Volume 130, Issue 16, 28 April 2009
Index of content:
A density functional theory is used to investigate adsorption of colloids on the surfaces grafted by polymers of different architectures, including linear, star, branched, and dendritic structures. In order to calculate the direct bonding connectivity integral, a new numerical algorithm is proposed for polymers with complex architecture. A good agreement of the calculated results and the simulation and experimental data in studying grafted hard chain brushes confirm that our approach does lead a correct prediction. Accordingly, adsorption of colloids in the negative exponential attractive surface was studied. The effects of grafting density, attractive strength, molecular concentration, and size on adsorption were considered. The contour maps of excluded rate show that a complex architecture of polymer chains is much more effective in preventing adsorption than linear polymer brush. The results also show that the grafting density and complex architecture are two key factors to prevent colloidaladsorption, while the surface attractive strength only exhibits slight effect on colloidaladsorption. For polymer brushes with complex architecture, the height of potential of mean force is strongly dependent on the colloidal size. The larger the size, the higher is the potential of mean force, which means that the larger colloidal molecules are harder to penetrate the brush. In short, to prevent colloidaladsorption, it is more suitable to use the polymer brushes with complex architecture.
130(2009); http://dx.doi.org/10.1063/1.3126582View Description Hide Description
The process of biomineralization occurs in various natural organisms with astonishing ease by the interplay between polymers and mineralization but eludes a fundamental understanding. In addressing how specific polymers direct selection of mineral morphologies and their growth kinetics, we present a new model based on a competition between adsorption of polymers onto selective interfaces and nucleationgrowth of minerals. The model is couched in the context of zinc oxide, crystallized from solutions containing polypeptides, where systematic experimental data are available. Adsorption of the polymer onto certain crystallographic planes leads to poisoning of the surfaces, and as a result these surfaces are arrested from further growth. By this mechanism, originally disfavored growth sectors are promoted to grow by suppressing the initial faster growing sectors. Our theory predicts the relative growth rates of different sectors altered by selective adsorption of polymers. Theoretical prediction of the dependence of the aspect ratio on polypeptide concentration is in agreement with experimental results, providing credence to the applicability of adsorption-nucleation models to polymer-mediated biomineralization.