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Developing new simulation techniques

We are developing versatile simulation techniques -- mostly based on dissipative particle dynamics (DPD) and coarse-grained molecular dynamics (CGMD), to faithfully describe polymer physical properties at mesoscale and provide high-performance simulation toolkits to the polymer simulation community. Please contact Prof. Lu for further details.

Self-assembly of soft matter systems (polymers, colloids, lipids, and so on)

We are interested in the self-assembly mechanism and process of amphiphilic block copolymers, (patchy) nanoparticles, lipids and so on. Their self-assembly behavior in bulk, in solution, and in confined space are studied using coarse-grained simulation methods. We have also used kinetic network analysis to elucidate their self-assembly pathways. Please contact Prof. Lu for further details.

Structure and dynamics of polymer materials

Understanding structural and dynamic properties and their correlation of polymer materials is of great importance to optimize polymer mechanical and processing properties in industry. Molecular dynamics simulation is an ideal tool to elucidate the relation between polymer structural and dynamic properties at microscopic level. Please contact Prof. Lu for further details.

Structure and dynamics properties at various polymer/NP interfaces

It is crucial to understand how much and how far the structure and dynamics properties of the polymer melt can be affected by incorporating nanoparticles (NPs) in the system. In this project, we are aiming to investigate the structure and dynamics properties at interphase region in various polymer/NP composite systems using both atomistic and coarse grained molecular dynamics simulation techniques. Please contact Prof. Qian for further details.

Self-assembly of NPs in polymer melts

Controllable distribution of NPs in PNC systems is a challenge in material science. An important method is grafting chains that are chemically identical to the polymer matrix on NPs. By using dissipative particle dynamics simulation techniques, we are studying the influences of graft density, relative chain length of graft and free melt polymers, and the dispersity in chain length distribution on the NP self-assembly behaviors in polymer melts. Self-assembly behavior and locations of such grafted NPs in different domains in block copolymer systems are also under investigation. Please contact Prof. Qian for further details.

Mechanical properties of polymer/NP composites

For polymer/NP composite systems with different self-assembly structures formed by polymer-grafted NPs, or the composite systems with different NP/polymer interphase structures, we are performing large-scale coarse-grained tensile simulations. By analyzing the distribution of interior modulus, void distribution in the system during different stages of the tensile simulation, we are trying to understand the influence mechanism of various NP self-assembly structures and NP/polymer interphase structures on the mechanical properties of composite systems. Please contact Prof. Qian for further details.

A kinetic chain growth algorithm in coarse-grained simulations

We propose a kinetic chain growth algorithm for coarse-grained simulations in this work. By defining the reaction probability, it delivers a description of consecutive polymerization process. This algorithm is validated by modeling the process of individual styrene monomers polymerizing into polystyrene chains, which is proved to correctly reproduce the properties of polymers in experiments. By bridging the relationship between the generic chain growth process in coarse-grained simulations and the chemical details, the impediment to reaction can be reflected. Regarding to the kinetics, it models a polymerization process with an Arrhenius-type reaction rate coefficient. Moreover, this algorithm can model both the gradual and jump processes of the bond formation, thus it readily encompasses several kinds of previous CG models of chain growth. With conducting smooth simulations, this algorithm can be potentially applied to describe the variable macroscopic features of polymers with the process of polymerization. The algorithm details and techniques are introduced in this paper. Please contact Assoc. Prof. Liu for further details.

Controlling factors in the surface-initiated polymerization

The surface initiated polymerization with different initiator densities and different polymerization rates is investigated using molecular dynamics simulation method. We find that the initiator density, together with the polymerization rate, greatly determines the polymer brush structure, the initiation efficiency, and the graft density, especially when the initiator density is high. The excluded volume effect also plays a crucial role in the system that the chains are densely grafted. By tuning the initiator density and modifying the polymerization rate, we can obtain the polymer brushes with different degrees of polydispersity. This study partially emphasizes the importance of considering the effects of polymerization rate in further investigations. We further study living polymerization initiated from concave surfaces. We clarify that depending on different criteria for ceasing the reaction, different relationships between grafted chain polydispersity index and the grafting surface curvature can be categorized. The average molecular weight of the grafted chains monotonically decreases as the grafting surface curvature increases. These results shed light on better control and design of functional porous materials for use in bio-implanting or chemical sensors. Please contact Assoc. Prof. Liu for further details.

Ligand number distribution in polymer-grafted nanoparticle systems

Knowing and controlling the distribution of the number of polymer chains grafted onto nanoparticles, polymer number distributions (PND) is crucial to understand the self-assembly of nanoparticles (NP) and design novel materials with advanced functions. By combining experiments and computer simulations, we demonstrate that PND for polymer grafted NPs fabricated via the grafting-to technique can be described without any fitting parameters as a function of the conversion of polymer chains. We further elucidate that this distribution can be generalized to describe the PNDs for polymer grafted NPs fabricated via the grafting-from technique, in which the conversion efficiency of the surface initiators is the only quantity to be measured in experiments. Please contact Assoc. Prof. Liu for further details.

Directed self-assembly of block copolymers on patterned nano-substrate

The self-assembly of block copolymers on the template modified with ordered posts are studied. The templates with hexagonally arranged and rectangularly arranged posts are both studied. We find by fining adjusting the distances between neighboring posts on both x and y directions, mesh-shaped structures with different angles between the bottom and the sub-bottom layers can be obtained. These results shed light on better designing lithographically patterned materials in the scale of 10 nm via the directed self-assembly of BCPs by templating. We further propose a facile inverse design strategy to generate three-dimensional (3D) nanopatterns by using either block-copolymers or binary homopolymer blend. This strategy is proved efficient on fabricating templates with desired topographical configuration, and the inverse design idea sheds lights on better control and design of materials with complex nanopatterns. Please contact Assoc. Prof. Liu for further details.

Multifunctional nanoparticle platforms for cancer therapy

Multifunctional photothermal chemotherapeutic platforms have received considerable attention in recent years. The synergy of photothermal therapy and chemotherapy can drastically overcome or reduce multidrug resistance, increase drug accumulation within targeted tumor and minimize the invasive damage to normal tissues. The therapeutic platforms are usually constructed from multi-functional blocks such as nanoparticles, porous structure and chemotherapeutics. Please contact Assoc. Prof. Zhao for further details.

Synthesis and application of covalent organic frameworks

Covalent organic frameworks (COFs) are two- or three-dimensional crystalline porous polymers that originate from the topological polymerization of building blocks with predesigned geometry and symmetry by virtue of dynamic covalent . This emerging family presents high and regular porosity, tunable pore size and pore wall chemistry, and structural predictability and stability. These characteristics endow COFs with outstanding performances for a wide-range of applications, such as gas storage, heterogeneous catalysis, proton conduction, luminescence, and photoconduction. Please contact Assoc. Prof. Zhao for further details.