Clustering and percolation effects in microcrystalline starch-reinforced thermoplastic

The use of starch microcrystals as biodegradable particulate filler is evaluated by processing composite materials with a weight fraction of starch ranging from 0 to 60%. In a previous work [Macromolecules, 29, 7624] the preparation technique of a colloidal suspension of hydrolyzed starch and the processing of composite materials by freeze drying and molding a mixture of aqueous suspensions of starch microcrystals and synthetic polymer matrix were presented. Starch microcrystals with dimensions of a few nanometers were obtained from potatoes' starch granules, and it was found that this filler produces a great reinforcing effect, especially at a temperature higher than T_g of the synthetic matrix. Classical models for polymers containing nearly spherical particles based on a mean field approach could not explain this reinforcing effect. The morphology of these nanocomposite systems is discussed in light of aggregate formation and percolation concepts. The sorption behavior of these materials is also performed. Starch is a hygroscopic material, and it is found that the composites absorb more water, as the starch content is higher. The diffusion coefficient of the penetrant is predicted from modified mechanical three branch series-parallel model based on a percolation approach. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2211–2224, 1998     

Photoconductive Polysilanes Bearing Charge-photogenerating Groups Based on Carbazole. 1 Synthesis via the Reductive Coupling of Diorganodichlorosilanes with Sodium

In order to prepare photoconductive organic materials with high charge-photogenerating quantum yield and high charge-carrier mobility, it was attempted to synthesize (9-carbazolyl)methyldichlorosilane, 1a , methyl-3-(9-carbazolyl)propyldichlorosilane, 1b , and methyl-4-(9-carbazolyl)phenyldichlorosilane, 1c and to homo- and copolymerize them with classical diorganodichlorosilanes in a Wurtz-type polymerization with sodium in the presence of polar additives. 1b did not homo- or copolymerize in these conditions. Low molecular weight homopolymers and copolymers with dimethyldichlorosilane and methylphenyldichlorosilane were easily obtained with 1c . Side reactions involving the ring-opening of tetrahydrofuran (THF) and occurring in the reaction of the Grignard derivative of 9-(4-bromophenyl)carbazole and methyltrichlorosilane in THF did not allow the isolation of 1c in a pure form. © 1997 John Wiley & Sons, Ltd.     

Photoconductive Polysilanes Bearing Charge-photogenerating Groups Based on Carbazole. 2 Synthesis via the Chemical Modification of Poly(alkylphenylsilane)s

The chemical modification of poly(alkylphenylsilane)s via the partial dearylation by reaction with triflic acid followed by the nucleophilic substitution of triflate groups by carbazolyllithium and 4-(9-carbazolyl)phenyllithium was applied to poly(methylphenylsilane)s and poly(ethylphenylsilane)s prepared under various experimental conditions in order to obtain polysilanes exhibiting photoconductive properties combining the high charge-photogenerating quantum yield of poly(vinylcarbazole) and the high charge-carrier mobility of polysilanes. Polymers containing 7–20% of the desired unit bearing the potential charge photogenerating site were synthesized by this way. The strong degradation of the Si chain induced by triflic acid limits the molecular weight and, in some cases, the amount of isolated derivatized polysilanes. When the charge-photogenerating sites are conjugated with the Si chain, the corresponding polysilanes doped with 2,4,7-trinitro-9-fluorenone (TNF) may exhibit improved photoconductive properties compared with those observed for the poly(vinylcarbazole)/TNF system. © 1997 John Wiley & Sons, Ltd.     

Polymers for electrochemical devices

Polymeric materials are already present in electrochemical storage devices such as batteries and PEM fuel cells. The polymer is an electro-active material in lithium polymer batteries. Several network based polymer electrolytes provide thermal, mechanical and redox stabilities, while insuring a high conductivity level. Linear unsaturated polyether precursors may be obtained either by step-growth polymerization from oligomeric polyethers, or by ring-opening polymerization from oxirane mixtures. Some prototype performances, performed on a 10 Wh lithium polymer cell, are presented and discussed.     

Dielectric properties under corona charging of thermoplastics for holographic optical switching

Photothermoplastics are materials which have been proposed for optical switching devices: a grating is recorded by surface deformation of the thermoplastic layer, coated on an organic photoconductive layer used, like in xerography, for an electrostatic image recording material. But first of all an electrical field is applied through a corona charging sequence and obviously dielectric properties of the abietic ester thermoplastic material are of importance. This paper discusses the behaviour of such a layered thermoplastic material in a corona set-up, by measuring the corona current and the surface voltage following thickness and temperature of the sample and charging or discharging times.     

Anion-π Interaction for Molecular Recognition of Anions: Focus on Cooperativity with Hydrogen Bonding

Anion recognition represents an active area of research in supramolecular chemistry. The last two decades have been marked by spectacular advances in the design of new anion receptors. Moreover, the development of approaches combining experimental and theoretical studies has proved to be particularly relevant, allowing for a better understanding and rationalization of the phenomena involved in anion complexation processes. In this context, the combination of weak interactions within the same receptor and their synergistic effects, called cooperativity, has attracted increasing interest within the scientific community. This Review focuses on the combination of anion-π and hydrogen bonds and the emerging concept of cooperativity. The most relevant anion-π donor families are presented. The concept of cooperativity is illustrated using the most recent examples present in current literature.