Thermally induced chemical evolution in polyimide films investigated by X‐ray photoelectron spectroscopy

Thermally modified polyimide films based on 1,4‐Phenylene diamine (p‐PDA) and 3,3′,4,4′ – Benzophenone tetracarboxylic dianhydride (BTDA) were prepared and their chemical structure transformation after thermal treatment at 350 °C–500 °C was investigated. X‐ray diffraction results revealed an increase in the polymer chain order for all treated PI samples as a consequence of the thermal treatment and chain interaction. TGA analysis showed that the heat treatment promoted different thermal degradation profiles. Electron spin resonance evidenced a large population of free radicals as a result of homogeneous bond cleavage when the thermal treatment was performed at 500 °C. X‐ray photoelectron spectroscopy analysis indicated that the chemical structure transformation not only occurs on the outer surface but also in the sub‐surface layer. These results show that controlled fast thermal treatment can produce materials with specific characteristics and may serve as a general strategy for changing both structural and chemical properties of the polymers. POLYM. ENG. SCI., 58:943–951, 2018. © 2017 Society of Plastics Engineers     

Analyzing the real advantages of bifunctional initiator over monofunctional initiator in free radical polymerization

Monofunctional initiators are extensively used in free radical polymerization. To enhance productivity, a higher temperature is usually used; however, this leads to lower molecular weights. Bifunctional initiators can increase the polymerization rate without decreasing the average molecular weight and this can be desirable. A bifunctional initiator is an important issue to be investigated, and it is of great interest to industries. The objective of this work is to study polymerization reactions with mono‐ and bi‐functional initiators through comprehensive mathematical models. Polystyrene is considered as case study. This work collects and presents some experimental data available in literature for polymerization using two different types of bifunctional initiators. Model prediction showed good agreement with experimental data. It was observed that the initial initiator concentration has a huge impact on the efficiency of initiators with functionality bigger than one and high concentrations of bifunctional initiator make the system behave as if it were a system operating with monofunctional initiator. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Vieillissement, parcours de trajet et competence environnementale.

Using an environmental psychology framework, this study proposes: (1) to evaluate elderly adults' macrospatial skills when they are confronted with a wayfinding task in an unknown real environment, and (2) to determine how these skills can link with the self-assessment their environmental competence. Sixty French women aged 71 to 92 and living in the Centre of France had to perform a wayfinding task by means of a map designed for the research project, and to answer the "Wayfinding" subscale of Pedersen's Environmental Competence Scale (1999). Results showed that the people who succeeded this wayfinding task needed two types of markers to effectively find their bearings (a mostly egocentric direction marker and a landmark such as a "building"), whereas those who failed preferentially used an allocentric direction marker. All the participants were able to estimate their environmental skills, such as defined by the "Wayfinding" subscale of Pedersen's Environmental Competence Scale. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A Fuzzy Statistical Rule Generation Method for Handwriting Recognition

This paper presents a statistical approach for rule-base generation of handwriting recognition. The proposed method integrates the heuristic feature selection with the statistical evaluation and thus improves the performance of the rule generation as well as of the fuzzy handwriting recognition system. Fuzzy statistical measures are employed to identify relevant features from a given large handwriting database. First an automatic rule-base mechanism is presented. To reduce the time needed for this generation mechanism an additional heuristic feature selection step is introduced. Tests show that this generated rule-base improved the recognition results over previous approaches.     

Synthesis and characterization of biodegradable poly(l-lactide)/layered double hydroxide nanocomposites

The effects of layered double hydroxide (LDH) composed by calcium/aluminum and magnesium/iron as divalent/trivalent cations and intercalated with dodecyl sulfate anion in the properties of poly(l-lactide) (PLLA) were analyzed. Two PLLA nanocomposites were produced by in situ intercalative bulk polymerization using 1 and 2 wt% of LDH. The PLLA nanocomposites were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and ultraviolet–visible spectroscopy (UV–VIS). XRD results demonstrated that PLLA nanocomposites showed a good dispersion of LDH in the polymeric matrix, which may have caused an increase in thermal stability indicated by thermogravimetric analysis. UV–VIS analyses showed that PLLA nanocomposites presented lower transmittance values when compared to the neat PLLA, which is an interesting characteristic for plastics used in food packaging. This enhancement in the properties of PLLA nanocomposites can enlarge the range of applications of this material in several areas.     

Study of intussusceptive angiogenesis in inflammatory regional lymph nodes by scanning electron microscopy

The aim of the present study was to verify the occurrence of intussusceptive angiogenesis in blood vessels from submandibular lymph nodes responsible for lymphatic drainage of the tongue. A surgical wound inflicted on the ventral tongue of male Wistar rats and submandibular regional lymph nodes were evaluated at different postoperative periods. Scanning electron microscopy (SEM) was used to observe 123 lymph nodes at times 2, 3, 7, 10, 14, and 21 postoperative days. During the analysis of the vascular models with SEM, intussusceptive angiogenesis was observed in all groups evaluated. This was more extensive on the second and third postoperative days (83.33% and 80%, respectively), representing in these groups the expansion of the vascular chain of lymph nodes. At 21 postoperative days, intussusceptive angiogenesis (42.85%) was suggestive of vascular remodeling. Microsc. Res. Tech. 2009. © 2009 Wiley‐Liss, Inc.     

Finite volume method as the numerical method for new emulsion polymerization tubular reactor with internal angle baffles

A finite volume method is used to solve a determinist mathematical model and to analyze the performance of an alternative design for an emulsion polymerization reactor with internal angular baffles as static mixer. It is assumed to be a steady‐state, cylindrical one‐dimensional model having a fully developed laminar plug flow. The Smith‐Ewart model is used to estimate the monomer conversion, the kinetics is of Arrhenius type, and laminar finite‐rate model is assumed to compute chemical source terms. The objective of this work is to develop the finite volume method for the new emulsion polymerization tubular reactor with internal angle baffles. The performance of the alternative reactor is compared with continuous tubular reactor with constant reaction temperature. The simulations were validated with experimental results for the isothermal and tubular reactor, with a good concordance. The results with baffles were better than without baffles in relation to desired properties such as particle size and viscosity. The problem is sufficiently well solved by finite volume method. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 6037–6048, 2006     

Modulation of Adhesion at Acrylic Adhesive-Silicone Elastomer Interfaces

We have recently reported a systematic investigation of the role of MQ resins (small silica-like nanoparticles) in the modulation of adhesion at silicone elastomer lens—nanometric thin acrylic surface anchored layer deposited on a silicon wafer through loading and unloading JKR experiments. This particular system was chosen as it allowed one to vary the MQ resin content in the elastomer, and to test its resulting effect on both the thermodynamic work of adhesion and the adhesive strength at elastomer—acrylic layer interfaces, avoiding any complication due to bulk mechanical properties of a relatively thick (in the micron range) acrylic layer. We present here a complementary investigation, aimed at understanding the role of the resins in the development of specific interactions at the interface. To do so the adhesive energy between silicone elastomers containing various amounts of MQ resins and model substrates made of self-assemble monolayers of thiol molecules with various amounts of carboxylic terminations have been measured through JKR tests. We show that the level adhesion at these interfaces results from a competition between increased interactions and decreased mobility associated with the incorporation of the resins inside the elastomer.     

Application of the Voronoï tessellation to study transport and segregation of grains inside 2D and 3D packings of spheres

This article provides a simple method to simulate the transport of a small bead through a static granular medium as a random walk on a network. This kind of displacement is strongly related to the geometry of the porous structure. A way to map the interparticle space is to calculate the Voronoï tessellation of the packing whose edges describe the network of pores of the medium. Then, the calculation of the probabilities to use each bond and a Monte-Carlo method for the choice of them, can simulate the displacement of the sphere. We introduce this technique for the inter-particle percolation of a fine particle through a packing of monosize spheres. We compare our numerical simulation with experiments performed in our laboratory. Then this technique is extended to the surface segregation. For the two kinds of segregation, we study the transverse diffusion and obtain a good agreement with experimental results. That our numerical simulation based on a rigorous geometric analysis of the medium is in agreement with inter-particle percolation and surface segregation experiments shows the importance of the study of the geometry of granular materials.