Y. Haba

Polymerization of aniline in the presence of DBSA in an aqueous dispersion

Abstract This paper describes a unique process of polymerization in an aqueous medium of an anilinium–dodecyl benzene sulfonic acid (DBSA) complex obtained by reacting aniline with DBSA prior to polymerization. The typical properties of the complex, appearing as fine needles, have been characterized and its polymerization behavior in the presence of DBSA upon addition of ammonium peroxydisulfate in an aqueous medium was investigated by visual color inspection, UV-VIS spectroscopy and pH measurements. The polymerization process was interrupted at different stages and polyaniline (PANI) powders were obtained by precipitation with methanol. The powders morphology was investigated using scanning electron microscopy (SEM) and their electrical conductivity was measured on compression molded strips. UV-VIS and pH measurements show that the average oxidation state of the formed PANI chains vary during polymerization from doped pernigraniline to doped emeraldine and correlate with the dispersions color. In the beginning of the polymerization course, the SEM studies show agglomerates consisting of spherical PANI particles. As polymerization proceeds, the voids among these particles are filled, forming a smooth surface of the PANI agglomerates. Simultaneously, the conductivity of the PANI powders increases with the polymerization time.

Polyaniline–DBSA/polymer blends prepared via aqueous dispersions

Abstract Stable polyaniline–dodecyl benzene sulfonic acid (PANI–DBSA) aqueous dispersions were obtained by a unique method of aniline polymerization in the presence of DBSA, through an anilinium–DBSA complex appearing as solid needle-like particles, in an aqueous medium. The average size of the PANI primary particles, determined by small angle X-ray scattering (SAXS), is 18.7 nm. These primary particles form aggregates, which further cluster into ∼50 μm agglomerates. PANI–DBSA/polymer blends were obtained by mixing an aqueous PANI–DBSA dispersion with an aqueous emulsion of the matrix polymer, followed by water evaporation. These blends exhibit electrical conductivity already at a very low PANI–DBSA content (0.5 wt.%). The conductivity level of the various blends depends on the PANI content, on the surfactant present in the polymer matrix emulsion, and it is practically independent of the polymer matrix nature. Thus, a similar structuring mechanism prevails in these blends, irrespective of the polymer matrix (contrary to solution and melt blends). The PANI–DBSA particles strongly segregate within the polymer matrix, already in the combined aqueous dispersion, and upon drying, a very fine conductive network is formed. This strong segregation tendency leads to a conductive network formation already at low PANI–DBSA contents, thus generating the conductive blends.

On the structure and electrical conductivity of polyaniline/polystyrene blends prepared by an aqueous‐dispersion blending method

This article describes electrically conductive polymer blends containing polyaniline-dodecyl benzene sulfonic acid (PANI-DBSA) dispersed in a polystyrene (PS) matrix or in crosslinked polystyrene (XPS). Melt blending of previously mixed, coagulated, and dried aqueous dispersions of PANI-DBSA and PS latices lead to high conductivities at extremely low PANI-DBSA concentrations (∼0.5 wt % PANI-DBSA). In these blends, the very small size of the PANI-DBSA particles and the surface properties (with surfactants used) of both the PANI and polymer particles play a major role in the PANI-DBSA particle structuring process. The PANI-DBSA behavior is characteristic of a unique colloidal polymeric filler with an extremely high surface area and a strong interaction with the matrix, evidenced by a significantly higher glass-transition temperature of the matrix. The effect of the shear level on the conductivity and morphology of the PS/PANI-DBSA blends was studied by the production of capillary rheometer filaments at various shear rates. An outstanding result was found for XPS/PANI-DBSA blends prepared by the blending of aqueous XPS and PANI-DBSA dispersions. Some of these blends were insulating at low shear levels; however, above a certain shear level, smooth surface filaments were generated, with dramatically increased and stable conductivities.

Structured electrically conductive polyaniline/polymer blends

This paper describes electrically conductive polymer blends consisting of polyaniline (PANI) dispersed in a polymer matrix. Melt blending of previously mixed, coagulated and dried aqueous dispersions of PANI and the polymer matrix lead to high conductivities at extremely low PANI concentrations (∼0.5 wt% PANI). In these blends the surface properties (surfactants used) of the PANI and the polymer particles play a major role in the structuring process, in addition to the very small size of the PANI particles. In another approach, i.e. conventional melt blending of PANI powder with a given polymer powder, the success of generating an efficient conductive network depends on the PANI/polymer interaction level. A high interaction level (for example, similar solubility parameters) leads under dynamic hot blending conditions to the formation of conductive networks, but still at relatively high PANI concentration (>10 wt% PANI). To further reduce the PANI conductivity threshold concentration, ternary PANI/polymer/polymer blends can be designed, in which PANI is selectively attracted to the minor polymer component, thus generating double-percolation structures. The threshold PANI concentration in the ternary blends may be reduced by a factor of ∼2 compared to the binary blends. Further reduction can be expected in special ternary blends designed so that the PANI particles will mostly locate at the interfaces, rather than within the dispersed minor polymer particles. The blending method of aqueous dispersions is limited to matrix polymers which can be synthesized by emulsion polymerization. Thus, the conventional melt blending procedure and also the formation of ternary blend systems are particularly beneficial for condensation-type polymers, whereas melt blending of PANI/polymer powders prepared by the aqueous dispersions method is beneficial for the addition-type polymers. Copyright

Polyaniline/PVAc blends: Variation with time of structure and conductivity of films cast from aqueous dispersions

Recently, a polymerization process of Anilinium-Dodecyl Benzene Sulfonic Acid (DBSA) complex in an aqueous dispersion was developed in our laboratories. Simple mechanical mixing of the aqueous PANI–DBSA dispersion with a PVAc aqueous latex leads to highly conductive blends at low PANI–DBSA contents. The percolation threshold of the dried films is extremely low (∼0.5 wt %). The combined aqueous PVAc/PANI–DBSA dispersions exhibit a gradually decreasing electrical conductivity accompanied by a gradually increasing viscosity, with the storage time. However, an aged cast film from these blends maintains its electrical conductivity with time. These phenomena are associated with acidic hydrolytic reactions of the ester group, resulting in the formation of vinyl acetate–vinyl alcohol copolymer and evolution of acetic acid, and also the interaction of the DBSA surfactant with the PVAc, causing swelling and disintegration of PVAc particles. A chemical structural model describing these changes with storage time is suggested.