FLIM nanoscopy resolves the structure and preferential adsorption in the co-nonsolvency of PNIPAM microgels in methanol-water

Journal of Colloid and Interface Science, vol. 678, pp. 210–220

Abstract

Polymer microgels are swollen macromolecular networks with a typical size of hundred of nanometers to several microns that show an extraordinary open and responsive architecture to different external stimuli, being therefore important candidates for nanobiotechnology and nanomedical applications such as biocatalysis, sensing and drug delivery. It is therefore crucial to understand the delicate balance of physical-chemical interactions between the polymer backbone and solvent molecules that to a high extent determine their responsivity. In particular, the co-nonsolvency effect of poly(N-isopropylacrylamide) in aqueous alcohols is highly discussed, and there is a disagreement between molecular dynamics (MD) simulations (from literature) of the preferential adsorption of alcohol on the polymer chains and the values obtained by several empirical methods that mostly probe the bulk solvent properties. It is our contention that the most efficacious method for addressing this problem requires a nanoscopic method that can be combined with spectroscopy and record fluorescence spectra and super-resolved fluorescence lifetime images of microgels labeled covalently with the solvatochromic dye Nile Red. By employing this approach, we could simultaneously resolve the structure of sub-micron size objects in the swollen and in the collapsed state and estimate the solvent composition inside of them in - mixtures for two very different polymer architectures. We found an outstanding agreement between the MD simulations and our results that estimate a co-solvent molar fraction excess of approximately 3 with a very flat profile in the lateral direction of the microgel.

Authors 6

1. Silvia P. Centeno corresponding Aachen DWI - Leibniz Institute for Interactive Materials (DWI) Leibniz Institute for Interactive Materials

   DWI – Leibniz Institute for Interactive Materials · RWTH Aachen University

   Affiliation as printed

   DWI Leibniz Institute for Interactive Materials, Forckenbeckstrasse 50, Aachen, 52074, Germany. Electronic address: centeno@dwi.rwth-aachen.de

   Leibniz Institute for Interactive Materials, Forckenbeckstrasse 50, Aachen, 52074, Germany

2. Katja Nothdurft Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

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

3. Andrey S. Klymchenko

   Laboratoire de bioimagerie et pathologies · Université de Strasbourg

   Affiliation as printed

   Laboratoire de Bioimagerie et Pathologies, UMR 7021 CRS, Université de Strasbourg, 74 Route du Rhin, Illkirch, 67401, France

4. Andrij Pich Aachen DWI - Leibniz Institute for Interactive Materials Functional and Interactive Polymers Institute of Technical and Macromolecular Chemistry Functional and Interactive Polymers Institute of Technical and Macromolecular Chemistry (DWI) Leibniz Institute for Interactive Materials

   Maastricht University · DWI – Leibniz Institute for Interactive Materials · RWTH Aachen University

   Affiliation as printed

   DWI Leibniz Institute for Interactive Materials, Forckenbeckstrasse 50, Aachen, 52074, Germany; Functional and Interactive Polymers Institute of Technical and Macromolecular Chemistry, Worringerweg 2, Aachen, 52074, Germany; Maastricht Institute for Biobased Materials (AMIBM), Maastricht University, Brightlands Chemelot Campus, Urmonderbaan 22, RD Geleen, 6167, the Netherlands

   Functional and Interactive Polymers Institute of Technical and Macromolecular Chemistry, Worringerweg 2, Aachen, 52074, Germany

   Leibniz Institute for Interactive Materials, Forckenbeckstrasse 50, Aachen, 52074, Germany

   Maastricht Institute for Biobased Materials (AMIBM), Maastricht University, Brightlands Chemelot Campus, Urmonderbaan 22, RD Geleen, 6167, the Netherlands

5. Walter H. Richtering Aachen DWI - Leibniz Institute for Interactive Materials Institute of Physical Chemistry Institute of Physical Chemistry (DWI) Leibniz Institute for Interactive Materials

   DWI – Leibniz Institute for Interactive Materials · RWTH Aachen University

   Affiliation as printed

   DWI Leibniz Institute for Interactive Materials, Forckenbeckstrasse 50, Aachen, 52074, Germany; Institute of Physical Chemistry, RWTH-Aachen University, Landoltweg 2, Aachen, 52074, Germany

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

   Leibniz Institute for Interactive Materials, Forckenbeckstrasse 50, Aachen, 52074, Germany

6. Dominik Wöll corresponding Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry, RWTH-Aachen University, Landoltweg 2, Aachen, 52074, Germany. Electronic address: woell@pc.rwth-aachen.de

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