Abstract
Previous studies have shown that copolymer compositions can significantly impact self-healing properties. This was accomplished by enhancement of van der Waals (vdW) forces which facilitate ...self-healing in relatively narrow copolymer compositional range. In this work we report the acceleration of self-healing in alternating/random hydrophobic acrylic-based copolymers in the presence of confined water molecules. Under these conditions competing vdW interactions do not allow H
2
O-diester H-bonding, thus forcing nBA side groups to adapt L-shape conformations, generating stronger dipole-dipole interactions resulting in shorter inter-chain distances compared to ‘key-and-lock’ associations without water. The perturbation of vdW forces upon mechanical damage in the presence of controllable amount of confined water is energetically unfavorable leading the enhancement of self-healing efficiency of hydrophobic copolymers by a factor of three. The concept may be applicable to other self-healing mechanisms involving reversible covalent bonding, supramolecular chemistry, or polymers with phase-separated morphologies.
Seventy-five years after its invention, transmission electron microscopy has taken a great step forward with the introduction of aberration-corrected electron optics. An entirely new generation of ...instruments enables studies in condensed-matter physics and materials science to be performed at atomic-scale resolution. These new possibilities are meeting the growing demand of nanosciences and nanotechnology for the atomic-scale characterization of materials, nanosynthesized products and devices, and the validation of expected functions. Equipped with electron-energy filters and electron-energy-loss spectrometers, the new instruments allow studies not only of structure but also of elemental composition and chemical bonding. The energy resolution is about 100 milli-electron volts, and the accuracy of spatial measurements has reached a few picometers. However, understanding the results is generally not straightforward and only possible with extensive quantum-mechanical computer calculations.
Polyurethanes have many properties that qualify them as high-performance polymeric materials, but they still suffer from mechanical damage. We report the development of polyurethane networks that ...exhibit self-repairing characteristics upon exposure to ultraviolet light. The network consists of an oxetane-substituted chitosan precursor incorporated into a two-component polyurethane. Upon mechanical damage of the network, four-member oxetane rings open to create two reactive ends. When exposed to ultraviolet light, chitosan chain scission occurs, which forms crosslinks with the reactive oxetane ends, thus repairing the network. These materials are capable of repairing themselves in less than an hour and can be used in many coatings applications, ranging from transportation to packaging or fashion and biomedical industries.
Although significant advances have been achieved in dynamic reversible covalent and non-covalent bonding chemistries for self-healing polymers, an ultimate goal is to create high strength and ...stiffness commodity materials capable of repair without intervention under ambient conditions. Here we report the development of mechanically robust thermoplastic polyurethane fibers and films capable of autonomous self-healing under ambient conditions. Two mechanisms of self-healing are identified: viscoelastic shape memory (VESM) driven by conformational entropic energy stored during mechanical damage, and surface energy/tension that drives the reduction of newly generated surface areas created upon damage by shallowing and widening wounds until healed. The type of self-healing mechanism is molecular weight dependent. To the best of our knowledge these materials represent the strongest (S
= 21 mN/tex, or σ
≈ 22 MPa) and stiffest (J = 300 mN/tex, or E ≈ 320 MPa) self-healing polymers able to repair under typical ambient conditions without intervention. Since two autonomous self-healing mechanisms result from viscoelastic behavior not specific to a particular polymer chemistry, they may serve as general approaches to design of other self-repairing commodity polymers.
Key-and-lock commodity self-healing copolymers Urban, Marek W; Davydovich, Dmitriy; Yang, Ying ...
Science (American Association for the Advancement of Science),
10/2018, Letnik:
362, Številka:
6411
Journal Article
Recenzirano
Self-healing materials are notable for their ability to recover from physical or chemical damage. We report that commodity copolymers, such as poly(methyl methacrylate)/n-butyl acrylate p(MMA/nBA) ...and their derivatives, can self-heal upon mechanical damage. This behavior occurs in a narrow compositional range for copolymer topologies that are preferentially alternating with a random component (alternating/random) and is attributed to favorable interchain van der Waals forces forming key-and-lock interchain junctions. The use of van der Waals forces instead of supramolecular or covalent rebonding or encapsulated reactants eliminates chemical and physical alterations and enables multiple recovery upon mechanical damage without external intervention. Unlike other self-healing approaches, perturbation of ubiquitous van der Waals forces upon mechanical damage is energetically unfavorable for interdigitated alternating/random copolymer motifs that facilitate self-healing under ambient conditions.
Recent advances of supramolecular chemistry utilized in the development of self‐healing polymers have revealed that the rate and equilibrium constants of bond dissociation/re‐association, bonding ...directionality, chain relaxation time, decay rate of chain relaxation after damage, and cluster formation may impact the healing efficiency in a given environment. This review provides an assessment of supramolecular chemistries responsible for self‐healing using H‐bonding, metal–ligand, host–guest, ionic, π–π, and hydrophobic interactions. The impact of these chemistries on self‐healing is examined for various polymeric systems with multifunctional applications which are unique to supramolecular networks. This review also discusses the driving forces leading to physical damage closure in the context of supramolecular bond dynamics, providing insights into the design principles to achieve efficient recovery.
Self‐healing of polymers using supramolecular reversible bonding, including H‐bonding, metal–ligand, host–guest, ionic, π–π, and hydrophobic interactions, is discussed. Physicochemical features of polymer networks are examined in the context of network dynamics and driving forces responsible for restoration of physical damages. New insights and recent advances delineating the design principles to achieve efficient self‐healing via supramolecular chemistries are presented.
Sugar moieties were incorporated into cross‐linked polyurethane (PUR) networks in an effort to achieve self‐repairing in the presence of atmospheric carbon dioxide (CO2) and water (H2O). When ...methyl‐α‐D‐glucopyranoside (MGP) molecules are reacted with hexamethylene diisocyanate trimer (HDI) and polyethylene glycol (PEG) to form cross‐linked MGP‐polyurethane (PUR) networks, these materials are capable of self‐repairing in air. This process requires atmospheric amounts of CO2 and H2O, thus resembling plant behavior of carbon fixation during the photosynthesis cycle. Molecular processes responsible for this unique self‐repair process involve physical diffusion of cleaved network segments as well as the formation of carbonate and urethane linkages. Unlike plants, MGP‐PUR networks require no photo‐initiated reactions, and they are thus capable of repair in darkness under atmospheric conditions.
Self‐repairing materials were obtained by reacting sugar moieties with hexamethylene diisocyanate trimer and polyethylene glycol to form cross‐linked MGP‐polyurethane networks. The repair process requires atmospheric amounts of CO2 and H2O, thus resembling plant behavior of carbon fixation during photosynthesis.
The design, development, and manufacturing of new materials continue to be an ongoing challenge for scientists and engineers. Because of similarities to biological systems having self-repairable ...properties, polymer networks are of particular importance and interest, and if designed properly, may provide an unprecedented opportunity for mimicking biological systems. This can be accomplished through the formation of nanostructured stimuli-responsive networks that individually or collectively respond to internal or external stimuli. This article outlines selected recent developments and future trends that will formulate foundation for the development of stratified heterogeneous stimuli-responsive polymer networks capable of reorganizing, self-healing, or signaling. The primary focus is on the physico-chemical attributes of multi-component polymer networks with localized glass transition temperatures capable of stratification and exhibiting stimuli-responsiveness or recognition attributes.
The plural of an anecdote is not evidence, yet anecdotal international reports are accumulating from ear, nose, and throat (ENT) surgeons and other health-care workers on the front lines that ...anosmia, with or without dysgeusia, are symptoms frequently associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. To further complicate matters, immediate self-recognition of olfactory dysfunction is typically only present in the most severe cases, or it is only self-identified after a prolonged latency period.1,2 A scarcity of acute-phase advanced neuroimaging studies, difficulties in obtaining histopathological tissue specimens, and an absence of viral cultures of infected olfactory neuroepithelium compound the difficulties in studying this phenomenon. ...in the context of normal trans-nasal airflow of odorant molecules (ie, no oedema in the nasal vault or olfactory cleft), and in the absence of intranasal disease (eg, infectious rhinosinusitis, allergic or vasomotor rhinitis, or polyposis), until now patients with sensorineural viral anosmia have been seldom seen in general otolaryngology practice—on the order of approximately one to two new-onset patients each year. ...up until the coronavirus disease 2019 (COVID-19) pandemic, the low prevalence of sensorineural viral anosmia in society as a whole has made clinical research challenging.
Arterial elasticity has been proposed as an independent predictor of cardiovascular diseases and mortality. Identification of the different propagating modes in thin shells can be used to ...characterize the elastic properties. Ultrasound radiation force was used to generate local mechanical waves in the wall of a urethane tube or an excised pig carotid artery. The waves were tracked using pulse-echo ultrasound. A modal analysis using two-dimensional discrete fast Fourier transform was performed on the time-space signal. This allowed the visualization of different modes of propagation and characterization of dispersion curves for both structures. The urethane tube/artery was mounted in a metallic frame, embedded in tissue-mimicking gelatin, cannulated, and pressurized over a range of 10-100 mmHg. The k-space and the dispersion curves of the urethane tube showed one mode of propagation, with no effect of transmural pressure. Fitting of a Lamb wave model estimated Young's modulus in the urethane tube around 560 kPa. Young's modulus of the artery ranged from 72 to 134 kPa at 10 and 100 mmHg, respectively. The changes observed in the artery dispersion curves suggest that this methodology of exciting mechanical waves and characterizing the modes of propagation has potential for studying arterial elasticity.
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