The extensional rheology of polymer melts and dilute polymer solutions has been extensively examined through experiments and theoretical predictions. However, a systematic study of the extensional rheology of polymer solutions in the semidilute regime, in terms of examining the effects of concentration and molecular weight, has not been carried out so far. Previous experimental studies of the shear rheology of semidilute polymer solutions have demonstrated that their behaviour is distinctively different from that observed in the dilute and concentrated regimes. This difference in behaviour is anticipated to be even more pronounced in extensional flows, which play a critical role in a number of industrial contexts such as fiber spinning and ink-jet printing. In this work, the extensional rheology of linear, double-stranded DNA molecules, spanning an order of magnitude of molecular weights (25-289 kilobasepairs) and concentrations (0.03-0.3 mg/ml), has been investigated. DNA solutions are now used routinely as model polymeric systems due to their near-perfect monodispersity. Measurements have been carried out with a filament stretching rheometer since it is the most reliable method for obtaining an estimate of the elongational stress growth of a polymer solution. Transient and steady-state uniaxial extensional viscosities of DNA dissolved in a solvent under excess salt conditions, with a high concentration of sucrose in order to achieve a sufficiently high solvent viscosity, have been determined in the semidilute regime at room temperature. The dependence of the steady state uniaxial extensional viscosity on molecular weight, concentration and extension rate is measured with a view to determining if data collapse can be observed with an appropriate choice of variables. Steady state shear viscosity measurements suggest that sucrose-DNA interactions might play a role in determining the observed rheological behaviour of semidilute DNA solutions with sucrose as a component in the solvent.

中文翻译：

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半稀释DNA溶液的单轴拉伸粘度

聚合物熔体和稀聚合物溶液的拉伸流变学已通过实验和理论预测得到了广泛研究。但是，迄今为止，尚未通过系统研究浓度和分子量影响的半稀释状态的聚合物溶液的延伸流变学。先前对半稀释聚合物溶液的剪切流变学的实验研究表明，它们的行为与在稀溶液和浓溶液中观察到的行为截然不同。行为上的这种差异预计将在延伸流动中更加明显，延伸流动在许多工业环境（例如纤维纺丝和喷墨印刷）中起着至关重要的作用。在这项工作中，线性双链DNA分子的延伸流变学 已经研究了跨越分子量（25-289碱基对）和浓度（0.03-0.3 mg / ml）的数量级。由于DNA溶液具有近乎完美的单分散性，现在通常用作模型聚合物系统。由于它是获得聚合物溶液的伸长应力增长估计的最可靠的方法，因此已经用长丝拉伸流变仪进行了测量。已经在室温下的半稀溶液中确定了在过量盐条件下溶解于溶剂中的DNA的瞬态和稳态单轴延伸粘度，其中蔗糖的浓度高，以实现足够高的溶剂粘度。稳态单轴拉伸粘度对分子量的依赖性，浓度和延伸率，以确定是否数据倒塌可以提供变量的适当选择可以观察测定。稳态剪切粘度测量表明，蔗糖与DNA的相互作用可能在确定观察到的以蔗糖为溶剂的半稀释DNA溶液的流变行为中起作用。