Edge-On (Cellulose II) and Face-On (Cellulose I) Adsorption of Cellulose Nanocrystals at the Oil–Water Interface: A Combined Entropic and Enthalpic Process

Abstract

Nanocelluloses can be used to stabilize oil–water surfaces, forming so-called Pickering emulsions. In this work, we compare the organization of native and mercerized cellulose nanocrystals (CNC-I and CNC-II) adsorbed on the surface of hexadecane droplets dispersed in water at different CNC concentrations. Both types of CNCs have an elongated particle morphology and form a layer strongly adsorbed at the interface. However, while the layer thickness formed with CNC-I is independent of the concentration at 7 nm, CNC-II forms a layer ranging from 9 to 14 nm thick with increasing concentration, as determined using small-angle neutron scattering with contrast-matched experiments. Molecular dynamics (MD) simulations showed a preferred interacting crystallographic plane for both crystalline allomorphs that exposes the CH groups (100 and 010) and is therefore considered hydrophobic. Furthermore, this study suggests that whatever the allomorph, the migration of CNCs to the oil–water interface is spontaneous and irreversible and is driven by both enthalpic and entropic processes.

Evaluation of Surface Free Energy Inducing Interfacial Adhesion of Amphiphilic Cellulose Nanofibrils

“…The experimental data closely matched the estimations based on vOCG theory. The absolute values of the W ad indicating CNF desorption from the hexadecane–water interface (28.2 mJ m –2 ) are also close to the simulation result of Gibbs free energy variation in adsorption of CNC to the heptadecane–water interface reported by Haouache et al (−26 ± 7 mJ m –2 ) …”

“…Figure 3 shows a Pickering emulsion stabilized by an aqueous dispersion containing 0.10 wt % ACC-BCNFs. The appearance (Figure 3) and significant increase in transparency (Table S8 56 Only the nitrobenzene result having a W ad value closest to 0 differed from the predicted behavior. This mismatch was presumably owing to the influence of the amphiphilic structures of the CNF films prepared from CNF-stabilized oil droplets.…”

“…7,27,56 In other words, the non-polar CH plane with surface free energy values similar to the hydrophobic oil phase effectively would stabilize the oil−water interface. 7,27,56 This implies a difference in interfacial stabilization efficiency between the averaged chemically isotropic CNF surface model (Figure 4a) and the actual anisotropic CNF surfaces (Figure 4b). It was considered that the difference led to the mismatch of the CNF adsorption at the nitrobenzene−water interface, which have the work of adhesion value closest to 0.…”

“…However, it is considered that the hydrophobic CH planes in the actual CNFs face the hydrophobic oil phase. ,, In other words, the non-polar CH plane with surface free energy values similar to the hydrophobic oil phase effectively would stabilize the oil–water interface. ,, This implies a difference in interfacial stabilization efficiency between the averaged chemically isotropic CNF surface model (Figure a) and the actual anisotropic CNF surfaces (Figure b). It was considered that the difference led to the mismatch of the CNF adsorption at the nitrobenzene–water interface, which have the work of adhesion value closest to 0.…”

Soy Protein Isolate/Genipin-Based Nanoparticles for the Stabilization of Pickering Emulsion to Design Self-Healing Guar Gum-Based Hydrogels

“…Pickering emulsion is an oil–water stabilization system, in which the surfactant is creatively replaced by solid particles. − It can be used to load external healing agents to assist in the healing of hydrogels . As Xu et al reported, a linseed oil (LO)-in-water Pickering emulsion stabilized by sulfated cellulose nanocrystals (CNCs) and octylamine-modified CNCs can be used in a vanish to realize self-healing performance after scratching as a result of the reaction of the LO with oxygen .…”