Definition
An emulsifier is a laboratory or industrial equipment used to mechanically disperse two or more immiscible liquids (usually oil and water) in one phase in the form of tiny droplets to form a stable or semi-stable emulsion. This process also covers homogenization, dispersion and mixing functions in a broad sense, which is one of the key links in sample preparation and preparation.
Principle
The core of the emulsification process is to overcome the interfacial tension between the two phases and break the dispersed phase into micro- or nano-scale droplets through mechanical actions such as shear, impact, and cavitation. Its main working principle is based on structures such as stator-rotor systems or high-pressure homogenization valves. Under the centrifugal force generated by the high-speed rotating rotor, the material is sucked into the working chamber and subjected to strong mechanical shear and turbulence in the narrow gap between the rotor and the stator. For the high-pressure homogenization model, the material passes through a special homogenization valve under high pressure, resulting in a hole effect and shear force due to pressure sudden drop and high-speed impact, so as to achieve the refinement and uniform dispersion of droplets. The reduction in droplet size is usually related to the energy density of the input and can be approximated by the following equation:
d ∝ (γ/ε)^k
where d is the average particle size of the droplet, γ is the interfacial tension, ε is the input energy per volume, and k is the constant associated with the system.
Main measurement and characterization methods
The evaluation of the emulsification effect is completed by measuring a series of physicochemical parameters. The most critical indicator is the particle size distribution and stability of the emulsion. Particle size distribution is usually measured by laser diffraction or dynamic light scattering to obtain key parameters such as D10, D50, D90, and polydispersion index. The stability of the emulsion can be assessed by centrifugal accelerated sedimentation experiments, multiple light scattering to monitor changes in backscatter light flux, or long-term standing observation of delamination time. In addition, viscosity, conductivity, and zeta potential (used to characterize the surface charge and electrostatic stabilization of droplets) are also important auxiliary evaluation indicators. All measurements should be performed in accordance with relevant international or national standards (e.g. ISO, ASTM) or industry-accepted methods.
Influencing factors
The emulsification effect is affected by multiple factors. In terms of equipment parameters, the structural design of the stator-rotor, the size of the gap, the linear speed of the rotor, the homogeneous pressure and the number of cycles are the key to determining the input energy and shear strength. Process parameters include emulsification time, temperature control, and dosing sequence and rate. Formulation factors are more complex and involve the volume ratio, viscosity, interfacial tension of the two phases, and the type and concentration of the emulsifier. Emulsifiers can adsorb at the oil-water interface, reduce interfacial tension and form a mechanical or electrical barrier to prevent droplet aggregation. In addition, the pH value and ionic strength of the material may also affect the emulsifier efficiency and the electrostatic stabilization mechanism of the emulsion.
Applications
The application of emulsifiers spans multiple research and industrial fields. In food science, it is used in the preparation of sauces, dairy products, beverages and fat substitutes. In the cosmetics and personal care industry, it is the basic equipment for the manufacture of creams, lotions and shampoos. In the pharmaceutical industry, it is used to prepare creams, liposomes, and emulsion-based injections. In the chemical field, it is used in the production of coatings, inks, pesticide emulsions and polymer emulsions. It also plays a role in the pretreatment process of nanomaterial synthesis, biofuel preparation, and environmental sample analysis.
Key points to consider in selection
Equipment selection needs to be comprehensively judged based on specific application requirements and material characteristics. First, the characteristics of the target product need to be defined, such as the expected particle size range, viscosity range, processing volume (batch or continuous), and thermal sensitivity. For systems with high viscosity or solid particles, a model with strong shear and dispersion capabilities may be required. For narrower particle size distributions, a high-pressure homogenizer may be a suitable choice. Material compatibility is crucial, and parts that come into contact with the material need to be made of stainless steel or special alloys according to the corrosive and hygienic level requirements of the material. In addition, equipment cleanability, noise levels, energy efficiency, and the availability of online monitoring and data logging capabilities are also factors that need to be weighed in modern laboratories and production. It is recommended to verify the suitability of the equipment for a specific process through a small or pilot test.