Simulation Study On The Surface Pattern Induced Self-assembly Of Diblock Copolymers

The system composed of block copolymers has a very strong self-assembling capability,and its assembled microphase structure brings a wealth of properties.Molecular structures,block ratios,and sequences of block copolymers have very large influences on the microphase structures and their evolutionary processes,and ultimately a direct impact on mechanical and other properties.In recent years,the self-assembly of block copolymers has attracted widespread attentions from scientists and researchers in academia and industries.Especially,the double-gyroid phase structures have particularly important application value in the field of battery solid electrolytes and solar cells.In this dissertation,the surface pattern induction on self-assembly of diblock copolymers is studied.The induced structures of the diblock copolymers are analyzed for the strip pattern and the circular pattern,respectively.After a series of simulation studies,the phase diagram is plotted.The radial distribution function and structure factor are used in the analysis of structures.First,the diblock copolymers A₂B₈,A₃B₇,A₄B₆,and A₅B₅ are simulated.It is found that A₅B₅ can form a very good lamellar phase.Considering the influence of chain length,we simulate A₁₀B₁₀ with the same component ratio as A₅B₅ and find that it can form a clearly structured lamellar phase like A₅B₅.All subsequent simulation studies are based on the diblock copolymer A₁₀B₁₀0 model.Secondly,adding substrate-induced conditions to the diblock copolymer system,we do the simulation study on the induction of the diblock copolymer by the band pattern.There are 4 particle types in the system.The A and B particles constitute the diblock copolymer and C,D particles constitute the substrate.By adjusting the parameters,we find that the minimum repulsive interaction with?=40 can make the directon of A₁₀B₁₀ lamellar phase change.When the proportions of C and D particles in the strip substrate change,the structure of the system will be affected.The lamellar structures with different widths at diferent distance from the induced surface will be formed.Finally,the induction on the self-assembly of diblock copolymer by the circular pattern is studied.The A and B particles similarly constitute the diblock copolymer,and the C and D particles similarly constitute the substrate.The C particles form the circular pattern on the substrate.When the radius R of the circle become large enough,a perforated structure with an unequal number of holes will be formed.We do the simulation with R=4.5¹4.It is found that when R reaches 5.5,a perforated structure appears in the system.Two holes appear in the system with R=5.5.Three holes appear in the system with R=6 and four holes are found in the system with R=9.In response to this discovery,a series of simulations are performed on the critical R by changing film thickness H.The structures were classified according to the characteristics of the structure.They are classied into four major categories,labled as PLS-?,PLS-?,PLS-?,PLS-?.The phase diagram of the system is plotted for these four structures.The thickness of the periodic lamellar phase structure formed by block copolymer in the bulk is about 10.The circular pattern with R=10 has the most significant induction effect.Therefore,we consider that the degree of the pattern matching the feature size of phase separation has a large impact on the structure.When the induction pattern periodically matches the phase size,an optimal double-gyroid phase structure of diblock copolymer could be formed.