Solid-State Low-Temperature Thermoresponsive and Reversible Color Changes of Conjugated Polymer in Layered Structure: Beyond Infrared Thermography

A highly sensitive friction-imaging device based on cascading stimuli responsiveness

Imaging and measurement of friction forces are required in a variety of fields. If the friction forces originating from the motions of professionals are quantitatively analyzed, the data can be applied to a motion-copying system by a robot. However, weak friction forces have not been visualized and quantified using conventional sensing materials and devices because of their low sensitivity. Here we present a highly sensitive friction-imaging device based on the cascading responses of stimuli-responsive materials, namely polydiacetylene (PDA) and dry liquid (DL). Weak friction forces disrupt the DL, which is composed of liquid droplets surrounded by solid particles. The outflowing liquid under chemical stress changes the color of PDA. The cascading responses enable colorimetric imaging and measurement of weak friction forces in the range of 0.006-0.080 N. Furthermore, the device visualizes the force distribution of handwriting in calligraphy depending on the individual characteristics of an expert, a practician, and a beginner. A high-sensitivity friction-imaging device can be used to understand various motions.

Coatable 2D Conjugated Polymers Containing Bulky Macromolecular Guests for Thermal Imaging

Dynamic properties are derived from the structural flexibility of 2D polymers. Softening layered structures has the potential for tuning and enhancing the dynamic properties. In the present work, the flexibility of layered polydiacetylene (PDA) is tuned by the interlayer polymeric guests with different branching structures. PDA shows thermoresponsive color-change properties through shortening the effective conjugation length with molecular motion. Whereas the blue-to-red color transition is observed at certain threshold temperatures for the layered PDA without the interlayer guest, the intercalation of the bulky polymer guests lowers the starting temperature and widens the temperature range for the thermoresponsive color changes. The resultant layered composite of PDA and bulky polymer affords the homogeneous coating on substrates on the centimeter scale. The thermoresponsive color-change coating is applied to temperature-distribution imaging. The specific heat of liquids is colorimetrically estimated using the coating on the bottle. The coating on a silk cloth visualizes the temperature distribution on a simulated tissue during surgical operation using an ultrasonic coagulation cutting device. The coating can be applied to thermal imaging in a variety of fields. Moreover, the softening strategy contributes to explore dynamic properties of soft 2D materials.

Nanoarchitectonics for conductive polymers using solid and vapor phases

Conductive polymers have been extensively studied as functional organic materials due to their broad range of applications. Conductive polymers, such as polypyrrole, polythiophene, and their derivatives, are typically obtained as coatings and precipitates in the solution phase. Nanoarchitectonics for conductive polymers requires new methods including syntheses and morphology control. For example, nanoarchitectonics is achieved by liquid-phase syntheses with the assistance of templates, such as macromolecules and porous materials. This minireview summarizes the other new synthetic methods using the solid and vapor phases for nanoarchitectonics. In general, the monomers and related species are supplied from the solution phase. Our group has studied polymerization of heteroaromatic monomers using the solid and vapor phases. The surface and inside of solid crystals were used for the polymerization with the diffusion of the heteroaromatic monomer vapor. Our nanoarchitectonics affords to form homogeneous coatings, hierarchical structures, composites, and copolymers for energy-related applications. The concepts using solid and vapor phases can be applied to nanoarchitectonics for not only conductive polymers but also other polymers toward a variety of applications.

A Layered Polydiacetylene Containing Hydrogen-Bonding 4,4'-Bipyridyl Guests: Reversible Color Changes with a Wide-Range Temperature Response

Layered organic polymers have intercalation capabilities and dynamic properties. In classical intercalation chemistry, the interlayer guests are intercalated in the host layers via electrostatic interaction. The present work shows the organic layered materials with the host-guest interlayer interaction via hydrogen bond. Polydiacetylene (PDA) exhibits color changes from blue to red with the application of external stimuli, such as thermal and mechanical stresses. Here we report on a layered PDA containing 4,4'-bipyridyl in the interlayer space as a hydrogen-bonding guest. Whereas the layered PDA without interlayer guest shows the color transition at 65 °C, gradual color changes with two-stage reversibility are observed in the temperature range of -20-240 °C by the introduction of the hydrogen-bonding guest. The weaker interlayer interaction via the hydrogen bond promotes the dynamic motion directing the thermoresponsive color changes in a wide temperature range.