Quantum dot-based sensor layer in lightweight structures

• A quantum dot/polyvinylcarbazole composite layer was prepared on PET-ITO.
• Embedding of the functional layer in a glass fiber-reinforced composite successful.
• No layer detachment was visible under process conditions, 3 bar and 60 °C.
• Photoluminescent quenching of the embedded QD layer was shown via external voltage.

Quantum dots can be used to detect, store and make visually apparent mechanical loading conditions. The fluorescent properties of the nanocrystals are selectively influenced by the injection of electric charges. By applying an external electric voltage, it is possible to suppress photoluminescence completely. If the quantum dots, as part of a functional layer system, are integrated in smart components, the integrated material system allows for energy-autonomous condition monitoring. We present for the first time a quantum dot-based system in a glass fiber-reinforced epoxy composite with a layer structure which is suitable for impact visualization. The quantum dots dispersed in poly (9-vinylcarbazoles) were applied on a PEDOT:PSS layer on an ITO-coated PET substrate. Silver electrodes were sputtered as a structured layer. For integration of the layer stack, which measured 25 × 25 × 0.1 mm, in an epoxy composite, two process variants and sample geometries were used: a 2D curved component for hand lay-up and a plate for resin transfer molding. The epoxy composite components had a material thickness of 1.5 mm and included eight layers of fiberglass cloth. The quantum dot-layer stacks were positioned either between the first two layers of glass fiber or directly at the component surface which had only a thin epoxy layer. By applying an external voltage, we suppressed the photoluminescence of the integrated quantum dots; the suitability of the coating system for integrated material sensors was evident.

Integration of a functional layer stack containing nanocrystals in an glass-fiber-reinforced composite structure. Left: (1) PET-ITO-substrate, (2) ITO-layer, (3) PEDOT:PSS, (4) Nanocrystal/PVK composite, (5) Aluminium electrode. Right: (1) Functional layer stack, (2) Epoxy resin matrix, (3) Glass-fiber plies.Figure optionsDownload as PowerPoint slide