Self-assembled polyelectrolyte nanorings observed by liquid-cell AFM

Abstract

Self-assembled polyelectrolyte nanorings formed by polyelectrolytes are presented for thefirst time in this work. They are formed by poly(ethylenimine) (PEI) and poly(sodium4-styrenesulfanate) (PSS) during the two first steps of the formation of the self-assembledpolyelectrolyte films (SAPFs). These are formed on a negatively charged glass surface andobserved by an in situ liquid-cell AFM technique, which has recently been introduced as analternative technique to follow polyelectrolyte multilayer formation without drying effects(Menchaca et al 2003 Colloids Surf. A 222 185). Nanoring formation strongly depends on thepreparation method and parameters such as polyelectrolyte filtration, air andCO2 presence during SAPFs formation and buffer solution. A necessary condition to obtainnanorings is that polyelectrolyte solutions have to be filtered prior to injection into theliquid-cell AFM. The outer diameter of nanorings can be varied from hundreds ofnanometres to microns by changing these parameters. Nanorings are stable inthe liquid cell for hours but they disappear on contact with air. Additionally,carbonate ions seem to be mainly responsible for the formation of this novel structure.