STUDIES ON ULTRASONIC ABSORPTION AND VISCO-RELAXATION OF POLY (ETHYLENE GLYCOL) AQUEOUS SOLUTIONS

Ultrasonic absorption and velocity measurements were made on aqueous solutions of poly (ethylene glycol)(PEG)of different molecular weights and concentrations, using a pulse sender-receiver ultrasonic generator, Measurements were obtained at a frequency of 2MHz. , and a temperature of 293 K. The results show a linear increase of the Values of velocity, density and viscosity with increase of molecu lar weight and concentration of PEG. On the contrary, the attenuation values decreased with increase of molecular weight and concentration of PEG. A mathematical equation correlating relaxation amplitude and molecular weight of the polymer is suggested. This was applied to calculate the molecular weights of unknown samples of PEG from their measured relaxation amplitude. The results obtained were in good agreement with those obtained from osmometry.     

固态Photo-CIDNP效应

光化学诱导动态核极化(photo-CIDNP)是一种在光照条件下由于产生非玻尔兹曼核自旋极化而使核磁共振(NMR)波谱信号强度发生明显变化的效应。这种效应在液体NMR中已为人所熟知,并通过经典的自由基对机理得到解释。固态photo-CIDNP效应发现的较晚,本文介绍了在光合反应中心及蓝光受体中发现的固态photo-CIDNP效应,详细阐述了固态photo-CIDNP效应产生的自由基对自旋动力学的机理,包括三旋混合(TSM)、衰变差异(DD)和弛豫差异(DR),重点介绍了类球红杆菌光合反应中心固态photo-CIDNP效应的磁场依赖性,这种场依赖性在同一分子中的不同核之间表现出明显的差异。本文综述了固态photo-CIDNP效应的现象、理论及其磁场依赖特性的最新进展。