title: Dynamic light scattering investigations of nanoparticle aggregation following a light-induced pH jump.
abstract: There are many important processes where the stability of nanoparticles can change due to changes in solution environment. These processes are often difficult to study under controlled changes to the solution conditions. Dynamic light scattering was used to measure the initial kinetics of aggregation of carboxylated polystyrene nanoparticles after well-defined pH jumps using aqueous solutions of photoacid generator (PAG). With this approach, the pH of the solution was controlled by exposure to ultraviolet (UV) light without the delays from mixing or stirring. The aggregation kinetics of the nanoparticles was extremely sensitive to the solution pH. The UV exposure dose is inversely correlated with the resulting surface charge of the nanoparticles. Decreasing pH decreases the electrostatic repulsion force between particles and leads to aggregation. The reaction-limited or diffusion-limited aggregation kinetics was sensitive to the pH quench depth, relative to the acid-equilibrium constant (pK(a)) of the surface carboxylic acid groups on the nanoparticles. Since numerous PAGs are commercially available, this approach provides a flexible method to study the aggregation of a variety of solvent-dispersed nanoparticle systems.
authors.affiliation: Polymers Division, National Institute of Standards and Technology, 100 Bureau Dr., Gaithersburg, Maryland 20899-8541, USA. ryan.murphy@us.rhodia.com
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Murphy
authors.forename: Denis
authors.initials: D
authors.lastname: Pristinski
authors.forename: Kalman
authors.initials: K
authors.lastname: Migler
authors.forename: Jack F
authors.initials: JF
authors.lastname: Douglas
authors.forename: Vivek M
authors.initials: VM
authors.lastname: Prabhu
mesh_terms: D000143:Acids / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008027:Light; D056004:Molecular Dynamics Simulation; D053758:Nanoparticles / Q000737:chemistry*; D010777:Photochemistry; D011137:Polystyrenes / Q000737:chemistry*; D012542:Scattering, Radiation; D012996:Solutions; D014466:Ultraviolet Rays; D014867:Water / Q000737:chemistry
chemical_list: D000143:Acids; D011137:Polystyrenes; D012996:Solutions; D014867:Water