Investigation of the scaling law on gelation of oppositely charged nanocrystalline cellulose and polyelectrolyte

• Gelation behavior of QHEC and NCC with opposite charge was investigated.
• Winter and Chambon theory was applicable for determining the gel point.
• The gel was composed of both electrostatic interaction and chain entanglements.
• Scaling law was only feasible when electrostatic interaction can be neglected.

The sol–gel transition in the mixture system of oppositely charged polyelectrolyte (quaternized hydroxyethylcellulose ethoxylate, QHEC) and nanocrystalline cellulose (NCC) induced by electrostatic adsorption interaction was investigated by rheological means. Winter and Chambon theory was validated to be applicable for the critical gel point determination, and critical gel point have been successfully determined. With QHEC concentration increasing, more NCC were needed to form a critical gel, and smaller loss tangent and relaxation exponent (n) values at the gel point were observed, indicating the elastic nature of mixture was enhanced with QHEC increase. Gel strength behaved as a function of both QHEC and NCC concentrations, suggesting the gel network at the critical point was composed of entanglements and association of QHEC macromolecular chains, as well as the electrostatic adsorption interaction between QHEC chains and NCC rods. The calculated number of NCC rods per junction decreased from 0.30 to 0.01 when the QHEC concentration increased from 1.0 wt% to 3.0 wt%, indicating the electrostatic adsorption interaction between the NCC rods and QHEC chains was less significant to gel formation at higher QHEC concentrations. Therefore, the exponents of scaling law η0 ∝ ϵ–γ and Ge ∝ ϵ z for the QHEC/NCC mixtures revealed that the scaling law n = z/(z + γ) between n, γ, and z was only feasible at highest QHEC concentration, since the intermolecular interaction (electrostatic adsorption interaction in this article) was so weak that can be neglected and the critical gel network was dominated by QHEC chain entanglements and association.