Colloidal Deposition by Polymer-Surfactant Complexes with Dilution and Shear

Depositionof silica microparticles on glass substrates was measuredas a function of cationic polymer-anionic surfactant composition andshear rate. Particles were initially deposited in quiescent conditions in differentpolymer-surfactant compositions, which were chosen based on priormeasurements of composition-dependent polymer-surfactant interactionsand deposition behavior (up to 0.5 wt % polymer and 12 wt % surfactant).Programmed shear and dilution profiles in a flow cell together withoptical microscopy observation were used to continuously track particledeposition, detachment, and redeposition. Knowledge of the shear-dependenttorque on each particle provides information on adhesive torque mediatedby polymer-surfactant complexes. Detachment of colloids initiallydeposited by depletion interactions occurs at low shear rates (similar to 100s(-1)) due to lack of tangential forces or an adhesivetorque. Further dilution produced redeposition of particles that resisteddetachment (up to similar to 2000 s(-1)) as the resultof strong cationic polymer bridge formation, presumably due to preferentialsurfactant removal. Dilution from different initial compositions indicatesa pathway dependence of polymer-surfactant de-complexation into shear-resistantcationic bridges. These findings demonstrate the ability to programdeposition behavior via the informed design of initial polymer-surfactantcompositions and shear profiles. The particle trajectory analysisdeveloped in this work provides an assay to screen composition-dependentcolloidal deposition in diverse materials and applications.

Automated summary

The deposition of silica microparticles on glass substrates was investigated as a function of cationic polymer-anionic surfactant composition and shear rate. The study demonstrated the ability to control deposition behavior by designing initial polymer-surfactant compositions and shear profiles. The particle trajectory analysis developed in this work provides an assay for screening composition-dependent colloidal deposition in various materials and applications.