Mass transport of low molecular weight penetrants in polyimide and silica/polyimide hybrids has b... more Mass transport of low molecular weight penetrants in polyimide and silica/polyimide hybrids has been investigated using time-resolved FTIR spectroscopy and gravimetric analysis. In particular, transport of reacting (ammonia) and non-reacting (water) penetrants has been studied as a function of penetrant concentration, evidencing peculiar features related to the presence of the inorganic phase in the hybrid systems. For the case of water, diffusivity and sorption equilibrium have been evaluated in an activity range between 0.1 and 0.75. Free water as well as molecular aggregates have been detected in both systems. In the case of ammonia, its reactivity with polyimide has been directly observed, and the rection mechanism elucidated. Furthermore, it has been possible to discriminate diffusion and reaction phenomena due to the different time scales of the two processes.
In this contribution, we review and critically compare the results of the analyses we have previo... more In this contribution, we review and critically compare the results of the analyses we have previously performed on water sorption thermodynamics in a series of polyimides. The experimental investigation was performed by combining gravimetric tests and in situ vibrational spectroscopy. A non-equilibrium theory, based on a compressible lattice framework accounting for the glassy state of the polymer and for the occurrence of hydrogen bonding interactions, has been used to interpret data. Information at a molecular level gained by vibrational spectroscopy has been used to tailor the model equations. The main features of water sorption thermodynamics are well captured, qualitatively and quantitatively, by the adopted model which displays a remarkable agreement with experimental results.
Abstract The paper proposes a mixed strain- and stress-based topology optimization method for des... more Abstract The paper proposes a mixed strain- and stress-based topology optimization method for designing the ideal geometry of carbon fibers in composite laminates subjected to either applied tractions or prescribed displacements. On the basis of standard micromechanical approaches, analytical elastic solutions for a single cell, assumed to be a Representative Volume Element (RVE), are ad hoc constructed by involving anisotropy induced by fiber orientation and volume fraction, also taking into account inter-laminar stresses and strains. The analytical solutions are then implemented in a Finite Element (FE) custom-made topology optimization-based procedure rewritten to have as output the best curves the reinforcing fibers have to draw in any composite laminate layer to maximize the overall panel stiffness or to minimize the elastic energy. To verify the effectiveness of the proposed strategy, different structures undergoing either in-plane or out-plane boundary conditions have been selected and theoretically investigated, determining the optimal fibers' maps and showing the related results in comparison to standard sequences of alternate fibers disposition for the same composites. Two optimized panels were at the end actually produced using an innovative Automated Fiber Placement (AFP) machine and consolidating the materials by means of autoclave curing processes, in this way replicating the fiber paths obtained from theoretical outcomes. As a control, two corresponding composite structures were also built without employing the fiber optimization strategy. The panels have been tested in laboratory and the theoretical results have been compared with the experimental findings, showing a very good agreement with our predictions and confirming the capability of the proposed algorithm in suggesting the arrangement of the fibers to obtain enhanced mechanical performances. It is felt that the hybrid analytical-FE topology optimization strategy, in conjunction with the possibilities offered by AFP devices, could pave the way for a new generation of ultra-lightweight composites for aerospace, automotive and many industrial applications.
Hyaluronic acid esters belong to a new class of polymers which have been developed in order to ov... more Hyaluronic acid esters belong to a new class of polymers which have been developed in order to overcome water sensitivity displayed by hyaluronic acid. In this paper the effects of the substituting group on the water vapor transport properties were investigated. In particular, water sorption isotherms and kinetics for three types of hyaluronic acid esters (ethyl, dodecyl and benzyl esters) were determined. The type of substituent group has been found to affect polymer hydrophilicity and, consequently, the water swelling properties.
Self-assembling of reduced graphene oxide (RGO) and graphene oxide (GO) platelets, as a tailored ... more 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.
In-situ Fourier transform infrared (FTIR) measurements have been carried out at different relativ... more 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.
A film of syndiotactic polystyrene (sPS) in the nanoporous crystalline δ form has been used for t... more A film of syndiotactic polystyrene (sPS) in the nanoporous crystalline δ form has been used for the detection of chloroform in the vapor phase at very low concentration The variation of the refractive index due to the chloroform sorption within the polymer has been used as transduction property. Reflectivity measurements by a fiber optic refractometer, coated with a nanometric (73nm)
Abstract The aim of the present work is the study of the migration from active LDPE polymer films... more Abstract The aim of the present work is the study of the migration from active LDPE polymer films of alpha-tocopherol adsorbed onto purely siliceous and amino-functionalized SBA-15 mesoporous silica. In particular, the effect of the pore size and the chemical functionality of the internal walls of the mesophase was thoroughly investigated.
Mass transport of low molecular weight penetrants in polyimide and silica/polyimide hybrids has b... more Mass transport of low molecular weight penetrants in polyimide and silica/polyimide hybrids has been investigated using time-resolved FTIR spectroscopy and gravimetric analysis. In particular, transport of reacting (ammonia) and non-reacting (water) penetrants has been studied as a function of penetrant concentration, evidencing peculiar features related to the presence of the inorganic phase in the hybrid systems. For the case of water, diffusivity and sorption equilibrium have been evaluated in an activity range between 0.1 and 0.75. Free water as well as molecular aggregates have been detected in both systems. In the case of ammonia, its reactivity with polyimide has been directly observed, and the rection mechanism elucidated. Furthermore, it has been possible to discriminate diffusion and reaction phenomena due to the different time scales of the two processes.
In this contribution, we review and critically compare the results of the analyses we have previo... more In this contribution, we review and critically compare the results of the analyses we have previously performed on water sorption thermodynamics in a series of polyimides. The experimental investigation was performed by combining gravimetric tests and in situ vibrational spectroscopy. A non-equilibrium theory, based on a compressible lattice framework accounting for the glassy state of the polymer and for the occurrence of hydrogen bonding interactions, has been used to interpret data. Information at a molecular level gained by vibrational spectroscopy has been used to tailor the model equations. The main features of water sorption thermodynamics are well captured, qualitatively and quantitatively, by the adopted model which displays a remarkable agreement with experimental results.
Abstract The paper proposes a mixed strain- and stress-based topology optimization method for des... more Abstract The paper proposes a mixed strain- and stress-based topology optimization method for designing the ideal geometry of carbon fibers in composite laminates subjected to either applied tractions or prescribed displacements. On the basis of standard micromechanical approaches, analytical elastic solutions for a single cell, assumed to be a Representative Volume Element (RVE), are ad hoc constructed by involving anisotropy induced by fiber orientation and volume fraction, also taking into account inter-laminar stresses and strains. The analytical solutions are then implemented in a Finite Element (FE) custom-made topology optimization-based procedure rewritten to have as output the best curves the reinforcing fibers have to draw in any composite laminate layer to maximize the overall panel stiffness or to minimize the elastic energy. To verify the effectiveness of the proposed strategy, different structures undergoing either in-plane or out-plane boundary conditions have been selected and theoretically investigated, determining the optimal fibers' maps and showing the related results in comparison to standard sequences of alternate fibers disposition for the same composites. Two optimized panels were at the end actually produced using an innovative Automated Fiber Placement (AFP) machine and consolidating the materials by means of autoclave curing processes, in this way replicating the fiber paths obtained from theoretical outcomes. As a control, two corresponding composite structures were also built without employing the fiber optimization strategy. The panels have been tested in laboratory and the theoretical results have been compared with the experimental findings, showing a very good agreement with our predictions and confirming the capability of the proposed algorithm in suggesting the arrangement of the fibers to obtain enhanced mechanical performances. It is felt that the hybrid analytical-FE topology optimization strategy, in conjunction with the possibilities offered by AFP devices, could pave the way for a new generation of ultra-lightweight composites for aerospace, automotive and many industrial applications.
Hyaluronic acid esters belong to a new class of polymers which have been developed in order to ov... more Hyaluronic acid esters belong to a new class of polymers which have been developed in order to overcome water sensitivity displayed by hyaluronic acid. In this paper the effects of the substituting group on the water vapor transport properties were investigated. In particular, water sorption isotherms and kinetics for three types of hyaluronic acid esters (ethyl, dodecyl and benzyl esters) were determined. The type of substituent group has been found to affect polymer hydrophilicity and, consequently, the water swelling properties.
Self-assembling of reduced graphene oxide (RGO) and graphene oxide (GO) platelets, as a tailored ... more 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.
In-situ Fourier transform infrared (FTIR) measurements have been carried out at different relativ... more 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.
A film of syndiotactic polystyrene (sPS) in the nanoporous crystalline δ form has been used for t... more A film of syndiotactic polystyrene (sPS) in the nanoporous crystalline δ form has been used for the detection of chloroform in the vapor phase at very low concentration The variation of the refractive index due to the chloroform sorption within the polymer has been used as transduction property. Reflectivity measurements by a fiber optic refractometer, coated with a nanometric (73nm)
Abstract The aim of the present work is the study of the migration from active LDPE polymer films... more Abstract The aim of the present work is the study of the migration from active LDPE polymer films of alpha-tocopherol adsorbed onto purely siliceous and amino-functionalized SBA-15 mesoporous silica. In particular, the effect of the pore size and the chemical functionality of the internal walls of the mesophase was thoroughly investigated.
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Papers by G. Mensitieri