title: Functional oligomers for the control and fixation of spatial organization in nanoparticle assemblies.
abstract: Interactions in nanoparticle assemblies play an important role in modulating their interesting magnetic and optical properties. Controlling and fixing the distance between nanoparticles is therefore crucial to the development of next-generation nanodevices. Here, we show that the interparticle distance in two-dimensional assemblies can be quantitatively controlled by functionalizing the nanoparticles with short polymers containing one functional end group that binds to the nanoparticle. Carboxy-functional poly(dimethylsiloxane) (PDMS) ligands are attached to the nanoparticle surface by a simple ligand exchange process with the oleic acid synthesis ligands. The distance between nanoparticles is manipulated by adjusting either the number of PDMS ligands per molecule or their molecular weight. The use of PDMS ligands is unique in that they provide a means to permanently and robustly fix the spatial distribution of nanoparticles because PDMS is readily converted to silicon oxide by a simple UV/ozone treatment. The distance between nanoparticles can be designed a priori, as it is found to scale well with theoretical predictions for the thickness of the surface-bound polymer brush layer.
authors.affiliation: Department of Chemical Engineering, Materials Research Science and Engineering Center, Columbia University, New York, New York 10027, USA.
authors.forename: Chun-Kwei
authors.initials: CK
authors.lastname: Wu
authors.forename: Kristi L
authors.initials: KL
authors.lastname: Hultman
authors.forename: Stephen
authors.initials: S
authors.lastname: O'Brien
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: Koberstein