(623h) Structural Discreteness and Granularity of Interactions in Suspensions of Nanoparticles

During the last twenty years, there has been significant progress in the synthesis of nanoparticles and their use as a new type of “building blocks” to more complex structures.  Size- and shape-dependent physical phenomena characteristic for nanoscale dimensions brought about their utilization in electronics, optics, energy storage, biology, medicine, catalysis, load-bearing elements, and other technologies. All of these emergent areas of knowledge, related applications, as well as further advances in synthesis/purification of nanocolloids required some understanding of inter-nanoparticle interactions.  Despite progress in description of forces between nanoparticles, there are fundamental difficulties with both quantitative and qualitative account of forces acting between nanoparticle that we just begin to appreciate. The forces between nanoparticles are commonly described by the classical DLVO theory that relies on a mean-field approximation of the electrostatics in electrolyte solutions and a continuum description of the relevant media. NPs due to their size, intrinsic polarizability, their large and non-uniform surface area, provide conditions that challenge and in many case invalidate the most basic assumptions in the classical description of colloidal interactions. Examples include the assumption of uniform distribution of charges, the non-existence of dielectric discontinuities, the description of ions as point charges, and the irrelevance of the chemical identity of ions. The objective of this talk is to provide a survey of the limitations of classical theories, experimental results that challenge classical theories, and the methods available to overcome such limitations. This account will provide insight into new parameters that could be explored in experimental design and how we can profit from not taking the classical assumptions for granted, as supported by an interesting set of emerging experimental results that demonstrates the size, polarizability and ligands of NPs are all relevant parameters and surpass the idea of ions as point charges.