Coating thickness and coverage effects on the forces between silica nanoparticles in water.
The structure and interactions of coated silica nanoparticles have been studied in water using molecular dynamics simulations. For 5 nm diameter amorphous silica nanoparticles, we studied the effects of varying the chain length and grafting density of polyethylene oxide on the nanoparticle coating's shape and on nanoparticle-nanoparticle effective forces. For short ligands of length n = 6 and n = 20 repeat units, the coatings are radially symmetric while for longer chains (n = 100) the coatings are highly anisotropic. This anisotropy appears to be governed primarily by chain length, with coverage playing a secondary role. For the largest chain lengths considered, the strongly anisotropic shape makes fitting to a simple radial force model impossible. For shorter ligands, where the coatings are isotropic, we found that the force between pairs of nanoparticles is purely repulsive and can be fit to the form (R/2r(core) - 1)(-b) where R is the separation between the center of the nanoparticles, r(core) is the radius of the silica core, and b is measured to be between 2.3 and 4.1.
Sandia National Laboratories, Albuquerque, New Mexico 87185, USA.
K Michael
KM
Salerno
Aachener Verfahrenstechnik: Molecular Simulations and Transformations, Faculty of Mechanical Engineering, RWTH Aachen University, D-52056 Aachen, Germany.
Ahmed E
AE
Ismail
Sandia National Laboratories, Albuquerque, New Mexico 87185, USA.
J Matthew D
JM
Lane
Sandia National Laboratories, Albuquerque, New Mexico 87185, USA.
Gary S
GS
Grest
D000327:Adsorption; D016880:Anisotropy; D003102:Colloids / Q000737:chemistry*; D003198:Computer Simulation; D008956:Models, Chemical; D008958:Models, Molecular; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D012822:Silicon Dioxide / Q000737:chemistry*; D013314:Stress, Mechanical; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
D003102:Colloids; D014867:Water; D012822:Silicon Dioxide