Star Diblock Copolymer Concentration Dictates the Degree of Dispersion of Carbon Black Particles in Nonpolar Media: Bridging Flocculation versus Steric Stabilization

The solution behavior of a polystyrene–hydrogenated polyisoprene star diblock copolymer (Mn ∼ 384 K; 6 mol % polystyrene) is examined in nonpolar media. Variable temperature 1H NMR studies using deuterated n-dodecane confirm that the outer polystyrene blocks are only partially solvated in n-dodecane at 25 °C: the apparent polystyrene content of 3.2 ± 0.2 mol % remains essentially constant on heating up to 100 °C. Physical adsorption of this star diblock copolymer onto carbon black particles is examined, with particular attention being paid to the effect of copolymer concentration on colloidal stability. An isotherm is constructed for copolymer adsorption onto carbon black from n-dodecane at 20 °C using a supernatant depletion assay based on UV spectroscopy analysis of the aromatic chromophore in the polystyrene block. Langmuir-type adsorption is observed with a maximum adsorbed amount, Γ, of ∼2.2 ± 0.1 mg m–2. In addition, thermogravimetric analysis is used to directly determine the amount of adsorbed cop...