Ethanol­-water liquid mixture was analyzed by the method of Molecular Dynamics, over the whole composition range to elucidate its micro structure. A recently introduced concept of microheterogeneity was used to describe mixture's behaviour. It was discovered that there are at least three structural regimes with respect to composition range in aqueous ethanol at ambient conditions. Up to approximately 0.15 mole fraction of ethanol, hydrophobic ethanol's sites distribution declines from homogenous. From 0.15 to approximately 0.65 mole fraction of ethanol, ethanol and water form bi­continuous intertwined microheterogenous mixture of segregated domains, and above 0.65 mole fraction of ethanol water network loses its connectivity over the whole system. Results from the novel approach in cluster analysis, performed for the first time on this kind of system, namely the calculation of cluster radial distribution function, were especially important for supporting the picture of three structural regimes. This is the first time that such detailed overall picture of the microscopic level structure of this liquid mixture is given. Besides, in­-detail analysis of different ethanol models in their ability to reproduce this structural change with mole fraction is presented; models that are parametrized on pure substance thermodynamical properties, as well as one model parametrized on the solute activity in the aqueous mixture.

Metodom molekularne dinamike analizirana je mikroskopska struktura tekuće mješavina etanola i vode pri sobnim uvjetima, u cijelom rasponu koncentracija. Definirana su tri strukturna režima miješanja od kojih svaki predstavlja različitu realizaciju koja ima svojstvo mikroheterogenosti, odnosno lokalnog nemiješanja komponenti. Pri malim koncentracijama etanola zbog hidrofobnog efekta vode distribucija hidrofobnih dijelova molekula etanola nije homogena kao u čistom etanolu. Dodavanjem etanola, na otprilike 0.15 molarnog udjela, etanol i voda počinju graditi bi­kontinuiranu isprepletenu mrežu u cijelom sustavu. Drugi prijelaz je definiran na otprilike 0.65 molarnog udjela etanola gdje voda više ne može formirati kontinuiranu strukturu mreže vodikovih veza preko cijelog sustava. U prvom redu ovi režimi su potvrđeni analizom radijalne distribucijske funkcije koja se odnosi na klastere, što predstavlja novi pristup u analizi strukture molekularnih otopina. Osim toga provedena je detaljna analiza različitih modela za etanol i testirana je njihova sposobnost reproduciranja promjene strukture s promjenom molarnog udjela komponenti. Testirani su modeli parametrizirani na termodinamičkim svojstvima čistih tekućina i jedan model parametriziran na aktivitetu otopljene tvari u vodenoj otopini.