Influence of Cellulose Nanocrystals and Surfactants on Catastrophic Phase Inversion and Stability of Emulsions

Equilibrium surface tension (aqueous/air) and oil–water interfacial tension (aqueous/WO-15) were reported as a function of NCC or surfactant concentration (Figures 8–9).

The Dropometer is cited as a “smartphone-based pendant drop tensiometer (Droplet Lab, Markham, ON, Canada)” using droplet-profile fitting with the Young–Laplace equation via axisymmetric drop shape analysis (ADSA).

The surface- and interfacial-tension trends are used to contrast NCC’s weak surface activity with the strong tension reductions observed for molecular surfactants and to discuss how interfacial tension behavior relates to concentration-dependent catastrophic phase inversion behavior.

Each measurement was repeated 10 times per solution, and average values were reported.

For NCC, equilibrium surface tension remains relatively high across the tested range, decreasing from 63.4 mN/m at 0.1 wt% to 62.3 mN/m at 2.0 wt% (Figure 8), and the paper characterizes this as negligible surface-tension reduction.

SDS and OTAC show large decreases in equilibrium surface tension from 0.1 wt% to 1.0 wt% (SDS: 44.23 → 33.74 mN/m; OTAC: 54.80 → 38.22 mN/m), while Amphosol and Alfonic reach 31.25 mN/m and 26.11 mN/m at 0.5 wt%, respectively (Figure 8).

The interfacial tension data show large reductions for surfactant systems, including SDS decreasing from 57.2 mN/m (no surfactant) to 4.61 mN/m at 0.1 wt% and 3.02 mN/m at 1 wt%, and Amphosol reaching 2.81 mN/m at 0.2 wt% while remaining below 3.4 mN/m across the tested range (Figure 9).

For NCC, the paper reports an initial decrease in interfacial tension at 0.1–0.2 wt% reaching a minimum of 38.3 mN/m, followed by a plateau or slight increase at higher concentrations (Figure 9).

The paper describes a sharp reduction in interfacial tension at lower surfactant concentrations before stabilizing near a minimum and states that this rapid initial drop coincides with a delay in catastrophic phase inversion; it also describes a higher-concentration threshold where the interface becomes saturated and further IFT decreases are minimal, while inversion occurs at lower aqueous phase fractions as excess surfactant accumulates in the bulk or micellar phase.

The paper reports pendant-drop measurements for surface tension (droplet suspended in air) and interfacial tension (droplet dispensed into WO-15 oil in a sealed quartz cuvette) using Young–Laplace fitting with ADSA.

Each surface/interfacial tension measurement was repeated 10 times per solution and reported as an average at 22 ± 1 °C.

The reported surface-tension data keep NCC near ~63 mN/m across concentration while surfactants substantially reduce surface tension (Figure 8), supporting a direct contrast in surface activity.

The paper links a sharp low-concentration IFT decrease and a higher-concentration near-minimum/plateau (interface saturation) to the observed concentration-dependent catastrophic phase inversion behavior (Figure 9).

The interfacial tension results differentiate very low IFT values for SDS and Amphosol from more moderate reductions for Alfonic and a more gradual decrease for OTAC (Figure 9).