Margarita G. Prolongo

Polymer viscoelasticity : stress and strain in practice

Structure of polymers crystalline and amorphous states in polymers rubber elasticity stress-strain relations for ideal solids and ideal liquids linear viscoelasticity - viscoelastic functions dynamic viscoelastic functions experimental determination of viscoelastic properties viscoelastic behaviour of polymers above the glass-transition retardation and relaxation spectra viscoelastic models molecular models of the viscoelastic polymers viscoelasticity of glassy and semicrystalline polymers flow behaviour of polymer melts and solutions yield crazing and fracture reinforced polymers multiaxial analysis of linear viscoelastic stress flexion and torsion of viscoelastic rods.

Melting behavior, miscibility, and hydrogen-bonded interactions of poly(ε-caprolactone)/poly(4-hydroxystyrene-co-methoxystyrene) blends

The miscibility of poly(4-hydroxystyrene-co-methoxystyrene) (HSMS) and poly(e-caprolactone) (PCL) was investigated by differential scanning calorimetry and Fourier transform infrared spectroscopy (FTIR). HSMS/PCL blends were found to be miscible in the whole composition range by detecting only a glass transition temperature (Tg), for each composition, which could be closely described by the Fox rule. The crystallinity of PCL in the blends was dependent on the Tg of the amorphous phase. The greater the HSMS content in the blends, the lower the crystallinity. The polymer–polymer interaction parameter, χ32, was calculated from melting point depression of PCL using the Nishi-Wang equation. The negative value of χ32 obtained for HSMS/PCL blends has been compared with the value of χ32 for poly(4-hydroxystyrene) (P4HS)/PCL blends. The specific nature, quantitative analysis, and average strength of the intermolecular interactions in HSMS/PCL and P4HS/PCL blends have been determined at room temperature and in the molten state by means of Fourier transform infrared spectroscopy (FTIR) measurements. The FTIR results have been in good correlation with the thermal behavior of the blends.

Influence of the molecular architecture on the adsorption onto solid surfaces: comb-like polymers

The processes of adsorption of grafted copolymers onto negatively charged surfaces were studied using a dissipative quartz crystal microbalance (D-QCM) and ellipsometry. The control parameters in the study of the adsorption are the existence or absence on the molecular architecture of grafted polyethyleneglycol (PEG) chains with different lengths and the chemical nature of the main chain, poly(allylamine) (PAH) or poly(L-lysine) (PLL). It was found out that the adsorption kinetics of the polymers showed a complex behavior. The total adsorbed amount depends on the architecture of the polymer chains (length of the PEG chains), on the polymer concentration and on the chemical nature of the main chain. The comparison of the thicknesses of the adsorbed layers obtained from D-QCM and from ellipsometry allowed calculation of the water content of the layers that is intimately related to the grafting length. The analysis of D-QCM results also provides information about the shear modulus of the layers, whose values have been found to be typical of a rubber-like polymer system. It is shown that the adsorption of polymers with a charged backbone is not driven exclusively by the electrostatic interactions, but the entropic contributions as a result of the trapping of water in the layer structure are of fundamental importance.

Epoxy resins modified with poly(vinyl acetate)

Abstract Miscibility and curing behaviour have been studied in blends of poly(vinyl acetate) (PVAc) with diglycidyl ether of bisphenol A (DGEBA) resin and 4,4′-diaminodiphenylsulphone (DDS) used as curing agent. The PVAc component was used as a potential toughness modifier. Binary mixtures DGEBA+PVAc show complete miscibility over the whole composition range. Ternary mixture DGEBA+DDS in stoichiometric ratio +10% (w/w) PVAc behaves also as homogeneous phase. However PVAc was found to be inmmiscible with the highly amine-cross-linked epoxy resin. It was found that phase separation in DGEBA+DDS+PVAc blends occurred as the conversion reaches a value close to 40%. In the final cured material two phases are present: an epoxy phase and a PVAc phase. It was also found a slow down of the reaction when PVAc was present.

DYNAMIC-MECHANICAL AND LIGHT SCATTERING STUDY OF THE GLASS TRANSITION OF POLY(VINYLACETATE) AND A POLY(VINYLACETATE) +POLY(4-HYDROXYSTYRENE) BLEND

The dynamics of poly(vinylacetate) (PVAc) and of a blend of PVAc and 20% in weight of poly(4‐hydoxystyrene) have been studied in the glass transition region using dynamic‐mechanical and photon‐correlation spectroscopies. Both kinds of data show the overlapping of the main α relaxation with a faster one. The complex part of the elastic modulus shows the existence of a β’ sub‐Tg transition overlapping with the α one in the high‐frequency region. The light scattering data show some degree of overlapping of the α and β transitions. As a consequence, at least two Kohlraush–Williams–Watts terms are needed to describe the relaxation functions. The results show a good agreement with the predictions of the mode coupling theory except for the fact that the calculated critical temperature seems to be lower than the calorimetric glass transition temperature.

Dielectric study of poly(methylacrylate) plus poly(4-hydroxystyrene) or plus poly(4 hydroxystyrene-co-4-methoxystyrene) blends near the glass transition

The dynamics of blends of poly(methylacrylate) (PMA)+poly(4-hydroxystyrene) (P4HS) and poly(4- hydroxystyrene-co-4-methoxystyrene) (MP4HS) have been studied by dielectric relaxation in the frequency range 20 < ω/Hz < 105. The results have been analysed in terms of the Havriliak-Negami function plus a conductivity contribution. The time-temperature superposition principle breaks down for the blends, while it seems to be valid for PMA. The width of the relaxation region increases with the content of P4HS or MP4HS, in accordance with previous dynamic mechanical relaxation data. For a given composition, the data of the blends follow the scaling curve proposed by P. W. Dixon (Phys. Rev. Lett., 1990, 42, 8179), however in the low frequency region each sample follows a different scaling curve, which slope is related to the α parameter of the Havriliak-Negami function. The increase of the width of the relaxation curves with decreasing the PMA content can be well correlated by the coupling model when a gaussian distribution of coupling parameters is taken into account.

Perturbed hard-core equations of state for fluids

Abstract The abilities of several equations of state in fitting p-V-T data of pure fluids have been compared. Also the temperature dependence of the characteristic parameters of each substance has been studied. All the equations of state discussed are of the form: p = p (ref) + p (att) where p(ref) accounts for the repulsive contributions to the pressure, while p(att) contains the contributions from the attractive forces. The best results correspond to an equation derived by Miyano and Masuoka from a perturbation theory, though Deiters equation gives results which are almost comparable to Miyanos one and it seems that Deiters equation is more suitable for further improvements and extension to more complex fluids.