Effect of Cooling and Heating Temperature Cycles During Emulsification

What is Emulsification Reaction?

Emulsification is the process where tiny droplets of one liquid are evenly dispersed in another immiscible liquid. It is a liquid-liquid interface phenomenon. When two immiscible liquids, such as oil and water, are placed in a container, they separate into two distinct layers—oil, with its lower density, floats on top of water. Adding an appropriate surfactant and vigorously stirring the mixture can disperse the oil in water to form an emulsion. This process, known as emulsification, often relies on temperature changes, solvent adjustments, or phase transitions to optimize droplet dispersion. The surfactant’s preferred curvature changes during these conditions, facilitating droplet breakup into a high-energy state under controlled temperature cycles.

Demonstrating the separation of two immiscible liquids, oil and water, and the process of forming a uniform emulsion by adding surfactants

Global Energy Efficiency Challenges in Emulsification

Global emulsification processes produce approximately 100 million tons of emulsions annually. However, the energy efficiency of traditional emulsification techniques is alarmingly low—less than 0.01% for microdroplets. This efficiency drops further for sub-micron emulsions, as high shear or high-pressure mechanical devices generate excessive heat, incompatible with many pharmaceutical, cosmetic, and food ingredients.

Phase Inversion Self-Emulsification Technology

For non-polar oils with larger molecules, phase inversion self-emulsification technology has been developed. This technique relies on temperature changes or surfactant concentration adjustments to modify the preferred interfacial curvature. The principle involves a temperature cycle that freezes and subsequently melts droplets in a coarse emulsion, causing spontaneous droplet breakup. Conventional emulsification methods typically heat both the internal and external phases to 75°C–90°C before stirring and cooling, which is energy-intensive.

Temperature’s Impact on Emulsion Quality

Emulsification temperature significantly affects emulsion quality. While there is no strict temperature limit, key factors such as the melting points of high-melting substances, the type of emulsifier, and the solubility of the oil and water phases must be considered. Additionally, both phases’ temperatures should remain nearly identical. For instance, when emulsifying waxes or high-melting-point oils (above 70°C), introducing a low-temperature aqueous phase can cause wax or fat crystals to precipitate, resulting in a coarse emulsion. In general, emulsification is performed at 75°C–85°C. For high-melting-point oils, temperatures may need to increase further.

Particle Size Variations with Temperature

The emulsification temperature can also influence emulsion particle size. For example, fatty acid soap anionic emulsifiers produce emulsions with a particle size of approximately 1.8–2.0 μm when emulsified at 80°C, compared to around 6 μm at 60°C. However, for non-ionic emulsifiers, temperature has a weaker influence on particle size.

Mechanisms of Droplet Breakup During Temperature Cycling

The cooling and heating cycles applied to dispersed alkane droplets induce significant droplet shape transitions and breakup mechanisms:

• M1: Droplets spontaneously rupture during cooling.
• M2/M3: Frozen droplets rupture upon melting.

Microscopic images of droplets in pentadecane emulsions stabilized by 1.5 wt% C16SorbEO20 surfactant reveal structural changes before and after temperature cycling. These cycles, measured at cooling rates of 0.2 K/min and heating rates of 1.6 K/min, show a reduction in average droplet diameters (e.g., dN50 and d32) as the number of freeze-thaw (F/T) cycles increases.

Experimental Study of Bulk Emulsion

In bulk emulsion experiments, a 15 ml sample was frozen at 7°C for 2 hours, followed by melting at 25°C. Initial cooling and heating rates were measured at ≈0.4 K/min, gradually tapering to ambient temperature. These cycles effectively reduced droplet sizes, highlighting their potential in temperature-sensitive emulsification processes.

Applications Across Industries

The self-emulsification process holds significant promise for producing emulsions in industries requiring strict temperature control, such as pharmaceuticals, cosmetics, and food. This approach addresses challenges posed by conventional methods, such as high energy consumption and compatibility issues with sensitive ingredients.

Energy Efficiency and Environmental Benefits

By optimizing cooling/heating rates and temperature ranges, the technology can improve energy efficiency and reduce environmental impact. Additionally, this method could be extended to other applications, such as stabilizing nanodispersions or producing complex emulsions for advanced material synthesis.

Challenges and Future Prospects

Despite its potential, self-emulsification faces certain limitations. For instance, its reliance on specific temperature ranges or surfactants may constrain its applicability across a broad spectrum of materials. Moreover, optimizing the process for scalability and economic viability requires further research.

Future advancements could include:

• Integration with molecular dynamics simulations to better understand interfacial phenomena.
• Development of hybrid emulsification methods combining self-emulsification with ultrasonic or mechanical techniques.
• Exploration of environmentally friendly surfactants and energy-efficient temperature control systems.

Conclusion

In conclusion, temperature cycle-driven self-emulsification is a promising technology for creating high-quality emulsions with improved efficiency and sustainability. By addressing current challenges and leveraging innovative approaches, this technique could revolutionize emulsification processes across various industries.

LNEYA’s SUNDI series dynamic temperature control systems offer precise and intelligent temperature management, with a wide range from 120°C to 350°C and cooling capacities from 0.5 to 1200kW. These systems ensure exceptional production stability and repeatability. Equipped with advanced plate heat exchangers and tube heaters, they deliver rapid heating and cooling performance.


Featuring ultra-high temperature cooling technology, the systems can directly cool from 300°C without evaporating the heat transfer medium, enabling continuous temperature control across various ranges: -80°C to 190°C, -70°C to 220°C, -88°C to 170°C, -55°C to 250°C, and -30°C to 300°C.


In emulsification reactions, the SUNDI series not only reduces labor costs but also enhances product quality and production efficiency. These systems are ideal for optimizing industrial processes with precision and reliability.