Self-assembly of diblock copolymer mixtures in confined states: A Monte Carlo study

The self-assembly of diblock copolymer mixtures (A-b-B/A-b-C or A-b-B/B-b-C mixtures) subjected to cylindrical confinement (two-dimensional confinement) was investigated using a Monte Carlo method. In this study, the boundary surfaces were configured to attract blocks A but repel blocks B and C. Relative to the structures of the individual components, the self-assembled structures of mixtures of the diblock copolymers were more complex and interesting. Under cylindrical confinement, with varying cylinder diameters and interaction energies between the boundary surfaces and the blocks, we observed a variety of interesting morphologies. Upon decreasing the cylinder's diameter, the self-assembled structures of the A(15)B(15)/A(15)C(15) mixtures changed from double-helix/cylinder structures (blocks B and C formed double helices, whereas blocks A formed the outer barrel and inner core) to stacked disk/cylinder structures (blocks B and C formed the stacked disk core, blocks A formed the outer cylindrical barrel), whereas the self-assembled structures of the A(15)B(7)/B7C15 mixtures changed from concentric cylindrical barrel structures to screw/cylinder structures (blocks C formed an inside core winding with helical stripes, whereas blocks A and B formed the outer cylindrical barrels) and then finally to the stacked disk/cylinder structures.

Study of controllable aggregation morphology of ABA amphiphilic triblock copolymer in dilute solution by changing the solvent property

We have studied, both experimentally and theoretically, the aggregation morphology of the ABA amphiphilic triblock copolymer in dilute solution by changing the solvent property. Experimental results showed that the micellar morphology changed from spheres to rods and then to vesicles by changing the common solvent from N-N-dimethylformamide (DMF) to dioxane and then to tetrahydrofuran (THF). These controllable aggregates were also obtained by Monte Carlo simulation. The simulative results showed that the solvent property is a key factor that determines the copolymer aggregation morphology. The morphology changed from spheres to rods and then to vesicles by increasing the solvent solubility, corresponding to the change of stretched of the copolymer chains in the micellar cores. This result is in good agreement with the experimental one. Moreover, the simulative results revealed that the end-to-end distant of the ABA triblock copolymer in the vesicle was larger than that in the spheres and rods, indicating that the copolymer chains were more stretched in vesicles than in the spheres and rods. Furthermore, we gave the distribution of the fraction of the chain number with the end-to-end distance. The results indicated that the amount of folded chains is almost the same as that of stretched chains in the vesicle. Although most chains were folded, stretched chains could be found in the rod and sphere micelles.

Fabrication of conductive metallized nanostructures from self-assembled amphiphilic triblock copolymer templates: Nanospheres, nanowires, nanorings

Various metallized nanostructures (such as rings, wires with controllable lengths, spheres) have been successfully fabricated by coating metallic nanolayers onto soft nanotemplates through simple electroless methods. In particular, bimetallic nanostructures have been obtained by using simple methods. The multiple functional polymeric nanostructures, were obtained through the self-assembly of polystyrene/poly(4-vinyl pyridine) triblock copolymer (P4VP-b-PS-b-P4VP) in selective media by changing the common solvent properties. By combining field emission scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) characterization, it was confirmed that polymer/metal and bimetallic (Au@Ag) core-shell nanostructures could be achieved by chemical metal deposition method.

Monte Carlo simulation of the compatibility of graft copolymer compatibilized two incompatible homopolymer blends: Effect of graft structure

Compatibility of graft copolymer compatibilized two incompatible homopolymer A and B blends was simulated by using Monte Carlo method in a two-dimensional lattice model. The copolymers with various graft structures were introduced in order to study the effect of graft structure on the compatibility. Simulation results showed that incorporation of both A-g-B (A was backbone) and B-g-A (B was backbone) copolymers could much improve the compatibility of the blends. However, A-g-B copolymer was more effective to compatibilize the blend if homopolymer A formed dispersed phase. Furthermore, simulation results indicated that A-g-B copolymers tended to locate at the interface and anchor two immiscible components when the side chain is relatively long. However, most of A-g-B copolymers were likely to be dispersed into the dispersed homopolymer A phase domains if the side chains were relatively short. On the other hand, B-g-A copolymers tended to be dispersed into the matrix formed by homopolymer B. Moreover, it was found that more and more B-g-A copolymers were likely to form thin layers at the phase interface with decreasing the length of side chain.

Online study of the formation of PA6 droplets in PP matrix under shear flow

Breakup process of polyamide 6 (PA6) in polypropylene (PP) matrix under shear flow was online studied by using a Linkam CSS 450 stage equipped with optical microscopy. Both tip streaming and fracture breakup modes of PA6 droplets were observed in this study. It was reported that the droplet would break up by tip streaming model when the radio of the droplet phase viscosity to the matrix phase viscosity (n(r) = n(d)/n(m)) is smaller than 0.1 (Taylor, Proc R Soc London A 1934, 146, 501; Grace, Chem Eng Commun 1982, 14, 225; Bartok and Mason, J Colloid Sci 1959, 14, 13; Rumscheidt and Mason, J Colloid Sci 1961, 16, 238; de Bruijn, Chem Eng Sci 1993, 48, 277). However, the tip streaming model was observed even when the viscosity ratio was much greater than 0.1 (n(r) = 1.9). In this study for the tip streaming mode, small droplets were ruptured from the tip of the mother droplet. On the other hand, the mother droplet was broken into two or more daughter droplets with one or several satellite droplets between them for the fracture mode. It was found that PA6 droplet was much elongated at first, and then broke up via tip streaming or fracture to form daughter droplets or small satellite droplets with the shape of fiber or ellipse.

Well-organized structures of ZnS semiconductor nanocrystals using amphiphilic triblock copolymer aggregates as templates

Ring- and rod-shaped P4VP-b-PS-b-P4VP ( PS, polystyrene; P4VP, poly( 4-vinylpyridine)) triblock copolymer aggregates are used as templates to synthesize ZnS nanocrystals. Herein, PVP serves as both a stabilizing agent and a structure- directing agent. The resulting ZnS nanocrystals could be aligned along the corona of the copolymer aggregates in near-perfect structures through control of both the molar ratio of Zn2+ to P4VP and the reaction time. The diameter of the as-synthesized ZnS layer on the surface of polymer template is approximate 2 - 3 nm. High-resolution transmission electron microscopy images reveal that the ZnS particles are single crystal in a zinc blende structure. This method provides a simple, reproducible route at room temperature to prepare assembled hybrid polymer - semiconductor nanocrystal nanocomposites.

A Monte Carlo simulation for the micellization of ABC 3-miktoarm star terpolymers in a selective solvent

We have used Monte Carlo simulation to study the micellization of ABC 3-miktoarm star terpolymers in a selective solvent (good to A segment, bad to B and C segments). The simulation results reveal that the self-assembled morphology is determined by the block length, molecular architecture, terpolymer concentration and insolubility of insoluble block in the solvent. In dilute solution, symmetric terpolymers (N-B = N-C = 30) tend to aggregate into a novel wormlike pearl-necklace structure linked by an alternating arrangement of B and C spheres, whereas the asymmetric terpolymers (NB = 10, NC = 50) are likely to aggregate into spherical or cylindrical micelles (formed by C blocks) connected with some small B spheres, when the concentration of terpolymer is relatively low (chain number is 100). However, when the concentration of terpolymer is relatively high (chain number is 250), the symmetric terpolymers tend to aggregate into a netlike structure linked by an alternation of B and C spheres, whereas the asymmetric terpolymers are likely to aggregate into wormlike micelles (formed by C blocks) connected with some of small spheres (formed by B blocks). Moreover, when the insolubility of insoluble block in the solvent is weak, the insoluble blocks aggregate into some incompact micelles.

Monte Carlo simulation of the aggregation of rod-flexible triblock copolymers in a thin film

The aggregation of rod-flexible ABA and BAB triblock (A was rod block and repulsive with block B) copolymers in a thin film was studied as a function of varying the rigidity (eta) and the length of the rod block by Monte Carlo simulation. The rigidity of block A was defined as eta = R-c/R-max in this study. R-c, was the end-to-end distance below which the conformation of the block was not allowed, whereas R-max, was the longest end-to-end distance that the block could be. If eta = 0 the block was flexible, whereas if eta = 1 the block was a straight rod. The simulation results showed that the ABA triblock copolymer film were likely to form lamella structure with increasing the rigidity (eta) of block A. The lamellas were parallel each other and perpendicular to the film surface. However, the aggregation of BAB triblock copolymers tended to change from lamella to cylinder structure with increasing the rigidity (eta) of block A. Typical lamella and cylinder co-exist structure was obtained at eta = 0.504 for the BAB copolymer film. On the other hand, the simulation results indicated that the film changed from disorder to order, then to disorder structure with increasing the relative length of B block for both ABA and BAB copolymer films.

Nano-reactors for controlling the selectivity of the free radical grafting of maleic anhydride onto polypropylene in the melt

This paper reports on a successful application of the concept of nanoreactors to effectively controlling the selectivity of the free radical grafting of maleic anhydride (MAH) onto polypropylene (PP) in the melt, an industrially relevant process. More specifically, a free radical initiator of type ROOR was first confined into (or encapsulated by) the galleries of an organically modified montmorillonite (o-MMT) whose interdistance was 2.4 nm. Primary free radicals (RO center dot) formed inside the o-MMT galleries had to diffuse out before they could react with the PP backbone. The controlled release of the primary free radicals significantly increased the grafting degree of MAH onto PP and greatly reduced the level of the chain scission of the latter. Those results were better understood by electron spin resonance studies on model systems and by Monte Carlo simulations.

Monte Carlo simulation of the grafting of maleic anhydride onto polypropylene at higher temperature

The graft of maleic anhydride (MAH) onto isotactic polypropylene (iPP) initiated by dicumyl peroxide (DCP) at 190 degreesC was studied by means of the Monte Carlo method. The ceiling temperature theory, i.e., no possibility for the homopolymerization of MA-H to occur at higher temperatures, was used in this study. The simulation results show that most MAH monomers were grafted onto the radical chain ends arising from beta scission at a lower MAH concentration, whereas the amount of MAH monomers attached to the tertiary carbons was much larger than that grafted onto the radical chain ends at a higher MAH concentration for various DCP concentrations. This conclusion gives a good interpretation for the disagreement on the grafting sites along a PP chain. Moreover, it was found that the grafting degree increased considerably up to a peak value; thereafter, it decreased continuously with increasing MA-H concentration. The peak shifted in the lower MAH concentration direction and became lower and lower with increasing DCP concentration. When the DCP concentration was below 0.1 wt %, the peak was hardly observed. Those results are in good agreement with the experiments.

THE CHARACTERIZATION OF 2 COPPER PHTHALOCYANINE LANGMUIR-BLODGETT-FILMS AND THEIR GAS-SENSITIVE PROPERTIES

The monolayer and deposition behaviour of a symmetrically substituted copper tetra-4-(2, 4-di-t-amylphenoxy) phthalocyanine (tapCuPc) and an asymmetrically substituted copper [tri-4-(2, 4-di-t-amylphenoxy)-mono-4-(-2-methoxyethoxy)]phthalocyanine (AsyCuPc) were investigated. The results on monolayer behaviour and spectroscopic characterization of the LB films show that both CuPc molecules in a monolayer at the air-water interface and the LB films are stacked and inclined. The gas-sensitive properties show that the responding speed of AsyCuPc LB film is faster than that of tapCuPc LB film.

MONOLAYER FORMATION OF A NOVEL AMPHIPHILIC POLYMER PAMC16S

Poly(2-acrylamido-hexadecylsulfonic acid) (PAMC16S) forms a stable monolayer on a pure water surface. More closely packed monolayers can be obtained when the subphase contains Cd2+ or Ca2+. Self-assembled monolayers have been formed on gold surfaces and characterized by contact angle measurement, XPS and electrochemical analysis. The results show that the monolayers are hydrophobic with the hydrophilic sulfonic acid groups adjacent to the metal surfaces and with the hydrocarbon chains extended from the surfaces. The monolayers exhibit great adsorption stability during the faradaic reactions, illustrating the advantage of polymeric LB films in potential applications.