Morphologies of mesoporous SBA-15 particles explained by the competition between interfacial and bending energies

Abstract

The morphology control of the (sub)micrometer particles of mesoporous silica materials can be crucial in many applications. For particles of the SBA-15 material, the morphology happens to be easily tuned by simply changing the synthesis temperature, and well defined shapes are obtained, ranging from hexagonal columns, rice grains and rods to nano-donuts. Here we show that all these shapes can be explained using a very simple energetic model, based on the idea that the final shape of the particles is at thermodynamic equilibrium. This model contains two terms, the interfacial energies (surface tensions γ₁ and γ₂) on one hand, and the bending energy (bending constant K₃) on the other hand. The two ratios γ₂/γ₁ and K₃/γ₁ are determined from the average dimensions (diameter, length, radius of curvature) measured by SEM and TEM for rod-like and torus-like particles and the evolution of the particles morphology with temperature can be simply explained based on the values of these two ratios. This approach could be easily extended to other soft matter systems where the formation of particles is governed by both surface tension's anisotropy and bending.