The effect of charge screening for cationic surfactants on the rigidity of interfacial nanoparticle assemblies

Henrik Siegel; Mariska de Ruiter; Tagbo H R Niepa; Martin F Haase

doi:10.1016/j.jcis.2024.08.133

The effect of charge screening for cationic surfactants on the rigidity of interfacial nanoparticle assemblies

J Colloid Interface Sci. 2025 Jan 15;678(Pt A):201-208. doi: 10.1016/j.jcis.2024.08.133. Epub 2024 Aug 20.

Authors

Henrik Siegel¹, Mariska de Ruiter¹, Tagbo H R Niepa², Martin F Haase³

Affiliations

¹ Van't Hoff Laboratory for Physical and Colloid Chemistry, Department of Chemistry, Debye Institute for Nanomaterials Science, Utrecht University, Utrecht, The Netherlands.
² Carnegie Mellon University, College of Engineering, Biomedical Engineering, Chemical Engineering, Pittsburgh, PA, United States.
³ Van't Hoff Laboratory for Physical and Colloid Chemistry, Department of Chemistry, Debye Institute for Nanomaterials Science, Utrecht University, Utrecht, The Netherlands. Electronic address: m.f.haase@uu.nl.

PMID: 39191099
DOI: 10.1016/j.jcis.2024.08.133

Abstract

Hypothesis: Functionalizing colloidal particles with oppositely charged surfactants is crucial for stabilizing emulsions, foams, all-liquid structures, and bijels. However, surfactants can reduce the attachment energy, the driving force for colloidal self-assembly at interfaces. An open question remains on how the inherent interfacial activity of cationic surfactants influences the interfacial rigidity of particle-laden interfaces. We hypothesize that charge screening among cationic surfactants regulates the rigidity of oil/water interfaces by reducing the attachment energy of nanoparticles.

Experiments: We investigate the interfacial rigidity of cetyltrimethylammonium bromide (CTAB) functionalized silica nanoparticles (Ludox® TMA) by analyzing the shape deformation of 1,4-butanediol diacrylate (BDA) droplets under varying salt and alcohol concentrations. The nanoparticle packing density is assessed using scanning electron microscopy. Attachment energy is characterized through interfacial tension measurements, three-phase contact angle analysis, and CTAB adsorption studies. We also examine the effects of interfacial rigidities on the structure of bijel films formed via roll-to-roll solvent transfer-induced phase separation (R2R-STrIPS) using confocal laser scanning microscopy.

Findings: Increasing salt and alcohol concentrations decrease the interfacial rigidity of CTAB-functionalized nanoparticle films by reducing the interfacial tension. The contact angle has a minor influence on the rigidity. These results indicate that CTAB charge screening weakens the nanoparticle attachment energy to the interface. Controlling the rigidity enables the mass production of bijel sheets with consistent flatness, which is crucial for their potential applications in catalysis, energy storage, tissue engineering, and filtration membranes.

Keywords: Bijels; Interfacial rheology; Interfacial tension; Ionic strength; Particles at interfaces; Pickering emulsions; STrIPS; Solvent transfer induced phase separation; Structured liquids; Surfactants.