Recently, the development of directly writable techniques for depositing functional materials on solid substrates has received great attention. These pen‐on‐paper approaches enable generation of ...diverse patterned images on solid substrates in a flexible, easy handling, and inexpensive manner. Herein, the development of a directly writable conjugated polymer is described. Mechanically, drawable colorimetric polydiacetylene (PDA)–wax composites are readily fabricated by using a simple mixing‐molding method. Images are mechanically drawn on a paper substrate using the PDA–wax composites, display thermochromism, and mechanothermochromism. The thermochromic transition temperature is dependent on the melting point of the wax and, as a result, can be precisely controlled by the type of wax used. Optical microscopic analysis shows that formation of the DA–wax composite involves movement of wax molecules into a single diacetylene (DA) crystal. This process results in growth of the crystal. Importantly, the PDA crystal, obtained after UV light irradiation, undergoes significant shrinkage upon heating because of the release of monomers and the embedded wax molecules from the crystal. The release of these molecules creates void in the PDA supramolecules, allowing the PDA chains to undergo C–C bond rotation and hence the blue‐to‐red color transition.
Hand‐writable colorimetric polydiacetylene (PDA)–wax composite sensors are readily fabricated by using a simple mixing‐molding polymerization method. Images, mechanically drawn using these PDA–wax composites on a paper substrate, display thermochromism and mechnothermochromism. The thermochromic transition temperature can be precisely controlled by the melting point of the wax used.
High sensitivity and high stretchability are two conflicting characteristics that are difficult to achieve simultaneously in elastic strain sensors. A highly sensitive and stretchable strain sensor ...comprising a microstructured metal nanowire (mNW)/elastomer composite film is presented. The surface structure is easily prepared by combining an mNW coating and soft‐lithographic replication processes in a simple and reproducible manner. The densely packed microprism‐array architecture of the composite film leads to a large morphological change in the mNW percolation network by efficiently concentrating the strain in the valley regions upon stretching. Meanwhile, the percolation network comprising mNWs with a high aspect ratio is stable enough to prevent electrical failure, even under high strains. This enables the sensor to simultaneously satisfy high sensitivity (gauge factor ≈81 at >130% strain) and high stretchability (150%) while ensuring long‐term reliability (10 000 cycles at 150% strain). The sensor can also detect strain induced by bending and pressure, thus demonstrating its potential as a versatile sensing tool. The sensor is successfully utilized to monitor a wide range of human motions in real time. Furthermore, the unique sensing mechanism is easily extended to detect more complex multiaxial strains by optimizing the surface morphology of the device.
Microstructured metal nanowire/elastomer composite films are used as highly efficient stretchable piezoresistors for wearable strain sensor applications. Based on the unique surface design, high sensitivity and stretchability of sensor are achieved simultaneously by concentrating stretching‐induced strains in specific regions without electrical failure, even at high strains. The sensor architecture is further optimized to impart multiaxial strain sensing capability.
The micropatterning of conductive composites is of great importance for the integration of elastic conductors with functional micro-geometries in a stretchable platform. We present a simple and rapid ...micropatterning method for conductive composites that relies on single-step contact transfer printing (sCTP). A conductive polydimethylsiloxane (PDMS) composite is readily synthesized by dispersing conductive carbon black nanoparticles into a PDMS matrix and is easily patterned on insulative PDMS substrates with negligible dimensional errors by the proposed method. In addition to simplicity and accuracy in fabrication, superior process scalability is revealed through investigation of both multiple-stack and large-area patterning approaches. We also demonstrate an all-elastomeric-platformed piezoresistive strain sensor capable of measuring higher tensile strains compared to conventional metal foil gauges, with highly linear, good cyclic electrical performance, and mechanical robustness. As a potential application, we integrate the strain sensors onto a glove to measure the motions of human fingers in real time. We further demonstrate a rosette-type gauge that can detect both the magnitude and direction of the principal strains with patterning accuracy and uniformity facilitated by the proposed sCTP technique.
Hydrochromic materials find great utility in a wide range of applications including humidity sensing and measuring the water contents of organic solvents, as well as substrates for rewritable paper ...and human sweat pore mapping. Herein, an inkjet printable diacetylene (DA) is described that can be transformed by UV irradiation to a hydrochromic‐conjugated polymer on conventional paper. Specifically, an amphiphilic DA that contains an imidazolium ion head‐group is found to be compatible with a common office inkjet printer. Various computer‐designed images are printed on paper using this substance. UV irradiation of the printed images results in the generation of blue‐colored images associated with formation of a polydiacetylene (PDA). The resolutions of the images are almost identical to those generated using a conventional black ink. Importantly, the printed images undergo a blue‐to‐red color change upon exposure to water and the hydrochromism is found to be temperature dependent. The facile color change that occurs near body temperatures enables use of the hydrochromic PDA‐coated paper for rapid and precise mapping of human sweat pores from fingers, palms, and feet.
Inkjet printing of an aqueous solution of amphiphilic diacetylene followed by UV‐irradiation results in the generation of hydrochromic polydiacetylene on conventional paper. The polydiacetylene‐coated paper, which displays temperature‐dependent hydrochromism corresponding to a facile color change at near body temperature, enables a rapid and precise mapping of human sweat pores from fingers, palms, and feet.
Exceptional challenges have confronted the rational design of colorimetric sensors for saturated aliphatic hydrocarbons (SAHCs). The main reasons for this difficulty are the extremely nonpolar nature ...of these targets and their lack of functional groups that can interact with probes. By taking advantage of a mechanochromic conjugated polydiacetylene (PDA) and the hydrocarbon‐induced swelling properties of polydimethylsiloxane (PDMS), a sensor film that enables simple, colorimetric differentiation between a variety of C5 to C14 aliphatic hydrocarbons is fabricated. The unprecedented PDA–PDMS composite sensor undergoes a blue‐to‐red colorimetric transition on a timescale that is dependent on the chain length of the hydrocarbon target. In addition, the development of the red color is directly proportional to the swelling ratio of the film. This straightforward approach enables naked‐eye differentiation between n‐pentane and n‐heptane. The versatility of the sensor system is demonstrated by using it for the colorimetric determination of kerosene in adulterated diesel oil. Finally, the observation that a PDA microcrystal in the film undergoes significant expansion and tearing in concert with a blue‐to‐red colorimetric transition during the swelling process provides direct evidence for the mechanism for the mechanochromic behavior of the PDA.
By taking advantage of a mechanochromic conjugated polydiacetylene (PDA) and the hydrocarbon‐induced swelling properties of polydimethylsiloxane (PDMS), a sensor film that enables colorimetric differentiation among saturated aliphatic hydrocarbons (SAHCs) is developed. The unprecedented PDA–PDMS composite sensor undergoes a blue‐to‐red colorimetric transition that is dependent on the chain length of the hydrocarbon target.
Because of their unique structural and optical properties, 1D perylene diimide (PDI) derivatives have gained attention for use in optoelectronic devices. However, PDI‐containing self‐assembled ...supramolecular systems often are of limited use because they have supramolecular architectures that are held together by weak noncovalent π–π stacking, hydrogen bonding, and hydrophobic interactions. As a result, they are intrinsically unstable under solution‐processing conditions. To overcome this limitation, a polydiacetylene (PDA)‐based strategy is developed to construct a solvent‐resistant and stable PDI assembly. For this purpose, first the monomer PDI–BisDA is generated, in which two polymerizable diacetylene (DA) units are covalently linked to a PDI core. Importantly, 254 nm UV irradiation of self‐assembled PDI–BisDA nanofibers forms solvent‐resistant and stable PDI–PDA fibers. Owing to the presence of PDA, the generated polymer fibers display an increased photocurrent. In addition, the existence of PDA and PDI moieties in the fiber leads to the occurrence of switchable on–off fluorescence resonance energy transfer (FRET) between the PDI and reversibly thermochromic PDA chromophores.
UV (254 nm) irradiation of self‐assembled PDI–BisDA, containing two polymerizable diacetylene (DA) units covalently bonded to a core perylene diimide (PDI) molecule, forms covalently linked and solvent‐resistant stable PDI‐containing nanofibers (PDI–PDA). The presence of polydiacetylene (PDA) in the formed nanofibers gives rise to a conductivity enhancement as well as a reversible fluorescence resonance energy transfer (FRET) phenomenon.
Self‐assembly process represents one of the most powerful and efficient methods for designing functional nanomaterials. For generating optimal functional materials, understanding the pathway ...complexity during self‐assembly is essential, which involves the aggregation of molecules into thermodynamically or kinetically favored pathways. Herein, a functional perylene diimide (PDI) derivative by introducing diacetylene (DA) chains (PDI‐DA) is designed. Temperature control pathway complexity with the evolution of distinct morphology for the kinetic and thermodynamic product of PDI‐DA is investigated in detail. A facile strategy of UV‐induced polymerization is adopted to trap and capture metastable kinetic intermediates to understand the self‐assembly mechanism. PDI‐DA showed two kinetic intermediates having the morphology of nanosheets and nanoparticles before transforming into the thermodynamic product having fibrous morphology. Spectroscopic studies revealed the existence of distinct H‐ and J‐aggregates for kinetic and thermodynamic products respectively. The polymerized fibrous PDI‐DA displayed reversible switching between J‐aggregate and H‐aggregate.
Temperature control pathway complexity with the evolution of distinct morphology for the kinetic and thermodynamic product of PDI‐DA is investigated. PDI‐DA showed two kinetic intermediates having the morphology of nanosheets and nanoparticles before transforming into the thermodynamic product having fibrous morphology. UV‐induced polymerization is found to trap the metastable kinetic intermediates to understand the self‐assembly mechanism.
Hydrochromic materials have been actively investigated in the context of humidity sensing and measuring water contents in organic solvents. Here we report a sensor system that undergoes a brilliant ...blue-to-red colour transition as well as 'Turn-On' fluorescence upon exposure to water. Introduction of a hygroscopic element into a supramolecularly assembled polydiacetylene results in a hydrochromic conjugated polymer that is rapidly responsive (<20 μs), spin-coatable and inkjet-compatible. Importantly, the hydrochromic sensor is found to be suitable for mapping human sweat pores. The exceedingly small quantities (sub-nanolitre) of water secreted from sweat pores are sufficient to promote an instantaneous colorimetric transition of the polymer. As a result, the sensor can be used to construct a precise map of active sweat pores on fingertips. The sensor technology, developed in this study, has the potential of serving as new method for fingerprint analysis and for the clinical diagnosis of malfunctioning sweat pores.
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