The ability of cellulose nanocrystals (CNC) to modifiy the rheology of the medium they are dispersed in is a very important property that paves the way to a large number of applications. Parallely, shear flow can be considered as a way to obtain macroscopically oriented CNC dispersions that could be used to design materials with controlled architecture and degree of alignment. The understanding of the effect of shear flow on the structural and rheological behavior of cellulose nanocrystals (CNC) is therefore a prerequisite for the development of new bio-based materials with better performances and controlled structural organizations. In order to access to this understanding, it is necessary to link the mechanical responses under flow (shear stress, shear rate) to structural observations at different length scales: from the nanometer length scales of the CNC to upper length scales corresponding to their mutual organizations. In this aim several in situ structural characterization techniques have been combined to rheometric measurements. Firstly local birefringence measurements under shear have been performed thanks to specific shear flow cells. Secondly a combined rheology and small angle X-ray scattering (Rheo-SAXS) setup available at the European Synchrotron Radiation Facility (ID02 High brilliance beamline) have allowed us to access to in situ and time-resolved CNC orientations and structure properties in the volume of the dispersions under flow. Analysis of transient and steady-state regimes revealed the main characteristics of the shear flow properties of the CNC dispersions as a function of the volume fraction. The changes in viscosity as a function of shear rate has been linked to the birefringence and to the order parameter deduced from the scattering intensity of the SAXS patterns. In transient states, time-dependent changes in the order parameter made it possible to identify the timescales at which the CNC become aligned in the shear flow and over which they relax after the cessation of shear.

In situ Rheo-SAXS study of cellulose nanocrystals suspensions

253rd National Meeting (2017)

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