Effect of Confinement on Melting in Slit-Shaped Pores: Experimental and Simulation Study of Aniline in Activated Carbon Fibers
Effect of Confinement on Melting in Slit-Shaped Pores: Experimental and Simulation Study of Aniline in Activated Carbon Fibers
复制标题
狭缝状孔内约束对熔融的影响：活性炭纤维中苯胺的实验与模拟研究
DOI：
--
复制
发表时间：
2001
期刊：
影响因子：
--
通讯作者：
K. Gubbins
中科院分区：
文献类型：
--
作者：
M. Śliwińska;R. Radhakrishnan;K. Gubbins
摘要我们报道了对具有狭缝状孔的活性碳纤维中的苯胺熔融行为的实验和分子模拟研究。介电弛豫谱被用来测量在240-340K温度范围内的转变温度和介电弛豫时间。对于受限系统，观察到两个转变，一个在298K，第二个转变在324K。测量的驰豫时间表明，低温相(298K以下)是结晶或部分结晶的固相，而高于324K的相是类液体相；对于中间相，在298K-324K范围内，弛豫时间约为10−5s，这是典型的六方相。受限体系的熔化温度远高于体相苯胺的267K，用大正则蒙特卡罗方法结合Landau自由能计算进行了模拟，相变被定位为两个受限相的宏观自由能相等的状态点。这些相位的性质是通过分析面内对的位置和取向相关函数来确定的。模拟还显示了两个转变。第一个转变是在296K从二维六方晶体相转变为六方相，第二个转变是在336K从六方相转变为类液体相，狭缝状孔内的限制似乎稳定了六方相，与准二维薄膜相比，六方相在更宽的温度范围内是稳定的相。
Abstract We report both experimental and molecular simulation studies of the melting behavior of aniline confined within an activated carbon fiber having slit-shaped pores. Dielectric relaxation spectroscopy is used to determine the transition temperatures and also the dielectric relaxation times over the temperature range 240 to 340 K. For the confined system two transitions were observed, one at 298 K and a second transition at 324 K. The measured relaxation times indicate that the low temperature phase (below 298 K) is a crystalline or partially crystalline solid phase, while that above 324 K is a liquid-like phase; for the intermediate phase, in the range 298–324 K, the relaxation times are of the order 10−5s, which is typical of a hexatic phase. The melting temperature of the confined system is well above that of bulk aniline, which is 267 K. The simulations are carried out using the Grand Canonical Monte Carlo method together with Landau free energy calculations, and phase transitions are located as state points where the grand free energies of two confined phases are equal. The nature of these phases is determined by analysis of in-plane pair positional and orientational correlation functions. The simulations also show two transitions. The first is a transition from a two-dimensional hexagonal crystal phase to a hexatic phase at 296 K; the second transition is from the hexatic to a liquid-like phase at 336 K. Confinement within the slit-shaped pores appears to stabilize the hexatic phase, which is the stable phase over a wider temperature range than for quasi-two-dimensional thin films.