Regensburg 2007 – scientific programme

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SYPE: Symposium Polyelectrolytes

SYPE 1: Polyelectrolytes Poster

SYPE 1.12: Poster

Wednesday, March 28, 2007, 16:00–18:30, Poster B

Direct evidence of Layer-by-Layer assembly of polyelectrolyte multilayers on soft and porous temperature sensitive PNiPAM-microgel using fluorescence correlation spectroscopy — •John Erik Wong¹, Walter Richtering¹, and André Laschewsky² — ¹RWTH Aachen University — ²Potsdam University

We describe the Layer-by-Layer assembly of polyelectrolyte multilayers on soft and porous temperature-sensitive poly(N-isopropylacrylamide) (PNiPAM) microgel. Microgels are not hard and rigid but rather soft and porous particles and polyelectrolytes can not only interdigitate with each other during multilayer formation but also interpenetrate with the microgel. Because of this difference, there could be concerns about the feasibility of the Layer-by-Layer technique on these systems. The argument being that the layer being deposited is stripping the underlying layer instead of anchoring to the latter, and common methods of characterizing film growth on particles such as zeta-potentials will still show *successful* charge reversal.

To address this issue, we used two differently labeled-polyelectrolytes during the deposition. Due to the small size of the microgel (400 nm) studied, we cannot distinguish between polyelectrolytes adsorbed on or in the microgel. However with fluorescent correlation spectroscopy we can clearly distinguish between free labeled-polyelectrolytes and those that are bound to the microgel. Dual-color correlation confirms the presence of both polyelectrolytes bound to the same particle while fluorescence imaging (on a dry sample) provides the visual proof.