Electrostatically Stabilized Metal Oxide Particle Dispersions in Carbon Dioxide

Abstract

We report electrostatic stabilization of micrometer-sized TiO(2) particles at long range (several micrometers) in liquid and supercritical CO(2) despite the ultralow dielectric constant, as low as 1.5. The counterions were solubilized in dry reverse micelles, formed with a low-molecular weight cationic perfluoropolyether trimethylammonium acetate surfactant, to prevent ion pairing with the particle surface. Dynamic light scattering and settling velocities indicate a particle diameter of 620-740 nm. The electrophoretic mobility of -2.3 x 10(-8) m(2)/V s indicated a particle charge on the order of -1.7 x 10(-17) C, or 105 elementary negative charges per particle. The balance of particle compression by an electric field versus electrostatic repulsion generated an amorphous arrangement of particles with 5-9 mum spacing, indicating Debye lengths greater than 1 mum. Scattering patterns also indicate that chains of particles may be achieved in CO(2) by dielectrophoresis with alternating fields. The electrostatic stabilization has been achieved by solubilizing a small concentration of counterions in only a small fraction of the reverse micelles in the double layer. Whereas many low-molecular weight surfactants have been shown to form reverse micelles in CO(2), very few polymers are able to stabilize micrometer-sized colloids sterically. Thus, electrostatic stabilization has the potential to expand markedly the domain of colloid science in apolar supercritical fluids.

Templated Open Flocs of Nanorods for Enhanced Pulmonary Delivery with Pressurized Metered Dose Inhalers

“…Particles of BSA suspended in acetonitrile were analyzed by a custom-built dynamic light scattering (DLS) apparatus (49). The scattering angle was set to 90°and the data were analyzed using a digital autocorrelator (Brookhaven BI-9000AT) and a non-negative least-squares (NNLS) routine (Brookhaven 9KDLSW32).…”

Nanoparticle-stabilized carbon dioxide-in-water foams with fine texture

“…The weak solvent strength of CO 2 causes A TC to be very small compared to A HW . Thus, a key to increasing the HCB of a surfactant is to minimize the tail-tail interactions, A TT , which can be achieved by using surfactants that contain ''stubby'', low cohesive energy density tails [9,[18][19][20][21], e.g. through the use of branching.…”

Electrophoretic mobility of concentrated carbon black dispersions in a low-permittivity solvent by optical coherence tomography

“…Electrostatic stabilization of colloids in low-permittivity solvents with a dielectric constant less than five generally requires additives such as polymers or surfactants to separate ions in the bulk from the surface and to avoid ion pairing [5][6][7][8][9][10][11][12][13][14][15][16][17]. Ion separation for a 1:1 electrolyte is given by the Bjerrum length (specified by equating electrostatic interaction energy and thermal energy), given as…”