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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - DoDyNet (Double Dynamics for design of new responsive polymer networks and gels)

Teaser

Summary

Polymer gels and networks are fascinating versatile soft materials which are ubiquitous in daily life (foodstuff, cosmetics) and high-added value applications (tissue engineering, sensors, drug storage and delivery, portable batteries), and can exhibit both solid-like and liquid-like properties. Classical methods of crosslinking these networks fall into two categories, chemical and physical, and the properties of the respective networks generally encompass two extreme cases: (i) Permanent networks, covalently crosslinked, able to resist flow and creep, and to swell without losing their coherence, but with limitations in terms of their processing and recycling. (ii) Physical networks, which are reversible, easily processable and recyclable, but creep at long times and show residual deformations in loading/unloading cycles. Today, the biggest challenge with this important class of responsive materials is to efficiently combine and control within the same material all distinct features that make them ideal for applications, such as high mechanical strength, large reversible deformability in shear and extension, substantial reversible swelling, and self-healing properties. It is important to transfer the knowledge acquired from bulk networks (elastomers) to the properties of solvent-mediated swollen gels. This has emerged as a priority theme for the development of so-called smart (i.e., multiply responsive) materials.

Objectives:

Within DoDyNet, we would like to address this challenge, inspired by the recent progress made in this field, reached thanks to the development of new types of polymer networks. While different, these new materials share a common concept, which is the combination of at least two distinct dynamic modes within the same material in order to display multiscale viscoelastic responses under the influence of an external stress or deformation field. Consequently, they are characterized by a â€˜doubleâ€™ mechanical behavior, which offers a better balance between the desired properties.

Therefore, we would like to design, synthesize and characterize new double polymer networks, which will allow us to investigate and understand how to control their dynamics by playing with their composition. Based on these results, we would like to develop models to relate the properties of these polymer networks and their architecture. Such fundamental understanding will help us to answer the requests from our industrial partners about developing new materials based on this strategy.

Organization of DoDyNet and Double Dynamics Networks

In order to accomplish our objectives, the institutions in DoDyNet have been chosen in order to cover, all together, the necessary expertise for the project, i.e. a strong expertise in synthesizing responsive networks, the use of many state-of-the art (home-made) measurement techniques, most accurate models, detailed questions and advices from major companies, and large support of visiting experts. Our work packages have been organized in respect to this expertise.

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Work performed

In order to answer our questions, we are studying the properties of new DDNs which fulfil the criteria that we believe are important in order to obtain polymer networks with novel properties. These materials are transient networks based on metal-ligand interactions, entanglement and phase separation, Double Dynamics thermoplastic elastomers, Double Dynamics Networks (DDN) based on reversible covalent bonding, pressure sensitive adhesive DDNs or slide-ring gels. Up to now, the main components of these DDNs have been synthetized and distributed to the consortium.

Dynamics and flow properties of sticky polymer chains:

An example of systems we are studying is the sticky polymer chains. They consist of polymer chains bearing sticky groups along their backbone. Our metallo-supramolecular sticky polymers (ClÃ©ment Coutouly, UCL), ionomers (Wendy Wang, DTU), reversible covalent sticky chains (Larissa Hammer, ESPCI) and associating block copolymers (Simone Sbrescia, DSM) enter within this category. Statistical tool have been developed to determine the composition of these samples (Yanzhao Li, UCL). Hongwei Liu (UN) has developed simulations which account for End modes and Trapped modes of the Rouse dynamics of unentangled sticky chains in order to understand how these samples can relax their stress when a constant deformation is applied, while Yanzhao Li (UCL) is investigating the role of possible inter-chain entanglements in their relaxation process.

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Wendy Wang (DTU) has investigated how such materials deform under a large elongational deformation, while Jianzhu Ju (ESPCI) has studied the fracture mechanisms and corresponding structure of associating block-copolymers under large deformations. In parallel, Simone Sbrescia (DSM) investigated how these thermoplastic elastomers could better resist deformation at high temperature.

Next step is to study similar systems containing stickers with two different lifetimes. Preliminary studies have been achieved by Consiglia Carillo (FORTH) in collaboration with our associated partner tesa on DDNs containing both reversible and covalent bonds. An in depth study of these materials should help us understanding how to optimize the stickiness of these pressure-sensitive adhesives!

Final results

The strength of our project is the combination of diverse expertise\'s for the same objective: make the link between sample composition and its macroscopic properties, to develop new, smart, materials, for new applications. The added value of DDNs is potentially very important. Today, they are already used in several fields, but there is still large room for new materials and new applications. To this end, designing new DDNs and decoding their fundamental structure-dynamics relationships by altering material parameters is of prime importance and will yield materials with optimized properties for the development of sustainable energy-saving materials, high-productivity processes or high-throughput responsive materials.The re-usability offered by the DDNs is also a key property that we would like to exploit.
To utilize DDNs in industry, a number of pre-requisites need to be fulfilled in terms of cost and processing. In this respect, morphological separation along with hydrogen bonded supramolecular associations offers an economically sound approach to introduce DDNs starting from commercial compounds requiring no or little chemical modification.

Beside the industrial impact, we aim at building a strong collaborative network of researchers in the field of polymer gels and networks, taking the consortium of DoDyNet as the starting point for the development of a larger structure. Thanks to the summer school open to researchers outside the consortium, to the presentations of our results at international conferences, or to the active role of the visiting experts, the research performed within DoDyNet starts to have a good visibility, that we would like to enhance even more in the future!