The Research Of Phase Behavior And Application Of Spherical Polyelectrolyte Brushes In Supercritical/Compressed Carbon Dioxide

Spherical polyelectrolyte brushes (SPB), consisted of colloidal particles which long linear polyelectrolyte chains grafted densely onto surface, have aroused significant interest and attention due to their unique structure and characteristics. It can be used as nano-reactors for the immobilization of metallic nanoparticles and also as idea carriers for absorption of enzymes or proteins. SPB have offered a lot of opportunities for novel potential applications in catalysis and bio-engineering. Supercritical carbon dioxide (scCO2) is the most often used supercritical fluid because it has unique properties and it is also environmentally benign that satisfies green chemistry. In this paper, CO2 was employed as the "pressure switch" to tune the properties of SPB solution and induce the microphase separation of the absorbate from the SPB system. The absorbate and SPB can be precipitated respectively and recovered by this simple and effect way. We hope the way for the separation and recovery of SPB can promote a wider range of applications of SPB.The main works and results are summarized as follows:1. The SPB consisted of a polystyrene (PS) core and poly (acrylic acid) (PAA) chains was synthesized. The phase behavior of PS-PAA brushes-CO2-solvent ternary system was investigated in detail. The cloud point of the system was measured under different temperatures, the solid contents and the sizes of the PS-PAA brushes. The results showed the cloud point pressure of system increased with the increasing of temperature and increasing of the solid content increased while it decreased with the size of PS-PAA increased. The PS-PAA brushes can be separated from the solution and recovered by controlling the pressure. After the several cycles of separation and redissolution by adjusting pressure, the size of PS-PAA brushes were almost not change. Then the Ag nanoparticles were loaded on the PS-PAA brushes. The Ag nanoparticles and PS-PAA brushes can be precipitated successively by compressed CO2 at suitable pressures. In this way, the Ag nanoparticles were seperated from the PS-PAA brushes and well-dispersed Ag nanoparticles were obtained.2. In this experiments, the PS-PAA brushes were selected as the carriers for the absorption of bull serum albumin (BSA). The absorption-desorption process between BSA and PS-PAA brushes was adjusted by CO2. Differnet techniques, such as phase state research, dynamic light scattering (DLS), UV-vis, and zeta potential were used to study the process. With the increasing of CO2 pressure, the complex aggregation was formed between the BSA and SPB at first, then the complex was redissolved in the solution, and finally the BSA can be desorbed from the PS-PAA brushes with increasing of CO2 pressure. The UV-vis spectrum results showed the desorbed BSA could keep their activity. From the circular dichroism spectrometer, the secondary structure of desorbed BSA remains stable without obvious changes. It indicated the absorption-desorption process has a rare effect on the activity and structure of the BSA. The desorbed BSA can be absorbed on the PS-PAA brushes again, and the absorption-desorption cycle can be repeated several times.3. We have synthesized the polybutadiene (PB) core with the PAA chains grafted onto its surface. The phase behavior of the PB-PAA brushes-solvent-CO2 system was also studied which was similar with the PS-PAA system. As expected, the results were also consistent with the PS-PAA system. In the meantime, water was selected as the cosolvent to investigate the influence of different content of solvent on the system. The cloud point pressure of the system increased with the increasing of volume fraction of water in the solvent. The Ag nanoparticles were synthesized on the PB-PAA brushes. The effect of the chloride ion on the Ag nanoparticles loaded on the PB-PAA brushes under compressed CO2 was investigated. In the absence of CO2, the UV spectrum displayed that the red shift of the absorption of Ag nanoparticles at maximum wavelength (λmax) was occurred. While with the collaboration of CO2 and Cl", the UV absorption peak of Ag nanoparticles decreased in intensity and the peak position at λmax showed a blue shift. TEM photograph showed the size of Ag nanoparticles decreased as a result of the fabrication of Ag nanoclusters near around the original Ag nanoparticles.