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Description
Urea-based cationic gemini surfactants with polymethylene spacers containing 2 to 10 methylene units were investigated with respect to their micellization behavior and their role as pore-forming agents in the synthesis of mesoporous silica nanoparticles. Micellar structures were characterized using small-angle neutron scattering (SANS) with various form-factor of core–shell and homogeneous ellipsoid models [1]. All models consistently demonstrated a strong influence of spacer length on micellar geometry, aggregation number, and hydration. The surfactant with 4 methylene groups in the spacer formed the largest micelles with the highest aggregation number, whereas increasing spacer length to 10 methylene groups both micelle size and aggregation number decreased progressively.
Shell hydration decreased systematically with increasing spacer length, reflecting the increasing hydrophobicity of the headgroup–spacer region. Intermicellar interactions were modeled using the rescaled mean spherical approximation (RMSA) for screened Coulomb repulsion. Micelles with 4 methylene groups in the spacer exhibited the most pronounced interaction peak and the largest intermicellar separation.
Using the same surfactants as structure-directing agents, mesoporous silica nanoparticles were synthesized by a sol–gel process under basic conditions [2]. Particle morphology and pore structure was investigated using nitrogen porosimetry, SAXS, USANS, SEM and TEM. All materials exhibited 2D hexagonal pore structure of MCM-41. The spacer length influenced the lattice spacing and the size of the ordered domains. TEM analysis revealed a 10–20% variation in lattice spacing across crystalline domains. The finite domain size was the dominant contribution, whereas the lattice-spacing variation gave a smaller contribution to the diffraction line broadening. Surfactants exhibiting weaker intermicellar interactions, produced predominantly spherical silica particles, suggesting a possible influence of intermicellar interactions on particle morphology. While this trend was not systematic across the entire series, a possible connection between spacer-controlled molecular architecture, micellar structure, and the structural characteristics of the resulting mesoporous silica could be established.
Acknowledgements
This research was supported by grants no. APVV SK-HU-24-0023 and APVV-23-0349 of the Slovak Research and Development Agency and grant no. TÉT-1.2.5-2024-00068 of the Hungarian National Research, Development and Innovation Fund.
References
[1] S. Kurbonov et al., “Quantitative SANS and multi-model analysis of spacer-dependent micellization of urea-based gemini surfactants” JCIS Open, vol. 23, 100189, 2026. doi:10.1016/j.jciso.2026.100189.
[2] S. Kurbonov et al., “Structural Characterization of Ordered Mesoporous Silica Prepared by a Sol–Gel Process Using Urea-Based Cationic Gemini Surfactants“ Gels, vol. 11, 804, 2025. doi:10.3390/gels11100804.
