Sorption and Diffusion of CO₂/N₂ in gas mixture in thermally-rearranged polymeric membranes: A molecular investigation

Rizzuto, Carmen,Caravella, Alessio,Brunetti, Adele,Park, Chi Hoon,Lee, Young Moo,Drioli, Enrico,Barbieri, Giuseppe,Tocci, Elena Elsevier 2017 Journal of membrane science Vol.528 No.-

<P><B>Abstract</B></P> <P>In this work, we study the adsorption and diffusion of nitrogen and carbon dioxide through an atomistically detailed model of a thermally rearranged polybenzoxazole (TR-PBO) polymer membranes, <I>via</I> equilibrium molecular dynamics (MD) simulations. This work represents a first explicit molecular modelling of the behavior of CO<SUB>2</SUB>/N<SUB>2</SUB> binary mixture in TR-PBO and demonstrates how diffusivity and solubility in mixtures can be coherently obtained. In particular, the number of molecules present in the polymer matrix is estimated using the Gran Canonical Monte Carlo approach. As for the sorption in mixture conditions, MD simulations are used in a synergistic pairing with GCMC and Ideal Adsorption Solution Theory (IAST). For this purpose, the single-gas isotherms calculated from GCMC simulations are fitted with Langmuir and Dual-Langmuir adsorption models to obtain the parameters needed for the IAST simulations.</P> <P>As for diffusion, single-gas and mixture (Maxwell-Stefan) diffusion coefficients are performed by MD simulations. As main results, it is observed that the evaluated diffusion coefficients of CO<SUB>2</SUB> and N<SUB>2</SUB> are in a satisfactory agreement with the values estimated using the available experimental permeability data. More specifically, the CO<SUB>2</SUB> diffusivity in mixture conditions is found to be the same as that in the single-gas one, whereas the N<SUB>2</SUB> diffusivity is slightly higher. These differences are explained in terms of the effect of both the mutual gas diffusion and the competing occupancy of the available free space preferentially occupied by the CO<SUB>2</SUB> molecules in mixture.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Sorption of gas mixture are characterized by the Monte-Carlo method and IAST. </LI> <LI> The Maxwell-Stefan diffusivities are calculated by molecular dynamics simulations. </LI> <LI> The N<SUB>2</SUB> diffusivity in mixture slightly increases with respect to the single-gas case. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

PIM-polyimide multiblock copolymer-based membranes with enhanced CO₂ separation performances

Hossain, Iqubal,Nam, Sang Yong,Rizzuto, Carmen,Barbieri, Giuseppe,Tocci, Elena,Kim, Tae-Hyun Elsevier 2019 Journal of membrane science Vol.574 No.-

<P><B>Abstract</B></P> <P>Multiblock copolymers based on both a PIM-PI block and a 6FDA-PI block, that are [(PIM-PI)x-<I>b</I>-(PI)y], with different block compositions (x:y = 1:4, 1:6 and 1:8) have been prepared for the first time. Through a combination of experimental and simulation approaches, the effects of the compositions of the PIM-PI units on the void distribution and gas transport properties in [(PIM-PI)x-<I>b</I>-(PI)y] block copolymer membranes are fully explored. By combining the effects of the high free volume of amorphous PIMs (polymers with intrinsic microporosity) brought about by the rigidity of the macromolecular chains and their contorted backbones with the excellent chemophysical properties of PIs (polyimides) in a block copolymer approach, our [(PIM-PI)x-<I>b</I>-(PI)y] membranes showed excellent thermomechanical properties as well as very good gas-separation performances, placing them well above the upper bound for CO<SUB>2</SUB>/N<SUB>2</SUB> and CO<SUB>2</SUB>/CH<SUB>4</SUB>, especially at low pressures, and making them comparable to even the highly permeable PIM-1. The block copolymer membrane, with a 1:4 block ratio between the (PIM-PI) and (6FDA-PI) units, denoted here as (PIM-PI)-<I>b</I>-(PI)(1:4), showed a well-connected morphology of the permeable phase and displayed very high CO<SUB>2</SUB> permeability of 3011 Barrer as well as moderate CO<SUB>2</SUB>/CH<SUB>4</SUB> (16.0) and CO<SUB>2</SUB>/N<SUB>2</SUB> (17.0) permselectivities, together with <I>T</I> <SUB> <I>max</I> </SUB> above 520 °C and Young’s modulus above 2.1 GPa.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Multiblock copolymers based on PIM-PI and 6FDA-PI were prepared. </LI> <LI> High free volume nature of PIM was combined with physical stability of polyimide. </LI> <LI> Transport properties of block copolymer membranes were investigated by molecular modeling. </LI> <LI> Excellent thermomechanical properties and good gas-separation performances were achieved. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Nonequilibrium dressing in a cavity with a movable reflecting mirror

Armata, Federico,Kim, M. S.,Butera, Salvatore,Rizzuto, Lucia,Passante, Roberto American Physical Society 2017 Physical Review D Vol.96 No.4

<P>We consider a movable mirror coupled to a one-dimensional massless scalar field in a cavity. Both the field and the mirror's mechanical degrees of freedom are described quantum mechanically, and they can interact with each other via the radiation pressure operator. We investigate the dynamical evolution of mirror and field starting from a nonequilibrium initial state, and their local interaction which brings the system to a stationary configuration for long times. This allows us to study the time-dependent dressing process of the movable mirror interacting with the field, and its dynamics leading to a local equilibrium dressed configuration. Also, in order to explore the effect of the radiation pressure on both sides of the movable mirror, we generalize the effective field-mirror Hamiltonian and previous results to the case of two cavities sharing the same mobile boundary. This leads us to address, in the appropriate limit, the dynamical dressing problem of a single mobile wall, bounded by a harmonic potential, in the vacuum space.</P>

Evaluation of the influence of creep and shrinkage determinants on column shortening in mid-rise buildings

B-Jahromi, Ali,Rotimi, Abdulazeez,Tovi, Shivan,Goodchild, Charles,Rizzuto, Joseph Techno-Press 2017 Advances in concrete construction Vol.5 No.2

The phenomenon of concrete column shortening has been widely acknowledged since it first became apparent in the 1960s. Axial column shortening is due to the combined effect of elastic and inelastic deformations, shrinkage and creep. This study aims to investigate the effects of ambient temperature, relative humidity, cement hardening speed and aggregate type on concrete column shortening. The investigation was conducted using a column shortening prediction model which is underpinned by the Eurocode 2. Critical analysis and evaluation of the results showed that the concrete aggregate types used in the concrete have significant impact on column shortening. Generally, aggregates with higher moduli of elasticity hold the best results in terms of shortening. Cement type used is another significant factor, as using slow hardening cement gives better results compared to rapid hardening cement. This study also showed that environmental factors, namely, ambient temperature and relative humidity have less impact on column shortening.

Steel Reinforced Self-Compacting Concrete (SCC) Cantilever Beams: Bond Behaviour in Poor Condition Zones

Wael Mohamed Montaser,Ibrahim Galal Shaaban,Joseph P. Rizzuto,Amr Hussein Zaher,Ahmed Rashad,Shorouk Mohamed El Sadany 한국콘크리트학회 2023 International Journal of Concrete Structures and M Vol.17 No.3

Previous investigations carried out on reinforced self-compacted concrete (SCC) beams have reported contradictory results on reinforcement bond behaviour occurring in the zones defined for good bond conditions according to Eurocode2. Cantilevered SCC beams’ critical upper tension reinforcement bond behaviour has previously had limited reporting. In this study, the bond behaviour in normally vibrated concrete (NVC) and self-compacted concrete (SCC) in poor conditions zones are compared and the differences are highlighted. The effect of four parameters, including (i) concrete type (SCC and NVC), (ii) characteristic strength of SCC, (iii) lap splice length, and (iv) depth of concrete cover for the reinforcement is investigated. It was found that for the studied beams, increasing splice length improved the energy absorption and changed the failure mode to a more ductile manner even at the poor bond conditions zones. The maximum measured steel strains in SCC beams in the lap splice zones, were higher than those for NVC specimens. The mean bond stress values, for SCC beams with 25–50% lap splice lengths, were higher than those of NVC beams, with the same lap splice lengths, by 16–13%, respectively. The results of the current study showed that the empirical equations from the literature overestimated the bond strength of the splice lap length for cantilever upper steel in SCC beams with long splices which agrees with the state of the art as these equations were developed originally for short anchorage lengths.