Gruener Simon, Huber Patrick
Faculty of Physics and Mechatronics Engineering, Saarland University, D-66041 Saarbrücken, Germany.
Phys Rev Lett. 2009 Oct 23;103(17):174501. doi: 10.1103/PhysRevLett.103.174501. Epub 2009 Oct 20.
Capillary filling dynamics of liquid n-tetracosane (n-C24H50) in a network of cylindrical pores with 7 and 10 nm mean diameter in monolithic silica glass (Vycor) exhibit an abrupt temperature-slope change at Ts = 54 degrees C, approximately 4 degrees C above bulk and approximately 16 degrees C, 8 degrees C, respectively, above pore freezing. It can be traced to a sudden inversion of the surface tension's T slope, and thus to a decrease in surface entropy at the advancing pore menisci, characteristic of the formation of a single solid monolayer of rectified molecules, known as surface freezing from macroscopic, quiescent tetracosane melts. The imbibition speeds, that are the squared prefactors of the observed square-root-of-time Lucas-Washburn invasion kinetics, indicate a conserved bulk fluidity and capillarity of the nanopore-confined liquid, if we assume a flat lying, sticky hydrocarbon backbone monolayer at the silica walls.
在整体石英玻璃（Vycor）中，平均直径为7纳米和10纳米的圆柱形孔隙网络内，液态正二十四烷（n-C₂₄H₅₀）的毛细管填充动力学在Ts = 54摄氏度时呈现出温度斜率的突然变化，该温度分别比体相温度高约4摄氏度，比孔隙冻结温度高约16摄氏度和8摄氏度。这可以追溯到表面张力的温度斜率突然反转，进而导致在前进的孔隙弯月面处表面熵降低，这是形成单层规整分子固体的特征，从宏观静止的十四烷熔体来看，这被称为表面冻结。如果我们假设在二氧化硅壁上存在平躺的粘性烃主链单层，那么作为观察到的时间平方根形式的卢卡斯-沃什伯恩侵入动力学的平方前置因子的吸液速度，表明纳米孔限制液体的体相流动性和毛细作用是守恒的。
