Investigation of polymers towards advanced functional materials
With the rational design and modification of the fundamental polymers, new polymer complexes and composites can be developed with unique properties as functional materials. These new materials with enhanced and specialized functionality can thus replace the traditional materials and advance new technology. Here, two advanced functional materials are developed and investigated for applications in wearable strain sensing and toxic Cr(VI) removal from aqueous solutions. Chapter 2 & 3 focus on developing a soft electronic polymer material that possesses the properties of skin—compliant, elastic, stretchable, and self-healable—which would be ideal for bioelectronics such as wearable strain sensors. Current materials have limited on stretchability and durability (self-healing ability). A regenerative polymer complex composed of poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAAMPSA), polyaniline (PANI) and phytic acid (PA) that exhibits ultrahigh stretchability (1935 %), repeatable autonomous self-healing ability (repeating healing efficiency > 98 %), quadratic response to strain ( R2 > 0.9998), and linear response to bending ( R2 > 0.9994) is rationally designed. The hydrogen bonds and electrostatic interactions between PAAMPSA, PA and PANI synergistically construct a homogeneous regenerative network, which contribute to the elasticity and soft compliant nature of the as-prepared electronic material, along with extremely high omni-directional stretchability and excellent self-healing ability. Sensitive strain responsive geometric and piezoresistive mechanisms provide excellent linear responses to omnidirectional tensile strain and bending deformations. Furthermore, this material is scalable and simple to process in an environmentally friendly manner. In Chapter 4, the catalytic effects of metallic iron on morphologies, chemical structures, graphitic carbon growth, and thermal behavior of pyrolyzed carbon nanofibers are investigated. Polyacrylonitrile / iron nitrate (PAN/Fe(NO3)3) precursor nanofibers were prepared via electrospinning and subsequently converted into carbon/iron nanocomposite fibers via pyrolysis. It was found that the existence of iron nitrate has significant effects on the morphology of the resulting carbon fibers, as they can direct the initially non-woven nanofiber assembly into aligned nanofibers. The presence of catalytic iron can facilitate the stabilization and carbonization of precursor PAN fibers resulting in an increased carbon fiber yield, being more ordered on the nanoscale, and having larger graphitic crystallites. In Chapter 5, the developed carbon/iron nanocomposite fibers are used as the nanoadsorbent to remove the Cr(VI) in water. The nanoadsorbents show a fast and powerful performance in Cr(VI) removal through reduction and adsorption. CF-50 with abundant surface-bound α-iron nanoparticles performs ~ 1000% of amorphous carbon CF-0 in terms of Cr(VI) removal rate and capacity. The metallic iron on the carbon fiber surface is first oxidized to reduce the Cr(VI). Subsequently, diffusion controlled redox reactions between iron inside of carbon fiber matrix and Cr(VI) achieves a sustained removal for 30 days. Moreover, due to the magnetic nature, the nanoadsorbent can be easily separated from the treated water by a neodymium magnet.