Essential meaning of high pressure measurements in discerning the properties of monohydroxy alcohols with a single phenyl group

Abstract

Three isomeric alcohols, 1-phenyl-2-butanol, 2-phenyl-1-butanol and 1-(4-methylphenyl)-1-propanol differentiated in terms of the position of phenyl ring and hydroxyl group, were the subject of molecular dynamic studies. The investigations carried out by means of broadband dielectric spectroscopy, mechanical spectroscopy and differential scanning calorimetry revealed numerous similarities such as surprising identity of temperature dependencies of relaxation times under atmospheric pressure conditions for 1-phenyl-2-butanol and 1-(4-methylphenyl)-1-propanol. However, these compounds are differentiated in terms of pressure characteristics of molecular dynamics. It has been shown that among many factors that may affect the obtained image, spatial packing of molecules and their stiffness are of key importance. Moreover, the conducted pressure measurements revealed that intermolecular bonding that exists for both compounds at ambient pressure, becomes markedly disturbed at elevated pressure, exceeding 500 MPa. Another important finding revealed in course of high-pressure investigations was the crystallization of 2-phenyl-1-butanol. It was found that this alcohol can be supercooled at ambient pressure, however after applying pressure it undergoes continuous crystallization. Thus it has been explicitly shown that measurements at high pressure conditions are of key importance for revealing the complex features of associated liquids.