Abstract
The effect of the tacticity of poly methyl methacrylate (PMMA) on the morphology of free volume in PMMA membranes was studied by using a molecular dynamics simulation technique. The chain flexibility, chain interaction, end-to-end distance of a chain and the time course of the free volume variation in the various stereo-regular PMMA, were obtained by an MD simulation technique. Simulation results depict that the construction of distinct tacticity has a significant influence on the flexibility of a molecular chain and the morphology of free volume in the syndiotactic (s-) and isotactic (i-) PMMA oligomers. MD calculation of the dynamic microstructure of a PMMA matrix shows that the s-PMMA membrane gives less flexibility in the backbone and a longer end-to-end distance than in the i-PMMA membrane. The less flexibility and longer end-to-end distance in the s-PMMA matrix causes the shapes and sizes of s-PMMA free volume to be longer and larger than those in an i-PMMA membrane. Furthermore, by adopting conformation energy minimization and molecular dynamics simulation techniques, various tacticity models of PMMA were constructed and their effect on the size of accessible free volume and free volume morphology was analyzed. Finally, the adsorbed gas on the surface free volume in s-PMMA was also compared with i-PMMA membrane.
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Abbreviations
- ai(t):
-
acceleration function of atoms [-]
- b:
-
bond length [deg]
- b0 :
-
original bond length [deg]
- Dα :
-
self diffusion coefficient of number atoms [cm2/s]
- dmin :
-
minimum distance among atoms [å]
- E:
-
potential energy of force field [kJ/mol]
- f(v):
-
Maxwell-Boltzmann distribution function [-]
- g(vi):
-
Gaussian distribution equation [-]
- Nα :
-
numbers of diffusion molecule [-]
- ri(t):
-
position function of atoms [-]
- θ :
-
bond angle [deg]
- θ0 :
-
original bond angle [deg]
- Φ :
-
torsion angle [deg]
- Φ 0 :
-
original torsion angle [deg]
- V:
-
potential energy of force field [kJ/mol]
- x:
-
improper torsion angle [deg]
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Lu, KT., Tung, KL. Molecular dynamics simulation study of the effect of PMMA tacticity on free volume morphology in membranes. Korean J. Chem. Eng. 22, 512–520 (2005). https://doi.org/10.1007/BF02706635
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DOI: https://doi.org/10.1007/BF02706635