Release Behavior of Polymeric Vesicles in Solution Controlled by External Electrostatic Field

We found that the polymeric vesicles from the self-assembly of amphiphilic block copolymer polystyrene-<i>block</i>-poly­(acrylic acid) (PS₁₄₄-<i>b</i>-PAA₂₂) in the dioxane/water mixture can be deformed, broken and finally divided into smaller ones via the external electrostatic field. The higher the electrostatic field intensity, the smaller the vesicles. More importantly, this fission phenomenon induced by electrostatic field can be used to control the release behavior of the vesicles. Our experimental results show that the Nile Red (NR) molecules encapsulated inside the cavity of vesicles can be accurately released by controlling the electrostatic field intensity and the release time. These findings not only enrich the knowledge for the external field induced transformation of polymer structures, but also provide a new and highly convenient approach for the controllable release of polymersomes in solution

Design of Electrical Conductive Composites: Tuning the Morphology to Improve the Electrical Properties of Graphene Filled Immiscible Polymer Blends

Polystyrene (PS) and poly­(methyl methacrylate) (PMMA) blends filled with octadecylamine-functionalized graphene (GE-ODA) have been fabricated to obtain conductive composites with a lower electrical percolation threshold according to the concept of double percolation. The dependence of the electrical properties of the composites on the morphology is examined by changing the proportion of PS and PMMA. Our results reveal that the electrical conductivity of the composites can be optimal when PS and PMMA phases form a cocontinuous structure and GE-ODA nanosheets are selectively located and percolated in the PS phase. For the PS/PMMA blend (50w/50w), the composites exhibit an extremely low electrical percolation threshold (0.5 wt %) because of the formation of a perfect double percolated structure. Moreover, the rheological properties of the composites are also measured to gain a fundamental understanding of the relationship between microstructure and electrical properties

Self-Assembly of AB Diblock Copolymer Confined in a Soft Nano-Droplet: A Combination Study by Monte Carlo Simulation and Experiment

The self-assembly of AB-type diblock copolymers confined in a three-dimensional (3D) soft nanodroplet is investigated by the combination of Monte Carlo simulation and experiment. The influences of two critical factors, i.e., confinement degree of the imposed confinement space and the interfacial interaction between each individual block and boundary interface, on the 3D soft confined self-assembly are examined systematically. The simulation results reveal that block copolymer chains become more and more folded as the confinement degree (it can be monitored by the ratio of <i>D</i>/<i>L</i>, where <i>L</i> is the length of polymer chain and <i>D</i> is the reduced diameter of the final polymeric particle) is enhanced, causing a series of morphological transitions. Based on the simulation prediction, we perform the corresponding experiments by the 3D confined self-assembly of both symmetric and asymmetric block copolymers within the emulsion droplets. The experimental results well reproduce the confinement degree induced morphological transitions predicted by the simulations, such as the transition from segmented pupa-like particle to hamburger particle and the transition from raspberry-like particle to triangle-like particle, and then to hamburger particle. The current study implies that self-assembled nanostructures under 3D soft confinement can be simply controlled by tuning the confinement degree and interfacial property, i.e., the ratio of <i>D</i>/<i>L</i> and the interfacial interaction between each individual block and boundary interface

Controllable Cooperative Self-Assembly of PS‑<i>b</i>‑PAA/PS‑<i>b</i>‑P4VP Mixture by Tuning the Intercorona Interaction

The cooperative self-assembly of amphiphilic polystyrene-<i>block</i>-poly­(acrylic acid) (PS₁₄₄-<i>b</i>-PAA₂₂) and polystyrene-<i>block</i>-poly­(4-vinylpyridine) (PS₁₄₄-<i>b</i>-P4VP₃₃) diblock copolymers in DMF/H₂O mixtures has been investigated. Both copolymers self-assemble into small spherical micelles (SSMs) if used individually. However, the equimolar mixture of these two copolymers cooperatively self-assembles into vesicles. It is found that the formation of vesicles is attributed to the complex interactions between PAA and P4VP chains, including the hydrogen bonds between un-ionized acrylic acid units and pyridine units as well as the electronic attractions between ionized acrylic acid units and protonated pyridine units. Since these interactions between PAA and P4VP chains depend on pH value, the cooperatively self-assembled morphology can be easily tuned by the addition of HCl or NaOH. At high addition of H⁺ or OH^–, the intercorona interaction is repulsive and the copolymer mixture tends to form SSMs (basic condition) or cylindrical micelles (acidic condition), whereas it prefers to aggregate into vesicles at low addition of H⁺ or OH^– because the intercorona interaction is attractive. Interestingly, the same morphology of the self-assembled aggregates can be obtained either at high H⁺ addition or at low OH^– addition, which results from the nonmonotonic variation of the intercorona interaction along with the addition of HCl or NaOH. The current study implies that it is the intercorona interaction rather than the chemical condition that dominates the cooperatively self-assembled morphology

Online Rheological Investigation on Ion-Induced Micelle Transition for Amphiphilic Polystyrene-<i>block</i>-Poly(acrylic acid) Diblock Copolymer in Dilute Solution

The ion-induced micellar transition is online-investigated by the time dependence of the viscosity of the solution under shear flow for the first time. During the morphological transition, the change in the micellar structure can be tracked by the change in viscosity. Adding HCl or CaCl₂ into pre-prepared spherical micelle solution from the self-assembly of polystyrene-<i>block</i>-poly­(acrylic acid) (PS₁₄₄-<i>b</i>-PAA₂₂) in the <i>N</i>,<i>N</i>-dimethylformamide (DMF)/water mixture, the micellar structures change into short cylinders, long, entangled cylinders, and then lamellae or vesicles, corresponding to the viscosity increasing first and then declining. When HCl or CaCl₂ is added to the pre-prepared spherical micelle solution formed by PS₁₄₄-<i>b</i>-PAA₅₀ in the dioxane/water mixture, the micellar structures are quickly transformed into cylinders or lamellae before carrying out the rheological measurement and then are turned to vesicles or spheres under the shearing, corresponding to a gradual decline in viscosity. This study shows that the rheology can be a very simple and effective online method on the investigation of the micellization, which plays an important role in understanding the micellization mechanism and micellar transition pathway of block copolymers in dilute solution

Shear Flow Controlled Morphological Polydispersity of Amphiphilic ABA Triblock Copolymer Vesicles

Self-assembled polymeric aggregates are generally polydisperse in morphology due to the existence of many metastable states in the system. This shortcoming becomes a bottleneck for preparing high quality self-assembled polymeric materials. An important concern is the possibility of controlling morphological polydispersity through the modulation of the metastable states. In this study, both simulative and experimental results show that the metastable states can be modulated. As a typical example, the morphological polydispersity of amphiphilic ABA triblock copolymer vesicles have been successfully controlled by shear flow. A higher shear rate results in more uniform and smaller vesicles. However, if the shear rate is extremely high, small spheres and short rods can be observed. These findings not only give a deeper insight into the metastable behavior of self-assembled polymeric aggregates but also provide a new strategy for improving the uniformity of vesicles

Entropy-Driven Hierarchical Nanostructures from Cooperative Self-Assembly of Gold Nanoparticles/Block Copolymers under Three-Dimensional Confinement

The cooperative self-assembly of polystyrene-<i>b</i>-poly­(4-vinylpyridine) block copolymers (BCPs) and gold nanoparticles (AuNPs) confined within the emulsion droplets is studied by combining both the experiments and Monte Carlo simulations. The results indicate that the entropic interaction between the AuNPs and BCP domain is a critical parameter to dominate the spatial arrangement of AuNPs and the nanostructure of the hybrid nanoparticles, which can be utilized to design novel hierarchical hybrid nanoparticles. Based on this theoretical observation, a large number of unique Janus hybrid nanoparticles, including pupa-like nanoparticles with AuNPs concentrated at one pole of the particles, spherical nanoparticles with AuNPs enriched in a bulge on the sphere surface, and the gourd-like, clover-like, and four-leaf-clover-like nanoparticles from the further hierarchical assembly of small hybrid Janus nanoparticles, are fabricated via three-dimensional (3D) confined self-assembly

Inorganic Nanoparticle Induced Morphological Transition for Confined Self-Assembly of Block Copolymers within Emulsion Droplets

Recently, it has been reported that the incorporation of functional inorganic nanoparticles (NPs) into the three-dimensional (3D) confined self-assembly of block copolymers (BCPs) creates the unique nanostructured hybrid composites, which can not only introduce new functions to BCPs but also induce some interesting morphological transitions of BCPs. In the current study, we systematically investigate the cooperative self-assembly of a series of size-controlled and surface chemistry-tunable gold nanoparticles (AuNPs) and polystyrene-<i>b</i>-poly­(2-vinylpyridine) (PS-<i>b</i>-P2VP) diblock copolymer within the emulsion droplets. The influences of the size, content, and surface chemistry of the AuNPs on the coassembled nanostructures as well as the spatial distribution of AuNPs in the hybrid particles are examined. It is found that the size and content of the AuNPs are related to the entropic interaction, while the surface chemistry of AuNPs is related to the enthalpic interaction, which can be utilized to tailor the self-assembled morphologies of block copolymer confined in the emulsion droplets. As the content of PS-coated AuNPs increases, the morphology of the resulting AuNPs/PS-<i>b</i>-P2VP hybrid particles changes from the pupa-like particles to the bud-like particles and then to the onion-like particles. However, a unique morphological transition from the pupa-like particles to the mushroom-like particles is observed as the content of P4VP-coated AuNPs increases. More interestingly, it is observed that the large AuNPs are expelled to the surface of the BCP particles to reduce the loss in the conformational entropy of the block segment, which can arrange into the strings of necklaces on the surfaces of the hybrid particles

Controllable Location of Inorganic Nanoparticles on Block Copolymer Self-Assembled Scaffolds by Tailoring the Entropy and Enthalpy Contributions

Precisely controlling the spatial location and alignment of functional nanoparticles (NPs) on polymeric scaffolds is of great importance to not only create novel nanostructures but also enhance the properties of the hybrid nanomaterials. Herein, we demonstrate a strategy of tailoring the entropic and enthalpic contributions to precisely position gold nanoparticles (AuNPs) on block copolymer (BCP) scaffolds through the confined coassembly of BCPs and AuNPs within the emulsion droplet. According to this strategy, entropic effect arisen by the loss in conformational entropy and the enthalpic attraction between ligands on AuNPs and surfactants at the oil/water interface induce the solid AuNPs to move to the BCP surface, while the enthalpic interaction between the ligands on AuNPs and the corresponding polymer chains guides the AuNPs to position at the appropriate place. By this strategy, both the location and alignment of AuNPs on BCP scaffolds can be controlled at will, such as at the two terminals or along the lamellar boundary of the pupa-like scaffolds, or at the bases of pinecone-like or bud-like scaffolds, or at the head of one hemisphere, the entire hemisphere, or along the boundary between the two distinct hemispheres of the Janus-like scaffolds. We believe that this methodology can offer a universal route to achieve the precise positioning of functional NPs on the BCP scaffolds

Parallel Carbon Nanotube Stripes in Polymer Thin Film with Remarkable Conductive Anisotropy

In our previous study (Mao et al. J. Phys. Chem. Lett. 2013, 4, 43−47), we proposed a novel method, that is, the shear-flow-induced hierarchical self-assembly of two-dimensional fillers (octadecylamine-functionalized graphene) into the well-ordered parallel stripes in a polymer matrix, to fabricate the anisotropic conductive materials. In this study, we extend this method to one-dimensional multiwalled carbon nanotubes (MWCNTs). Under the induction of shear flow, the dispersed poly­(styrene ethylene/butadiene-styrene) (SEBS) phase and MWCNTs can spontaneously assemble into well-ordered parallel stripes in the polypropylene (PP) thin film. The electrical measurements indicate that the electrical resistivity in the direction parallel to the stripes is almost 6 orders of magnitude lower than that in the perpendicular direction, which is by far the most striking conductive anisotropy for the plastic anisotropic conductive materials. In addition, it is found that the size of the MWCNT stripe as well as the electrical property of the resulting anisotropic conductive thin film can be well-controlled by the gap of the shear cell