Yangwei Jiang

Phase separation and crystallization of binary nanoparticles induced by polymer brushes

The aggregation behaviors and phase separation of binary nanoparticles immersed in semiflexible polymer brushes are explored using molecular dynamics simulations. The conformations of the binary nanoparticle–brush mixtures are very sensitive to the size ratio q = σl/σs, where σl and σs are the diameters for large and small nanoparticles, respectively, and the attractive interactions eM between the nanoparticles and polymer brushes. The phase separation of the binary nanoparticles is observed at a relatively strong attractive interaction under the effects of inter-nanoparticle depletion attractions provided by polymer brushes. Furthermore, the crystallization of small nanoparticles occurs at a strong interaction and a hexagonal close-packed-like (hcp-like) ordered structure is formed. The present results may promise a new approach for controlling the self-assembling behavior of nanoparticles and constructing a better macroscopic performance of the material.

Ordered structures of diblock nanorods induced by diblock copolymers

The self-assembly of diblock copolymer (DBCP)/diblock nanorod (DBNR) mixtures are studied by using a dissipative particle dynamics simulation method. The microstructures of DBCP/DBNR blends depend on the type of DBCPs as well as the number of DBNRs. For the asymmetric DBCPs of A3B7, the morphological transition of DBCP/DBNR blends from cylinder phase to lamellar phase is observed for the DBNRs with suitable length and component. Meanwhile, for the symmetric DBCPs of A5B5, the lamellar morphologies of DBCP/DBNR blends can always maintain during the process of adding DBNRs to the blends except for the case of component length mismatch between the DBCPs and the DBNRs. On the other hand, DBCPs can also affect the orientation and the spatial distributions of DBNRs deeply, and the ordered structures of DBNRs are formed for the DBCP/DBNR blends with a large number of DBNRs. Comparisons with homopolymer/DBNR blends are made, and only the aggregation structures are observed in homopolymer/DBNR blends. This investigation can provide valuable assistance in exploring and designing complicated polymer/nanoparticle composites with the desired properties.

Glassy dynamics of nanoparticles in semiflexible ring polymer nanocomposite melts

By employing molecular dynamics simulations, we explore the dynamics of NPs in semiflexible ring polymer nanocomposite melts. A novel glass transition is observed for NPs in semiflexible ring polymer melts as the bending energy (Kb) of ring polymers increases. For NPs in flexible ring polymer melts (Kb = 0), NPs move in the classic diffusive behavior. However, for NPs in semiflexible ring polymer melts with large bending energy, NPs diffuse very slowly and exhibit the glassy state in which the NPs are all irreversibly caged be the neighbouring semiflexible ring polymers. This glass transition occurs well above the classical glass transition temperature at which microscopic mobility is lost, and the topological interactions of semiflexible ring polymers play an important role in this non-classical glass transition. This investigation can help us understand the nature of the glass transition in polymer systems.

The adsorption-desorption transition of double-stranded DNA interacting with an oppositely charged dendrimer induced by multivalent anions

The adsorption-desorption transition of DNA in DNA-dendrimer solutions is observed when high-valence anions, such as hexavalent anions, are added to the DNA-dendrimer solutions. In the DNA-dendrimer solutions with low-valence anions, dendrimers bind tightly with the V-shaped double-stranded DNA. When high-valence anions, such as pentavalent or hexavalent anions, are added to the DNA-dendrimer solutions, the double-stranded DNA chains can be stretched straightly and the dendrimers are released from the double-stranded DNA chains. In fact, adding high-valence anions to the solutions can change the charge spatial distribution in the DNA-dendrimer solutions, and weaken the electrostatic interactions between the positively charged dendrimers and the oppositely charged DNA chains. Adsorption-desorption transition of DNA is induced by the overcharging of dendrimers. This investigation is capable of helping us understand how to control effectively the release of DNA in gene/drug delivery because an effective gene delivery for dendrimers includes non-covalent DNA-dendrimer binding and the effective release of DNA in gene therapy.

Self-assembly of binary nanoparticles on soft elastic shells.

The self-assembly behaviors and phase transitions of binary nanoparticles (NPs) adsorbed on a soft elastic shell are investigated through molecular dynamics simulation. The conformations of adsorbed binary NPs depend on the bending energy K(b) of elastic shell and the binding energy D0 between the NPs and the elastic shell. The ordered structures of binary NPs are observed at the moderate adhesive strength and bending energy, in which the small NPs are located near the vertices of regular pentagons as well as the large NPs are distributed along the sides of the regular pentagons. The shape of soft elastic shell can be adjusted by adding the adsorbed binary NPs, and this investigation can provide an effective way to regulate and reshape surfaces or membranes with the sizes in the micrometer range or smaller.

Rotational Diffusion of Soft Vesicles Filled by Chiral Active Particles

We investigate the dynamics of two-dimensional soft vesicles filled with chiral active particles by employing the overdamped Langevin dynamics simulation. The unidirectional rotation is observed for soft vesicles, and the rotational angular velocity of vesicles depends mainly on the area fraction (ρ) and angular velocity (ω) of chiral active particles. There exists an optimal parameter for ω at which the rotational angular velocity of vesicle takes its maximal value. Meanwhile, at low concentration the continuity of curvature is destroyed seriously by chiral active particles, especially for large ω, and at high concentration the chiral active particles cover the vesicle almost uniformly. In addition, the center-of-mass mean square displacement for vesicles is accompanied by oscillations at short timescales, and the oscillation period of diffusion for vesicles is consistent with the rotation period of chiral active particles. The diffusion coefficient of vesicle decreases monotonously with increasing the angular velocity ω of chiral active particles. Our investigation can provide a few designs for nanofabricated devices that can be driven in a unidirectional rotation by chiral active particles or could be used as drug-delivery agent.