Preparation Of Silver Nanocrystal Clusters Via Unimolecular Micelle Template And Its Antibacterial Properties

Silver（Ag）nanomaterials have been widely investigated due to their broad-spectrum antimicrobial actions.Bare Ag nanoparticles,with diameter less than 10 nm have high antibacterial activity,but it have poor stability.Its easy agglomeration and high reducibility hinder its long-term antibacterial applicataions.It is still a tough work to balance the high antibacterial efficiency with the low damage to biological cells of silver nanostructures.The cluster structure assembled by small-sized grains seems to have the potential to maintain the small size effect and large size stability,and give us a new idea to solve the contradiction between size and stability,antibacterial efficiency and cytotoxicity in the design of Ag antibacterial nanomaterials.In this dissertation,star-shaped copolymersα-CD-g-[(PEO₄₀-g-PAA₅₀)-b-PEO₅]₁₈have been synthesized by a combination of anionic copolymerization and atom transfer radical polymerization（ATRP）,and used as template to prepared Ag nanocrystal clusters.The main work is summarized as follows:（1）α-CD-g-[(PEO₄₀-g-PAA₅₀)-b-PEO₅]₁₈ have been synthesized by a combination of anionic copolymerization and ATRP.It has narrow molecular weight distribution and clear structure.The micelle behavior ofα-CD-g-[(PEO₄₀-g-PAA₅₀)-b-PEO₅]₁₈ in three typical polar solvents,including DMF,CH₃OH and H₂O,was investigated.AFM and DLS together illustrates the micelles are spherical with uniform size,and they are all in a stable state.However,the difference of solvent polarity and solubility parameters affect the sizes of micelles.The star copolymer obtained unimolecular micelle in DMF with hydrodynamic diameter（D_h）of 39.7±8.0 nm,which provided a stable template structure for the preparation of Ag nanocrystal clusters.（2）Ag nanocrystal clusters（Ag NC）were prepared by using the unimolecular micelle as the soft template,DMF as the solvent,silver nitrate（Ag NO₃）as the precursor and tetrabutylammonium borohydride（TBAB）as the reducing agent.TEM characterization shows that the average diameter of Ag NCs（the aggregates of small primary Ag grains）are around 40 nm.The dimensions of Ag grains can be adjusted precisely by changing molar ratio of Ag NO₃ to AA repeating units.When the molar ratios of Ag NO₃ to AA units was 1:10 to 1:1,the average diameter of Ag grains was1.6±0.3 nm to 5.6±0.9 nm.At room temperature,Ag NCs exhibited higher stability and water dispersibility than Ag nanoparticle（Ag NPs）.（3）The antibacterial tests and cytotoxicity tests indicate that Ag NCs display much better performance than Ag NPs,and the antibacterial properties of Ag NCs have a significant size dependence.Ag NCs have low minimum inhibitory concentration（MIC）and minimum bactericidal concentration（MBC）values for E.coli and S.aureus.The MIC values of Ag NC（the size of grains is 1.6±0.3 nm）are as low as 5μg/m L and 10μg/m L,the MBC values are as low as 10μg/m L and 20μg/m L.For L02 cells,no cytotoxicity was detected in Ag NC（the size of Ag grains is 2.4±0.4 nm）at a concentration of 80μg/m L（8 times the MIC value of E.coli）.In the Ag⁺release experiment,Ag NCs showed long-term antibacterial ability and lower release amount than Ag NP,and Ag NCs released nearly 30%in 21 days.The Ag nanocrystal clusters structure prepared in this dissertation can achieve the unification of the goals of small size and high stability,high antibacterial activity and low toxicity,it provides a new idea for the preparation of Ag antibacterial nanomaterials,and makes Ag nanocrystal clusters have broader application prospects.