Giuseppe Scherillo

Tailoring Assembly of Reduced Graphene Oxide Nanosheets to Control Gas Barrier Properties of Natural Rubber Nanocomposites

Self-assembling of reduced graphene oxide platelets, as a tailored interconnected network within a natural rubber matrix, is proposed as a mean for obtaining nanocomposites with improved gas barrier, as compared to neat natural rubber. Interestingly, this nanocomposite structure results to be much more effective than homogeneous dispersion of graphene platelike particles, even at low graphene loadings. Such behavior is interpreted on the grounds of a theoretical model describing permeability of heterogeneous systems specifically accounting for self-segregated graphene morphology.

Combining gravimetric and vibrational spectroscopy measurements to quantify first- and second-shell hydration layers in polyimides with different molecular architectures.

In-situ Fourier transform infrared (FTIR) measurements have been carried out at different relative pressures of water vapor to study the H(2)O diffusion in three polyimides differing in their molecular structure and fluorine substitution. Spectral data have been analyzed by difference spectroscopy, least-squares curve fitting, and two-dimensional (2D) correlation spectroscopy, which provided molecular level information on the diffusion mechanism. In particular, two distinct water species were identified corresponding, respectively, to the first and second-shell hydration layers. The spectroscopic analysis demonstrated that the relative population of these species is a function of the total water content in the system. A method has been devised to quantify the water concentration in the two hydration layers, based on a combination of spectroscopic and gravimetric data. The results have been compared with those from an earlier spectroscopic approach reported in the literature and based on the analysis of the carbonyl region.

Time-resolved Fourier transform infrared spectroscopy, gravimetry, and thermodynamic modeling for a molecular level description of water sorption in poly(ε-caprolactone).

Sorption of water in poly(ε-caprolactone) (PCL), with specific focus on the hydrogen-bonding interactions, has been analyzed by combining ab initio calculations, macroscopic thermodynamics modeling, and relevant features emerging from spectroscopic and gravimetric measurements. Fourier transform infrared (FTIR) data, analyzed by difference spectroscopy, two-dimensional correlation spectroscopy, and least-squares curve-fitting analysis associated with gravimetric determination of water sorption isotherm provided information on the systems behavior and on the molecular interactions established between the polymer and the penetrant. A consistent physical picture emerged pointing to the presence of two spectroscopically discernible water species (first-shell and second-shell layers) that have been quantified. Water molecules are present in the form of dimers within the polymer equilibrated with water vapor up to a relative humidity of 0.65. At higher humidities, clustering of water sorbed molecules starts to take place. The multicomponent ν(OH) band representative of absorbed water has been interpreted with the aid of ab initio calculations performed on suitably chosen model systems. The outcomes of spectroscopic analyses were interpreted at a macroscopic level by modeling the thermodynamics of water sorption in PCL based on a nonrandom compressible lattice theory accounting for hydrogen-bonding (HB) interactions. Starting from the fitting of the gravimetric sorption isotherm, the model provided quantitative estimates for the amount of self- and cross-HBs which compare favorably with the FTIR results.

Water Sorption Thermodynamics in Polymer Matrices

Water sorption is a key issue in assessing the durability of polymer matrix composites. In fact absorbed water can adversely affect mechanical properties of the matrix and fibre-matrix interface integrity. In this contribution the general issue of water sorption thermodynamics in polymers is addressed from the experimental and theoretical point of view. The case of both rubbery and glassy polymers is considered modelling thermodynamics of water-polymer systems using lattice fluid theories accounting also for the occurrence of possible self- and cross-hydrogen bonding interactions. Outcomes of theoretical analyses are compared to experimental results obtained by vibrational spectroscopy and gravimetric measurements.

Raman Line Imaging of Poly(ε-caprolactone)/Carbon Dioxide Solutions at High Pressures: A Combined Experimental and Computational Study for Interpreting Intermolecular Interactions and Free-Volume Effects

In the present study, a Raman line-imaging setup was employed to monitor in situ the CO2 sorption at elevated pressures (from 0.62 to 7.10 MPa) in molten PCL. The method allowed the quantitative measurement of gas concentration in both the time-resolved and the space-resolved modes. The combined experimental and theoretical approach allowed a molecular level characterization of the system. The dissolved CO2 was found to occupy a volume essentially coincident with its van der Waals volume and the estimated partial molar volume of the probe did not change with pressure. Lewis acid-Lewis base interactions with the PCL carbonyls was confirmed to be the main interaction mechanism. The geometry of the supramolecular complex and the preferential interaction site were controlled more by steric than electronic effects. On the basis of the indications emerging from Raman spectroscopy, an equation of state thermodynamic model for the PCL-CO2 system, based upon a compressible lattice fluid theory endowed with specific interactions, has been tailored to account for the interaction types detected spectroscopically. The predictions of the thermodynamic model in terms of molar volume of solution have been compared with available volumetric measurements while predictions for CO2 partial molar volume have been compared with the values estimated on the basis of Raman spectroscopy.

Thermodynamics of water sorption in high performance glassy thermoplastic polymers

Sorption thermodynamics of water in two glassy polymers, polyetherimide (PEI) and polyetheretherketone (PEEK), is investigated by coupling gravimetry and on line FTIR spectroscopy in order to gather information on the total amount of sorbed water as well as on the different species of water molecules absorbed within the polymers, addressing the issue of cross- and self-interactions occurring in the polymer/water systems. Water sorption isotherms have been determined at temperatures ranging from 30 to 70°C while FTIR spectroscopy has been performed only at 30°C. The experimental analysis provided information on the groups present on the polymer backbones involved in hydrogen bonding interactions with absorbed water molecules. Moreover, it also supplied qualitative indications about the different “populations” of water molecules present within the PEEK and a quantitative assessment of these “populations” in the case of PEI. The results of the experimental analysis have been interpreted using an equation of state theory based on a compressible lattice fluid model for the Gibbs energy of the polymer-water mixture, developed by extending to the case of out of equilibrium glassy polymers a previous model intended for equilibrium rubbery polymers. The model accounts for the non-equilibrium nature of glassy polymers as well as for mean field and for hydrogen bonding interactions, providing a satisfactory quantitative interpretation of the experimental data.

ON THE MECHANISM OF MASS TRANSPORT OF LOW MOLECULAR WEIGHT COMPOUNDS IN POLYIMIDES: MODELING AND 2D‐FTIR ANALYSIS

Mass transport mechanism of low molecular weight compounds (water and carbon dioxide) into polyimide films has been analysed and modelled on the basis of the relevant findings of an in situ FTIR spectroscopic analysis. In particular, in the case of water, it has been assumed that concurrent diffusion occurs of single water molecules and water dimers, which display different mobilities. A non‐linear instantaneous equilibrium between the local concentrations of these two species has been imposed, based on a two layers BET theory. The proposed approach is able to give a good qualitative and quantitative interpretation of both sorption equilibrium and of sorption/desorption kinetics data.

Controlling the assembly of graphene based nanosheets within a rubber matrix: Nanocomposite morphology probed by measuring gas permeation and dielectric properties

Self-assembling of reduced graphene oxide (RGO) and graphene oxide (GO) platelets, as a tailored interconnected network within natural rubber and butyl rubber matrices, is proposed as a mean for obtaining nanocomposites with significantly enhanced functional properties as compared to unloaded rubber, i.e. gas barrier properties and electric conductivity, even at very low filler contents. Interestingly, the prescribed spatial arrangement of the nanoparticles (‘segregated arrangement’) results to be much more effective in improving properties than homogeneous dispersion (‘not segregated’ arrangement) of platelets, even at low loadings. The ‘segregated’ structure originates from the confinement of platelets within the interstices of the coagulated latex particles, which act as a template for the network formation. The platelets are assembled on the latex particles giving rise to spheres with a core-shell structure, with a partial or complete covering depending on graphene amount. Conversely, the ‘not-segregated’ structure is obtained by destroying this interconnected network by further processing the nanocomposite masterbatch via twin-roll mixing, thus determining a uniform orientation of exfoliated platelets.

Probing effect of solvent concentration on glass transition and sub-Tg structural relaxation in polymer solvent mixtures: The case of polystyrene-toluene system

A novel experimental method for the analysis of volume relaxation induced by solvents in glassy polymers is presented. A gravimetric technique is used to evaluate the isothermal solvent mass uptake at controlled increasing/decreasing solvent pressure at constant rate. Fundamental properties of the solvent/polymer system can be obtained directly, and models can be applied, combining both nonequilibrium thermodynamics and mechanics of volume relaxation contribution. The fundamental case of polystyrene and toluene mixtures are thus accounted for, and various experimental conditions have been explored, varying the temperature, and spanning over different pressure increase/decrease rates. The results obtained allowed to evaluate the isothermal second order transition induced by solvent sorption, as well as the determination of the effect of the pressure rate. Therefore, this work proposes a new standard for the characterization and the understanding of the relaxational behavior of glassy polymers.