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Hydrogels with thermo-responsive mechanical properties - stage pourvu

Laboratoire Sciences et Ingénierie de la Matière Molle, (SIMM)

Adresse:ESPCI, 10 Rue Vauquelin 75005 Paris

Directeur du laboratoire : Christian Frétigny

Responsables du stage : Dominique HOURDET
Contact : Dominique Hourdet / 0140794643 / 0140794683


Scientific project :
By covalently crosslinking water-soluble polymers, it is possible to get soft elastic materials with defined shape (nano-, micro- or macroscopic) that display very interesting swelling and sieving properties. They are actually involved in many applications as superabsorbants, electrophoresis, contact lenses, drug delivery and scaffolds for tissue engineering. However an important issue with hydrogels is that these elastic materials are generally very brittle as they do not have many intrinsic mechanisms to retard fracture propagation. 
Recent works on hydrogels have shown that their mechanical properties could be drastically reinforced by introducing weak interactions in the covalent network. This is typically the case when hydrophobic interactions are introduced inside a hydrophilic 3D structure1,2 or when the polymer matrix specifically interacts with inorganic particles3-5. Whereas these secondary interactions cannot be finely triggered within these hybrid hydrogels, we have recently designed original networks where the physical interactions can be easily switched “on/off” by tuning the temperature6,7
Initially based on a graft copolymer strategy, combining a water-soluble polymer with a polymer exhibiting by a Lower Critical Solution Temperature in aqueous media (LCST), these new hydrogels have shown a dramatic enhancement of their mechanical properties upon heating which are correlated with the micro-phase separation induced by the collapse of the thermoresponsive polymer ; the water-soluble macromolecular counterpart allowing to keep the volume integrity of the gel during the phase transition (see Figure 1). 
This strategy, which was successfully extended to other architectures like interpenetrated networks (IPN), is really exciting as it paves the way to new ideas for developing soft materials with stimuli-responsive toughness playing with the chemical nature of macromolecules and/or their architectures.

Figure 1. Thermo-toughening of hydrogels under isochoric conditions7 : the collapse of red polymer chains can be triggered by temperature, while water-soluble blue chains prevent drastic volume change.
The project of this master internship, that will come to support the PhD work of Cécile Mussault, will be devoted to the synthesis and characterization of new hydrogels designed with grafted and/or semi-interpenetrated architectures based on different thermo-responsive precursors. 

This work will be divided into 3 main parts :

  1. the synthesis of hydrophilic and thermo-responsive polymer (or macromonomer) precursors and their copolymerization with antagonistic monomers in order to design grafted or semi-IPN networks,
  2. the characterization of the thermodynamic behaviour of prepared hydrogels by swelling experiments, differential scanning calorimetry and/or UV spectroscopy,
  3. the analysis of the mechanical properties under low (dynamic rheology) and large deformations (tensile test). These experiments will be carried out at various temperatures in order to quantitatively analyze the variation and the reversibility of the mechanical reinforcement induced by the micro-phase separation process.
    Required background
    Master student at the Master 2 level (or equivalent) with academic knowledge in polymer chemistry and physical chemistry.

1. G. Miquelard-Garnier, S. Demoures, C. Creton, D Hourdet, Macromolecules 39, 8128 (2006).
2. M. A. Haque, T. Kurokawa, G. Kamita, J. P. Gong, Macromolecules 44, 4997 (2011).
3. K. Haraguchi, T. Takehisa, Adv. Mat. 14, 1120 (2002)
4. L. Petit, L. Bouteiller, A. Brûlet, F. Lafuma, D. Hourdet, Langmuir 23, 147 (2007).
5. S. Rose, A. Dizeux, T. Narita, D. Hourdet, A. Marcellan, Macromolecules 46, 4095 (2013)
6. H. Guo, N. Sanson, D. Hourdet, A. Marcellan, Advanced Materials 28, 5857–5864 (2016)
7. H. Guo, C. Mussault, A. Brûlet, A. Marcellan, D. Hourdet, N. Sanson, Macromolecules 49, 4295-4306 (2016)

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