Effects of humidity on the rheology of supramolecular organogels

It is known that organic oils typically contain tiny amountss of water (0.01% by weight) which can influence the self-assembly as well as the macroscopic properties of supramolecular gelators. We explore here the rheological consequences of this phenomenon which has been overlooked. Specifically, we investigate the properties of biphenyl tricarboxamides (BPTA) in dodecane which exhibit structural transitions with varying temperature. The driving force behind these transitions is the fact tat the humidity content of the supramolecular polymer changes with temperature. We perform shear rheological measurements under controlled humidity conditions in both humid (~60% relative humidity) and dry (~5% relative humidity) conditions and observe that in a humid environment the linear and nonlinear rheological properties are ubstantially affected by the temperature. At temperatures where the systems strongly interacts with water the plateau modulus is lower, the relaxation faster and there is absolutely no sign of strain hardening behaviour. These findings are discussed in the context of existing theories of living polymers. It is concluded that humidity effects cannot be ignored when working in oily environments.
Work in collaboration with N.J. Van Zee and E.W. Meijer (T. U. Eindhoven).