Newsletter  2026.3  Index

Theme : "The Eleventh JSME-KSME Thermal and Fluids Engineering Conference (TFEC11) " Preface Hyun Jin PARK, Shoichi MATSUDA, Chungpyo HONG Post-Lecture Summary: Engine Knock Prediction – Building on Combustion Fundamentals Kaoru MARUTA, Youhi MORII (Tohoku University) Electrical Tomography × Flow Visualization × Startups  – Chiba University Spin-off Startups and the Future of Fluid Engineering – Songshi LI, Masahiro TAKEI (Chiba University) Turbulent drag reduction effects by streamwise traveling waves with spanwise phase shifts Kyohei OISHI (Keio University), Senri MIURA (Keio University), Yusuke NABAE (Tokyo University of Science), Koji FUKAGATA (Keio University) Effect of a sidewall height on the instability of an inclined falling liquid film in a minichannel Shogo Matsui(Yokohama National University), Georg F. Dietze(CNRS, FAST, Université Paris-Saclay, Orsay), Koichi Nishino(Yokohama National University), Misa Ishimura(Yokohama National University) Development of a ReaxFF Force Field for CO2 Separation in PVAm/PVA Composite Membranes: Molecular-Level Insights into Aqueous Transport Mechanism Yukiko TOMITA, Kohei SATO, Ikuya KINEFUCHI (Tokyo University) Flow characteristics of multiple jets and their flow in a chamber Asuka KONDO, Masaki FUCHIWAKI (Kyushu Institute of Technology) Experimental investigation of combined blowing-suction control on a Clark-Y airfoil Senri MIURA, Koji FUKAGATA (Keio University)

 

Turbulent drag reduction effects by streamwise traveling waves with spanwise phase shifts

Yuiko TOMITA The University of Tokyo	Kohei SATO The University of Tokyo	Ikuya KINEFUCHI The University of Tokyo

Abstract

Facilitated transport membranes based on polyvinylamine/polyvinyl alcohol (PVAm/PVA) composites are promising candidates for CO₂ capture, yet the molecular-level role of water in promoting CO₂ transport through these membranes remains poorly understood. This study develops a ReaxFF reactive force field parameterized to describe the chemical reactions between CO₂ and amine groups (NH²) in the presence of water within PVAm/PVA composite membranes. Training data were generated using density functional theory (DFT) calculations at the B3LYP/6-311+G** level, including geometry optimizations, transition state searches, and intrinsic reaction coordinate analyses. The ReaxFF parameters were optimized from an existing parameter set using the covariance matrix adaptation evolution strategy (CMA-ES), targeting intramolecular interactions and reaction pathway energetics with a mean absolute error below 5.0 kcal/mol. The optimized force field reproduced the bulk-phase density of PVA (1.21 g/cm³) in close agreement with the experimental value (1.19 g/cm³) and achieved mean absolute errors of 2.9 kcal/mol for intramolecular interactions and 2.2 kcal/mol for reaction pathway energies. Radial distribution functions computed with the developed ReaxFF showed excellent agreement with those obtained from the non-reactive GAFF2 force field. DFT calculations revealed that the activation energy barrier decreased from 21.0 kcal/mol without excess water to 4.8 kcal/mol with four excess water molecules, and that the reaction product HCO₃^- became thermodynamically more stable than the reactants under high water content conditions. Metadynamics simulations confirmed the formation of HCO₃^- species during a 1.0 ns trajectory without structural degradation, validating the developed force field for studying aqueous CO₂ transport mechanisms in facilitated transport membranes.

Key words

Reactive Force Field, Molecular Dynamics, Facilitated Transport Membranes, Density Functoinal Theory, The Solution-Diffusoin Mechanism

Figures

Fig. 1  (a) PVAm and PVA polymer structures. (b) A representative snapshot of PVA with a degree of polymerization of 100. Carbon, oxygen, and hydrogen atoms are represented by gray, red, and white, respectively.

Fig. 2  Comparison of the intramolecular interactions computed by the ReaxFF and DFT for 4000 configurations of PVA with a degree of polymerization of 5.

Fig. 3   Radial distribution functions of (a) all atoms (b) C atoms on polymer chains, (c) terminal H atoms, (d) O atoms, (e) H atoms on polymer chains, and (f) H atoms bonded to O atoms.

Fig. 4   Energy profiles along the reaction pathway calculated by new ReaxFF, original ReaxFF, and DFT with (a) no excess H₂O, (b) 1 excess H₂O, (c) 2 excess H₂O , (d) 3 excess H₂O , and (e) 4 excess H₂O.

Fig. 5   A representative snapshot of reaction pathways with (a) 1 excess H₂O, (b) 2 excess H₂O , (c) 3 excess H₂O , and (d) 4 excess H₂O.

Fig. 6   A representative snapshot of reaction pathways: (a) H₂O + CO₂ + R-NH₂, (b) HCO₃^- + R-NH₃⁺. Carbon, oxygen, nitrogen and hydrogen atoms are represented by gray, red, blue, and white, respectively.