Transparent Poly Research Articles

Biocompatible, Transparent, and High-Areal-Coverage Kirigami PEDOT:PSS Electrodes for Electrooculography-Derived Human-Machine Interactions.

Electronic skin sensors prepared from biocompatible and biodegradable polymeric materials significantly benefit the research and scientific community, as they can reduce the amount of effort required for e-waste management by deteriorating or dissolving into the environment without pollution. Herein, we report the use of polylactic acid (PLA)-a promising plant-based bioplastic-and highly transparent, conductive, biocompatible, and flexible poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) materials to fabricate kirigami-based stretchable on-skin electrophysiological sensors via a low-cost and rapid laser cutting technique. The sensor stack with PEDOT:PSS and PLA layers exhibited high transparency (>85%) in the wavelength range of 400-700 nm and stay attached conformally to the skin for several hours without adverse effects. The Y-shaped kirigami motifs inspired by the microcracked gold film endowed the sensor with attributes such as high areal coverage (∼85%), breathability (∼40 g m-2 h-1), and multidirectional stretchability. The sensor has been successfully applied to monitor electrophysiological signals and demonstrated with an eye movement-supported communication interface for controlling home electronic appliances.

Dense Hydrogen-Bonding Network Boosts Ionic Conductive Hydrogels with Extremely High Toughness, Rapid Self-Recovery, and Autonomous Adhesion for Human-Motion Detection.

The construction of ionic conductive hydrogels with high transparency, excellent mechanical robustness, high toughness, and rapid self-recovery is highly desired yet challenging. Herein, a hydrogen-bonding network densification strategy is presented for preparing a highly stretchable and transparent poly(ionic liquid) hydrogel (PAM-r-MVIC) from the perspective of random copolymerization of 1-methyl-3-(4-vinylbenzyl) imidazolium chloride and acrylamide in water. Ascribing to the formation of a dense hydrogen-bonding network, the resultant PAM-r-MVIC exhibited an intrinsically high stretchability (>1000%) and compressibility (90%), fast self-recovery with high toughness (2950 kJ m−3), and excellent fatigue resistance with no deviation for 100 cycles. Dissipative particle dynamics simulations revealed that the orientation of hydrogen bonds along the stretching direction boosted mechanical strength and toughness, which were further proved by the restriction of molecular chain movements ascribing to the formation of a dense hydrogen-bonding network from mean square displacement calculations. Combining with high ionic conductivity over a wide temperature range and autonomous adhesion on various surfaces with tailored adhesive strength, the PAM-r-MVIC can readily work as a highly stretchable and healable ionic conductor for a capacitive/resistive bimodal sensor with self-adhesion, high sensitivity, excellent linearity, and great durability. This study might provide a new path of designing and fabricating ionic conductive hydrogels with high mechanical elasticity, high toughness, and excellent fatigue resilience for skin-inspired ionic sensors in detecting complex human motions.

The preparation and mechanism of permanently flame retardancy, antistatic, good toughness and high transparent poly(methyl methacrylate)

AbstractA novel kind of poly(methyl methacrylate) (PMMA) copolymer, P(MMA‐co‐HEMAP), with permanently flame retardancy, antistatic, good toughness and high transparency properties was synthesized through the addition of 2‐hydroxyethyl 2‐methyl‐2‐propenoate phosphated (HEMAP), which was chosen as the flame retardant and the antistatic agent. The included phosphine group is necessary for flame retardancy and acryl phosphate group that could absorb water to realize antistatic property while having good compatibility with methyl methacrylate (MMA). Different from the significantly reduction of transparency happened in traditional modification method, the optical property of the P(MMA‐co‐HEMAP) copolymers keeps almost unchanged comparing to that of neat PMMA in the visible range. And the peak Heat Release Rate (pHRR) and Total Heat Release (THR) of the 30PhrHEMAP were significantly reduced by 40% and 36.2%, respectively, while the Limiting Oxygen Index (LOI) increased from 17.8 to 24.5%. The HEMAP decomposed during the combustion process to form polyphosphoric acid, which promotes dehydration and carbonization of polymer matrix to form a cross‐linking yield char and it would reduce fire spread. Besides, the surface resistance of the 30PhrHEMAP could be reduced down to 1010Ω which could achieve antistatic effect. The hydrophilic groups, acryl phosphate on the surface of copolymer was able to absorb moisture from the air for antistatic effects. Furthermore, the toughness of the copolymers was also greatly improved compared to that of neat PMMA. This research provided a method for preparing PMMA copolymer and the resultant P(MMA‐co‐HEMAP) copolymers can significantly improve the three properties simultaneously for the first time.

A self-powered skin-patch electrochromic biosensor

One of the limitations of many skin-patch wearable sensors today is their dependence on silicon-based electronics, increasing their complexity and unit cost. Self-powered sensors, in combination with electrochromic materials, allow simplifying the construction of these devices, leading to powerful analytical tools that remove the need for external detection systems. This work describes the construction, by screen-printing, of a self-powered electrochromic device that can be adapted for the determination of metabolites in sweat by the naked eye in the form of a 3 × 15 mm colour bar. The device comprises a lactate oxidase and osmium-polymer –based anode connected to a coplanar 3 × 15 mm Prussian Blue, PB, cathode printed over a transparent poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, PEDOT:PSS electrode. An ion-gel composed of Poly(vinylidene fluoride-co-hexafluoropropylene), PVDF-co-HFP, a gelling agent, and ionic liquid 1-Ethyl-3-methylimidazolium trifluoromethanesulfonate, EMIM-Tf, effectively separates the cathode display from the biosensing anode, protecting it from the sample. Despite its cathodic electrochromism, the PEDOT:PSS has a transmission above 90% and does not mask the Prussian Blue colour change because the cathode does not operate below 0 V vs Ag/AgCl at any time. The sensor displays lactate concentrations in the range of 0–10 mM over the length of the electrochromic display, which has a contrast ratio of 1.43. Although full response takes up to 24 min, 85% of the colour change is displayed within 10 min.

Reversible stimuli-responsive luminescent polymers with adaptable mechanical properties based on europium-malonate complex

Luminescent polymers that are dynamic in reversible response to external stimuli are of profound interest for the development of advanced optical devices and sensors. Here, we fabricate a new class of transparent poly(urea-urethane) containing malonate moieties through simple one-pot polycondensation. When blended with different amounts of europium ions, the resultant polymer complexes show a tunable broad spectrum of mechanical properties with their modulus adjusted from 5 MPa to 60 MPa. In the meantime, the incorporation of europium endows the metallo-supramolecular polymers with fluorescence that can reversibly respond to organic solvents like acetylacetone/triethylamine as well as temperature due to the formation of dynamic europium-malonate coordination. Given that each optical or sensor field has its own requirement for materials’ mechanical properties, we believe therefore our designed stimuli-responsive luminescent polymers with adaptable mechanical properties show great potential in the applications.

Flexible ZnO Nanoparticle-Poly(methyl methacrylate) Hybrid Films and Their Ultraviolet Shielding Behaviors

Flexible hybrid films are finding increasing applications in functional devices. In this work, transparent ZnO nanoparticle and poly(methyl methacrylate) (PMMA) hybrid films are made for ultraviolet (UV) shielding with significantly higher ZnO contents than what has been reported. The tensile strength increases with the ZnO nanoparticle volume percent, from ~ 10 MPa for the pure PMMA samples to ~ 24 MPa for the 20 vol.% ZnO samples, a 150% increase. The elongation at break also increases with the ZnO content increase until 10 vol.% (a 67% increase), after which the elongation at break stays constant. All the ZnO-PMMA films show UV absorption at ~ 365 nm wavelength, with an increasing degree for higher ZnO content samples and a corresponding light transmittance decrease at longer wavelengths. Long-term UV irradiation leads to a reduction in tensile strength and elongation at break, along with lower UV shielding performance. This work proposes that the optimal ZnO content is 5–10 vol.% for the overall UV shielding performance while maintaining good mechanical properties.

Electrical, and Magnetic Characteristics of Homo- and Hetero-Bimetallic Macromolecular Complexes with π-Conjugated Imine-oxime Backbone

Seven homo- and hetero-bimetallic macromolecular complexes (BMCs) were prepared via an in-situ multi-step complexation reaction of CuII, NiII and FeIII metal centers with imine- oxime π-conjugated ditropic spacer (1,4-phenylene-bis(2,3-butanedeimineoxime, L2−). The structures of the obtained [M-L2-M]x, [M`-L2-M`]x, [M-L2-M`]x and their μ-oxo-[M-L2-Fe]x BMCs (M = CuII, NiII; M` = FeIII) were elucidated using different spectroscopic (UV–Vis, FT-IR), powder X-ray diffraction (p-XRD) and microscopic (SEM) techniques. The SEM images indicate that the obtained BMCs exhibit nano/micro globular and rod-like textures. The electrical and magnetic characteristics of the obtained BMCs can be described as magneto-semiconducting materials. The structural, electrical, and magnetic properties inherited in the prepared regime demonstrate that the examined semiconducting π-spacer has clear ability to semi-conduct electron transport and delocalize spin leading to antiferromagnetic coupling, thus offering a favorable magnetic exchange pathway between the paramagnetic metal sites. However, ferromagnetic enhancement is observed in the μ-oxo-[M-L2-Fe]x BMCs where the μ-oxo-bridge overplays the role of the π-spacer. A magnetic responsive thin film was conveniently obtained by solvent casting of the μ-oxo-[Ni-L2-Fe]x BMC in a transparent poly(methamethylacrylate) matrix.

Novel glucose-responsive of the transparent nanofiber hydrogel patches as a wearable biosensor via electrospinning

Micro- and nanofiber (NF) hydrogels fabricated by electrospinning to typically exhibit outstanding high porosity and specific surface area under hydrated conditions. However, the high crystallinity of NFs limits the achievement of transparency via electrospinning. Transparent poly(vinyl alcohol)/β-cyclodextrin polymer NF hydrogels contacted with reverse iontophoresis electrodes were prepared for the development of a non-invasive continuous monitoring biosensor platform of interstitial fluid glucose levels reaching ~ 1 mM. We designed the PVA/BTCA/β-CD/GOx/AuNPs NF hydrogels, which exhibit flexibility, biocompatibility, excellent absorptivity (DI water: 21.9 ± 1.9, PBS: 41.91 ± 3.4), good mechanical properties (dried: 12.1 MPa, wetted: 5.33 MPa), and high enzyme activity of 76.3%. Owing to the unique features of PVA/β-CD/GOx containing AuNPs NF hydrogels, such as high permeability to bio-substrates and rapid electron transfer, our biosensors demonstrate excellent sensing performance with a wide linear range, high sensitivity(47.2 μA mM−1), low sensing limit (0.01 mM), and rapid response time (< 15 s). The results indicate that the PVA/BTCA/β-CD/GOx/AuNPs NF hydrogel patch sensor can measure the glucose concentration in human serum and holds massive potential for future clinical applications.

Nanofibrillated Bacterial Cellulose Modified with (3-Aminopropyl)trimethoxysilane under Aqueous Conditions: Applications to Poly(methyl methacrylate) Fiber-Reinforced Nanocomposites.

The development of eco-friendly fiber-reinforced composite resins is an important objective from an environmental perspective, and nanofibrillated bacterial cellulose (NFBC), with extremely long high-aspect-ratio fibers, is a filler material with high potential for use in such composite resins. In this study, we investigated chemical modification of the surfaces of NFBC fibers by coupling with (3-aminopropyl)trimethoxysilane and fabricated nanocomposite materials using the prepared surface-modified NFBC. The product prepared by the one-pot reaction of (3-aminopropyl)trimethoxysilane with NFBC microfibrils dispersed in aqueous acid retained the same nanofibril structure as the intact NFBC. The degree of molar substitution and the silicon states on the surface of the product depended on the NFBC/(3-aminopropyl)trimethoxysilane ratio. The thermal analysis revealed that the thermal degradation temperature of the products increases with an increase of degree of molar substitution. Highly transparent (78–89% at 600 nm) poly(methyl methacrylate)-based nanocomposites were prepared by solvent casting; the nanocomposite containing 1.0 wt % (3-aminopropyl)trimethoxysilylated NFBC was only 8% less transparent than neat poly(methyl methacrylate) at 600 nm. In addition, the tensile strength of the nanocomposite was more than twice that of neat poly(methyl methacrylate) when 1 wt % of the surface-modified NFBC was added. The surface-modified NFBC is expected to be a reinforcing nanofiber material that imparts excellent physical properties to fiber-reinforced resins.

Selective Plasma Etching of Polymer-Metal Mesh Foil in Large-Area Hydrogen Atmospheric Pressure Plasma

We present a novel method of surface processing of complex polymer-metal composite substrates. Atmospheric-pressure plasma etching in pure H2, N2, H2/N2 and air plasmas was used to fabricate flexible transparent composite poly(methyl methacrylate) (PMMA)-based polymer film/Ag-coated Cu metal wire mesh substrates with conductive connection sites by the selective removal of the thin (~10–100 nm) surface PMMA layer. To mimic large-area roll-to-roll processing, we used an advanced alumina-based concavely curved electrode generating a thin and high-power density cold plasma layer by the diffuse coplanar surface barrier discharge. A short 1 s exposure to pure hydrogen plasma, led to successful highly-selective etching of the surface PMMA film without any destruction of the Ag-coated Cu metal wires embedded in the PMMA polymer. On the other hand, the use of ambient air, pure nitrogen and H2/N2 plasmas resulted in undesired degradation both of the polymer and the metal wires surfaces. Since it was found that the etching efficiency strongly depends on the process parameters, such as treatment time and the distance from the electrode surface, we studied the effect and performance of these parameters.

Mechanically strong waterborne poly(urethane‐urea) films and nanocomposite films

AbstractA series of transparent waterborne poly(urethane‐urea) (PUU) films and nanocomposite films were prepared using isocyanate excess (5–50 mol% excess relative to the hydroxyl groups) and omitting the common chain‐extension step in the acetone method of the preparation. The surplus isocyanate groups were converted into urea and eventually biuret linkages via the reaction with water during the last phase inversion step. Nanocomposites were prepared by the direct mixing of the PUU nanoparticles in water with aqueous nanosilica or montmorillonite powder followed by slow water evaporation. Variable urea/biuret content is responsible for substantially different tensile properties; the neat organic films show elongation‐at‐break values of 100%–1120%, tensile strength values of 0.07–22.1 MPa, and energy‐to‐break of 0.1–85 mJ × mm−3. All of the materials can be potentially used as soft‐to‐hard topcoats, depending on the specific demands. The most promising materials are films prepared at 30 and particularly 40 mol% isocyanate excess.

Partially Bio-based Colorless and Transparent Poly(amide-imide)s Derived from 2,5-Furandicarboxylic Acid

Two series of partially bio-based colorless and transparent poly(amide-imide)s (CPAIs) derived from bio-based 2,5-furandicarboxylic acid (FDCA) were synthesized by a two-step condensation reaction. 4,4′-(Hexafluoroisopropylidene) diphthalic anhydride, 2,2′-bis(trifluoromethyl)benzidine, and terephthaloyl chloride were used as basic monomers for the CPAIs. The highest bio-based content of the CPAIs was 11.32%. With increasing contents of FDCA units in the CPAIs, their glass transition temperatures and mechanical properties decreased gradually due to the decreased intermolecular interactions, whereas their transparency and yellowness indices were not significantly affected. The overall properties of the CPAIs are believed to be suitable for applications in optoelectronic device industries.

Light management using CsPbBr3 colloidal quantum dots for luminescent solar concentrators

CsPbBr3 colloidal quantum dots have been synthesized by hot-injection method showing spherical shape with an average diameter of ∼10.5 nm. UV–vis absorption of CsPbBr3 colloidal quantum dots shows a broad spectrum with an optical bandgap of ∼2.3682 eV. The steady-state photoluminescence measurement reveals a narrow emission peak at 2.352 eV with full-width at half maximum of 0.113 eV. Absolute photoluminescence quantum yield of colloidal quantum dots dispersed in poly(methyl methacrylate) was found to be 60 ± 1%. The time-resolved photoluminescence data recorded at 266 nm excitation were well fitted using a mono-exponential curve with a decay time of 25.36 (5) ns. A luminescent solar concentrator was fabricated using colloidal quantum dots in transparent poly(methyl methacrylate) polymer uniformly coated over glass substrate that shows an external optical conversion efficiency of ∼5.4% under one sun illumination. The experimental results presented in this manuscript reveals that luminescent solar concentrator prepared using colloidal CsPbBr3 quantum dots shows absorption in wide spectral range, high absorption coefficient, high photoluminescence quantum yield, high external optical conversion efficiency, and good photostability, thermal stability and long-term stability under ambient conditions and therefore are in many ways superior to the other luminescent materials explored for LSC devices.

A facile preparation method for anti-freezing, tough, transparent, conductive and thermoplastic poly(vinyl alcohol)/sodium alginate/glycerol organohydrogel electrolyte

Facile preparation of organohydrogel electrolyte integrated with good anti-freezing property, toughness, transparency, conductivity and thermoplasticity is important and still remains challenging. Novel conductive and tough poly(vinyl alcohol)/sodium alginate/glycerol (PVA/SA/Gly) composite organohydrogel electrolytes were obtained by a simple method in this paper. PVA and SA was firstly dissolved in a mixed solution of distilled water and glycerol and the PVA/SA/Gly organohydrogel was obtained by the freezing-thawing process, then PVA/SA/Gly organohydrogel was immersed into the saturated NaCl aqueous solution. During the soaking process NaCl would enter into the PVA/SA/Gly organohydrogel to increase the gel strength and conductivity. The PVA/SA/Gly organohydrogel electrolytes performed the high toughness with the tensile strength and elongation at break of 1.43 MPa and 558%, respectively. Moreover, the PVA/SA/Gly organohydrogel electrolytes behaved high transparency, anti-freezing property, conductivity and thermoplasticity due to the incorporation of glycerol. This paper provides a new preparation method for the high-performance organohydrogel electrolyte.

Implementation of Flexible Embedded Nanowire Electrodes in Organic Light‐Emitting Diodes

The implementation of silver nanowires (NWs) as flexible transparent electrodes (FTEs) in solution‐processed organic light‐emitting diodes (OLEDs) still faces two major challenges: the high roughness of NW films and heat sensitivity of the most commonly used transparent substrate poly(ethylene terephthalate) (PET). A solution‐based, roll‐to‐roll, and sheet‐to‐sheet scalable process to create indium tin oxide (ITO)‐free FTEs is reported. This FTE is realized by spraying NWs on PET, without the necessity of postdeposition heat treatment. To overcome the roughness limitation, NW films are reverse transfer embedded on another PET substrate. As a result, the FTE shows a low roughness, as well as high mechanical, thermal, organic‐solvent, and plasma stability. This developed FTE shows comparable transmittance with ITO but lower sheet resistance and higher mechanical stability. The FTE is implemented in a solution‐processed OLED with PDY‐132 (Super Yellow) as the emissive layer. In contrast to many other works in this field, a ZnO‐nanoparticle electron‐injection layer is used on the NWs instead of poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) or other organic hole injectors. The use of ZnO nanoparticles instead of organic layers yields many advantages in terms of process and device stability. The resulting devices show greater flexibility, conductivity, and luminance than PET/ITO reference devices, while having the same power efficacy.

Physical and Morphological Properties of Tough and Transparent PMMA-Based Blends Modified with Polyrotaxane.

We prepared several novel, tough, and transparent poly(methyl methacrylate) (PMMA) blends modified with polyrotaxane (PR) and evaluated their physical properties and morphologies. A styrene/methyl methacrylate/maleic anhydride (SMM) copolymer that was miscible with PMMA was used as a reactive compatibilizer to enhance interfacial adhesion between the matrix resin and PR. A twin-screw melt-kneading extruder was used to prepare the polymer blends, and their thermal, morphological, optical, and mechanical properties were characterized. The effect of PR was evaluated by analyzing the deformation behavior of the blends in notched three-point bending tests. A PMMA/PR blend was immiscible and appeared to be a phase-separated system. However, when SMM was added as a compatibilizer, PR was partially miscible and did not form observable PR domains. Viscosity increased, and the glass transition temperature (Tg) of the matrix resin decreased. The surface hardness of a PMMA/SMM/PR blend was only 15% lower than that of PMMA. A 2.5-fold increase in elongation at breakage was observed, and the tensile strength and Young’s modulus decreased by 16%. The PMMA/SMM/PR blend had 60% higher impact strength than PMMA in notched Charpy impact test, which indicated that the balance between stiffness and ductility was excellent. PR served as a starting point for plastic deformation in the PMMA/SMM/PR blend. We found that PR could initiate void and craze formation, even when it was finely dispersed at the nanoscale. The stress-relieving effect of PR was effective when it was tightly bound at the interfaces. The materials obtained in this study are expected to make a significant contribution to reducing the weight of the products by applying them as a replacement for glass.

Measuring Crack Growth and Rise in Temperature around a Cylindrical Defect in Explosive Simulants under Low‐Pressure and Long‐Pulse Loadings

AbstractLow‐pressure and long‐pulse loadings are critical loading modes in research on non‐shock ignition. Under such loadings, viscoplastic deformation, fracture, and a local rise in temperature may occur around inherent defects in condensed explosives to cause non‐shock ignition. In this study, transparent poly(methyl methacrylate) was chosen as an explosive simulant to elucidate the processes of crack growth, pore collapse, and rise in temperature at a cylindrical defect by using a set of modified split Hopkinson pressure bars. A recently developed optical temperature‐sensing technique that uses the multiphonon‐assisted anti‐Stokes‐to‐Stokes fluorescence intensity ratio was used to monitor the rise in temperature in the cracks. By combining the work here with our previous research, two significant conclusions are arrived at: 1) Around the cylindrical defect, the opening‐mode crack initiated earlier than the shearing‐mode crack did but its rate of propagation was considerably lower. Moreover, the smaller the cylindrical defect was, the lower was the rate of propagation of the cracks. 2) The rise in temperature in shearing‐mode cracks was higher than that of the opening‐mode cracks. It can be inferred that the local rise in temperature caused by shearing was the major factor leading to the non‐shock ignition of condensed explosives

A synthesized semi‐aromatic copolyamaide through synergy of three different kinds of monomers: Toward high transparency, excellent heat resistance and melt flowing property

AbstractTo fabricate the low‐cost transparent polyamide with high heat resistance and good melt flowing property simultaneously is a huge challenge in many high‐end fields due to the contradiction between these two properties. In order to balance this contradiction, in this paper, by using isophthalic acid (IPA, aromatic monomer), 4,4′‐methylenebis(cyclohexylamine) (PACM, alicyclic monomer) as rigid stereoscopic monomers, 1,6‐hexanediamine (HMD, aliphatic monomer) as the flexible monomer, a series of transparent poly(hexamethylene isophthalamide/poly(m‐benzoyl4,4′‐methylenebis(cyclohexylamine)) (PA6I/PACMI) with rigid and stereoscopic structure (corresponding to the large distance between adjacent molecular chains) were successfully synthesized. The results indicated that the newly synthesized PA6I/PACMI copolymer has an intrinsically amorphous structure and high optical transparency, which could reach as high as 90%. Furthermore, the highest glass transition temperature (Tg) of the copolymer is over 153.9°C, at the same time, the copolymer also possesses excellent melt flowing property, which can be melt processed easily. Therefore, the newly synthesized copolymer has great advantages in many fields, and it can also shed light on the design and fabrication of high‐performance materials.

Rapid Fabrication of a Flexible and Transparent Ag Nanocubes@PDMS Film as a SERS Substrate with High Performance.

Flexible and transparent surface-enhanced Raman scattering (SERS) substrates have long been sought-after for nondestructive detection of analytes on nonplanar surfaces, but there is still a lack of one convenient and robust way to fabricate such SERS substrates rapidly. Herein, we demonstrate the fabrication of a high-performance SERS substrate consisting of plasmonic Ag nanocube (Ag NC) arrays anchored onto a flexible transparent poly(dimethylsiloxane) (PDMS) membrane. Through a simple organic/water interfacial self-assembly method, arrays of presynthesized Ag NCs are obtained and directly retrieved onto the PDMS membrane without the aid of rigid substrates (e.g., Si wafers or glass slides). The plasmonic Ag NC arrays can produce strong electromagnetic enhancement, achieving high SERS enhancement factor (∼3.43 × 106) and ideal detection capability for methylene blue (MB) and Rhodamine 6G (R6G) at respective trace amounts of 10-10 and 10-9 M. Moreover, without the need to transfer from substrate to substrate, the regular Ag NC arrays are kept intact, thereby yielding a good reproducibility (RSD ∼12%). We demonstrate further that our as-fabricated SERS substrate displays ideal selectivity toward different kinds of analyte molecules (R6G, crystal violet (CV), and MB) based on principal component analysis. The PDMS membrane owns excellent transparency and flexibility; thus, the substrate enables the conformal contact with nonplanar surfaces and allows the penetration of a laser to reach the analytes from the reverse side of the substrate. This thus facilitates in situ SERS detection of trace residual crystal violet on fish skin, with limit of detection (LOD) reaching 0.6 ppm. This fabrication method reported here is economical and easily implemented. The robust Ag NCs@PDMS could be readily prepared and stored to meet diverse SERS sensing applications, especially for in situ detection of analytes on irregular nonplanar surfaces.

Thermostable and Redispersible Cellulose Nanocrystals with Thixotropic Gelation Behavior by a Facile Desulfation Process

As a ecofriendly and promising nanomaterial, cellulose nanocrystals (CNCs) have attracted significant interest. However, the intrinsic sulfate-modified surface and self-aggregation behavior of the most common acid-hydrolyzed CNCs with sulfuric acid lead to the low thermostability and poor redispersion of solid-state CNCs materials, which limit their practical applications. In this work, we propose a simple and effective strategy to not only remove the sulfates in CNCs but also resuscitate their dispersibility by a facile post-treatment process, including an acid-triggering gelation, solvent exchange with ethanol, and supercritical CO2 drying. The resultant CNC powder exhibits a high thermostability, much higher than that of the common acid-hydrolyzed CNCs and similar to that of the pristine cellulose. Moreover, the CNC powder can be readily redispersed in various solvents by a short ultrasonic treatment. Subsequently, as the CNC concentration increases, CNC gels spontaneously form and exhibit thixotropic behaviors. Taking advantage of these characteristics of the above desulfated CNC powder, we fabricated a CNC/Ag nanoparticle gel, magnetic CNC/Fe3O4 nanoparticle gel, pressure-sensitive polymer/CNC composite gel, and colorless and transparent poly(lactic acid)/CNC thermoplastic films. Therefore, the highly thermostable, redispersible, and easy-to-gel CNC powder has a huge potential as a building block for various stable, well-dispersed, and functional nanocomposite materials.