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Forschungsarbeit

Synthesis and Characterization of linearly thermoresponsive core-shell

microgels

by Ines Freudensprung (17.03.2015)

This research topic discusses the preparation of smart thermoresponsive core-shell microgels based on acrylamide derivatives. The use of polymer materials with specific thermoresponsive properties in core and shell gives rise to a linear size/temperature correlation.

Microgels have been extensively studied in the last several decades due to their great potential for applications such as photonic materials, smart substrates or carriers for catalytic and biotechnological agents. [1, 2] By increasing the complexity of synthesized systems, e.g. with multi-compartment-structures, specific particle surfaces and modifications of the interior can be accessed.

[Bildunterschrift / Subline]: Schematic illustration of a core-shell microgel that undergoes different swelling behavior.

We present a new synthesis strategy of thermoresponsive core-shell microgels, with crosslinked PNNPAM (LCST = 21°C) being the shell and crosslinked PNIPMAM (LCST = 44°C) being the core material. Due to the large LCST gap of 23°C, these microgels exhibit a unique linear temperature response. With this core-shell microgel design, we get access to a fully reversible, temperature-dependent swelling/deswelling behavior, which can be categorized into three distinct regions.

[Bildunterschrift / Subline]: Figure 2: a) Hydrodynamic radius Rh as a function of temperature T for a PNIPMAM-core-PNNPAM-shell microgel. b) Rh(T)-diagram of the magnified region II.

In region I a nonlinear decrease of the particle size with increasing temperatures up to 25°C can be observed. This phenomenon can be addressed to the collapse of PNNPAM in the shell with a volume phase transition temperature at around 21°C. Region II covers the temperature range between 25°C and 41°C where the hydrodynamic radius of the microgel is linearly changing with temperature. It is interesting to note, that this linear correlation occurs in the intermediate temperature range in between the two LCSTs of the unperturbed materials in core and shell. Since the synthesis is performed at elevated temperatures above both LCSTs, the shell material covers fully collapsed seeds. Due to the presence of this shell-“corset”, the core cannot retain its original shape and is mechanically stressed at each point of the swelling process (“corset-effect”). Hence, the shell actively compresses the core, which retains its shape because of its network elasticity. Within the third regime the core actively collapses at temperatures above 40°C. The core is already pre-compressed because of the shell and only a minor change in terms of particle size can be observed in this region.

In our study, we were able to show that the combination of distinct polymer materials leads to a new system class with extraordinary thermoresponsive properties. As a result of the enhanced “corset-effect” – based on two polymers with largely different LCSTs – a region of ΔT ≈ 15°C was found where the hydrodynamic radius is linearly dependent on the applied temperature. This opens up various possibilities for applications in new sensor materials as well as actuator designs.

 

References

[1] M. Zeiser, I. Freudensprung, T. Hellweg, Polymer 2012, 53, 6096.
[2] S. Schmidt, M. Zeiser, T. Hellweg, C. Duschl, A. Fery, H. Möhwald, Adv. Funct. Mater. 2010, 20, 3235.


Wissenschaftlicher Werdegang
  • seit 2012
  • Promotion am Max-Planck-Institut für Polymerforschung MPI-P in Mainz unter Professor Dr. Klaus Müllen
  • seit 2010
  • Studentin im Elitestudienprogramm „Macromolecular Science“ im Rahmen des Elitenetzwerks Bayern, Universität Bayreuth
  • 2010-2012
  • Masterstudiengang Chemie (Master of Science), Technische Universität München
  • 2008-2010
  • Bachelorstudiengang Chemie (Bachelor of Science), Universität Bayreuth
  • 2006-2008
  • Grundstudium B.Sc. Chemie, Hochschule Niederrhein; Krefeld

Preise und Auszeichnungen
  • * Kurzstipendium für Doktoranden beim Deutschen Akademischen Austausch Dienst DAAD (2014-2015)
  • * Studienförderung der RWE AG „RWE Fellows“ (2009-2012)

Veröffentlichungen
  • * M. Zeiser, I. Freudensprung, T. Hellweg, Linearly thermoresponsive core-shell microgels: Towards a new class of nanoactuators, Polymer 2012, 53, 6096-6101.