Answer to Question #125525 in General Chemistry for Nimra Shaheen

Question

How thermodynamics parameters of material vary from bulk to nano sizing

Answer 1

The physico chemical properties of the nanosolids are a function of its shape and size. Nanoparticles with diameter varying from a few nanometers to several hundreds of nanometers are of great interest for many technological purposes and primary research due to their very special physical and chemical properties, which are unlike from its bulk counterparts. The surface energy of materials is a fundamentally important thermodynamic quantity to characterize the surface effect such as crystal growth, surface faceting, growth and stability of thin films, etc., Thermodynamic properties such as melting, surface melting, superheating, cohesive energy, specific heat capacity of nanomaterials also differ from those of corresponding bulk materials due to surface effects. It is known that the melting temperature depression results from the high surface-to-volume ratio, and the surface substantially affects the interior bulk properties of these materials. Many theories have been discussed to explain the size dependent melting temperature like liquid drop model and Jiang’s model. The variation of cohesive energy, Debye temperature, specific heat and energy band gap is studied for the polyhedral shapes of nanosolids. The melting temperature, Debye temperature are found to decrease as the particle size is reduced, however the band gap and the specific heat capacity are found to increase with decrease in particle size. Neha et al.,  derived a model to analyze the vacancy formation energy of size and shape dependent nanoparticle and predicted that as particle size reduces the vacancy formation energy increases. Experimental Research are carried out on size- and shape-dependent thermodynamic properties of the actual melting Process of Nanoparticles. By chemical reduction methods, Ag nanospheres, nanowires, and nanotubes with different sizes were prepared; and differential scanning calorimetry was employed to determine the melting temperature, the melting enthalpy and the melting entropy, and it is investigated that melting thermodynamic properties decrease with the particle size decrease. Guisbiers et al., calculated the melting enthalpy by adopting top down approach using classical thermodynamics to study the size and shape effects of nanostructured materials. It is reported that, particularly for size lower than 10 nm, size and shape effect on melting entropy. Based on Mott’s equation a physical model for size dependent melting enthalpy and entropy of Sn and Al nanocrystals are developed, and shown the reduced entropy with size. A unified analytical model about the size dependent elastic modulus and vibration frequency of Cu, Ag, Si and TiO2 nanocrystalline metals, ceramics and nano scale semiconductors is explained based on the inherent strain and the binding energy change of nanocrystals. It has been registered that when the size reduces to nanoscale, ferromagnetic solids may exhibit lower Curie temperature. Based on cohesive energy, Fei et al., reported the size and shape effects on Curie temperature of ferromagnetic nanoparticles.

In the latest decade, nanosolids have acknowledged more attention because of their special properties.