Session: 04-26-01: Advanced Material Innovations in Wearable Biomedical Devices and Structures

Paper Number: 150890

150890 - Mechano-Luminescent Light Emission Characteristics of Functionally Graded Zns-Pdms Composites 

Zinc sulfide (ZnS) phosphors are known to emit light when subjected to external mechanical stimuli – mechano-luminescent (ML) light emission. Fabrication of micro-composites is a typical approach to harness the ML characteristics of the ZnS phosphors for devising self-powered sensors and energy harvesters. Polydimethylsiloxane (PDMS) is widely used for preparing ZnS-embedded elastomeric composites by blending ZnS and PDMS and curing the ZnS-PDMS mixture. Commercially available ZnS phosphors exhibit stable ML characteristics with a long shelf life thanks to alumina coating protecting the ML phosphors from ambient environment. Also, an ML irradiance spectrum of a ZnS phosphor is tunable by varying a doping material and a concentration. There are commercially available ML ZnS phosphor products emitting blue, green, and orange color light. When ZnS is doped with a copper, ML color spectrum covers from blue to green range, and increasing copper doping concentration results in a green shift in the ML irradiance spectrum. With manganese doping in ZnS, an orange-colored ML light emission can be accomplished. This color tunable characteristic of ML ZnS phosphors makes it one of the most popular ML materials along with its reasonable strong light intensity.

The ML ZnS-based elastomeric composites have been studied to use a strain sensing material based on its unique strain-sensitive light emission characteristic. While it is well known how the ML light intensity of the ZnS-based elastomeric composites varies with strain and strain rate under dynamically applied uniaxial strains, there is still a knowledge gap in how an ML irradiance spectrum varies with external mechanical stimuli. In Ryu’s previous studies, an ML color shifts with varying a loading rate – blue shift with increasing loading rate – and an ML irradiance spectrum could be modified by simply blending different colors (i.e., blue, green, and orange) of ML ZnS phosphors. This ML color-tunable characteristic can broaden application of the ML ZnS-PDMS micro-composites with rich mechanical sensing information that can be extracted from the ML profile, such as color and intensity.

In this study, we aim to design functionally graded ML ZnS-PDMS micro-composites based on our approach to tune the ML irradiance spectrum by blending three different colors of ZnS phosphors at various mixing ratios. First, ML ZnS-PDMS micro-composites with one of various blends of blue, green, and orange ZnS phosphors will be fabricated in PDMS matrix. The ML composites will be tested for accumulating database on how ML light intensity, color, and irradiance spectrums vary with strain and strain rate under dynamic cyclic loadings. Color high speed cameras will record ML light to produce video footages, which will be subjected to image processing to quantify ML light intensity and color along with strain and strain rate. In addition, a spectroradiometer will be used for obtaining ML irradiance spectrums from the ML composites. Second, in an ML micro-composites specimen, varying mixtures of three colored phosphors will be sequentially placed along the strip in a continuous manner. This will create a distributed ML sensor nodes along the strip, which can provide strain sensor signals along with a coordinate information of a respective sensor node based on the acquired ML database. Lastly, the functionally graded ZnS-PDMS composites will be tested for validation of the distributed strain sensing under dynamic cyclic loadings.

Presenting Author: Matthew Moore New Mexico Tech

Presenting Author Biography: Matthew Moore is an M.S. student in the Department of Mechanical Engineering at New Mexico Tech. He obtained a B.S. (2024) in the Department of Mechanical Engineering at New Mexico Tech. Matthew is currently studying to understand multiphysics properties of ZnS:Cu for use in self-powered strain sensors and health monitoring wearables. This research is being sponsored by NASA and NSF.

Authors:

Matthew Moore New Mexico Tech
William Fawcett New Mexico Tech
Myeong-Lok Seol NASA Ames Research Center
Jessica Koehne NASA Ames Research Center
Donghyeon Ryu New Mexico Tech