Percolation and phase behavior in cellulose nanocrystal suspensions from nonlinear rheological analysis

Isotropic Gels of Cellulose Nanocrystals Grafted with Dialkyl Groups: Influence of Surface Group Topology from Nonlinear Oscillatory Shear

“…Overall, network buildup and consolidation in pristine CNC suspensions having isotropic–isotropic gel transitions (non-self-assembling) bear both similarities and differences to our previous results on self-assembling CNC suspensions. First, the k = k (ω), where I 3/1 ∝ γ 0 k , nonlinear scaling at percolation ( ϕ g ) is not only similar to other CNC suspensions but also similar when using different preparation methods, desulfated CNC systems, and even in nanocomposites . We can therefore emphasize that there is by now ample evidence supporting a scenario where a form of weakly interconnected networks is disrupted by the nonlinear deformations as the most striking nonlinearities (oddities) are recorded for the lowest imposed ω while with increasing ω there is a tendency toward the theoretically predicted quadratic MAOS scaling, k = 2.…”

“…The nonquadratic scaling behavior and angular frequency dependence of I 3/1 , i.e., nonlinear oddities, , have been associated with the percolation threshold and subsequent network buildup in polymer nanocomposites containing electrically conductive fillers as well as other systems . In addition, we have previously shown similar results for (sulfated) commercial CNC suspensions and their desulfated counterparts. , We, therefore, consider the nonlinear material signature described as evidence of a percolation threshold, ϕ c in Figure , meaning that a weakly percolated network is formed that can be easily distorted by flow. With respect to stress decomposition, we focus on two nonlinear parameters, S , T i.e., the strain-stiffening and shear-thickening ratios.…”

“…The nonlinear data analysis of the shear stress output signal was performed in the framework of Fourier-transform rheology and stress decomposition analysis. The nonlinear material parameters analyzed in this study, the third relative higher harmonic, I 3/1 , and strain-stiffening S and shear-thickening T ratios were determined using the procedures outlined in Wojno et al , and are described in detail elsewhere. ,,, …”

“…In general, depending on whether attractive or repulsive forces between CNCs dominate, aqueous CNC suspensions either form isotropic, biphasic (containing both liquid crystalline and isotropic domains), liquid crystalline, and repulsive glasses so-called phases or form isotropic suspensions, isotropic (attractive) gels . We briefly note that the assigning of the term “gel” can vary between different nomenclatures, and here, we refer to it strictly from a rheological perspective . While in the case of nonself-assembling CNC systems their photonic properties are lost, they are important for applications as rheology modifiers and fillers in nanocomposites …”

“…Nonlinear parameters from FTrheology and stress-decomposition analysis effectively distinguished the isotropic, biphasic, and liquid crystalline phases. Subsequently, we extended the study of the relevance of nonlinear material parameters to include a decoupling between phase transitions and percolation and gel point through desulfation …”