| Recent progress in surface-initiated polymerization techniques facilitates the synthesis of polymer-grafted particles or colloids (so-called 'particle brushes') with precise control of density, molecular weight, and dispersity of surface-grafted chains. This thesis presents a systematic evaluation of the effect of polymer-graft modification on the structure formation and mechanical characteristics of inorganic (silica) nanoparticle solids as function of the degree of polymerization of surface-grafted chains. A general transition from 'hard-sphere-like' to 'polymer-like' mechanical characteristics of particle solids is observed with increasing degree of polymerization that is accompanied by an order-of-magnitude increase of the fracture toughness of the particle brush solid. The transition to polymer-like deformation characteristics is adequately captured by adopting a scaling model that interprets the structure of the polymer shell of polymer grafted particles as effective 'two-phase' systems consisting of a stretched inner region and a relaxed outer region. The model allows the prediction of the minimum degree of polymerization needed to induce polymer-like deformation and thus provides a basis for establishing design criteria for the synthesis of polymer-modified particles that are capable of forming mechanically robust and formable particle solid structures. Furthermore, the dominant interparticle interactions associated with the respective regime were found to be responsible for the evolution of the particle arrangement in each regime. Thus, the control on the interpacticle interactions ranging from short-range hard-sphere-type to long-range repulsive interaction affords new opportunities for the engineering of novel material properties toward quasi-one-component nanocomposite materials in which microstructural characteristics are intimately related to the molecular architecture of the particle brush building blocks. The particle brush-based composites hold the promise to realized novel high-performance engineering materials with a wide range of applications, for example, in the area of energy storage or optical materials. |
