Salt doping to improve thermoelectric power factor of organic nanocomposite thin films.

Thermoelectric materials with a large Seebeck coefficient (S) and electrical conductivity (σ) are required to efficiently convert waste heat into electricity, but their interdependence makes simultaneously improving these variables immensely challenging. To address this problem, bilayers (BL) of poly(diallyldimethylammonium chloride) (PDDA) and double-walled carbon nanotubes (DWNT), stabilized by KBr-doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) were deposited using layer-by-layer (LbL) assembly. Doping PEDOT:PSS with KBr, prior to DWNT dispersion and LbL assembly, results in a six-fold improvement in electrical conductivity with little change in the Seebeck coefficient. A maximum power factor (PF = S 2 σ) of 626 ± 39 µW m-1 K-2 is obtained from a 20 BL PDDA/PEDOT:PSS-DWNT film (∼46 nm thick), where PEDOT:PSS was doped with 3 mmol KBr. This large PF is due to the formation of a denser film containing a greater proportion of DWNT, which was influenced by the charge-screening effects imparted by the salt dopant that separates PSS from PEDOT. This study demonstrates a relatively simple strategy to significantly increase the thermoelectric performance of fully organic nanocomposites that are useful for low temperature thermoelectric devices.

UV-protection from chitosan derivatized lignin multilayer thin film.

Lignin is one of the most abundant renewable materials on the earth. Despite possessing useful antioxidant and UV absorbing properties, its effective utilization in technology has been hampered by its relative insolubility and difficulty to process. In this work, a simple chemical derivatization process is utilized which yields water-soluble lignin possessing anionic carboxylate groups. These carboxylate groups give lignin polyanionic behavior and enable its utilization in the growth of a functional film via layer-by-layer (LbL) assembly with biologically sourced chitosan. The growth mechanism of this film is hypothesized to be a result of both hydrogen bonding and ionic interactions. The film demonstrates excellent UV-absorptive capability. A 100 nm thick chitosan/lignin coating was applied to a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) film and shown to reduce its degradation sixfold over the course of a 1 hour exposure to harsh UV light. This is the first demonstration of lignin being utilized in a fully biologically derived LbL film. Utilization of lignin in LbL assembly is an important step in the development of renewable nanotechnology.

Enzymatic Modification of Polyamide for Improving the Conductivity of Water-Based Multilayer Nanocoatings.

Enzymatic modification, using a protease from Bacillus licheniformis (Subtilisin A), was carried out on polyamide 6.6 (PA6.6) fabric to make it more amenable to water-based nanocoatings used to impart electrical conductivity. The modified PA6.6 fibers exhibit a smoother surface, increased hydrophilicity due to more carboxyl and amino groups, and larger ζ-potential relative to unmodified polyamide. With its improved hydrophilicity and surface functionality, the modified textile is better able to accept a water-based nanocoating, composed of multiwalled carbon nanotubes (MWCNT) stabilized by sodium deoxycholate (DOC) and poly(diallyldimethylammonium chloride) (PDDA), deposited via layer-by-layer assembly. Relative to unmodified fabric, the enzymatically modified fibers exhibit lower sheet resistance as a function of PDDA/MWCNT-DOC bilayers deposited. This relatively green technique could be used to impart a variety of useful functionalities to otherwise difficult-to-treat synthetic fibers like polyamide.