posted on 2014-05-20, 00:00authored byN. Schonbeck, K. Kvale, T. Demarcy, J. Giermanska, J.-P. Chapel, J.-F. Berret
A critical advantage of electrostatic
assemblies over covalent
and crystalline bound materials is that associated structures can
be disassembled into their original constituents. Nanoscale devices
designed for the controlled release of functional molecules already
exploit this property. To bring some insight into the mechanisms of
disassembly and release, we study the disruption of molecular electrostatics-based
interactions via competitive binding with ionic surfactants. To this
aim, free-standing micrometer-size wires were synthesized using oppositely
charged poly(diallyldimethylammonium chloride) and poly(acrylic acid)
coated iron oxide nanoparticles. The disassembly is induced by the
addition of sodium dodecyl sulfates that complex preferentially the
positive polymers. The process is investigated at two different length
scales: the length scale of the particles (10 nm) through the quartz
crystal microbalance technique and that of the wires (>1 μm)
via optical microscopy. Upon surfactant addition, the disassembly
is initiated at the surface of the wires by the release of nanoparticles
and by the swelling of the structure. In a second step, erosion involving
larger pieces takes over and culminates in the complete dissolution
of the wires, confirming the hypothesis of a surface-type swelling
and erosion process.