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We study the linear viscoelastic properties of polymeric networks formed by poly(n-butyl acrylate) telechelic stars end-capped with 2,2:6,2″-terpyridine (Star-PnBA-tpy4) and two types of metal-ligand cross-links with different lifetimes. The influence of interactions, mediated by temperature, nature of metal ions, and ion content, on the linear viscoelastic behavior of both single and double dynamics transient networks is systematically investigated by small amplitude oscillatory shear and creep rheometry. The experimental results reveal that the dynamics of networks with two different metal-ligand cross-links is much faster than expected, characterized by the average sticker lifetime rather than a discrete contribution of each metal-ligand complex. We model the dynamics with the help of our modified tube-based time marching algorithm by accounting for both association/dissociation dynamics of metal-ligand coordination and the entanglement dynamics. Two parameters are defined in the model, namely, the proportion of dangling ends and the average time during which a sticker is free. This allows us to quantify the transient dynamics of the network and, in particular, to determine how the sticker dynamics depend on temperature and ion content.

We present a systematic experimental study of the shear rheology of metallosupramolecular assemblies based on entangled telechelic star polymers comprising one (single dynamic network) or two (double dynamics network) types of physical bonds with the aim to unravel the role of concentration and strength of these bonds on the nonlinear response. Model dynamic networks functionalized with terpyridine ligands were formed by adding different metal ions with increasing bonding strength, zinc, copper, and cobalt. The dynamics are driven by entanglement/disentanglement processes and a ligand exchange mechanism. Steady-state viscosities of single and double dynamics networks collapse onto a universal curve over a wide range of Weissenberg numbers based on terminal time (up to about 300 for single and 1000 for double), exhibiting stronger shear thinning (with an exponent of −0.76) compared to entangled neutral star polymers. Double dynamics networks consisting of two different metal ions (with different lifetimes) exhibit stronger mechanical coherence (rate-dependent fractional viscosity overshoot) and accumulate larger strain at steady-state flow compared to single-ion counterparts. The shear stress growth function signals exhibit weak, albeit unambiguous shear strain hardening, which becomes more pronounced for stronger associations. They also exhibit double overshoot, which reflects the interplay of association strength and chain deformation. Increasing the strength of associations leads to the failure of the Cox–Merz rule, which is more severe for single dynamic networks. The markedly different behavior of double dynamics networks is attributed to the fact that at sufficiently high ion content, the weaker bond acts as a sacrificial component, which provides local energy dissipation and enhances the overall deformability. This bears analogies with their linear viscoelastic response, which has revealed that the arm disentanglement (delayed due to the reversible bonds) effe

PURPOSE: The aim of this study is to optimize fibrin matrix composition in order to mimic human ovarian tissue architecture for human ovarian follicle encapsulation and grafting. METHODS: Ultrastructure of fresh human ovarian cortex in age-related women (n = 3) and different fibrin formulations (F12.5/T1, F30/T50, F50/T50, F75/T75), rheology of fibrin matrices and histology of isolated and encapsulated human ovarian follicles in these matrices. RESULTS: Fresh human ovarian cortex showed a highly fibrous and structurally inhomogeneous architecture in three age-related patients, but the mean ± SD of fiber thickness (61.3 to 72.4 nm) was comparable between patients. When the fiber thickness of four different fibrin formulations was compared with human ovarian cortex, F50/T50 and F75/T75 showed similar fiber diameters to native tissue, while F12.5/T1 was significantly different (p value < 0.01). In addition, increased concentrations of fibrin exhibited enhanced storage modulus with F50/T50, resembling physiological ovarian rigidity. Excluding F12.5/T1 from further analysis, only three remaining fibrin matrices (F30/T50, F50/T50, F75/T75) were histologically investigated. For this, frozen-thawed fragments of human ovarian tissue collected from 22 patients were used to isolate ovarian follicles and encapsulate them in the three fibrin formulations. All three yielded similar follicle recovery and loss rates soon after encapsulation. Therefore, based on fiber thickness, porosity, and rigidity, we selected F50/T50 as the fibrin formulation that best mimics native tissue. CONCLUSIONS: Of all the different fibrin matrix concentrations tested, F50/T50 emerged as the combination of choice in terms of ultrastructure and rigidity, most closely resembling human ovarian cortex.

Associating polymers, based on the dynamic metal-ligand (M-L) coordination, form an interesting class of materials because of the richness in their tunable properties and the design of various self-assembled materials. These adaptable systems have potential applications in various domains such as tissue engineering, coatings, adhesives or shock absorbers. Regardless of the final application, the possible exploitation of the transient nature hinges on the rheological behavior and resulting processability. In this respect, the design of responsive entangled supramolecular polymers is dependent on our fundamental understanding of their structure and dynamics in the melt state. This thesis addresses this grand challenge, and aims at a deeper understanding of how the combination of M-L interactions with entanglements impacts the structure, the relaxation dynamics and the mechanical properties of well-defined entangled metallo-supramolecular polymers over a wide timescale or temperature range. The structure-property relationships are established based on several experimental techniques (RAFT polymerization, shear and extensional rheology, DSC, DRS and X-ray scattering) combined with theoretical tube-based models (upgraded TMA). Results showed that the viscoelasticity of these systems are affected by both the disentanglement process of the polymers and the dissociation mechanism of the metal-ligand complexes. By altering the temperature, we systematically vary the relative importance of the M-L interactions, which allows us to determine their specific contribution to the viscoelastic properties. Through this systematic investigation, general guidelines are achieved to unambiguously control the design of supramolecular materials with specific rheological features that can be engineered over a wide window of mechanical properties., (FSA - Sciences de l'ingénieur) -- UCL, 2018

This work studies the linear viscoelastic properties of a series of low-dispersity poly(n-butyl acrylate) chains endfunctionalized with 2,2′;6′,2″-terpyridine, able to self-associate by metal−ligand coordination. Depending on the architecture and functionality of the chains, the polymers self-assemble into different metallo-supramolecular bulk structures once metal ions are added. Linear building blocks (monofunctional or bifunctional) form longer chains while four-arm stars form networks. The properties of the obtained materials can be finely tuned depending on the length of the polymer chains and the type of metal. In this respect, enhanced control is gained over the dynamics of this class of metallo-supramolecular assemblies. Hence, they are extremely interesting for specific applications such as adhesives or mechanosensors

This work focuses on the linear viscoelastic properties of entangled telechelic bulk metallo-supramolecular polymers. The latter are based on linear and star poly(n-butyl acrylate)s functionalized with a terpyridine ligand at each chain extremity, in the presence of transition metal ion of varying nature. The systems are investigated both experimentally and theoretically using small amplitude oscillatory shear and a modified version of the tube-based time marching algorithm (TMA), respectively. The experimental data reveal that sample relaxation depends on both disentanglement and association dynamics, with the respective importance of these two processes depending on the nature of the metal ion and on the temperature. A good description of the data is achieved using the modified TMA model, provided that dissociation events of metal-ligand complexes occur via ligand exchange. The model contains two fitting parameters, i.e., the fraction of unassociated stickers and the longest time needed in order to ensure that all the chains were dissociated at least once. This latter time is found to be independent of the chain architecture and is well described by an Arrhenius equation, which allows the derivation of the related activation energy. This work provides the necessary framework to explore other metallo-supramolecular networks, built from different chain architectures, and exploit the large richness of their dynamics.

We propose and verify methods based on the slip-spring(SSp) model [Macromolecules 2005, 38, 14] for predicting the effect of any monodisperse, binary, or ternary environment of topological constraints on the relaxation of the end-to-end vector of a linear probe chain. For this purpose we first validate the ability of the model to consistently predict both the viscoelastic and dielectric response of monodisperse and binary mixtures of type A polymers, based on published experimental data. We also report the synthesis of new binary and ternary polybutadiene systems, the measurement of their linear viscoelastic response, and the prediction of these data by the SSp model. We next clarify the relaxation mechanisms of probe chains in these constraint release (CR) environments by analyzing a set of “toy” SSp models with simplified constraint release rates, by examining fluctuations of the end-to-end vector. In our analysis, the longest relaxation time of the probe chain is determined by a competition between the longest relaxation times of the effective CR motions of the fat and thin tubes and the motion of the chain itself in the thin tube. This picture is tested by the analysis of four model systems designed to separate and estimate every single contribution involved in the relaxation of the probe’s end-to-end vector in polydisperse systems. We follow the CR picture of Viovy et al. [Macromolecules 1991, 24, 3587] and refine the effective chain friction in the thin and fat tubes based on Read et al. [J. Rheol. 2012, 56, 823]. The derived analytical equations form a basis for generalizing the proposed methodology to polydisperse mixtures of linear and branched polymers. The consistency between the SSp model and tube model predictions is a strong indicator of the compatibility between these two distinct mesoscopic frameworks.

“Smart” materials have considerably evolved over the last few years for specific applications. They rely on intelligent macromolecules or (supra-)molecular motifs to adapt their structure and properties in response to external triggers. Here, a supramolecular stimuli-responsive polymer gel is constructed from heterotelechelic double hydrophilic block copolymers that incorporate thermo-responsive sequences. These macromolecular building units are synthesized via a three-step controlled radical copolymerization and then hierarchically assembled to yield coordination micellar hydrogels. The dynamic mechanical properties of this particular class of materials are studied in shear flow and finely tuned via temperature changes. Notably, rheological experiments show that structurally reinforcing the micellar network nodes leads to precise tuning of the viscoelastic response and yield behavior of the material. Hence, they constitute promising candidates for specific applications, such as mechano-sensors.