系列烷基芳基磺酸盐在水溶液中胶束化的焓-熵补偿现象

以表面张力法研究了系列烷基芳基磺酸盐在水溶液中胶束化的热力学性质,并考察了温度与分子结构对胶束化的影响.结果表明,烷基芳基磺酸盐在水溶液中胶束化是一个自发过程,主要来自熵驱动;随着温度升高,先有利于胶束化而后又不利于胶束化,且熵变对吉布斯自由能变的贡献有下降趋势,而焓变的贡献有增大趋势;胶束化存在焓-熵补偿现象,补偿温度Tc均在(306±2)K,基本不随烷基芳基磺酸盐的分子结构的改变而变化;随着芳环上短烷基链或长烷基链碳数的增加,胶束化能力和胶束的稳定性均提高,而随着芳环向长烷基链中间位置移动,胶束化能力和胶束的稳定性均下降.     

含Janus粒子组装体的构筑、调控及功能的模拟与理论分析

Janus粒子由于其表面性质与形状特征的不对称性而展现出独特的力学、光学、电学、磁学和表面两亲性能,在构筑复杂组装结构及设计新型功能材料方面有着广阔的应用前景.本文主要从计算机模拟与理论分析的角度,结合相关实验体系,系统地总结了目前对含Janus粒子组装体的体系构筑、结构调控及材料功能等的相关研究进展.从Janus粒子自组装结构的精确构筑与动态响应性、界面结构的熵驱调控、非平衡组装动力学及含Janus粒子组装体功能的模拟与预报等4个方面,详细阐述了Janus粒子的复杂多级组装结构及其背后蕴含的热力学与动力学的机理,并介绍了一系列基于含Janus粒子组装体的聚合物基复合材料独特的功能及其潜在应用.在此基础上,指出合理设计Janus粒子的非对称性质以及巧妙调控组装体内的熵、焓平衡,是控制其多级组装结构,进而开发相应新型功能材料的关键,并对Janus粒子未来的理论和模拟研究趋势进行了展望.     

Critical conditions of entropy-driving nucleation in binary colloidal system

In a binary colloidal hard-sphere system, due to the entropic depletion interactions, large spheres may be pushed to pack into clusters. If a cluster is taken as a new kind of component, then the binary colloidal system turns to be a ternary one and it therefore can be dealt in the framework of a multi-component system. It is known that, under certain conditions, a cluster can grow larger and larger and turn into a nucleation, even a kind of phase transition will take place. In this paper, the critical conditions, including the critical size of the nucleating cluster and the corresponding volume fraction of the colloidal system, were determined by analyzing entropy variation through the multi-component of Carnahan–Starling (CS) state equation and the principle of entropy maximum. The results obtained in this way are in good agreement with that of the experiments. In addition, the results also show that, when the critical volume fraction of the system increases from 0.18 to 0.19, the cluster’s density ?$?$ will change from 0.74 to 0.58. Except for the size ratio of large to small spheres, the critical size of the nucleating cluster is almost independent of its density and the volume fraction of the system.     

Thermodynamics of Molecular Chains with a Local Asymmetric Double-Well Potential

The thermodynamics of one dimensional chains with asymmetric double-well on-site potential is investigated. Pseudo-Schrödinger equation resulting from the transfer integral method is solved numerically and in terms of semiclassical approximation. This allows exact calculation and qualitative interpretation of the partition function, free energy and the specific heat function. The specific heat exhibits a characteristic hump similar to the one observed in the structures with a symmetric double-well potential. In some systems, another extremely narrow and extremely high, peak might be developed indicating an entropy driven phase transformation. Comparison between this highly simplified model and more practical approaches to the phenomena of photoinduced phase transformations is discussed underlying the possibility of manifestation of quantum effects in some (spin-crossover) systems.     

Entropy-driven reactions in living cells for assay let-7a microRNA

Imaging of microRNA (miRNA) in living cells could facilitate the monitoring of the expression and distribution of miRNA and research on miRNA-related diseases. Given the low expression levels and even down-regulation of cellular miRNA that is associated with some diseases, enzyme-free amplification strategies are imperative for intracellular miRNA assay. In this work, we report an entropy-driven reaction for amplification assay miRNA with a detection limit of 0.27 pM. The resulting signal amplification provides excellent recognition and signal enhancement of specific miRNAs in living cells. This method supplies accurate information regarding cellular miRNA-related biological events and provides a new tool for highly sensitive and simultaneous imaging of multiple low-level biomarkers, thereby improving the accuracy of early disease diagnosis.