Tough Glass with Mechanical Bonding Network Anchored by High-Mobility Polymers

A series of mechanically interlocked supramolecular glasses were prepared from a bio-based cyclic oligosaccharide with small amounts of polymer. The rigid glassy materials were readily thermo-moldable, and their mechanical properties were tuned by the substituents on the oligosaccharide. In the presence of even small amounts (<18 wt %) of polymer, fragile oligosaccharide derivatives turned into tough bio-based plastics, as long as the polymer penetrated through the cyclic molecules. A small difference in acyl substituents on the ring components resulted in a significant difference in the mechanical properties. Bulkier substituents monotonically decreased Young’s modulus and the glass transition temperature (Tg), indicating the predominance of interactions between ring components that maintain the material framework. However, the toughness dramatically changed, independent of the interactions, forming two glasses with the same Young’s modulus and Tg into different materials: brittle and ductile. A clear difference between brittle and ductile glasses was observed in their confined polymer mobility. Analysis of the dynamics revealed that the higher mobility of the polymer was maintained in the material frameworks of ductile glasses compared with that of brittle glasses, whereas a comparable glass prepared from a mixture of the two components of ductile glass was very fragile. These results suggest the necessity of a mechanical bonding network formed by high-mobility polymers so that the confined polymers can work as an anchor rapidly in response to crack formation in the framewor

A Versatile Synthesis of Diverse Polyrotaxanes with a Dual Role of Cyclodextrin as both the Cyclic and Capping Components

We report herein a versatile synthesis of cyclodextrin-based polyrotaxanes (CD-PRs). Three different CD-PRs were synthesized from different linear polymers and different CDs with relatively good yields by a novel single method. This method requires no additional capping reagents, because CDs play a dual role as both the cyclic components and the end-capping groups. The end-capping is achieved by transesterification with excess CDs at both ends of pseudopolyrotaxanes activated with p-nitrophenyl ester. As a result of this versatile method, we also demonstrate the first synthesis of a novel CD-PR based on poly(butadiene)

Tough Glass with Mechanical Bonding Network Anchored by High-Mobility Polymers

A series of mechanically interlocked supramolecular glasses were prepared from a bio-based cyclic oligosaccharide with small amounts of polymer. The rigid glassy materials were readily thermo-moldable, and their mechanical properties were tuned by the substituents on the oligosaccharide. In the presence of even small amounts (<18 wt %) of polymer, fragile oligosaccharide derivatives turned into tough bio-based plastics, as long as the polymer penetrated through the cyclic molecules. A small difference in acyl substituents on the ring components resulted in a significant difference in the mechanical properties. Bulkier substituents monotonically decreased Young’s modulus and the glass transition temperature (Tg), indicating the predominance of interactions between ring components that maintain the material framework. However, the toughness dramatically changed, independent of the interactions, forming two glasses with the same Young’s modulus and Tg into different materials: brittle and ductile. A clear difference between brittle and ductile glasses was observed in their confined polymer mobility. Analysis of the dynamics revealed that the higher mobility of the polymer was maintained in the material frameworks of ductile glasses compared with that of brittle glasses, whereas a comparable glass prepared from a mixture of the two components of ductile glass was very fragile. These results suggest the necessity of a mechanical bonding network formed by high-mobility polymers so that the confined polymers can work as an anchor rapidly in response to crack formation in the framewor

Tough Glass with Mechanical Bonding Network Anchored by High-Mobility Polymers

A series of mechanically interlocked supramolecular glasses were prepared from a bio-based cyclic oligosaccharide with small amounts of polymer. The rigid glassy materials were readily thermo-moldable, and their mechanical properties were tuned by the substituents on the oligosaccharide. In the presence of even small amounts (<18 wt %) of polymer, fragile oligosaccharide derivatives turned into tough bio-based plastics, as long as the polymer penetrated through the cyclic molecules. A small difference in acyl substituents on the ring components resulted in a significant difference in the mechanical properties. Bulkier substituents monotonically decreased Young’s modulus and the glass transition temperature (Tg), indicating the predominance of interactions between ring components that maintain the material framework. However, the toughness dramatically changed, independent of the interactions, forming two glasses with the same Young’s modulus and Tg into different materials: brittle and ductile. A clear difference between brittle and ductile glasses was observed in their confined polymer mobility. Analysis of the dynamics revealed that the higher mobility of the polymer was maintained in the material frameworks of ductile glasses compared with that of brittle glasses, whereas a comparable glass prepared from a mixture of the two components of ductile glass was very fragile. These results suggest the necessity of a mechanical bonding network formed by high-mobility polymers so that the confined polymers can work as an anchor rapidly in response to crack formation in the framewor

Mechanical Properties of Ultrathin Polystyrene‑<i>b</i>‑Polybutadiene‑<i>b</i>‑Polystyrene Block Copolymer Films: Film Thickness-Dependent Young’s Modulus

This study investigated the mechanical properties of ultrathin polystyrene-b-polybutadiene-b-polystyrene (SBS) block copolymer films with thicknesses ranging from 20 to 600 nm using a pseudo-free-standing tensile test carried out using an ultrathin film floating on water. The Young’s moduli of ultrathin SBS films increased drastically with decreasing thickness for films thinner than 100 nm, i.e., 2 or 3 times the domain spacing of the SBS. We analyzed the depth profiles of the polystyrene (PS) domain in the SBS thin films by dynamic secondary ion mass spectrometry and the surface and interface in-plane morphology using atomic force microscopy. The PS-rich continuous subsurface layer was observed to be a major factor for the drastic increase in Young’s modulus under ultrathin film conditions. Therefore, we propose a simple two-layer model consisting of a hard PS-rich layer and a soft bulk layer to explain the specific increase in Young’s modulus with decreasing film thickness

Fracture Process of Mechanically Interlocked Ductile Glass Under Uniaxial Tension

A unique toughening mechanism in ductile glass was elucidated by multiscale in situ structural analysis. A brittle glass of a cyclic oligosaccharide derivative was significantly toughened by a small amount of a polymer that penetrated the molecular cavity. In situ scanning electron microscopy and synchrotron X-ray scattering under uniaxial tension revealed strain-induced nanovoid formation and growth accompanied by molecular-level structural changes. Nanovoids were widely formed in the sample before yielding, and then, they clustered into a disk-shaped slit a few micrometers in size and perpendicular to the tensile direction. Owing to the strain concentration through necking, the slit formed by the nanovoid cluster was widely opened in the tensile direction to form fibrils and then became stabilized, whereas the craze in a conventional polymer glass generally splits under a small strain. After the initial glass structure maintained by interactions between the homogeneously dispersed cyclic components collapsed, a high strain was applied to the polymers. The transfer of polymers through the cavity led to the conversion to another structure that had a shorter distance between the main components and a high molecular orientation. Because the reconstructed structure was considerably harder than the initial structure, this strain-induced hardening delocalized the strain at the fibrils and tips of the slits, leading to stable propagation of necking. This mechanism is similar to that of transformation-induced plasticity in advanced ductile steels. The results suggest that intuitive molecular designs focusing on the unique structural changes in mechanically interlocked glass are promising for creating advanced hard and ductile glasses

Viscoelastic Properties of Slide-Ring Gels Reflecting Sliding Dynamics of Partial Chains and Entropy of Ring Components

A systematic study of the viscoelastic relaxation of slide-ring gels revealed the dynamics of chains sliding through the cross-links, based on a precise assignment of the plateau moduli and on detailed consideration of the correlation between relaxation times and the molecular weights between cross-links. The slide-ring gels exhibit finite equilibrium moduli that are much smaller than those of the rubbery plateau, indicating a significant contribution of the ring components’ entropy to the elasticity. Viscoelastic measurements were performed on two series of slide-ring gels with polybutadiene or poly­(ethylene glycol) as the axis polymers. The elastic moduli at the rubbery plateaus and the measured densities of the elastic bodies allow derivation of the average molecular weights between the cross-links, <i>M</i>_<i>x</i>. The relaxation time in each gel series indicates a cubic power dependence on <i>M</i>_<i>x</i>. By analogy to polymer entanglement, the relaxation can be attributed to a reptation-like local diffusion of partial chains

Mechanical Properties of Ultrathin Polystyrene‑<i>b</i>‑Polybutadiene‑<i>b</i>‑Polystyrene Block Copolymer Films: Film Thickness-Dependent Young’s Modulus

This study investigated the mechanical properties of ultrathin polystyrene-b-polybutadiene-b-polystyrene (SBS) block copolymer films with thicknesses ranging from 20 to 600 nm using a pseudo-free-standing tensile test carried out using an ultrathin film floating on water. The Young’s moduli of ultrathin SBS films increased drastically with decreasing thickness for films thinner than 100 nm, i.e., 2 or 3 times the domain spacing of the SBS. We analyzed the depth profiles of the polystyrene (PS) domain in the SBS thin films by dynamic secondary ion mass spectrometry and the surface and interface in-plane morphology using atomic force microscopy. The PS-rich continuous subsurface layer was observed to be a major factor for the drastic increase in Young’s modulus under ultrathin film conditions. Therefore, we propose a simple two-layer model consisting of a hard PS-rich layer and a soft bulk layer to explain the specific increase in Young’s modulus with decreasing film thickness

SANS Studies on Spatial Inhomogeneities of Slide-Ring Gels

Slide-ring gels (SR gel) [previously termed as topological or polyrotaxane gels:  Okumura, Y.; Ito, K. Adv. Mater. 2001, 13, 485] have remarkable physical properties, such as large extensibility and mechanical strength. The SR gels are cross-linked polyrotaxane (PR) consisting of poly(ethylene glycol) (PEG) chains and α-cyclodextrin (CD), in which the cross-linkers are made of CD dimers and capable of sliding along the PEG chains. To elucidate the physical picture and properties, the scattering functions, I(q)s, of SR gel in NaOD aqueous solutions (NaODaq) and in deuterated dimethyl sulfoxide (d-DMSO) were investigated by small-angle neutron scattering (SANS) and were compared with those of pregel solutions, where q is the magnitude of the scattering vector. The following facts were disclosed: (1) The polyrotaxane chains take a rodlike conformation in d-DMSO, whereas a Gaussian chain in NaODaq. (2) The degree of inhomogeneities of SR gel in NaODaq has a minimum around the sol−gel transition, whereas that in d-DMSO increases monotonically with increasing cross-linker concentration. (3) I(q) of SR gel in NaODaq can be described by a Lorentz function, while that in d-DMSO is given by the sum of a squared Lorentz function and a scattering function for a rod. These differences in I(q) are ascribed to the difference in the stacking behavior of CD molecules on PEG chains in PR