Showing papers by "Wei Jiang published in 2005"

Self-Assembly of ABC Triblock Copolymer into Giant Segmented Wormlike Micelles in Dilute Solution

Abstract: We report the self-assembly of a linear ABC triblock copolymer into the previously unknown architecture of giant segmented wormlike micelles (SWMs). The lengths and diameters of these giant SWMs were as high as ca. 10 μm and 500 nm, respectively. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) analysis revealed that the SWMs comprised sequences of repeated elemental parts, i.e., disks having a thickness of ca. 65 nm. A most interesting feature is that disks having different diameters became connected through threads to form various giant segmented wormlike micelles. A kinetic study indicated that the process of SWM formation occurred basically through three stages: (1) the ABC triblock copolymer self-assembled into small spheres of ca. 38 nm diameter; (2) these small spheres joined together to form intermediate shuttlelike structures; (3) the spheres within the shuttlelike structures rearranged and underwent further adjustment to form the fina...

Morphological Transition of Aggregates from ABA Amphiphilic Triblock Copolymer Induced by Hydrogen Bonding

Abstract: The hydrogen-bonding-induced aggregate morphological transition of the triblock copolymer poly(4-vinylpyridine)43-b-polystyrene366-b-poly(4-vinylpyridine)43 (P4VP-b-PS-b-P4VP) in dilute solution was studied by introduction of a surfactant (pentadecylphenol, i.e., PDP) into the solution. The P4VP-b-PS-b-P4VP triblock copolymer exhibits spherical aggregates in 1 wt % of the surfactant (PDP)-free solution. However, the aggregate morphologies changed from short rods to networks and looped structures and then to vesicles and compound vesicles by increasing PDP content at the same copolymer concentrations to the PDP-free solutions. The striking feature is that a trace amount of PDP (molar ratio of 4VP/PDP = 1000) addition can change the aggregate morphologies to wormlike morphologies. The nature of the influence that PDP exercise over the copolymer aggregates was determined by comparing the results with those obtained for the addition of the m-cresol (without the long tail of linear alkyl) and pentadecylbenzene...

Effects of filler size and heat treatment on the crystallization behavior of glass bead-filled polypropylene

Abstract: The effects of glass bead (GB) size and annealing temperature on the formation of β-crystals of glass bead-filled polypropylene (PP) are studied in this articles. Differential scanning calorimetry (DSC) measurements indicated that the amount of β-form in PP crystals was a function of the glass bead content and size. For a fixed glass bead content, it was found that the smaller the diameter of the glass bead, the higher was the content of β-crystals formed in the PP. On the other hand, wide-angle X-ray diffraction (WAXD) measurements revealed that the annealing temperature was also a major factor that affected the crystallization behavior of glass bead-filled PP. It seemed that the blends with different glass bead contents had their own optimal annealing temperatures for β-crystal formation. As an example, when the glass bead content was 48 wt %, the optimal annealing temperature for β-crystal formation was about 108 °C, whereas it shifted to 100 °C for 14 wt % glass bead-filled polypropylene. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 306–313, 2005

Multiscale dewetting of triblock copolymer thin film induced by solvent vapor

Abstract: Multiscale dewetting of poly(styrene-b-ethylene/butylenes-b-styrene) (SEES) triblock copolymer thin films induced by volatile solvent vapor treatment were observed in this study. Film rupture occurred at first and produced macroscopic holes. Near-regular droplets (which represented a compromise between complete disorder and perfect order) could be formed at the last stage. The mechanism of solvent-driven dewetting was discussed by comparing with that of thermal-induced dewetting. Similar to thermal-induced dewetting, the block copolymer thin films initially break up through the nucleation of holes that perforated the films. The rapid growing holes became unstable and formed nonequilibrium fingering patterns. The films exhibit autophobic or autodewetting phenomena. The velocity of the holes growth was nearly a constant (3.3 μm/min). The stages of the dewetting were quite similar to that found for homopolymer and block copolymer thin films dewetting on solid or liquid substrates under thermal treatment.

Competing effect between filled glass bead and induced β crystal on the tensile properties of polypropylene/glass bead blends

Abstract: The blends of the polypropylene (PP-1) with various glass bead contents were prepared via melt blending. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) results indicated that the β crystal existed in PP-1 and increased with increasing glass bead content up to 6 wt %. It was generally known that the stiffness of a polymer increased with introducing rigid particles, and the stiffness of the β crystal was less than that of the α crystal. This competing effect thus leads to the tensile modulus of PP-1/glass bead blend decreasing with increasing glass bead content up to 6 wt %; thereafter, it increased with increasing glass bead content. For the purpose of comparison, the polypropylene (PP-2) without the β crystal was employed to blend with glass bead. The tensile tests showed that the modulus of the PP-2/glass bead blend increased continuously with increasing glass bead content. This result further supported that the tensile modulus behavior of PP-1/glass bead blends resulted from the competing between the filled glass bead and the induced β crystal. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1729–1733, 2005

Two-dimensional lattice Monte Carlo simulation of the compatibility of A/B/functionalized A ternary polymer mixtures coupled with chemical reaction

Abstract: Compatibility of A/B and functionalized A ternary polymer mixtures was studied by Monte Carlo simulation in a two-dimensional lattice. Polymer A was a nonreactive polymer, whereas polymer B was a reactive polymer and immiscible with polymer A. Functionalized polymer A could react with the end group of polymer B, leading to the formation of block copolymers. Simulation results showed the phase domain sizes dropped considerably with increasing functionalized polymer A content, indicating that the compatibility between polymer A and B could be markedly improved with the introduction of functionalized polymer A. Moreover, it was shown that the resulting block copolymers tended to distribute at the phase interface between polymer A and B, and the block copolymer conformation depended on the structures of polymer B and functionalized polymer A. In case 1, i.e., both polymer B and functionalized polymer A were with single end group, it could be found that the block A and block B of resulting A–B copolymer inserted into polymer A and polymer B phase domains, respectively. In case 2, i.e., functionalized polymer A was with single end group and polymer B was with double end groups, it was found that the resulting A–B–A triblock copolymer tended to connect two neighbor separated polymer A phase domains. However, in case 3, namely functionalized polymer A was with double end groups and polymer B was with single end group, it was found that the resulting B–A–B triblock copolymer was likely to form a folding conformation. These lead to the different compatibilizing effects for different polymer structures. Comparing with case 1 and case 2, functionalized polymer A with double end groups (case 3) had less effective to compatibilize the A/B polymer blends. For the purpose of comparison, same simulations were carried out in a three-dimensional lattice. The results showed the compatibility behavior of the mixtures was similar to those in the two-dimensional lattice with the addition of functionalized polymer A. However, the conformation of the resulting block copolymers was different from that in the two-dimensional lattice.