title: Nanoparticle stability in semidilute and concentrated polymer solutions.
abstract: The wetting of PDMS-grafted silica spheres (PDMS- g-silica) is connected to their depletion restabilization in semidilute and concentrated PDMS/cyohexane polymer solutions. Specifically, we found that a wetting diagram of chemically identical graft and free homopolymers predicts stability of hard, semisoft, and soft spheres as a function of the bulk free polymer volume fraction, graft density, and the graft and free polymer chain lengths. The transition between stable and aggregated regions is determined optically and with dynamic light scattering. The point of demarcation between the regions occurs when the graft and free polymer chains are equal in length. When graft chains are longer than free chains, the particles are stable; in contrast, the particles are unstable when the opposite is true. The regions of particle stability and instability are corroborated with theoretical self-consistent mean-field calculations, which not only show that the grafted brush is responsible for particle dispersion in the complete wetting region but also aggregation in the incomplete wetting region. Ultimately, our results indicate that depletion restabilization depends on the interfacial properties of the nanoparticles in semidilute and concentrated polymer solutions.
authors.affiliation: Department of Chemical Engineering, University of Virginia, 102 Engineers Way, Charlottesville, Virginia 22904, USA.
authors.forename: Nupur
authors.initials: N
authors.lastname: Dutta
authors.forename: David
authors.initials: D
authors.lastname: Green
mesh_terms: D001703:Biophysics / Q000379:methods; D002627:Chemistry, Physical / Q000379:methods; D003510:Cyclohexanes / Q000737:chemistry; D004129:Dimethylpolysiloxanes / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D015233:Models, Statistical; D053758:Nanoparticles / Q000737:chemistry*; D036103:Nanotechnology / Q000379:methods*; D009757:Nylons / Q000737:chemistry*; D019999:Pharmaceutical Solutions / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry; D011108:Polymers / Q000737:chemistry*; D012996:Solutions; D013499:Surface Properties; D017155:Wettability
chemical_list: D003510:Cyclohexanes; D004129:Dimethylpolysiloxanes; D009757:Nylons; D019999:Pharmaceutical Solutions; D011108:Polymers; D012996:Solutions; C085707:poly(dimethylsiloxane)-polyamide copolymer; D011092:Polyethylene Glycols; C506365:Cyclohexane