Paul Bernazzani

Volume recovery of polystyrene: evolution of the characteristic relaxation time

Abstract We have developed a new experimental technique that uses intermittent temperature perturbations during volume recovery in order to obtain quantitative information concerning the evolution of the characteristic relaxation time for volume during structural recovery. The experiments are analogous to the intermittent creep experiments developed by Struik. Using an automated capillary dilatometer and a polystyrene sample, the time-temperature history dependence of the characteristic relaxation time for volume was investigated. Our preliminary results show that for the set of temperature down jumps and memory experiments investigated, the characteristic relaxation time appears to depend only on the instantaneous state of the material. However, the results are not totally consistent with the Tool–Narayanaswamy model/Kovacs–Aklonis–Hutchinson–Ramos model.

Effect of substrate interactions on the melting behavior of thin polyethylene films

Polymer films have been known to change their physical properties when film thickness is decreased below a certain value. The cause of this phenomenon is still unclear but it has been suggested that interactions and/or chain free-volume changes at the surface of the films are largely responsible for this behavior. In this paper, the effect of substrate interactions on the behavior of polymer thin films is evaluated quantitatively. The infrared spectra of nanothin polyethylene (PE) films were recorded as a function of temperature and amount of substrate covering the surface of the film. The evolution of specific bands in the CH2 rocking region of the spectra was used to determine the melting temperature (Tm) of the material. Results show different variations in Tm depending on the nature of the substrate, indicating that interactions dominate free-volume considerations in PE thin films. By varying the amount of surface coverage, a quantitative estimate of the heat of interaction was determined, which confirmed the importance of surface interactions.

A new pressurizable dilatometer for measuring the time-dependent bulk modulus and pressure-volume-temperature properties of polymeric materials

A new piston-cylinder-type pressurizable dilatometer controlled by a stepper motor has been developed to measure the time-dependent bulk modulus and pressure-volume-temperature (PVT) behavior of polymeric materials. The dilatometer can be operated from 35 to 230 degrees C and at pressures of up to 250 MPa. The sample cell, which contains the sample and a fluorinated oil as the confining fluid, is totally submerged into a high precision oil bath to achieve a temperature stability of better than 0.01 degrees C. The instrument is calibrated with mercury and quartz. The total instrument volume is 4.0 cm(3), of which 2.3 cm(3) is the sample cell; the total volume can be measured with an average absolute error of better than 5.0x10(-4) cm(3). To demonstrate the instruments capabilities, the time-dependent bulk modulus and the PVT behavior of a polystyrene are obtained and compared to the literature.

Phase change in amylose–water mixtures as seen by Fourier transform infrared

The phase content of amylose-water mixtures (0.7/0.3 w/w) has been analyzed by transmission Fourier transform infrared (FTIR) spectroscopy in the 1175-950 cm(-1) region. Spectra are obtained under three different conditions: (a) as a function of temperature (T) from 25 to 97 degrees C; (b) at room temperature (RT), after slow cycles of T; and (c) at RT after quenching. T(max), the maximum temperature in the cycle, ranges from 50 to 120 degrees C. The quality of the seven-band spectra allows for an unambiguous determination of each band area. Unexpectedly, slow cooling after different T(max) brings about wide changes in the spectra while quenching does not. Two jumps in the absorbance are found: one at 70 degrees C and the other above 105 degrees C. Previous work on slow calorimetry of amylose-water mixtures suggests that these temperatures correspond to the beginning and the end of the same physical phenomena that takes place slowly between these two temperatures-namely the dissolution of the strained network phase. The spectra have two distinct regions, the low wavenumber region (1078-950 cm(-1)) and the high wavenumber region (1175-1078 cm(-1)). A distinct gain in the integrated absorbance of the 1175-1078 cm(-1) region at the expanse of that of the 1078-950 cm(-1) region when T(max) increases is interpreted as a change from strained to unstrained environments. A nonequilibrium state between the chains is a strained environment. In light of the (13)C NMR evaluation of the change of molecular order with T, the observed changes of the ir spectra could correspond to a transformation of a network of double helices into freer chains, possibly single helices. The present in-depth analysis of equilibrium or near equilibrium states by FTIR can serve to understand, through in situ spectra, molecular mechanisms during the gelation/crystallization of amylose and other gel-forming polymers.

Analysis of physical and chemical networks by slow DSC and turbidimetry

Semicrystalline polymers are made of a crystalline phase and of an amorphous phase. Recently, NMR, Raman and FTIR experiments have identified a third phase comprised of defects such as tie-molecules, in the organization of chains. Our investigation of physical gels has led us to believe that by following the heat flow in a very slow temperature ramp (0.05 K min−1), phasechanges, unnoticed in the usual fast ramp, could be detected. These are associated to a physical network strained in the temperature ramp. In order to obtain more information on the network phase, the polymer has been crosslinked The characteristics obtained by slow calorimetry and turbidimetry of the original and modified materials are compared.

Enhanced Physical Properties of Thin Film Nanocomposites

The addition of nanoparticles to epoxy resins often results in changes in the physical properties of the material particularly when dealing with thin coatings. By characterizing the mechanism of interactions between nanoparticles and polymer chains the material could be tailored for specific applications or properties such as enhanced biodegradability. This study compared the characteristics of common DGEBA resin coated on a silicon substrate and embedded with nanoparticles of TiO2 and Fe2O3. Specifically, we investigated the rate of curing, and the thermal stability of these nanocomposites. Results show changes in the stability for compounds containing TiO2, while Fe2O3 significantly enhanced the curing rates of the nanocomposites while maintaining similar physical properties.

Potential of Magnetotactic Bacteria for the Fabrication of Iron Nanoparticles

Magnetotactic bacteria are typically found in soils rich in iron. These prokaryote bacteria have the property of using ingesting atoms of iron and generating magnetosomes of nanoparticles of either diamagnetic or paramagnetic nature within each cell. We report on the use of magnetotatic bacteria for the production of uniform nanoparticles of iron mineral magnetite (Fe3O4). The potential for mass production was investigated along with the molecular, physical, and magnetic properties of the magnetosomes using various growth and microscopy techniques. Results reveal that the magnetic particles are stable and that bacteria growth can be optimized to produce magnetosomes with different magnetic properties, suggesting that the industrial development of these bio manufactures lies in the foreseeable future.

Variation with temperature (50-250*C) of the absorption spectrum in the CH2 rocking region of polyethylene

Recent studies, mainly by DSC and NMR spectroscopy, have suggested the existence of a third phase in polymeric materials which is believed to be semi-ordered. The melting trace of polyethylene using a very slow temperature ramp (3K/h) reveals an order-disorder phase change in the melt. We want to confirm this important find by other techniques. This paper presents the use of FTIR to follow the melting process by analyzing the variation with temperature of the absorbance.

Melting of deuterated polyethylene as studied by FTIR and calorimetry

Polymers are considered to be composed of two phases: one crystalline and the other amorphous. Recent work by N.M.R. and differential scanning calorimetry (DSC), suggest that a third semi-ordered phase exists. Our objective is to prove the existence of this phase using a third independent method. The fusion of a nascent sample of polyethylene is investigated by IR absorption spectroscopy and corroborates the results of the other techniques. The study concluded that chain movements and strain could be followed by FTIR. The melting characteristics of this phase and other properties are similar to that of a physical network whose cohesive junctions, the entanglements, are submitted to strain during a temperature rise.