表面活性剂在溶液中聚集形态的动力学模拟

用耗散颗粒动力学模拟方法(DPD)展示了表面活性剂分子在溶液中的聚集形态，用扩散程度表征了表面活性剂溶液中的自组装情况。结果发现：这种分子动力学模拟方法能够直观地得到表面活性剂的聚集形态；随着表面活性剂的浓度增加，聚集形态依次从球状胶束、棒状或虫状胶束，六角状相，向层状相变化。     

聚合物PVP与表面活性剂AOT相互作用的介观模拟

用耗散颗粒动力学模拟(DPD)方法研究了聚乙烯吡咯烷酮(PVP)与2-乙基己基琥珀酸酯磺酸钠(AOT)之间的相互作用.在三维模拟格子中,聚合物链均方末端距〈r²〉随着表面活性剂浓度的增加呈现一种首先减小,接着增加,然后又减小的趋势.构型和结构分析表明,AOT的加入能够引起聚合物链的二面角分布发生改变,这意味着AOT与PVP产生了相互作用.同时表面活性剂/聚合物体系的聚集形态也可以在DPD三维模拟格子中直观显现出来.     

介观模拟方法研究高分子表面活性剂在水介质中的聚集行为

高分子表面活性剂已广泛应用于许多领域, 其构型复杂、分子量大等特点使其聚集行为不同于小分子表面活性剂. 从微观上认识其聚集行为可为应用提供指导, 因而此方面的研究倍受关注. 计算机模拟技术的发展使我们能成功地在微观或介观水平上获得高分子表面活性剂聚集行为的信息. 本文综述了耗散粒子动力学(DPD)和介观动力学(MesoDyn)在高分子表面活性剂聚集行为研究中的应用. 着重介绍了这两种介观模拟方法研究单一高分子表面活性剂溶液的相行为及其与低分子表面活性剂之间的相互作用, 揭示了实验中难以观测的微观相分离及聚集体结构形态的变化规律. 这些信息可以为实验研究提供指导和补充.     

聚合物与表面活性剂相互作用的分子模拟研究进展

聚合物与表面活性剂复配体系已广泛应用于医药、生物、石油石化等领域。从微观上认识其相互作用机理对指导其生产实际有着重要作用,因而此方面的研究倍受关注。随着分子模拟技术的发展,聚合物与表面活性剂在分子水平上的相互作用机理研究已经被广泛开展,并获得了大量有用的信息。本文综述了耗散粒子动力学(DPD)和粗粒度分子动力学(CG-MD)在聚合物与表面活性剂相互作用方面的应用,分别对中性聚合物与离子型表面活性剂,以及带相反电荷的聚电解质和表面活性剂在溶液相和界面相的相互作用进行了阐述,并揭示了聚合物/表面活性剂聚集体结构形态的变化规律。     

计算机模拟技术在表面活性剂研究中的应用

根据表面活性剂溶液行为的模拟所需的时间和空间尺度,介绍了三种主要的计算机模拟方法:原子模拟、粗粒模拟和介观模拟.综述了这些模拟方法在表面活性剂单体、缔合体系及与聚合物相互作用等研究中的应用.指出了用计算机模拟方法研究表面活性剂体系的发展前景.     

新型疏水缔合聚合物P(AM/POEA)与表面活性剂的相互作用

采用粘度法、荧光探针和透射电镜研究了新型疏水缔合聚合物P(AM/POEA)和表面活性剂SDS和CTAB在水溶液中的相互作用. 聚合物P(AM/POEA)结构中, 疏水体(2-苯氧乙基丙烯酸酯)呈嵌段状无序地分布在聚丙烯酰胺主链上. 这类聚合物很容易和表面活性剂相互作用, 通过疏水缔合, 形成混合胶束状聚集体, 导致溶液粘度剧增. 随聚合物溶液中SDS的加入, 溶液粘度发生大幅度起伏变化, 出现最大值. 粘度最大值对应的表面活性剂浓度c_S,max位于表面活性剂CMC附近, 并发现它的位置不随聚合物微结构而变化. 然而它们缔合作用的增粘程度却与聚合物疏水体含量X_H及疏水嵌段尺寸N_H有关. 在实验浓度范围内, X_H和N_H愈大, 溶液的粘度越高. 此外用透射电镜直接观察到聚合物/表面活性剂体系中聚集体的交联结构形貌.     

环境刺激响应型表面活性剂*

表面活性剂在溶液中可通过自组装形成胶束、囊泡、液晶等多种有序结构。这些有序自组装结构在催化化学、材料制备、生物医药等领域有着重要而广泛的用途。控制和改变表面活性剂在溶液中的聚集方式对表面活性剂的应用具有重要的意义。近年来,通过对外界环境的调控来改变表面活性剂的物理化学性能如表面张力、聚集形式等研究已成为表面活性剂研究的一个新方向。本文以外界环境变化对表面活性剂在溶液中的聚集方式的影响为基础,介绍了可对环境刺激产生响应的表面活性剂的种类、结构、性能及研究进展,并总结了它们的结构与环境刺激响应性能之间的关系。     

水溶性聚电解质—表面活性剂复合物的聚集行为

聚电解质在溶液中与相反电荷的表面活性剂通过解电作用与疏水作用可形成聚电解质－表面活性剂复合物，依据反应条件生成的复事物可以是水溶性也可以是非水溶性的。水溶性的聚电解质－表面活性剂复合物由于有许多工业应用，因此近几十上来水溶性聚电解质－表面活性剂复合物的形成和结构已爱到人们的广泛重视。本文对水溶性聚电解质－表面活性剂复合物的聚集过程、聚集结构作了简要概述，此外对荧光光谱在这一领域的应用进行了重点介绍     

表面活性剂与高分子链混合体系的模拟

计算机模拟了高分子链对表面活性剂胶束形成过程的影响，以及高分子链构象性质随胶束化过程的变化.结果表明,当高分子链与表面活性剂之间的相互作用强度超过临界值后，高分子链的存在有利于表面活性剂胶束的形成.临界聚集浓度（CAC）与临界胶束浓度（CMC）的比值CAC/CMC随高分子链长的增大和相互吸引作用的增强而减小.在CAC之前，高分子链与表面活性剂分子只有动态的聚集；但在CAC之后，表面活性剂胶束随表面活性剂浓度X的增加而增大，并静态地吸附在高分子链上，形成表面活性剂/高分子聚集体.随着表面活性剂分子的加入，高分子链的均方末端距和平均非球形因子先保持恒定；从X略小于CAC开始， 和快速减小，至极小值后又逐渐增大.模拟结果支持高分子链包裹在胶束表面的实验模型.     

两亲无规聚合物的聚集行为及其与非离子表面活性剂的相互作用

以2-丙烯酰胺基-十二烷基磺酸(AMC12S)与2-丙烯酰胺基-2-甲基丙磺酸(AMPS)进行无规共聚,合成了含AMC12S摩尔分数(X)较高(X=0.1,0.3,0.5)的一系列两亲聚合物.采用稳态荧光及动态光散射技术对聚合物在水溶液中的聚集行为及其与三种非离子表面活性剂(HO(CH2CH2O)10C12H25(C12E10)、HO(CH2CH2O)20C12H25(C12E20)和HO(CH2CH2O)40C12H25(C12E40))的相互作用进行了研究,并考察了X对聚集行为的影响以及表面活性剂亲水基团长度对相互作用的影响.随着X的增大,聚合物的临界聚集浓度(CAC)明显减小,X=0.5时聚合物的CAC低达0.0039g·L-1.聚集体的流体力学半径(Rh)都大于26nm,并随着聚合物浓度的升高而增大,说明聚合物分子主要以分子间的聚集方式聚集,形成多分子聚集体.随X的增大,聚集体Rh减小,同时Rh随聚合物浓度升高而增大的幅度减小,说明聚集体结构变得更加紧实.表面活性剂与聚合物之间存在很强的相互作用,在混合溶液中表面活性剂浓度达到临界胶束浓度(CMC)左右时聚合物聚集体开始解离,形成混合聚集体.亲水基团长度增长,表面活性剂对聚合物聚集体的解离能力随之增强.C12E40与X=0.5的聚合物形成的混合聚集体Rh为6.8nm,与C12E40自身形成的聚集体尺寸相当.     

水溶液中嵌段共聚物的耗散颗粒动力学模拟

用耗散颗粒动力学(dissipative particle dyanmics)模拟方法研究了Pluronic L64(PL64)和Pluronic 25R4(25R4)三嵌段共聚物水溶液中的介观相分离,模拟了聚合物聚集的动力学变化过程. 结果发现,在水溶液中,不同浓度的聚合物溶液表现出不同的介观结构,如分散相、球形胶束、双连续相(bicontinuous)等；而Pluronic L64在低浓度时更容易形成双连续相. 耗散颗粒动力学模拟可以作为实验的一个辅助,提供介观层次上的信息,对实验起到指导作用.     

Mesoscopic simulation study on the interaction between polymer and C12NBr or C9phNBr in aqueous solution

The interaction of partially hydrolyzed polyacrylamide (HPAM) with dodecyl-oxypropyl-ß-hydroxyl trimethyl-ammonium bromide (C ₁₂NBr) and nonyl-phenyl-oxypropyl-ß-hydroxyl trimethyl-ammonium bromide (C ₉phNBr) in the solution was investigated by the Dissipative Particle Dynamics (DPD) method. The calculated interaction parameters between HPAM and C ₁₂NBr or C ₉phNBr showed that C ₁₂NBr is most likely to form polymer/surfactant complex with HPAM in contrast to C ₉phNBr. The experiment of binding isotherm was used to validate the DPD results via surfactant-selective electrode and equilibrium dialysis method. In DPD method, the mean square end-to-end distance 2> of polymer chain firstly increased, then reduced, and finally increased again. In addition, some polymer/surfactant complexes were also shown. One conclusion is that mesoscopic simulation can be considered as an adjunct to experiments and provide otherwise inaccessible (or not easily accessible) information in the experiment.     

Hydrodynamic interaction in polymer solutions simulated with dissipative particle dynamics

The authors analyzed extensively the dynamics of polymer chains in solutions simulated with dissipative particle dynamics (DPD), with a special focus on the potential influence of a low Schmidt number of a typical DPD fluid on the simulated polymer dynamics. It has been argued that a low Schmidt number in a DPD fluid can lead to underdevelopment of the hydrodynamic interaction in polymer solutions. The authors' analyses reveal that equilibrium polymer dynamics in dilute solution, under typical DPD simulation conditions, obey the Zimm [J. Chem. Phys. 24, 269 (1956)] model very well. With a further reduction in the Schmidt number, a deviation from the Zimm model to the Rouse model is observed. This implies that the hydrodynamic interaction between monomers is reasonably developed under typical conditions of a DPD simulation. Only when the Schmidt number is further reduced, the hydrodynamic interaction within the chains becomes underdeveloped. The screening of the hydrodynamic interaction and the excluded volume interaction as the polymer volume fraction is increased are well reproduced by the DPD simulations. The use of soft interaction between polymer beads and a low Schmidt number do not produce noticeable problems for the simulated dynamics at high concentrations, except for the entanglement effect which is not captured in the simulations.     

Phase behavior of lyotropic rigid-chain polymer liquid crystal studied by dissipative particle dynamics

The phase behavior of lyotropic rigid-chain liquid crystal polymer was studied by dissipative particle dynamics (DPD) with variations of the solution concentration and temperature. A chain of fused DPD particles was used to represent each mesogenic polymer backbone surrounded with the strongly interacted solvent molecules. The free solvent molecules were modeled as independent DPD particles, where each particle includes a lump of solvent molecules with the volume roughly equal to the solvated polymer segment. The simulation shows that smectic-B (S(B)), smectic-A (S(A)), nematic (N), and isotropic (I) phases exist within certain regions in the temperature and concentration parameter space. The temperature-dependent S(B)∕S(A), S(A)∕N, and N∕I phase transitions occur in the high concentration range. In the intermediate concentration range, the simulation shows coexistence of the anisotropic phases and isotropic phase, where the anisotropic phases can be the S(B), S(A), or N phases. Mole fraction and compositions of the coexisted phases are determined from the simulation, which indicates that concentration of rigid rods in isotropic phase increases as the temperature increases. By fitting the orientational distribution function of the systems, the biphasic coexistence is further confirmed. From the parameter α obtained for the simulation, the distribution of the rigid rods in the two coexistence phases is quantitatively evaluated. By using model and simulation methods developed in this work, the phase diagrams of the lyotropic rigid-chain polymer liquid crystal are obtained. Incorporating the solvent particles in the DPD simulation is critical to predict the phase coexistence and obtain the phase diagrams.     

部分水解的疏水改性聚丙烯酰胺分子构型与体相行为的关系

采用介观模拟耗散颗粒动力学(DPD)方法研究分子构型变化对聚电解质疏水改性聚丙烯酰胺(HMHPAM)在水溶液中的行为和性质的影响. 模拟中采用均方根末端距量化表征聚合物的伸展程度, 并通过计算溶液中水分子的扩散系数考察大分子形态和构型变化对体系粘度的影响, 探讨了聚合物的浓度、聚合方式、疏水改性比例及水解程度对聚合物溶液的影响机制, 预测了重复单元的种类和排列方式对聚合物构型和溶液性质的影响规律, 为HMHPAM聚合物的分子设计、合成及应用提供指导.     

高分子表面活性剂的分子设计

简要讨论高分子表面活性剂的俣成和表征方法，分析了在水溶液中两亲性聚合分子形态与表面活性的关系，单分子／多分子胶束多的形成是导致聚合物表面活性变差的主要因素，提出了高分子表面活性剂的分子设计原则，设计了多种在高分子量下将能够优质优良表面活性的高分子表面活性剂分子结构模型。     

Crystallization and aggregation behaviors of calcium carbonate in the presence of poly(vinylpyrrolidone) and sodium dodecyl sulfate

An anionic surfactant interacts strongly with a polymer molecule to form a self-assembled structure, due to the attractive force of the hydrophobic association and electrostatic repulsion. In this crystallization medium, the surfactant-stabilized inorganic particles adsorbed on the polymer chains, as well as the bridging effect of polymer molecules, controlled the aggregation behavior of colloidal particles. In this presentation, the spontaneous precipitation of calcium carbonate (CaCO3) was conducted from the aqueous systems containing a water-soluble polymer (poly(vinylpyrrolidone), PVP) and an anionic surfactant (sodium dodecyl sulfate, SDS). When the SDS concentrations were lower than the onset of interaction between PVP and SDS, the precipitated CaCO3 crystals were typically hexahedron-shaped calcite; the increasing SDS concentration caused the morphologies of CaCO3 aggregates to change from the flower-shaped calcite to hollow spherical calcite, then to solid spherical vaterite. These results indicate that the self-organized configurations of the polymer/surfactant supramolecules dominate the morphologies of CaCO3 aggregates, implying that this simple and versatile method expands the morphological investigation of the mineralization process.     

Dissipative particle dynamics simulations of polymersomes

A DPD model of PEO-based block copolymer vesicles in water is developed by introducing a new density based coarse graining and by using experimental data for interfacial tension. Simulated as a membrane patch, the DPD model is in excellent agreement with experimental data for both the area expansion modulus and the scaling of hydrophobic core thickness with molecular weight. Rupture simulations of polymer vesicles, or "polymersomes", are presented to illustrate the system sizes feasible with DPD. The results should provide guidance for theoretical derivations of scaling laws and also illustrate how spherical polymer vesicles might be studied in simulation.