(217f) Ordering pH-Responsive Polymer-Grafted Nanoparticles in Flow Coating Process

Poly(acrylic acid) (PAA)-grafted silica nanoparticles with different grafting densities and brush lengths were synthesized via surface-initiated ATRP, and their deposition patterns on silicon substrates were investigated by systematically varying the speed of moving substrates, pH values, and free polymer poly(vinylpyrrolidone) (PVP) concentrations in aqueous solution. Brush-brush interactions are tuned by varying the PAA chain conformations with pH and also with the addition of free PVP. Different deposition patterns were observed for nanoparticles at low grafting density and long brush length at a velocity of 0.4 mm/min and a PVP concentration of 0.24 mg/ml. At pH 11, nanoparticles assembled into well-regulated lines parallel to the moving direction of the blade. However, at pH 9, nanoparticles showed stronger repulsion, which led to Rayleigh-instability, and a dot pattern formation. At pH 3, particle attractions get strong due the hydrogen bonding between PAA and PVP, hence Bénard cell patterns were observed. The mechanisms of hydrogen bonding between two different polymers and also physical bridging within particles are demonstrated to organize the grafted nanoparticles in a flow-coating process. Our findings will enable the easy fabrication of patterned particle domains for functional polymer films.