Block Copolymer PS-b-PMMA Self-assemble To Synthesize Nano Arrays And Monodisperse Magnetic Nanoparticles

Magnetic particles at nanoscale can be prepared by physical or chemical method; however,the wide size distribution of the particles,the exposing of the bare grain surface,and the intergranular existence strong magnetism interaction between particles,make it very easy to have the reunion,causing the magnetic material to lose the single domain magnetic pole and the nanomaterials unique nature.The modification on the surface of nanoparticles,is the main method to get monodisperse magnetic nanoparticles.Because the block copolymer incompatibility between the different blocks,it can occur microphase separation.On the one hand,by changing the relative ratio of constituent blocks,the copolymer can self-assemble into all kinds of ordered nanometer structure,and it has already brought to the widespread attention in optical material's research.On the other hand,using the hydrophilic/hydrophobic property of different blocks,it can be used to modify the surface of nanometer magnetic particles,thus we can obtain monodisperse magnetic nanoparticles.We used the anion polymerization method to synthesize narrow molecular weight distribution block copolymer PS-b-PMMA,with molecular weight of 161022 and the PDI of 1.29.Block copolymer PS-b-PMMA films were prepared on Si substrates using spin coating technique,and the solvent annealing or high temperature annealing process was used to control the self-assembly.TEM morphology shows that: we have got two-phase separation films with uniform distribution.PMMA nano-dots uniformly distribute in the PS substrates,with a diameter of about 20 nm,spacing of 40 nm,density of 6.25×10¹⁰cm^-2.Then we studied the effect of the block proportion, the solvent annealing time,the post-processing method and the choice of solvent to the nanometer appearance.We find that:To a certain extent,with the increase of PMMA block proportion,the diameter of PMMA nano-phase increased significantly; Using solvents annealing method,the block copolymer self-assemble in a saturation vapor pressure,and the speed of proliferation and self-assembly can be restrained. This is conducive to the formation of small uniform morphology;The suitable extension of solvent annealing time is helpful to an enhancement nanometer dispersion degree,and structure regularity;For PS-b-PMMA films,when use the solvent annealing to control self-assembly,the film morphology using toluene as solvent,is more uniform than the film using THF.Finally;we attempted to use block copolymer PS-b-PMMA to enwrap magnetic Fe₃O₄ nanoparticles.The diameter of modified particles is 60 nm,and display obvious ultra-paramagnetism.It indicatesd that block copolymer modified magnetic nanoparticles may realize monodisperse state.