title: Electrolyte effect on gelation behavior of oppositely charged nanocrystalline cellulose and polyelectrolyte.
abstract: The electrolyte (NaCl) influences on the sol-gel transition of the complex solution composed of oppositely charged nanocrystalline cellulose (NCC) and polyelectrolyte (quaternized hydroxyethylcellulose ethoxylate, QHEC) were investigated by the rheological means in the present paper. Winter and Chambon theory was applicable to describe the sol-gel transition, and the critical gel points have been successfully determined. When increasing the NaCl concentration, more NCC were needed to form a critical gel due to the screening of the electrostatic interaction, and the larger loss tangent and relaxation exponent (n) values at the gel point demonstrated a less elastic nature of the complex solution with more NaCl. The results indicated the gel network was composed of entanglements and association of QHEC (as polymer network), as well as the electrostatic adsorption interaction between QHEC chains and NCC rods (as cross-linking). With the addition of NaCl, the screening effect led to the enhancement of the entanglements and weakening of the electrostatic adsorption, however, the gel strength decreased with increasing the NaCl amount, suggesting the electrostatic adsorption interaction played a more dominant role than the entanglements when the gel was formed. Moreover, the exponents of the scaling law η0∝ɛ(-γ) and Ge∝ɛ(z) of the QHEC/NCC/NaCl solution revealed that the scaling law n=z/(z+γ) between n, γ, and z was only feasible at the highest NaCl concentration, as a result of that the intermolecular electrostatic interaction was completely screened, indicating the scaling law was only feasible when intermolecular interaction was small enough to be neglected.
authors.affiliation: Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB, T6G 2G2, Canada; Department of Chemistry, Wuhan University, Wuhan 430072, China.
authors.forename: Ang
authors.initials: A
authors.lastname: Lu
authors.affiliation: Department of Agricultural, University of Alberta, Edmonton, AB, Canada T6G 2P5.
authors.forename: Yongbo
authors.initials: Y
authors.lastname: Song
authors.affiliation: Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB, T6G 2G2, Canada; National Institute for Nanotechnology, National Research Council of Canada, Edmonton, AB, Canada T6G 2M9. Electronic address: yaman.boluk@ualberta.ca.
authors.forename: Yaman
authors.initials: Y
authors.lastname: Boluk
mesh_terms: D002482:Cellulose / Q000031:analogs & derivatives* / Q000737:chemistry; D004573:Electrolytes / Q000737:chemistry; D005782:Gels / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry*; D012965:Sodium Chloride / Q000737:chemistry*
chemical_list: D004573:Electrolytes; D005782:Gels; C531250:hydroxyethyl cellulose ethoxylate; D012965:Sodium Chloride; D002482:Cellulose
keywords: Electrolyte; Gelation; Nanocrystalline cellulose; Opposite charge