PHYSICAL AND CHEMICAL PROPERTIES. Nanoscaled and bulk materials significantly differ in several physical-chemical properties, such as the higher surface area and quantum size effects of the former. These factors, in turn, govern nanomaterials’ structural transformations, interaction with light, and even solubility, and enhance their mechanical strength and optical, magnetic, and electrical properties, to name a few. The atoms near the surface of the nanoscale particles show partial saturation, resulting in an energy state distinct from the rest.2 Surface effects are crucial in nanotechnology, especially considering nanomaterials in various states. Nanomaterials in powder form, dispersed in a solvent as colloids, or in thin films display diverse surface energies and can interact differently with solvents and substrates. Indeed nanomaterials (thin films, dispersed particles, crystalline grains, or coatings) exist in a metastable thermodynamic state stabilized by their interactions with surroundings.3 These interactions occur at the nanomaterial-surrounding interfaces, which are divided into: - solid/liquid interface: typical of colloidal nanocrystals and can the inorganic/organic or inorganic/inorganic type. - solid/solid interface: characteristic of nanocrystals in a solid material, it is generally of the inorganic/inorganic type.4-5 For example, metal and semiconductor nanomaterials have different electronic structures than bulk materials and isolated atoms. Various metal nanocrystals feature forbidden bands similar to non- metals, and with decreasing size, the higher proportion of surface atoms increased the reactivity of the particles. The size of nanocrystals directly affects their electronic structure, as shown in Figure 2: unlike bulk materials, the energy levels of electrons in small particles are discrete rather than continuous due to the confinement of the electronic wave functions caused by the physical size of the particles.6 <.. image(Immagine che contiene design, scaricatore, presa Descrizione generata automaticamente con attendibilità media) removed ..> Figure 2: Density of states for metals (left) and semiconductors (right). The Fermi level is in the middle of the band for metals, and kT should exceed the energy jump between levels even at room temperature and for nanometric dimensions. For semiconductors, the jump is larger and increases for smaller sizes (bottom).6 Overall, nanomaterials’ uniqueness can be rationalized in the following points: -the high surface area and sur...
