Determination of Effective Particle Density for Sterically Stabilized Carbon Black Particles: Effect of Diblock Copolymer Stabilizer Composition

Abstract

Two poly(styrene-b-hydrogenated isoprene) (PS-PEP) copolymers and a poly(styrene-b-hydrogenated butadiene) (PS-PB) diblock copolymer of differing polystyrene content (20, 28 or 35 mol %) and molecular weight (117-183 kg mol(-1)) are examined. These copolymers form star-like micelles in n-dodecane, as judged by TEM, DLS, and SAXS studies. At ambient temperature, such micelles are known to adsorb intact onto a model colloidal substrate such as carbon black, conferring a high degree of dispersion (Growney, D. J.; Mykhaylyk, O. O.; Armes, S. P. Langmuir 2014, 30, 6047). Isotherms for micellar adsorption on carbon black at 20 °C are constructed using a supernatant depletion assay based on UV spectroscopy by utilizing the aromatic chromophore in the polystyrene block. Perhaps surprisingly, the diblock copolymer with the lowest polystyrene content has the strongest affinity for the carbon black particles. Assuming that the star-like diblock copolymer micelles adsorb onto carbon black to form hemi-micelles with a stabilizer layer thickness equal to the mean micelle radius, the effective particle density of the resulting sterically stabilized carbon black particles in n-dodecane can be estimated from the SAXS micelle dimensions based on geometric considerations. As an approximation, a spherical core-shell morphology was assumed, and the primary grain size of the carbon black particles was determined to be 74 nm diameter as judged by BET surface area analysis. Using this approach, effective particle densities of 0.90, 0.91, and 0.92 g cm(-3) were calculated for sterically stabilized carbon black particles prepared using the PS-PB20, PS-PEP28, and PS-PEP35 diblock copolymers, respectively. These densities are significantly lower than that of carbon black (1.89 g cm(-3)), which indicates that the sterically stabilized carbon black particles are substantially solvated. Since the rate of sedimentation of the sterically stabilized carbon black particles depends on the density difference between the effective particle density and that of n-dodecane (0.75 g cm(-3)), particle size analysis via analytical centrifugation incurs large sizing errors unless the above corrected effective particle densities are utilized. This is important because analytical centrifugation is a highly convenient technique for assessing the relative degree of dispersion of sterically stabilized carbon black particles, which are utilized to inkjet inks and coatings formulations.

How Do Spherical Diblock Copolymer Nanoparticles Grow during RAFT Alcoholic Dispersion Polymerization?

“…We feel that this is a more debatable hypothesis because it is well-known that DLS is a rather low resolution particle size analysis technique. 113 The 3D fusion of spheres to produce larger spheres is a widely accepted particle growth mechanism for conventional free radical dispersion polymerization. 114 Moreover, we note that a hypothetical sphere–sphere fusion event involving the inelastic collision of two identical spheres each of radius r and mass m to form a single larger sphere of mass 2 m only results in a 26% increase in the particle radius.…”

The internal structure of poly(methyl methacrylate) latexes in nonpolar solvents

“…However, the approach has predominantly been employed in water, due to application in the study of biomolecules [93,94]. Growney et alrecen tlyusedthetec hniqueto study polymer-stabilized carbon black particles in n-alkanes, which shows its versatility in nonpolar solvents as well [95][96][97]. To enable more precise determination of colloidal properties, sedimentation measurements can be performed in isotopically-labeled solvents, which are chemically identical but differ in fluid properties.…”

Flocculation of kaolin particles with cationic lignin polymers

“…Electro luminescent diode light at 880 nm scanned the cell from bottom to top at a 40 µm height interval. The scanning process was conducted every 25 s and the experiment lasted for 1 h 58 .…”

“…The hydrodynamic diameter of the suspended particles in the system (d h,s ) was determined by the transmission data from the top layer and the mean volume fraction of particles after settling for 1 h based on Lambert-Beer law (equations (1) and (2)).where r i represents the internal radius of the measurement cell, l is photo mean free path, T 0 is the transmittance of continuous phase (i.e., water), and T is the transmittance of suspension (i.e., kaolin suspension) 58,59 . Therefore, the transmission data collected by the instrument directly depended on the mean hydrodynamic diameter of the suspended particles, d h,s , and their volume fraction, ϕ s .…”