Mixed micelle formation between amino acid-based surfactants and phospholipids

The mixed micelle formation in aqueous solutions between an anionic gemini surfactant derived from the amino acid cystine (C(8)Cys)(2), and the phospholipids 1,2-diheptanoyl-sn-glycero-3-phosphocholine (DHPC, a micelle-forming phospholipid) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC, a vesicle-forming phospholipid) has been studied by conductivity and the results compared with the ones obtained for the mixed systems with the single-chain surfactant derived from cysteine, C(8)Cys. Phospholipid-surfactant interactions were found to be synergistic in nature and dependent on the type of phospholipid and on surfactant hydrophobicity. Regular solution theory was used to analyse the gemini surfactant-DHPC binary mixtures and the interaction parameter, β(12), has been evaluated, as well as mixed micelle composition. The results have been interpreted in terms of the interplay between reduction of the electrostatic repulsions among the ionic head groups of the surfactants and steric hindrances arising from incorporation of the zwitterionic phospholipids in the mixed micelles.     

Thermodynamic properties of liquid mixtures of carbon monoxide and methane

The equations of state of liquid methane at 125.00 K and of six liquid mixtures of carbon monoxide and methane at 116.30, 120.00 and 125.00 K have been measured from just above the saturation vapour pressure to the freezing pressure of methane. The results show that the excess volume V^E is large and negative at low pressures but becomes less negative as the pressure is increased, being almost zero at the highest pressures. The curve of V^E against the mole fraction x is very asymmetrical at low pressures, but becomes more symmetrical with rising pressure.The effect of pressure on the excess functions G^E, H^E and T·S^E has been calculated. H^E and T·S^E prove to be much more sensitive to pressure than G^E.Conformal solution theory, in the van der Waals one-fluid form, reproduces the experimental results very successfully.     

Surface tension for octafluorocyclobutane,n-butane and their mixtures from 233 K to 254 K,and vapour pressure,excess Gibbs function and excess volume for the mixture at 233 K

The surface tensions of octafluorocyclobutane (234 to 267 K), n-butane (238 to 273 K) and of their mixtures (232 to 254 K) have been measured by differential capillary rise; there is a slight minimum in the isotherms near x(c-C₄F₈) ≈ 0.8 but no maximum. The total vapour pressure and density of the liquid mixture were measured at the triple point temperature of c-C₄F₈, 233 K. The mixture displays marked positive azeotropy. The excess Gibbs function and excess volume are both large and positive but the deviation from ideality is insufficient for liquid—liquid immiscibility whose absence was confirmed by visual observation at temperatures down to the solid—liquid phase boundary. All the foregoing are consistent with theoretical expectations based upon the dominant effect of an interaction energy between the unlike components which is smaller than that predicted by the Berthelot geometric mean rule. No inferences can be drawn as to the role of chain flexibility.     

Transient behavior of Boger fluids under extended shear flow in a cone-and-plate rheometer

Three different dilute solutions of high molecular weight polymers in viscous, binary solvents were used in experiments performed in a cone-and-plate rheometer. The solutions all fall into the class of fluids referred to as Boger fluids and were previously used in studies of viscoelastic Taylor-Couette instabilities. Under prolonged shearing in the cone-and-plate geometry, these fluids all exhibited a decrease of the first normal stress growth function N₁⁺(t) from an initial plateau value to a second, lower plateau value. This behavior has been previously observed, but is here reported for widely used polyisobutylene-based Boger fluids for the first time. As in earlier studies (Magda JJ, Lee C-S, Muller SJ, Larson RG (1993) Macromolecules 26:1696–1706; MacDonald M, Muller SJ (1997) J Rheol Acta 36:97–109), the time at which this decrease occurs (the decay time) is much longer than the polymer molecules relaxation time. Here, we focus on three issues: 1) the time-temperature superposition of the first normal stress growth function N₁⁺(t), including the decay time and the value of the second plateau, 2) the sample recovery time required to reproduce the initial plateau value of N₁⁺ and the decay time, and 3) the relationship between the time scales for this decay of normal stresses and the onset of viscous heating induced instabilities in the Taylor-Couette geometry. Our results suggest that shear-induced conformational changes, possibly coupled to viscous heating of the sample, may be responsible for the decrease in the first normal stress growth function during prolonged shearing.     

Electrochromic and spectroelectrochemical properties of polythiophene β-substituted with alkyl and alkoxy groups

Journal of Solid State Electrochemistry - Polythiophenes are conjugated polymers that are highly promising candidates for use as an active layer in flexible optoelectronic devices. The...     

Thermal analysis of less common lignocellulose fibers

The thermal behavior of four unusual lignocellulose fibers — namely Caroa, Curaua, Piassava and Sponge gourd — is described. Caroa and Curaua fibers showed a more homogeneous thermal degradation, with a single peak dominating in the DTG curve. Piassava and Sponge gourd showed two separated peaks, revealing the more pronounced amounts of hemicellulose present at these fibers. All four fibers are, however, thermally stable up to temperatures of around 200°C. The activation energies for the thermal degradation of the fibers were similar, except for the Caroa fiber. The lower activation energy associated to this fiber was attributed to its higher hemicellulose to cellulose ratio.     

Synthesis and electrochemical investigation of <Emphasis Type="Italic">beta</Emphasis>-substituted thiophene-based donor–acceptor copolymers with 3,4-ethylenedioxythiophene (EDOT)

The present work reports the synthesis of four electron-acceptor beta-substituted thiophenes that were studied as monomers for electrochemical polymerization with 3,4-ethylenedioxythiophene (EDOT), an electron-donating monomer, aiming the combination of electron-acceptor and donor monomer thiophene to a simpler and convenient build up of novel donor–acceptor copolymeric materials via electrochemical polymerization. Four novel copolymers poly(EDOT-co-3-thiophene phenylacetate), (PEDOT-co-PPhTAc-2a), poly(EDOT-co-3-thiophene(4-nitrophenyl)acetate) (PEDOT-co-PPhTAc-2b), poly(EDOT-co-3-thiophenephenylcarboxylate) (PEDOT-co-PPhTCb), and poly(EDOT-co-3-(phenoxymethyl)thiophene) (PEDOT-co-PPhOMT) were electrochemically polymerized. The monomers were characterized by spectrometric techniques (FTIR, ¹H NMR, and ¹³C NMR), and the copolymers were identified by electrochemical analyses and FT-IR. Although the corresponding homopolymers could not be obtained, in the presence of EDOT, the copolymers were formed in a quasi-reversible electrochemical kinetics. The infrared spectra of the copolymers as well the electrochemical profile corroborates their obtaining. The mass variation during the electrosynthesis was analyzed using a quartz crystal microbalance. The film’s morphologies were investigated by SEM. Interestingly, the combination of electron-rich monomer thiophene (EDOT) and these electron-deficient carboxy-substituted thiophenes might be a convenient building block couple to increase the performance control of physic-chemical properties of mixed polythiophenes with innovative applications and they also showed a possible applicability as charge storage device.     

Liquid mixtures of xenon with fluorinated species: xenon + sulfur hexafluoride

The vapor-liquid equilibrium of binary mixtures of xenon + SF6 has been measured at nine temperatures from 235.34 to 295.79 K and pressures up to 6.5 MPa. The mixture critical line is found to be continuous between the critical points of the pure components, and hence, the system can be classified as type I phase behavior in the scheme of van Konynenburg and Scott. The excess Gibbs free energies have been calculated, and the experimental results have been interpreted using the statistical associating fluid theory for potentials of variable range (SAFT-VR). Additionally, the SAFT-VR equation has been used to model other systems involving SF6 and alkanes, illustrating the predictability of the approach and further demonstrating the transferability of parameters between binary mixtures involving alkanes and xenon.     

Effect of surface treatments on the dynamic mechanical behavior of piassava fiber–polyester matrix composites

The effect of several fiber surface treatments upon the dynamic mechanical behavior of piassava fiber-reinforced composites was evaluated. In the light of the experimental results obtained the critical volume fraction for the fibers to effectively perform as reinforcement was established. The results show that all treatments performed (mercerization, acetylation, and mercerization + acetylation) enhance the fiber/matrix adhesion, but some treatments also affect the fiber’s integrity. At the elastic region the storage modulus of the composites fabricated with treated fibers was higher than that of the untreated fiber-reinforced composite. However, only the composite manufactured with 10 wt% mercerized fibers showed a statistically significant increase of the storage modulus. Above T _g the storage modulus was primarily governed by the volume fraction of fibers. Therefore, raw and treated fiber composites had essentially the same behavior.     

Simple synthesis of mixed cellulose acylate phosphonates applying n-propyl phosphonic acid anhydride

Cellulose mixed esters containing alkylphosphonate and carboxylate groups were prepared homogeneously by a new one-pot method using n-propyl phosphonic acid anhydride (T3P^?) in LiCl/N-methyl-2-pyrrolidone (NMP). n-Propyl phosphonic acid anhydride acts as both an activating agent for carboxylic acids and phosphonation reagent. Cellulose mixed esters with DS_acyl ranging from 1.4 to 1.8, and DS_phos up to 0.7 could be prepared. The structure of the cellulose mixed esters was elucidated by FTIR- and NMR spectroscopy, as well as by GPC and solubility tests.