Haojun Liang

Self-assembly of the symmetric diblock copolymer in a confined state: Monte Carlo simulation

Self-assembly of symmetric diblock copolymers in confined state has been investigated by means of Monte Carlo simulation method. The symmetric diblock copolymers were confined in two- (parallel walls or circle) or in three-dimensional (spherical or cylindrical) space. There are interactions between these boundaries and the symmetric diblock polymers. These interactions and boundary shape resulted in the formation of novel self-assemble structures, e.g., strip, circle, core-multishell, and multibarrel-layer structures. Simulation results predicated that it is possible to design different phase structures for block copolymers by adjusting boundary shape and boundary-block copolymer interactions.

Brittle-tough transition in PP/EPDM blends: effects of interparticle distance and temperature

Abstract The toughness of PP/EPDM blends was measured over a wide range of temperature (25–132°C) and composition 0–26 wt% EPDM). It was found that increasing temperature and decreasing interparticle distance have equivalent effects on the brittle-tough transition of toughening PP with EPDM, and the shift factor increases with increasing temperature. A correlation was also found between temperature and critical interparticle distance. When critical interparticle distance was plotted versus T g − T , where T g is defined as the brittle-tough transition temperature of the matrix itself, the curves for different blends systems converge to a single master curve.

Effect of surface field on the morphology of a symmetric diblock copolymer under cylindrical confinement

We have used lattice Monte Carlo simulations to investigate the molecular assembly of symmetric diblock copolymer melts within cylindrical nanochannels. We studied the effect that the surface field has on the copolymer morphology in three cylinders having different diameters. Upon varying the strength of the surface field, we observed a variety of morphologies, including stacked-disk, single-helix, catenoid-cylinder, gyroidal, stacked-circle, and concentric cylindrical barrel structures. The results of these simulations should be helpful when designing polymeric nanomaterials confined in cylindrical nanochannels.

Kinetics and mechanism of G-quadruplex formation and conformational switch in a G-quadruplex of PS2.M induced by Pb2+

DNA sequences with guanine repeats can form G-quartets that adopt G-quadruplex structures in the presence of specific metal ions. Using circular dichroism (CD) and ultraviolet-visible (UV–Vis) spectroscopy, we determined the spectral characteristics and the overall conformation of a G-quadruplex of PS2.M with an oligonucleotide sequence, d(GTG3TAG3CG3TTG2). UV-melting curves demonstrate that the Pb2+-induced G-quadruplex formed unimolecularly and the highest melting temperature (Tm) is 72°C. The analysis of the UV titration results reveals that the binding stoichiometry of Pb2+ ions to PS2.M is two, suggesting that the Pb2+ ions coordinate between adjacent G-quartets. Binding of ions to G-rich DNA is a complex multiple-pathway process, which is strongly affected by the type of the cations. Kinetic studies suggest that the Pb2+-induced folding of PS2.M to G-quadruplex probably proceeds through a three-step pathway involving two intermediates. Structural transition occurs after adding Pb(NO3)2 to the Na+- or K+-induced G-quadruplexes, which may be attributed to the replacement of Na+ or K+ by Pb2+ ions and the generation of a more compact Pb2+–PS2.M structure. Comparison of the relaxation times shows that the Na+→Pb2+ exchange is more facile than the K+→Pb2+ exchange process, and the mechanisms for these processes are proposed.

Self-assembled hybrid nanoparticles for targeted co-delivery of two drugs into cancer cells

A therapeutic aptamer-lipid-poly(lactide-co-glycolic acid) hybrid nanoparticle-based drug delivery system was prepared and characterized. This system can co-deliver two different drugs with distinct solubility and different anticancer mechanisms to target cancer cells with high specificity and efficiency.

Synergistic co-delivery of doxorubicin and paclitaxel by porous PLGA microspheres for pulmonary inhalation treatment.

PLGA porous microspheres loaded with doxorubicin (DOX) and paclitaxel (PTX) were developed for in situ treatment of metastatic lung cancer. The synergistic effect of the combined drugs was investigated against B16F10 cells to obtain the optimal prescription for in vivo studies. The combination therapy showed great synergism when DOX was the majority in the combination therapy, while they showed moderate antagonism when PTX is in major. The combination of DOX and PTX at a molar ratio of 5/1 showed the best synergistic therapeutic effect in the free form. However, the drugs exhibited more synergism in the PLGA microspheres at a molar ratio of 2/1, due to the difference in drug release rate. The in vivo study verified the synergism of DOX and PTX at the optimal molar ratio. These results suggested that dual encapsulation of DOX and PTX in porous PLGA microspheres would be a promising technology for long effective lung cancer treatment.

Interparticle distance-temperature-strain rate equivalence for the brittle-tough transition in polymer blends

From the angle of energy transformation an equation was obtained for the brittle transition in polymer blends. The effects of interparticle distance, temperature and strain rate on the brittle-tough transition in polymer blends were characterized by this equation. The calculations show that, for this transition: (1) increasing temperature and decreasing interparticle distance are equivalent and the shift factor increases with increasing temperature; (2) decreasing strain rate and decreasing interparticle distance have equivalent effects on the transition; (3) the strain rate must be optimum in order to find the brittle-tough transition phenomena for a given temperature region

Effect of KBr on the micellar properties of CTAB

The effect of KBr on the size, shape and microviscosity of CTAB micelles has been investigated by means of laser light scattering (LLS),1H NMR measurements and fluorescence probe. The data obtained from the various techniques are quantitatively in agreement. The Rh of micelles in 0.01 rnol · L−1 CTAB solution increases from 3.5 nm to 43 nm andRg increases to 89 nm with addition of KBr salt. In this process, both the microviscosity and molecular weight of micelles Mw have noticeable increases, too. The rod-like micelles are formed at 0.1 rnol · L1 KBr and the worm-like micelles are formed at above 0.2 rnol · L-1 KBr.

Solvent-Induced Self-Assembly of Polymer-Tethered Nanorods

Self-assembly behaviors of polymer-tethered nanorods in the selective solvent are systematically investigated via a dissipative particle dynamics (DPD) simulation method. Three types of polymer-tethered nanorods are considered: one end tethered, both ends tethered, and middle tethered. The solvent-induced diverse morphologies and morphological transitions depend on the topology, rod/tether length ratio, solvent selectivity, and mixed solvent content. In the pure rod-selective solvent (solvent I) or the pure tether-selective solvent (solvent II), the ordered micellar structures include: cylinders, hexagonal cylinders, bilayer lamellae, lamellae/cylinder mixed phases, inverted hollow cylinders, and nematic bundles. These micelles are formed by the competition among the stretching of tethers, liquid crystalline of rods, interfacial energy, and solvent selectivity. In the I/II mixed solvent, with varying mixed solvent content in sequence (i.e., changing the solvent quality for the blocks), the reversible morphological transitions and fantastic intermediate phases (e.g., liquid crystalline phase) are observed, which correspond directly to the case of that induced by varying the rod/tether length ratio in the pure solvent. It is concluded that improving the selective solvent content is equivalent to increasing the soluble block ratio. The present study reveals that the morphology and morphological transition of polymer-tethered nanorods could be significantly manipulated through topology, block length, and solvent, especially the selectivity.

The effects of nanoparticles on the lamellar phase separation of diblock copolymers.

The phase separation of diblock copolymers containing some energetically neutral/biased nanoparticles is studied by means of large-scale dissipative particle dynamics (DPD) simulations. The effects of the volume fraction of nanoparticles, the size of nanoparticles, and the interaction strength between nanoparticles and blocks on the lamellar phase separation of diblock copolymers are investigated. When these effects are up to a critical value, the diblock copolymer nanocomposites can form a new bicontinuous morphology, which is well consistent with the experimental results. It is also found that the degree of order of phase separation for a given system increases slightly and then decreases abruptly until the bicontinuous morphology is formed as the volume fraction of nanoparticles increases. Furthermore, we discuss the microphase transition through the position distributions of nanoparticles and present a phase diagram in terms of the nanoparticle volume fraction, size, and surface interaction strength.