Mechanism Surfactants, as interfacial modifiers, significantly alter the pore structure characteristics of the final product during powder drying by affecting the interactions and packing behavior between particles. This paper systematically explores the influence mechanism, regulation rules, and application significance of surfactants on the pore distribution of dried powders, and analyzes relevant experimental data.
I. Basic Phenomena of Surfactant Regulation of Pore Distribution
Taking the drying experiment of ultrafine aluminum hydroxide powder as an example, the sample without surfactant formed hard agglomerates after drying, with extremely uneven pore size distribution. The maximum pore size exceeded 3 μm, while the minimum pore size was only 0.05 μm, a difference of up to 60 times. In contrast, after adding an appropriate amount of surfactant, the powder remained loose, with pore sizes concentrated between 0.02–0.1 μm, and the maximum pore size not exceeding 0.5 μm, significantly improving the uniformity of pore distribution.
Similar phenomena were observed in various powder systems. For example, in the preparation of ZAO nanoparticles, when the molar ratio of PEG-400 to Zn²⁺ was 1:16, the resulting powder had a particle size of less than 10 nm and no obvious agglomeration, with a pore volume increase of approximately 42% compared to the system without surfactant. These results demonstrate that surfactants play a significant role in inhibiting agglomeration and optimizing pore structure.
II. Mechanism of Surfactant Action
The regulation of pore structure by surfactants mainly stems from their adsorption behavior at the solid-liquid interface and their intervention in interparticle forces during drying. Specifically, this can be summarized into the following two mechanisms:
Reducing Capillary Pressure and Inhibiting Hard Agglomeration Formation
During the drying process of wet powder, the evaporation of the liquid generates capillary negative pressure between particles, causing them to clump together and form hard agglomerates. After surfactants adsorb onto the particle surface, they can reduce the solid-liquid interfacial tension, thereby reducing the capillary pressure from approximately 10⁴ Pa to the order of 10³ Pa, effectively mitigating particle aggregation caused by capillary contraction.
Steric hindrance hinders interparticle chemical bonding.
The long-chain molecular structure of surfactants forms a steric barrier on the particle surface, inhibiting the formation of hydrogen bonds and bridging hydroxyl groups between particles, thereby reducing irreversible aggregation. Experimental data show that adding surfactants can reduce the total number of particles during drying from 99.9% to below 30%, indicating that particle aggregation is significantly suppressed.
