Assessing differences between Ostwald ripening and coalescence by rheology, laser diffraction and multiple light...

Area of Science:

• Colloid and Surface Science
• Materials Science
• Chemical Engineering

Background:

• Emulsions are crucial for agrochemical delivery, but their stability is often challenged by destabilization mechanisms.
• Biosolvent mixtures offer potential as environmentally friendly carriers, necessitating stable emulsion formulations.
• Surfactant structure and ratio critically influence emulsion stability and performance.

Purpose of the Study:

• To investigate the influence of surfactant ratio (Pluronic PE9400 to Levenol C201) on the physical stability of biosolvent emulsions.
• To elucidate the distinct destabilization mechanisms (Ostwald ripening vs. coalescence) governed by different surfactants.
• To demonstrate the combined utility of multiple light scattering, rheology, and laser diffraction in monitoring emulsion aging.

Main Methods:

• Formulation of emulsions using a mixture of N,N Dimethyl Decanamide and D-limonene biosolvents.
• Analysis of physical stability using laser diffraction for mean droplet size and multiple light scattering (TSI parameter) over time.
• Rheological property measurements to assess emulsion structure and behavior during aging.
• Investigating the impact of varying ratios of triblock copolymer (Pluronic PE9400) and polyoxyethylene glycerol fatty acid ester (Levenol C201).

Main Results:

• Emulsions stabilized with Pluronic PE9400 exhibited Ostwald ripening, irrespective of concentration.
• Emulsions stabilized solely with Levenol C201 demonstrated coalescence as the primary destabilization mechanism.
• Different surfactant structures at the oil/water interface (multilayers for Pluronic, compact layer for Levenol) were proposed to cause distinct destabilization pathways.
• Combined analytical techniques effectively detected and monitored Ostwald ripening and coalescence.

Conclusions:

• Surfactant selection is paramount for achieving physical stability in biosolvent-based emulsions for agrochemical applications.
• The ratio and type of surfactant dictate the dominant destabilization mechanism, impacting long-term emulsion performance.
• Integrated analysis of droplet size, rheology, and light scattering provides comprehensive insights into emulsion aging and stability.