EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

In this work, we have developed a multi-stimuli responsive sensor for artificial skin applications. The sensor can detect surrounding changes in pressure, temperature and humidity. The proposed design consists of a hydrogel core, responsive to temperature and humidity changes; and a piezoelectric shell for pressure sensing. Swelling of the hydrogel core upon stimuli results in a mechanical strain on the piezoelectric shell, which results in a measurable electric potential, detected by metal electrodes. The two materials are combined into core-shell nanorod structures, using novel vapor-based deposition techniques. Such deposition techniques provide control over material’s mechanical, optical and electrical properties as well as layer conformity and uniformity. Additionally, the core-shell nanorods are deposited into a nanostructured UV-curable resin, providing mechanical stability against structural collapse.

• Fabrication of hydrogel core: humidity and temperature responsive hydrogel, Poly-N-vinylcaprolactam (pNVCL), is synthesized using intitiated chemical vapor deposition (iCVD). The dry vapor-phase technique gives control over the lower critical solution temperature (LCST), amongst other material properties. (1) Tailoring the hydrogel’s LCST improves response over a wide temperature range.

• Fabrication of piezoelectric shell: piezoelectric zinc oxide shell is synthesized using plasma-enhanced atomic layer deposition (PE-ALD). In PE-ALD, substrate temperature defines the crystalline properties of the deposited material. An interchange between (100) and (002) crystallographic orientation gives control over zinc oxide’s piezoelectric properties. In this work, highly-resistive and piezoelectric zinc oxide layer with (100) preferential crystallographic orientation is deposited at room temperature. Using low substrate temperature is advantageous for the use of flexible substrates, such as PET. (2)

• Nanostructuring of UV-curable resin: The multi-stimuli responsive core-shell nanorods are deposited into a nanostructured UV-curable polyurethane acrylate (PUA) resin serving as a template layer for mechanical stability. Patterning the template material is realized using UV nanoimprint lithography (UV-NIL). For this purpose, a UV-transparent nanopatterned polymeric stamp is used.

1. F. Muralter, A. Perrotta, O. Werzer, A. M. Coclite, Macromolecules, 2019, 52, 6817-6824
2. Abu Ali et al., Phys. Status Solidi a, 2020, 2000319