As an important disperse system, emulsions are widely used in pharmaceuticals, cosmetics, food and other fields. However, emulsions are thermodynamically unstable, and dispersed droplets tend to coalesce to minimize the interfacial area, eventually separating into two phases over time. This seriously affects product quality and effectiveness. Recently, the industry has made a series of progress in emulsion stability regulation technologies, providing key support for the R&D and production of related products. The instability of emulsions shows multi-stage characteristics. Flocculation is prone to occur in the initial stage: droplets aggregate into clusters due to attractive forces under Brownian motion, but their particle size remains unchanged. Subsequently, creaming or sedimentation occurs, which is affected by droplet radius, density difference between two phases and continuous phase viscosity, and the rate can be evaluated by Stokes equation. Coalescence, as an irreversible process, will lead to droplet fusion and system breakdown, which is the core difficulty in emulsion stability regulation. In addition, Ostwald ripening and phase inversion can also damage emulsion stability: the former is driven by Laplace pressure difference between droplets, while the latter is prone to occur during homogenization or sterilization. Current stabilization technologies have formed a multi-dimensional solution. Optimizing interface properties by reducing droplet size, matching HLB value and adding co-surfactants can enhance steric/electrostatic stabilization; adjusting the density matching degree of two phases and increasing continuous phase viscosity can effectively inhibit creaming and sedimentation; adding high molecular weight components can slow down Ostwald ripening, and preservatives and antioxidants can resist microbial contamination and oxidative decomposition. In terms of quality control, indicators such as droplet size D90, PDI, Zeta potential and viscosity have become key parameters for evaluating emulsion stability. Combined with microscopic observation and accelerated stability test, product quality can be fully guaranteed. These technological breakthroughs have laid a foundation for the innovative development of emulsion products. Especially in fields with strict stability requirements such as sterile preparations and high-end cosmetics, they are expected to promote product performance upgrading.

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