ABA两亲性嵌段共聚物在双选择性溶剂中自组装行为的Monte Carlo模拟

采用Monte Carlo模拟方法研究了ABA两亲性三嵌段共聚物在两种选择性溶剂中的自组装行为.模拟结果表明,在保证溶剂总浓度一定的情况下,改变两种选择性溶剂的体积比对于ABA两亲性嵌段共聚物自组装所形成的胶束形貌结构有很大影响.随着双选择性溶剂体积比的改变,体系中胶束形貌结构将会发生由囊泡到层状,再到环状、棒状直至球...     

AB型聚乙二醇单甲醚-聚(L-丙氨酸)嵌段共聚物自组装过程的核磁共振研究

利用核磁共振方法研究了AB型双嵌段共聚物(MPEG45-b-PA32)在选择性溶剂中的自组装行为及胶束化过程.嵌段共聚物在三氟乙酸中聚氨基酸和聚乙二醇链段均处于自由运动状态,聚丙氨酸链段为无规线团结构.在向该溶液中逐渐加入氘代水的过程中,聚丙氨酸链段又重新聚集形成规整的二级结构.结合1H-NMR和COSY谱分析,结果显示这一自组装过程伴随着聚(L-丙氨酸)链段由无规线团向α-螺旋结构的构象转变,同时嵌段共聚物逐渐形成核-壳型胶束结构.利用透射电镜观察了所形成胶束的形态,嵌段共聚物主要形成粒径150 nm到220 nm的球形胶束.     

ABC三嵌段共聚物胶束从多间隔结构到多核结构转变的Monte Carlo模拟

采用Monte Carlo模拟方法研究了疏水-亲水-疏水(H-P-H)型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, 通过调节A嵌段和C嵌段的疏水性和二者之间的不相容性, 体系中可以形成多种形貌各异的胶束. 根据胶束中疏水核结构的特点, 这些胶束大体上可以被分为多核型胶束和多间隔型胶束两种类型. 通过增强疏水嵌段的疏水性或降低A嵌段和C嵌段间的不相容性, H-P-H型ABC三嵌段共聚物胶束能够发生从多核型胶束向多间隔型胶束的转变. 进一步分析胶束中聚合物的链构象等微观结构信息发现, A嵌段和C嵌段间的排斥作用和疏水作用之间存在竞争关系, 而这种竞争关系是影响体系中形成多核型胶束还是多间隔型胶束的决定性因素.     

ABC三嵌段共聚物的聚合诱导自组装研究

聚合诱导自组装(PISA)是一种在高浓度溶液中可连续大量制备纳米材料的新技术,结合计算模拟方法,研究其动力学过程可强化对PISA的认识和调控.通过耗散粒子动力学(DPD)模拟,研究了ABC三嵌段共聚物的聚合诱导自组装过程.先利用亲溶剂A链段引发B单体聚合,随着疏溶剂B链段的增长,AB二嵌段共聚物可组装并发生聚集体结构的连续转变,由球形胶束→蠕虫状胶束→层状结构→囊泡.再将C单体逐步聚合到AB共聚物上,调控C链段的亲疏溶剂性,可聚合诱导组装或解组装形成不同的ABC三嵌段共聚物聚集体.     

苯乙烯-p-乙烯基苯甲酸两亲性嵌段共聚物在乙醇中自组装行为的电镜观察

两亲性嵌段共聚物在只对其中一链段为良溶剂的选择性溶剂中 ,能够自组装形成胶束 .胶束的形态和尺寸大小依赖于两链段的性质 ,共聚物的组成、浓度、溶剂的性质等[1] .这一性质使得嵌段共聚物在分子识别、药物和其他物质的输送、基因疗法、水系涂料、污染物的除去、纳米复合材料的制备、催化剂以及传感器等方面展示着潜在的应用前景 .因此 ,两亲性嵌段共聚物的合成及其在选择性溶剂中的自组装行为的研究近年来颇受关注[2 ] .依据两链段的比例不同 ,嵌段共聚物可形成星状胶束和“板寸头”(Ｃｒｅｗ ｃｕｔ)型胶束[3 ] .当可溶段远比不溶段长时…     

用SAXS/WAXS研究聚氧乙烯/聚氧丁烯嵌段共聚物在n-己烷中的结晶性球形胶束结构

嵌段共聚物在选择性溶剂中能够自组装形成胶束,胶束的不同形状与嵌段共聚物的结构、溶剂和浓度有关．无定形嵌段共聚物通常形成球形胶束,在某些情况下也可以形成其它形状的胶束,关于结晶性嵌段共聚物在无定形链段选择性溶剂中的胶束结构和形状的报道非常少．由于结晶和相似相溶两种作用力的竞争,使得这类胶束的形状丰富多变．通常结晶作用较强时,结晶性嵌段共聚物形成片状的胶束,当结晶组分比较少时,可形成棒状胶束,尽管理论上已经指出存在球形胶束,但尚无关于这方面的报道。     

嵌段共聚物在选择性溶剂中自组装过程的计算机模拟

嵌段共聚物由于各嵌段性质不同,在选择性溶剂中能够自发地组装形成众多形态结构各异的纳米结构,如纳米级的球状、棒状、环状、片层状、囊泡及复合胶束等。这些胶束结构在药物传输、催化、电子信息等众多领域都有潜在的应用价值。通过计算机模拟可以在线监控嵌段共聚物的组装过程、揭示其组装机理,明确各种因素对组装结构的影响规律,为实验研究提供思路和理论支持,因此越来越受到人们的广泛关注。本文主要综述了通过计算机模拟对嵌段共聚物在选择性溶剂中自组装研究的一些最新进展,详细讨论了影响嵌段共聚物自组装过程和胶束形貌的各种因素,并对这个领域未来的发展进行了展望。     

嵌段共聚物结晶性胶束

近年来嵌段共聚物在选择性溶剂中由结晶驱动形成胶束的自组装过程因其较好的可控性逐渐受到人们的关注.本文首先综述了嵌段共聚物结晶性胶束形貌和尺寸的影响因素,包括溶剂环境、共聚物结构、结晶温度等.然后介绍了结晶性胶束的活性生长以及"嵌段共胶束";最后提出了该研究领域目前存在的问题和今后可能的发展方向.     

溶剂尺寸对ABA两亲性三嵌段共聚物在选择性溶剂中自组装行为影响的Monte Carlo模拟

采用Monte Carlo模拟方法研究了溶剂尺寸对ABA两亲性三嵌段共聚物在选择性溶剂中自组装行为的影响。模拟结果表明,溶剂尺寸是决定共聚物聚集形态的重要因素之一。随着溶剂尺寸的增大,嵌段共聚物自组装所形成的胶束可以发生从球状到棒状再到囊泡状的转变。通过对各组分的相互作用对数随溶剂尺寸变化曲线的分析发现,增大溶剂尺寸会使溶剂的溶解性变差,由此引发体系中的一系列形态转变。此外,通过对体系自组装形貌结构相图的分析发现,增大溶剂尺寸或增加疏水作用同减小亲水作用对于自组装形态的改变具有同等效果。     

多嵌段共聚物(P4VP-b-PS-b-P4VP)_n的胶束化行为研究

研究了一系列具有不同链段长度和组成的聚4-乙烯基吡啶-聚苯乙烯-聚4-乙烯基吡啶多嵌段共聚物(P4VP-b-PS-b-P4VP)n在其选择性溶剂甲苯和pH<3的水中的胶束化过程,主要研究了多嵌段共聚物链段长度、溶液浓度和溶剂对其胶束形态的影响.透射电镜和原子力显微镜结果表明随着P4VP段链的相对增长,多嵌段共聚物在甲苯中的胶束形态由蠕虫链状向短棒状到球状胶束变化,而其在pH<3的水溶液中均形成球形胶束.由于特殊的链结构,聚合物的浓度对(P4VP-b-PS-b-P4VP)n多嵌段共聚物的胶束行为和胶束形态有着重要的影响.同时,(P4VP-b-PS-b-P4VP)n多嵌段共聚物分子量分布的多分散性对其在选择性溶剂中的胶束形态也有所影响.     

嵌段序列对聚合物囊泡形成过程影响的Monte Carlo模拟

采用Monte Carlo模拟方法研究了具有相同链长和组分比的不同嵌段序列的AB两嵌段共聚物与ABA三嵌段共聚物在选择性溶剂中形成囊泡的动力学过程. 模拟结果表明, AB两嵌段共聚物囊泡的形成与ABA三嵌段共聚物囊泡的形成的动力学过程不同. 在慢速退火条件下, ABA三嵌段共聚物囊泡是通过亲水链段向胶束的表面和中心扩散而形成的, 而AB两嵌段共聚物囊泡则由片层弯曲闭合而形成. 相对而言, 退火速度对AB两嵌段共聚物囊泡形成的动力学过程没有显著影响, 其改变仅影响亲水链段与疏水链段发生相分离的难易程度. 当退火速度较快时, 亲水链段和疏水链段发生相分离的速度较快且相分离发生在囊泡形成之前; 而当退火速度较慢时亲水链段和疏水链段之间的相分离在囊泡形成之后仍在进行.     

Self-assembly of amphiphilic ABC star triblock copolymers and their blends with AB diblock copolymers in solution: self-consistent field theory simulations

The self-assembled morphologies of amphiphilic ABC star triblock copolymers consisting of hydrophilic A blocks and hydrophobic B and C blocks and the blends with their counterpart linear AB diblock copolymers in solution are investigated by 2D real-space implementation of self-consistent field theory (SCFT) simulation. The star triblock copolymers self-assemble in solution to form various micellar structures from hamburger, to segmented wormlike, to toroidal segmented micelles, and finally to vesicles with simultaneously increasing hydrophobic lengths of blocks B and C. When the length of hydrophobic blocks B and C is asymmetric, specific bead-on-string worm micelles are found. Particularly, when the star ABC triblock copolymer is in a strong segregation regime and both B and C blocks are strongly hydrophobic, quite long segmented wormlike micelles are obtained, which had not been found in previously investigated diblock and linear ABC triblock copolymers solution. Additionally, raspberry micelles with beads dispersed on the core also occur in the strong segregation regime of bulk star ABC triblock copolymers. Furthermore, the aggregate morphology of ABC star triblock copolymers is strongly influenced by the addition of linear AB diblock copolymers. The most significant feature is that the long segmented worms will become shorter, to form hamburger micelles with the addition of AB diblock copolymers. These simulations are in good agreement with the experimental findings by Lodge's group.     

Highly Symmetric Patchy Multicompartment Nanoparticles from the Self-Assembly of ABC Linear Terpolymers in C-Selective Solvents

Multicompartment micelles, especially those with highly symmetric surfaces such as patchy-like, patchy, and Janus micelles, have tremendous potential as building blocks of hierarchical multifunctional nanomaterials. One of the most versatile and powerful methods to obtain patchy multicompartment micelles is by the solution-state self-assembly of linear triblock copolymers. In this article, we applied the simulated annealing method to study the self-assembly of ABC linear terpolymers in C-selective solvents. Simulations predict a variety of patchy and patchy-like multicompartment micelles with high symmetry and also yield a detailed phase diagram to reveal how to control the patchy multicompartment micelle morphologies precisely. The phase diagram demonstrates that the internal segregated micellar structure depends on the ratio between the volume fractions of the two solvophobic blocks and their incompatibility, whereas the overall micellar shape depends on the copolymer concentration. The relationship between the interfacial energy, stretching energy of chains and the micellar morphology, micellar morphological transition are elucidated by computing the average contact number among the species, the mean square end-to-end distances of the whole terpolymers, the AB blocks in the terpolymers, the AB diblock copolymers, and angle distribution of terpolymers. The anchoring effect of the solvophilic C block on micellar structures is also examined by comparing the morphologies formed from ABC terpolymers and AB diblock copolymers.     

A hierarchical self-assembly route to three-dimensional polymer-quantum dot photonic arrays

We demonstrate a new hierarchical self-assembly strategy for the formation of photonic arrays containing quantum dots (QDs), in which sequential self-assembly steps introduce organization on progressively longer length scales, ranging from the nanoscale to the microscale regimes. The first step in this approach is the self-assembly of diblock copolymers to form block ionomer reverse micelles (SA1); within each micelle core, a single CdS QD is synthesized to yield the hybrid building block BC-QD. Once SA1 is completed, the hydrophobic BD-QD building blocks are blended with amphiphilic block copolymer stabilizing chains in an organic solvent; water addition induces secondary self-assembly (SA2) to form quantum dot compound micelles (QDCMs). Finally, aqueous dispersions of QDCMs are slowly evaporated to induce the formation of three-dimensional (3D) close-packed arrays in a tertiary self-assembly step (SA3). The resulting hierarchical assemblies, consisting of a periodic array of hybrid spheres each containing multiple CdS QDs, exhibit the collective property of a photonic stop band, along with photoluminescence arising from the constituent QDs. A high degree of structural control is possible at each level of organization by judicious selection of experimental variables, allowing various parameters governing the collective optical properties, including QD size, nanoparticle spacing, and mesocale periodicity, to be independently tuned. The resulting control over optical properties via successive self-assembly steps should provide new opportunities for hierarchical materials for QD lasers and all-optical switching.     

Mechanistic insights for block copolymer morphologies: how do worms form vesicles?

Amphiphilic diblock copolymers composed of two covalently linked, chemically distinct chains can be considered to be biological mimics of cell membrane-forming lipid molecules, but with typically more than an order of magnitude increase in molecular weight. These macromolecular amphiphiles are known to form a wide range of nanostructures (spheres, worms, vesicles, etc.) in solvents that are selective for one of the blocks. However, such self-assembly is usually limited to dilute copolymer solutions (<1%), which is a significant disadvantage for potential commercial applications such as drug delivery and coatings. In principle, this problem can be circumvented by polymerization-induced block copolymer self-assembly. Here we detail the synthesis and subsequent in situ self-assembly of amphiphilic AB diblock copolymers in a one pot concentrated aqueous dispersion polymerization formulation. We show that spherical micelles, wormlike micelles, and vesicles can be predictably and efficiently obtained (within 2 h of polymerization, >99% monomer conversion) at relatively high solids in purely aqueous solution. Furthermore, careful monitoring of the in situ polymerization by transmission electron microscopy reveals various novel intermediate structures (including branched worms, partially coalesced worms, nascent bilayers, "octopi", "jellyfish", and finally pure vesicles) that provide important mechanistic insights regarding the evolution of the particle morphology during the sphere-to-worm and worm-to-vesicle transitions. This environmentally benign approach (which involves no toxic solvents, is conducted at relatively high solids, and requires no additional processing) is readily amenable to industrial scale-up, since it is based on commercially available starting materials.     

Effect of poly(acrylic acid) block length distribution on polystyrene-b-poly(acrylic acid) block copolymer aggregates in solution. 2. A partial phase diagram

The first paper of the series, which focused on the effect of polydispersity on the self-assembly of block copolymer vesicles, showed that an increase in the width of the poly(acrylic acid) (PAA) block length distribution resulted in a decrease in the size of the vesicles formed. In this paper, the rest of the phase diagram is explored. For the present study, a series of polystyrene-b-poly(acrylic acid) copolymers of an identical polystyrene length of 325 units but of varying degrees of polymerization of PAA was synthesized. Mixtures of the copolymers were made to artificially broaden the molecular weight distribution of PAA at a constant number average of 48 in the polydispersity index (PDI) range of 1.1-3.3. The mixtures were dissolved in dioxane, and water was added slowly to predetermined amounts. Transmission electron microscopy was used to observe aggregate morphologies at different water contents and PAA PDIs. At low water contents, dynamic light scattering was also used to measure the sizes of the aggregates. A partial phase diagram as a function of the water content and PAA PDI was obtained. Large compound micelles and spherical micelles (average diameter of 40 nm) were found at low water contents; however, at a water content of 12% (w/w), a continuum of morphologies from spheres to rods to vesicles was found with increasing PAA PDI. In addition, each copolymer was investigated by itself under identical conditions to those used for the mixtures to determine if there was any segregation of the individual polymers into separate aggregates. No evidence for such segregation was found.     

Influence of the macromolecular architecture on the self-assembly of amphiphilic copolymers based on poly(N,N-dimethylamino-2-ethyl methacrylate) and poly(epsilon-caprolactone)

The self-assembly of amphiphilic copolymers consisting of poly( N, N-dimethylamino-2-ethyl methacrylate) (PDMAEMA) and poly(-caprolactone) (PCL) segments arranged in graft and linear diblock architectures was investigated in this work by means of dynamic light scattering (DLS) in aqueous solution and by atomic force microscopy (AFM) on thin deposits. The solid-state deposits of the micelles were generated by a "freeze-drying" technique that preserves the initial micelle morphology in solution. A comparison between the morphological properties of graft copolymers with corresponding diblock copolymers was established to demonstrate the effect of the copolymer architecture on the micelle structure and organization.     

基于非共价键作用的二嵌段共聚物/均聚物超分子体系的自组装行为

采用实空间求解的自洽场理论,研究了两亲性二嵌段共聚物(AB)/均聚物(C)超分子体系在溶液中的自组装行为,其中B疏水嵌段的自由末端与C均聚物的一个末端形成可逆的非共价键.在稀溶液中,AB/C超分子聚合物体系通过自组装形成了一系列不同形貌的胶束,如核-壳-冠的三层胶束和蠕虫状胶束等.研究发现,胶束形貌受到非共价键强度和初...     

Preparation of ABA triblock copolymer assemblies through “one-pot” RAFT PISA

Poly(N,N-dimethyl acrylamide)-block-poly(styrene)-block-poly(N,N-dimethyl acrylamide)(PDMAc-bPSt-b-PDMAc) amphiphilic triblock copolymer micro/nano-objects were synthesized through reversible addition-fragmentation chain transfer(RAFT) dispersion polymerization of St mediated with poly(N,Ndimethyl acrylamide) trithiocarbonate(PDMAc-TTC-PDMAc) bi-functional macromolecular RAFT agent.It is found that the morphology of the PDMAc-b-PSt-b-PDMAc copolymer micro/nano-objects like spheres,vesicles and vesicle with hexagonally packed hollow hoops(HHHs) wall can be tuned by changing the solvent composition.In addition,vesicles with two sizes(600 nm,264 nm) and vesicles with HHHs features were also synthesized in high solid content systems(30 wt% and 40 wt%,respectively).Besides,as compared with typical AB diblock copolymers(A is the solvophilic,stabilizer block,and B is the solvophobic block),ABA triblock copolymers tend to form higher order morphologies,such as vesicles,under similar conditions.The finding of this study provides a new and robust approach to prepare block copolymer vesicles and other higher order micelles with special structure via PISA.