COMPUTATIONAL STUDY OF THE INTERACTION BETWEEN MOLECULES OF TECHNOLOGICAL INTEREST AND MODIFIED NANOTUBULAR CLAYS

Halloysite nanotube (HNT) is an aluminosilicate arranged in a spiral shape, made up of a silicon oxide on the outer and an aluminium hydroxide on the inner surface. These two layers are bonded through oxygen atoms. The different chemical environment of the two surfaces as well as their fine tuning possibility (e.g. by changing the pH value), the inexpensiveness and easy availability are at the basis of the halloysite wide range of applications. As a matter of fact, the HNT nanocomposites are exploited in drug carrier and delivery, polymer enhancement, sustained and controlled release of species and self-healing materials, just to cite a few. In the development of new technological materials, the comprehension of the interaction between the substrate and the target molecules plays a crucial role. So far the HNT nanomaterials are investigated by means of laboratory techniques that are unable of getting hints at atomistic level of detail, which in turn can be obtained from a computational study. At first, this was conducted by means of DFT approach on the pristine HNT, providing informations about the nanotube surfaces as well as its most stable forms under different pH conditions. After the structural and energetic aspects of the pure HNT was well-established, the computational design on HNT nanocomposites for slow-released corrosion inhibitors took place and then experimentally tested in a neutral pH environment. It was concluded that the computational approach is a valuable tool in the HNT composites material design. The next step of the investigation regarded the interactions of water molecules on the HNT surfaces under different pH conditions. The informations acquired allowed to set up the basis for future HNT nanomaterial design on modified surfaces and provided informations about the HNT systems stability under different operative conditions. Besides, it turns out that the stabilization provided by the inter-arms water molecules to the HNT structure can be due to random and small energy gains all over the nanotube surfaces and that the modification of one layer actually affects the water adsorption energetics on the other one. The final step of the computational investigation regarded the creation of Slater-Koster parameters set for DFTB calculation. The modus operandi used for the parametrization process has a general validity, namely it is applicable also to other type of materials. The new parameters allow, in future studies, the usage in a DFTB calculation of species that posses in their structure most of the element used in the HNT nanocomposite. The DFTB method will also guarantee the possibility of enlarging the investigated model, making the future computational approaches able to reproduce the adsorbate-adsorbate interactions as well as the structural modifications on the halloysite nanotube surfaces