Study Of Polymer Grafted Gold Nanoparticles And Polymer Colloidial Particles

Fabrication of micro/nano colloidal by polymers have became a hot topic in recent decades due to their extensive application in small molecule simulation,sensor,catalysis,material detection,assembly,drug delivery and release.The applications of traditional nanoparticles have been restricted because they had the poor stability and their surface properties were not controllable.The polymer component can serve as either steric stabilizers in solution and in polymer matrix to prevent the agglomeration of the attached nanoparticles,or functional linkers to control the structure and collective properties of the assembly of nanoparticles.So,it is critical to develop efficient methods for synthesis monodispersed polymer-grafted nanoparticles with high grafting density,uniform grafting density distribution,and low polydispersity index(PDI)of polymer ligands.Colloidal particles are the ultimate building blocks for assembly from the bottom-up.The interactions between them can be designed and adjusted,for example,by decorating the particles with ligands.Moreover,colloids are often big enough and move sufficiently slowly to be individually tracked with optical microscopes;hence,one can easily study their dynamics and arrangement into ordered or amorphous aggregates.Many consider model colloidal systems to be ‘big atoms’,much easier to play with than the real ones.As such,colloids can mimic some of the behaviour of nanocrystals,proteins,liquid crystals,vesicles,bacteria.Herefore,it is critical to fabrication colloidal with special structure and ligands.In the chapter 2,we reported a facile yet general in-suit seed-mediated method for the synthesis of polymer grafted gold nanoparticles(GNPs)with narrow size distributions(<10%).Gold seeds with sizes of below 2 nm in aqueous solution were synthesized.1-Methylpyrrolidine(1-MPR)was used as reducing agent and thiolterminated polystyrene(PS-SH)was used as ligangds.Because the 1-MPR and PS-SH were large excess,the reaction was the “living reaction”.The size of the produced PS grafted GNPs(GNP@PS)was accurately fine-tuned from 9.0±0.5 to 23.7±1.8 nm depending on the re-growth steps(i.e.gold precursor to seed ratio).Importantly,the GNP@PS prepared by in-situ seed-mediated method showed better colloidal stability than that prepared by grafting-to method with the same size of GNPs and molecule weight of PS-SH ligands.Different molecular weights of PS-SH(4200 to 40000 g/mol)showed negligible effect on the size and size distribution of the resulting GNP@PS,but can be used to control their hydrodynamic radius.We also demonstrated that the in-situ seed-mediated method was applicable for the synthesis of GNPs with other polymer ligands.This method can be extended for the preparation of polymer grafted gold nanoparticles with other shapes,e.g.GNR(gold nanorods)@PS by using preformed GNRs as the seeds.In the chapter 3,we studied the effect of thiol-terminated polystyrene(PS)synthesized by Reversible Addition-Fragmentation Chain Transfer Polymerization(RAFT)on ligand exchange of gold nanoparticles with polymer.2-Phenyl-2-propyl benzodithioate(CDB)was used as Chain transfer reagents.CDB had an absorption peak on the UV spectra.Using this absorption peak,we developed a method for quantifying the content of PS-CDB in PS with UV-visible spectroscopy and the PS-SH was determined.And then we synthesized PS with different molecular weight by RAFT polymerization.With the increasing of the molecular weight,the percentage of PS-SH was decreasing.The PS with different molecular weight was used to perform a ligand replacement reaction.The results showed with the increasing of the PS molecular weight,the result of ligand substitution reaction was worse.This explains why the ligand replacement efficiency of the polymer with large molecular weight synthesized by RAFT polymerization method was very low.Then we found that with the PS-SH content decreased,the ligand replacement reaction effect was poor.The larger molecular weight of the PS needed higher concentration.In this chapter,we demonstrated that the success rate of the ligand replacement reaction was determined by the proportion and absolute content of the thiol end-group polymer in the system.In the chapter 4,we demonstrated a microcolloidal analogue of supramolecular host–guest system consisting of polymer microrings as micro-hosts(μHs)and spherical particles as micro-guests(μGs).A facile two-step selective plasma etching process was used for the fabrication of μHs with accurately size-controlled hollow structures on substrates.The surface charge of μHs can be tuned through wet-chemistry sulfonation and supramolecular layer-by-layer(L-b-L)deposition of cationic polyelectrolytes.The 200 nm PS nanoparticles with diffferent charges were adsorbed onto the inner surface of the PS microrings uniformly,demonstrated the surface charge of PS microrings was uniformity.The electrostatic attraction between oppositely charged μGs and μHs resulted in a high inclusion yields(up to 98.7%)for the entrapment of multiple small μGs by one μH on the substrate and for the bigger μGs the assembly yields reached 87.0%.The yields strongly depended on the μHs and μGs size ratio and their charges.We had also demonstrated that the resulting μHs and μGs compounds(μG@μHs)were stably dispersed in aqueous solution even after being peeled off from the substrate.