Soft Composites with Tunable Optical and Electrical Properties

The complexity and integration demands of modern electronics require innovative materials addressing the requirements of flexibility and functionality in terms of electrical or optical properties [1–3]. One of the main challenges is to combine two properties that are mutually exclusive in flexible electronics applications, such as stretchability and low electrical resistance. Elastomeric conductive composites have shown promise for sustainable high-strain and recoverable conductivity [4–6]. Integrating stretchable and electrical conductivity functionalities in an electrode material is advantageous for many electronics applications, such as wearable and printable electronics. Examples of such multifunctional conductive materials exist in the literature and their elastic recovery has been demonstrated for stretch ratios beyond λ> 3 (λ= final length/initial length) [7, 8]. These promising and resilient composites show recoverable performance under cyclical strain, are attractive for tissues that are flexible, and are subjected to large deformations under mechanical loading [9–12]; quantifying these large strains in real time, such as those taking place in skin and muscles, is very important for mechanical characterization of these tissues toward understanding of their mechanical functions under stress in physiological conditions. In this chapter, we will consider three different classes of soft composites: soft color composites whose light transmittance can be actively tuned and controlled through mechanical stretching; viscoelastic polymers that, coupled with hybrid nanoparticles, can be tuned into long-range ordered structures; and elastomeric conductive composites that are promising for sustainable high-strain and recoverable conductivity.