Synthesis, Application And Small Angle X-ray Scattering Characterization Of Spherical Polyelectrolyte Brushes

Spherical Polyelectrolyte Brushes (SPB) with many unique properties, such as high grafting density and relatively constant pH and ionic strength in brush layer, can be widely applied in selective adsorption of metal ions, protein immobilization, nanocatalyst preparation, controllable release of drug. In this paper, anionic and cationic SPB were prepared. Magnetic nanoparticles were either synthesized with SPB as nanoreactor or covered within the core of SPB to prepare magnetic SPB. Small Angle X-Ray Scattering (SAXS) was employed to study the adsorption amount and distribution of magnetic nanoparticles or bovine serum albumin (BSA) within brush. The results in this paper lay the theoretical basis of SPB application in protein separation, enzyme immobilization, and nanometal (or metal oxides) preparation. The details are shown as follows:Anionic and cationic SPB were synthesized by grafting poly(acrylic acid) (PAA) and poly(2-aminoethyl methacrylate hydrochloride) (PAEMH) respectively densely onto polystyrene (PS) core by photo-emulsion polymerization. The effects of concentration, pH and ionic strength on structure and interactions among anionic SPB at high concentration were investigated by SAXS. The model of five subsequent subshells was introduced to describe the profile of electron density contrast in SPB layer and obtain the size and size distribution of SPB which was compared with transmission electron microscopy (TEM), scanning electron microscope (SEM) and dynamic light scattering (DLS). The results showed that the interactions among PAA chains increased with the rise of SPB concentration. The ionization degree as well as electrostatic repulsion and SPB thickness increased and reached maximum upon increasing pH. The local ordering structure among PAA chains formed at appropriate ionic strength, while too high ionic strength screened the interactions among SPB chains, even led to the aggregation of SPB.Magnetic manoparticles (Fe3O4) was prepared with anionic SPB as nanoreactor. The distribution of magnetic nanoparticles within SPB layer and the effects of pH, ionic strength and loading times were studied by SAXS. The SAXS results revealed that magnetic nanoparticles mainly located nearby the surface of PS core. As pH increased, the thickness of SPB layer increased and reached the maximum after pH 8. Furthermore, magnetic nanoparticles were synthesized by coprecipitation method, and then covered into PS core by miniemulsion polymerization to prepare the magnetic SPB which are responsive to magnetic field. The SPB with magnetic nanoparticles in the PS core were responded to pH and ionic strength. However, SAXS results revealed that the magnetic nanoparticles in the PS core contributed most of the scattering intensity, so the effects of pH and ionic strength on the microstructure were not reflected by SAXS.Immobilization of bovine serum albumin in anionic SPB immobilized with was studied by SAXS. The results indicated that upon increasing BSA concentration, BSA amount increased uniformly until reaching saturated adorption. With the rise of pH from 3 to 5, the adsorption amount of BSA within SPB layer increased, then decreased when pH further increased from 5 to 7. The BSA adsorption amount in SPB was affected obviously by ionic strength. To sum up, the driving force for BSA adsorption onto SPB layer was electrostatic interactions.The BSA adsorption onto cationic SPB was investigated by SAXS. The effect of BSA concentration on the adsorption onto cationic SPB was very similar to that of anionic SPB. As pH increased from 4 to 6.1, the adsorption amount of BSA increased, then decreased after pH> 6.1. With the rise of ionic strength, the adsorption amount of BSA in SPB layer decreased. Time-resolved SAXS was employed to study the dynamic adsorption process of BSA onto cationic SPB. The SAXS results revealed that in very short mixing time (< 0.16 s) of SPB and BSA, SPB were aggregated bridged by BSA. As mixing time increased, the BSA within SPB layer dispersed and reached the adsorption equilibrium. Meanwhile, the aggregated SPB were also dispersed.