Low-temperature, ultra-fast, and recyclable self-healing nanocomposites reinforced with non-solvent silylated modified cellulose nanocrystals.

Developing polymeric materials with remarkable mechanical properties and fast self-healing performance even at low temperatures is challenging. Herein, the polymeric nanocomposites containing silane-treated cellulose nanocrystals (SCNC) with ultrafast self-healing and exceptional mechanical characteristics were developed even at low temperatures. First, CNC is modified with a cyclic silane coupling agent using an eco-friendly chemical vapor deposition method. The nanocomposite was then fabricated by blending SCNC with matrix prepolymer, prepared from monomers that possess lower critical solution temperature, followed by the inclusion of dibutyltin dilaurate and hexamethylene diisocyanate. The self-healing capability of the novel SCNC/polymer nanocomposites was enhanced remarkably by increasing the content of SCNC (0-3 wt%) and reaching (≥99 %) at temperatures (5 & 25 °C) within <20 min. Moreover, SCNC-3 showed a toughness of (2498 MJ/m3) and SCNC-5 displayed a robust tensile strength of (22.94 ± 0.4 MPa) whereas SCNC-0 exhibited a lower tensile strength (7.4 ± 03 MPa) and toughness of (958 MJ/m3). Additionally, the nanocomposites retain their original mechanical properties after healing at temperatures (5 & 25 °C) owing to the formation of hydrogen bonds via incorporation of the SCNC. These novel SCNC-based self-healable nanocomposites with tunable mechanical properties offer novel insight into preparing damage and temperature-responsive flexible and wearable devices.

Self-healing polymers for surface scratch regeneration.

Recently, there has been a significant increase in academic and industrial interest in self-healing polymers (SHPs) due to their remarkable ability to regenerate scratched surfaces and materials of astronomical significance. Scientists have been inspired by the magical repairing mechanism of the living world. They transformed the fiction of self-healing into reality by designing engrossing polymeric materials that could self-repair mechanical abrasions repeatedly. As a result, the durability of the materials is remarkably improved. Thus, the idea of studying SHPs passively upholds economic and environmental sustainability. However, the critical areas of self-healing (including healing efficiency, healing mechanism, and thermo-mechanical property changes during healing) are under continuous scientific improvisation. This review highlights recent notable advances of SHPs for application in regenerating scratched surfaces with various distinctive underlying mechanisms. The primary focus of the work is aimed at discussing the impact of SHPs on scratch-healing technology. Beyond that, insights regarding scratch testing, methods of investigating polymer surfaces, wound depths, the addition of healing fillers, and the environmental conditions maintained during the healing process are reviewed thoroughly. Finally, broader future perspectives on the challenges and prospects of SHPs in healing surface scratches are discussed.

Polyether-based waterborne synergists: effect of polymer topologies on pigment dispersion.

Control of polymer topologies is essential to determine their unique physical properties and potential applications. The polymer topologies can have a critical effect on pigment dispersion owing to their unique architectures; however, studies using polymer topologies on pigment dispersion in aqueous systems are scarce. Thus, this study proposes various topologies of polyether-based waterborne synergists, such as linear, hyperbranched, and branched cyclic structures. Specifically, we applied branched types of polyglycidols (PGs) as a synergist to provide polymer topology-dependent dispersibility for the surface-modification of Red 170 particles through adsorption and steric hindrance. The topology-controlled PG synergists (PGSs) were successfully prepared by post-polymerization modification with phthalimide and benzoyl groups. Particularly, the branched types of PGSs, branched cyclic PGS (bc-PGS), and hyperbranched PGS (hb-PGS) exhibited improved dispersibility through adsorption on top of the pigment, interaction between dispersant (BYK 190) and pigment, and steric effect. Surprisingly, hb-PGS conferred the Red 170 pigment particles with superior storage stability than that of bc-PGS despite their similar structural features. This study suggests the widespread potential application of PGSs as waterborne synergists for various dispersion applications.

NIR-Triggered High-Efficiency Self-Healable Protective Optical Coating for Vision Systems.

Recently, self-healing materials have evolved to recover specific functions such as electronic, magnetic, acoustic, structural or hierarchical, and biological properties. In particular, the development of self-healing protection coatings that can be applied to lens components in vision systems such as augmented reality glasses, actuators, and image and time-of-flight sensors has received intensive attention from the industry. In the present study, we designed polythiourethane dynamic networks containing a photothermal N-butyl-substituted diimmonium borate dye to demonstrate their potential applications in self-healing protection coatings for the optical components of vision systems. The optimized self-healing coating exhibited a high transmittance (∼95% in the visible-light region), tunable refractive index (up to 1.6), a moderate Abbe number (∼35), and high surface hardness (>200 MPa). When subjected to near-infrared (NIR) radiation (1064 nm), the surface temperature of the coating increased to 75 °C via the photothermal effect and self-healing of the scratched coatings occurred via a dynamic thiourethane exchange reaction. The coating was applied to a lens protector, and its self-healing performance was demonstrated. The light signal distorted by the scratched surface of the coating was perfectly restored after NIR-induced self-healing. The photoinduced self-healing process can also autonomously occur under sunlight with low energy consumption.

Cellulose nanocrystal nanocomposites capable of low-temperature and fast self-healing performance.

The development of low-temperature self-healing polymers is crucial because high-temperature or softening conditions for rapid self-healing inevitably reduce their mechanical strength. Herein, we first report cellulose nanocrystal (CNC)/polymer nanocomposites with a rapid low-temperature self-healing performance. The nanocomposite was prepared by simple blending of grafted CNC and matrix prepolymer made from the monomers having metal-ligand coordination and lower critical solution temperature functionalities along with the presence of hexamethylene diisocyanate and dibutyltin dilaurate. Owing to the dynamic nature of both hydrogen bonds and metal-ligand coordinated covalent bonds, the resultant nanocomposites showed excellent self-healing efficiency (99 %, within 1 h) at a low temperature (5 °C) with robust mechanical properties including a high stretchability (230 %), high toughness (2538 MJ/m3), enhanced tensile strength (25.49 ± 0.02 MPa), and improved thermomechanical properties. Self-healing performance of the coordinated covalent bonds requiring active hydrogen was considerably improved by the introduction of CNCs with abundant hydrogen bonds.

Simultaneous removal of heavy metal ions using carbon dots-doped hydrogel particles.

Heavy metal ions (HMI) have attracted worldwide concern due to their serious environmental pollution which led to the risk of health conditions. From Red Malus floribunda fruits, nitrogen-doped carbon dots (N-CDs) were prepared, followed by hybrid-spherical shaped hydrogel particles (CGCDs) were prepared. The prepared CGCDs were utilized as adsorbents for HMI-(Hg(II), Cd(II), Pb(II), and Cr(III)) from water. N-CDs with about 4.0 nm in diameter were characterized by various techniques such as field emission-scanning electron microscopy (FE-SEM) and attenuated total reflection-fourier transform infrared spectroscopy (ATR-FTIR) that confirm the presence of nitrogen, oxygen, and carbon functionalities. The prepared spherical CGCDs were characterized very well before it was used as HMI adsorbents. The sizes of the CGCDs were ranges between 20 and 300 µm and the degree of swelling was calculated as 1320 %. ATR-FTIR and X-ray diffraction analyses reveal the presence of N-CDs in CGCDs. Further, FE-SEM confirms the spherical shape morphology of CGCDs. Three different concentrations of HMI solutions were 500 mg/L, 1000 mg/L, and 1500 mg/L. Hg(II) adsorbed proficiently by CGCDs in single metal ion systems with ~72 % and almost complete removal of Hg(II) ions (99 %) in multiple metal ion systems was observed. Moreover, all metal ions Hg(II), Cd(II), Pb(II), and Cr(III) were efficiently (>70 %) removed in multiple systems by CGCDs. After HMI adsorption experiments, the elemental mapping from FE-SEM and X-ray photoelectron spectroscopy studies conveys the presence of HMI on CGCDs. This suggests that CGCDs would be a suitable adsorbent for the simultaneous removal of multiple HMI from wastewater.

Recent Studies on Dispersion of Graphene-Polymer Composites.

Graphene is an excellent 2D material that has extraordinary properties such as high surface area, electron mobility, conductivity, and high light transmission. Polymer composites are used in many applications in place of polymers. In recent years, the development of stable graphene dispersions with high graphene concentrations has attracted great attention due to their applications in energy, bio-fields, and so forth. Thus, this review essentially discusses the preparation of stable graphene-polymer composites/dispersions. Discussion on existing methods of preparing graphene is included with their merits and demerits. Among existing methods, mechanical exfoliation is widely used for the preparation of stable graphene dispersion, the theoretical background of this method is discussed briefly. Solvents, surfactants, and polymers that are used for dispersing graphene and the factors to be considered while preparing stable graphene dispersions are discussed in detail. Further, the direct applications of stable graphene dispersions are discussed briefly. Finally, a summary and prospects for the development of stable graphene dispersions are proposed.

Noncovalent Functionalized Graphene Nanocarriers from Graphite for Treating Thyroid Cancer Cells.

Here, biocompatible graphene (G) nanocarriers decorated with iron oxide nanoparticles (IONPs) were prepared using 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) and poly(ethylene glycol) monomethacrylate (PEGMA). For this, we report the use of graphite directly instead of graphene oxide or reduced graphene oxide. Graphene nanocarrier (in situ GIOPMPC) was prepared in one-pot by in situ copolymerization of MPC and PEGMA monomers in the presence of IONPs and G. GIOPMCP nanocarriers were prepared by sonication using PMPC-co-PEGMA copolymers in the presence of IONPs and G. The prepared graphene nanocarriers were thoroughly characterized by various techniques. The analyses confirmed the successful preparation of nanocarriers with even distributions of PMPC-co-PEGMA and IONPs on surface G. The IONPs were coordinated through the phosphate groups in PMPC. Excellent dispersibility of the graphene nanocarriers in water enabled drug delivery applications. The prepared nanocarriers did not show significant cytotoxicity to the thyroid cancer cells up to 8 mg/mL (IC50: 38.26 mg/mL). Thyroid cancer cells were stably transduced with a bioluminescent reporter to monitor cell cytotoxicity. Doxorubicin (DOX) was loaded onto in situ GIOPMPC nanocarriers at two different concentrations and was successfully delivered to thyroid cancer cells, resulting in strong cytotoxicity. Moreover, signaling mechanistic analyses showed apoptosis activation, inhibition of anti-apoptosis and proliferation, and increased DNA damage in the thyroid cancer cells.

Influence of Material Properties on the Damage-Reporting and Self-Healing Performance of a Mechanically Active Dynamic Network Polymer in Coating Applications.

We conducted a detailed investigation of the influence of the material properties of dynamic polymer network coatings on their self-healing and damage-reporting performance. A series of reversible polyacrylate urethane networks containing the damage-reporting diarylbibenzofuranone unit were synthesized, and their material properties (e.g., indentation modulus, hardness modulus, and glass-transition temperature) were measured conducting nanoindentation and differential scanning calorimetry experiments. The damage-reporting and self-healing performances of the dynamic polymer network coatings exhibited opposite tendencies with respect to the material properties of the polymer network coatings. Soft polymer network coatings with low glass-transition temperature (~10 °C) and indentation hardness (20 MPa) exhibited better self-healing performance (almost 100%) but two times worse damage-reporting properties than hard polymer network coatings with high glass-transition temperature (35~50 °C) and indentation hardness (150~200 MPa). These features of the dynamic polymer network coatings are unique; they are not observed in elastomers, films, and hydrogels, whereby the polymer networks are bound to the substrate surface. Evidence indicates that controlling the polymer's physical properties is a key factor in designing high-performance self-healing and damage-reporting polymer coatings based on mechanophores.

Environmentally Adaptable and Temperature-Selective Self-Healing Polymers.

Development of polymeric materials capable of self-healing at low temperatures is an important issue since their mechanical strength and self-healing performance are often in conflict with each other. Herein, random copolymers with self-healing capability in a wide temperature range prepared from 2-(dimethylamino)ethyl methacrylate (DMAEMA), glyceryl monomethacrylate (GlyMA), and butyl methacrylate monomers via free-radical polymerization and subsequent cross-linking with hexamethylene diisocyanate are reported. Wound closure is facilitated by swelling below the lower critical solution temperature or by heating above the glass transition temperature (T g ) of the polymer. GlyMA units form metal-ligand coordination complexes with dibutyltin dilaurate, leading to the formation of new carbonate bonds under ambient CO2 and H2 O conditions. Although swelling/heating reduces the polymer's mechanical strength, it is fully restored following chemical re-bonding/drying at room temperature. The swelling and degree of scratch healing are affected by pH, temperature, and the DMAEMA content.

Interaction of Zwitterionic and Ionic Monomers with Graphene Surfaces.

Measurement of the interaction force between two materials provides important information on various properties, such as adsorption, binding, or compatibility for coatings, adhesion, and composites. The interaction forces of zwitterionic and ionic monomers with graphite platelets (G) and reduced graphene oxide (rGO) surfaces were systematically investigated by atomic force microscopy (AFM) in air and water. The monomers examined were 2-(methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate (MPC), [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBE), [2-(acryloyloxy)ethyl]trimethylammonium chloride (ATC), and 2-methyl-2-propene-1-sulfonic acid sodium (MSS). The AFM studies revealed that MSS and SBE monomers with sulfonate units have stronger interaction forces with G surface in air and that MPC and ATC monomers with quaternary ammonium units have higher interaction forces in water. In the case of rGO surface, the monomers with quaternary ammonium units showed stronger interactions regardless of the medium. These interactions could be rationalized by the interaction mechanism between the monomers with graphene surfaces, such as cation-π for MPC and ATC and anion-π for MSS and SBE. Overall, cation-π interactions were effective in water, whereas anion-π interactions are effective in air with G surface. The adhesion values of MPC, SBE, ATC, and MSS on rGO were lower than the values measured on G surface. Among the monomers, MPC showed the highest dispersibility for aqueous graphene dispersions. Further, the adsorption of MPC on G and rGO surfaces was verified by high-resolution transmission electron microscopy and X-ray diffraction patterns.

A study on amphiphilic fluorinated block copolymer in graphite exfoliation using supercritical CO2 for stable graphene dispersion.

In this study, poly(2,2,2-trifluoroethyl methacrylate)-block-poly(4-vinylpyridine) (PTFEMA-b-PVP) was synthesized by stepwise reversible addition-fragmentation chain transfer (RAFT) polymerization for the preparation of graphene by the exfoliation of graphite nanoplatelets (GPs) in supercritical CO2 (SCCO2). Two different block copolymers (low and high molecular weights) were prepared with the same block ratio and used at different concentrations in the SCCO2 process. The amount of PTFEMA-b-PVP adsorbed on the GPs and the electrical conductivity of the SCCO2-treated GP samples were evaluated using thermogravimetric analysis (TGA) and four-point probe method, respectively. All GP samples treated with SCCO2 were then dispersed in methanol and the dispersion stability was investigated using online turbidity measurements. The concentration and morphology of few-layer graphene stabilized with PTFEMA-b-PVP in the supernatant solution were investigated by gravimetry, scanning electron microscopy, and Raman spectroscopy. Destabilization study of the graphene dispersions revealed that the longer block copolymer exhibited better affinity for graphene, resulting in a higher yield of stable graphene with minimal defects.

High-concentration graphene dispersion stabilized by block copolymers in ethanol.

This article describes a comprehensive study for the preparation of graphene dispersions by liquid-phase exfoliation using amphiphilic diblock copolymers; poly(ethylene oxide)-block-poly(styrene) (PEO-b-PS), poly(ethylene oxide)-block-poly(4-vinylpyridine) (PEO-b-PVP), and poly(ethylene oxide)-block-poly(pyrenemethyl methacrylate) (PEO-b-PPy) with similar block lengths. Block copolymers were prepared from PEO using the Steglich coupling reaction followed by reversible addition-fragmentation chain transfer (RAFT) polymerization. Graphite platelets (G) and reduced graphene oxide (rGO) were used as graphene sources. The dispersion stability of graphene in ethanol was comparatively investigated by on-line turbidity, and the graphene concentration in the dispersions was determined gravimetrically. Our results revealed that the graphene dispersions with PEO-b-PVP were much more stable and included graphene with fewer defects than that with PEO-b-PS or PEO-b-PPy, as confirmed by turbidity and Raman analyses. Gravimetry confirmed that graphene concentrations up to 1.7 and 1.8mg/mL could be obtained from G and rGO dispersions, respectively, using PEO-b-PVP after one week. Distinctions in adhesion forces of PS, VP, PPy block units with graphene surface and the variation in solubility of the block copolymers in ethanol medium significantly affected the stability of the graphene dispersion.

Stimuli-triggered Formation of Polymersomes from W/O/W Multiple Double Emulsion Droplets Containing Poly(styrene)-block-poly(N-isopropylacrylamide-co-spironaphthoxazine methacryloyl).

We report stimuli-triggered fabrication of polymersomes from water-in-oil-in-water (W/O/W) multiple double emulsion droplets and the dual-stimuli (temperature and UV) responsive behavior of corresponding polymersomes. The polymersome comprises Tween20, cholesterol, and poly(styrene)-block-poly(N-isopropylacrylamide-co-spironaphthoxazine methacryloyl), i.e., PS-b-P(NIPAAm-co-SPO), synthesized by stepwise reversible addition-fragmentation chain transfer (RAFT) polymerization. Amphiphilic PS-b-P(NIPAAm-co-SPO) copolymer forms micelles in water above the critical micelle concentration (CMC) of 0.7 g/L at 23 °C. The micelles show a temperature-driven aggregation among the micelles above 30.6 °C, confirmed by a decrease in UV-vis transmittance. The micelles also show a color change without colloidal instability under 365 nm UV at room temperature. PS-b-P(NIPAAm-co-SPO) plays not only a role of the polymeric surfactant in the preparation of W/O/W multiple double emulsions but also an important role in the stimuli-triggered transformation from multi- to single-core double emulsion droplets under heat and UV light irradiation. It was found that the morphological transformation of W/O/W multiple double emulsions by UV irradiation was much faster than temperature change. Dual-responsive polymersomes were simply prepared after solvent removal and they exhibit stable and reversible size and color variations under temperature and UV-visible changes, respectively.

PVP-b-PEO block copolymers for stable aqueous and ethanolic graphene dispersions.

The ability to disperse pristine (unfunctionalized) graphene is important for various applications, coating, nanocomposites, and energy related systems. Herein we report that amphiphilic copolymers of poly(4-vinyl pyridine)-block-poly(ethylene oxide) (PVP-b-PEO) are able to disperse graphene with high concentrations about 2.6mg/mL via sonication and centrifugation. Ethanolic and aqueous highly-ordered pyrolytic graphite (HOPG) dispersions with block copolymers were prepared and they were compared with the dispersions stabilized by P-123 Pluronic® (P123) and poly(styrene)-block-poly(ethylene oxide) (PS-b-PEO) synthesized. Transmission electron microscopy, scanning electron microscopy, atomic force microscopy, X-ray diffraction, Raman and UV-visible spectroscopic studies confirmed that PVP-b-PEO block copolymers are better stabilizers for HOPG graphene than P123 and PS-b-PEO. X-ray photoelectron spectroscopy and force-distance (F-d) curve analyses revealed that the nitrogen of vinyl pyridine plays a vital role in better attractive interaction with surface of graphene sheet. Thermogravimetric analysis showed that larger amount of PVP-b-PEO was adsorbed onto graphene with longer poly(4-vinyl pyridine) (PVP) block length and in aqueous medium, respectively, and which was consistent with electrical conductivity decreases. This study presents the dispersion efficiency of graphene using PVP-b-PEO varies substantially depending on the lengths of their hydrophobic (PVP) domains.

Amphiphilic Fluorinated Block Copolymer Synthesized by RAFT Polymerization for Graphene Dispersions.

Despite the superior properties of graphene, the strong π⁻π interactions among pristine graphenes yielding massive aggregation impede industrial applications. For non-covalent functionalization of highly-ordered pyrolytic graphite (HOPG), poly(2,2,2-trifluoroethyl methacrylate)-block-poly(4-vinyl pyridine) (PTFEMA-b-PVP) block copolymers were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization and used as polymeric dispersants in liquid phase exfoliation assisted by ultrasonication. The HOPG graphene concentrations were found to be 0.260⁻0.385 mg/mL in methanolic graphene dispersions stabilized with 10 wt % (relative to HOPG) PTFEMA-b-PVP block copolymers after one week. Raman and atomic force microscopy (AFM) analyses revealed that HOPG could not be completely exfoliated during the sonication. However, on-line turbidity results confirmed that the dispersion stability of HOPG in the presence of the block copolymer lasted for one week and that longer PTFEMA and PVP blocks led to better graphene dispersibility. Force⁻distance (F⁻d) analyses of AFM showed that PVP block is a good graphene-philic block while PTFEMA is methanol-philic.

Near-Room Temperature Synthesis of Core/Shell-Structured Quantum Dots.

Core/shell-structured quantum dots (QDs) are considered as important active materials for optoelectronic devices. There have been a lot of synthesis procedures developed so far. Real epitaxial growth of shell layer, however, has not been reported yet. Here, a simple method for the synthesis of CdSe/CdS core/shell QDs is presented. Epitaxial growth of CdS shell on CdSe core is carried out by near room temperature successive ion layer adsorption and reaction (RT-SILAR). Our method for shell formation is conducted at room temperature, which facilitates the separation of resulting products from shell growth solution. After full coverage with one monolayer (ML) of CdS on CdSe QDs surface, photoluminescence (PL) quantum yield (QY) reaches up to 60%. Produced CdSe/CdS QDs have an elongated morphology, implying that CdS layers are formed in an epitaxial manner without etching or deteriorating CdSe QDs surface. We believe that our synthesis method for core/shell-structured QDs would be an ideal model for practical implication of QDs as well as fundamental studies.

Facile Synthesis of Monodispersed Cubic and Spherical Calcite Nanoparticles in the Presence of Cetyltrimethylammonium Bromide.

We report the synthesis of monodisperse calcium carbonate (CaCO3) (nano)particles having either a cubic or spherical structure by reacting calcium nitrate with either sodium carbonate or citric acid, respectively, in the presence of cetyltrimethylammonium bromide (CTAB) via the sonication method. For comparison, CaCO3 (nano)particles were synthesized by the same method in the absence of CTAB and also via the standard hydrothermal method using CTAB. The synthesized CaCO3 (nano)particles were analyzed by various physico-chemical characterization techniques such as X-ray diffraction (XRD), Fourier transform infra-red spectroscopy, thermogravimetric analysis, and scanning electron microscopy with energy-dispersive spectrometer. It was found that the CaCO3 (nano)particles were highly pure with high crystallinity and exhibited the calcite polymorph phase as revealed by the XRD analysis. In addition, the analytical results showed that the (nano)particles prepared in the presence of CTAB by the sonication method had high structural ordering and no agglomeration as compared to the (nano)particles prepared by the hydrothermal method. Therefore, our sonication method is a new way to prepare shape-controlled CaCO3 (nano)particles under mild reaction conditions.

Fluorescent Molecular Rotor-in-Paraffin Waxes for Thermometry and Biometric Identification.

Novel thermoresponsive sensor systems consisting of a molecular rotor (MR) and paraffin wax (PW) were developed for various thermometric and biometric identification applications. Polydiphenylacetylenes (PDPAs) coupled with long alkyl chains were used as MRs, and PWs of hydrocarbons having 16-20 carbons were utilized as phase-change materials. The PDPAs were successfully dissolved in the molten PWs and did not act as an impurity that prevents phase transition of the PWs. These PDPA-in-PW hybrids had almost the same enthalpies and phase-transition temperatures as the corresponding pure PWs. The hybrids exhibited highly reversible fluorescence (FL) changes at the critical temperatures during phase transition of the PWs. These hybrids were impregnated into common filter paper in the molten state by absorption or were encapsulated into urea resin to enhance their mechanical integrity and cyclic stability during repeated use. The wax papers could be utilized in highly advanced applications including FL image writing/erasing, an array-type thermo-indicator, and fingerprint/palmprint identification. The present findings should facilitate the development of novel fluorescent sensor systems for biometric identification and are potentially applicable for biological and biomedical thermometry.