Stabilizing effect of TMAO on globular PNIPAM states: preferential attraction induces preferential hydration.
We study the effect of the organic co-solute trimethylamine N-oxide (TMAO) on the volume phase transition of microgel particles made from poly(N-isopropylacrylamide) (PNIPAM) using dynamic light scattering (DLS) and all-atom molecular dynamics (MD) simulations. The DLS measurements reveal a continuous TMAO-induced shrinking process from a coil to a globular state of PNIPAM microgel particles. Analyzing the DLS data by the phenomenological Flory-Rehner theory verifies the stabilization of the globular state of the particles in the presence of TMAO. Complementary atomistic MD simulations highlight a pronounced accumulation of TMAO molecules around PNIPAM chains. We observe a significant preferential attraction between TMAO and the globular state of PNIPAM, which is additionally stabilized by a larger number of hydrating water molecules compared to pure aqueous solutions. Further DLS measurements were also conducted on PNIPAM suspensions with the co-solute urea added. The observed differences compared with the results obtained for TMAO support the proposed mechanism.
Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany. martin.schroer@embl-hamburg.de and The Hamburg Centre for Ultrafast Imaging (CUI), Luruper Chaussee 149, 22761 Hamburg, Germany.
Martin A
MA
Schroer
Institut für Computerphysik, Universität Stuttgart, Allmandring 3, 70569 Stuttgart, Germany. smiatek@icp.uni-stuttgart.de.
Julian
J
Michalowsky
Institut für Physikalische Chemie, Universität Hamburg, Grindelallee 117, 20146 Hamburg, Germany.
Birgit
B
Fischer
Institut für Computerphysik, Universität Stuttgart, Allmandring 3, 70569 Stuttgart, Germany. smiatek@icp.uni-stuttgart.de.
Jens
J
Smiatek
Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany. martin.schroer@embl-hamburg.de and The Hamburg Centre for Ultrafast Imaging (CUI), Luruper Chaussee 149, 22761 Hamburg, Germany.
Gerhard
G
Grübel