Yutian Zhu

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.

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.

Tailored Parallel Graphene Stripes in Plastic Film with Conductive Anisotropy by Shear-Induced Self-Assembly.

We present a simple but efficient route to prepare a highly anisotropic conductive plastic thin film from the polypropylene/(styrene-ethylene/butadiene-styrene) triblock copolymer/graphene blend via shear-induced self-assembly. Under the shear-flow induction, GE nanosheets dispersed in the polymer matrix can spontaneously assemble into ordered parallel stripes, which endow the materials significantly conductive anisotropy. The electrical resistivity in the direction parallel to the graphene stripes is almost four orders of magnitude lower than that which is perpendicular to the stripes. This study provides a new method for the precise control of the organization of functional nano-objects in polymer matrix, which can be widely extended to the fabrication of other multifunctional anisotropic materials of interest in various fields.

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.

Multicompartment micellar aggregates of linear ABC amphiphiles in solvents selective for the C block: a Monte Carlo simulation

In the current study, we applied the Monte Carlo method to study the self-assembly of linear ABC amphiphiles composed of two solvophobic A and B blocks and a solvophilic C block. A great number of multicompartment micelles are discovered from the simulations and the detailed phase diagrams for the ABC amphiphiles with different block lengths are obtained. The simulation results reveal that the micellar structure is largely controlled by block length, solvent quality, and incompatibility between the different block types. When the B block is longer than or as same as the terminal A block, a rich variety of micellar structures can be formed from ABC amphiphiles. By adjusting the solvent quality or incompatibility between the different block types, multiple morphological transitions are observed. These morphological sequences are well explained and consistent with all the previous experimental and theoretical studies. Despite the complexity of the micellar structures and morphological transitions observed for the self-assembly of ABC amphiphiles, two important common features of the phase behavior are obtained. In general, the micellar structures obtained in the current study can be divided into zero-dimensional (sphere-like structures, including bumpy-surfaced spheres and sphere-on-sphere structures), one-dimensional (cylinder-like structures, including rod and ring structures), two-dimensional (layer-like structures, including disk, lamella and worm-like and hamburger structures) and three-dimensional (vesicle) structures. It is found that the micellar structures transform from low- to high- dimensional structures when the solvent quality for the solvophobic blocks is decreased. In contrast, the micellar structures transform from high- to low-dimensional structures as the incompatibility between different block types increases. Furthermore, several novel micellar structures, such as the CBABC five-layer vesicle, hamburger, CBA three-layer ring, wormlike shape with bumps on the sides, and disk shape with bumps on the edge, are predicted in this study. The formation pathways of ring, hamburger, and worm-like micelles are also examined and their formation mechanisms are well elucidated.

Templated Self-assembly of Block copolymers and Morphology Transformation Driven by the Rayleigh Instability

In the current study, we investigate the self-assembly of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) confined in the nanopores of the anodic aluminum oxide (AAO) template and the subsequent morphology transformation induced by the Rayleigh instability. PS-b-P4VP nanotubes and nanorods with various internal nanostructures are fabricated by wetting the AAO template with PS-b-P4VP/chloroform solution, and then followed by solvent evaporation. After the removal of AAO template by potassium hydroxide solution, several different solvents (chloroform, toluene, and N,N-dimethylformamide) with different qualities are used to swell and anneal those nanotubes and nanorods suspended in aqueous media. Morphology transformation from nanostructured PS-b-P4VP nanotubes or nanorods to ordered nanospheres is observed by annealing upon chloroform and toluene while the morphology remains unchanged upon N,N-dimethylformamide annealing, indicating that solvent quality is a key factor in tuning the morphology and internal structures. Kinetics study and theoretical analysis for the morphology transition from two-dimensional (2D) block copolymer (BCP) nanotubes and nanorods to three-dimensional (3D) BCP nanospheres are further performed. From the morphological evolution and the quantitative calculation, it is confirmed that this transition is induced by the Rayleigh instability. This study provides a simple but promising method, that is, solvent annealing method, for the fabrication of BCP nanospheres with ordered internal nanostructures, which may have great application in drug delivery and other nanotechnology.

Janus-like spheres, disks, rings, cylinders, and vesicles from the self-assembly of mixture of AB and BC diblock copolymers in A- and C-selective solvents

Janus particles with two different compartments have enormous potential as building blocks of hierarchically multifunctional nanomaterials. One of the most versatile and powerful methods to fabricate Janus micelles is through the solution-state self-assembly of block copolymers. In this study, we applied the Monte Carlo simulation to study the self-assembly of a AB/BC diblock copolymer mixture in A- and C-selective solvents. Our simulations predicted a variety of novel Janus micelles, which include Janus-like cylinders, lamellas, vesicles, and rings, all of which were self-assembled from amphiphilic A4B6/B6C4 copolymers. The effects of control parameters, which include the solvent quality for solvophobic B blocks (eBS) and the incompatibility between the solvophilic A and C blocks (eAC), on the formation of Janus micelles were examined, and a generic phase diagram in eBS × eAC was constructed. The phase diagram demonstrates that the micellar shape mainly depends on eBS, whereas the formation of the Janus architecture is controlled by eAC. Moreover, the formation pathways of the Janus lamella, vesicle, and ring were investigated and their formation mechanisms were investigated.

Morphology Control and Stabilization in Immiscible Polypropylene and Polyamide 6 Blends with Organoclay

Abstract In the current study, 70/30 (w/w) polypropylene (PP)/polyamide 6 (PA6)/organoclay ternary blends were prepared by melt mixing in three different blending sequences, i. e., organoclay premixed with PA6 and then mixed with PP (S1 blending sequence), organoclay premixed with PP and then mixed with PA6 (S2 blending sequence), and organoclay, PA6 and PP mixed simultaneously (S3 blending sequence). The effects of organoclay on the phase morphologies, rheological properties and mechanical properties of the blends are examined to reveal the role of organoclay in these immiscible blends. First of all, the dispersion and distribution of organoclay is investigated using XRD and TEM techniques. The organoclay is exfoliated and distributed in the dispersed PA6 phase as well as at the interface between PA6 and PP. Interestingly, more organoclay sheets are observed at the interface when the S2 or S3 blending sequences are utilized. From the SEM images, it is clear that the domain size of the PA6 phase decreases remarkably after introducing organoclay into the PP/PA6 blends. Two different rheological protocols are applied to probe the effect of organoclay on the morphology of the blend by in-situ monitoring the morphological evolution. The rheological results reveal that the phase morphology of the PP/PA6 blends remains relatively stable during shear for a wide range of shear rates when 1.0 wt% organoclay has been added. For the blends with a relatively high clay loading (5.0 wt%), a characteristic and pronounced “plateau” is observed in the low frequency range of the G′-ω curves, which indicates the presence of a percolating network of clay nanosheets. From the mechanical measurements, we find that the tensile strength of the blends increases slightly first and then declines dramatically with increasing organoclay content. Moreover, the elongation at break drops sharply as the organoclay content increases. In summary, it is clear that the organoclay can effectively reduce the domain size of the dispersed PA6 phase and stabilize the phase morphology in shear flow. However, the mechanical properties of the blends are not really improved by clay addition, even though a cocontinuous morphology with a percolated clay network was generated.

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-b-poly(2-vinylpyridine) (PS-b-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-b-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.

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.