Probing structure in colloidal gels of thermoreversible rodlike virus particles: Rheology and scattering

Aggregated suspensions of rodlike particles are commonly encountered in soft biological materials and their solidlike response at extremely low volume fractions is also exploited technologically. Understanding the link between the physicochemical parameters such as size, aspect ratio, volume fraction, and interparticle forces with the resulting microstructure and the subsequent rheological response remains challenging. In the present work, suspensions of monodisperse rodlike virus particles, whose surface is modified by grafting with a thermoreversible polymer poly(N-isopropylacrylamide), are used as a model system. The repulsive and attractive contributions to the total interaction potential can be changed independently by varying the ionic strength and the temperature. The effects of these changes on the strength and structure of gels have been studied near the gel transition using a combination of rheological and scattering measurements. Rheological measurements of the near critical gel properties as a function of concentration and ionic strength proved to be more sensitive compared to scattering in resolving the structural differences. A percolating structure can be formed at very low volume fractions, which show a weak dependence on the ionic strength with the anisotropy of the repulsive interactions playing the main role in creating more "open" structures. The intrinsic stiffness of the rodlike particles does not affect the moduli of the gel states very strongly. (C) 2012 The Society of Rheology. [http://dx.doi.org/10.1122/1.4728335