Hygroscopic study of hydroxypropylcellulose : Structure and strain-induced birefringence of capillary bridges.

The hygroscopic method developed previously for studies of lyotropic liquid crystals is used for the first time in experiments with millimetric capillary bridges made of a hydroxypropylcellulose/water mixture. Composition of such very small samples is controlled via humidity of the surrounding air. By a slow and well-controlled drying of initially isotropic samples, the isotropic/anisotropic phase transition is crossed and polydomain pseudo-isotropic capillary bridges are prepared. Kept in an atmosphere of constant humidity, these bridges are stretched and the strain-induced birefringence [Formula: see text] n is measured as a function of the draw ratio [Formula: see text] . The variation of [Formula: see text] n with [Formula: see text] is interpreted in terms of an affine uniaxial deformation of the initial pseudo-isotropic texture.

Mechanical properties of thin confined polymer films close to the glass transition in the linear regime of deformation: theory and simulations.

Over the past twenty years experiments performed on thin polymer films deposited on substrates have shown that the glass transition temperature T(g) can either decrease or increase depending on the strength of the interactions. Over the same period, experiments have also demonstrated that the dynamics in liquids close to the glass transition temperature is strongly heterogeneous, on the scale of a few nanometers. A model for the dynamics of non-polar polymers, based on percolation of slow subunits, has been proposed and developed over the past ten years. It proposes a unified mechanism regarding these two features. By extending this model, we have developed a 3D model, solved by numerical simulations, in order to describe and calculate the mechanical properties of polymers close to the glass transition in the linear regime of deformation, with a spatial resolution corresponding to the subunit size. We focus on the case of polymers confined between two substrates with non-negligible interactions between the polymer and the substrates, a situation which may be compared to filled elastomers. We calculate the evolution of the elastic modulus as a function of temperature, for different film thicknesses and polymer-substrate interactions. In particular, this allows to calculate the corresponding increase of glass transition temperature, up to 20 K in the considered situations. Moreover, between the bulk T(g) and T(g) + 50 K the modulus of the confined layers is found to decrease very slowly in some cases, with moduli more than ten times larger than that of the pure matrix at temperatures up to T(g) + 50 K. This is consistent with what is observed in reinforced elastomers. This slow decrease of the modulus is accompanied by huge fluctuations of the stress at the scale of a few tens of nanometers that may even be negative as compared to the solicitation, in a way that may be analogous to mechanical heterogeneities observed recently in molecular dynamics simulations. As a consequence, confinement may result not only in an increase of the glass transition temperature, but in a huge broadening of the glass transition.

Rhabdomyomatous (mesenchymal) hamartoma of the tongue: report of a case.

A 12-year-old girl presented with three yellowish polypoid lesions in the lateral border of tongue since birth. Histological examination showed oral mucosa covered by squamous epithelium and an underlying vascularized fibrous stroma, containing small and short bundles of striated muscle, corresponding to a rhabdomyomatous hamartoma.

Heterogeneous nature of the dynamics and glass transition in thin polymer films.

Recent experiments have demonstrated that the dynamics in liquids close to and below the glass transition temperature is strongly heterogeneous, on the scale of a few nanometers. We use here a model proposed recently for explaining these features, and show that the heterogeneous nature of the dynamics has important consequences when considering the dynamics of thin films. We show how the dominant relaxation time in a thin film is changed as compared to the bulk, as a function of the thickness, the interaction energy with the substrate, and the temperature. The corresponding time scales cover the so-called VFT (or WLF) regime and vary between 10(-8) s to 10(4) s typically. In the absence of interaction, our model allows for interpreting suspended films experiments, in the case of small polymers for which the data do not depend on the polymer weight. The interaction leads to an increase of T(g) for an interaction per monomer of the order of the thermal energy T. This increase saturates at the value corresponding to strongly interacting films for adsorption energies slightly larger and still of order T. In particular, we predict that the T(g) shift can be non-monotonous as a function of the film thickness, in the case of intermediate interaction strength.

The crossover from 2D to 3D percolation: theory and numerical simulations.

We describe here the crossover between 2D and 3D percolation, which we do on cubic and square lattices. As in all problems of critical phenomena, the quantities of interest can be expressed as power laws of /p-pc(h)/, where pc(h) and h are the percolation threshold and the thickness of the film, respectively. When these quantities are considered on the scale of the thickness h of the films, the corresponding numerical prefactors are of order one. However, for many problems, the scale of interest is the elementary one. The corresponding expressions contain then prefactors in power of h which we calculate. For instance, we show that the mass distribution n(m) of the clusters is given by a master function of h(-D+1/sigma2nu3)/p-pc(h)/1/sigma2(m), where h is the thickness of the film and D, nu3, sigma2 are tabulated 2D and 3D critical exponents. We consider also the size R2( m) of the clusters as a function of their mass m, for which we provide both scaling laws and numerical data. Therefore, any property corresponding to a given moment of mass and size can be obtained from our results. These results might be useful for describing transport properties, such as electric conductivity, or the mechanical properties of thin films made of disordered materials.

Porocarcinoma ecrino asociado a poroma ecrino, leucemia linfática crónica y tumor de colisión metacrónico / Eccrine porocarcinoma in association with eccrine poroma, chronic lymphocytic leukemia and cutaneous collision tumor

Se presenta el caso de un paciente de sexo masculino de 78 años, con porocarcinoma ecrino del brazo, de 18 meses de evolución, asociado a un poroma ecrino en la piel del abdomen. Se realiza tratamiento quirúrgico de ambas lesiones. El estudio complementario demuestra una leucemia linfática crónica. Además, presentó en la evolución un tumor de colisión carcinoma basocelular-queratosis seborreica. Se revisan las características clínicas e histopatológicas del porocarcinoma ecrino y se discute esta rara asociación con el poroma ecrino y la leucemia linfática crónica (AU)

Devil's staircase-type faceting of a cubic lyotropic liquid crystal

The faceting of monocrystals of the lyotropic cubic liquid crystals in equilibrium with a humid atmosphere is observed. Experiments reveal the presence of more than 60 different types of facets on the surface of a spherical crystal of radius R = 1 mm. The devil's staircase type of faceting has been predicted theoretically when the interaction between steps on the crystal surface is repulsive.