Are you familiar with the preparation techniques for phase-change microcapsule materials?

In the preparation of phase change microcapsule materials, the currently mainly used film-forming methods include in-situ polymerization, interfacial polymerization, emulsion-solvent evaporation method, complex condensation method, sol-gel method, and spray drying method.

In-situ polymerization: refers to the process of adding reactive monomers and catalysts to the core material dispersion medium during encapsulation, characterized by the monomers and catalysts being located entirely inside or outside the phase change material emulsion droplets. In-situ polymerization requires that the monomer be soluble in the continuous phase of the microcapsule system, and that the polymer monomer can produce relatively low molecular weight insoluble prepolymers. Therefore, the polymerization reaction occurs on the dispersed phase core material, and the monomer first undergoes polymerization at the beginning of the reaction. When the polymer size increases, it deposits on the surface of the core material. Due to the continuous polymerization and crosslinking, a solid microcapsule shell that can cover the entire surface of the core material droplets is finally formed. Homopolymerization, copolymerization, and polycondensation are commonly used film-forming methods in in-situ polymerization. The commonly used monomers in this method are mainly urea-formaldehyde, melamine-formaldehyde, and their copolymer-modified polymer monomers.

Interfacial polymerization: requires at least two monomers, and the two monomers must exist in incompatible phase change material emulsion systems. This system can be divided into a continuous phase and a dispersed phase, usually setting the phase change emulsion in the dispersed phase. When polymerization occurs, the two monomers move from the dispersed phase and the continuous phase to the interface of the two phases, and then the monomers undergo a polymerization reaction to form a polymer film that encapsulates the core material into microcapsules. The main reactions are interfacial addition polymerization and interfacial condensation polymerization, which are applicable to both water-soluble and oil-soluble core material microcapsules. This method has mild conditions, fast speed, and low requirements for monomer purity and raw material ratio, so it is widely used. The monomers used for interfacial polymerization are mainly diisocyanate acetate, diamine, diphthaloyl chloride, etc. In recent years, research using styrene, divinylbenzene, and vinyl acetate as capsule wall materials has gradually increased.

Emulsion-solvent evaporation method: Usually, under stirring conditions, the oil phase and water phase form a stable emulsion under the action of a surfactant, and then the oil phase solvent volatilizes through the continuous phase, and the core material and wall material form a shell/core structure due to different surface tensions. This method can directly disperse the oil phase into the water phase for emulsification, or it can use the reverse emulsification method. The size of the microcapsules can be controlled by emulsification using equipment such as a high-shear dispersion emulsifier or an ultrasonic cell crusher.

Complex condensation method: refers to using two or more polymeric materials with opposite charges as wall materials, dispersing the core material in the wall material solution, and forming a film under appropriate conditions due to the electrostatic interaction between polymers with opposite charges. After the interaction of polymeric materials with opposite charges, the solubility decreases and phase separation occurs, condensing to form microcapsules. In this process, the number of charges carried by the two polymers with opposite charges must be exactly equal, and this condition can be obtained by adjusting the pH value of the solution. Commonly used reactants are gelatin, gum arabic, etc. In order to enhance the waterproof performance, formaldehyde, glutaraldehyde, or tannic acid can also be used for crosslinking. Sol-gel method: First, the precursor is dissolved in a solvent to form a uniform solution, and then the solute and solvent undergo hydrolysis or alcoholysis reaction to form a stable sol; then, the phase change core material is added, and the sol forms a gel on the surface of the core material particles, thereby preparing phase change microcapsules encapsulating the core material, which is a commonly used method for preparing microcapsules.

Spray drying method: First, the core material is dispersed in a pre-liquefied wall material solution, and then the mixture is atomized in a high-speed air stream, so that the solvent of the dissolved wall material quickly evaporates, thereby solidifying the wall material and finally microencapsulating the core material. The spray drying method is most suitable for the microencapsulation of lipophilic liquids, and the stronger the hydrophobicity of the core material, the better the embedding effect.