The stability of the emulsion formed after spraying oil cleaner is a key indicator of its cleaning effectiveness and durability. Its stability is influenced by multiple factors, including emulsifier properties, formulation ratio, operating conditions, environmental factors, and the synergistic effects of additives.
The selection and structure of the emulsifier are the primary factors affecting emulsion stability. The emulsifier in oil cleaners must possess an appropriate hydrophilic-lipophilic balance (HLB) value, with the hydrophilic and hydrophobic groups in its molecular structure matching the properties of the oil and water. For example, nonionic emulsifiers form a stable interfacial film through steric hindrance, while ionic emulsifiers prevent droplet aggregation through charge repulsion. If the emulsifier's HLB value falls outside the required range, the interfacial film may be insufficient, leading to emulsion separation or demulsification.
The ratio of the aqueous phase, oil phase, and emulsifier in the formulation directly influences the emulsion type and stability. Oil cleaners typically form oil-in-water (O/W) emulsions, with water as the external phase and oil as the internal phase. If the oil phase ratio is too high, the carrying capacity of the emulsifier may be exceeded, leading to droplet aggregation. Insufficient emulsifier concentration results in incomplete interfacial film coverage, making droplets prone to collision and merging. Furthermore, ingredients added to the formulation, such as cosolvents and preservatives, may indirectly affect the long-term stability of the emulsion by altering the system viscosity or charge distribution.
Temperature and stirring parameters are crucial to the emulsion formation process. Increasing temperature reduces the viscosity of the emulsifier and accelerates molecular motion, but excessive temperatures can cause emulsifier degradation or interfacial film expansion and rupture. For example, some oil cleaners emulsify effectively at high temperatures, but temperature control is necessary during long-term storage to prevent demixing. Stirring speed influences the initial droplet size distribution. Appropriate stirring can form uniform, fine droplets, enhancing the stability of the emulsion. However, insufficient or excessive stirring can result in uneven droplet size, reducing overall stability.
Environmental factors such as pH and salt content significantly influence emulsion stability. Changes in pH can alter the charge state of emulsifier molecules. For example, under acidic conditions, the ionization of some emulsifiers decreases, weakening charge repulsion and facilitating droplet aggregation. The addition of salt compresses the double layer on the droplet surface, reducing electrostatic repulsion and thus destabilizing the emulsion. Therefore, oil cleaner formulations must be adjusted according to the application scenario to accommodate varying water quality or environmental conditions.
The synergistic effect of additives is a key means of optimizing emulsion stability. Thickeners (such as glycerin and gum arabic) increase the viscosity of the external phase, slowing droplet settling. Dispersants prevent droplet agglomeration and maintaining uniform distribution. Rust and corrosion inhibitors, for example, indirectly extend the life of the emulsion by protecting the metal surface or inhibiting microbial growth. For example, in industrial cleaning applications, the addition of a small amount of nanoparticles can form a denser interfacial film, significantly improving the mechanical stability of the emulsion.
The stability of an emulsion is also closely related to the droplet size distribution and interfacial film strength. Small, uniform droplets have a larger surface area, allowing them to be more effectively covered by the emulsifier, forming a stable interfacial film. Conversely, large droplets tend to settle due to gravity, leading to stratification. The elasticity and toughness of the interfacial film determine the emulsion's ability to withstand external disturbances, such as mechanical vibration or temperature fluctuations.
In practical applications, the stability of oil cleaner emulsions requires a balance between formulation optimization and process control. For example, by adjusting the type and concentration of emulsifier, it can be adapted to different oil types (such as animal, vegetable, or mineral oils). Centrifugal separation or rheological testing can also be used to assess the long-term stability of the emulsion. Future advances in nanotechnology and molecular design are expected to further enhance the stability of oil cleaner emulsions, meeting even more stringent industrial and environmental requirements.
