The coarse-grained method of soft matter molecular interaction is a hot topic in current research.Grasping the influence of molecular interactions on the long-term relaxation and endocytosis behavior of large systems of soft materials from the mesoscopic scale is of great significance for guiding the design of new polymer-based composite materials and nanomedicine.Traditional molecular simulation technology is difficult to reach the corresponding time and space scale.The existing coarse-grained models have problems such as low degree of coarse-graining,cumbersome coarse-graining process,and poor portability.In this paper,the coarse-grained Brownian dynamics model is studied for the interaction between soft matter molecules.Taking chains,rods,membranes and particles as the basic units,and in the order of interaction between chain and chain,rod and chain,rod and membrane,and particle and particle,the following four aspects of research work are carried out:First,for entanglements between chains in polymer melts,using the slip-spring model,by changing the entanglement update strategy,the relaxation behavior of the monodisperse melt and the probed chain melted in the long-chain matrix are simulated.The results show that the constraint release in the monodisperse melt accelerates the dielectric relaxation and viscoelastic relaxation of the polymer chains,and the relaxation strength and relaxation time obtained are consistent with the literature experiment.A single-chain slip-spring model with entanglement lifetime version is proposed.Through self-consistent description of the sliding dynamics and constraint release of polymer chains,the lifetime distribution of entanglement is determined.The relaxation results obtained by simulation are consistent with literature experiments.A multi-chain slip-spring model with fluctuation entanglements numbers is realized by introducing the exclusion volume interaction for the inhomogeneous system,which can accurately simulate the relaxation behavior of polymer melt and the unentanglement under nonlinear shear flow.Secondly,for interactions between nanorods and polymer chains in polymer melts doped with nanorods,based on the absolute nodal coordinate formulation and the Brownian dynamics framework,a beam element describing the motion of the nanorod is proposed,and combining with the polymer melt model,the diffusion of the nanorod in the unentangled melt and the entangled melt are studied respectively.The results show that in the unentangled melt,the diffusion of the nanorods becomes slower with the increase of the chain length.In the entangled melt,when the diffusion speed of the nanorods is slower than that of the polymer chains,the relaxation of the polymer chains dominates the diffusion behavior of the nanorods.When the diffusion of nanorods is much faster than the relaxation of polymer chains,the translational diffusion coefficient of nanorods don’t depend on the length of the polymer chains.When the volume fraction of the nanorods is low,compared with the immobile case of the nanorods,the mobility of the nanorods accelerates the diffusion of the polymer chains.As the volume fraction of the nanorods further increases,the diffusion of the polymer chains slows down.Due to the additional entanglement of the nanorods on the polymer chains,the viscosity of the system increases significantly.Third,a coarse-grained nanorod and cell membrane model combining Brownian dynamics and absolute nodal coordinates is proposed.Through the contact detection and the establishment of the LJ potential energy interaction model,the contact area and the interaction force are determined,The diffusion of the cell membrane is studied and the validity of the proposed formula is verified.The rebound or adhesion behavior caused by the collision of the different size ends of the tapered nanorods with the cell membrane is accurately predicted.The receptor-ligand dynamic binding process in the simulation is realized,indicating that the ligand-receptor binding plays an important role in improving the endocytosis efficiency of the nanorod.It is studied whether two nanorods interact with the cell membrane in a cooperative or separate endocytosis configuration.When the interaction of the nanorods is strong,the nanorods tend to stick together to be internalized cooperatively.When the interaction between the nanorods and the cell membrane is stronger,the nanorods are internalized separately.Finally,studies on the cooperative endocytosis of nanoparticles and the use of cooperative relationships to achieve targeted functions have been carried out using the coarsegrained one-bead thickness lipid membrane model.It is revealed that the mechanism of the phenomenon that two small particles can cooperatively internalized but a single particle cannot be endocytosed is that the smaller curvature of the contact edge between the two particles co-wrapped and the phospholipid membrane leads to greater wrapping force.The two particles may cause the destruction of the phospholipid membrane under the strong receptor-ligand strength or at a specific concentration of nanoparticles.For the cooperative endocytosis of two elastic nanoparticles,when the interaction between the two particles is stronger,the cooperative endocytosis efficiency is improved because the soft particles can combine to form a larger nanoparticle cluster,and when the interaction strength between the two particles is small,soft nanoparticles need to overcome a larger energy barrier,which leads to a decrease in the efficiency of cooperative endocytosis.The nanoparticles with different endocytosis properties were composited,and two nanomedicines were designed: composite nanoparticles modified by different ligands and composite nanoparticles formed by physical adsorption of nanoparticles with different sizes.Both composite nanoparticles have the targeting ability.This paper provides a reference for realizing long-term and large-scale coarse-grained simulation methods of soft matter systems. |