Structural Study of Star Polyelectrolytes and Their Porous Multilayer Assembly in Solution
Star polyelectrolytes with responsive properties to external stimuli, such as pH, temperature and ionic condition, were utilized to fabricate layer-by-layer (LbL) microcapsules . The microstructure of star polyelectrolytes was first studied in semi-dilute solution by in situ small-angle neutron scattering (SANS). These measurements show that with the addition of salts, arms of strong cationic star polyelectrolytes will contract and the spatial ordering of the stars would be interrupted. SANS measurements were also performed on the microcapsules in order to study their internal structure and responsive properties in solution. The results show that with the increase of shell thickness, microcapsules undergo a change of fractal dimension. Microcapsules with thinner shell have a surface fractal structure with rough interface, while those with thicker shell generally have a mass fractal structure of 3D random network. With the change of surrounding environment (pH, temperature, or ionic condition), the morphology and permeability of microcapsules are changed concurrently, for example, with the addition of multivalent salt, there is a surface- to mass-fractal transition, with the correlation length decreasing by around 50 %. This study provides insight into the mechanism of the responsiveness of novel star polyelectrolytes and their assembled multilayer structures.
This work is supported by the NSF-DMR 1002810 grant. Research conducted at ORNL’s High Flux Isotope Reactor and Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy.
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