Interaction of organic molecules with layer silicates, oxides and hydroxydes and related surface-nano characterization techniques

The knowledge of the surface properties of layered minerals is of great importance to understand both basic and applicative technological issues, such as, for example liquid/surface interactions, microfluidity, friction or tribology and biomolecules self-assembly and adhesion. Recent developments of Scanning Probe Microscopy (SPM) have widened the spectrum of possible investigations that can be performed at a nanometric level on the surface of minerals. They range from physical properties such as surface potential and electric field topological determination to chemical and spectroscopical analysis both in air, in liquid or in a gaseous environment. After a brief introduction on new technological developments which stand behind SPM, we will present recent achievements in the field of the characterization and application of nanomorphology, surface potential and cleavage patterns of minerals, in particular the behaviour of some layer silicates. Two general research directions will be presented: organic molecules interaction with layer silicate and synthetic substrates, and mineral hydrophilicity/phobicity and friction/adhesion issues. SPM is used to assess the force-curve, force-volume, adhesion and surface potential characteristics of layer silicates by working in Electric Force Microscopy (static and dynamic EFM) and in Kelvin probe modes of operation. For instance, EFM allowed us to measure the thickness of silicate layers and, from frequency, amplitude, phase modulation and Kelvin analysis, to derive the electrostatic force experienced by the probe. We can then directly relate these measurements with the electrostatic force gradient at the mineral surface. The transverse dynamic force microscopy, also known as shear force microscopy will be introduced and examples on the investigation of attractive, adhesive and shear forces of water onto layer silicate and other mineral surfaces will be presented. The study of water in confined geometries is very important because it can provides simple models for fluid/mineral interactions. The ability to control the binding of biological and organic molecules to a crystal surface is central in particular for biotechnology, catalysis, molecular microarrays, biosensors and environmental sciences. For instance, recent achievements showed that DNA molecules have different binding affinities and assume different conformations when adsorbed to different layered silicate surfaces. On certain crystals the electrostatic surface potential anisotropy is able to order and stretch the DNA filament and also inducing a natural change in its conformation. The active stretching of DNA on extensive layer silicates is a clear indication of the basic and technological potential carried by these minerals when used as substrates for biomolecules. Other examples on enzymes/proteins, nucleotides, RNA and cells will be reported. Finally a comparison between experimental data and simulation will be presented as well