Determination of the adsorbed layer thickness of functional anionic polymers utilizing chemically modified polystyrene nanoparticles

• Dynamic light scattering was used to study adsorbed layer thicknesses (ALTs) of polymers.
• Cationic polystyrene nanoparticles (d ∼ 77 nm) were utilized as adsorbents.
• Various anionic polyelectrolytes representing functional polymers in cement were tested.
• Highly reproducible values for ALTs were obtained, even at pH ∼ 13.
• Adsorbed conformation of the polymers accessible from comparison of ALT with rh values.

Dynamic light scattering (DLS) was found to present a facile method to directly measure the adsorbed layer thickness (ALT) of various functional polymers. Monodisperse polystyrene nanoparticles (d ∼ 77 nm) modified with zinc palmitate to attain a positive surface charge were identified as a suitable adsorbent. These particles are chemically inert and stable even at very high pH values, e.g. of ∼13. As polymers, two cement dispersants, two retarders and four water-retention admixtures were investigated. At first, adsorption isotherms were developed to probe whether single or multiple polymer layers were present on the particles’ surfaces. Next, the adsorbed layer thickness of each polymer on polystyrene nanoparticles was measured using DLS and the results were compared with the hydrodynamic radius of the polymers in solution. From this data, the adsorbed conformation of the polymers was assessed. The method allows quick determination of the ALT at reasonable accuracy.

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