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Polyolefins, such as polyethylene and polypropylene, are low-surface-energy materials that are poorly adhesive owing to weak van der Waals (VDW) forces. While physical bonding offers an attractive alternative to conventional VDW-based adhesion, the development of adhesion methods based on this mechanism requires an understanding of the fracture mechanism of adhesive interfaces. Herein, we reveal the fracture mechanism associated with "nailing adhesion," in which two polymers are tightly bound physically by needle-like polyolefin crystals at a polyurethane/polyolefin adhesive interface. The mechanism was directly observed by transmission electron microscopy using the modified copper-grid technique. The peel strength and fracture mechanism depended on the polyolefin type (polyethylene or polypropylene). During crack growth at the adhesive interface, needle-like polyethylene crystals deform and finally break, whereas needle-like polypropylene crystals snap with crazing. The deformation of needle-like polyethylene crystals enhances peel strength more than the crazing and snapping of needle-like polypropylene crystals. [Display omitted] • Needle-like polyolefin crystals physically bind two polymers via nailing adhesion. • Fracture at the adhesion interface was directly observed by TEM. • Polyethylene crystals deform, whereas polypropylene crystals snap with crazing. • Deformation of needle-like crystals enhances peel strength by energy dissipation. [ABSTRACT FROM AUTHOR]

In this work, we introduce a new “mobile crosslink” concept for the fabrication of solid polymer electrolytes (SPEs) through the crosslinking of α-cyclodextrins (α-CDs) in a poly(ethylene glycol)-based (PEG-based) polyrotaxane. The PEG axis facilitates the conduction of lithium ions, while the crosslinked CDs that are not chemically bound to the PEG form mobile crosslinks that suppress the crystallization of PEG, maintaining its segmental mobility even after crosslinking. To weaken the strong hydrogen bonds between the abundant hydroxyl groups on the CDs, which restrict the segmental motion of PEG resulting in lower ionic conductivity, an appropriate amount of propyl isocyanate is added to effectively enhance the ionic conductivity and robustness of the SPE. [ABSTRACT FROM AUTHOR]

While the mechanical properties of ultrathin polymer films have been extensively studied, only few studies have focused on the ultrathin block copolymer films with complex topologies. The structure-property relationship of ultrathin films (thickness = 35–1000 nm) of polystyrene- b -polyisoprene- b -polystyrene (SIS) containing 14 wt% polystyrene (PS) is established in this study. Grazing-incidence small-angle X-ray scattering, dynamic secondary ion mass spectrometry, and atomic force microscopy were used to characterize the film structure. The difference in surface energy and interfacial energy of the domains resulted in the SIS thin films to primarily consist of three layers: a PS-rich subsurface layer (30 wt%), a spherical PS bulk layer (14 wt%), and a PS-rich interface layer (20 wt%). The film-on-water tensile test was used to investigate both the film thickness and strain rate dependences of mechanical properties. We found that the Young's modulus increased dramatically as film thickness decreased, although only few PS-rich layers consisting of disperse cylindrical and spherical PS domains existed at the surface and interface. Furthermore, the strain rate dependence of the modulus and stress relaxation was more significant for thinner films than for thicker films. The increase in modulus and unusual relaxation behavior are hypothesized to be the result of a combination of different factors, including PS domain alignment, confinement effects, and surface and interface interactions. [Display omitted] • The structure-property relationship of ultrathin SIS films is analyzed. • Young's modulus increases upon decreasing thickness. • The extent of stress relaxation is larger for thinner films. • The stiffening may result from PS domain alignment. [ABSTRACT FROM AUTHOR]

Abstract: In mechanically interlocked molecules like rotaxanes and catenanes, each component has asynchronous microscopic motion within the topological restrictions. The motions can be expressed macroscopically by incorporating the mechanically interlocked molecules in polymers and their networks. Rotaxane develops into polyrotaxane having a polymer axis, and then polyrotaxane forms a polymer network so-called slide-ring material. Because the polymer chains in the material are topologically connected to each other via a figure-eight crosslink, the chains can slide through the crosslink. This microscopic slidability at the crosslink drastically affects the mechanical properties. This article first presents an overview of significant studies on slide-ring materials in the first decade that deal with single species material consisting of polyethylene glycol and α-cyclodextrin. These studies have revealed abnormal statics and network structures, most of which can be interpreted in terms of slidability. Next, we describe our recent designs of materials and findings in mechanical properties attributed to the slidable crosslinks that are built on a synthetic breakthrough that yields a new series of slide-ring materials composed of various backbone polymers. The finding of a sliding transition reveals the dynamics of sliding, the significance of the entropy of uncrosslinked cyclic compounds, and helps in determining the mechanical properties of slide-ring materials. [Copyright &y& Elsevier]

Abstract: We have recently developed a novel type of gel called slide-ring gel or topological gel by using the supramolecular architecture with topological characteristics. In this gel, polymer chains with bulky end groups exhibit neither covalently cross-links as in chemical gels nor attractive interactions as in physical gels but are topologically interlocked by figure-of-eight cross-links. Hence, these cross-links can pass along the polymer chains freely to equalize the tension of the threading polymer chains similarly to pulleys; this is called pulley effect. The slide-ring gel is a new cross-linking concept for the polymer network as well as a real example of a slip-link model or sliding gel, which was previously considered only theoretically. Here we review the synthesis, structure, and mechanical properties of the slide-ring gels with freely movable cross-linking junctions based primarily on our recent studies. The pulley effect of the slide-ring gels has been recently confirmed by mechanical measurements, small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), quasi-elastic light scattering (QELS), etc. This concept can be applied to not only gels but also to a wide variety of polymeric materials without solvents. In particular, the slide-ring elastomer shows remarkable scratch-proof properties to be applied to coating materials for automobile, cell phone, mobile computer, fishing rod, golf club and so on. [Copyright &y& Elsevier]

Abstract: Polyrotaxane (PR), in which cyclic molecules are threaded into a linear polymer chain, has generated great interest because the sliding and rotation of the cyclic molecules on the axial polymer chain lead to unique functional nanomaterials with novel dynamical properties. A typical example of the functional materials is a polyrotaxane network, called slide-ring (SR) material, prepared by cross-linking the cyclic molecules on different PRs. The cross-links composed of two cyclic molecules in a shape of figure-of-eight slide along the polymer chains and the sliding motion gives rise to remarkable physical properties of the SR materials. In order to understand the unique features of the functional materials including SR materials and develop novel applications of PR, it is necessary to reveal the physical properties of PR, especially the sliding motion of the cyclic molecules in PR. In this article, we review the static structure and molecular dynamics of PR based primarily on our recent studies. Furthermore, the difference between SR materials and usual chemical gels in deformation behavior is also described. The findings summarized in this review indicate the significance of the sliding motion of cyclic molecules characterizing PR and SR materials. [Copyright &y& Elsevier]

Abstract: A strong thixotropic viscosity behavior was observed when polyrotaxane prepared from α-cyclodextrins (CDs) and poly(ethylene glycol) (PEG) with a molecular weight of 2000 was dissolved in dimethylsulfoxide (DMSO). A 10wt% solution liquefied by vigorous shaking was rapidly gelated by standing – this sol–gel transition was reversible. The time for recovering the viscosity was dependent on the polyrotaxane concentration, i.e., a 10wt% solution regelated within 30s, whereas several hours were required for the gelation of a 2.5wt% solution. The thixotropic nature of the solution was also confirmed by the clockwise hysteresis curve of the viscosity when the shear rate was increased and decreased. The gel permeation chromatography (GPC) measurement of the polyrotaxane in DMSO exhibited peaks in the high molecular weight region. The peak disappeared after the phenylcarbamoylation of polyrotaxane, suggesting that the peak was due to loose aggregations of polyrotaxane in DMSO. On the other hand, the DMSO solution of polyrotaxane prepared from CD and PEG with a molecular weight of 3350 – whose inclusion ratio (51%) is slightly lower than that of PEG2000 polyrotaxane (72%) – neither demonstrated the abovementioned thixotropic viscosity nor the peak corresponding to the aggregations occurring during the GPC measurement. The thixotropic behavior was speculated to be caused by the combined contribution of intermolecular attractive hydrogen bonding and higher rigidity of polyrotaxane prepared from PEG2000 than that of polyrotaxane prepared from PEG3350, presumably due to the higher inclusion ratio of the former than that of the latter. [Copyright &y& Elsevier]

Polyethylene is the most consumed plastic globally; however, its poor adhesiveness poses serious challenges, particularly in the fabrication of composites and the recycling of mixed plastic waste. While these unfavorable properties are conventionally improved by pretreating the polyethylene surface, the treated surface frequently reverts to its original state over time, which is an unresolved drawback. Here, we describe a novel adhesion system; a polyurethane adhesive penetrates an amorphous part of untreated polyethylene and they form a mixing layer at the adhesive interface. The interfacial mixing layer forms upon heat treatment, even below the melting point of polyethylene and the polymers bind tightly at the interface via entanglement. The peel strength increases with increasing the thickness of the mixing layer. While decreasing the molecular weight of polyurethane promotes inter-diffusion, it also causes a decline in the mechanical strength of the polyurethane adhesive layer. Polyurethanes with optimally balanced molecular weight exhibit superior adhesion due to balance diffusivity and mechanical strength. [Display omitted] • Our engineered polyurethane (PU) adhesive penetrates into untreated PE at 80 °C. • Neutron reflectometry confirms the formation of an interfacial mixing layer. • The thickness of the mixing layer depends on the molecular weight of PU. • PU diffuses into the amorphous portion of polyethylene, resulting in adhesion. • The optimal molecular weight of PU enhanced the mechanical strength. [ABSTRACT FROM AUTHOR]

Advanced polyrotaxane elastomers were fabricated by the synthesis of poly( ε -caprolactone)-grafted polyrotaxanes with significantly lower coverage than previously achieved. The time course for the complexation of α -cyclodextrin with an end-functionalized polyethylene glycol (PEG) was analyzed by subsequent end-capping and polyrotaxane isolation, which revealed that the bulkiness of the PEG end group affects the time required for complex nucleation and the resulting coverage. Low-coverage poly( ε -caprolactone)-grafted polyrotaxanes were synthesized in a facile and large-scale manner by optimizing the simultaneous hydrolysis of the end-capping groups and the solubility of the product during the ring-opening polymerization of ε -caprolactone. Cross-linking the thermoplastic graft polyrotaxanes yielded elastomers that are much more extensible than conventional elastomers with fivefold higher coverages. Elastomers with lower coverages behave as ideal elastic bodies due to chain sliding through the cross-links, which suggests that the arrangement entropy of the cyclic components, which counteracts chain sliding, is substantially decreased by reduced coverage. [ABSTRACT FROM AUTHOR]

In general, self-standing polymer ultra-thin films are difficult to be handled, and therefore their mechanical properties have been poorly understood. We carried out the uniaxial tensile test of ultra-thin films floating on the surface of water and measured the stress-strain curves of polystyrene (PS) ultra-thin films with thickness of around 100 nm. We found that in the stress-strain curves of PS ultra-thin films, yielding points similar to ductile materials appear. We also employed Brewster's angle reflection imaging to follow the visual appearance of ultra-thin films during tensile tests. We found that the narrow shear deformation zones (SDZs), which are 2D analogue of crazes, appear at the yield point, and both the yield and equivalently crazing stresses decrease with decreasing the film thickness. Moreover, the reduction of crazing stress is more significant for the higher molecular weight polystyrene. [ABSTRACT FROM AUTHOR]

Nanoporous materials have been attracting considerable attention for various applications. We have reported the preparation method of nanoporous block copolymers (BCPs) by CO 2 treatment. In this study, the difference between CO 2 -swollen and nanoporous BCPs was analyzed: nanoporous BCPs after CO 2 treatment were compared with the CO 2 -swollen BCPs during the process in terms of nanoscopic structure and macroscopic volume. Although CO 2 was depressurized well below the glass transition temperature of continuous matrix domain, both structural change and volume decrease of the swollen BCPs were observed depending on the CO 2 pressure during the treatment. When the CO 2 treatment was carried out at relatively low pressure (below 15 MPa), the volume decrease was well described by de-swelling of the matrix domain, and internal structures were unaffected by the depressurization. At higher pressure, the volume decrease was more significant. The large decrease is most likely derived from the partial collapse of the CO 2 -filled space in the swollen BCPs, and is correlated with the reappearance of spatial correlation in nanoporous structures. [ABSTRACT FROM AUTHOR]

Abstract: A systematic study on the elasticity of slide-ring gels in which polymer chains can slide through cross-links and ring components slide on the chains reveals the contributions of entropy of both the chains and rings to the elasticity. The equilibrium modulus exhibits a significantly weak power dependence on the cross-linking density (estimated from the modulus at the rubbery plateau and determined by dynamic viscoelastic measurements). This suggests the considerably smaller contribution of chain entropy to the equilibrium elasticity in comparison to chemically cross-linked gels. Increasing stress with temperature indicates entropic origins of the elasticity. The stress–compression curve exhibits a strong non-linearity with a strain hardening: the modulus at the linear regime, within 1% strain, increases drastically (one full order of magnitude) and becomes constant at the intermediate regime strains from 2 to 6%. The modulus of the intermediate strain is in close agreement with that of the rubbery plateau observed by dynamic viscoelastic measurements at the high frequency limit. This suggests that the stress at the intermediate strain originates mainly from the chain entropy in a way similar to that of conventional chemical gels. The fact that chain entropy that contributes hardly to the stress at the linear regime conversely dominates the elasticity at the intermediate regime indicates the counteraction of the entropy of rings, which decreases with the degree of chain sliding. [Copyright &y& Elsevier]

Abstract: In situ catalytic hydrogenation of polybutadiene-based polyrotaxane (BPR) that has 20% of its backbone covered with γ-cyclodextrin moieties induced a crystal structure transition attributed to competing crystal formations of the backbone and rings. Temperature- and time-controlled reactions of emulsified BPR with sodium dodecyl sulphate (SDS) yielded hydrogenated BPRs (H-PRs) with different degrees of hydrogenation; homogeneous reactions resulted in lower degrees of hydrogenation. The hydrogenation rate of BPR was higher than that of polybutadiene itself, indicating that the amphiphilic polyrotaxane with hydrophilic rings and a hydrophobic backbone is advantageous for the emulsion reaction. Crystallization of the H-PR backbones was detected by differential scanning calorimetry and the amount of heat generated increased with increasing degree of hydrogenation. Powder X-ray diffraction revealed that the crystal structures resemble orthorhombic polyethylene and the crystals of the ring components decreased with hydrogenation. This demonstrates that in situ hydrogenation of BPR endows the backbone with sufficient crystallinity to compete with the crystalline rings that generally govern the entire crystal structures of polyrotaxanes through efficient hydrogen-bonding networks that are independent of the backbones. [Copyright &y& Elsevier]

The toughening of epoxy resins is important for their applications in coatings, adhesives, and composite materials. In our previous study, we introduced polyrotaxane (PR), which comprises poly- ε -caprolactone (PCL)-grafted α -cyclodextrins (α -CDs) and a polyethylene glycol (PEG) axial chain, into epoxy resins as an additive and observed that the presence of PR causes an additional viscoelastic relaxation and enhances the mechanical toughness. In this study, we modified the side chain ends of PR with epoxy groups (PR-E) to enable incorporation into crosslinked epoxy networks. The chemical bonding of PR-E to the epoxy resins suppressed the local dynamics of the PCL graft chains and enhanced the mechanical properties. [Display omitted] • Epoxy-Modified Polyrotaxane (PR-E) is incorporated into cross-linked epoxy networks. • Dynamics of the PCL chains was suppressed by end-reaction of PR-E with epoxy matrix. • Chemical binding between PR-E and epoxy matrix can reinforce the interfaces. • Containing of PR-E in epoxy resins can improve the mechanical properties. [ABSTRACT FROM AUTHOR]

Supramolecular slide-ring (SR) elastomers without solvent were fabricated by cross-linking of polymer-grafted polyrotaxane in which α -cyclodextrins (CDs) with poly- ε -caprolactone (PCL) side chains are threaded on a polyethylene glycol (PEG) axial linear chain. The cross-links in the SR elastomers are capable of sliding along the backbone in response to applied stress. Mechanical properties of the SR elastomers with different cross-linking densities were compared with those of fixed cross-link (FC) elastomers prepared from PCL-grafted hydroxypropyl cellulose (HPC) to understand the influence of the slidable cross-links. The SR elastomers are found to undergo less strain-hardening at large strains and demonstrate higher strains at break than the conventional FC elastomers with the same Young's moduli. [ABSTRACT FROM AUTHOR]

We propose using a slide-ring (SR) gel electrolyte to achieve a gel polymer electrolyte with both sufficient mechanical strength and high ionic conductivity. The SR gel is made from polyrotaxane, which has a structure that consists of cyclic molecules, α-cyclodextrins (CDs), threaded by an axial polymer chain, polyethylene glycol (PEG), and cross-linked by divinyl sulfone. The SR gel electrolyte was made from SR gels which were swollen by an electrolyte solution (ES) prepared with lithium salt and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMITFSI). The swelling behavior of SR gel in the ES by the formation of coordination bonds between lithium cations and oxygen atoms on CDs was investigated. The swelling behavior and ionic conductivity of the SR gel swollen with ES had a peak at 0.8 M lithium ion in the ES and the molar conductivity of the SR gel swollen with ES was 85% more than that of pristine ES. The puncture resistance of the SR gel electrolyte was also investigated; the puncture elongation was more than 1000% and the Young’s modulus increased with the lithium ion concentration due to an increase in the coordination bonds between lithium cations and the oxygen atoms on CDs. [ABSTRACT FROM AUTHOR]

A mechanically interlocked supramolecule polyrotaxane (PR) was utilized as a functional additive to modify the hydrogen bonding (H-bonding) and cross-linking network of polybenzoxazine (PBa). Epoxide and hydroxyl groups at the terminal end of polycaprolactone grafted on CDs were chosen to investigate how these functional groups influence H-bonding, morphology, and mechanical properties of PBa matrix. Fourier transform infrared spectroscopy and differential scanning calorimetry results show evidence of successful manipulation of H-bonding and curing kinetics of PBa in the presence of the functionalized PR. After curing, epoxide functionalized PR (EPR) shows a strong interaction with PBa, leading to molecular level dispersion in PBa compared to PR with the hydroxyl functional group. By introducing only 4 wt% of EPR in PBa, the ductility and fracture toughness of PBa are greatly improved without a noticeable drop in Young's Modulus, which is attractive for aerospace and microelectronic applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Polymer gel electrolytes with both high ionic conductivity and mechanical ductility are produced using a slide-ring (SR) gel swollen with an electrolyte solution (ES) composed of propylene carbonate (PC) and lithium salt. The SR gel was derived from polyrotaxane (PR), in which cyclic molecules known as cyclodextrins (CDs) are threaded on the axial polymer chain of polyethylene glycol (PEG) capped by bulky ends, through intermolecular crosslinking between the CDs. The molar conductivity of the SR gel electrolyte with a high swelling ratio and small crosslinking density was more than 95% for pristine ES, and the activation energy and potential window of the SR gel electrolyte was close to that of pristine ES. The compressive properties of the SR gel electrolyte were also investigated; the Young's modulus of the SR gel electrolyte decreased with the crosslinking density and the SR gel electrolyte with a low crosslinking density was not fractured under compression to almost half of the original thickness. [ABSTRACT FROM AUTHOR]

A series of highly dielectric polyrotaxane derivatives consisting of axle polyethylene glycol (PEG) and threated α-cyclodextrins (CDs) were synthesized by modifying the hydroxyl groups of CDs with cyanoethyl or dicyanobutyl groups. We found that the introduction of poly(2-hydroxyethyl methacrylate) (PHEMA) side chain with a number of hydroxyl groups and subsequent cyanoethylation give particularly high dielectric constant (23.4), which is comparable to those of commercially available highly dielectric polymeric materials. We also succeeded in preparing a highly dielectric ( ε ′ ∼ 16 at 10 kHz) and flexible (Young's modulus ∼ 3.4 MPa) elastomer film without any inorganic filler, which is a desirable material for insulator of dielectric elastomer actuators. [ABSTRACT FROM AUTHOR]

Abstract: Volume phase transition is a phenomenon in which gels drastically swell or shrink with an infinitesimal change in the external environment. This behavior is well explained by the Flory–Rehner–Tanaka theory. However, some assumption in the theory breaks down in a slide-ring gel composed of grand canonical chains in which the segment number between cross-linking junctions can change. The stress–strain behavior of the slide-ring gel is in a qualitative agreement with the free junction model, in which the segment number changes to maximize the entropy under the condition that the total sum of the segment number is constant. However, the model cannot work well to isotropic swelling of the slide-ring gel. To describe the volume phase transition of the slide-ring gel, we propose a new theory based on the free junction model with the effects of dangling strands, uncross-linked cyclic molecules (free rings), and high elongation. As a result, it turns out that the exchange of segments between effective and dangling strands leads to the suppression of the volume phase transition in the highly cross-linked gel and the promotion in the loosely cross-linked one. The suppression and promotion of the volume phase transition became more obvious as free rings decreased. [Copyright &y& Elsevier]

Abstract: In this work, two different polyhedral oligomeric silsesquioxanes (POSS)—octaisobutyl-POSS (OIBS) and allylisobutyl-POSS (AIBS)—were incorporated into poly(methylvinylsiloxane) (VMQ) by melt mixing and then the corresponding blends were chemically crosslinked by peroxide. NMR analysis revealed that AIBS molecules containing double bonds were successfully grafted onto VMQ macromolecular chains during the crosslinking of VMQ. Morphology and thermal stability studies by various methods discovered that the in-situ formation of chemical linking between POSS molecules and VMQ chains could significantly improve the dispersion of POSS particles and the thermal stability of VMQ. For the VMQ with 5 wt% POSS, AIBS exhibited nano-dispersion in VMQ matrix and improved the thermal stability of VMQ, but inert OIBS molecules aggregated extensively to form crystals and adversely affected the thermal stability, although AIBS and OIBS have similar solubility parameters and thermal stabilities. Further studies on the thermal stability of VMQ with different contents of AIBS showed that the thermal stability first increased with increasing content of AIBS but then began to decrease as the content of AIBS exceeded 7.5 wt%. X-ray diffraction and extraction experiments showed that extensive ungrafted AIBS molecules and their aggregates started to appear in the VMQ matrix as the content of AIBS exceeded 7.5 wt%. The study revealed that the grafted POSS hindered the thermal degradation of silicone rubber to cyclic oligomers but the ungrafted POSS favored the thermal degradation. [Copyright &y& Elsevier]

Abstract: The slide-ring (SR) gels derived from polyethylene glycol (PEG) threatened with polyrotaxane or hydroxypropyl polyrotaxane and crosslinked by 1,4-butanediol diglycidil ether were swollen with ionic liquids (ILs) and their ionic conduction was investigated. The molar conductivity of an SR gel swollen with 1-ethyl-3-methylimidazolium ethylsulfate (EMIES) with a high swelling ratio and with a small crosslinking density was more than 92% of that of neat IL. With increasing crosslinking density, the swelling ratio and molar conductivity decreased due to increasing disturbance of ion transport by the polymer networks, wherein the hydrodynamic radius of the ionic motion unit was estimated to be 9.7 nm from the relation between the mesh size of SR gels and conductivity. Further, the ionic conduction of SR gels swollen with ILs under compressive deformation was measured. With increasing compressive deformation, the ionic conductivity first increased to a peak at a compression ratio of about 0.75 and then subsequently decreased. This conductivity change can be explained by anisotropic deformation of SR gel networks under compressive deformation. [Copyright &y& Elsevier]

Abstract: Polyrotaxane fiber and polyrotaxane/cellulose blend fibers were prepared by wet-spinning of the polyrotaxane or polyrotaxane/cellulose blend solution dissolved in the new solvent system, i.e. dimethylacetamide/lithium chloride (DMAc/LiCl), into methanol and a subsequent annealing. In the resultant polyrotaxane/cellulose fiber, some undissolved rodlike cellulose microcrystals were oriented along with the fiber axis, resulting in formation of nanocomposite-like structure. From tensile measurements, it was found that the Young''s modulus and tensile strength of the fibers with polyrotaxane/cellulose ratio of 1:1 and 2:1 were higher than those of the pure cellulose fiber. Although the mechanical properties of the fiber with polyrotaxane/cellulose ratio of 4:1 and the pure polyrotaxane fiber were lower than those of the pure cellulose fiber, these fibers showed significantly large strain at break (up to 90% strain), presumably due to the sliding of the cyclodextrin rings of the polyrotaxane in the fibers. [Copyright &y& Elsevier]

The slide-ring (SR) effect in composite materials is demonstrated by comparing the mechanical properties of plasma-modified boron nitride (p-BN)/SR elastomers and p-BN/fixed crosslinked (FC) elastomer composite materials that include a large amount of plasma-surface-modified BN (∼56 vol%). The toughness of p-BN/SR was ∼7 times that of p-BN/FC. Such SR effect was not observed in the raw BN/SR composite material but only in the p-BN/SR composite material. Time-domain nuclear magnetic resonance measurements suggested that the plasma-surface modification of BN formed crosslinking points to the SR and suppressed the decrease in the molecular mobility of SR in the composite materials. [Display omitted] [ABSTRACT FROM AUTHOR]

To develop flexible and tough composite materials with out-of-plane aligned thermally conductive pathways, a novel freeze-casting method was developed using dimethyl sulfoxide (DMSO), carbon nanofibers (CFs), slide-ring polymers (SRs), and cross-linkers. Porous composite materials composed of SR and plasma-surface-modified CFs were obtained. Using DMSO, which has a high melting point (19 °C) and high polymer solubility, the SR cross-linking reaction was performed during freeze-casting. The CFs were treated with plasma before composite preparation for better affinity and dispersibility to the composites. The obtained porous composites contained thermally conductive pathways in the out-of-plane direction and exhibited a low Young's modulus (0.14 MPa). The composite with a thermoplastic polyurethane (TPU) elastomer embedded into its pores exhibited a low Young's modulus (3.62 MPa), high toughness (10.0 MJ/m3), and high thermal conductivity in the out-of-plane direction (0.57 W/mK). The proposed freeze-casting method can be applied for the fabrication of various polymers and fillers and is promising for the development of flexible porous composite elastomers with out-of-plane aligned thermally conductive pathways. [Display omitted] [ABSTRACT FROM AUTHOR]

We investigate the fracture toughness of slide-ring (SR) gels, in which polymer chains are cross-linked by ring molecules, at various strain rates to evaluate the sliding speed of the cross-linking points. SR gels show a drastic decrease of the fracture energy at crack velocities higher than a critical value, since the sliding motion of the rings cannot catch up with the high deformation rates. From the critical transition velocity, we estimated the characteristic time scale of the sliding dynamics to be micro-seconds under the single-layer fracture assumption. [Display omitted] • Fracture toughness of Slide-Ring (SR) gel drops drastically under fast stretching. • Single-layered model connects the toughness transition with the sliding transition. • Ring molecules in stretched network slide at the time scale of micro-seconds. [ABSTRACT FROM AUTHOR]

Thermally conductive flexible materials must be mechanically compatible with flexible electronic devices. They must have a low Young's modulus, high tensile strength, and toughness, in addition to a high thermal conductivity. These requirements have motivated researchers to develop composites of flexible rubber combined with a large amount of high thermally conductive carbon fibers/nanotubes. However, such composites become brittle because of the poor affinity between the rubber and carbon fibers/nanotube and local stress concentrations in the polymer matrix around the carbon fibers/nanotubes. Herein, to reduce this brittleness and achieve a high thermal conductivity, composite materials containing a slide-ring (SR) material and plasma-surface-modified carbon nanofiber (CNF)/carbon nanotube (CNT) aligned via the application of an electric field are described. The addition of a small amount of plasma-surface-modified CNTs to plasma-surface-modified CNF composites and the electric field alignment of these carbon materials produces a clear synergistic effect, facilitating an increase in the thermal conductivity. Furthermore, although this composite contains 45 wt% CNF and 5 wt% CNT, the toughness and tensile strength are no lower than in the case of raw SR. This composite material has a thermal conductivity similar to that of some metals, a low Young's modulus typical of elastomers, and a high tensile strength. [ABSTRACT FROM AUTHOR]

A series of amphiphilic polyisoprene- b -poly[oligo(ethylene glycol) methyl (and tert -butyldimethylsilyl) ether methacrylate] (PIsp- b -PR3, R = methyl (M), tert -butyldimethylsilyl (Si)) diblock copolymers were prepared with varying PR3 compositions. The PIsp- b -PR3s were synthesized by the sequential anionic copolymerization of isoprene and corresponding methacrylate monomer (M3 or Si3). The obtained polymers had narrow molecular weight distributions (M w / M n ≤ 1.04) and predictable molecular weights. The bulk-state self-assembled nanostructure was studied by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). We also evaluated the surface energy of PR3s having an inherent amphiphilic character by pendant drop method along with PIsp. In addition, the surface structure of the block copolymer thin films was investigated by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) measurement. It was concluded that the estimated surface energy values (PM3 (37.3 ± 0.3 (mJ/m2)) and PSi3 (32.4 ± 1.4 (mJ/m2))) were authentic by comparison with the observation result of surface structure and depended on side chain ω-function. Image 1 • Water soluble PM3 containing amphiphilic block copolymers were synthesized. • LCST behavior of amphiphilic PM3- b -Polyisoprene was observed. • The surface energy of PM3 was evaluated by the pendant drop method. • The polymer film surface structure depended on the estimated surface energy. [ABSTRACT FROM AUTHOR]

The crack propagation behavior of pre-cut slide-ring (SR) gels with movable cross-links is investigated and compared to that of fixed cross-link (FC) gels under uniaxial stretching at a constant speed. Two fracture stages with 20-fold difference in crack velocity are observed for both SR and FC gels. At the beginning, the crack propagates slowly, and the crack propagation resistance is in good accordance with the evaluation based on tearing modulus T r , the initial slope of J -integral – crack tip opening displacement (CTOD) curve. Higher T r and slower crack velocity are observed in SR gels compared to FC gels with similar modulus. Moreover, T r decreases and crack velocity increases with increasing modulus (cross-linking density) for FC gels, whilst both parameters are modulus-independent for SR gels. This means that the slow mode crack propagation resistance of SR gels is dominated by the sliding movement of cross-links instead of the cross-linking density. However, as the strain energy input exceeds a critical value, crack accelerates abruptly and overtakes the sliding dynamics of the cross-links, thus the fracture behavior of SR gels resembles that of FC gels. Our results have revealed the strong correlation between the cross-link mobility and crack propagation resistance of SR gels. Image 10330 • Tearing modulus T r obtained via J -integral – CTOD method is for the first time used to estimate crack propagation resistance of gel materials. • Sliding of cross-links improves the crack propagation resistance of slide-ring (SR) gels. • Crack propagation behavior of SR gels changes from modulus-independent to modulus-dependent when the sliding of cross-links cannot catch up with the opening of crack tip. [ABSTRACT FROM AUTHOR]

To construct well-defined microstructures, strict controls of the temperature and sophisticated techniques are generally required because microstructure formation is usually based on crystallization, which easily results in a kinetic trap of disordered structures. Herein, we report the formation of various microstructures such as rods, cubes, plates, and nanosheets via supramolecular self-assembly between γ-cyclodextrin (CD) and polyethers in water without temperature change. We revealed the relationships between the guest polymer structures and the resulting microstructure: (1) Short guest homopolymers lead to the formation of rod microstructures, whilst long congeners result in plates. (2) A hydrophilic backbone polymer is necessary to isolate the plates in water, otherwise hydrophobic interaction leads to aggregation of the plates and the formation of polycrystalline γ-CD complexes. (3) Spatial confinement of the γ-CDs on the central segment of a guest triblock copolymer plays a key role in the fabrication of nanosheets with uniform thickness. Image 1 ∙Well-defined microstructures were formed by complexation of γ -cyclodextrin. ∙The microstructure morphologies were controlled by the axis polymer structure. ∙Molecular weight, chemical property, and sequence of axis affects the morphologies. [ABSTRACT FROM AUTHOR]