Rheological assessment of the sol-gel transition for self-assembling low molecular weight gelators

The complexity of the transition from solution to gel for low molecular weight gelators in apolar solvents makes it incredibly difficult to assess the gel point. Since both nucleation and crystal growth occurs prior to the formation of a continuous three dimensional network numerous techniques, such as calorimetry and inflection point of the complex modulus, are invalid when probing the gel point. However, monitoring the frequency dependence of G′ and G″ illustrates the transition from a dilute solution to a weak gel which may be differentiated from the gel point observed by the decreasing value of the complex viscosity as a function of frequency. For 3% 12-hydroxystearic acid in mineral oil once the gelator nucleates the material behaves as a dilute solution, upon crystal growth (67 °C) we observe the true cross over point which is independent of frequency and finally a strong gel is formed at 64 °C where G′ and G″ are independent of frequency.