Star diblock copolymer concentration dictates the degree of dispersion of carbon black particles in nonpolar media: bridging flocculation versus steric stabilization

DOI: 10.1021/acs.macromol.5b00517

Authors: David Growney (University of Sheffield) , Oleksandr Mykhaylyk (The University of Sheffield) , Thibault Derouineau (The University of Sheffield) , Lee Fielding (University of Sheffield) , Andrew J. Smith (Diamond Light Source) , Najib Aragrag (BP Formulated Products Technology) , Gordon D. Lamb (BP Formulated Products Technology) , Steven P. Armes (University of Sheffield)
Co-authored by industrial partner: Yes

Type: Journal Paper
Journal: Macromolecules , VOL 48 (11)

State: Published (Approved)
Published: May 2015
Diamond Proposal Number(s): 9490

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 copolymer on the carbon black particles, which are essentially incombustible under an inert atmosphere. Analytical centrifugation, optical microscopy, and transmission electron microscopy studies indicate that the star diblock copolymer acts as an effective flocculant at low concentration, with steric stabilization only being observed above a certain critical copolymer concentration (∼5.5% w/w based on carbon black). This is attributed to the spatial location of the polystyrene block and the star copolymer architecture, which enables copolymer adsorption onto multiple carbon black particles at low coverage, leading to bridging flocculation. Above 5.5% w/w copolymer, the surface coverage is sufficiently high that all of the polystyrene “stickers” adsorb onto single carbon black particles, resulting in colloidally stable, sterically stabilized carbon black dispersions. Small-angle X-ray scattering (SAXS) is also used to characterize the copolymer-coated carbon black particles: this technique provides useful complementary insights regarding the rather subtle changes in the fractal morphology that occur with increasing copolymer concentration. Moreover, SAXS also provides direct evidence for the presence of the copolymer chains at the particle surface.

Journal Keywords: Aromatic compounds; Colloids; Copolymers; Hydrocarbons; X-ray scattering

Subject Areas: Chemistry, Materials


Instruments: I22-Small angle scattering & Diffraction

Added On: 30/05/2015 11:02

Documents:
acs.macromol.5b00517.pdf

Discipline Tags:

Soft condensed matter physics Chemistry Materials Science Organic Chemistry Polymer Science

Technical Tags:

Scattering Small Angle X-ray Scattering (SAXS)