Preparation And Small Angle X-ray Scattering Characterization Of Functional Nanoparticles

Functional nanoparticles with unique properties, e. g., magnetic, catalytic and biocompatible properties, have significant potential applications in the chemical and biological field, such as controllable catalysis, targeted drug delivery and biosensors. In this thesis, four kinds of functional nanoparticles system were prepared and characterized by small angle X-ray scattering (SAXS), including spherical polyelectrolyte brushes responsive to the pH and saline ionic strength of the solution, spherical polyelectrolyte brushes immobilized with magnetic nanoparticles or silver nanoparticles, spherical polyelectrolyte brushes adsorbed with bovine serum albumin (BSA), asymmetric magnetic polymer particles and asymmetric polyelectrolyte brushes. The influence of pH and ionic strength on these functional nanoparticles was investigated and the distribution of metal nanoparitlces or BSA in spherical polyelectrolyte brushes was obtained. Details for this thesis are listed as follows:The polystyrene cores were grafted with poly(acrylic acid)(PAA) chains by photoemulsion polymerization and the products were spherical polyelectrolyte brushes. The solution of spherical polyelectrolyte brushes at different pH and saline ionic strength was tested by SAXS. Lognormal distribution was first introduced to describe the excess electron density profile of the shell of spherical polyelectrolyte brush and the calculated curves fitted well with the experimental SAXS intensities. The size, polydispersity index and the formation of PAA chains were achieved from the fitting result, which is in accordance with the TEM and dynamic light scattering results. The SAXS results proved that the size of spherical polyelectrolyte brushes increased as the pH increased, due to the increased degree of ionization of PAA and electrostatic repulsion. As the salt concentration increased, the scattering intensities increased, which meant that Na+had entrered into the brush shell, demonstrating the spherical polyelectrolyte brushes’capability of concentrating counterions.Using spherical polyelectrolyte brushes as nanoreactors, magnetic nanoparitlces or silver nanoparticles were prepared, whose amount were both increased by multiple loading reactions. The SAXS results showed that the polydispersity of spherical polyelectrolyte brushes immobilized with magnetic particles was increased as the loading times were increased. The fitting result revealed the distribution of magnetic nanoparticles in polyelectrolyte chains, which was the result from the static interaction and space resistance. The spherical polyelectrolyte brushes immobilized with silver nanoparticles demonstrated the same behaviors and silver nanoparticles were mainly distributed in the vicinity of polystyrene cores. Since there existed PAA chains where no magnetic nanoparticles were located, spherical polyelectrolyte brushes loaded with nanoparticles also responded to pH and ionic strength.Spherical polyelectrolyte brushes immobilized with BSA were investigated by SAXS. The fitting results indicated that BSA was adsorbed within the PAA shells by static interaction. Because of the spherical geometry and lipophilic property of polystyrene cores, the BSA was mainly located in the vicinity of polystyrene cores. As the pH increased (pH>5), a scattering peak appeared in the large q zone, which demonstrated that more and more BSA came out of spherical polyelectrolyte brushes, redispersed in the solution and aggregated, agreeing with the ultraviolet spectrophotometry results.Asymmetric magnetic polymer particles of100nm were prepared with magnetic nanopartilces and styrene by miniemulsion polymerization. Then after further1and2times of seed emulsion polymerizaiton, the size was increased to200nm or450nm, respectively. As the polymerization was carried, the phase separation between magnetic nanoparticles covered with oleic oils and polystyrene was found to be intensified. Some magnetic nanoparticles were pushed out of the polymer beads. The polystyrene part of asymmetric magnetic nanoparticles of200nm was grafted with PAA, where there were no magnetic nanoparticles to inhibit the grafting. Thus the asymmetric magnetic polyelectrolyte brushes were fabricated. Like the regular polyelectrolyte brushes, the asymmetric magnetic polyelectrolyte brushes responded to pH and could adsorb protein. This asymmetric spherical polyelectrolyte brushes has great potential application in interfacial enzymic catalysis.