(4l) Colloidal Linkers With Soft-to-Hard Interactions: Understanding and Application in the Assembly of Novel Functional Materials

The interaction of charged colloids with soft matter covers a wide range of phenomena which play an important role in the natural environment as well as in various industrial and biomedical applications. My research has been focused on understanding soft matter interactions at nano and micro level and further applying this understanding to fabricate responsive functional materials. My doctoral research at Technische Universität, Berlin in the group of Prof. Gerhard Findenegg was aimed towards investigating the interaction of soft matter (surfactants and globular proteins) with hard nanomaterials (silica nanoparticles, nanoporous solids). The influence of surface curvature and surface modification on the self-assembly of the nonionic surfactant at silica nanoparticles[1] and in the nanopores of SBA-15 silica material[2] was studied using adsorption measurements and Small-Angle Scattering  techniques (SANS and SAXS).We also studied the interaction of the globular protein lysozyme with silica nanoparticles over a wide range of pH. We demonstrated that the adsorbed protein induces pH-dependent bridging aggregation of the silica particles.[3] My present post-doctoral research in the group of Prof. Orlin Velev at North Carolina State University and Triangle Materials Research and Engineering Center (ΔMRSEC) deals with the programmed assembly of particles into stiff or flexible permanent chains. We have used heteroaggregating particle pairs as the chain precursor and dielectrophoresis (DEP) as a structure directing tool to directionally  assemble permanent chains of oppositely charged particles. We demonstrated that the assembly process depends on the size ratio as well as the number ratio of the two particles, and based on the structures resulting from the process a set of assembly rules was derived .[4] The permanent chains formed by the pair of oppositely charged particles have a rigid structure. We have established an alternative novel route for the fabrication of ultra-flexible composite magnetic chains which can be assembled into a variety of hierarchal structures. A fatty acid dispersion of 12-hydroxystearic acid containing FeO nanoparticles was subjected to magnetic field. The applied field pulls the FeO particles to near surface contact point where the fatty acid irreversibly binds the particles into chains. The chains were shown to wind/unwind reversibly into rings, hooks or infinity type structures. This approach forms a basis for the fabrication of highly functional magneto-responsive flexible materials. This research in the future will be extended into the design of new functional materials with unusual optical, electrical and heat transport properties.