Study On The Self-assembly Of Block Copolymers And Its Co-assembly With Gold Nanoparticles Under Three-dimensional Confinement

Block copolymers (BCPs) can self-assemble into various nanostructures such asspherical，cylindrical，vesicle and onion micellesor lamella phases in dilute solution.These novel BCP aggregates have received intensive attention these years because oftheir potential applications in the fields of medicine, biology, electronics, andcatalysis.Based on the previous studies, this paper studied the self-assembly behavior offour types of block copolymers under3-dimensional confinement. The emulsionsolvent-evaporation method is used in this study. The obtained nanoparticles haveobvious phase-separated nanostructures.Several control parameters on the micellarstructures， including block contention and surfactants， have been investigatedsystematically. Subsequently, we can get the following conclusions:(1) Sincepoly(vinyl alcohol)(PVA) has comparable interaction with both PS and P4VP block,introducing of PVA as a surfactant into the system can change the interfacialproperties of PS and P4VP blocks, resulting in the change in the overall shape and theinternal nanostructures of the micelles.(2) When PVA concentration is fixed，thedifferent contention of the molecular weight will lead to the diverse micellarmorphology for different block copolymers under the constant concentration of PVA.Moreover, this paper also studied the co-assembly of PS9800-b-P4VP10000，PS35000-b-P4VP2700block copolymers and gold nanoparticles under3-dimensionalconfinement. The influences of entropy and enthalpy on the spacial arrangement ofgold nanoparticles within the block copolymer matrix are examined. Typically,incorporation of nanoparticles into the polymer matrix can lead to obvious entropyeffect and enthalpy effect. Among them, the enthalpy effect mainly depends on the compatibility between nanoparticle surface ligands and polymer matrix. Entropyeffect mainly depends on the translational entropy of the nanoparticles and theconformation entropy of polymer chains. Incorporation of nanoparticles into thepolymer matrix will occupy the position of the polymer chains and lead to polymerchains bypass the nanoparticles to rearrange and cause conformational entropy loss.As the the nanoparticle size is greater, there will be more conformational entropy loss.In experiment, PS and P4VP are used to modify gold nanoparticles., thus minimizingthe enthalpy repulsion. So entropy repulsion is the main factor in co-assembly ofblock copolymers and gold nanoparticles. We can see that1.7nm gold nanoparticlescan uniformly distribute in the polymer matrix, while the3.5nm gold nanoparticlestend to distribute at one end of polymer nanoparticles to compensate entropy losscaused by the introduction of nanoparticles. This reduces the free energy of systemand makes stable of polymer micelle morphology.