Structure and mechanical properties of suspensions and gels

Contact: Elena Tervoort or Frank Filser

Fig. 1: Intensity auto-correlation functions obtained from Diffusing-wave-spectroscopy on gels coagulated either by pH or ionic strength shift.

Fig. 2: Compressive strength of gels obtained by pH or ionic strength shift.

Fig. 3: Cryo-SEM images of stable suspensions and gels coagulated by pH or ionic strength shift.

Controlling the structural and mechanical behavior of concentrated colloidal suspensions and gels is important in many technological areas. The fabrication of products such as paper, paint, pharmaceuticals, composites, or ceramics is often based on colloidal processing.
Although extensive investigations have been carried out in relatively diluted suspensions, our knowledge on the relations between structural and mechanical properties of highly concentrated colloidal systems is rather limited. This is mainly due to the fact that conventional destabilization techniques do not allow the controlled formation of particle gels with significantly different microstructures at high volume fractions, as well as the considerable difficulties involved in experimentally characterizing the microstructure of highly concentrated suspensions. These problems have been circumvented by using a novel in-situ destabilization method developed in our group (see the DCC method in Colloidal Forming Techniques) based on enzyme-catalyzed chemical reactions. Such method allows the formation of gels of highly concentrated particles without significantly disturbing the microstructures that develop during the gelation process. Additionally, these gels can be produced by two different destabilization means: either the pH of the suspension is shifted towards their isoelectric point or the ionic strength of the suspensions is increased at a constant pH.
We have been using such particle gels as model systems to investigate the relations between the kinetics of the destabilization process, the dynamics of particles, the evolving microstructure, and the resulting mechanical behavior. Diffusing-wave spectroscopy (DWS), static light scattering, Cryo-SEM, rheology and mechanical testing have been the main techniques utilized in this investigation.

For more information, consult the papers by Wyss, Tervoort, Hütter, Hesselbarth and Filser in our literature database.