Organothiol (R-SH) (OT) adsorption onto silver nanoparticles (AgNPs) in water was studied for a series of aromatic OTs including p-methylbenzenethiol (p-MBT), p-benzenedithiol (p-BDT), and 2-mercaptobenzimidazole (2-MBI). Unlike the common view that OT forms monolayer adsorption on AgNPs, we found that these aromatic OTs continuously reacted with AgNPs through formation of RS–Ag complexes until complete OT or AgNP consumption occurred. The RS–Ag complex can remain on the AgNP surface, converting the AgNPs into core–shell structures. The OT adsorption onto AgNPs occurs predominately through reaction with silver oxide present on the AgNP surfaces before the OT addition or formed from environmental oxygen in the presence of OT. The RS–H protons are completely released when both p-MBT and 2-MBI reacted with AgNP, Ag2O, and AgNO3. However, a substantial fraction of S–H bonds remained intact when p-BDT, the only dithiol used in this work, is adsorbed on AgNPs or reacted independently with Ag2O and AgNO3. The new insights from this work should be important for understanding OT interaction with AgNPs in water and the SERS spectra of the OT adsorbed onto AgNPs.

Science at the nanoscale has been one of the most exciting areas of recent investigation, with activities that are of both fundamental and technological significance. New physical phenomena and revolutionary nanoeletronic devices based on novel nanomaterials are anticipated. Organic conjugated systems have been successfully applied to electronics because of their versatile electronic properties and their adaptability to a broad range of processing methods. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] However, the development of polymer electronics at the nanoscale is in its infancy.Here we report the first synthesis of polythiophene nanoneedles that exhibit fast, field-induced conductance switching in a single nanocrystalline element.Most of the bulk conducting-polymer systems studied contain regions that are inhomogeneous. The investigation of processes in a nanodomain of a single crystal is critical in ascertaining the inherent electronic properties of polymer nanoelements. Single nanocrystals of conducting polymers have not been reported, although needle-shaped bulk crystals of the quarterphenyl cation radical salt have previously been studied, [15,16] and highly ordered polymer structures have been prepared by methods including electrochemical epitaxial polymerization, [10] solution spin-coating on functionalized surfaces, [17] and solid-state polymerization of monomer crystals. [18] To date, polythiophenes, together with polyanilines and polypyrroles, represent the most important classes of conducting polymers. [19] Applying an interfacial polymerizationcrystallization process, we have prepared single crystals of poly(3,4-ethylenedioxythiophene) (PEDOT) as nanoneedles.The aqueous/organic interface used consists of 3,4-ethylenedioxythiophene (EDOT) in an organic solvent and an oxidant, ferric chloride, in deionized (DI) water. The use of ferric chloride as an oxidant in the precipitation polymerization of thiophenes has been documented. [20][21][22] In these reactions, polymer chains are generally formed first, followed by the precipitation of crystals. Our system uses, for the first time, ferric chloride in the interfacial polymerization of thiophenes.As the crystal growth is simultaneous with polymerization, more ordered crystal packing can be expected. In a typical synthesis, EDOT dissolved in dichloromethane (DCM, 5 mL, 1 mg mL -1 ) served as the lower organic layer, and FeCl 3 dissolved in DI water (5 mL, 1 mg mL -1 ) formed the upper layer. After 2 days, the aqueous layer was carefully collected for purification. To prevent the hydrolysis of FeCl 3 , 5 drops of concentrated HCl (37 %) were added to the collected suspension. The nanoneedle suspension was then centrifuged, and the precipitate was re-suspended. This process was repeated twice and was followed by a final dialysis step in ultrapure water (resistivity 18.2 MX cm, total organic carbon level 10 ppb) for 10 h. The oxidative coupling polymerization of EDOT at the aqueous/organic interface was facilitated by FeCl 3 [23] and is an example of a s...

Determination of the true surface areas, concentrations, and particle sizes of gold nanoparticles (AuNPs) is a challenging issue due to the nanoparticle morphological irregularity, surface roughness, and size distributions. A ligand adsorption-based technique for determining AuNP surface areas in solution is reported. Using a water-soluble, stable, and highly UV-vis active organothiol, 2-mercaptobenzimidazole (MBI), as the probe ligand, we demonstrated that the amount of ligand adsorbed is proportional to the AuNP surface area. The equivalent spherical AuNP sizes and concentrations were determined by combining the MBI adsorption measurement with Au(3+) quantification of aqua regia-digested AuNPs. The experimental results from the MBI adsorption method for a series of commercial colloidal AuNPs with nominal diameters of 10, 30, 50, and 90 nm were compared with those determined using dynamic light scattering, transmission electron microscopy, and localized surface plasmonic resonance methods. The ligand adsorption-based technique is highly reproducible and simple to implement. It only requires a UV-vis spectrophotometer for characterization of in-house-prepared AuNPs.

Polyaniline (PANI) is one of the most accessible conducting polymers and is known for its environmental stability in its partially oxidized conductive state. However, it is difficult to process and undergoes electrochemical degradation between its partially and fully oxidized states. While there have been several approaches to address PANI’s processability, little has been done to address its electrochemical instability. We have prepared two polyaniline derivatives that contain a phenoxazine unit copolymerized with 2,5-dimethyl-p-phenylenediamine (P1) and p-phenylenediamine (P2) and determined their optoelectronic properties, processability, morphology, and electrochemical stability. Camphor sulfonic acid (CSA) doped polymers were dissolved in organic solvents and cast into films, which were analyzed by absorption spectroscopy, cyclic voltammetry, and conductivity measurements. Importantly, the films exhibit outstanding electrochemical stability over multiple redox and spectroelectrochemical cycles and conductivity in the high semiconductive regime (0.1 to 1 S/cm) when exposed to m-cresol vapors. Additionally, P1 exists as aggregates in the absence of m-cresol vapors, but as highly conductive sheet-like structures in the presence of m-cresol as shown by SEM, TEM, and AFM images. These results show that P1 and P2 would be outstanding candidates for applications that required stable redox conductive polymers.

Utilizing the inherent negative charge of mica surfaces, amine-functionalized magnetic nanoparticles (Fe3O4/NH2) were electrostatically adsorbed onto the mica such that surface-initiated ATRP could be used to grow poly(n-isopropylacrylamide) (PNIPAM) from the exposed hemisphere. By reducing the solution pH, a positive charge generated on the mica was used to release the nanoparticles from the substrate. A second ATRP reaction was carried out to grow poly(methacrylic acid) (PMAA) from the initiated surfaces. As a result, the Fe3O4/NH2 core has a polymer shell with one hemisphere PMAA and the other hemisphere PNIPAM-b-PMAA resulting in the PMAA-Fe3O4-PNIPAM-b-PMAA bicompartmental polymer Janus nanoparticles. Elemental and functional group compositions were confirmed using ATR-FTIR, XPS, and EDS. Imaging with AFM, SEM, and TEM showed the evolution of the Janus nanoparticle morphology. This study demonstrates a facile and innovative scheme involving a noncovalent solid protection technique combined with sequential, surface-confined controlled radical polymerizations for the production of multicomponent nanocomposites.

Nanoparticle self-assembly is fundamentally important for bottom-up functional device fabrication. Currently, most nanoparticle self-assembly has been achieved with gold nanoparticles (AuNPs) functionalized with surfactants, polymeric materials, or cross-linkers. Reported herein is a facile synthesis of gold and silver nanoparticle (AgNP) films assembled onto thiophene oil by simply vortex mixing neat thiophene with colloidal AuNPs or AgNPs for ∼1 min. The AuNP film can be made using every type of colloidal AuNPs we have explored, including sodium borohydride-reduced AuNPs with a diameter of ∼5 nm, tannic acid-reduced AuNPs of ∼10 nm diameter, and citrate-reduced AuNPs with particle sizes of ∼13 and ∼30 nm diameter. The AuNP film has excellent stability and it is extremely flexible. It can be stretched, shrunken, and deformed accordingly by changing the volume or shape of the enclosed thiophene oil. However, the AgNP film is unstable, and it can be rapidly discolored and disintegrated into small flakes that float on the thiophene surface. The AuNP and AgNP films prepared in the glass vials can be readily transferred to glass slides and metal substrates for surface-enhanced Raman spectral acquisition.

Abstract:We report the preparation of carbon-based nanomaterials from biopolymer kraft lignin via an iron catalytic thermal treatment process. Both the carbonaceous gases and amorphous carbon (AC) from lignin thermal decomposition were found to have participated in the formation of graphitic-carbon-encapsulated iron nanoparticles (GCEINs). GCEINs originating from carbonaceous gases have thick-walled graphitic-carbon layers (10 to 50) and form at a temperature of 700 • C. By contrast, GCEINs from AC usually have thin-walled graphitic-carbon layers (1 to 3) and form at a temperature of at least 800 • C. Iron catalyst nanoparticles started their phase transition from α-Fe to γ-Fe at 700 • C, and then from γ-Fe to Fe 3 C at 1000 • C. Furthermore, we derived a formula to calculate the maximum number of graphitic-carbon layers formed on iron nanoparticles via the AC dissolution-precipitation mechanism.

The aim of this work was to enhance poly(lactic acid)'s (PLA) flexibility and ductility by blending it with another bioplastic. Poly(trimethylene malonate) (PTM), developed as part of this study, was synthesized from 1,3-propane diol and malonic acid via melt polycondensation. Blend films of PLA and PTM were prepared by solvent casting from chloroform. Differential scanning calorimetry and thermogravimetric analysis were used to show shifted phase transitions and a single glass-transition temperature, indicating miscibility of PTM in the blend films. Morphology and mechanical characterizations of the PLA/PTM blend films were performed by atomic force microscopy using a quantitative nanomechanical property mapping mode, tensile testing, and scanning electron microscopy. Miscible blends exhibited Young's modulus and elongation at break values that can significantly extend the usefulness of PLA in commercial applications. The blending of PTM with PLA resulted in films with a 27-fold increase in toughness compared with neat PLA film.