Impact of wormlike micelles on nano and macroscopic structure of TEMPO-oxidized cellulose nanofibril hydrogels

In this work, we investigated the effect of adding surfactant mixtures on the rheological properties of TEMPO-oxidized cellulose nanofibrils (OCNF) saline dispersions. Three surfactant mixtures were studied: cocamidopropyl betaine (CAPB)/sodium dodecyl sulfate (SDS), which form wormlike micelles (WLM); cocamidopropylamine oxide (CAPOx)/SDS, which form long rods; and CAPB/sodium lauroyl sarcosinate (SLS), which form spherical micelles. The presence of micelles from these surfactant mixtures, independent of their morphology, leads to an increase of tan δ, making the gels less solid-like, therefore, acting as a plasticizer. WLM were able to suppress strain stiffening normally observed in OCNF gels at large strains. OCNF/WLM gels have lower G′ values than OCNF gels while the other micellar morphologies have reduced impact on G′ . The presence of unconnected micelles leads to increased dissipative deformation in OCNF gels without affecting the connectivity of the fibrils, while the presence of entangled micelles interferes with the OCNF fibril network.