Zakaria Salmi

Core/shell, protuberance-free multiwalled carbon nanotube/polyaniline nanocomposites via interfacial chemistry of aryl diazonium salts

Highly uniform core-shell like multi-walled carbon nanotubes-polyaniline (MWCNT-PANI) nanocomposites were prepared in two steps (i) surface modification of MWCNTs with a 4-aminodiphenylamine group via in situ diazonium generation process; and (ii) polymerization of aniline onto surface modified MWCNTs. This functionalization helped to easily disperse the MWCNTs in acidic solutions; hence it is suitable for the chemical oxidative polymerization of aniline. It was found that MWCNT-PANI nano-composites with higher MWCNTs loading yield PANI chains with more quinoid units than the pure PANI, which results in significant improvement in the conductivity of the composites. This facile approach of synthesizing core-shell nanocomposites highlights the efficiency of the interfacial chemistry of aryl diazonium salts in generating conductive polymer/MWCNT nanocomposites with enhanced conductivity and high surface area.

One-step UV-induced modification of cellulose fabrics by polypyrrole/silver nanocomposite films

Cellulose fabrics were coated with polypyrrole-silver (PPy/Ag) nanocomposite films via one pot photopolymerization in aqueous media. This process was optimized for various concentrations of pyrrole/textile weight ratios with fixed molar ratio of [pyrrole]/[AgNO(3)] as 2.5. Simple weight measurements of the fabrics indicated progressive coating of PPy/Ag versus initial pyrrole/fabric weight ratio and photopolymerization time. X-ray diffraction (XRD) data confirm the nano-size (10-30 nm) and metallic state of Ag crystallites. The metallic state of silver particles was also confirmed by X-ray photoelectron spectroscopy (XPS). We demonstrate that UV-induced polymerization of pyrrole in the presence of AgNO(3) is simple and fast compared to chemical oxidative polymerization in the absence of UV light. More importantly, it permits to coat cellulose fabrics in one pot by polypyrrole/Ag nanocomposites films in environmentally friendly aqueous solutions at room temperature.

On the interfacial chemistry of aryl diazonium compounds in polymer science

This review emphasises the role of aryl diazonium compounds as a new class of coupling agents for grafting polymer thin layers onto carbon, diamond, metals, metal oxides, alloys, semi-conductors, ceramics, and polymers. Physical and chemical methods are first reported for anchoring aryl layers to the surfaces, then the review concentrates on the modification of the above substrates by thin polymer films via a range of the “grafting from” and “grafting onto” strategies. Some applications are described which highlight the important role that diazonium salts will continue to play in the near future in the polymer and surface sciences.

One step synthesis of highly ordered free standing flexible polypyrrole-silver nanocomposite films at air–water interface by photopolymerization

Free standing polypyrrole-silver nanocomposite films were prepared by interfacial photopolymerization of pyrrole (in DCM) using AgNO3 (aqueous) as photosensitizer. During the photopolymerization process, film formation starts first at the DCM–water interface and later at the air–water interface. The films prepared at the air–water interface are thin (<1 μm), flexible, having a very low content of uniformly distributed metallic Ag nanoparticles and exhibiting high electrical conductivity ∼14.8 S cm−1. The thick films (∼200 μm) prepared at the DCM–water interface are porous, mechanically weak, contain a very high amount of Ag micro and nanoparticles and exhibit two orders of magnitude lower conductivity ∼0.1 S cm−1. High conductivity of PPy-Ag films formed at the air–water interface is attributed to controlled polymerization due to the limited availability of pyrrole and Ag+ ions at this interface.

Bending stress induced improved chemiresistive gas sensing characteristics of flexible cobalt-phthalocyanine thin films

We report chemiresistive gas sensing characteristics of cobalt phthalocyanine films deposited on flexible bi-axially oriented polyethylene terephthalate substrates. Charge carrier mobility in these films systematically decreases upon bending, which implies that bending reduces π-π interactions among molecules. At room temperature, these films exhibited a reversible change in resistance on exposure to ammonia (5–50 ppm) along with high sensitivity and selectivity as well as fast response and recovery. The chemiresistive sensing properties were found to improve significantly under bend conditions owing to creation of more numbers of interaction sites.

Electrochemical investigation of free-standing polypyrrole–silver nanocomposite films: a substrate free electrode material for supercapacitors

We report a facile route for synthesis of free standing polypyrrole–silver (PPy–Ag) nanocomposite films by photopolymerization of pyrrole using AgNO3 as photosensitizer in aqueous medium. In this process PPy–Ag films were formed at the air–water interface and at the bottom of the beaker. The films formed at the air–water interface are thin (≤2 μm), flexible, have a uniform distribution of metallic Ag nanoparticles and exhibit electrical conductivity (∼1.5 S cm−1). The thick (∼200 μm) PPy–Ag films prepared at the bottom of the beaker exhibit lower conductivity (∼0.15 S cm−1). Interestingly, the more conductive thin PPy–Ag films exhibit a low specific capacitance of 58 F g−1 as compared to the specific capacitance of 282 F g−1 for the thicker PPy–Ag films at a 1 mV s−1 scan rate in 0.5 M K2SO4 electrolyte. The better electrochemical activity and high specific capacitance of the thicker PPy–Ag films is attributed to their porous structure, which provides a larger electrolyte accessible conductive surface for redox reactions. This simple approach for the synthesis of PPy–Ag films along with their promising electrochemical properties allows their possible application as a substrate free electrode material for supercapacitors.

Flexible cobalt-phthalocyanine thin films with high charge carrier mobility

The structural and charge transport characteristics of cobalt phthalocyanine (CoPc) films deposited on flexible bi-axially oriented polyethylene terephthalate (BOPET) substrates are investigated. CoPc films exhibited a preferential (200) orientation with charge carrier mobility of ∼118 cm2 V−1 s−1 (at 300 K). These films exhibited a reversible resistance changes upon bending them to different radius of curvature. The charge transport in CoPc films is governed by a bias dependent crossover from ohmic (J–V) to trap-free space-charge limited conduction (J–V2). These results demonstrate that CoPc films on flexible BOPET having high mobility and high mechanical flexibility are a potential candidate for flexible electronic devices.

Erratum to: “Zakaria Salmi, Sarra Gam-Derouich, Samia Mahouche-Chergui, Mireille Turmine, Mohamed M. Chehimi: On the interfacial chemistry of aryl diazonium compounds in polymer science”

Fig. 15. Survey spectra of AuC6H4CH2Br, AuC6H4CH2SCSNEt2, and Au–PHEMA (obtained by surface-initiated iniferter). AuC6H4CH2Br is prone to displacement of aryl groups by dithiocarbamate due to a favourable reaction between the latter and gold. If displacement is only partial, iniferter is successful as PHEMA is grafted (Au–PHEMA) as proved by high resolution C 1s feature. Conditions: AuC6H4CH2Br was prepared according to Mahouche et al. (2009) then allowed to react in 10 mL anhydrous tetrahydrofurane with 1.02 g (6 mmol) of Et2NCS2Na at r.t. for 3 h. SIPP was conducted in chloroform flushed with nitrogen under conditions similar to those reported by Gam-Derouich et al. (2010a).