Design of novel emulsion microgel particles of tuneable size

In this study, we designed a one-step solvent-free route to prepare emulsion microgel particles, i.e., microgel particles containing several sub-micron sized emulsion droplets stabilised by heat-treated whey protein. The heat treatment conditions were optimized using aggregation kinetics via fluorimetry and dynamic light scattering. Emulsions were gelled and microgel particles were formed simultaneously via turbulent mixing with calcium ions using two specific processing routes (Extrusion and T-mixing). By varying the calcium ion concentration and mixing conditions, we identified the optimal parameters to tune the size and structure of the resultant emulsion microgel particles. Microscopy at various length scales (confocal laser scanning microscopy, scanning electron microscopy) and static light scattering measurements revealed a decrease in particle size (100–10 μm) with lower turbulent mixing time (ca. 4 × 10−4 s) and lower concentrations of calcium ions (0.1–0.02 M). Larger particle sizes (500–1000 μm) were achieved with an increase in the turbulent mixing time (ca. 2 × 10−2 s) and higher concentrations of calcium ions (1–1.4 M). Using gelation kinetics data (small deformation rheology) and theoretical considerations, creation of smaller sized emulsion microgel particles was explained by the increased flux of calcium ions to the denatured whey protein moieties coating the emulsion droplets, enabling faster gelation of the particle surfaces. These novel emulsion microgel particles of tuneable size formed as a result of complex interplay between calcium ion concentration, heat treatment of whey protein, gelation kinetics and mixing time, may find applications in food, pharmaceutical and personal care industries.