【作者】 王子璐；

【导师】 何学浩；

【作者基本信息】 天津大学 ， 材料化学工程， 2013， 博士

【摘要】 高分子稀溶液体系的热力学和动力学性质与单链高分子结构的复杂性有密切的联系。本文利用计算机模拟方法研究单链体系的相行为受支化结构与序列结构的影响及其在非平衡体系下的输运过程，有助于加深对高分子单链体系性质的结构依赖性认识，扩展其在单分子功能材料以及纳米器件领域的应用。主要内容包括：1、研究了单链星型高分子的相转变随星型分子结构的变化规律。提出了采用形状因子来表征Liquid-Crystal（LC）和Coil-Globule（CG）这两个转变的方法。相比于比热曲线，该方法可以更加精确而有效地确定这两个转变。发现随着星型分子臂数的增加，LC转变温度的标度规律与线性高分子相比没有发生显著的变化，而CG转变逐渐向液固转变移动，其原因是由于单体密度的增大使得星型高分子在塌缩时需要更低的温度来使其吸引作用克服体积排除效应。2、研究了单链树枝型高分子的相转变随支化度的变化规律。研究发现不仅支化度对相转变过程中的两个转变温度有显著的影响，在支化度相同的情况下转变温度也受结构规整度的不同而发生着改变。随着支化度的增加，CG转变逐渐减弱最终无法观察到，而液固转变则逐渐向高温方向移动。其原因在于高支化度使得高分子不需要更低的温度即可得到致密的塌缩态。两种支化规整度不同的高分子，即完美树形高分子和随机超支化高分子，在支化度相同的情况下，前者具有更高的液固转变温度。这是因为规整的完美树形高分子具有更接近于完美晶体的结构，进而降低了结晶条件使得在更高的结晶温度下出现转变。3、研究了单链类蛋白质共聚物（Protein-like copolymer，PLC）在水环境中的塌缩结晶行为。利用HP和AB两种PLC模型研究了随着嵌段长度m变化的相转变机理。研究表明存在两种机理，即疏水聚集效应与相分离效应，共同支配着PLC的塌缩结晶过程。随着m的增加，HP-PLC的低能态构象从管形结构向蝌蚪结构演化，而AB-PLC则从多层结构向两个分开球变化。当m很小时，LC转变消失，而在m较大时，AB-PLC呈现出两个一级转变分别对应于两组分相分离转变和LC转变，而HP-PLC只呈现出一个一级相转变。在AB-PLC塌缩结晶过程中，存在一个核壳结构的中间态。4、研究了交变场下带电大分子在溶剂存在下的棘轮狭缝内的输运过程。带电大分子呈现出复杂的净移动行为，其不仅依赖于狭缝形状，还受到外电场和电荷分布的影响。特定的序列条件下发现了负向净移动现象。该负移动现象起源于构象相关的几个因素，即：熵棘轮效应，构象反转效应和耗散阻力效应。由于该负移动和序列结构与交变场频率有关，可以为设计新型纳米分离器件提供思路。更多还原

【Abstract】 The thermodynamics and kinetics properties of the dilute polymer solution arestrongly related with the structural complexity of a single polymer chain. We performa computer simulation to study the influence of phase behavior from the branchedstructure and the linear sequence of a single polymer chain as well as its transportprocess under nonequilibrium condition. It may provide a deeper understanding on thedependence of the structure on the property of a single polymer chain, which mayextend its application in single molecular functional material and the fabrication ofnano-scale devices. The research content of this thesis include:1. The phase transition behaviors of a single star polymer are studied. We proposeusing the shape factor to locate the Liquid-Crystal (LC) transition and Coil-Globule(CG) transition, which show a higher accuracy compared with the specific heatfunction. It is found that with the increase of the star arm, the scaling behavior of theLC transitions has no significant variation compared with linear polymers, however,the CG transitions shift toward the LC transition. The main reason for that is thelarger density of star polymer need a lower temperature for the attractive force toovercome the excluded volume effect.2. The phase transition behaviors of a single dendritic polymer are studied. It isfound that not only the DB acts great influence on the phase transition temperature,but the structural regularity can also change the transition behaviors. With the increaseof DB, the CG transition becomes weaker and finally disappears for highly branchedpolymer, and the LC transition temperatures shift toward higher direction. Two typesof dendritic polymer, i.e. a dendrimer and a hyperbranched polymer, with differentbranching regularity show different LC transition temperature, even they have thesame DB and the former one shows a higher temperature. A higher DB indicates thata lower temperature is no need for the polymer to collapse and to freeze due to itsdenser structure and a more regular structure further reduces the freezing conditionbecause the structure is already more close to a perfect crystal.3. The phase behaviors of a single Protein-like Copolymer (PLC) are studied. Usingtwo PLC models, i.e. HP and AB model, we studied the phase transition mechanismwith the variation of the block length m, It is found that two mechanism, i.e. hydrophobic aggregation effect and phase separation effect dominate the collapsingand freezing process of a single PLC chain. With the increase of m, the lowest energyconformations for HP-PLC evolve from a tube-like aggregation to a tadpole structure,while for AB-PLC, it changes from a multilayered structure to two separated spheres.When m is very small, the LC transition disappeared. When m is larger, AB-PLCsshow two first order transition corresponding to the phase separation transitionbetween the two components and LC transition, while, the HP-PLC only show onefirst order transition. During the freezing process of AB-PLC, a special intermediatestate with a core-shell structure, is found.4. The net mobility of a charged macromolecule in a ratchet slit with explicitsolvents under AC electric field is studied. It is found that, the chargedmacromolecule shows complex net mobility depending not only on the structure ofthe ratchet slit, but also on the external electric field and charge sequence. Purelynegative mobility is discovered for certain charge sequence condition. This negativemobility originates from many conformation related factors, i.e. the entropic ratcheteffect, the conformation inversion effect and the dissipative effect. Due to the relationbetween the mobility and charge sequence and the frequency of the AC electric field,these mechanisms can provide new way to design novel nano-scale separationdevices.更多还原