258: Effect of Fe²⁺ on the Thermal and Long-Term Stability of CNC-Stabilized Pickering Emulsions

Introduction

Pickering emulsions, stabilized by solid particles instead of surfactants, are gaining interest in food, pharmaceutical, and industrial applications due to their biocompatibility and sustainability. Cellulose nanocrystals (CNCs) are commonly used as stabilizing agents, but maintaining long-term stability is challenging.

Methods

The emulsions were prepared by vortexing corn oil with CNC dispersion for 1 minute, followed by adding 0.1 M Fe2+ solution and further mixing for 1 minute. Physicochemical properties, including particle size, zeta potential, and rheological characteristics, were analyzed to assess stability and structural behavior. Stability tests were conducted by storing emulsions at 40°C for three weeks, with the creaming index used to evaluate phase separation.

Results

The results showed that the presence of Fe²⁺ reduced the particle size of emulsions. The average size with Fe²⁺ was 26.4 μm, compared to 34.9 μm without Fe²⁺. Zeta potential measurements indicated that emulsions with Fe²⁺ had a more negative charge (−49.96 mV) compared to those without Fe²⁺ (−31.2 mV), suggesting improved electrostatic stabilization.

Rheological analysis revealed that emulsions with Fe²⁺ exhibited a higher storage modulus (G') than loss modulus (G") with no crossover point, indicating elastic behavior. Both G' and G" showed a slight, consistent increase with angular frequency, confirming an elastic-dominant system. The emulsions demonstrated shear-thinning behavior, with apparent viscosity decreasing as the shear rate increased, indicating network disruption under stress. Thermal stability tests showed consistent dynamic moduli between 20°C and 80°C, suggesting structural integrity under thermal stress. Long-term stability tests at 40°C showed no creaming in samples with Fe²⁺, whereas emulsions without Fe²⁺ exhibited significant phase separation, with a creaming index up to 75% in samples with 11.1% oil fraction.

Significance

These findings indicate that Fe²⁺ enhances CNC-stabilized Pickering emulsions by improving electrostatic interactions and structural stability, making them suitable for various industrial applications, particularly in food and pharmaceutical formulations.

Authors: Jiannan Feng, Fanbin Kong