Investigation On The Interactions And Microstructure Of Spherical Polyelectrolyte Brushes

The core-shell spherical polyelectrolyte brushes (SPB) consist of spherical polymeric core and on which the linear polyelectrolyte chains are densely grafted covalently. Polyelectrolyte chains can not only enhance the stability of the system, but also can response uniquely to the environmental conditions, including pH and added salt concentration. All the unique characteristics make SPB applicable in wastewater treatment, separation films, new catalysts and delivery of drugs.In this paper, PMMA/PAA brushes have been synthesized by thermo-controlled with poly(methyl methacrylate) (PMMA) core and poly(acrylic acid) (PAA) shell; PS/PAA brushes have been prepared through photo-controlled emulsion with polystyrene (PS) core and poly(arylic acid) (PAA) shell. The microstructure of SPB has been characterized by transmission electron microscopic (TEM), and the diameter of SPB and its response to environmental factors (pH and added salt concentration) has been investigated by dynamic light scattering (DLS). The interactions and microstructure of concentrated (weight concentration> 15%) brushes latex have been characterized by the rheology from macroscopic view and by SAXS from microscopic view. The innovation of this work lies in the discovery of local order formed among SPB using SAXS equipment from Shanghai Synchrotron Radiation Facility (SSRF), which is combined with rheologial properties to further explore the interactions and microstructure. The main work has been described as following:(1) The PMMA/PAA and PS/PAA brushes have been prepared by thermo-controlled and photo-controlled emulsion polymerization, respectively and characterized by DLS and TEM. The results indicate that interactions of SPB and the thickenss of the PAA shell can be controlled by pH and added salt concentration. Moreover, effects of pH and added salt concentration on inter-chains interactions and shell thickness of PMMA/PAA brushes is similar to that of PS/PAA brushes.(2) In this paper, the interactions of SPB have been investigated as function of inter-chains interactions, microstructure of SPB and the effect of pH and added salt concentration through rheological measurements. The results indicate that with the increasing concentration, the viscosity and moduluses of concentrated SPB will increase. That is because the increase in concentration, length of chains, pH and added salt concentration can raise interactions and the stability of microstructure.(3) To further investigate inter-chain interactions of concentrated spherical polyelectrolyte brushes and microstructure, SAXS measurements have been carried out on 15wt% PS/PAA latex under various pH and added salt concentration. It has been proved that interactions (including electrostatic interactions, contra-ion effect, hydrogen bonds and volume effect) of 15wt% SPB will increase with increased pH and the stretched PAA chains will form some local order. The interactions of countra ions, local order and physical cross-linking controlled by concentration, pH and added salt concentration may transform the microstructure of SPB from isolated shrink nano-particles to the stable network. The results can illustrated the rheological behavior of spherical polyelectrolyte brushes with different weight concentration, pH and added salt concentration.