant. Effects of polymer molecular weight M and concentration c on the steady-state viscosity η before the gel point and the equilibrium modulus Geq after the gel point were examined in terms of critical exponents, k and z, defined by power laws, η ∼ (t − tc|tc)−k ∼ e−k and Geq ∼ ez, respectively (e being the relative distance from the gel point). The three exponents n, k and z were found to take universal values of n = 0.66 ± 0.02, k = 1.0 ± 0.1 and z = 2.0 ± 0.1 irrespective of M and c for unentangled systems. In these systems, the reduced plot of Geq(e)G∞versus e gave a single composite curve in the range of 0.1 < e < 0.7, where G∞ was the modulus for the ideal network in which all functional groups reacted. The presence of entanglement coupling in the prepolymer solutions made the critical behaviour of η and Geq obscure and affected the exponent values. The results were briefly compared with theoretical predictions.

Structure and dynamics of ovalbumin gels: II. Gels induced by heat treatment at 80°C

Abstract Dynamic viscoelastic measurements were made on ovalbumin gels prepared by two different thermal denaturation methods for a study of their gel structures. Results are discussed in the light of the fractal concept developed for the critical gel structure of synthetic polymers at the sol–gel transition point. Especially, a role of added salt on association kinetics of denatured proteins as well as on the resulting gel structures are described in detail.

Structure and dynamics of ovalbumin gels: 1. Gel induced by high-temperature heat treatment

Abstract Dynamic viscoelastic (DVE) measurements are made on seven ovalbumin (OVA) gel samples induced by thermal denaturation of aqueous suspensions of OVA with OVA concentration C ranging from 12 to 45 wt% at 160°C for 5 min and subsequent moulding under pressure, and also on four OVA gels with higher C prepared by slow evaporation of water from the 45 wt% gel. The storage and loss shear moduli, G ′( ω ) and G ″( ω ), of OVA gels with C in the range of 30–59 wt% show angular frequency ω dependence characteristic of the critical gel with the fractal structure, i.e. G ′( ω ) ∼ G ″( ω ) ∼ ω ″ and tan δ = tan(nπ/2) over the whole ω range of 0.14–100 rad s −1 measured at three temperatures of 5.0, 25.0 and 45.0°C. This finding is confirmed by shear creep and creep recovery measurements as well as dynamic light scattering measurements on the same gels. The critical gel structure, however, is not formed either for gels with C C > 59 wt%.

Reentrant Atrial Tachycardia Originating from the Superior Vena Cava

A 52-years old man with a previous pericardiotomy for idiopathic constrictive pericarditis underwent catheter ablation for drug-resistant atrial tachycardia (AT). The mechanism of the AT was considered as reentry because of resetting response and the entrainment phenomenon during AT. We introduced a 64-electrode basket catheter into the superior vena cava (SVC) during AT to obtain precise mapping. A fractionated potential preceding local atrial electrogram was recorded in the SVC. The earliest activation site of the potential was located at the anterior aspect of the SVC, 2 cm above the SVC-right atrium junction determined fluoroscopically. The fractionated potential at this site preceded the onset of the P wave by 115 msec. Radiofrequency catheter ablation at this site eliminated the tachycardia. At 6 months follow-up, the patient is free of AT. Reentrant AT involving the SVC is a candidate of RF ablation. Multielectrode basket catheter is useful for a detailed mapping of the SVC.