Abstract
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...
Highlights
small-angle X-ray scattering (SAXS) provides direct evidence for the presence of the copolymer chains at the particle surface. It is well-documented that soluble polymers can influence the stability of colloidal dispersions via four different mechanisms: bridging flocculation, steric stabilization, depletion stabilization, and depletion flocculation.[1−12] The mechanism depends on the precise system and on the polymer concentration
THF gel permeation chromatography (GPC) analysis of the commercial star diblock copolymer used in this study indicated an Mn of 384 000 g mol−1 and an Mw/ Mn of approximately 1.40
Article that the star diblock copolymer acts as a flocculant for carbon black in n-dodecane at relatively low copolymer concentrations, since bridging of the copolymer chains between multiple carbon black particles leads to the formation of aggregates and larger agglomerates
Summary
It is well-documented that soluble polymers can influence the stability of colloidal dispersions via four different mechanisms: bridging flocculation, steric stabilization, depletion stabilization, and depletion flocculation.[1−12] The mechanism depends on the precise system and on the polymer concentration. We examine the influence of a commercial star diblock copolymer on the colloidal stability of carbon black particles in nonpolar media (e.g., n-dodecane). The LUMiSizer is a microprocessorcontrolled analytical centrifuge and is convenient for the analysis of diblock copolymer-stabilized carbon black dispersions described in this work, since it allows simultaneous characterization of multiple dispersions in organic solvents over a wide range of operating temperature (4−60 °C). The LUMiSizer employs STEP-Technology (space- and time-resolved extinction profiles) allowing the measurement of the intensity of transmitted light as a function of time and position over the entire cell length simultaneously The progression of these transmission profiles contains information on the rate of sedimentation and, given knowledge of the particle density, enables assessment of the particle size distribution. Spectra were typically acquired from at least two separate sample areas
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