Spherical Polyelectrolyte Brushes: Synthesis, Characterization And Application

If long linear polyelectrolyte chains are grafted densely to a solid surface, a polyelectrolyte brushes results. In principle, such systems can be achieved either by grafting polyelectrolyte chains to planar substrate or to strongly curve surfaces of colloidal particles, the spherical polyelectrolyte brushes formed by the solid spherical substrate with a densely grafted polyelectrolyte shell. Spherical polyelectrolyte brushes constitute a new class of materials. The strong electrostatic interactions involved bring a number of entirely new properties compared to mono-layers of end-grafted uncharged macromolecules. Polyelectrolyte brushes have therefore become the subject of intense research which is partly due to interesting fundamental questions involved when trying to understand these systems, partly due to a great number of potential applications in nanotechnology, biotechnology and medical science. Therefore a great number of theoretical and experimental papers are available so far and polyelectrolyte brushes present certainly one of the most active fields at the interface of polymer and surface science.In this thesis, the spherical polyelectrolyte brushes (SPB) were prepared by the photo-emulsion polymerization. Two novel photo-initiators,4-acryloxybenzophenone (ABP) and benzoin acrylate (BA) were synthesized. Their performances in preparation of SPBs by photo-emulsion polymerization were compared with those of the previously reported photo-initiator 2-[p-(2-hydroxy-2-methyl-propio-phenone)]-ethylene glycol-methacrylate (HMEM).The properties of the SPBs prepared by these three photo-initiators were compared and discussed in detail. Their difference in structure, UV absorption, and mechanism of photo-initiation resulted in significant differences in kinetics during photo-emulsion polymerization. The reactivity sequence is BA> HMEM> ABP, while the grafting density sequence of SPBs prepared by them is the opposite. The brush structures for all SPBs were confirmed by determining the grafting density of PAA chains on the core surface. The grafting densities of SPBs were tunable ranging from 0.012 to 0.084 nm-2 by employing different photo-initiators. The SPB thickness is sensitive to pH and ionic strength as determined by DLS. Brushes with higher grafting density show smaller changes in size upon varying pH value or ionic strength. SEM and TEM results indicated the well-defined spherical structure and narrow size distribution of core for all SPBs prepared by three photo-initiators. A novel method of thermo-controlled emulsion polymerization is employed to synthesize spherical polyelectrolyte brushes which consist of a solid polystyrene core and a poly (acrylic acid) (PAA) shell covalently attached on the core surface densely by one end. The growth of brushes from the core surface is monitored by dynamic light scattering (DLS). The particle size of PS core latex shows a narrow size-distribution as observed by scanning electron microscopy (SEM). The brush size is changed significantly upon the change of pH-value and ionic strength, which displays the similar behaviors with brushes prepared by photo-emulsion polymerization.Bifunctional spherical polyelectrolyte brushes (SPB) with tunable thermo-and pH-sensitivity are synthesized by combining thermo-controlled emulsion polymerization and photo-emulsion polymerization. They consist of a spherical polystyrene core and a shell of mixed brushes of poly(N-isopropylacrylamide) (PNIPAM) and poly(acrylic acid) (PAA) whose composition can be easily modulated by the dose of monomers. The kinetics of SPB synthesis as well as their size change with temperature and pH is determined by dynamic light scattering (DLS). The scanning electron microscopy (SEM) images show that the bifunctional SPB have a defined spherical morphology with a narrow size distribution. And the dual-pH responsive polyelectrolyte brushes with a shell of PAA and PVP also prepared with same method.A rheological study of the semi-dilute and concentrated regime of the spherical polyelectrolyte brushes has been presented. The data demonstrate that mutual interactions lead to a marked dependence of the measured viscosity as a function of shear rate. Data of the Zero-shear viscosity obtained by extrapolation to vanishing shear rates can be described in terms of the hydrodynamic radius and the effective volume fraction derived from DLS. The interactions between SPB particles could be well described by the data of Zero-shear viscosity.SPB combine films are prepared on glass substrates with film thickness could be tuned from 100nm to 1200nm by combining spin-coating and dip-coating technology with photo-emulsion polymerization. In this film, the SPB particles performed as a functional particle while the PAA and PNIPA which cross-linked by BIS performed as the substrates of films. The well defined multilayer SPB films could be prepared by layer-by-layer polymerization in this thesis. The application of SPB films in recovering of precious metal ions in waste water was also studied; the results showed that the low concentrated metal ions could be removed efficiency by using SPB films.