Gustavo M. Morales

Effects of high hydrochloric acid concentration on aniline chemical polymerization

The rate of aniline polymerization, measured by calorimetry, decreases when the hydrochloric acid concentration in the polymerization solution is increased from 2 to 6 M. The amount of chloride covalently bonded to the aromatic rings of the polymer backbone, estimated from the presence of new vibrational bands in the i.r. spectra, increases with an increment of hydrochloric acid concentration. The enlarged substitution on the polymer backbone is correlated with a decrease of the extension of the electronic conjugation, as shown by the shift towards higher energy of the broad band due to extended conjugation. The trend is related with a simultaneous decrease of the polymer d.c. conductivity.

An EQCM electroacoustic study of poly(vinylferrocene) modified electrodes in different aqueous electrolytes

Abstract In this paper we report the study of poly(vinylferrocene) films cast on Au electrodes by the electrochemical quartz crystal microbalance (EQCM) electroacoustic impedance technique. The simultaneous recording of the quartz resonant frequency and the surface electro-acoustic impedance of the quartz-film-liquid electrolyte composite system and a viscoelastic analysis of these parameters provide an estimate of the viscoelastic changes as a function of redox conversion and the mass changes as a result of solvent and ion exchange with the electrolyte. The changes in mass obtained by this method have been compared to the values calculated with the Sauerbrey approximation. By comparison of this information with results of probe beam deflection (PBD) technique under similar conditions for different electrolytes, the number of water molecules exchanged per electron/ion transferred, the ionic exchange mechanism and the shear modulus could be obtained. It has been found that they depend on the nature of the anion in the electrolyte. While the EQCM is sensitive to the total mass of ions and solvent exchanged with the electrolyte, the PBD detects the flux of ions exchanged but it is insensitive to the flux of solvent. We also describe for the first time the viscoelastic changes that take place during film conditioning by incorporation of solvent and ions during ‘break in’. Solvation of PVF+ produces an increase in the shear modulus at 10 MHz as a result of viscoelastic losses in the swollen polymer film with segmental motion of polyion strands and electrolyte trapped in the polymer structure.

A soluble and electroactive polyaniline obtained by coupling of 4-sulfobenzenediazonium ion and poly(N-methylaniline)

Abstract A modified polyaniline was obtained by coupling of the 4-sulfobenzenediazonium ion with poly ( N -methylaniline) (PNMANI) at temperatures below 5°C and in basic or neutral pH conditions. The FT-IR spectra of the product show all bands due to the poly( N -methylaniline). Additional bands at 1007, 1003 and 623 cm −1 are assigned to the vibrations of the sulfonate group, incorporated in the polymer matrix. A new band at 1485 cm −1 is also present, assigned to the stretching of the azo bond. The polymer is soluble in aqueous base. The results suggest the formation of an azo-substituted poly ( N -methylaniline): poly(4-sulfobenzenazo-( N -methylaniline)) (p(4SBA-NMANI)). The solution spectra show absorption bands at 242, 310 and 595 nm. Thin films deposited on glassy carbon show clear electroactivity. The method could be used to produce electroactive films with bonded functionalities.

Anion effects on aniline polymerisation

The polymerisation of aniline by oxidation with ammonium persulfate was studied, by potentiometry and calorimetry, in presence of different anions. It was observed that the nature of the anion affects clearly the polymerisation rate. Possible reaction mechanisms are proposed.

New methods of polyaniline functionalization

Abstract Novel synthetic methods of PANI functiooalization are described. We investigated coupling of diazonium salt and electrophilic nitration of the aromatic ring, amine group protection by amide formation, nucleophilic reaction with activated aromatic moieties and nucleophilic addition of sulfite ions to the ring. The structure of the products and their properties were studied by FTIR, UV-vis spectroscopy and electrochemistry.

Flexible film materials from conjugated dye-modified polymer surfactant-induced aqueous graphene dispersions

A novel polymeric surfactant composed of a hydrophobic perylene dye covalently linked to hydrophilic poly(vinyl alcohol) (PVA) chains was employed to prepare stable aqueous dispersions of graphene. The presence of well-dispersed few layer graphene was demonstrated by UV-visible, Raman and fluorescence spectroscopy. This polymeric surfactant has an additional advantage in that it can be used to immobilize graphene within stable films that are transparent, flexible and easily processed. Indirect evidence of a strong interaction between perylene and graphene was obtained from the analysis of the physical properties of the polymer films. A complete loss of crystallinity and a remarkable reduction in segmental mobility manifested by an increase of around 50 °C in the glass transition temperature were observed. The imaginative molecular design of polymers covalently modified with planar aromatic molecules presents important opportunities in the development of new application possibilities of graphene.

Cofacial porphyrin multilayers via layer-by-layer assembly

This paper reports a new layer-by-layer assembly approach to fabricate multilayers of cofacially aligned porphyrins on solid supports by a selective siloxane formation utilizing tetraphenylporphyrinatosilicon(IV) chloride as the building block.

Synthesis of ultra-small cysteine-capped gold nanoparticles by pH switching of the Au(I)-cysteine polymer.

We report a synthetic approach for the production of ultra-small (0.6 nm) gold nanoparticles soluble in water with a precise control of the nanoparticle size. Our synthetic approach utilizes a pH-depending Au-cysteine polymer as a quencher for the AuNPs grown. The method extends the synthetic capabilities of nanoparticles with sizes down to 1 nm. In addition to the strict pH control, the existence of free -SH groups present in the mixture of reaction has been observed as a key requirement for the synthesis of small nanoparticles in mild conditions. UV-Vis, SAXS, XANES, EXAFS and HR-TEM, has been used to determinate the particle size, characterization of the gold precursor and gold-cysteine interaction.

Photolithography of Polyaniline on Solid Substrates Using Photoassisted Polymerization of Aniline

The time span of the induction period, present in aniline oxidative polymerization, is reduced by illumination of the solution with UV light. In that way, aniline polymerization rate is increased. Based on such effect a photolithographic process to produce conductive polyaniline patterns is demonstrated.

Covalent chlorine incorporation during aniline polymerisation

Polyaniline formed electrochemically at high HCl concentration shows changes in its electrochemical properties which could be caused by covalent chlorine bonding to the polymer backbone. The bonding could be concluded from the analysis of the films infrared spectra.