Polyethyleneimine–Oleic Acid Complex as a Polymeric Dispersant for Si₃N₄ and Si₃N₄-Based Multicomponent Nonaqueous Slurries

Abstract

Polymeric dispersants that adsorb onto various types of fine particles have been designed through complex formation between cationic polyethyleneimine (PEI) and anionic oleic acid (OA) to improve particle surface compatibility with nonaqueous solvents. Complex formation involves the OA-assisted dissolution of PEI in a nonaqueous solvent (toluene) by ultrasonication. While PEI itself is immiscible in toluene, various molecular weights (MWs) of PEI (M w = 600, 1800, and 10 000) visibly dissolved when, in the presence of more than 5-mol % PEI (based on the ethyleneimine (EI) unit of PEI), a complex formed between the carboxyl group of OA and the amines of PEI in toluene. Si3N4 and one of the typical multicomponent compositions for Si3N4 ceramic fabrication, Si3N4–Y2O3–MgO, were chosen to demonstrate the usage of PEI–​OA complexes for improving nonaqueous slurry stability. While nontreated Si3N4 particles rapidly formed dense slurry aggregates followed by solidification in toluene, PEI associated with 30 mol % OA effectively adsorbed on Si3N4 fine particles and drastically improved the flow properties with ∼1.8 mg/m2 treatment. Surprisingly, the flow properties were maintained even for dried and redispersed slurries. The effect of the MW of PEI–​OA and its additive content on the stability of Si3N4/toluene slurries has been clarified, and their applicability toward Si3N4–Y2O3–MgO multicomponent systems is discussed.

Effect of fatty acids complexed with polyethyleneimine on the flow curves of TiO2 nanoparticle/toluene suspensions

“…The procedure for characterization of the adsorbed amount of the PEI-fatty acid complex was also similar to our previous report [22]. Briefly, 19.00 g of a toluene solution of the PEI-fatty acid complex (PEI-OA, PEI-ISA, or PEI-SA) was prepared, where the concentration of PEI-fatty acids was controlled to 0-2.4 mg/m 2 based on the total surface area of particles added in the following process.…”

“…From the FT-IR spectra of the original reagents, signals are observed for the aromatic C C stretching modes (1603 and 1496 cm −1 ), and CH 3 deformation vibration (1460 and 1384 cm −1 ) from toluene [22,23], and N H bending of amines (1600 cm −1 ) and CH 2 scissoring (1462 cm −1 ) from PEI [20,22]. From OA, stretching vibration of hydrogen-bonded C O from COOH (1710 cm −1 ), C O H bending (1418 cm −1 ) and CH 2 scissoring (1462 cm −1 ) can be observed [22,[24][25][26]. The spectra from ISA had adsorption peaks attributed to the stretching vibration of hydrogen-bonded C O from COOH (1710 cm −1 ), C O H bending (1418 cm −1 ), CH 2 deformation (1377 cm −1 ), and CH 2 wagging (1460 cm −1 ) [27].…”

“…The procedure used for the preparation of PEI-fatty acid complexes was similar to that described in our previous report [22]. 0.125 g of PEI and 0-0.827 g of fatty acids (0-100 mol% of fatty acids based on the number of PEI monomer units, calculated assuming all amines were secondary amines) were mixed with toluene (to make a 5.0 g solution) in a 50-mL glass vial and treated in an ultrasonic bath for 5 min.…”

“…To address this need, we previously proposed a versatile structure-tuning protocol for polymer dispersants involving simple mixing of the cationic polymer (polyethyleneimine) and anionic fatty acid (oleic acid) in a non-aqueous solvent. It was confirmed that the carboxyl groups of oleic acid complexes with the amine groups of polyethyleneimine (PEI), and the resulting PEI-OA complex, effectively adsorb on various species of particles, such as Si 3 N 4 , Y 2 O 3 , and MgO, in toluene [22]. The saturated adsorption of the PEI-OA complex on particles led to improvement of the dispersion of dense toluene suspensions, and their flowing properties could be controlled by varying the molecular weight of the PEI-OA complex.…”

Surface modification techniques toward controlling the dispersion stability and particle-assembled structures of slurries

“…16),17) The PEI-fatty acid complex can be simply prepared by mixing PEI with a fatty acid in a lowpolar solvent, such as toluene or ¡-terpineol. PEI itself is not soluble in low-polar solvents because it is a hydrophilic cationic polymer; however, PEI complexed with a fatty acid can be visibly dissolved in low-polar solvents.…”