A new class of luminescent materials switches on—brightening or changing colour—when pressed, stretched, or struck, rather than dimming like existing pressure-sensitive paints. Current pressure-sensitive paints used in wind tunnels and on aircraft surfaces rely on oxygen quenching, which dims their emission under pressure. This “turn-off” signal suffers from poor photostability, temperature sensitivity, and low signal-to-noise ratios, limiting their use in real-world stress detection. The researchers are building composite materials that combine aggregation-induced emission molecules with metal-organic frameworks, then embedding them into polymer fibres. In pilot studies, these composites produce a strong, stable “turn-on” signal only when mechanical force is applied. If successful, the materials could enable non-contact optical pressure mapping over aerodynamic surfaces, structural health monitoring of bridges and buildings, fatigue inspection of engineering components, tamper-proof security packaging, and mechanosensing in soft robotics. The high signal-to-noise ratio and resistance to photodegradation would allow robust pressure mapping across diverse flow environments and strain rates. This is fundamental materials science with clear engineering applications—the work generates new design principles for resilient structural systems, clean energy technologies, and transportation infrastructure.
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Luminescent mechanoresponsive materials could display an immediate change in optical behaviour, by switching colour or emission intensity as they experience a mechanical stimulus, such as applied pressure, shear stress, tensile/compressive deformation, high-rate impact, cracking and fracture. These 'smart' materials have attracted considerable interests, because such mechano-fluoro-chromic (MFC) systems can be capitalised for a vast range of advanced technological applications. For exemplar: in non-contact optical imaging of pressure distributions over aerospace and hydrodynamic surfaces; structural health monitoring of buildings and bridges; non-invasive fatigue inspection of engineering components; tamper-proof security packaging; and mechanosensory in soft robotics. Pressure-sensitive paints (PSP) used in today's aerodynamics sector for surface pressure imaging have certain limitations, particularly luminescence quenching ('turn-off' emission), poor photostability, and temperature sensitivity. These intrinsic characteristics of current PSPs are hindering effective implementation in innovative technologies elucidated above. To address these challenges, the vision of this proposal is to design and engineer new 'turn-on' type MFC materials with an attractive combination of properties: high fluorescent quantum yield, large Stokes shift, excellent photostability, tuneable reversibility, ratiometric emission and long lifetime. That will require unconventional development of bespoke composite systems, by integrating aggregation-induced emission (AIE) and metal-organic framework (MOF) materials. Going further, to construct tuneable architectures and bespoke functions, we will engineer polymer-based composite fibres incorporating AIE-MOFs. Our pilot studies have demonstrated the efficacy of the general concepts underpinning the proposed materials engineering strategy. Efficient AIE-based PSPs with turn-on luminescence will be a game changer in the field. The high signal-to-noise ratio and improved resistance against photodegradation or other environmental factors will enable, robust pressure mapping in diverse flow environments, extending to stress visualisation in experimental solid mechanics subject to a wide range of strain rates encountered in different engineering applications. More broadly, the research outcomes stand to benefit the academia, the industry, and the general public through the generation of new materials information to realise future design and implementation of more resilient structural multiphysics, clean energy and transportation systems.
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