Visualized Bond Scission in Mechanochemiluminescent Polymethyl Acrylate/Cellulose Nanocrystals Composites

Mechanochromic Hydrogel Fibers with Multiple Fluorescent Colors

Mechanochromic polymers can change their color in response to external force and have shown promising applications in stress sensing and failure warning. They are usually obtained as thin films or bulky specimens. The mechanochromic fibers, which can be used to make smart fabrics, have been seldom reported due to the lack of efficient fabrication techniques. In this work, a general method using photo-polymerization of microgel solution in a template tube to produce mechanochromic hydrogel fibers is reported. The obtained hydrogel fibers can generate visible and fluorescent color changes upon deformation. The diameter of the mechanochromic fibers can be easily adjusted by using different template tubes. The mechanochromic fibers can be fabricated as long as 1 m. By reducing the fiber diameter or increasing the microgel concentration, the mechanical properties of the mechanochromic fibers can be improved, leading to more obvious mechanochromic behavior. The polymethacrylate (PMA) is further used to coat the hydrogel fibers, prevent the loss of water in the fibers, and increase the storage time. The mechanochromic fibers with multiple fluorescent colors are further fabricated by utilizing different microgel solutions. This work provides an easy and effective method to fabricate mechanochromic fibers with different color change abilities.

Multi-material 3D Printing of Mechanochromic Double Network Hydrogels for On-Demand Patterning

Cephalopods can change their color and patterns by activating the skin chromatophores for camouflage. However, in the man-made soft material systems, it is greatly challenging to fabricate the color-change structure in the desired patterns and shapes. Herein, we employ a multi-material microgel direct ink writing (DIW) printing method to make mechanochromic double network hydrogels in arbitrary shapes. We prepare the microparticles by grinding the freeze-dried polyelectrolyte hydrogel and immobilize the microparticles in the precursor solution to produce the printing ink. The polyelectrolyte microgels contain mechanophores as the cross-linkers. We adjust the rheological and printing properties of the microgel ink by tailoring the grinding time of freeze-dried hydrogels and microgel concentration. The multi-material DIW 3D printing technique is utilized to fabricate various 3D hydrogel structures which could change into a colorful pattern in response to applied force. The microgel printing strategy shows great potential in the fabrication of the mechanochromic device with arbitrary patterns and shapes.

Hybrid phenol-rhodamine dye based mechanochromic double network hydrogels with tunable stress sensitivity

Mechanochromic hydrogels, which can switch their color in response to the applied external force, have shown great potential in the stress visualization and damage indication. However, the kinds of the colors in the reported mechanochromic hydrogels are limited. It is challenging to develop the mechanochromic hydrogels with new kinds of color change. Herein, we report a kind of mechanochromic double network (DN) hydrogel based on the hybrid phenol-rhodamine (HPR) mechanophore. The hydrogels turn into orange color with an emission wavelength of around 566/574 nm in response to tensile and compressive stress. The DN hydrogels show great reversibility. The color of DN hydrogels vanishes slowly after releasing the stress. The stress sensitivity can be tailored by the crosslinking density and the mechanophore concentration of the first network. In addition, the influence of the pH on the mechanochromic properties of DN hydrogels is also studied. This study provides an insightful study in tuning the stress sensitivity in the mechanochromic hydrogel, which would be beneficial for the development of the mechanochromic materials. This article is protected by copyright. All rights reserved.

Mechanochemiluminescent hydrogels for real-time visualization of chemical bond scission

Quantitative and real-time characterization of mechanically induced bond scission events taken place in polymeric hydrogels is essential to uncover their fracture mechanics. Herein, a class of mechanochemiluminescent swelling hydrogels have been synthesized through a facile micellar copolymerization method using chemiluminescent bis(adamantyl)-1,2-dioxetane (Ad) as a crosslinker. This design and synthetic strategy ensure intense mechanochemiluminescence from Ad located in a hydrophobic network inside micelles. Moreover, the mechanochemiluminescent colors can be tailored from blue to red by mixing variant acceptors. Taking advantages of the transient nature of dioxetane chemiluminescence, the damage distribution and crack evolution of the hydrogels can be visualized and analyzed with high spatial and temporal resolution. The results demonstrate the strengths of the Ad mechanophore and micellar copolymerization method in the study of damage evolution and fracture mechanism of swelling hydrogels.

Mechanical Force for the Transformation of Aziridine into Imine

Force-selective mechanochemical reactions may be important for applications in polymer mechanochemistry, yet it is difficult to achieve such reactions. This paper reports that cis-N-phthalimidoaziridine incorporated into a macromolecular backbone undergoes migration of N-phthalimido group to afford imine under mechanochemical condition and not thermal one. The imine is further hydrolyzed by water bifurcating into amine and aldehyde. These structural transformations are confirmed by ¹ H NMR and FT-IR spectroscopic analyses. Computational simulations are conducted for the aziridine mechanophore to propose the mechanism of reaction and define the substrate scope of reaction.

Prevent or Cure-The Unprecedented Need for Self-Reporting Materials

Self-reporting smart materials are highly relevant in modern soft matter materials science, as they allow for the autonomous detection of changes in synthetic polymers, materials, and composites. Despite critical advantages of such materials, for example, prolonged lifetime or prevention of disastrous material failures, they have gained much less attention than self-healing materials. However, as diagnosis is critical for any therapy, it is of the utmost importance to report the existence of system changes and their exact location to prevent them from spreading. Thus, we herein critically review the chemistry of self-reporting soft matter materials systems and highlight how current challenges and limitations may be overcome by successfully transferring self-reporting research concepts from the laboratory to the real world. Especially in the space of diagnostic self-reporting systems, the recent SARS-CoV-2 (COVID-19) pandemic indicates an urgent need for such concepts that may be able to detect the presence of viruses or bacteria on and within materials in a self-reporting fashion.

State-of-art review on preparation, surface functionalization and biomedical applications of cellulose nanocrystals-based materials

Cellulose nanocrystals (CNCs) are a class of sustainable nanomaterials that are obtained from plants and microorganisms. These naturally derived nanomaterials are of abundant hydroxyl groups, well biocompatibility, low cost and biodegradable potential, making them suitable and promising candidates for various applications, especially in biomedical fields. In this review, the recent advances and development on the preparation, surface functionalization and biomedical applications of CNCs-based materials have been summarized and outlined. The main context of this paper could be divided into the following three parts. In the first part, the preparation strategies based on physical, chemical, enzymatic and combination techniques for preparation of CNCs have been summarized. The surface functionalization methods for synthesis CNCs-based materials with designed properties and functions were outlined in the following section. Finally, the current state about applications of CNCs-based materials for tissue engineering, medical hydrogels, biosensors, fluorescent imaging and intracellular delivery of biological agents have been highlighted. Moreover, current issues and future directions about the above aspects have also pointed out and discussed. We believe this review will attract great research attention of scientists from materials, chemistry, biomedicine and other disciplines. It will also provide some important insights on the future development of CNCs-based materials especially in biomedical fields.

Enhancing and toughening plant oil-based polymeric materials through synergetic supramolecular and covalent interactions by introducing nucleobase-functionalized celluloses

Renewable plant oil-based polymeric materials were enhanced and toughened through complementary H-bonding interactions by introducing nucleobase-functionalized celluloses.

Mechanically Induced Bright Luminescence from 1,2-Dioxetane Containing PDMS Boosted by Fluoroboron Complex as an In-Chain Fluorophore

Improving mechanochemiluminescent (MCL) sensitivity of 1,2-dioxetane containing polymers is important for the applications of stress-reporting soft materials. Herein, a series of MCL poly(dimethylsiloxane) (PDMS) have been synthesized by simultaneously incorporating difluoroboron β-diketonate dye and 1,2-dioxetane as the co-crosslinkers to tune the energy transfer process across polymer chains. By covalently linked fluoroboron complex in PDMS network, the aggregation of the complex is overcome. Owing to its excellent opto-physical properties, this fluoroboron complex is shown to be an effective in-chain fluorophore to effectively enhance the chemiluminescence from polymeric 1,2-dioxetane that is broken either thermally or mechanically. Studies on the optomechanical properties of these PDMS show that MCL intensity is increased with the concentration of fluoroboron complex and the wavelength of the emission is shifted. The results of the present study appear to be broadly useful for designing elastomeric networks with chemiluminescent property not only attractive for optical technology, but also useful for damage self-reporting.

Facile preparation and adsorption performance of low-cost MOF@cotton fibre composite for uranium removal

A novel composite MOF@cotton fibre (HCF) was prepared and characterized by FTIR, SEM, XPS and TGA. The effect of various parameters on the adsorption efficiency, such as the solution pH, contact time, initial U(VI) concentration and temperature, was studied. The maximal sorption capacity (Qm) is 241.28 mg g-1 at pH 3.0 for U(VI) according to the Langmuir isotherm adsorption model, and the kinetic and thermodynamic data reveal a relatively fast entropy-driven process (ΔH0 = 13.47 kJ mol-1 and ΔS0 = 75.47 J K-1 mol-1). The removal efficiency of U(VI) by HCF is comparable with that of pure cotton fibre and as-prepared MOF (noted as HST). However, the HST composite with cotton fibre significantly improved the treatment process of U(VI) from aqueous solutions in view of higher removal efficiency, lower cost and faster solid-liquid separation. Recycling experiments showed that HCF can be used up to five times with less than 10% efficiency loss.

Semi-IPNs Reinforced with Silica Janus Nanoparticles and Their Stress Sensing with Mechanoluminescent Probe

A series of nanocomposite elastomers are prepared by dispersing surface-modified silica Janus nanoparticles into semi-interpenetrating network (Semi-IPN) of polyurethane/polyethyl methacrylate. Benefiting from the hierarchically crosslinked structures that consist of physical interlocking mediated by hydrogen-bond-rich silica Janus nanoparticles and permanent crosslinking by Semi-IPN, these elastomers exhibit excellent mechanical properties. Moreover, the Janus nanosheet is found more effective in strengthening and toughening the Semi-IPN, in comparison to Janus hollow sphere. Since 1,2-dioxetane is covalently embedded in these elastomers as a mechanoluminescent stress probe, stress transfer between the polymer and Janus nanoparticles and the toughening mechanism can be illuminated, which offer exciting opportunities to study the failure process of complex polymer nanocomposites with high spatial and temporal resolution.

Current State of Applications of Nanocellulose in Flexible Energy and Electronic Devices

Novel and unique applications of nanocellulose are largely driven by the functional attributes governed by its structural and physicochemical features including excellent mechanical properties and biocompatibility. In recent years, thousands of groundbreaking works have helped in the development of targeted functional nanocellulose for conductive, optical, luminescent materials, and other applications. The growing demand for sustainable and renewable materials has led to the rapid development of greener methods for the design and fabrication of high-performance green nanomaterials with multiple features, and consequently new challenges and opportunities. The present review article discusses historical developments, various fabrication and functionalization methods, the current stage, and the prospects of flexible energy and hybrid electronics based on nanocellulose.