Giuseppe Mensitieri

Sodium montmorillonite silylation: Unexpected effect of the aminosilane chain length

In this work, the silylation of sodium montmorillonite (Na-MMT) was performed in glycerol using 3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and 3-[2-(2-aminoethylamino)ethylamino]-propyl-trimethoxysilane. The effects on the d-spacing of sodium montmorillonite (Na-MMT) upon reaction with three aminosilanes of different chain length were studied in details by combining experimental and computational techniques. Infrared spectroscopy was used to monitor the grafting process, while the degree of grafting was calculated using thermogravimetric analysis. X-ray diffraction experiments were carried out to evaluate the shift of the (0 0 1) basal spacing. It was found that the degree of silylation of Na-MMT increases with increasing the length of the aminosilane organic moieties, the overall aminosilane concentration, and temperature. The same beneficial effects were observed on the silicate d-spacing, as its value increases with increasing silane concentration and reaction temperature. Remarkably, however, increasing the length of the organic chains in the silane modifiers resulted in decreasing values of the Na-MMT interlayer distance. A rationale for this behavior is proposed on the basis of atomistic molecular dynamics simulation evidences.

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.

Molecular Sensing by Nanoporous Crystalline Polymers

Chemical sensors are generally based on the integration of suitable sensitive layers and transducing mechanisms. Although inorganic porous materials can be effective, there is significant interest in the use of polymeric materials because of their easy fabrication process, lower costs and mechanical flexibility. However, porous polymeric absorbents are generally amorphous and hence present poor molecular selectivity and undesired changes of mechanical properties as a consequence of large analyte uptake. In this contribution the structure, properties and some possible applications of sensing polymeric films based on nanoporous crystalline phases, which exhibit all identical nanopores, will be reviewed. The main advantages of crystalline nanoporous polymeric materials with respect to their amorphous counterparts are, besides a higher selectivity, the ability to maintain their physical state as well as geometry, even after large guest uptake (up to 10–15 wt%), and the possibility to control guest diffusivity by controlling the orientation of the host polymeric crystalline phase. The final section of the review also describes the ability of suitable polymeric films to act as chirality sensors, i.e., to sense and memorize the presence of non-racemic volatile organic compounds.

Probing the degree of crosslinking of a cellulose based superabsorbing hydrogel through traditional and NMR techniques

The network structure of a cellulose-based superabsorbing material has been probed by using three different techniques: 13C solid state NMR, free swelling in water and uniaxial compression of water swollen samples. A good agreement between the three apporaches has been found in terms of concentration of crosslinks per unit volume. The results have been discussed taking into account that NMR technique is able to detect only chemically effective crosslinks while free swelling and compression are sensitive to elastically effective physical and chemical crosslinks. A depression of swelling capacity and an apparent increase of degree of crosslinking with time, promoted by ageing of the cellulosic material, has been experimentally evidenced and discussed in terms of development of intermolecular physical interactions.

Modulation of drug release from hydrogels by using cyclodextrins: the case of nicardipine/β-cyclodextrin system in crosslinked polyethylenglycol

A simple approach is presented to modulate drug delivery from swellable systems by using complexants. The effect of complexants has been interpreted by means of simple mass balances on diffusing species and the involved relevant parameters have been individuated. The application of this strategy to the release of nicardipine (NIC) from swellable systems by using beta-cyclodextrin (CD) as complexant has evidenced the potential of the approach to tailor drug release. Crosslinked polyethyleneglycol has been synthesized, characterized and used as the swellable matrix. Swelling kinetics, NIC and CD diffusivities in the swollen matrix and NIC/CD phase solubility studies have been performed. The polymer matrix has been loaded with pure NIC or with NIC and CD at different ratios and release kinetics evaluated. Release profiles have shown that the presence of CD significantly affected drug delivery by decreasing the effective diffusivity of NIC. The higher the CD/NIC ratio the slower is the release. This effect has been interpreted on the basis of the proposed model and physically sound assumptions.

Optical sensor based on ultrathin films of δ-form syndiotactic polystyrene for fast and high resolution detection of chloroform

In this work are analyzed the performances of an optoelectronic sensor based on a sensitive nanoscale film of semicrystalline syndiotactic polystyrene (sPS) with a nanoporous crystalline phase developed for fast and high resolution detection of chloroform. In particular, the change of the polymer refractive index due to chloroform sorption into the polymer layer when the sensor is exposed to CHCl3 has been used as transduction property. Reflectance measurements have been performed using a fiber optic refractometer, coated with nanometric sPS film at very low pressure of chloroform, demonstrating high sensitivity and fast-time response combined with excellent reversibility. Mass sorption experiments have also been performed on the same polymeric material with an electronic microbalance at the same conditions at which the optical sensor has been characterized. This allowed a quantitative correlation between the mass of the analyte sorbed within the polymer layer and the refractive index variation, which has...

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.

Molecular Simulation of Carbon Dioxide Sorption in Nanoporous Crystalline Phase of Sydiotactic Polystyrene

Nanoporous crystalline δe-form of syndiotactic polystyrene (sPS) is characterized by the rather peculiar behavior of being able to absorb considerable amounts of low molecular weight penetrants, in contrast to the general behavior reported for the crystalline phase of polymers that is impervious to penetrants. In particular, the δe nanoporous crystalline form of sPS displays a sorption capacity of penetrants that is several times higher than the one of the amorphous phase of sPS. In this paper, sorption thermodynamics of carbon dioxide in the δe nanoporous crystalline form of semicrystalline sPS is analyzed by means of Grand Canonical Monte Carlo (GCMC) molecular simulation methods, evaluating sorption isotherms as well as isosteric heats of sorption based on a semi-empirical molecular force-field. In fact, in the last years, this technique has been successfully used to investigate sorption properties of periodic crystals of a wide range of materials, including zeolites and polymers, supplying reliable estimates and representing a valid support to the experimental activity. While computational techniques allow direct determination of sorption properties of purely crystalline systems, experimental characterization of sorption in a semicrystalline polymer, as is the case of sPS under investigation, does not give a straight estimation of sorption capacity of the crystalline phase since sorption measurement incorporates other contributions related to the amorphous phase and interphases, as well as to possible defects of the crystalline phase. However, in the case of sPS at the investigated gas pressures, contribution of the amorphous and non-crystalline phases to carbon dioxide sorption can be neglected, and it has been possible to directly compare simulation predictions with experimental results, showing that GCMC computations supply excellent estimates for sorption isotherms and isosteric heats of sorption.