Study On The Modulation Of Structures And Properties Of Soft Matter Films Using Computer Simulations

Soft matter is a kind of matter that the structures and properties could be changed under a mild external perturbation.The block copolymer films and biomembrane films are the typical systems of soft matters.The research on the modulation for the structures and properties of soft matter has been attracted great attention because the characteristic size of soft matter is in the range of mesoscopic scale.In this thesis,we proposed two strategies for removing defects in block copolymer thin films by using dissipative particle dynamics(DPD)simulation method.We also studied the curvature-mediated interactions between soft nanoparticles on a cell membrane using molecular dynamics(MD)simulation method.Dibolck copolymer thin films are important in the semiconductor industry.In the process of self-assembly of diblock copolymer thin films,the structures of diblock copolymers can be easily trapped in the thermodynamic non-equilibrium state,which impedes the applications of diblock copolymer films in industry owing to the easier formed defect structures.It’s therefore very important to obtain a highly-regulated diblock copolymer films through molecular structure design and external modulation process.Up to now,there are several strategies which can be used to remove the defects of diblock copolymer films,including thermal annealing,solvent annealing,shear field and directed self-assembly processes.In this thesis,two new strategics are proposed to remove the defect structures of diblock copolymer films.The first one is modulating the particle attractive and repulsive interactions through a time-oscillatory manner,and the second one is catassembly.The defect structures in diblock copolymer films could be annihilated by avoiding the thermodynamic non-equilibrium state using these two new strategies,and the thermal equilibrium state could be reached quickly.The kinetic process and the mechanism for the annihilation of defects in diblock copolymer films were studied through the modulation of particle interactions and by using the strategy of catassembly.The results show that the defect structures could be annihilated by controlling the attractive duration time,repulsive duration time and interaction strength between the two units of diblock copolymers through a time-oscillatory strategy.At the same time,we also studied the process for the annihilation of defects in diblock copolymer films by using single-particle or two-particle catalytic assemblers.We found that the thermodynamic equilibrium state in diblock copolymer films could be obtained in a short periods of time through annihilating the defect structures by controlling the contents and properties of catalytic assemblers.Biomembrane is another kind of soft matter.The curvature-mediated interactions by cell membranes are crucial in many biological processes.In this thesis,we systematically studied the curvature-mediated wrapping of two soft nanoparticles by a tensionless membrane and the underlying pair interactions between nanoparticles in determining it by using MD.The results show that the size and softness for nanoparticles,the adhesion strength between nanoparticles and cell membrane are found to be strongly related with the wrapping mechanism.We found that there are three types of wrapping pathways,namely,independence,cooperation and tabulation.Reducing the adhesion strength transforms the wrapping pathway from cooperation to independence,while enhancing the nanoparticles softness requires a stronger adhesion to achive the cooperative wrapping.Our results provide a mechanistic understanding in detail about the membrane-mediated interactions between nanoparticles and their interactions with cell membrane,which is helpful to understand the curvature-mediated assemblies of adhesive proteins or nanoparticles on membranes,and provide novel possibilities for the design of an effective nanoparticle based vehicle for controlled drug delivery.