Colloidal stability of oleic- and ricinoleic-acid-coated magnetic nanoparticles in organic solvents

• Published in: Journal of colloid and interface science Vol. 354; no. 2; pp. 498 - 505
• Main Authors: Gyergyek, Sašo, Makovec, Darko, Drofenik, Miha
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 15-02-2011; Elsevier
• Subjects: Acid-base theory; Attraction; Bonding; Chemistry; Colloidal state and disperse state; Colloidal suspensions; Colloids; Contact angle; decane; energy; Exact sciences and technology; General and physical chemistry; iron oxides; Magnetic nanoparticles; Nanoparticles; Oleic acid; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Ricinoleic acid; Solid-liquid interface; Solvation; Solvents; Stability; Surface free energy; Surface physical chemistry; Colloidal suspensions; Contact angle; Surface free energy; Magnetic nanoparticles; Acid-base theory; Iron oxide; Force; Nanoparticle; Theory; Agglomeration; Particle; Precipitation; Oleic acid; Surface properties; Monomer; Attraction; Stability; Polar solvent; Transition element compounds; Base; Free energy; Decane; Organic solvent; Solvation; Colloidal suspension; Thermodynamic properties; Methyl methacrylate; Electron acceptor; Electron donor; Surface energy
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2010.11.043

Overall energy of interaction between two oleic- and ricinoleic-acid-coated nanoparticles in different organic solvents. The additional repulsion between the ricinoleic-acid-coated nanoparticles exist, because of the polar interactions, in contrast to the oleic-acid-coated nanoparticles.
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► Colloidal stability of suspensions is correlated to dielectric constant of solvent. ► OA-nanoparticles cannot be dispersed in solvents that have
ε > 5. ► RA-nanoparticles can be dispersed in solvents that have
ε > 5. ► RA-nanoparticles are electron-acceptors; OA- nanoparticles are electron-donors. ► Solvation forces improved colloidal stability of RA-nanoparticles.
The colloidal stability of oleic- and ricinoleic-acid-coated nanoparticles in organic solvents with dielectric constants
ε
r ranging from 2.0 to 9.8 was studied. Although the acids are structurally similar, there is an
OH group in the ricinoleic acid’s tail, a marked improvement in the colloidal stability of the ricinoleic-acid-coated magnetic nanoparticles in moderately polar organic solvents and monomer methyl methacrylate was observed as a result. The bonding of both acids provokes a significant change in the surface properties of the iron-oxide nanoparticles. A clear shift from a strong electron-donor to a weak electron-donor was confirmed with the bonding of the oleic acid. The effect of ricinoleic acid bonding is even more dramatic: a clear shift toward a weak electron-acceptor is evident. A detailed analysis of the total energy of interaction, including the vOCG theory, between two particles was used to describe the different behaviors of the coated nanoparticles. In the case of the oleic acid nanoparticles in an apolar medium, such as decane, a small net attraction of ∼0.84
k
B
T, which is insufficient to cause nanoparticles agglomeration, exists. In polar media the net attraction is larger than 1.5
k
B
T, resulting in precipitation of the oleic-acid-coated nanoparticles. The same findings apply to the ricinoleic-acid-coated nanoparticles, but only when dispersed in the apolar medium. In the polar medium an additional repulsion due to polar solvation forces exists, resulting in a decrease of the net attraction to as low as ∼0.14
k
B
T.