WP 1 : Management
Lead Beneficiary : E. van Ruymbeke, UCL
Deliverable timing : M1- M48
Objectives : To ensure effective management of the project, including scientific and financial coordination and monitoring of the project’s progress. Achievement of the technical and scientific objectives of the project. Provide the interface between the European Commission and other stakeholders. Handle IPR and Gender issues.
Task 1.1: (all) Legal, Financial and Administrative Coordination. Supervision of legal, financial and administrative issues
Task 1.2: (all) Scientific Coordination Supervision of the research progress in view of the scientific objectives of the project.
Task 1.3: (all) Develop and enforce the IPR protection protocol
Task 1.4: (all) Monitor success in employing female ESRs. Allocate funding to facilitate female participation in conferences.
WP 2 : Synthesis and preparation of new DDNs
Lead Beneficiary : C.A. Fustin, UCL
Deliverable timing : M1-M48
Objectives: To synthesize different DDNs which will be used to develop a deep conceptual understanding of their dynamics and mechanical properties.
Synthesis of model DDNs
Task 2.1.: Synthesis of telechelic star polymers:7 star polymers end-functionalized with a terpyridine ligand will be obtained either starting from commercially available PEO stars that will be functionalized (for melts and solutions), or by RAFT using a multi-functional chain transfer agent (CTA) bearing terpyridines, which allows using a wide variety of monomers and functional groups. These two procedures have already been successively used by partner P112. Poly(nbutyl acrylate) (PnBA) stars will be the starting choice for melt studies, but other polymers will also be prepared from the same functional CTA.
Task 2.2.: (Functionalized) ABA triblock copolymers will be obtained by RAFT.13 A bifunctional CTA will be used to insure a polymer growth from both sides, for controlling the equal length of the outer A blocks, which will be of various nature and length to change their glass temperature Tg and escape dynamics. The central B block will either be made of PnBA (for melts) or of poly(dimethylacrylamide) (PDMAA) (for solutions), with an appropriate comonomer bearing a terpyridine ligand for functionalized triblocks. Partner P1 is well experienced in the use of such monomers.7 Some ABA triblocks are also commercially available.
Task 2.3.: Long linear functionalized polymers will be obtained by RAFT by copolymerizing the B monomer with a comonomer bearing a terpyridine ligand as for the functionalized ABA triblocks.13
Task 2.4.: Elaboration of DDN and role of their composition: Different DDN will be prepared by combining the building blocks in various ways (see 1.1.3). In general, DDN will be prepared by co-dissolving the precursors of the metal-ligand network (stars or linear polymers) and the ABA triblock in a selective solvent of the B block. The phase separated network will thus form in the presence of the precursors of the metal-ligand network, insuring a better homogeneity. Swelling this network in a solution of metal cations will then induce the formation of the metal-ligand supramolecular network within the phase separated one.
Synthesis of DDNs based on reversible covalent chemistry
Task 2.5.: Design and synthesis of new reversible covalent networks for new properties:4,8,9 The two chosen reversible chemistries are the thiol-disulfide coupling and the Diels-Alder reaction between furan and maleimide derivatives, since they can be selectively and reversibly dissociated (by oxido-reduction and thermal treatment, respectively) and are stable in aqueous media (for hydrogels). The first dense network will be prepared by radical copolymerization of DDMA with a bisacrylamide crosslinker containing a disulfide bond. The DDN will then be obtained by radical copolymerization, within the swollen first network, of DDMA with a bisacrylamide crosslinker containing a Diels-Alder cycloadduct. Partner 3 has the needed competences to prepare such samples. The crosslinking density, functionality and molecular weight of the constituting chains will be easily tuned. Also, it is possible to vary the structure of the disulfide moiety and of the Diels-Alder adduct in order to obtain a large variety of dynamics and mechanical properties (both hydrogel and elastomer) and adjusted to specific behaviors.
Synthesis of DDNs involving slide-ring gels
Task 2.6.: Synthesis of slide-ring DDN:5 These systems will be composed of a first network of telechelic polymers crosslinked by metal-ligand bonds, and of a second network based on slide-ring crosslinks, following the chemistry developed by Ito (based on free radical polymerization and polyrotaxanes made of functionalized cyclodextrins threaded onto a PEO chain as crosslinker). The DDN will be prepared by a one-pot approach. Typical monomers will be of the acrylamide family with a charged co-monomer for better performance. The polyrotaxane crosslinker is commercially available or can be made using classical cyclodextrin chemistry.
Task 2.7.: Optimizing the performances of slide-ring DDN: Amount of metal-ligand precursors (star or linear polymer), length of the precursors, lifetime of the metal-ligand, amount of polyrotaxane crosslinker, preparation conditions and protocol will be important parameters to tune and optimize the performances of the obtained DDN.
Creation of DDNs based on industrial building blocks
Task 2.8.: Creation of DD thermoplastic elastomers
Task 2.9.: Creation and distribution of DDNs for pressure sensitive adhesives
WP 3 : Structure and quiescent dynamics
Lead Beneficiary: S. Seiffert, U.M.
Deliverable timing : M1 – M48
Objectives: Polymer networks often exhibit structural heterogeneity on multiple scales, ranging from a few nanometers (polydisperse mesh sizes, connectivity defects) to several hundreds of nanometers (spatial heterogeneity of crosslinking), which reduces the materials strength substantially. For reversible polymer networks, spatial heterogeneity on 10–1000 nm scale has been found to arise from clustering of the supramolecular crosslinks.14a,b But in contrast to their covalent counterparts, such clustering of the crosslinker reinforces the material.14c We shall quantitatively characterize the nano- to microstructural complexity of DDNs (due to supramolecular crosslinks or nanophase separation) by the mutually synergistic use of scattering and fluorescence-microscopy techniques.
Task 3.1.: Dynamic light scattering (DLS): By means of DLS we shall assess the network dynamic structure, focusing on two modes in particular. First, at long correlation times, we will investigate slow non-diffusive viscoelastic modes of network relaxation and relate these to potential longtime relaxation found in linear rheology. Second, at short correlation times, we will focus on the cooperative diffusive mode of network-strand fluctuation, allowing us to quantify the network-strand hydrodynamic length that may be viewed as a measure of the network mesh size.15 This will help us to relate the precursor polymer composition to the sample mechanics as probed by linear rheology. The present DDNs may show bi- or even multimodal times, as they are composed of two or even more dynamic polymer-crosslinking contributors; careful data analysis will allow to separate the effect of these different contributors. Only transparent samples can be investigated, which is expected to be the case for a large part of the proposed DDNs.
The temporal evolution (from a minute up to few days) of these DDNs will also be studied. A setup developed at UM that allows static and dynamic light scattering at 8 detection angles at a time shall be used to assess the sample ageing at different time scales, while a new setup developed at FORTH will allow measuring DLS at different angles and times just after shearing the sample in a rotating cone-plate fixture. These results will be compared against respective rheological information (task 2.2).
Task 3.2.: Microscopy-based techniques of fluorescence recovery after photobleaching (FRAP) and fluorescence correlation spectroscopy (FCS): They will be used to further deepen the insight on the polymer network mesh topology. Based on methodology developed by Partner P5, we will probe the diffusive penetration of small non-adsorbing mesoscopic probes embedded into the networks and explore their structures by means of the impairment exerted on the probe motion. Whereas FRAP is most suited to probe diffusivities slower than 10 µm2 s–1 on scales larger than 10 µm, FCS is most suited to probe diffusivities faster than 1 µm2 s–1 on scales of smaller than 1 µm, which yields information on possible non-Fickian diffusion due to temporal trapping of the probes within small network meshes or dense local network domains.
Task 3.3.: Small-angle X-ray (SAXS) and neutron scattering (SANS): Using these techniques we shall quantify both the network mesh structures at scales of a few nanometers and potential further structural complexity at larger scales, including spatial inhomogeneity of the crosslinking density of the network.14b The goal is to bridge length scales accessible to different scattering techniques (light, X-rays, neutrons) and obtain a global picture based on different features (contrast): X-ray (available at CNRS) are particularly sensitive to heavy atoms such as the metal ions in the supramolecular crosslinkers, thereby probing their positions. Neutrons sense specific parts of the polymer networks based on selective deuteration. These experiments will be performed in facilities such as ESRF or ILL (Grenoble), DESY (Hamburg), PSI (Villigen) and HZB (Berlin) on the basis of beam-time proposals.
WP 4 : Viscoelasticity, nonlinear rheology and mechanical properties
Lead Beneficiary: D. Vlassopoulos, FORTH
Deliverable timing : M6 –M48
Objectives: Understanding and decoding the exact role of molecular parameters of DDNs such as entanglements, dangling ends or chain architecture on the dynamics of DDNs. Special emphasis will be put on bridging rheological and mechanical properties into an emerging general picture. In this direction, we will also investigate the elasto-capillary effects in these networks in conjunction with their nonlinear rheology. Assessing the rheological and mechanical properties of the DDNs is central to this project. In this direction we will use external fields (shear, extension) in order to (i) diagnose the viscoelastic character of the materials and (ii) induce deformation in order to probe their deformability and fracture. The tasks have been organized by techniques:
Task 4.1.: Diagnostic tests involving linear viscoelastic measurements (LVE) and in particular, oscillatory measurements. First, the thermal properties of the samples will be determined by differential scanning calorimetry (DSC) in order to establish the temperature range for rheological measurements. Since associating networks are essentially metastable systems, dynamic time sweep tests will be performed following thermal annealing or pre-shear in order to follow possible ageing and determine quasisteady-state conditions, assess the sample’s stability, and determine the proper protocol to use, which is necessary for comparing samples. Strain amplitude sweeps will be performed for determining the limits of the linear viscoelastic regime and, finally, frequency sweep measurements will provide important information about the relaxation time spectrum of a sample, which is of prime importance to understand and model their equilibrium dynamics, and will allow us to explore the influence of the structural and external parameters. Special attention will be paid to the reduction of degradation risks (by using of nitrogen or a special humidity-control chamber mounted on the rheometer).
The expected by-design distinct relaxation modes of DDNs will be decoded and their features (time, modulus, broadness) linked to molecular characteristics (molar mass, composition, strength of association). Time-temperature superposition will be tested and assessed (it is expected to fail due to different bonding interactions). Hence, to analyze the viscoelasticity, spectra over a very wide range of frequencies are needed, which will be achieved by creep measurements. To extend the spectra to higher frequencies a piezo-rheometer will be used. This setup has been recently developed by Partner P2. In conjunction with WP2, the latter insight will be cross-related to the complementary information from dynamic light scattering. With this method, we shall particularly focus on two modes: at long correlation times, we will look out for non-diffusive, viscoelastic modes of network relaxation and relate these to the low-frequency end of the elastic plateau in rheology. At short correlation-times, we will focus on diffusive modes of network-strand fluctuation and relate these to the high-frequency end and the level of this plateau.
Task 4.2.: Step shear measurements of the DDNs will provide information about relaxation process and time of the dense network and how they are influenced by a nonlinear (out of equilibrium) deformation. By performing measurements under constant (large) shear rates, we shall obtain information about the shear thinning (or shear thickening) behavior in function of the lifetime of the two transient networks, and about important potential issues such as yielding, wall slip, and shear banding, in order to further understand the material response but also to determine guidelines for efficient processing of the networks. In order to avoid artifacts (primarily edge fracture), a customized cone-partioned plate fixture developed by Partner P217 will be implemented in a straincontrolled rheometer, which allows measuring both shear and normal stresses reliably. Further, to assess the elastic memory of the networks and self-healing potential, shear deformation will cease at different levels of stress during its transient response and their relaxation will be analyzed and compared against its linear response and DLS in WP2. The long-time relaxation will be examined to detect possible residual stresses associated with the metastable nature of the DDNs and possible heterogeneities. In this direction, we’ll take advantage of structural information obtained from in-situ light scattering experiments or selected rheo-SANS experiments (in conjunction with task 2.3). Results will be compared against those obtained by means of light scattering (task 2.1).
Task 4.3.: Nonlinear creep tests at stresses above yielding will be performed and analyzed, to discern internal partial break of the network or loss of entanglements, i.e. loss of macroscopic cohesion. They will be also compared against step shear measurements.
Task 4.4.: Transient elongation: In order to relate rheological and mechanical properties, we need to assess their fracture in tensile mode. To this end, nonlinear rheological measurements will be performed under uniaxial extension by using the state-of-theart filament stretching rheometer (FSR) of Partner P718. We shall investigate the effect of structural and external parameters as well as deformation rates in order to understand how to control the maximum extensibility in DDNs. Possible fracture will be investigated by coupling the FSR with a high-speed camera which will allow comparing photos of the filament’s outer surface at different stretch rates and times. Results will be compared against CPP data in shear at the same deformation rates.
Task 4.5.: Cyclic mechanical compression and tensile tests: They will be performed in order to elucidate the mechanisms of fatigue and elasticity of the DDNs. A critical comparison with nonlinear rheological results will be made. This will also allow us to bridge rheological and mechanical properties, towards a global picture.
Task 4.6.: Elasto-capillary effects: The objective is to understand and rationalize how double dynamics will impact elastocapillary effects in DDNs, which essentially involves a competition between the bulk elastic strain energy and the surface energy. In solid materials, capillarity is negligible at macroscopic scales except for ultra-soft solids (with Young modulus ≾ 100 Pa). We expect drastically different and original behavior for DDNs, which should strongly vary with the lifetime and/or elastic modulus of each constituting network. 19 To explore these effects, we propose an original approach that Partner P6 has recently developed, and which is based on the imaging with a fast camera of the dynamical expansion and destabilization of liquid sheets resulting from the impact of a drop of material on a small target and which has shown promising results with ultra-soft permanent polymer gels. To elucidate the origin of the observed phenomena, a link with nonlinear rheological results of tasks 3.2 and 3.4 will be attempted.
WP 5 : Atomistic and mesoscopic modelling towards DDN design guidelines
Lead Beneficiary E. van Ruymbeke, UCL
Deliverable timing: M1 – M48
Objectives: The knowledge acquired from WP2, WP3 and WP5 will be implemented into two different models, at the mesoscopic and at the atomistic levels. Both will be used in order to explore and design new systems with enhanced properties. A continuous interplay between experiments and modelling will shed light on the effect of structural parameters on both processing and application properties. Modelling will account for all relevant features of the DDN structures, which include: (i) association due to metal-ligand interactions, phase separation or reversible covalent bonding, corresponding to specific association times, themselves being a function of the deformation. (ii) topological interactions formed by entanglements or by sliding rings. (iii) frictional interactions. Modelling will provide information about linear viscoelasticity of the material, useful for characterization, and its nonlinear response typical of both processing and application properties (response of the double networks to large deformations).
Task 5.1.: Tube models for describing the linear viscoelasticity (LVE) of telechelic DDNs: We will extend the tube model of Partner P1 for describing the LVE of telechelic supramolecular chains to DDNs, with or without entanglements. 20 We will account for a large number of physical crosslinks, governed by two different dynamics (fast and slow), and for a potentially large contribution to the elastic modulus from the dense network. To this end, we will combine usual tube models, which include both local Rouse dynamics and chain disentanglement (or constraint release) processes, with more classical network theories.
Task 5.2.: Statistical models to describe the location and number of cross-linking points: When cross-links are located along the chain backbone, their statistical position and their association state (associated or free) need to be determined through time. Partner P1 has developed such approaches for sticky long chains, which will serve as starting point for this task.20
Task 5.3.: Tube models in order to describe the LVE of DDNs based on sticky building blocks: We need to account for the cooperative effect of stickers and for two different association dynamics on the relaxation spectrum and modulus of the samples. We will start from the model developed by Partner P1 for linear chains bearing few long-lived stickers and extend it to the DDNs. The role of dangling ends will be considered, since they can quickly relax stress, and release constraints of less mobile strands.
Task 5.4.: Modelling the nonlinear viscoelastic response of DDNs: This will be performed by Partner P4 who developed models for entangled polymers that incorporate two important, recently discovered effects21a: (i) friction reduction due to monomer coalignment induced by large deformations, and (ii) molecular tumbling in fast shear flow21b. They also studied the flow of solutions of associating telechelic polymers, switching between bridge and loop with concentrations. In the nonlinear regime, important features must be taken into account: (i) chain stretch will reduce the lifetime of transient bonds, (ii) non-Gaussian effects will determine strain hardening behavior, (iii) chain stretch and chain orientation due to topological constraints must be correctly separated. Such a separation is typically observed in entangled systems, while it is ignored in models of crosslinked networks.
Task 5.5.: Modelling the LVE of slide-ring networks: Due to the specific mobility of crosslinks, the behavior of slide-ring DDNs cannot be modelled as the other DDNs. We will account for ring sliding and the fact that chains cannot escape from the rings due to the bulky end-groups. The interactions between the slide-ring networks and the supramolecular network will be taken into account through Constraint-Release-Rouse processes.
WP 6 : Design and properties of responsive DDNs for new application
Lead Beneficiary C. Creton, ESPCI
Deliverable timing: M1 – M48
Objectives: The results of WP1–WP4 will be combined in WP5 in order to link molecular, macromolecular, and supramacromolecular structure of DDNs with application properties. This will yield design criteria for polymeric structures with desired performance. Main tasks in WP5 will be to (i) identify target industrial applications and relevant properties, (ii) determine the structure and composition of specific DDNs exhibiting desired properties, (iii) choose the appropriate synthesis scheme in order to produce such DDNs in large amount, and (iv) test and validate the above ideas and concepts. Application properties: We will explore the roles of molecular parameters and reversible bonds on mechanical properties like fracture resistance, extensibility and reversibility of the deformation upon cyclic deformation, which are important for applications. In order to bridge rheological properties of WP3 to application properties, we will focus on:
Task 6.1. Adhesive properties: 11 Polymers in adhesives provide a finely tuned balance between creep resistance and high extensibility. The use of dynamic bonds in adhesives is mostly limited to the use of acrylic or methacrylic acids to provide bonding to the surface and provide strain hardening in extension to stabilize the fibrils during debonding. Here, we will elucidate the relationship between DDN composition and adhesive properties, with industrial standard tests and with advanced probe tack tests. These results will be related to the detailed characterization of the molecular structure (WP2) and the rheological properties (WP3).
Task 6.2. Fracture mechanisms of DDNs: If too much elasticity is stored in a stretched viscoelastic fluid, small defects can propagate and cause a fracture. Predicting the effect of the DDN structure on such fracture process is a major challenge. Recently, Partner P3 has shown that chemoluminescent molecules can be incorporated into polymers and emit light when the bonds break.22 This provides unique information on the way chemical bonds are loaded in a complex material. We will study systematically the tensile behavior of the systems 1 (WP1) in order to identify the conditions during which melt fracture occurs. Other experimental situations will also be considered such as (i) the impact dynamics of a solid sphere falling into a DDN, (ii) the motion of a DDN around a cylinder to investigate flow and fracture behavior. These types of experiments have been already successfully used to probe the flow and fracture behavior of simple transient networks (entangled wormlike of micellar fluids).
Task 6.3.: Physical ageing and slow dynamics in applications: Controlling these phenomena is essential in many applications where the gels are submitted to cyclic variations of the environment and/or mechanical stresses (as in artificial cartilage). Moreover, slow relaxation can be at the origin of spontaneous motion or deformation at rest after the material has stored elastic energy. This can be a nuisance but also can be exploited to induce motility. 23 This will be studied here with the rheo-optical technique recently developed by Partner P3, which combines time-resolved creep or step rate experiments with in-situ real time micro-PIV imaging of the deformation field inside the material. This method, which gives access to non-affine properties, spatial heterogeneities, band formation, or strain localization effects, will be compared to ageing properties of Task 3.1. Results interpretation will account for a competition between several antagonist effects: solvent permeation, dynamics of exchangeable bonds, and chain mobility.
Task 6.4. Tribology of DDNs: Understanding the dynamic networks when sheared near solid surfaces (such as their adherence to substrates or their release of solvent) is important in many applications and is essential to correctly characterize the mechanical behavior of DDNs in highly nonlinear situations, and to control the motion of gels in contact with solid surfaces. Therefore, a systematic study of the tribology of DD gels and mechanical coupling between gels and surfaces will be performed in order to measure the kinetics of swelling/de-swelling and the friction laws at work when the composition and architecture of the gels are varied. This will be completed by real time visualization of the dynamical bonding/debonding of DD gels at solid interfaces. Results will be compared with data on instabilities in nonlinear shear (task 3.2) and extension (task 3.4).
Task 6.5. Self-healing properties: We will investigate the healing properties of DDNs or single gels, in particular when dynamic covalent bonds are incorporated inside the networks. The objective is to establish a relation between local dynamics, the nature of polymers involved in the DDN structure and the capacity of dynamic DDN structure to heal and exhibit self-adhesion.
Task 6.6. Target applications have been detailed in Section 1.1.3. At each stage of the project, the new results will be assessed in view of possible use in applications and new strategies to improve the properties of the samples will be proposed.
WP 7 : Training
Lead Beneficiary G. Ianniruberto (UN)
Deliverable timing: M1 – M48
Objectives: To organize, execute and monitor the training program of DoDyNet – see Section 1.2.1
Task 7.1: Establish the Personal Career Development Plan (PDCP) for each ESR
Task 7.2: Organize Basic and Advanced Training Modules
Task 7.3: Organize the summer school
Task 7.4: Organize and monitor the inter-sectorial secondments of the ESRs
Task 7.5: Organize the job fair at the end of the project
Task 7.6: Organize podcasts on DDNs
Task 7.7: Oversee and monitor ESRs participation and presentation in conferences
Task 7.8: Oversee organization of poster session and industrial session by ESRs for the second industrial workshop
Task 7.9: Monitor mentoring of the ESRs and secure their graduation with a PhD
WP 8 : Industrial exposure
Lead Beneficiary P. Steeman, DSM
Deliverable timing: M1 – M48
Objectives: To ensure that each ESR is exposed to industrial environment and relevant applications. To link academic and industrial research toward potential applications. To this end, a close link with WP6 is anticipated.
Task 8.1: Organize inter-sectorial secondments in cooperation with WP6
Task 8.2: Organize Industrial Workshops I and II
Task 8.3: Link the research of the ESR to potential applications in adhesive, coating and film applications
WP 9 : Communication and Dissemination
Lead Beneficiary L. Ramos, CNRS
Deliverable timing: M1 – M48
Objectives: To disseminate the most important scientific and training results of DoDyNet (see Section 2.3.1)
Task 9.1: (UCL) Setup and maintain a website for DoDyNet
Task 9.2: (FORTH – UCL) Organize the International Meeting
Task 9.3: Oversee publication of articles in peer-reviewed international journals and Edition of special issue on DDNs
Task 9.4: Monitor that the proposed outreach activities (see Section 2.3.1) are achieved
Task 9.5: Publication of perspectives or news and views for articles published in high impact journals for a broad public
Task 9.6: Organization of ‘My thesis in 180s’
Task 9.7: Oversee flow of information in website, concerning training events, student newsletter, conferences
Task 9.8: Podcasts on DDNs on You tube
Task 9.9: Monitor organization of dissemination events (public talks, visit high schools) during bi-annual project meetings, in cooperation with local organizers.
