Forces are at the heart of almost every major biological process. The widespread use of molecular machines in nature has inspired scientists to synthesize mechanically interlocked molecules (MIMs) in which controlled, relatively large amplitude motion of one component relative to another can potentially result in net directional forces. This review examines force-related processes in MIMs, namely, catenanes, rotaxanes and knots, and in the polymers that include them. We first discuss the single-molecule force spectroscopy studies, performed on well-defined mechanically linked systems, one molecule at a time, and show how these experiments have provided unprecedented insights into their operation, dynamics, and comprehensive understanding of their performance metrics. Then the use and effects of these mechanical links on mechanically activated polymers are addressed. We examine the unique mechanochemical reactivity of MIMs and how it is exploited to create force-responsive molecular devices and materials or elicit new mechanochemical reactions in response to external force. Finally, we focus on the use of mechanical links as crosslinks, giving rise to the so-called slide-ring materials. The review highlights the unprecedented mechanochemical properties that are emerging from the integration of MIMs into polymers and the quick pace of progress in the field that should give rise to more advanced systems.

The viscoelastic behavior of vitrimers is closely linked to the nature of the dynamic bonds, the functional group density and distribution, and the topology of the network. The aim of this study is to investigate the influence of segmental motion versus exchange dynamics on the viscoelastic response of vitrimers. To this end, we synthesized two unentangled model polyacrylate-based vitrimers with varying cross-linking densities, using a low-T g poly(n-butyl acrylate) (PnBA) precursor and a bis-dioxaborolane cross-linker. Small-amplitude oscillatory shear (SAOS) experiments were conducted across a wide range of temperatures. In addition to the high frequency Rouse relaxation, the relaxation modulus of these vitrimers displays two relaxation processes, which show different dependencies on temperature. Consequently, thermo-rheological complexity is obtained in the viscoelastic data. To understand the origin of these two relaxation processes, we modified the time marching algorithm (TMA) tube-based model to account for the exchange dynamics of the reversible bonds, in order to separate the influence of the segmental dynamics from that of bond exchange dynamics. This analysis allows us to attribute the slower relaxation process to the relaxation of the molecular segments which are unable to move without activating the bond exchange mechanism, and the intermediate relaxation process to the relaxation of molecular segments containing dynamic bonds poorly trapped in the network. The temperature dependence of these relaxation processes was quantified and rationalized, combining the Arrhenius-like temperature dependence of the exchange dynamics and the WLF-like temperature dependence of the segmental dynamics. The influence of the molar mass of the precursor and of the cross-linker density is also discussed and considered in our model. This study brings new insights on how to understand and control the viscoelastic properties of vitrimers.

Polymeric materials containing weak sacrificial bonds can be designed to engineer self-healing and higher toughness, improve melt-processing, or facilitate recycling. However, they usually exhibit a lower mechanical strength and are subject to creep and fatigue. For improving their design, it is of interest to investigate their mechanical response on the molecular scale. We report on a computational study of the response to a mechanical external force of a Zinc(II) bis-methyl phenyl-terpyridine ([Zn-bis-Terpy]2+) complex included in a cyclic poly(ethylene glycol) (PEG) tether designed to maintain the two partners of the metal-ligand bonds in close proximity after the rupture of the complex. The mechanical response is studied as a function of the pulling distortion by using the CoGEF isometric protocol, including interactions with a polar solvent (DMSO). We show that tethering favors recombination but destabilizes the complex before bond rupture because of the interactions of the PEG units with Terpy ligands. Similar effects occur between the DMSO molecules and the complex. Our results on the molecular scale are relevant for single-molecule force spectroscopy experiments. Interactions of the complex with solvent molecules and/or with the tether lead to a dispersion of the rupture force values, which could obscure the interpretation of the results.

We investigate the linear viscoelastic properties of poly(n-butyl acrylate) (PnBA) metallo-supramolecular networks in the melt state, based on bis-complexes formed by terpyridine (tpy) ligands and divalent metal ions. These networks are constructed from telechelic stars, entangled or not, bearing tpy chain-ends. The nature of the metal ions is varied (Zn(II) and Cu(II) ions, blended or not) as well as the used amount (stoichiometric amount or excess). By systematically varying the network composition (building block architecture and ion content), we elucidate the influence of stickers on terminal relaxation with a focus on the interplay between sticker and entanglement dynamics. The delayed terminal relaxation of the transient networks is rationalized by the means of modified Rouse and time-marching algorithm (TMA) tube models. Our theoretical analysis supports a multistep relaxation mechanism involving repeated dissociation/reassociation events. It also allows us to extract an intrinsic value of approximately 40 kJ/mol for the activation energy for the dissociation of Zn2+/tpy bis-complexes, regardless of the building block topology or the ion content. In the presence of entanglements, this activation energy cannot be found by only looking at the temperature dependence of the terminal relaxation time, which demonstrates the importance of separating the sticker and entanglement dynamics to unravel the viscoelastic response of these transient networks.

ABA triblock copolymers can form microphase separated structures where the B blocks form bridges between A domains, leading to reversible networks interesting for a variety of applications such as pressure sensitive adhesives or thermoplastic elastomers. However, a major drawback of these systems is their rapid loss of mechanical properties upon temperature increase. A potential way to circumvent this limitation would be to design ABA triblock copolymers that keep their microphase separation at high temperatures. In this paper, we report on all-soft ABA triblock copolymers having a poly(n-butyl acrylate) (PnBA) central block and poly(heptafluorobutyl acrylate) (PHFBA) outer blocks. By introducing fluorinated units, the incompatibility between the blocks is largely increased, allowing strong segregation between the block domains, which preserve the microphase separation up to high temperatures despite the low glass transition temperature of the blocks, as shown by temperature dependent SAXS measurements. We study the properties of different copolymers, with similar PHFBA volume fractions but different block lengths. Linear shear rheology measurements revealed the presence of a second, low frequency, plateau whose onset and length depend on the PnBA and PHFBA length, respectively. This plateau also persists up to higher temperatures for longer PHFBA blocks.

Selecting the appropriate polymer structure for use as both a solid electrolyte and catholyte is essential for enhancing the electrochemical performance of all-solid-state lithium metal batteries. In this study, we are pioneering the customization of solid electrolyte and catholyte synthesis based on novel polyrotaxane (PRX)-containing polymer networks by altering the length of the polyether crosslinkers to tune the properties to meet specific needs of different components. On one hand, the modified PRX polymer networks based on the shorter crosslinker show good mechanical strength, high ionic conductivity (7.25 x 10-4 S cm- 1) and high lithium ions transference number (0.54) at 60 degrees C, allowing their use as solid polymer electrolyte (SPE) self-supporting membranes. On the other hand, all-solid-state lithium-ion batteries with this SPE demonstrate a much higher initial capacity (above 160 mAh/g using LiFePO4 as active material at the cathode and lithium metal as anode), and better cycling performance when paired with longer cross-linked PRX as catholytes than the other noncustomized combinations all solid lithium-ion batteries. Moreover, the cycling performance of the full cell can be further improved by incorporating different lithium salts in the electrolyte (LiTFSI) and cathode (LiClO4). This work highlights that the customized design of solid electrolytes and catholytes based on polymer networks is an efficient strategy to obtain high-performance all-solid-state lithium metal batteries.

Random cross-linking in polymeric gels leads to heterogeneities in the obtained network, resulting in poor mechanical properties and limitations of practical applications. To overcome this issue, networks with movable cross-links have been developed. Slide-ring gels (SRGs), which are polymer networks with cross-links that can slide along the network strands, belong to this category. These gels are softer, more stretchable, tougher, and with good recovery properties due to the sliding of cross-links, which equalizes the applied stress on polymer strands. Although the origin of the excellent mechanical properties of these gels has been well-studied, the specific viscoelastic properties of slide-ring gels remain ambiguous due to the complexity of controlling and detecting the ring mobility. In this study, the development of a palladium-based slide-ring gel from a metal-coordinated pseudorotaxane motif enables us, for the first time, to control the ring's mobility without changing any other parameters and keeping the overall network connectivity. The rheology data of fixed-ring versus free-ring gels, analyzed with a tube-based model, reveal that the softness and lower elasticity of the slide-ring gels originate from the sliding of cross-links, which increases the effective mesh size of the network well above the length of a single polyrotaxane chain. Moreover, we demonstrate the key role played by the entanglements, which limit the sliding distance of the rings. This study thus provides new insights for understanding the peculiar viscoelastic behavior and huge stretchability of slide-ring gels, toward the rational design of SRGs with controlled properties.

A mechanical bond serves as a distinctive approach for harnessing the most beneficial features of both covalent and supramolecular chemistries, offering stability and structural adaptability owing to its unique dynamic nature. Molecules formed by mechanical bonding, known as mechanically interlocked molecules (MIMs) including catenanes, rotaxanes, and knots have opened new possibilities. Notably, the introduction of mechanically interlocked structures into polymers has led to the emergence of novel polymeric materials referred to as mechanically interlocked polymers (MIPs), such as polyrotaxanes and polycatenanes. The interlocked nature of these architectures can lead to particular conformational freedom and high mobility of their components, resulting in exceptional properties, such as ultra-stretchability, toughness, and immediate recoverability. These properties have found potential applications in diverse fields, including the development of tough hydrogels, scratch-resistant coatings, smart actuators, and batteries. Recent years have witnessed a surge in the synthesis and investigation of a diverse array of rotaxanebased MIPs, an essential class that has enabled researchers to begin grasping the impact of incorporating mechanical bonds within polymer structures, and of their mobility, on material properties. In this review, an overview of the dynamics of ring-containing polymers is presented. The review encompasses macromolecular rotaxanes, polyrotaxanes, and slide-ring networks, including the role of ring mobility in shaping the dynamics and properties of rotaxane polymers. (c) 2024 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Hypothesis: The micellization of block copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) is driven by the dehydration of PPO at elevated temperatures. At low concentrations, a vis-cous solution of isolated micelles is obtained, whereas at higher concentrations, crowding of micelles results in an elastic gel. Alternating PEO-PPO multiblock copolymers are expected to exhibit different phase behavior, with altered phase boundaries and thermodynamics, as compared to PEO-PPO-PEO tri-block copolymers (Pluronics (R)) with equal hydrophobicity, thereby proving the pivotal role of copolymer architecture and molecular weight.Experiments: Multiple characterization techniques were used to map the phase behavior as a function of temperature and concentration of PEO-PPO multiblock copolymers (ExpertGel (R)) in aqueous solution. These techniques include shear rheology, differential and adiabatic scanning calorimetry, isothermal titration calorimetry and light transmittance. The micellar size and topology were studied by dynamic light scattering.Findings: Multiblocks have lower transition temperatures and higher thermodynamic driving forces for micellization as compared to triblocks due to the presence of more than one PPO block per chain. With increasing concentration, the multiblock copolymers in solution gradually evolve into a viscoelastic network formed by soluble bridges in between micellar nodes, whereas hairy triblock micelles jam into liquid crystalline phases resembling an elastic colloidal crystal.(c) 2023 Elsevier Inc. All rights reserved.

Dynamic hydrogels offer the opportunity to meet the expectations of smart materials with adaptable properties such as stimuli responsiveness, self-healing, shear thinning, stress relaxation, dynamic viscoelasticity, energy dissipation mechanisms, time-dependent adaptation, etc. In the past decades, reversible CN bonds including imine, hydrazone, and oxime have received great research interest in the design of dynamic polymer networks (DPNs). Moreover, reversible CN bonds can be well-integrated into DPNs in combination with permanent covalent crosslinks and/or other dynamic bonds (supramolecular interactions and dynamic covalent bonds), thus outfitting the hydrogels with enhanced mechanical properties, multiresponsiveness, printability, adhesion, and various other functions. This literature review first describes how reversible CN bonds can be introduced into hydrogels from the perspective of dynamic bonds and network topologies. The design strategies (building blocks, crosslink type combinations, network topologies) reported in the literature are then discussed, as well as the effects of dynamic crosslinking on the hydrogel properties and the potential applications.

Dual-cross-linked networks (DCNs), interpenetrating polymer networks (IPNs), and IPN-derived double networks (DNs) are increasingly utilized to fabricate hydrogels with unique mechanical properties. However, the relationship between the topology of these networks and the resulting dynamics is rarely compared and little understood. To tackle this shortcoming, this work presents a systematic investigation of the viscoelastic properties of DCN, IPN, and DN hydrogels as well as their corresponding single networks by oscillatory shear rheology using both frequency and strain sweeps. All the hydrogels are based on the same orthogonal combination of a supramolecular interaction: zinc(II)-terpyridine bis-complexes, and of a reversible covalent bond: oxime, as cross-links. To understand the contribution of each sub-network to the properties of the DCN, IPN, and DN hydrogels, the corresponding single networks, i.e., cross-linked by only one type of bond, are first studied in detail. All double dynamics hydrogels have a plateau modulus much higher than the sum of the plateau modulus of the single networks, evidencing a synergetic effect between the sub-networks. However, the origin of this modulus increase varies according to the network topology. We also show that the relaxation behaviors of the DCN, IPN, and DN hydrogels are influenced by the dynamics of the corresponding single dynamic networks. Finally, the strain sweeps reveal that, for all network topologies, the amplitude of deformation at which the linear viscoelastic region of the double dynamics networks stops is governed by the oxime network, while the metallo-supramolecular network governs the amplitude of deformation up to which the sample can resist before starting to break.

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) effectively interpolates between the two single dynamic network components, depending on composition. Our results suggest ways to tailor the mechanical properties of this class of materials by judicious choice of the type and content of the ion.

Magneto-responsive nanocomposites are prepared by mixing 1-5 vol % of Fe nanoparticles (NPs) in a metallo-supramolecular network made of poly(n-butyl acrylate) (PnBA) bearing terpyridine side groups and cross-linked by the addition of different amounts of Zn2+ ions. To have a clear understanding of the stepwise increase of complexity, the thermomechanical behavior of these materials was characterized through shear linear rheology at each step of their preparation. The metallo-supramolecular networks reveal a clear transition from polymer- to network-driven dynamics when passing progressively from low (<0 degrees C) to high temperature. While terpyridine (TPy)-Zn2+ complexes are usually treated as independent "stickers", the analysis of our master curves strongly suggests their aggregation. After the addition of 1-5 vol % of Fe nanoparticles within the supramolecular networks, we evidence the presence of TPy-NP bonds, resulting in a hybrid network of much longer relaxation time. Lastly, we combine thermal imaging and induction heating to emphasize the signature of sticker dissociation, offering new technical solutions to deepen our fundamental understanding of supramolecular networks.

This work focuses on the temperature-dependent structural and rheological characterization of polystyrene-b-poly(n-butyl acrylate)-b-polystyrene triblock copolymers (PS-b-PnBA-b-PS) in the melt and, in particular, on their ability to show a lower disorder-to-order temperature (LDOT). To this aim, copolymers of varying block lengths, but keeping the PnBA block as a major component, were synthesized. Small-angle x-ray scattering revealed that the copolymers with short PS blocks (∼10 kg/mol) approach an LDOT but do not cross it. At room temperature, these copolymers exhibit higher moduli compared to a PnBA homopolymer due to the reinforcing effect of the PS but are flowing at temperatures above the glass transition of the PS. Increasing the PS and PnBA block length, to keep the same PS fraction, induces more profound changes in the structural and viscoelastic behaviors. Such a copolymer crosses the LDOT, leading to a microphase-separated and ordered state at high temperature. Contrary to the copolymers with short PS blocks, the flow regime was not reached, even at temperatures well above the glass transition of the PS. Instead, a low-frequency plateau was observed in rheology, showing the increased lifetime of the microphase-separated PS domains. ABA triblock copolymers exhibiting an LDOT behavior could, thus, be of interest for the design of thermoplastic elastomers or pressure-sensitive adhesives that can resist the flow at high temperatures.

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. (C) 2022 The Society of Rheology.

We investigate the viscoelastic properties of double dynamic networks (DDNs) based on side-functionalized P nBA chains. One of these networks is highly crosslinked by metal-ligand junctions characterized by a fast association/dissociation dynamics, while the other network is sparsely crosslinked with slow dynamic covalent networks (DCNs). We first show that modulating the dynamics of the metallosupramolecular networks, by playing with the temperature, the density of reversible junctions, or the stress applied, has direct consequences on the local equilibration of the DCN. The latter takes place by a constraint release Rouse process at the rhythm of the association/dissociation of the metal-ligand junctions. Then, based on creep-recovery experiments, we investigate the ability of the DDNs to recover their initial shape after a creep test and show again the important role played by the metallosupramolecular network. In particular, the sample recovery strongly depends on the network connectivity, which is enhanced if a denser metallosupramolecular network is used as it reduces the possible creep of the double dynamic network and increases its elastic memory. The sample recovery also depends on the association-dissociation dynamics of the metallosupramolecular bonds as it fixes how fast the stretched DCN can come back to its equilibrium conformation and can recover its initial shape after a large deformation has been applied. Adjusting the dynamics of the weak network is thus a key process to govern the viscoelastic response of the slow network.

Since the Industrial Revolution, technological advances have generated enormous emissions of various pollutants affecting all ecosystems. The detection and degradation of pollutants has therefore become a critical issue. More than 59 different remediation technologies have already been developed, such as biological remediation, and physicochemical and electrochemical methods. Among these techniques, advanced oxidation processes (AOPs) have been popularized in the treatment of wastewater. The use of ZnO as a photocatalyst for water remediation has been developing fast in recent years. In this work, the goals are to produce ZnO photocatalysts with different morphologies, by using a green sol-gel process, and to study both the influence of the synthesis parameters on the resulting morphology, and the influence of these different morphologies on the photocatalytic activity, for the degradation of an organic pollutant in water. Multiple morphologies were produced (nanotubes, nanorods, nanospheres), with the same crystalline phase (wurtzite). The most important parameter controlling the shape and size was found to be pH. The photoactivity study on a model of pollutant degradation shows that the resulting activity is mainly governed by the specific surface area of the material. A comparison with a commercial TiO2 photocatalyst (Evonik P25) showed that the best ZnO produced with this green process can reach similar photoactivity without a calcination step.

We study the viscoelastic properties and the structure of a short hydrogenated polybutadiene (HPB) building block end-capped by terpyridine ligands. Adding metal ions in the sample leads to the formation of metallo-supramolecular junctions between the blocks, while the difference in polarity between the HPB chains and the metal complexes leads to the phase separation of the complexes into well-organized structures. By varying the nature and amount of metal ions added to the system, with the temperature, as well as with the sample thermal history, we show that it is possible to modulate these associations and obtain a very rich range of properties. In particular, while increasing the amount of metal ions leads to the sample reinforcement, it also causes a decrease of its melting temperature. This result is linked to the structure of the sample, which is characterized, in specific conditions, by the co-existence of two lamellar structures that we attribute to the existence of mono-complexes. The stability of these two lamellar structures is discussed based on the structural evolution during several heating and cooling ramps. We also show that the usually observed lamellar structure can be changed into a hexagonal structure if excess of metal ions are added to the sample.

We report here a synthetic platform toward mono-functionalized tridentate macrocycles based on a pyridine-2,6-bis-carboxamide motif. These macrocycles bear a variety of functional groups at the fourth position of the pyridine, giving access to a wide range of synthetic methods for further derivatisation or preparation of more complex structures such as mechanically interlocked molecules or polymer materials. To illustrate the potential of this family of macrocycles a series of square planar palladium complex-based pseudorotaxanes, containing different axles and functional groups on the ring, are synthesised, and then used to prepare a macro-pseudorotaxane, i.e. a polymer containing a rotaxane junction, and mechanically-linked gels by a one-pot and a polyrotaxane approach.

We report on the use of atomic force microscopy (AFM) to identify and characterize an intermediate state in macrocycle shuttling in a hydrogen bonded amide-based molecular shuttle. The [2]rotaxane consists of a benzylic amide macrocycle mechanically locked onto a thread that bears both fumaramide and succinic amide-ester sites, each of which can bind to the macrocycle through up to four intercomponent hydrogen bonds. Using AFM-based single-molecule force spectroscopy, we mechanically triggered the translocation of the ring between the two principal binding sites ("stations") on the axle. Equilibrium fluctuations reveal another interacting site involving the two oxygen atoms in the middle of the thread. We characterized the ring occupancy distribution over time, which confirms the intermediate in both shuttling directions. The study provides evidence of weak hydrogen bonds that are difficult to detect using other methods and shows how the composition of the thread can significantly influence the shuttling dynamics by slowing down the ring motion between the principal binding sites. More generally, the study illustrates the utility that single-molecule experiments, such as force spectroscopy, can offer for elucidating the structure and dynamics of synthetic molecular machines.