Textiles with Thermoelectric, Antimicrobial, and/or Flame Retardant Behavior from Aqueous Polyelectrolyte Complexes

Abstract

Layer-by-layer (LbL) assembly is a conformal coating “platform” technology capable of imparting a multiplicity of functionalities on nearly any type of surface in a relatively environmentally friendly way. At its core, LbL is a solution deposition technique in which layers of cationic and anionic materials (e.g. nanoparticles, polymers and even biological molecules) are built up via electrostatic attractions in an alternating fashion. Here we are producing nanocomposite multilayers (50 – 1000 nm thick) that can be completely transparent and impart self-extinguishing flame retardant behavior, antimicrobial (and/or antifouling) behavior, and even thermoelectric behavior (i.e., converting heat to electricity) to a variety of textiles. Polyaniline (PANi), graphene, and double-walled carbon nanotubes (DWNT) were alternately deposited from aqueous solutions using the layer-by-layer assembly technique. Graphene and DWNT are stabilized with an intrinsically conductive polymer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). A 1 µm thick film, composed of 80 PANi/graphene-PEDOT:PSS/PANi/DWNT-PEDOT:PSS quadlayers (QL) exhibits electrical conductivity (σ) of 1.88 X 105 S/m and a Seebeck coefficient (S) of 120 µV/K, producing a thermoelectric power factor (S2∙σ) of 2710 µW/(m∙K2). This is the highest value ever reported for a completely organic material measured at room temperature. Poly(diallyldimethylammonium chloride) and poly(acrylic acid) were used to create a nanocoating that reduces bacterial adhesion on polyester fabric. In an effort to impart flame retardant behavior to fabric using fewer processing steps, a water-soluble polyelectrolyte complex (PEC) was developed. This nanocoating is comprised of polyethylenimine and poly(sodium phosphate) and imparts self-extinguishing behavior to cotton fabric in just a single coating step. Adding a melamine solution to the coating procedure as a second step renders nylon-cotton blends self-extinguishing. Either of these two coating techniques can be deposited using roll-to-roll processing (e.g., pad-dry or spray-coating). Opportunities and challenges will be discussed.