Controlled nanoparticle assembly by dewetting of charged polymer solutions

In this paper, we present an alternative approach for controlled nanoparticle organization on a solid substrate by applying dewetting patterns of charged polymer solutions as a templating system. Thin films of charged polymer solutions dewet a solid substrate to form complex dewetting patterns that depend on the polymer charge density. These patterns, ranging from polygonal networks to elongated structures that are stabilized by viscous forces during dewetting, serve as potential templates for two-dimensional nanoparticle organization on a solid substrate. Thus, while nanoparticles dried in pure water undergo self-assembly to form close-packed arrays, addition of charged polymer in the dispersion leads to the formation of open structures that are directed by the dewetting patterns of the polymer solution. In this study, we focus on the application of elongated structures resulting from dewetting of high-charge-density polymer solutions to align nanoparticles of silica and gold into long chains that are several micrometers in length. The particle ordering process is a two-step mechanism: an initial confinement of the nanoparticles in the dewetting structures and self-assembly of the particles within these structures upon further drying by lateral capillary attractions.     

Toroid Formation through a Supramolecular “Cyclization Reaction” of Rodlike Micelles

Constructing polymeric toroids with a uniform, tunable size is challenging. Reported herein is the formation of uniform toroids from poly(γ-benzyl-l -glutamate)-graft-poly(ethylene glycol) (PBLG-g-PEG) graft copolymers by a two-step self-assembly process. In the first step, uniform rodlike micelles are prepared by dialyzing the polymer dissolved in tetrahydrofuran (THF)/N,N′-dimethylformamide (DMF) against water. With the addition of THF in the second step, the rodlike micelles curve and then close end-to-end to form uniform toroids, which resemble a cyclization reaction.     

Morphology transformation of hybrid micelles self-assembled from rod-coil block copolymer and nanoparticles

Hybrid polymeric micelles self-assembled from a mixture containing poly(γ-benzyl-L-glutamate)-block-poly(ethylene glycol) (PBLG-b-PEG) block copolymer and gold nanoparticles (AuNPs) were prepared. The effect of AuNPs on the self-assembly behavior of PBLG-b-PEG was studied both experimentally by transmission electron microscopy, scanning electron microscopy, and laser light scattering and computationally using dissipative particle dynamics (DPD) simulations. It was found that, the pure PBLG-b-PEG block copolymer self-assembles into long cylindrical micelles. By introducing AuNPs to the stock block copolymer solution, the formed aggregate morphology transforms to spherical micelles. The DPD simulation results well reproduced the morphological transformations observed in the experiments. And the simulation revealed that the main reason for the aggregate morphology transformation is the breakage of ordered packing of PBLG rods in micelle core by the added nanoparticles. Moreover, from the DPD simulations, the distribution information on nanoparticles was obtained. The nanoparticles were found to prefer to locate near the core/shell interface as well as in the core center of the micelles. The combination of experimental and simulation methods lead to a comprehensive understanding of such a complex self-assembly system.     

Effect of chain conformational change on micelle structures: experimental studies and molecular dynamics simulations

The effect of chain conformation change on the self-assembly behavior of poly(gamma-benzyl- l-glutamate)-block-poly(ethylene glycol) (PBLG-b-PEG) was studied both experimentally by transmission electron microscopy, laser light scattering, and circular dichroism and computationally using molecular dynamics (MD) simulation. It was found that, by introducing trifluoroacetic acid to the PBLG-b-PEG solution, the conformation of the PBLG chain transforms from alpha-helix to random coil, which results in a change of the micelle structures formed by PBLG-b-PEG from rod to sphere. Meanwhile, the MD simulations were performed by using Brownian dynamics on the self-assembly behavior of model AB-type diblock copolymers with various chain rigidities of the A-block. The results show that, by decreasing the fraction of rigid chain conformation of the A-block, which corresponds to the helix-coil transition in the PBLG-b-PEG sample, the aggregate structure transforms from rod to sphere. The MD simulations also provide chain packing information in the micelles. On the basis of both experimental and MD simulation results, the mechanism regarding the effect of the conformation change of the polypeptide block copolymer on its self-association behavior is suggested.     

The self-assembly of asymmetric block copolymers in films contacting a patterned surface

The preparation of ordered high-density polymer layers via the combined method of templated self-assembly is discussed. This approach combines the advantages of guided self-assembly of block copolymers and lithography on a topographical or chemical pattern. To implement the approach, a simulation has conducted for the first time through the use of the dissipative particle dynamics method in the NPAT ensemble. The pattern replication by asymmetric copolymers that form cylindrical phases in the bulk owing to their self-assembly near the patterned surface is studied. The effects of three patterns are described, i.e., hexagonal, rectangular, and triangular, which are characterized by one or two length scales. It is shown that the dense hexagonal pattern and the sparse rectangular and triangular patterns induce vertically oriented cylindrical domains in a thin film. The control of the orientation and ordering in the formed morphology heavily depends on the interaction between the minority component and the pattern. This effect is global in nature: The surface pattern propagates into the bulk of a film. In the case of rectangular and triangular patterns, two- and fourfold increases in their quantitites in the bulk are observed.     

Brownian dynamics simulation study on the self-assembly of incompatible star-like block copolymers in dilute solution

We study the self-assembly of symmetric star-like block copolymers (A(x))(y)(B(x))(y)C in dilute solution by using Brownian dynamics simulations. In the star-like block copolymer, incompatible A and B components are both solvophobic, and connected to the center bead C of the polymer. Therefore, this star-like block copolymer can be taken as a representative of soft and deformable Janus particles. In our Brownian dynamics simulations, these "soft Janus particles" are found to self-assemble into worm-like lamellar structures, loose aggregates and so on. By systematically varying solvent conditions and temperature, we build up the phase diagram to illustrate the effects of polymer structure and temperature on the aggregate structures. At lower temperatures, we can observe large worm-like lamellar aggregates. Upon increasing the temperature, some block copolymers detach from the aggregate; this phenomenon is especially sensitive for the polymers with less arms. The aggregate structure will be quite disordered when the temperature is high. The incompatibility between the two parts in the star-like block copolymer also affects the self-assembled structures. We find that the worm-like structure is longer and narrower as the incompatibility between the two parts is stronger.     

Pigment encapsulation by emulsion polymerization using macro-RAFT copolymers

A new method is described, based on living amphipathic random macro-RAFT copolymers, which enables the efficient polymeric encapsulation of both inorganic and organic particulate materials via free-radical polymerization. The mechanism for this new approach is examined in the context of the polymer coating of zirconia- and alumina-coated titanium dioxide particles and its breadth of application demonstrated by the coating of organic phthalocyanine blue pigment particles. The particulate materials were first dispersed in water using a macro-RAFT copolymer as a stabilizer. Monomer and water-soluble initiator were then added to the system, and the monomer polymerized to form the coating. If nucleation of new polymer particles in the aqueous phase was to be avoided, it was found necessary to use a macro-RAFT copolymer that did not form micelles; within this constraint, a broad range of RAFT agents could be used. The macro-RAFT agents used in this work were found not to transfer competitively in the aqueous phase and therefore did not support growth of aqueous-phase polymer. Successful encapsulation of particles was demonstrated by TEM. The process described enables 100% of the particles to be encapsulated with greater than 95% of the polymer finishing up in the polymeric shells around the particles. Moreover, the coating reaction can be carried out at greater than 50% solids in many cases and avoids the agglomeration of particles during the coating step.     

Influence of added particles on the phase behavior of polymer solutions. Analysis by mean-field lattice theory

The influence of added colloidal particles on the phase stability of polymer solutions is investigated theoretically. The polymer has an affinity to the particle surface. A mean-field lattice theory based on the Flory-Huggins theory is used to calculate the phase behavior in solutions containing a single polymer component and particles. The particles are described in two different ways. The first approach considers the surface free energy associated with added solid particles and the mixing entropy of the particles. In the second approach, the particles are simply modeled as large polymers. Both ways of describing the added particles show that the added particles decrease the stability of the polymer solution when the polymer-particle attraction is strong. A higher particle concentration enhances the effect. Experiments where polystyrene latex particles are added at different concentrations to aqueous dispersions of ethyl(hydroxyethyl)cellulose (EHEC) support the theoretical findings.     

Uniform Colloidal Polymer Rods by Stabilizer-Assisted Liquid-Crystallization-Driven Self-Assembly

The synthesis of anisotropic colloidal building blocks is essential for their self-assembly into hierarchical materials. Here, a highly efficient stabilizer-assisted liquid-crystallization-driven self-assembly (SA-LCDSA) strategy was developed to achieve monodisperse colloidal polymer rods. This strategy does not require the use of block copolymers, but only homopolymers or random copolymers. The resulting rods have tunable size and aspect ratios, as well as well-defined columnar liquid crystal structures. The integrated triphenylene units enable the rods to exhibit unusual photo-induced fluorescence enhancement and accompanying irradiation memory effect, which, as demonstrated, are attractive for information encryption/decryption of paper documents. In particular, unwanted document decryption during delivery can be examined by fluorescence kinetics. This SA-LCDSA-based approach can be extended to synthesize other functional particles with desired π-molecular units.     

由嵌段共聚物制备有形状的核壳结构聚合物纳米颗粒

嵌段共聚物可自发组装形成形貌丰富的纳米粒子和有序纳米结构的材料,为纳米材料和纳米技术领域提供了很重要的新材料和新手段.该领域的进一步发展提出了对嵌段共聚物的自组装体赋予功能性的要求,即需要通过可控聚合反应合成反应性嵌段共聚物,并且对其自组装的纳米粒子进行结构、形状及功能性的调控.本文针对以上研究目标,结合本课题组在该领...     

Temperature-responsive phase transition of polymer vesicles: real-time morphology observation and molecular mechanism

Novel thermosensitive polymer vesicles with controlled temperature-responsive phase transition at the lower critical solution temperature (LCST) varying from 8 to 81 degrees C were prepared via self-assembly of amphiphilic hyperbranched star copolymers having a hydrophobic hyperbranched poly[3-ethyl-3-(hydroxymethyl)oxetane] (HBPO) core and many hydrophilic polyethylene oxide (PEO) arms. Real-time optical microscopic observation revealed that the polymer vesicles have undergone sequential morphology changes including enrichment, aggregation, fusion, and vesicle-to-membrane transformation near the LCST. Molecular-level investigation indicates that the LCST transition results from the decreasing water solubility of the polymer vesicles with increasing temperature based on the partial dehydration of the PEO vesicle corona. On the basis of these results, a LCST transition mechanism, in view of the molecular configuration, balance of hydrophilic and hydrophobic moieties, and the vesicle morphology transformations, was proposed. As far as we know, the work presented here is the first demonstration of thermosensitive vesicles based on PEO, and the finding may be useful to design the thermosensitive core-shell structures by introducing the PEO segments.     

两亲性Janus粒子在蜂窝状多孔聚合物膜上的自组装性能

采用具有两亲性的两面体(Janus)粒子实现稳定的粒子界面组装与水滴模板法自组装过程相结合的方法获得了粒子在蜂窝状多孔聚合物薄膜内壁的高效定向修饰.通过与均质粒子组装形貌的对比,证明了Janus粒子因其特殊的界面自组装活性,可以获得高粒子加量条件下的规则多孔结构,解决了使用均质粒子时存在的结构有序性和粒子修饰密度之间的矛盾.而在较低粒子加量的条件下,Janus粒子也展示出与均质粒子极为不同的组装形貌.这一方法的建立,为新型表面功能化材料的制备提供了一个新的思路.     

Self-assembly and morphology control of new L-glutamic acid-based amphiphilic random copolymers: giant vesicles, vesicles, spheres, and honeycomb film

New amphiphilic random copolymers containing hydrophobic dodecyl (C12) chain and hydrophilic L-glutamic acid were synthesized, and their self-assembly in solution as well as on the solid surfaces was investigated. The self-assembly behavior of these polymers are largely dependent on their hydrophilic and hydrophobic balances. The copolymer with a more hydrophobic alkyl chain (～90%) self-assembled into giant vesicles with a diameter of several micrometers in a mixed solvent of ethanol and water. When the hydrophobic ratio decreased to ca. 76%, the polymer self-assembled into conventional vesicles with several hundred nanometers. The giant vesicles could be fused in certain conditions, while the conventional vesicles were stable. When the content of the hydrophilic part was further increased, no organized structures were formed. On the other hand, when the copolymer solutions were directly cast on solid substrates such as silicon plates, films with organized nanostructures could also be obtained, the morphology of which depended on solvent selection. When ethanol or methanol was used, spheres were obtained. When dichloromethane was used as the solvent, honeycomb-like morphologies were obtained. These results showed that through appropriate molecular design, random copolymer could self-assemble into various organized structures, which could be regulated through the hydrophobic/hydrophilic balance and the solvents.     

Morphological control and molecular recognition by bis-urea hydrogen bonding in micelles of amphiphilic tri-block copolymers

Hydrogen bonding between urea groups of amphiphilic tri-block copolymers considerably affects their self-assembly in water, which results in a strong modification of morphology and viscosity of aqueous solutions; the hydrogen bonding motif in these amphiphilic copolymers allows molecular recognition of small molecules with complementary hydrogen bonding units.     

甲壳型液晶高分子研究进展与展望

简要介绍了甲壳型液晶高分子的模型理论, 概述了当前国内外对甲壳型液晶高分子设计、 液晶相态、 性质及基于甲壳型液晶高分子的嵌段共聚物体系的设计和自组装性质等研究进展, 展望了今后的研究方向.     

RAFT polymerization of linear ABC triblock copolymer P<Emphasis Type="Italic">t</Emphasis>BA-<Emphasis Type="Italic">b</Emphasis>-PS-<Emphasis Type="Italic">b</Emphasis>-P2VP and regulation of its hierarchical self-assembly structure in solution

Linear ABC triblock copolymer PtBA₁₅₄-b-PS₃₀₀-b-P2VP₂₄₀ was successfully synthesized by RAFT polymerization. Block copolymer micelles were prepared by the two-step hierarchical self-assembly process. Size exclusion chromatography and ¹H NMR were used to characterize the structure of samples. Morphologies and size of micelles were determined by transmission electron microscope. The results showed that the densely dispersed spherical micelles of PtBA₁₅₄-b-PS₃₀₀-b-P2VP₂₄₀ were obtained in the first step of the hierarchical self-assembly process. In the second step, core-compartmentalized micelle strings with different lengths and distribution densities were obtained when the primary self-assembled solution was dialyzed in distilled water with pH ≈ 3. When distilled water with pH ≈ 3 was added drop-wise to this solution, uniformly dispersed spherical core-compartmentalized micelles of PtBA₁₅₄-b-PS₃₀₀-b-P2VP₂₄₀ were prepared. Thus, hierarchical self-assembly structure of linear ABC triblock copolymer was obtained successfully and the preparation of uniformly dispersed spherical micelles of triblock copolymers was realized simply by changing the secondary self-assembly methods.     

Preparation and characterization of MPEG–PCL diblock copolymers with thermo‐responsive sol–gel–sol phase transition

MPEG–PCL diblock copolymers consisting of methoxy polyethylene glycol (MPEG, 750 g/mol) and poly(?‐caprolactone) (PCL) were synthesized by ring‐opening polymerization. Aqueous solutions of the synthesized diblock copolymers were prepared by dissolving the MPEG–PCL diblock copolymers at concentrations in the range of 0–20 wt %. When the PCL molecular weight was 3000 or greater, the polymer was only partially soluble in water. As the temperature was increased from room temperature, the diblock copolymer solutions showed two phase transitions: a sol‐to‐gel transition and a gel‐to‐sol transition. The sol‐to‐gel phase transition temperature decreased substantially with increasing PCL length. The sol–gel–sol transition with the increase in temperature was confirmed by monitoring the viscosity as a function of temperature. The temperature ranges of the phase transitions measured by the tilting method were in full agreement with those determined from the viscosity measurements. The maximum viscosity of the copolymer solution increased with increasing hydrophobicity of the diblock copolymer and with increasing copolymer concentration. X‐ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses revealed that the diblock copolymers exhibited crystalline domains that favored the formation of an aggregated gel because of the tight aggregation and strong packing interactions between PCL blocks. Scanning electron micrographs of the diblock copolymer solutions in the sol state showed interconnected polyhedral pore structures, whereas those of the gel state revealed a fibrillar‐like morphology. Atomic force microscope (AFM) studies of the sol and gel surfaces showed that the sol surface was covered with fine globular particles, whereas the gel surface was covered with particles in micron‐scale irregular islets. These findings are consistent with uniform mixing of the diblock copolymer and water in the sol state, and aggregation of PCL blocks in the gel state. In conclusion, we confirm that the MPEG–PCL diblock copolymer solution exhibited a sol–gel–sol transition as a function of temperature. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5413–5423, 2006     

羧基氟碳共聚物纤维光催化剂载体的制备与耐光降解

通过溶液聚合法合成了聚(丙烯酸六氟丁酯-co-甲基丙烯酸)(P(HFBA-co-MAA))和聚(甲基丙烯酸十二氟庚酯-co-甲基丙烯酸)(P(DFHMA-co-MAA))羧基氟碳共聚物. 静电纺丝实验结果表明,随着 MAA 用量的减少,两种氟碳共聚物的可纺性逐渐变差,相应的纺丝液的浓度也逐渐降低,所用溶剂的极性和沸点呈现降低的趋势;当配制纺丝液所用低沸点溶剂丁酮用量增大时,所得纤维的直径呈增加趋势;P(DFHMA-co-MAA) 的可纺性优于 P(HFBA-co-MAA). 采用两步法在 P(DFHMA-co-MAA)共聚物纤维表面制备光催化剂 ZnS,XPS 结果表明锌离子先与共聚物纤维表面的羧酸根离子络合,然后络合的锌离子再与硫源 TAA 反应形成 ZnS. MAA 用量高的共聚物纤维表面形成的 ZnS 量与粒子尺寸较大,MAA 用量为 10 wt% 时,共聚物纤维表面形成了纳米级的 ZnS 粒子,通过紫外降解实验和红外分析表明制备的 ZnS/P(DFHMA-co-MAA)纤维复合物具有很好的耐紫外光降解性能.     

溶有增粘树脂的丙烯酸酯乳液共聚及压敏胶的性能

用一步法将溶有松香或氢化松香的丙烯酸酯单体进行乳液共聚合时，由于增粘树脂分子的自由基链转移作用使单体的转化率明显降低．先将大部分丙烯酸酯单体进行乳液共聚制得种子乳液，再将溶有增粘树脂的剩余丙烯酸酯单体加到种子乳液中进行第二步乳液共聚合，可显著提高单体的总转化率．用ＴＥＭ对分步聚合所得复合乳液的粒子形态进行了观察并对第二步乳液共聚合的机理进行了讨论．用分步乳液共聚合的方法制得的增粘树脂 丙烯酸酯复合乳液共聚物的压敏胶粘性能较一步法有很大的提高．     

Phase diagrams,mechanisms and unique characteristics of alternating-structured polymer self-assembly via simulations

Alternating-structured polymers(ASPs), like alternating copolymers, regular multiblock copolymers and polycondensates, are very important polymer structures with broad applications in photoelectric materials. However, their self-assembly behaviors,especially the self-assembly of alternating copolymers, have not been clearly studied up to now. Meanwhile, the unique characteristics therein have not been systematically disclosed yet by both experiments and theories. Herein, we have performed a systematic simulation study on the self-assembly of ASPs with two coil alternating segments in solution through dissipative particle dynamics(DPD) simulations. Several morphological phase diagrams were constructed as functions of different impact parameters. Diverse self-assemblies were observed, including spherical micelles, micelle networks, worm-like micelles, disklike micelles, multimicelle aggregates, bicontinuous micelles, vesicles, nanotubes and channelized micelles. Furthermore, a morphological evolutionary roadmap for all these self-assemblies was constructed, along with which the detailed molecular packing models and self-assembly mechanisms for each aggregate were disclosed. The ASPs were found to adopt a folded-chain mechanism in the self-assemblies. Finally, the unique characteristics for the self-assembly of alternating copolymers were revealed especially, including(1) ultra-fine and uniform feature sizes of the aggregates;(2) independence of self-assembled structures from molecular weight and molecular weight distribution;(3) ultra-small unimolecular aggregates. We believe the current work is beneficial for understanding the self-assembly of alternating structured polymers in solution and can serve as a guide for the further experiments.