Surfactant induced gelation of TEMPO-oxidized cellulose; using zwitterionic- surfactant based wormlike micelles to modulate rheological behaviour

Cellulose nanofibrils are colloidal sized fibrils obtained mostly from plant sources. The fibril surface may be chemically modified to impart new properties. TEMPO mediated oxidation produces water-dispersible, negatively charged cellulose nanofibrils (OCNF). Aqueous OCNF dispersions can form gels upon addition of surfactants, salts, or co-solvents and this potential for modulation of the dispersions makes OCNF a flexible rheological modifier.
Here, we explore the formation of wormlike micelles (WLM) and OCNF networks in saline aqueous solutions. The WLM are formed by a mixture of a zwitterionic surfactant (cocamidopropyl betaine, CAPB) and an anionic surfactant (sodium dodecyl sulfate, SDS) in the presence of NaCl. Three types of systems were investigated: OCNF, OCNF/single surfactant (SDS or CAPB) and OCNF/surfactant mixture (SDS+CAPB) dispersions. We observed that in absence or in the presence of short micelles, gels with slightly higher G’ and significant lower values of tan δ were produced compared to OCNF gels where WLM are present. The rise in tan δ derives from the additional reptation from the entangled WLM, not observed in shorter micelles. This shows that both WLM and OCNF networks can coexist. In terms of rheological modulation, the WLM leads to an increase of
inelastic deformation with a small loss of stiffness.