Eliane Espuche

A comparative study of the effects of ammonia and hydrogen plasma downstream treatment on the surface modification of polytetrafluoroethylene

Abstract Polytetrafluoroethylene (PTFE) was treated with hydrogen and ammonia microwave plasmas and the effects of treatment were evaluated by means of advancing and receding contact angle measurements, X-ray photoelectron spectroscopy, secondary-ion mass spectroscopy and atomic force microscopy analysis. Hydrogen plasma downstream treatment principally leads to defluorination and creation of Cue5f8C and Cue5f8H groups. This surface modification results in a slight decrease of the water contact angle and a large decrease of the methylene iodide contact angle. No evolution of the surface properties occurs over a period of at least two months following treatment. Ammonia plasma downstream treatment leads to defluorination and creation of Cue5f8C and Cue5f8H groups, as already observed with the H2 plasma, but also to the introduction of nitrogen-containing groups. The modification produces a decrease of both water and methylene iodide contact angles. A large hysteresis is found with water contact angles due to the reorientation of the polar groups when the surface is in contact with a polar liquid. The surface modifications that result after a NH3 plasma treatment are less stable than after a H2 treatment. Nevertheless, after two days of ageing the water contact angle reaches a constant value, which is largely inferior to that of the untreated PTFE.

Green synthesis of colloid silver nanoparticles and resulting biodegradable starch/silver nanocomposites

Environmentally friendly silver nanocomposite films were prepared by an ex situ method consisting firstly in the preparation of colloidal silver dispersions and secondly in the dispersion of the as-prepared nanoparticles in a potato starch/glycerol matrix, keeping a green chemistry process all along the synthesis steps. In the first step concerned with the preparation of the colloidal silver dispersions, water, glucose and soluble starch were used as solvent, reducing agent and stabilizing agent, respectively. The influences of the glucose amount and reaction time were investigated on the size and size distribution of the silver nanoparticles. Two distinct silver nanoparticle populations in size (diameter around 5 nm size for the first one and from 20 to 50 nm for the second one) were distinguished and still highlighted in the potato starch/glycerol based nanocomposite films. It was remarkable that lower nanoparticle mean sizes were evidenced by both TEM and UV-vis analyses in the nanocomposites in comparison to the respective colloidal silver dispersions. A dispersion mechanism based on the potential interactions developed between the nanoparticles and the polymer matrix and on the polymer chain lengths was proposed to explain this morphology. These nanocomposite film series can be viewed as a promising candidate for many applications in antimicrobial packaging, biomedicines and sensors.

Gas transport mechanism in sulfonated polyimides. Consequences on gas selectivity

Abstract Structure–properties relationships in terms of gas transport have been established for a large series of sulfonated copolyimides synthesized with a naphthalenic dianhydride, a sulfonated diamine [SD] and various non-sulfonated diamines. For these two phases systems, a phase inversion has been evidenced for sulfonated block content ranging between 30 and 50%. The contribution of the dispersed sulfonated phase to the gas transport greatly depends on the structure of the non-sulfonated diamine. As a consequence, a large range of permeability values can be obtained varying the nature of the non-sulfonated diamine, the sulfonated diamine content and the sulfonated block length. The diffusion coefficient is in all cases the dominant factor in the transport phenomena and good compromise between O 2 /N 2 selectivity and O 2 flux can be achieved with these systems.

Water vapour transport mechanism in naphthalenic sulfonated polyimides

Abstract The morphology and the water transport properties of a large series of sulfonated copolyimides synthesised with a naphthalenic dianhydride, a sulfonated diamine and various non-sulfonated diamines were studied. For a sulfonated diamine content in the total diamine amount higher than 30%, the copolymers are composed by a continuous ionic phase and a dispersed non-sulfonated phase. The water sorption isotherms are of BET type II for all the copolymers and they result from the contribution of both the sulfonated and non-sulfonated phases. For the sulfonated phase, a two step sorption mechanism has been identified. It consists at low activity in sorption on ionic sites but also in unrelaxed holes formed during the triethylammonium/H + ionic exchange and at high activity in a clustering process. The contribution of the non-sulfonated phase to the transport phenomenon can be modulated by the hindrance brought by the non-sulfonated diamine and by its more or less hydrophobic character.

Synthesis and physical properties of new layered silicates based on ionic liquids: improvement of thermal stability, mechanical behaviour and water permeability of PBAT nanocomposites

Ionic liquids based on tetraalkylphosphonium and dialkyl imidazolium cations with long alkyl chains have been investigated as new surfactant agents for cationic exchange of lamellar silicates. The effect of the chemical nature of the ionic liquids on the thermal stability and on the surface energies of phosphonium-(MMT-201) and imidazolium-(MMT-I) treated montmorillonites have been studied by thermogravimetric analysis (TGA) and sessile drop method. Poly(butylene adipate-co-terephthalate) (PBAT) nanocomposites filled with a low amount of these modified-montmorillonites (2, 5 wt%) have been processed by melt mixing using a twin screw extruder. The mechanical, thermal, water and gas barrier properties of the corresponding nanocomposites as well as the distribution of the clay layers in PBAT matrix were determined.

Starch/silver nanocomposite: Effect of thermal treatment temperature on the morphology, oxygen and water transport properties.

The present work reports a strategy involving the preparation of nanostructured starch based film containing silver nanoparticles (AgNPs) using a completely green chemistry process. The nanocomposite films were prepared by solution cast process. The AgNPs were in situ generated inside the polymer film by thermal treatment at different temperatures (25, 40 and 85 °C). The influence of the presence and the amount of reducing agent (glucose) were also investigated. For all nanocomposite films, the AgNPs were spherical with a diameter less than 15 nm. Contrary to the presence of glucose, thermal treatment condition was a key factor for the AgNPs structure. Crystalline AgNPs were obtained only after thermal treatment at 85 °C. Improvements of water and oxygen barrier properties near to one decade were observed in this last case and were explained by the formation of crystalline AgNPs associated to the establishment of strong interactions between AgNPs and starch polymer matrix.

Sulfonated copolyimides: influence of structural parameters on gas separation properties☆

Abstract Structure-properties relationships in terms of gas transport have been established for a large series of sulfonated copolyimides. The permeability and diffusion coefficients of different gases (H2, O2, CO2, N2) differing by their size and interaction capacity towards the polymers have been determined. CO2 sorption experiments have also been carried out allowing a direct determination of the solubility coefficients. The analysis of the transport parameters as a function of the copolyimides structure and composition underlines the predominant role of the non-sulfonated sequences and shows that the permeability is mainly governed by the diffusion coefficient. A large range of permeability values can thus be obtained by varying the nature and the content of the non-sulfonated diamine in the copolyimides and for some copolymers, H2 and CO2 permeability values are similar. Furthermore, O2/N2 selectivity coefficients determined for all the membranes are located near the Robeson curve. As a consequence, some systems, notably those based on (CARDO/ODA) diamines mixture, present a good selectivity/permeability balance.

Gas transport properties of sulfonated copolyimides: Influence of structural parameters and relative humidity

Structure-property relationships in terms of gas transport have been established for a large series of sulfonated copolyimides. At anhydrous state, a large range of permeability values can be obtained varying the nature of the non-sulfonated diamine, the sulfonated diamine content and the sulfonated block length. The diffusion coefficient is in all cases the dominant factor that explains the permeability level. The gas permeability coefficients decrease when the copolyimides are hydrated. A particular behaviour has been evidenced on some membranes for carbon dioxide.