Equilibrium thermal behavior and morphology of organophilic montmorillonite/poly(ε‐caprolactone) nanocomposites

With differential scanning calorimetry, we have demonstrated a peculiar behavior under equilibrium conditions of neat poly(ε‐caprolactone) and its organophilic montmorillonite nanocomposites. In particular, in the determination of the equilibrium melting temperature by the extrapolation of the data of the melting temperature (T_m) versus the crystallization temperature (T_c), a bimodal trend has been observed. At the lower T_c's, the data of T_m follow a constant trend, whereas at the higher ones, the usual increasing trend has been obtained. Morphological observations by atomic force microscopy (AFM) have provided evidence of two different crystalline morphologies for the lower and higher T_c ranges. Moreover, AFM has shown that the thermal treatments strongly influence the clay dispersion in the polymer matrix. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 22–32, 2006     

Cocrystallization in blends of random tetrafluoroethylene fluorinated copolymers: The effect of the chain structure and crystallization conditions

The possibility of the cocrystallization of random fluorinated tetrafluoroethylene copolymers was investigated with differential scanning calorimetry and wide‐angle X‐ray scattering. In particular, mixtures composed of poly(tetrafluoroethylene)‐co‐(hexafluoropropylene) containing 8 or 1 mol % comonomer or poly(tetrafluoroethylene)‐co‐perfluoromethylvinylether (2–10 mol % comonomer) were examined. The extent of cocrystallization was determined by the difference in the comonomer content, being higher when the difference was lower, and it was favored when quenching from the melt state was adopted. Nevertheless, a key to determining the extent of cocrystallization was the behavior of counits with respect to inclusion or exclusion from the crystal lattice: when the components were different with respect to this behavior, they were not likely to be miscible in the crystal state even if the difference in the comonomer content was low. Moreover, the similarity in the crystallization rates between the components played an important role: the cocrystallization decreased as the difference in the crystallization rate increased until, when the difference became high enough, the blend became immiscible. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1477–1489, 2002     

Microcanonical relation between continuous and discrete spin models

A relation between a class of stationary points of the energy landscape of continuous spin models on a lattice and the configurations of an Ising model defined on the same lattice suggests an approximate expression for the microcanonical density of states. Based on this approximation we conjecture that if a O(n) model with ferromagnetic interactions on a lattice has a phase transition, its critical energy density is equal to that of the n=1 case, i.e., an Ising system with the same interactions. The conjecture holds true in the case of long-range interactions. For nearest-neighbor interactions, numerical results are consistent with the conjecture for n=2 and n=3 in three dimensions. For n=2 in two dimensions (XY model) the conjecture yields a prediction for the critical energy of the Bere?inskij-Kosterlitz-Thouless transition, which would be equal to that of the two-dimensional Ising model. We discuss available numerical data in this respect.     

Uniqueness of the density in an inverse problem for isotropic elastodynamics

We consider the unique determination of the density of a nonhomogeneous, isotropic elastic object from measurements made at the surface. We model the behavior of the bounded, 3-dimensional object by the linear, hyperbolic system of operators for isotropic elastodynamics. The material properties of the object (its density and elastic properties) correspond to the smooth coefficients of these differential operators. The data for this inverse problem, in the form of the correspondence between applied surface tractions and resulting surface displacements, is modeled by the dynamic Dirichlet-to-Neumann map on a finite time interval. In an earlier paper we show that the speeds of (compressional and sheer) wave propagation through the object are uniquely determined by the Dirichlet-to-Neumann map. Here we extend that result by showing that the density is also determined in the interior by the Dirichlet-to-Neumann map in the case, for example, that at only isolated points in the object. We use techniques from microlocal analysis and integral geometry to solve this fully three-dimensional problem.

     

Subgrid modeling of intrinsic instabilities in premixed flame propagation

This work is devoted to the investigation and subgrid-scale modeling of intrinsic flame instabilities occurring in the propagation of a deflagration wave. Such instabilities, of hydrodynamic and thermodiffusive origin, are expected to be of particular relevance in recent technological trends such as in the use of hydrogen as a clean energy carrier or as a secondary fuel in hydrogen enriched combustion. A dedicated set of direct numerical simulations is presented and used, in conjunction with coherent literature results, in order to develop scaling arguments for the propagation speed of self-wrinkled flames which are also supported by the outcomes of a weakly non-linear model, namely the Sivashinsky equation. The observed scaling is based on the definition of the number of unstable wavelengths in a reference hydrodynamic lengthscale, in other words the ratio between the neutral or cutoff lengthscale of intrinsic instabilities and the lateral domain of a planar flame. The scalings are then employed to develop an algebraic model for the wrinkling factor in the context of a flame surface density closure approach. An a-priori analysis shows that the model correctly captures the flame wrinkling caused by intrinsic instability at sub grid level. A strategy to include the developed self-wrinkling model in the context of a turbulent combustion model is finally discussed on the basis of the turbulence induced cut-off concept.     

Enzymatic digestion and mass spectrometry in the study of advanced glycation end products/peptides

An extensive study was carried out on HSA and non-enzymatically glycated HSA by enzymatic digestion with trypsin and endoproteinase Lys-C, with the aim of identifying specific glycated peptides deriving from enzymatic digestion of glycated HSA. They may be considered, in pectore, as advanced glycation end products/peptides. These compounds, important at a systemic level in diabetic and nephropathic subjects, are produced by enzymatic digestion of in vivo glycated proteins: They are related to the pathological state of patients and have been invoked as responsible for tissue modifications. The digested mixtures obtained by the two enzymes were analyzed by MALDI/MS and LC/ESI/MSn, and clear cut differences were found. First of all, the digestion products of glycated HSA are generally less abundant than those observed in the case of unglycated HSA, accounting for the lower proclivity of the former to enzymatic digestion. MS/MS experiments on doubly charged ions, comparisons with a protein database, and molecular modeling to identify the lysine NH2 groups most exposed to glycation, identified some glycated peptides in digestion mixtures obtained from both types of enzymatic digestion. Residues 233K, 276K, 378K, 545K, and 525K seem to be privileged glycation sites, in agreement with the fractional solvent accessible surface values calculated by molecular modeling.     

New nanohybrids of poly(ε‐caprolactone) and a modified Mg/Al hydrotalcite: Mechanical and thermal properties

Novel composites based on poly(ε‐caprolactone) (PCL) and an organically modified layer double hydroxide (LDH) obtained using the melt‐extrusion technique have been characterized through structural, thermal, and mechanical analyses. Although exfoliation has not been achieved and despite the very low content of filler (from 1 to 3% by weight), significant enhancements are obtained in the physical and mechanical properties of the composites with respect to neat PCL. As a consequence, LDHs can substitute other nanofillers, in particular, cationic clays for polymeric matrices. They can be modified by a large number of organic anions, generally more numerous than the cationic ones, and can be mixed in very simple ways with polymers. This makes such nanofillers suitable to obtain new hybrid materials for a series of applications, from active food packaging to intelligent materials for biomedical device, for example, controlled drug release. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 945–954, 2007     

Galois connections among fuzzy groups, similarities, distances

Given a set S, we define Galois connections between the lattices of the fuzzy subgroups of transformations in S, the lattice of the similarities in S and the lattice of the distances in S.     

Selective Formylation of Diphenols

An improved procedure for the regioselective formylation of ortho-and para-diphenols is described.