(122g) Study of Gas Permeabilities In Styrene Ethyleneoxide (SEO) Block Copolymers

Study of Gas Permeabilities
in Styrene Ethyleneoxide (SEO) Block Copolymers

Matteo
Minelli¹, Marco Giacinti Baschetti¹, Daniel T. Hallinan
Jr.², Nitash P. Balsara²

1 Dipartimento di Ingegneria Chimica, Mineraria e delle Tecnologie
Ambientali (DICMA) Alma Mater Studiorum - Università di Bologna, via Terracini 28, 40131, Bologna,
Italy.

2 Materials Sciences Division and Environmental Energy
Technologies Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720, United States

Abstract

Transport
properties of different gases such as oxygen, nitrogen, methane and carbon
dioxide are characterized for a styrene-ethyleneoxide (SEO) triblock copolymer membrane
at different temperatures ranging from 20 to 80°C.

The
material consists of a PEO fraction of about 50% by weight and a crystalline
part of about 10% at room temperature. DSC analysis allowed the evaluation of
melting point at about 40°C whereas a lamellar structure with a domain spacing
of 95 nm was observed through SAXS analyses.

Permeation
experiments were carried out by means of a manometric [1]
device and were performed in a range of temperature covering the melting region
of PEO segment [2] allowing for the study of the
effect of crystallinity on the mass transport behaviour. This material, indeed,
is suitable for different applications such as membrane for gas separation as
well as solid electrolyte in polymeric batteries [3, 4a&b].

The
results of CO₂ permeability, reported in Figure 1, showed a
remarkable increases of both permeability and diffusivity (calculated through
time lag method) when temperature is raised, and the behaviour deviates significantly
from the Arrhenius law in the temperature range in which PEO melting takes
place. Interestingly, data show very similar activation energies both at high and
low temperature, but the calculated values are lower than those calculated by
other authors [4-6], and reported in the
literature, for amorphous PEO, which is expected to be the phase involved in
the permeation phenomenon.

Figure 1, CO₂ Permeability in
SEO block copolymer at different temperatures.

The
permeability data were analyzed by considering the block copolymer as a
multiphase system in which the two moieties are endowed with different permeabilities.
In this concern, the results show that at low temperature, the gas diffusion is
mainly located in the PS [7] phase due to crystallinity
of the PEO. On the contrary, at temperature above 50-60°C, the PEO (melt) is remarkably more permeable than the styrenic part and the observed P
for SEO copolymer is one order of magnitude higher than the value at room
temperature.

The
same behaviour of permeability with respect to temperature above described for
CO₂ was also observed for the case of the other gases (O₂,
N₂ and CH₄); the steep increase of P occurs at the
same temperature (between 40 and 60°C) and the trends at high and low temperature are once again comparable (similar activation energies) confirming the
prevalent role of crystallinity change in the materials behaviour.

References:

[1]        M. Minelli, M.G. De Angelis, F. Doghieri, M.
Marini, M. Toselli, F. Pilati, Oxygen permeability of novel organic?inorganic
coatings: I. Effects of organic?inorganic ratio and molecular weight of the organic
component, Eur. Polym. Jou. l44 (2008) 2581?2588.

[2]        H. Lin, B.D. Freeman, Gas solubility,
diffusivity and permeability in poly(ethylene oxide), J. Membr. Sci. 239 (2004)
105?117.

[3]        H. Lin, B.D. Freeman, Materials selection
guidelines for membranes that remove CO₂ from gas mixtures, J. Mol.
Struct. 739 (2005) 57?74.

[4]        a) Panday, A.; Mullin, S.; Gomez, E. D.;
Wanakule, N.; Chen, V. L.; Hexemer, A.; Pople, J.; Balsara, N. P. Macromolecules
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            b) Singh, M.; Odusanya, O.; Wilmes, G. M.;
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P.; Iatrou, H.; Hadjichristidis, N.; Cookson, D.; Balsara, N. P. Macromolecules
2007, 40, 4578-4585.

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[6]        D. Husken, T. Visser, M. Wessling, R.J.
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CO₂ permeation properties of poly(ethylene
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[7]        E. Sada, H. Kumazawa, H. Yakushiji, Y. Bamba,
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