A2B嵌段共聚物熔体的相分离

采用自洽场的方法对A2B共聚物熔体作了类似星形共聚物的处理，研究了该共聚物的相分离并给出了相图．与两嵌段共聚物的相图相比较而言，在A2B的相图中，只发现了三个经典的有序相：球状相、六角蜂窝形柱状相以及层状相．从两嵌段线形共聚物到Y形共聚物这一链结构上的变化使相图也发生了相应的改变：各相的相边界发生了很大的偏移并且层状相出现的区域被大大的拓宽了．因此，可以通过改变链的结构来控制高分子自组装的微相结构，从而代替传统的改变高分子链中各组分的比例．     

受限壁的选择性对软受限下星形三嵌段共聚物形貌的影响

基于嵌段共聚物在软受限条件下能够自组装形成很多有序结构,在催化、电子器件、光学传感等领域有广泛的应用价值,目前只对线性三嵌段共聚物在软受限下的自组装形貌做了分析,对星形三嵌段共聚物在软受限下的自组装行为还未有一个统一的定论.在这项研究中,应用模拟退火来研究ABC星形三嵌段共聚物在软受限下的自组装行为,嵌段与溶剂没有选择性下(中性壁),通过调整三个嵌段(f_A、f_B和f_C)的体积分数来构建相图,我们的模拟预测了各种独特的自组装纳米结构,包括薄片+球形、圆柱状,穿孔层,薄片+圆柱体,核壳补丁.然后通过改变嵌段与溶剂的选择性预测了链长度比为1:x:1的共聚物粒子形貌.通过计算接触数、均方根末端距与平均链长的比值以及平均键长随x的变化,验证了形貌转变机制.     

Monte Carlo模拟亲水性对ABC三嵌段共聚物自组装行为的影响

采用Monte Carlo模拟方法研究了线性ABC三嵌段共聚物在B嵌段的选择性溶剂中的自组装行为。模拟结果表明,改变B嵌段的亲水性,体系可以自组装得到多种形貌各异的胶束。随着亲水性的减弱,胶束发生了从Janus球状多核胶束到多间隔胶束再到圆盘状多核胶束的转变。通过进一步分析胶束中聚合物的链构象等微观结构信息,我们发现随着亲水程度的减弱,聚合物链构象发生了从伸展状态到伸展、折叠状态并存,最终再到伸展状态的一系列转变。     

受限于纳米孔的星型ABC三嵌段共聚物自组装形成核-壳-柱状相

在不同条件、不同形状与尺寸孔隙下,星型ABC三嵌段共聚物自组装形成的核-壳-柱状相的相行为,纳米结构形成与小孔几何形状有关,不同表面势能对星型ABC三嵌段共聚物的自组装过程有影响.     

两嵌段共聚物软受限自组装行为研究

采用模拟退火算法,系统研究了软受限条件下两嵌段共聚物自组装形貌极其转化机理。共聚物形貌可受到受限程度,组分体积分数,以及溶剂选择性3方面因素的调制。在弱受限条件下,共聚物形貌均为球状呈各向同性。核-壳-笼形貌可以极大的增加组分A和组分B之间的接触粒子数,达到增熵降能的效果,在我们的研究工作中是一种罕见的构型。形成多核结构的条件是： AB复合链末端距与其链长比值小于0.23。此次工作对于纳米颗粒的实验制作以及药品输运方面具有极大的理论指导意义。     

不对称二聚物粒子在两嵌段共聚物形成的支撑膜上的自组装

结合自洽场理论和密度泛函理论,研究了不对称的二聚物粒子在AB两嵌段共聚物形成的支撑膜上的自组装行为. 不对称的二聚物粒子是由两个不同的球组成的两性分子. 其中一个球与A嵌段相亲,另外一个喜欢B嵌段. 不对称粒子能在支撑膜上形成一个双层结构. 由于衬底的存在,所形成的支撑膜上下两叶的对称性被破坏,导致了二聚物粒子在膜上形成的结构也变的不对称. 随着二聚物粒子浓度的增加,在膜上的二聚物粒子的结构将发生变化,从稀四方、六角、密四方再到圆柱结构. 在一个高浓度的密堆积下,二聚物粒子将形成弯曲的圆柱结构. 在支撑膜     

PSSS50-b-PNIPAM300嵌段共聚物在二元溶剂中自组装的NMR研究

本文结合核磁共振（NMR）、动态光散射（DLS）和透射电子显微镜（TEM）等表征方法,对自主合成的聚阴离子型温敏嵌段共聚物—聚（苯乙烯磺酸钠）-b-聚（N-异丙基丙烯酰胺）（PSSS₅₀-b-PNIPAM₃₀₀）在纯水、水/甲醇以及水/丙酮三种溶剂中的温度响应性和自组装行为进行了系统研究.结果发现PNIPAM链段在水/丙酮以及水/甲醇二元溶剂中的临界溶解温度（LCST）比在纯水溶液中略低,而在水/丙酮体系中的塌缩程度却明显低于纯水和水/甲醇体系.同时,PSSS₅₀-b-PNIPAM₃₀₀在不同溶剂体系中的聚集形貌也存在显著差异,表明加入有机溶剂小分子可以有效地调控温敏嵌段共聚物在水溶液中的自组装过程和聚集形貌.     

嵌段共聚物受限于软孔内的自组装

利用自洽场方法研究两嵌段共聚物受限于接枝均聚物链(聚合物刷)圆孔中的自组装相形貌.研究表明,当圆孔内径一定时,嵌段比f和聚合物刷C的体积分数φ_C是调控嵌段共聚物相形貌的主要因素,聚合物刷的弹性熵也起着重要作用.当f＝0.7时,在聚合物刷的浸润下,贴近刷表面处AB嵌段共聚物构成环层状结构,随着φ_C的减小这种结构会周而复始地出现.当f处于0. 关键词： 嵌段共聚物 圆孔受限 聚合物刷 自洽场     

芘在Pluronic两亲嵌段共聚物胶团中的增溶

用稳态荧光法研究芘在Ｐｌｕｒｏｎｉｃ两亲嵌段共聚物胶团水溶液中的增溶,结果表明共聚物分子中的ＰＰＯ实际含量越大,越有利于Ｐｙ的增容,加入无机盐ＫＣｌ导致生成了表面较少水化的较大胶团,并且由于ＫＣｌ解离产生的离子使溶剂极性增加,这些因素促进了Ｐｙ的增溶。     

PEO-PPO-PEO嵌段共聚物的NMR研究进展

PEO-PPO-PEO嵌段共聚物是重要的非离子型高分子表面活性剂,在药物载体和基因治疗等领域有着广阔的应用前景. 核磁共振(NMR)作为重要的研究手段,在研究PEO-PPO-PEO嵌段共聚物胶团及液晶结构形成,揭示嵌段共聚物与各种添加剂或药物分子的相互作用机理,有着独特的优势. 本文重点介绍了¹H、¹³C和²H NMR波谱以及NMR弛豫时间和自扩散NMR等技术在研究PEO-PPO-PEO嵌段共聚物体系中的应用. 简要介绍了NMR技术在PEO-PPO-PEO 嵌段共聚物聚集、调控以及作为药物载体等方面的研究现状.     

Macroscopic alignment of nanoparticle arrays in soft crystals of cubic and cylindrical polymer micelles

We describe a method to organize nanometer-sized hydrophilic particles into ordered arrays by templating them in the soft, micelle-crystal phases (spherical and cylindrical) of a thermoreversible block copolymer. Small-angle neutron scattering (SANS) with contrast variation is used to show that the dispersed particles (in this case, proteins or silica) form structured arrays by being constrained in the interstitial cavities between the polymer micelles in the ordered micelle crystal. Simple shear is used to macroscopically align both phases of the nanocomposites (micelles and particles) into macro-domains. The temperature-induced order-order transition between templates of spherical and cylindrical micelles is demonstrated as a reversible technique to modify the structure of the templated nanoparticle arrays.     

Diblock and triblock copolymer thin films on a substrate with controlled selectivity

Using self-consistent field theory (SCFT), morphology development in symmetric linear ABC triblock copolymer films on neutral and selective substrates has been studied, and it is compared with the triblock copolymer morphologies in bulk. In particular, the effects of the substrate preferable to B (interior) block on nanopattern formation of the copolymer films are of our central interest. Here, we report various nanopatterns with tunable square morphologies. The domain patterns are much more diverse than those parallel to the substrate with substrate selectivity for end-block or those vertical to the substrate without substrate selectivity. Furthermore, in order to figure out an economical and efficient way to fabricate useful passive pattern transfer layers, which have potential applications in microelectronic processes and ultrahigh density storage media, we propose a two-step strategy and scrutinize the conditions for generating square symmetries using cylinder-forming or lamella-forming AB diblock copolymers deposited on substrates created from ABC triblock copolymer films. It is found that a thinner film with weak incompatibility can produce square patterns.     

Janus Nanoparticle Emulsions as Chiral Nanoreactors for Enantiomerically Selective Ligand Exchange

Janus nanoparticles capped with a hydrophobic and hydrophilic hemisphere of mercapto ligands can self‐assemble into hollow, emulsion‐like nanostructures in controlled media. As the nanoparticle emulsions are chiroptically active exhibiting a plasmonic circular dichroism absorption in the visible range, they can be exploited as a unique chiral nanoreactor by selective encapsulation of d ‐enantiomer into the water phase of the water‐in‐oil emulsions for directional functionalization of the nanoparticles and endow the resulting nanoparticles with select chirality. This is demonstrated in the present study with gold Janus nanoparticles functionalized with (hydrophobic) hexanethiolates and (hydrophilic) 3‐mercapto‐1,2‐propandiol, and d ,l ‐cysteine is used as the molecular probe. Experimental results demonstrate that d ‐cysteine is the preferred enantiomers entrapped within the nanoparticle emulsions, where the ensuing ligand exchange reaction is initially confined to the hydrophilic face of the Janus nanoparticles. This suggests that with a deliberate control of the reaction time, chiral Janus nanoparticles can be readily prepared by ligand exchange reactions even with a racemic mixture of ligands.     

Binary-component micelle and vesicle: Free energy and asymmetric distributions of amphiphiles between monolayers of vesicle

The real-space two-dimensional self-consistent field theory (SCFT) is employed to study the free energies of micelles and vesicles constituted by binary amphiphilic diblock copolymer AB in homopolymer A. With increasing volume fraction of copolymer AB, there are morphological transitions from the circle micelles to oblate circle-like micelles, to compound structure with inverted micelles in the inner center and micelles outer layer, and to vesicles. Special attentions are paid to the role of the copolymer AB in controlling free energies of the micelles and vesicles, by examining the effect of length ratio of A/B with the fixed whole chain length of AB copolymer, the length effect of A or B block with the corresponding fixed length of B or A block, for one component of copolymer, and the effect of different amphiphile compositions for binary-component copolymer system. The quantity η is provided to describe the asymmetric density distribution of amphiphiles between the inner and outer monolayers of vesicles, and to quantify the relative asymmetric extent of the density distribution between two species of copolymers in binary component vesicles.     

Small angle neutron scattering study on the aggregation behaviour of PEO-PPO-PEO copolymers in the presence of a hydrophobic diol

Small angle neutron scattering (SANS) measurements on aqueous solutions of four polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymers (commercially known as Pluronic®)F88, P85, F127 and P123 in the presence of hydrophobic C14Diol (also known as Surfynol® 104) reveal information on micellization, micellar size and micellar transitions. While most hydrophilic F88 (with least PPO/PEO ratio) remained unimers in water at 30°C, other copolymers formed micellar solutions. Surfynol® 104 is sparingly soluble in water to only about ～0.1 wt%, but on addition to pluronic solution, it gets incorporated in the micellar region of block copolymer which leads to increase in aggregation number and transformation of spherical to ellipsoidal micelles. The added diol-induced micellization in F88, though hydrophilic copolymers F88 and F127 did not show any appreciable micellar growth or shape changes as observed for P85 and P123 (which are comparatively more hydrophobic). The SANS results on copolymer pairs with same molecular weight PPO but different % PEO (viz. F88 and P85, F127 and P123) and with same molecular weight PEO but different PPO (F88 and F127) reveal that the copolymer with large PPO/PEO ratio facilitate micellar transition in the presence of diol. An increase in temperature and presence of added electrolyte (sodium chloride) in the solution further enhances these effects. The micellar parameters for these systems were found out using available software and are reported.     

Block copolymer morphologies confined by square-shaped particle:Hard and soft confinement

The self-assembly of diblock copolymers confined around one square-shaped particle is studied systematically within two-dimensional self-consistent field theory(SCFT).In this model,we assume that the thin block copolymer film is confined in the vicinity of a square-shaped particle by a homopolymer melt,which is equivalent to the poor solvents.Multiple sequences of square-shaped particle-induced copolymer aggregates with different shapes and self-assembled internal morphologies are predicted as functions of the particle size,the structural portion of the copolymer,and the volume fraction of the copolymer.A rich variety of aggregates are found with complex internal self-assembled morphologies including complex structures of the vesicle,with one or several inverted micelle surrounded by the outer monolayer with the particle confined in the core.These results demonstrate that the assemblies of diblock copolymers formed around the square-shaped particle in poor solvents are of immediate interest to the assembly of copolymer and the morphology of biomembrane in the confined environment,as well as to the transitions of vesicles to micelles.     

Aggregation processes in micellar solutions: a Raman study

Ionic surfactants such as sodium dodecyl sulfate (SDS) belong to the amphiphile family: they possess a long hydrophobic hydrocarbon chain and a polar hydrophilic headgroup. In a polar solvent and over the critical micellar concentration these molecules join to form micelles. The micellar solutions, in turn, if doped with various ligands tend to aggregate. Solid SDS, micelles of SDS in water and micelles of SDS doped with two types of macrocyclic ligands, Kryptofix 2.2.2 (K222) and crown ether 18‐Crown‐6 (18C6), at different concentrations are studied by Raman scattering, that represents a new approach to such systems. The experimental Raman spectrum, obtained on crystalline powders of SDS, is compared with the ab initio computed spectrum in order to assign the vibrational bands. After discriminating sensitive peaks by comparing the crystalline powders of the single components and their water solutions, the aggregation process and the action of the ligands are analyzed following the evolution of the intensity and wavenumber of these characteristic Raman peaks. This shows that Raman spectroscopy is sensitive to the aggregation dynamics and to the effects induced by the hydration layer on the molecules in solutions. A saturation effect in the aggregation process with the increase of the ligand concentration is observed. Copyright © 2012 John Wiley & Sons, Ltd.     

Diffusion-Limited Aggregation with Polygon Particles

Diffusion-limited aggregation (DLA) assumes that particles perform pure random walk at a finite temperature and aggregate when they come close enough and stick together. Although it is well known that DLA in two dimensions results in a ramified fractal structure, how the particle shape influences the formed morphology is still unclear. In this work, we perform the off-lattice two-dimensional DLA simulations with different particle shapes of triangle, quadrangle, pentagon, hexagon, and octagon, respectively, and compare with the results for circular particles. Our results indicate that different particle shapes only change the local structure, but have no effects on the global structure of the formed fractal cluster. The local compactness decreases as the number of polygon edges increases.     

Diffusion-Limited Aggregation with Polygon Particles

Diffusion-limited aggregation (DLA) assumes that particles perform pure random walk at a finite temperature and aggregate when they come close enough and stick together. Although it is well known that DLA in two dimensions results in a ramified fractal structure, how the particle shape influences the formed morphology is still unclear. In this work, we perform the off-lattice two-dimensional DLA simulations with different particle shapes of triangle, quadrangle, pentagon, hexagon, and octagon, respectively, and compare with the results for circular particles. Our results indicate that different particle shapes only change the local structure, but have no effects on the global structure of the formed fractal cluster. The local compactness decreases as the number of polygon edges increases.     

The bulk dynamics of a compositionally asymmetric diblock copolymer studied using dynamic light scattering

We have studied the bulk dynamics of a compositionally asymmetric poly(ethylene propylene)-poly(dimethylsiloxane) (PEP-PDMS) diblock copolymer in a large temperature range both in the ordered and in the disordered state. The volume fraction of the PEP block is 0.22. Apart from the disordered state, the sample shows three ordered morphologies. Using dynamic light scattering, we have investigated the dynamics in all four phases and combined these results with those obtained using pulsed field gradient NMR. In the disordered state, we find--apart from the slow cluster mode--the heterogeneity mode related to the self-diffusion of single chains. The relaxation time of this mode, reduced by temperature and the zero-shear viscosity , , increases with temperature. In the cubic phase right below the ODT temperature, we observe two diffusive processes, and we attribute the faster one to the mutual diffusion of micelles and block copolymers not bound to micelles (“free chains”) through the PDMS matrix. The slower mode may either be due to the mutual diffusion of free chains and chains bound to PEP micelles or to the cooperative diffusion of micellar aggregates. In the non-cubic ordered state at intermediate temperatures, an additional weak diffusive mode is observed. The low-temperature ordered state is body-centered cubic, and here, only the mutual diffusion of micelles and free chains lies in our experimental time window. Received 19 March 1999 and Received in final form 25 August 1999