Un modello realistico per visualizzazioni in didattica

In this work, two applications for the visualization of the aggregation and the solubilization of structureless interacting particles are presented. The applications allow to demonstrate on a qualitative basis as well as by quantitatively monitoring the time evolution of the surface/volume ratio and of the fractions of aggregated particles, that, on the one hand, the growth of nanoaggregates implies a decrease of their surface/volume ratio and, on the other, that the formation of homogeneous mixtures is the result of favorable solute-solvent interactions as well as of temperature. It is suggested that, along with the use of suitable macroscopic examples, visualizations by the present applications are useful in elucidating concepts related to reactivity and miscibility/solubility. The applications are based on a twodimensional realistic dynamic model where atoms move because of their thermal and interaction potential energies; the trajectories are determined by solving numerically Newton's laws according to a Molecular Dynamics (MD) scheme. For this purpose, a webbased MD engine was adapted as needed. It is suggested that, when possible, using realistic simulations, rather than simple animations, offers several advantages in the visualization of processes of interest in chemistry education. First of all, in a simulation the outcome of the process under study is not set a priori but it is the result of the dynamic evolution of the system; furthermore, specific parameters can be systematically varied and the effects of these changes can be investigated. The applications can be used at different levels of detail and in different instruction levels. Qualitative visual observations are suitable at all levels of instruction. Systematic investigations on the effect of changes in temperature and interaction parameters, suitable for senior high school and college courses, are also reported.