When microrheology, bulk rheology, and microfluidics meet: broadband rheology of hydroxyethyl cellulose water solutions

In this work, we present new insights related to a debate on the morphological structure of hydroxyethyl cellulose (HEC) molecules when dissolved in water, i.e., whether HEC adopts a linear-flexible or a rod-like fibrillar configuration. We have employed “seven” rheological techniques to explore the viscoelastic properties of HEC solutions at different time and length scales. This work demonstrates an excellent convergence between various rheological techniques over a broad range of frequencies and concentrations, allowing us to derive microstructural information for aqueous HEC solutions without the use of complex optical imaging techniques. We find that when dissolved in water unmodified HEC behaves like a linear uncharged polymer, with an entangled mass concentration of ce = 0.3 wt%. Moreover, for the first time we provide the concentration scaling laws (across ce) for the longest relaxation time λ of HEC solutions, obtained from direct readings and not inferred from fitting procedures of fluids shear flow curves