Experimental characterisation and micromechanical models for luminescent phosphors incorporated with nonwoven veil-polymer composites

The mechanical properties, thermal behaviour, and spectral characteristics of polydimethylsiloxane (PDMS) composites utilising a nonwoven polyetherimide (PEI) veil with SrAl₂O₄:Eu²⁺, Dy³⁺ (SAOED) phosphors have been investigated. Elasto-mechanoluminescence (EML) was characterised by observing the light emission under cyclic displacement testing. EML/PEI veil composites were fabricated in a scaled-down size according to ASTM D412-16 and showed improving mechanical properties compared to PEI veil with PDMS and bare PDMS. During cyclic displacement testing, the thermal temperature of EML/PEI veil composites varies according to the strain energy stored upon deformation around the interface area. The spectral data, i.e. light intensity and wavelength, were observed to increase at the maximum extended deformation of the SAOED embedded in the PEI veil within the PDMS composite. Micron-sized luminescent phosphors, SAOED, within the composites were studied by scanning electron microscopy, rheology, and nanoindentation tests. These techniques were employed to investigate the surface morphology, viscoelastic behaviour during the curing process, and hardness and elastic modulus, respectively, of the SAOED-PDMS. Halpin-Tsai and Mori-Tanaka micromechanical models were used to study the interphase effect as a function of thickness and elastic modulus, by correlating the properties of the filler and matrix. The interphase elastic modulus is introduced as a function of the interphase volume fraction and the ratio of filler modulus. The Mori-Tanaka model is in relatively good agreement with the experimental Young's modulus due to the average internal stress in a matrix material containing inclusions with eigenstrains.