Colloidal particles in a nonpolar media are closely correlated to industrial applications in particular particle-based electrophoretic display techniques. However, the synthesis of the commonly used poly(12-hydroxystearic acid)(PHSA)-based stabilizers for the dispersion polymerization of polymer particles in nonpolar solvent are troublesome. We report a sorbitan trioleate (Span 85)-based macromolecular copolymer stabilizer that can be easily synthesized and used for the preparation of PMMA particles in a nonpolar solvent. This is realized by synthesizing random copolymers of methyl methacrylate (MMA) and polymerizable sorbitan trioleate (M-Span 85), and the latter can be synthesized from the commercial product Span 85. Using this stabilizer, the resulting PMMA particles have narrow size distribution and tunable diameters. With the stabilizers, transferring water-dispersible particles to a nonpolar solvent and further preparing core/shell particles was verified to be a useful route. This provides an effective approach for using water-dispersible functional nanoparticles in nonpolar environments. In addition, the prepared PMMA particles are demonstrated to be a useful model system to study crystallization or glass transitions by quantitative confocal microscopy.
The impact of two nonionic surfactants, namely Span 20 and Span 85, on the electrorheological response and colloidal stability of urea-coated barium titanyl oxalate (BTRU)/silicone oil suspensions is investigated. We quantitatively analyze the surfactant effect on modified ER performance through the measurements of yield stress and current density, as well as the tuned suspension stability through calculation of the Turbiscan stability index (TSI) and naked-eye observations of sedimentation phenomena. The surfactant effect on particle–oil interactions and agglomeration effects is examined by measuring the permeability of silicone oil when mixed with the Span surfactant and the cluster size of particles in dispersing medium, respectively. Our results indicate that with the presence of a Span surfactant, the yield stress of the suspension exhibits a local maximum at certain Span concentrations. We hypothesize that below the optimal Span concentration, the ER properties are enhanced by the increase of the electrostatic interaction between particles. Above the limiting concentration, the ER activity is weakened by the formation of a double-layer surfactant structure that generates a steric hindrance effect. We discover that the addition of the Span surfactant favors the improvement of the particle agglomeration phenomenon, thereby promoting colloidal stability of the suspension. Consequently, in the consideration of both ER properties and suspension stability, an optimal ER fluid with the addition of 0.4 wt% Span 85 is acquired with remarkable integrated ER properties.
Silver powders were prepared by a chemical reduction method. Effects of different surfactants during this preparation process were examined. Using these silver powders, silver pastes were prepared for low temperature co-fired ceramics (LTCC) applications. Another batch of different surfactants were added into the silver paste and evaluated. Moreover, various organic thixotropic agents were used to modify the thixotropy behavior of the silver paste. It was found that the surfactants of PVP (Polyvinyl pyrrolidone, for preparation of the silver powder) and Span-85 (for the preparation of silver paste) exhibited the best performance, with an electrical resistivity of 0.11 mΩ mm. The silver paste with the thixotropic agent of hydrogenated castor oil shows the largest thixotropic index of 1.56. Using different organic additives, the microstructural, rheological and electrical properties of the silver paste can be considerably improved, and our results shed light on the optimization of the silver paste for LTCC applications.
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