No abstract

Carbon nanotubes (CNTs) are elongated members of the Nobel-prize decorated fullerene family.[1] Discovered in 1991, [2] their unique structural, mechanical, electronic, and thermal properties have stimulated multi-and interdisciplinary research activities in various fields of science. [3] With highly promising potential for applications, they are attractive building blocks for the development of future nanotechnology, resulting in novel materials and devices of great practical interest.[4] One strategy to achieving this goal is the fabrication of CNT/polymer composites with enhanced functionality. Matrices such as poly(vinyl alcohol) (PVA) [5,6] and epoxy [7] are examples where very low loading fractions of CNTs result in super-tough and highly reinforced materials. Additionally, due to the formation of conducting CNT networks, these types of composites are of interest for electronics applications, including electromagnetic shielding, electrostatic dissipation, antennas, and batteries. [5,8] Matrices of conjugated organic polymers with increased conductivity and thermal stability, two highly desired additional qualities for optoelectronic applications, [9] have been fabricated. In this area, composites of CNT/poly(p-phenylenevinylene) (CNT/PPV) [9±11] and CNT/poly (3,4-ethylenedioxythiophene) (CNT/PEDOT) [12] have proven their functionality in light-emitting diodes and photovoltaic cells. CNT/polyaniline (CNT/PANI) composites have already found use as printable conductors for thermalimaging techniques.[13]In all cases, two important factors for device applications, operational functionality and processability, are directly linked to favorable interactions between CNTs and the polymer chain conformation. In this sense, PANI deserves some more scrutiny. Its non-planar chain architecture (the three PANI amine-benzenoid units acquire certain ring-torsion angles with respect to its flat imine±quinoid units) should, in principle, reduce opportunities for strong interactions with CNTs. [14] However, all studies on CNT/PANI composites reveal good interactions between both components.[15±18] This is even more pronounced when polymerization takes place in the presence of CNTs. [15,16] In these in-situ studies, the CNTs used were arc-grown multiwalled carbon nanotubes (MWNTs), and aniline was polymerized into the conducting but non-soluble emeraldine salt (ES) [19] form, resulting in a non-processable MWNT/ES composite. In this communication, we report for the first time the formation of a soluble self-aligned CNT/PANI composite consisting of MWNTs and the non-conducting but soluble emeraldine base (EB) [19] form of PANI. Further processing of the composite into colored thin films was achieved. The characteristics of the composite in solution, in powder form, and as a film have been measured. The results provide evidence that polymerization in the presence of carbon nanotubes leads to a more planar conformation of PANI along MWNTs. This is stabilized by strong p±p interactions between both components and accompanied b...

One of the essential functions of mucous gel is protection of tissues against dehydration. The effect of hydration on the structural and thermodynamic properties of pig gastric mucin (PGM) and bovine submaxillary gland mucin (BSM) have been studied using atomic force microscopy (AFM), sorption, and differential scanning calorimetry (DSC). The analysis of sorption isotherms shows the higher water sorption capacity of PGM compared to BSM at RH levels lower than about 78%. The value of the hydration enthalpy at zero water content at 25 °C for both biopolymers is about -20 kJ/mol. Glass transitions of BSM and PGM occur at RH levels between 60 and 70% for both mucins. AFM indicates the presence of a dumbbell structure as well as a fiber-like structure in PGM samples. The experimental volume of the dry dumbbell molecule obtained by AFM is 3140 ± 340 nm(3). Using DSC data, the amount of nonfreezing water was calculated to be about 0.51 g/g of PGM. The phase diagram of PGM demonstrates two regions of different Tg: dependent and independent of hydration levels. In particular, at mucin concentrations from 0 to 67 wt %, the glass transition occurs at a constant temperature of about -15 °C. At higher concentrations of mucin, Tg is increasing with increasing mucin concentrations.

Two blue multicopper oxidases (MCOs) (viz. Trametes hirsuta laccase (ThLc) and Myrothecium verrucaria bilirubin oxidase (MvBOx)) were immobilized on bare polycrystalline gold (Au) surfaces by direct adsorption from both dilute and concentrated enzyme solutions. The adsorption was studied in situ by means of null ellipsometry. Moreover, both enzyme-modified and bare Au electrodes were investigated in detail by atomic force microscopy (AFM) as well as electrochemically. When adsorbed from dilute solutions (0.125 and 0.25 mg mL −1 in the cases of ThLc and MvBOx, respectively), the amounts of enzyme per unit area were determined to be ca. 1.7 and 4.8 pmol cm −2 , whereas the protein film thicknesses were determined to be 29 and 30 Å for ThLc and MvBOx, respectively. A wellpronounced bioelectrocatalytic reduction of molecular oxygen (O 2 ) was observed on MvBOx/Au biocathodes, whereas this was not the case for ThLc-modified Au electrodes (i.e., adsorbed ThLc was catalytically inactive). The initially observed apparent k cat app values for adsorbed MvBOx and the enzyme in solution were found to be very close to each other (viz. 54 and 58 s −1