Abstract
Highly advanced phase-change hybrids (PCHs), which consist of a phase-change material and conjugated polymer, were developed for new sensor and actuator applications. PCH films with excellent characteristics were obtained simply by depositing various molten paraffin waxes (PWs) in situ onto poly(diphenylacetylene) (PDPA) films with extremely large fractional free volumes. The phase-change enthalpy of the PWs in the hybrid films was quite high and remained constant over prolonged use. The PCH films underwent critical changes in both fluorescence (FL) intensity and color during the phase change of the PWs, which facilitated various sensor applications such as highly reversible writing/erasing, fingerprinting and array-type thermometer usage. In addition, a biaxially oriented polypropylene (BOPP)-supported PCH film exhibited extremely fast and highly reproducible thermomechanical actuation with reversible curling/uncurling during the phase change of the PWs. These findings will be useful for developing novel PCH materials with highly advanced functions and applications. South Korean scientists have formed a touch-responsive material that can record or remove bright, fluorescent images of human fingerprints. Giseop Kwak from Kyungpook National Univeristy and colleagues improved the optical capabilities of parrafin wax — a ‘phase change’ material that easily melts and releases thermal energy — by mixing it into the numerous microvoids within poly(diphenylacetylene) (PDPA), a fluorescent polymer. When the researchers touched the hybrid polymer with objects (a stamp or fingertip, for example) hotter than 25 °C, fluorescent emission ceased at the contact points due to melted wax disrupting the PDPA structure. This produced high-resolution, photonegative images, which disappeared on cooling the film. By combining their new material with a tough, polypropylene film, the team also built a thermal actuator that twists or uncurls in response to different temperatures. Multifunctional phase-change hybrid materials containing paraffin waxes (PWs) within a microporous conjugated polymer (CP) film were developed for new sensor and actuator applications. The hybrid films were prepared simply by depositing various PWs onto CP films to show critical changes in FL intensity and color during the phase change of PWs. This fascinating FL response behavior to external heat facilitated various applications such as reversible writing/erasing, fingerprinting and thermometer sensors. An appropriate layer-supported hybrid film showed extremely fast and highly reproducible thermomechanical actuation.
Highlights
Phase-change materials (PCMs) have recently attracted considerable attention because of their ability to reversibly store and release large amounts of latent heat, which can be applied for the thermal energy management of natural heat sources and waste heat.[1,2,3,4,5] For practical applications, PCMs have often been incorporated in organic or inorganic matrices to enhance their mechanical integrity and cyclic stability on repeated use
We developed phase-change hybrids (PCHs) by infiltrating PDPA films with paraffin waxes (PWs)
The PDPAC1 used in this study had a relatively high average molecular weight (Mw = 1.34 × 106 g mol–1) with a narrow polydispersity index (PDI = molecular weights (Mw)/Mn = 1.2)
Summary
Phase-change materials (PCMs) have recently attracted considerable attention because of their ability to reversibly store and release large amounts of latent heat, which can be applied for the thermal energy management of natural heat sources and waste heat.[1,2,3,4,5] For practical applications, PCMs have often been incorporated in organic or inorganic matrices to enhance their mechanical integrity and cyclic stability on repeated use. The matrix material can affect the phasechange properties of the resultant PCM-based composites, and some of these composites have exhibited highly enhanced phase-change enthalpy and thermal conductivity.[6,7,8,9,10,11] actuators based on PCMs have been developed for other purposes.[12,13,14] To the best of our knowledge, there are no reports on PCMs that can exhibit both optical output signals and thermomechanical actuation in the heat storage/release process Such sensory and actuation functions would make it possible to monitor the latent heat in real time and further enhance thermal energy management processes.
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