Characterization of thermosensitive PNIPAM microgels by analytical centrifugation - 42nd Meeting of the German Colloid Society - Kolloidgesellschaft

42nd Meeting of the German Colloid Society - Kolloidgesellschaft
Smart materials: foams, gels and microcapsules
September 26 - 28, 2005, Aachen, Germany

Poster

Characterization of thermosensitive PNIPAM microgels by analytical centrifugation

T. Sobisch and D. Lerche

L. U.M. GmbH, Rudower Chaussee 29 (OWZ) 12489 Berlin

e-mail info@lum-gmbh.de, www.lum-gmbh.com

I. Berndt

Institute of Physical Chemistry, University of Kiel

Olshausenstr. 40 – 60, 24098 Kiel

W. Richtering

Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, 52074 Aachen

Aqueous microgel suspensions are characterized by a strong dependence of particle size on temperature tuneable by the degree of cross linking.

Microgel particles are often applied as a physical model for soft deformable particles, for the study of rheological properties and phase transitions.

Relating to their specific tuneable properties microgel particles have wide ranging potential applications in the field of sensors, catalysis and controlled drug release. Physicochemical characterization of suspension behaviour and thermal and mechanical properties of these materials is essential for quality control and technical applications.

The paper describes the application of multisample analytical centrifugation for qualitative and quantitative characterization of microgel particles as function of concentration, temperature and centrifugal pressure applied.

The method allows to trace the distribution of light transmission over the whole sample length during centrifugation. Thereby the kinetics and extent of separation processes can be investigated in-situ.

The microgel particles were synthesized by emulsion polymerization of N-isopropylacrylamide in presence of the cross linker N,N´-Methylen-bis-acrylamide. The microgel particles were characterized by dynamic light scattering and capillary viscosimetry.

During centrifugation microgel dispersions split into a nearly particle free top layer, a normal microgel suspension middle layer and an ordered bottom layer showing Bragg diffraction. The layering remains stable even after prolonged standing after centrifugation.

The volume of the bottom layer changes with the overall microgel concentration, temperature and centrifugal pressure.