Transition from fractional to classical Stokes-Einstein behaviour in simple fluids

An optical technique for tracking single particles has been used to evaluate the particle diameter at which diffusion transitions from molecular behaviour described by the fractional Stokes-Einstein relationship to particle behaviour described by the classical Stokes-Einstein relationship. The results confirm a prior prediction from molecular dynamic simulations that there is a particle size at which transition occurs and show it is inversely dependent on concentration and viscosity but independent of particle density. For concentrations in the range 510-3 to 510-6mg/mL and viscosities from 0.8 to 150 mPa s, the transition was found to occur in the diameter range 150 to 300nm.

本研究采用单粒子光学跟踪技术，测定了扩散行为从分数斯托克斯-爱因斯坦（fractional Stokes-Einstein）关系描述的分子扩散模式，转变为经典斯托克斯-爱因斯坦（classical Stokes-Einstein）关系描述的粒子扩散模式时的临界粒径。研究结果验证了分子动力学模拟（molecular dynamic simulations）此前提出的预测：存在发生该转变的临界粒径，且该临界粒径与溶液浓度、黏度呈负相关，而与粒子密度无关。当溶液浓度处于5×10^-3 至 5×10^-6 mg/mL区间、黏度范围为0.8至150 mPa·s时，该扩散行为转变发生的粒径区间为150至300 nm。