Effect of Triton X-100 on the stability of aqueous dispersions of copper phthalocyanine pigment nanoparticles

• Published in: Journal of colloid and interface science 2011-10, Vol.362 (1), p.33-41
• Main Authors: Dong, Jiannan, Chen, Shuang, Corti, David S., Franses, Elias I., Zhao, Yan, Ng, Hou T., Hanson, Eric
• Format: Article
• Language: English
• Subjects: adsorption; aqueous solutions; Chemistry; Colloidal state and disperse state; COMPOSITES; COPPER PHTHALOCYANINE; Copper phthalocyanine pigment; Density; Dispersion stability; Dispersions; Electrostatic effects; Electrosteric effects; ethylene oxide; Exact sciences and technology; General and physical chemistry; high performance liquid chromatography; hydrophilicity; hydrophobicity; light scattering; micelles; Micelles. Thin films; MICROSTRUCTURES; Nanocomposites; Nanomaterials; nanoparticles; Nanostructure; Nonionic surfactant adsorption; octoxynol; PARTICLES; Physical and chemical studies. Granulometry. Electrokinetic phenomena; PIGMENTS; screening; sodium nitrate; Stability; Stabilization; Steric effects; Surface chemistry; Surface physical chemistry; surfactants; Triton X-100; zeta potential
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2011.04.050

Postulated conformations of Triton X-100 on CuPc-U (left) and CuPc-S (right) at their maximum densities studied. [Display omitted] ► The adsorption density of Triton X-100 is higher on the hydrophobic than on the hydrophilic CuPc particles. ► Some adsorbed surfactant remains irreversibly adsorbed after the solution is diluted. ► The stabilization mechanism for the hydrophobic CuPc particles is primarily steric. ► The stabilization mechanism for the hydrophilic CuPc particles is primarily electrostatic. ► For dispersions in water the zeta potential is not a good predictor of dispersion stability. The effect of Triton X-100 on the colloidal dispersion stability of CuPc-U (unsulfonated and hydrophobic) and CuPc-S (surface sulfonated and hydrophilic) particles in aqueous solutions (water and NaNO3) was investigated at 25°C. Its adsorption density was determined from surfactant concentrations analyzed by an HPLC method with a UV detector. The experimental dispersion stability ratios of the particles were determined from dynamic light scattering (DLS) data, with the Rayleigh-Debye-Gans (RDG) light scattering theory. The adsorption densities of Triton X-100 on both the CuPc-U and CuPc-S increase with increasing concentration of surfactant up to the critical micelle concentration (cmc), and then reach a plateau. The maximum adsorption density Γm is higher for the CuPc-U (dh=160nm) than that for the CuPc-S (dh=90nm). The hydrophobic chains are inferred to be adsorbed onto the surfaces, and the hydrophilic ethylene oxide chains are in a coil conformation. The Wapp-values for the CuPc-U dispersions are affected mainly by the surfactant fractional surface coverage θ. Adding NaNO3 has no significant effect on the dispersion stability. The stabilization mechanism for the CuPc-U is inferred to be primarily steric, as expected. The stability ratios for the CuPc-S in solutions with NaNO3 are higher than those for CuPc-U, and decrease with increasing concentration of NaNO3, indicating that the stabilization is affected by the screening of electrostatic repulsive forces. The zeta potential is not a good predictor of the electrostatic stabilization, pointing to the need for new and improved theories.