Electro-Mechanical Properties of Metallized Sodium Alginate Foils at the Limit of the Electrical Conduction

In recent years, much attention has been given to biopolymers and renewable raw materials obtained from nature to find alternatives to petroleum-based materials. In this context, we developed a free-standing and flexible conductive substrate by sputtering a thin layer of gold onto a foil of sodium alginate, producing conductive self-standing substrates. These substrates have been utilized for the fabrication of eco-designed solution-processed optoelectronic devices. Herein, we report experimental work to study the mechanism behind the dependence of electrical resistance on the mechanical deformation. Data obtained from mechanical measurements, such as strain, stress, deformation, and bending, are correlated with morphological (Atomic Force Microscopy and Transmission Electron Microscopy) and structural (X-ray Diffraction) data relative to both the surface and the subsurface regions of the metallized substrates. Collectively, these data enabled the elucidation of both the composition and spatial distribution of the metal clusters implanted within the polymer matrix. The substrates present an anisotropic Young modulus, making them more stretchable in-plane with respect to out-of-plane. In the elastic regime, the reproducibility of the electrical resistance variations with respect to the stress applied makes these substrates robust candidates for the realization of strain sensors.