Marianna M. Gorelova

Conducting SBS block copolymer–polyaniline blends prepared by mechanical mixing

Polyaniline was doped with dodecylbenzenesulfonic acid (Pani DBSA) in an agate mortar and used as a conductive additive in melt blends with styrenebutadiene-styrene (SBS) block copolymer. These blends exhibit relatively high levels of electrical conductivity at low-weight fractions of the polyaniline complex. The melt blending process, performed in a two-roll mill or in a Haake internal mixer, increased the protonation degree of the Pani DBSA, as indicated by X-ray photoelectron spectroscopy analysis. This result confirms the occurrence of a second doping process at high temperature. The mechanical performance decreases as the amount of Pani DBSA in the blend increases, indicating a plasticizing effect of the DBSA. The higher temperature used in blending imparts better conductivity value but gives rise to a strong crosslinked material because of the presence of the sulfonic acid and the high extent of double bonds in the SBS compound.

X-ray photoelectron spectroscopy and electrical conductivity of polyaniline doped with dodecylbenzenesulfonic acid as a function of the synthetic method

X-ray photoelectron spectroscopy (XPS) has been employed to investigate the protonation degree of polyaniline doped with dodecylbenzenesulfonic acid (Pani. DBSA) obtained by different synthetic methods. The protonation degree has been compared to electrical conductivity. Pani.DBSA prepared through the redoping process in an agate mortar displays conductivity values within the range of 1 S/cm. A protonation level of 48% with almost all imine groups being protonated. Pani.DBSA was also synthesized by oxidative polymerization of aniline in the presence of DBSA, which acts simultaneously as a surfactant and as protonating agent. This in situ doping polymerization was carried out in aqueous or toluene media. In both cases, protonation degrees higher than 50% have been achieved, indicating that a substantial portion of amine units have also been protonated. Higher doping degree has been achieved by aqueous dispersion polymerization of aniline. The C/N and S/N molar ratios obtained by XPS analysis indicate that the polyaniline chains obtained by in situ polymerization are protonated by both sulfonate and hydrogen sulfate anions.

Conductive polyaniline–polychloroprene blends

The electrical conductivity of polychloroprene (CR)/polyaniline (Pani) blends prepared by bulk and solution processes were investigated. Pani doped with HCl (Pani · HCl) and p-toluenesulfonic acid (Pani · TSA) were employed in vulcanized blends obtained by the bulk process. These blends showed an increase in the conductivity only for blend composition of CR/Pani = 50:50 wt %. At this composition, blends with Pani · HCl and Pani · pTSA presented conductivity values of 10−9 and 10−10 S · cm−1, respectively. CR/Pani · HCl blend films prepared by the solution process displayed surface conductivity values of 10−4 S · cm−1 with as low as 10–15 wt % of PAni · HCl. Surface analysis of these blends by X-ray photoelectron spectroscopy indicated no traces of the conductive additive. The surface composition was found to be exclusively constituted of CR.

Polyblend fibers from polypropylene and mercapto‐modified EVA

Polyblend fibers were made from mixtures of polypropylene (PP) and ethylene-vinyl acetate copolymers (EVA) or their mercapto-modified products [poly(ethyl-ene-co-vinyl acetate-co-vinyl mercaptoacetate)](EVASH). The presence of few EVA or EVASH in the PP fibers results in an increasing of the elastic modulus, indicating a reinforcing action of these functional polymers. The composition surface of the modified PP fibers was analyzed by X-ray photoelectron spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy.

Electroconducting composites based on polyaniline and monomer‐swollen polychloroprene

Electroconductive polychloroprene (CR)-polyaniline (Pani) composites were prepared by swelling the vulcanized rubber material in aniline followed by immersing the specimen in an aqueous solution of HC containing ammonium persulfate as the oxidant. The results obtained from surface and volume conductivity, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) analysis suggest that the Pani component is preferentially located in the surface layer. These composites display better electrical and mechanical performance than those obtained by mixing both polymer components in the bulk state.

Surface segregation of components in poly(vinyl chloride)-polydimethylsiloxane and polystyrene-poly(propylene oxide) solvent-cast blends

X-ray photoelectron spectroscopy and scanning electron microscopy are used to study the surface composition and morphology of poly(vinyl chloride)–polydimethylsiloxane (PVC–PDMS) and polystyrene–poly(propylene oxide) (PS–PPO) solvent-cast blends as a function of the blend composition and constituent molecular weights. The PVC–PDMS blends show a pronounced surface enrichment of PDMS, which is higher the lower the molecular weight of PDMS. The surface behavior ofthe PPO–PS blends is strongly dependent on the solvent used. Despite the much lower surface tension of PPO compared to that of PS, no surface segregation of PPO isobserved in the PPO–PS blends cast from tetrahydrofuran, while the blends cast from chloroform exhibit a high surface enrichment of PPO.

Effect of deformation on the surface composition of multicomponent polymers. II. Blends of polydimethylsiloxane–polysulfone block copolymers in polychloroprene

The effect of uniaxial stretching on the surface composition of dilute blends of polydimethylsiloxane/polysulfone 2500/44,000 and 2500/3500 block copolymers in polychloroprene is studied using X-ray photoelectron spectroscopy. The surface of the initial (unstretched) blends is found to be covered by a discontinuous copolymer overlayer with a thickness greater than the XPS sampling depth. The stretching leads to a substantial drop in the extent of the copolymer surface segregation. For the 2500/ 3500 block copolymer, the dependence of the surface composition of the blends on the stretching degree is well described by a homogeneous deformation model, whereas for blends of the 2500/44,000 copolymer, the stretching of the copolymer overlayer lags noticeably behind that of the polychloroprene matrix. In the blends of the 2500/3500 copolymer, the stretching has practically no effect on the distribution of the copolymer components in the near-surface region. By contrast, the 2500/44,000 copolymer shows a substantial surface depletion of siloxane with stretching.

Effect of deformation on the surface composition of multicomponent polymers. III. Behavior of surface-active additive on elastomer surface in stretching–contraction cycles

The effect of the stretching–contraction cycle on the surface composition and morphology of polychloroprene elastomer blended with small amounts of surface-active polydimethylsiloxane–polysulfone block copolymers was studied using X-ray photoelectron spectroscopy and scanning electron microscopy. Copolymers with a large concentration of rigid polysulfone block showed a substantial drop in the surface concentration of the copolymer additive after the stretching–contraction cycle, while copolymers with a large concentration of flexible siloxane segments retained their surface composition practically unchanged. Wrinkling of surface areas occupied by the additive, which occurred upon contraction of the sample to its initial dimensions, is believed to be the reason for the observed drop in surface concentration of the rigid copolymer additive.

An X-ray photoelectron spectroscopy study of the surface of siloxane-containing block copolymers

Abstract The formation of the surface of polysulphone-polymethylsiloxane and polycarbonate-polydimethylsiloxane block copolymers is studied by X-ray photoelectron spectroscopy over a wide range of block length ratios. When the bulk content of the polydimethylsiloxane block is 0·7–15·0% its surface concentration is 60–100%. Surface modification of the polycarbonate and polysulphone homopolymer films by introduction of block copolymers is studied. The surface layer morphology is described for various block length ratios in the block copolymers.

O Comportamento da Camada Superficial das Misturas Poliméricas nos Ciclos de Estiramento/Relaxamento. 1. Estiramento

Resumo: O efeito do estiramento uniaxial na superficie de varios compositos (misturas diluidas de copolimero polietersulfona/polidimetilsiloxano em policloropreno) foi estudado atraves do metodo de espectroscopia de fotoeletrons excitados por raios-X. A superficie inicial das misturas nao estendida foi beneficiada pelo copolimero (75-93%). O estiramento acarretou uma queda da segregacao superficial do copolimero. A comparacao dos dados experimentais com o estiramento teorico, para diversos modelos de extensao da camada superficial, permitiu concluir que o copolimero com o bloco de polisulfona curto, acompanha exatamente o estiramento da matriz, ao passo que o copolimero com o bloco de polisulfona longo se atrasa um tanto e se estende um tanto menos. Palavras-chave: Superficie, XPS, misturas polimericas, deformacao. The surface behavior of polymeric blends upon stretching/contraction 1. The stretching process Abstract: The effect of uniaxial stretching on the surface composition of blends of poly(dimethyl siloxane/poly(sulfone) block copolymers in polychloroprene is studied using X-Ray photoelectron spectroscopy. The surface of the initial (unstretched) blends was covered by copolymer overlayer. The stretching lead to a substantial drop of the copolymer surface segregation. The comparison of the experimental data with different models of deformation leads to the conclusion that copolymer overlayer with short segment of poli(sulfone) follows the deformation of CR matrix on stretching; however an overlayer with long poli(sulfone) segment is stretched with delay.