Preparation And Assembly Of Temperature Sensitive Composite Microgels Based On Gold Nanorod As Core

Intelligent composite microgels based on inorganic nanoparticles and intelligent microgels are the advanced intelligent materials which attracted much attention in recent years. They have unique properties from the inorganic nanoparticles, and these properties can be changed in response to external stimuli, so they have an attractive application prospect in drug targeted delivery and controlled release, medical diagnosis, biosensor, smart microreactor, etc. In this thesis, gold nanorods (AuNRs) with unique optical properties were loaded into poly(N-isopropylacrylamide)(PNIPAM) microgels to produce the temperature sensitive composite with core-shell structure. The composite microgels have the advantages of regular morphological structure, uniform AuNRs content and no interference between AuNRs. However, the intelligent microgels, like other intelligent microgels, usually exist as colloidal particles dispersed in water, or as powder after freeze drying, so they have limited practical applications, such as drug delivery carrier. Hence, the intelligent composite microgels were assembled to generate a product with stable structure and macroscopic size by centrifugation followd by post-crosslinking in the thesis. The assembly product would have wider application fields, such as sensors, biomaterials and surface-enhanced Raman scattering (SERS) substrates. The major research works and obtained results include the following three aspects.(1) The AuNRs with relatively regular shape and aspect ratios of less than5were synthesized by a seed growth method. Their aspect ratios can be adjusted by changing the used amount of AgNO3and seed solution in a certain range. High resolution transmission electron microscope (TEM), ultraviolet-visible-near infrared spectroscopy (UV-vis-NIR) and small angle X-ray scattering (SAXS) are used to measure their aspect ratios. The results from these three methods are very close when their aspect ratios are less than3. The shape of AuNRs and the mixed gold nanospheres content can directly observed by TEM, but their aspect ratio from TEM is the average result of a small portion. The average aspect ratio of the whole AuNRs can be obtained by UV-vis-NIR and SAXS methods, whereas their shape is difficult to be viewed and their aspect ratio dispersity cannot be acquired.(2) The surfaces of AuNRs are firstly modified by3-butenoic acid (3-BA), then the modified AuNRs were encapsuled by crosslinked PNIPAM by seed precipitation polymerization to produce AuNR@PNIPAM composite microgels. Images from TEM show that the composite microgels have regular core-shell structure and good monodispersity. The hydrodynamic diameters measured at different temperatures by dynamic laser light scattering (DLS) indicate that they have temperature sensitive property like pure PNIPAM microgels. Their volume phase transition temperature (VPTT) increases with decreasing the thickness of their PNIPAM shell and is independent of the crosslinking density of the shell. UV-vis-NIR results show that AuNR@PNIPAM composite microgels have localized surface plasmon resonance (LSPR) optical property. Their horizontal LSPR absorption wavelength is nearly independent of temperature, but longitudinal LSPR absorption wavelength is pronouncedly dependent on temperature. The thicker their PNIPAM shell, the more significant the wavelength variation with temperature; the smaller the shell’s crosslinking density, the less marked the wavelength change. In addition, the change of longitudinal LSPR absorption wavelength with temperature is reversible.(3) AuNR@PNIPAM composite microgels were firstly modified to provide amino groups on their surfaces by precipitation copolymerization, which can react with aldehyde groups. Their temperature sensitive property is not notably influenced by surface modification, while their zeta potential is dramatically raised and their particle size increases by20nm. Centrifugation method was used to assemble AuNR@PNIPAM composite microgels, then glutaraldehyde was added to covalently link the neighboring microgels by the condensation reaction between glutaraldehyde and amino groups on their surfaces. Ultrasonic oscillation experiment results show that the assembly product has good stability in water, and its reversible temperature sensitivity was observed by optical microscope.