Confinement of molecular liquids: Consequences on thermodynamic, static and dynamical properties of benzene and toluene
Confinement of molecular liquids: Consequences on thermodynamic, static and dynamical properties of benzene and toluene
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DOI：
10.1140/epje/i2003-10055-1
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发表时间：
2003-09-01
影响因子：
1.8
通讯作者：
Xia, Y
中科院分区：
文献类型：
--
作者：
Alba-Simionesco, C;Dosseh, G;Xia, Y
结合不同的实验方法（H-NMR，量热法，弹性和非弹性中子散射，数值模拟），我们将分子液体的动力学行为与热力学性质，热容和密度以及静态结构联系起来。在标准冷却条件下，限制大大减少或避免了结晶过程，而是在1000s时间尺度下观察到玻璃化转变温度T-g。当仔细应用“排除体积”修正时，受限制液体的孔隙平均局部结构不会受到明显影响，而是遵循由多孔基质的布拉格峰强度反映的密度变化。T-g的孔径依赖性主要受表面相互作用和有限尺寸效应两个因素的影响。对于最小的孔（小于或等于10sigma， sigma是分子的范德华半径），可以观察到T-g的增加和过渡区域的扩大，这与表面的相互作用有关，这种相互作用导致靠近壁的分子减速。中子散射实验和分子动力学模拟在较短的时间尺度和较高的温度下证实了这一点，这表明了冷冻分子的剩余部分。对于较大的孔径，考虑到约束条件下密度的减小，观察到T-g的减小。这可能与有限尺寸效应对假定协同长度的影响有关，协同长度通常被用来解释玻璃的形成。然而，无法定量确定这个长度（更不用说它的t依赖性），因为与墙本身的相互作用引入了额外的长度，从而增加了问题的复杂性。
We relate the dynamical behavior of molecular liquids confined in mesoscopic cylindrical pores to the thermodynamic properties, heat capacity and density and to the static structure by combining different experimental methods (H-NMR, calorimetry, elastic and inelastic neutron scattering, numerical simulations). The crystallization process is greatly reduced or avoided by confinement under standard cooling conditions, instead a glass transition temperature T-g at the 1000s time scale can be observed. The pore averaged local structure of the confined liquid is not noticeably affected when "excluded-volume" corrections are carefully applied, but follows the density changes reflected by the Bragg peak intensities of the porous matrices. The pore size dependence of T-g is dominated by two factors, surface interaction and finite-size effect. For the smallest pores (dless than or equal to10sigma, sigma being the van der Waals radius of a molecule), one observes an increase of T-g and a broadening of the transition region, related to the interaction with the surface that induces a slowing-down of the molecules close to the wall. This is confirmed by neutron scattering experiments and molecular-dynamics simulations at shorter time scales and higher temperatures, which indicate a remaining fraction of frozen molecules. For larger pore sizes, taking the decrease of density under confinement conditions into account, a decrease of T-g is observed. This could be related to finite-size effects onto the putative cooperativity length that is often invoked to explain glass formation. However, no quantitative determination of this length (not to mention its T-dependence) can be extracted, since the interaction with the wall itself introduces an additional length that adds to the complexity of the problem.