Study of self-assembly of symmetric coil-rod-coil ABA-type triblock copolymers by self-consistent field lattice method

The self-assembly of symmetric coil-rod-coil ABA-type triblock copolymer melts is studied by applying self-consistent field lattice techniques in a three-dimensional space. The self-assembled ordered structures differ significantly with the variation of the volume fraction of the rod component, which include lamellar, wave lamellar, gyroid, perforated lamellar, cylindrical, and spherical-like phases. To understand the physical essence of these phases and the regimes of occurrence, we construct the phase diagram, which matches qualitatively with the existing experimental results. Compared with the coil-rod AB diblock copolymer, our results revealed that the interfacial grafting density of the separating rod and coil segments shows important influence on the self-assembly behaviors of symmetric coil-rod-coil ABA triblock copolymer melts. We found that the order-disorder transition point changes from f(rod)=0.5 for AB diblock copolymers to f(rod)=0.6 for ABA triblock copolymers. Our results also show that the spherical-like and cylindrical phases occupy most of the region in the phase diagram, and the lamellar phase is found stable only at the high volume fraction of the rod.     

配体链包覆纳米粒子的表面相分离及自组装的模拟研究

通过耗散粒子动力学方法,模拟了二元配体链包覆的纳米粒子表面的相分离行为,并与现有的模拟和实验体系进行对比.研究结果印证了相分离驱动力是配体链错位所导致的构象熵的结论.进一步以相分离得到的Janus和三嵌段Janus结构纳米粒子作为构筑单元,研究了其在选择性溶剂中的自组装行为.结果表明,Janus粒子易自组装成为双层囊泡结构,而三嵌段Janus粒子则更易形成单层囊泡结构.对于从配体链包覆的纳米粒子出发,设计具有特殊功能的囊泡提供了理论支持.     

Computer simulations of block copolymer tethered nanoparticle self-assembly

We perform molecular simulations to study the self-assembly of block copolymer tethered cubic nanoparticles. Minimal models of the tethered nanoscale building blocks (NBBs) are utilized to explore the structures arising from self-assembly. We demonstrate that attaching a rigid nanocube to a diblock copolymer affects the typical equilibrium morphologies exhibited by the pure copolymer. Lamellar and cylindrical phases are observed in both systems but not at the corresponding relative copolymer tether block fractions. The effect of nanoparticle geometry on phase behavior is investigated by comparing the self-assembled structures formed by the tethered NBBs with those of their linear ABC triblock copolymer counterparts. The tethered nanocubes exhibit the conventional triblock copolymer lamellar and cylindrical phases when the repulsive interactions between different blocks are symmetric. The rigid and bulky nature of the cube induces interfacial curvature in the tethered NBB phases compared to their linear ABC triblock copolymer counterparts. We compare our results with those structures obtained from ABC diblock copolymer tethered nanospheres to further elucidate the role of cubic nanoparticle geometry on self-assembly.     

一种新型温度响应性聚氨基酸/聚类肽嵌段共聚物的合成与表征

以正己胺为引发剂, 通过γ-炔丙基-L-谷氨酸羧酸酐(PLG-NCA)和N-正辛基甘氨酸羧酸酐(Oct-NNCA)逐步开环聚合和后修饰策略合成了分子量分布较窄的温度响应性两嵌段共聚物寡聚乙二醇单元修饰的聚(γ-炔丙基-L-谷氨酸)-b-聚(N-正辛基甘氨酸)[(PPLG-g-EG₃)-b-PNOG]. 通过示差扫描量热法(DSC)研究了不同比例聚合物的结晶行为; 利用圆二色谱法(CD)研究了聚合物的二级结构, 并研究了聚合物在水溶液中的自组装行为, 采用透射电子显微镜(TEM)观察了组装后的形貌. 结果表明, 该温度响应性聚合物在室温下呈现α-螺旋结构, 随着温度升高, α-螺旋的构象减少. 该聚合物可以在水溶液中自发组装成棒状结构.     

Association of poly-N-[tris(hydroxymethyl)methyl] acrylamide with a water soluble β-cyclodextrin polymer

An acrylic polymer with pendent adamantyl groups was synthesized and its properties in an aqueous solution with a β-cyclodextrin (βCD) epichlorhydrin polymer examined. Viscosity properties of precursor and modified polymers show differences at low concentrations, but not at higher concentration probably due to very important hydrogen bonds which prevent the formation of intermolecular hydrophobic bonds. The association of both complementary polymers through the inclusion of adamantyl groups is evidenced by phases separation occurrence. Phase diagrams were established at two different concentrations of polymers. We have shown a maximal association of both polymers at these two concentrations, for the same ratio βCD moles/adamantyl groups: 2.4. Salt addition favors this association and displaces the two phases zone to smaller concentrations of modified polymer. Further, 4-nitrophenol can be extracted by the concentrated phase resulting from mixture of solutions of guest and host polymers, pointing out the availability of the associated phase to trap organic molecules.     

Biocompatible polymer vesicles from biamphiphilic triblock copolymers and their interaction with bovine serum albumin

The self-assembly of the biamphiphilic triblock copolymer poly(ethylene oxide)-b-poly(caprolactone)-b-poly(acrylic acid) into polymer vesicles is studied. The vesicles provide both biocompatibility and biodegradability. Moreover, the biamphiphilic nature of the triblock copolymer provides different surface properties in the interior and in the outer interface of the vesicles. Preparation of the aggregates by direct dissolution of the copolymer in a solution of albumin does not alter the morphology of the aggregates, and thus, they have the potential to immobilize protein molecules. Since a part of the protein is encapsulated in the interior of the vesicles, they can be used as nanocontainers. A further fraction of the protein is bound to the outer interface, which is primarily composed of the poly(acrylic acid) tails. Immobilization of protein on the outer interface can stabilize the colloidal particles and also provide them with a biofunctional component.     

Hierarchical mesostructures of biodegradable triblock copolymers via evaporation-induced self-assembly directed by alkali metal ions

Hierarchical mesostructures of poly(ε-caprolactone)-b-poly(ethylene oxide)-b-poly(ε-caprolactone) (PCL-PEO-PCL) triblock copolymers have been grown from evaporation-induced self-assembly directed by alkali metal ions. The self-assembly process began with a dilute homogeneous solution of the triblock copolymers in a mixture of tetrahydrofuran (THF) and water. THF preferentially evaporated under reduced pressure and induced the formation of amphiphilic polymer micelles. The spherical polymer micelles formed both in deionized water and NaOH aqueous solution. However, different mesostructures were discovered during the film depositing process for scanning electron microscopy observation. The polymer micelles were observed for the deposition sample in deionized water while sisal-like hierarchical mesostructures resulted from the film deposition of polymer micelles in NaOH aqueous solution. The sisal-like mesostructures and their formation process were observed through scanning electron microscopy, transmission electron microscopy, fluorescent microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Detailed study revealed that during evaporation-induced self-assembly of PCL-PEO-PCL amphiphilic triblock copolymer directed by alkali metal ions, the sodium ions and polymer micelles increasingly concentrated in NaOH aqueous solution and the solvent quality for the diblock progressively decreased, which resulted in the stronger coordination between alkali metal ions and PEO ligands in the block copolymer and PEO segment crystallization.     

Crystallization-driven self-assembly of semicrystalline block copolymers and end-functionalized polymers: A minireview

Self-assembly has been a powerful method to fabricate the polymer materials with well-defined structures and morphologies. Such assembled materials have shown wide potential applications in many fields such as nanomaterial, nanomedicine, lithography, and microelectronic. Crystallization has been a general behavior of stereoregular polymers. Besides the various noncovalent interactions, crystallization of polymer blocks or end groups can be an efficient way to manipulate the self-assembly pathway and assembled structures of polymers in both solid and solution. Crystallization-driven self-assembly has been widely implemented for the semicrystalline block copolymers (BCPs) and end-functionalized polymers. This minireview briefly presents the recent progresses in the crystallization-driven self-assembly of BCPs and end-functionalized polymers in both solid and solution states. Formation process, mechanism, and hierarchical structure of the crystallization-induced assemblies for BCPs and end-functionalized polymers are highlighted.     

Purification of protein and recycling of polymers in a new aqueous two-phase system using two thermoseparating polymers

In this study we present a new aqueous two-phase system where both polymers are thermoseparating. In this system it is possible to recycle both polymers by temperature induced phase separation, which is an improvement of the aqueous two-phase system previously reported where one of the polymers was thermoseparating and the other polymer was dextran or a starch derivative. The polymers used in this work are EO50PO50, a random copolymer of 50% ethylene oxide (EO) and 50% propylene oxide (PO), and a hydrophobically modified random copolymer of EO and PO with aliphatic C14H29-groups coupled to each end of the polymer (HM-EOPO). In water solution both polymers will phase separate above a critical temperature (cloud point for EO50PO50 50 degrees C, HM-EOPO, 14 degrees C) and this will for both polymers lead to formation of an upper water phase and a lower polymer enriched phase. When EO50PO50 and HM-EOPO are mixed in water, the solution will separate in two phases above a certain concentration i.e. an aqueous two-phase system is formed analogous to poly(ethylene glycol) (PEG)/dextran system. The partitioning of three proteins, bovine serum albumin, lysozyme and apolipoprotein A-1, has been studied in the EO50PO50/HM-EOPO system and how the partitioning is affected by salt additions. Protein partitioning is affected by salts in similar way as in traditional PEG/dextran system. Recombinant apolipoprotein A-1 has been purified from a cell free E. coli fermentation solution. Protein concentrations of 20 and 63 mg/ml were used, and the target protein could be concentrated in the HM-EOPO phase with purification factors of 6.6 and 7.3 giving the yields 66 and 45%, respectively. Recycling of both copolymers by thermoseparation was investigated. In protein free systems 73 and 97.5% of the EO50PO50 and HM-EOPO polymer could be recycled respectively. Both polymers were recycled after aqueous two-phase extraction of apolipoprotein A-1 from a cell free E. coli fermentation solution. Apolipoprotein A-1 was extracted to the HM-EOPO phase with contaminating proteins in the EO50PO50 phase. The yield (78%) and purification factor (5.5) of apolipoprotein A-1 was constant during three polymer recyclings. This new phase system based on two thermoseparating polymers is of great interest in large scale extractions where polymer recycling is of increasing importance.     

Efficient synthesis of single gold nanoparticle hybrid amphiphilic triblock copolymers and their controlled self-assembly

We report on a robust approach to the size-selective and template-free synthesis of asymmetrically functionalized ultrasmall (<4 nm) gold nanoparticles (AuNPs) stably anchored with a single amphiphilic triblock copolymer chain per NP. Directed NP self-assembly in aqueous solution can be facilely accomplished to afford organic/inorganic hybrid micelles, vesicles, rods, and large compound micelles by taking advantage of the rich microphase separation behavior of the as-synthesized AuNP hybrid amphiphilic triblock copolymers, PEO-AuNP-PS, which act as the polymer-metal-polymer analogue of conventional amphiphilic triblock copolymers. Factors affecting the size-selective fabrication and self-assembly characteristics and the time-dependent morphological evolution of NP assemblies were thoroughly explored.     

Tuning multiphase amphiphilic rods to direct self-assembly

New methods to direct the self-assembly of particles are highly sought after for multiple applications, including photonics, electronics, and drug delivery. Most techniques, however, are limited to chemical patterning on spherical particles, limiting the range of possible structures. We developed a lithographic technique for fabrication of chemically anisotropic rod-like particles in which we can specify both the size and shape of particles and implement multiple diverse materials to control interfacial interactions. Multiphase rod-like particles, including amphiphilic diblock, triblock, and multiblock were fabricated in the same template mold having a tunable hydrophilic/hydrophobic ratio. Self-assembly of diblock or triblock rods at a water/oil interface led to the formation of bilayer or ribbon-like structures.     

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.     

Surface-induced morphologies of ABC star triblock copolymer in spherical cavities

The morphologies and phase diagrams exhibited by symmetric ABC star triblock copolymer nanoparticles are investigated on the basis of real-space self-consistent field theory. The ABC star triblock copolymers were chosen to be tiling-forming with fixed polymer parameter and the spherical boundaries were modeled using the masking technique. We first study a number of examples where the ABC triblock copolymers confined in spherical cavities with neutral surface. Then, two types of spherical cavity distinct preferential surfaces are considered, including both A-block attractive and repulsive preferential surfaces. We aim at the effects due to various spherical cavity diameters and the degree of interactions between the polymer and the spherical surface. A variety of morphologies, such as ring-like structures, concentric sphere, and irregular cylinder, were identified in phase diagrams. The results show that both the degree of interactions and spherical diameters can influence the formation of morphologies so that ring-like structures and other novel structures could be obtained.     

Preparation of poly (styrene-methyl methacrylate)/SiO2 composite nanoparticles via emulsion polymerization. An investigation into the compatiblization

Inorganic/organic nanocomposite systems, in which inorganic particles are encapsulated into the polymer matrix, are new classes of polymeric materials. These materials combine the properties of both components. It means that polymer component with excellent optical property, flexibility and toughness could improve the brittleness of inorganic particles and besides, inorganic particles could increase the strength and modulus of polymers. There are various methods to make these inorganic/organic nanocomposites. One of them is the chemical process, in which polymerization is performed directly in the presence of the inorganic particles. Examples of miniemulsion, suspension or dispersion polymerization can be found in the literature but emulsion polymerization is by far the technique most frequently used.In this work, latex containing nanostructure hybrid of copolymer (styrene, methyl methacrylate, acrylic acid) and inorganic nanoparticles (silica) with core/shell structure was prepared via semi-batch emulsion polymerization. At first, silica nanoparticles were dispersed in water phase in an ultrasound bath to prevent the aggregation of nanoparticles, and then emulsion polymerization was performed in the presence of silica nanoparticles. Related tests and analysis confirmed the success in synthesis of nanostructure hybrids. Induced coupled plasma (ICP) analysis and thermal gravimetric analysis (TGA) showed the presence and amount of silica nanoparticles in the final latex. Dynamic light scattering (DLS) analysis confirmed the presence of 25-35 nm particles in the system and transmission electron microscopy (TEM) showed the core/shell morphology of nanoparticles. It has been shown that with an appropriate surfactant, adjusting the pH of media, using suitable monomers and under controlled conditions, it would be possible to produce stable organic/inorganic composite nanoparticles with core/shell structure. In another attempt and in order to investigate the effect of compatiblizing system, styrene-methyl methacrylate was copolymerized in the presence of modified silica particles with oleic acid as the inorganic dispersed phase at the same condition. Similar characterizations were performed in order to have a worthwhile comparison. The results for the late procedure show the effect of oleic acid in formation of aggregates as the core for polymeric nanocomposite particles.     

Coarse-grained molecular-dynamics simulations of the self-assembly of pentablock copolymers into micelles

Multiblock polymers in aqueous solution, where one or several blocks are hydrophobic, exhibit a rich variety of phases and states of aggregation. In this paper, we investigate a pentablock system ABCBA, where the B block is always hydrophilic and the A and C blocks have varying degrees of hydrophobicity depending on external conditions. We report coarse-grained molecular-dynamics simulations where the solvent is included explicitly and monomers interact via a 6-9 Lennard Jones potential function. The hydrophobic interaction is modeled by tuning the parameter controlling the strength of the interaction between the hydrophobic monomers and the solvent. We investigate the structure and morphology of the micelles for two concrete situations representing changes in temperature and the pH level. The simulated system is directly relevant to a recently synthesized pentablock system consisting of a triblock Pluronic with an added pH-sensitive end group [B. C. Anderson et al., Macromolecules 36, 1670 (2003)].     

三维宏观网络状囊泡薄膜的分级自组装研究

分别合成以疏水性超支化聚醚(HBPO)为核,以亲水性聚环氧乙烷(EO)和聚甲基丙烯酸N,N-二甲氨基乙酯(DMAEMA)为臂的两亲性超支化多臂共聚物HBPO-star-PEO和HBPO-star-PDMAEMA.通过两者在水溶液中的复合自组装制备得到具有pH响应性的巨型聚合物囊泡(1~10μm),并用zeta电位仪,激光共聚焦显微镜及光学显微镜对囊泡的自组装行为进行了研究.结果表明,在等电点以前,复合囊泡始终以单个囊泡形式存在;随着溶液pH的升高,囊泡逐步线型缔合成串珠结构;在更高的pH下,囊泡进一步二次聚集形成具有宏观尺度的三维蜘蛛网状超分子结构,这是一类新的自组装体.     

Phase behavior in thin films of confined colloid-polymer mixtures

Using self-consistent-field and density-functional theories, we first investigate colloidal self-assembly of colloid-polymer films confined between two soft surfaces grafted by polymers. With increasing colloidal concentrations, the film undergoes a series of transitions from disordered liquid --> sparse square --> hexagonal (or mixed square-hexagonal) --> dense square --> cylindrical structures in a plane, which results from the competition between the entropic elasticity of polymer brushes and the steric packing effect of colloidal particles. A phase diagram displays the stable regions of different in-layer ordering structures as the colloidal concentration is varied and layering transitions as the polymer-grafted density is decreased. Our results show a new control mechanism to stabilize the ordering of structures within the films.     

Self-assembly of ternary cubic, hexagonal, and lamellar mesophases using the lattice-Boltzmann kinetic method

We use a kinetic lattice-Boltzmann method to simulate the self-assembly of the cubic primitive (P), diamond (D), and gyroid (G) mesophases from an initial quench composed of oil, water, and amphiphilic particles. Here, we also report the self-assembly of the noncubic hexagonal phase and two lamellar phases, one with periodic convolutions. The periodic mesophase structures are emergent from the underlying conservation laws and quasi-molecular interactions of the lattice-Boltzmann model. We locate regions of the model's parameter space where the sequence of appearance of mesophases lamellar --> primitive --> hexagonal is in agreement with pressure jump experiments and the sequence cubic --> lamellar is in agreement with compositional variations reported in the literature. The ability of our lattice-Boltzmann model to simulate self-assembly of cubic and noncubic phases in a unified and consistent manner opens the way for further investigations into the transition pathways and kinetics of the phase transitions between these states as well as of the rheology of these phases.     

Self-organization behavior of methacrylate-based amphiphilic di- and triblock copolymers

Amphiphilic di- and triblock copolymers having different hydrophilic-to-hydrophobic block length ratio were synthesized using ATRP. The self-assembly behavior of these AB and ABA block copolymers consisting of poly(n-butyl methacrylate) (B) and poly(2,2-(dimethylaminoethyl methacrylate) (A) was investigated using a combination of dynamic light scattering, negative-stain transmission electron microscopy, cryoelectron microscopy, and atomic force microscopy. Two populations of self-organized structures in aqueous solution, micelles and compound micelles, were detected for diblock copolymers. Triblock copolymers assembled into vesicular structures of uniform sizes. Furthermore it was found that these vesicles tended to compensate the high curvature by additional organization of the polymer chains outside of the membrane. The chain hydrophilicity of the polymers appeared to have a critical impact on the self-assembly response toward temperature change. The self-reorganization of the polymers at different temperatures is discussed.     

Self-assembly in block polyelectrolytes

The self-consistent field theory (SCFT) complemented with the Poisson-Boltzmann equation is employed to explore self-assembly of polyelectrolyte copolymers composed of charged blocks A and neutral blocks B. We have extended SCFT to dissociating triblock copolymers and demonstrated our approach on three characteristic examples: (1) diblock copolymer (AB) melt, (2) symmetric triblock copolymer (ABA) melt, (3) triblock copolymer (ABA) solution with added electrolyte. For copolymer melts, we varied the composition (that is, the total fraction of A-segments in the system) and the charge density on A blocks and calculated the phase diagram that contains ordered mesophases of lamellar, gyroid, hexagonal, and bcc symmetries, as well as the uniform disordered phase. The phase diagram of charged block copolymer melts in the charge density--system composition coordinates is similar to the classical phase diagram of neutral block copolymer melts, where the composition and the Flory mismatch interaction parameter χ(AB) are used as variables. We found that the transitions between the polyelectrolyte mesophases with the increase of charge density occur in the same sequence, from lamellar to gyroid to hexagonal to bcc to disordered morphologies, as the mesophase transitions for neutral diblocks with the decrease of χ(AB). In a certain range of compositions, the phase diagram for charged triblock copolymers exhibits unexpected features, allowing for transitions from hexagonal to gyroid to lamellar mesophases as the charge density increases. Triblock polyelectrolyte solutions were studied by varying the charge density and solvent concentration at a fixed copolymer composition. Transitions from lamellar to gyroid and gyroid to hexagonal morphologies were observed at lower polymer concentrations than the respective transitions in the similar neutral copolymer, indicating a substantial influence of the charge density on phase behavior.