Salt-Responsive Pickering Emulsions Stabilized by Functionalized Cellulose Nanofibrils.

Yun Jin,Karen J. Edler,Kazi M. Zakir Hossain,Najet Mahmoudi,James C. Courtenay,Julien Schmitt,Janet L. Scott

doi:10.1021/acs.langmuir.0c03306

Abstract

Oil-in-water emulsions have been stabilized by functionalized cellulose nanofibrils bearing either a negative (oxidized cellulose nanofibrils, OCNF) or a positive (cationic cellulose nanofibrils, CCNF) surface charge. The size of the droplets was measured by laser diffraction, while the structure of the shell of the Pickering emulsion droplets was probed using small-angle neutron scattering (SANS), confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), and rheology measurements. Both OCNF- and CCNF-stabilized emulsions present a very thick shell (>100 nm) comprised of densely packed CNF. OCNF-stabilized emulsions proved to be salt responsive, influencing the droplet aggregation and ultimately the gel properties of the emulsions, while CCNF emulsions, on the other hand, showed very little salt-dependent behavior.

Highlights

Interest in biobased materials has grown significantly in recent years in response to a growing awareness of the need for chemicals and materials based on renewable resources rather than fossil carbon
We studied the oxidized cellulose nanofibrils (OCNF)- or Cationic cellulose nanofibrils (CCNF)-stabilized emulsions using laser diffraction for droplet size analysis, microscopy techniques, and small-angle neutron scattering to probe the shape of the droplets and cellulose partitioning in the emulsion as well as ζpotential measurements to monitor the overall surface charge of the droplets and compared these results with rheological studies
We previously suggested that the Kuhn length could be used qualitatively as an indication of the mesh size in a 3D network made of cellulose nanofibrils.[42]

Summary

■ INTRODUCTION

Interest in biobased materials has grown significantly in recent years in response to a growing awareness of the need for chemicals and materials based on renewable resources rather than fossil carbon (e.g., petroleum). The four first contrasts were fitted using the core−shell onion model described, while the last one was fitted using the combination of a signal for OCNF fibrils (with parameters fixed according to results given by Figure 1, except for the Kuhn length bKuhn) plus a shell sphere (core and water contrast matched and shell thickness fixed according to other contrasts) These fitting procedures allow the scattering length density (SLD) profiles along the radius of the droplets to be obtained for each contrast, as shown in Figure 6b (values found from the fitting procedure are given, Supporting Information). It is suggested that the rheological properties are due to the percolation network arising from the nanofibrils present in the thick shell stabilizing the oil droplets, in agreement with the CLSM, SANS, and ζ-potential measurements

■ CONCLUSION

■ ACKNOWLEDGMENTS

Findings

■ REFERENCES