Structure-property comparisons, mechanical and thermal properties of molecular gels based on alkanoic acids and ammonium alkanoates

Molecular gels are an important class of soft materials, that consists of a low concentration of a gelator (low molecular mass molecule) and a large amount of liquid. The gelator molecule self-assemble via intermolecular interaction (H-bonding, Van der Waals forces, and π-π stacking) to form a three-dimensional entangled network and immobilize the liquid. In the present study self-assembly and gelation studies of alkanoic acids (carbon chain length = 12, 14, 16, 18, and 20) and the ammonium salts have been compared. Thermal properties of the gels were determined using differential scanning calorimetric studies, and the gel melting temperatures. Mechanical properties of the 5 wt % toluene gels of ammonium alkanoates were investigated using rheology studies. Frequency sweep studies show that storage modulus (G') of a 5 wt % ammonium alkanoate in toluene increases on increasing the alkyl chain length of the ammonium alkanoate. Step strain experiments were conducted, in which the linear viscoelastic and destructive strain values were applied to examine the thixotropic properties of the 5 wt % toluene gels of ammonium alkanoate (carbon chain length= 12, 18, and 20). The step strain experiments results show that 5 % ammonium alkanoate in toluene (carbon chain length = 12, 18, and 20) recover a large part of the viscoelasticity after the application of destructive strain.