Small angle neutron scattering data of polymer electrolyte membranes partially swollen in water

In this article, we show the small-angle neutron scattering (SANS) data obtained from the polymer electrolyte membranes (PEMs) equilibrated at a given relative humidity. We apply Hard-Sphere (HS) structure model with Percus–Yervick interference interactions to analyze the dataset. The molecular structure of these PEMs and the morphologies of the fully water-swollen membranes have been elucidated by Zhao et al. “Elucidation of the morphology of the hydrocarbon multi-block copolymer electrolyte membranes for proton exchange fuel cells” [1].


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In this article, we show the small-angle neutron scattering (SANS) data obtained from the polymer electrolyte membranes (PEMs) equilibrated at a given relative humidity. We apply Hard-Sphere (HS) structure model with Percus-Yervick interference interactions to analyze the dataset. The molecular structure of these PEMs and the morphologies of the fully water-swollen membranes have been elucidated by Zhao et al. "Elucidation of the morphology of the hydrocarbon multi-block copolymer electrolyte membranes for proton exchange fuel cells" [1].
& 2016 Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Subject area
Materials science More specific subject area

Soft matter
Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/dib The dry membranes with an average thickness of $ 50 μm were prepared by solution casting onto a flat glass plate from its dimethyl sulfoxide solution with a concentration of 5 wt%. Partially water swollen membranes were prepared by putting the dry membranes into a humility controller at 30% relative humidity and 25°C. Experimental features

Type of data
The incident neutron beam was monochromatized with a velocity selector to have the average wavelength (λ) of 5 Å with a wavelength resolution of Δλ/ λ¼ 20%. All of the measurements were done at 25 70.5°C. The scattering patterns were collected with a two-dimensional scintillation detector, and circularly averaged to obtain scattering intensity profiles as a function of q, where q is the scattering vector, defined as q ¼(4π/λ)sin(θ/2) with θ being the scattering angle. The scattering profiles were corrected for the instrument background, detector sensitivity, and scattering from empty cell, and finally calibrated on the absolute scale (cm À 1 ) using a Plexiglas secondary standard. Data source location SANS measurements were performed with KWS-2 at the neutron source Heinz Maier-Leibnitz (FRM II reactor) in Garching, Germany.

Data accessibility
Data is with this article

Value of the data
Hard-sphere structure model is introduced to elucidate the morphology of polymer electrolyte membranes.
Data of partially swollen membranes together with that of fully swollen membranes leads to a thorough understanding of the morphology.
The method and model analysis are worthy being applied to other types of membranes.

Data
Partially water swollen membranes were prepared by putting the dry PEMs into a humility controller at 30% relative humidity and 25°C. The SANS measurements were performed with KWS-2 at the neutron source Heinz Maier-Leibnitz (FRM II reactor) in Garching, Germany, and the scattering intensity profiles has been corrected and calibrated on the absolute scale (cm À 1 ). Fig. 1a and b show the SANS intensity profiles of the two membranes, PSP 14 -b-PAEK 14 and PSP 28 -b-PAEK 14 , as a function of scattering vector q, respectively. The profile of the corresponding fully D 2 Oswollen membranes is plotted in the same figure as a reference. Hard-Sphere (HS) structure model with Percus-Yervick interference interactions was applied to analyze these scattering profiles [1,2]. The best fitting parameters are listed in Tables 1 and 2. Note that the profiles at high-q range (0.08oqo0.45 Å À 1 ) can be fitted well by Eq. (6) below, and the best fitted curve is summed up with the fitting curve in the middle-q range and shown in the figure.

Materials
Two multiblock copolymer poly(sulfonate phenylene)-b-poly(arylene ether ketone) with different block ratios, designated as PSP 14 -b-PAEK 14 and PSP 28 -b-PAEK 14 for brevity, were synthesized by varying the stoichiometry of the sulfonated monomers and hydrophobic oligomers via the nickel-catalyzed polymerization [3,4]. The subscript 14 or 28 refers to the repeating unit number in each block. The molecular structure and characteristics of these two polymers can be found elsewhere [1,2]. The dry membranes with an average thickness of $ 50 μm were prepared by solution casting onto a flat glass plate from its dimethyl sulfoxide solution with a concentration of 5 wt% [3].  Partially water swollen membranes were prepared by putting the dry membranes into a humility controller at 30% relative humidity and 25°C.

Methods
SANS measurements were performed with KWS-2 at the neutron source Heinz Maier-Leibnitz (FRM II reactor) in Garching, Germany [5]. The incident neutron beam was monochromatized with a velocity selector to have the average wavelength (λ) of 5 Å with a wavelength resolution of Δλ/λ¼ 20%. All of the measurements were done at 257 0.5°C. The scattering patterns were collected with a two-dimensional scintillation detector, and circularly averaged to obtain scattering intensity profiles as a function of q, where q is the scattering vector, defined as q ¼(4 π/λ)sin(θ/2) with θ being the scattering angle. The scattering profiles were corrected for the instrument background, detector sensitivity, and scattering from empty cell, and finally calibrated on the absolute scale (cm À 1 ) using a Plexiglas secondary standard.

Analysis
We assume that the topology of the swollen membranes can be described by an almost random distribution of n particles in a homogeneous matrix. Let Δb be the contrast of the particle density with respect to the matrix density and v be the of average volume of a single particle, then the observed scattering intensity, I(q), is [6] IðqÞ ¼ ðΔbÞ 2 nv 2 PðqÞSðqÞ ¼ KPðqÞSðqÞ ð 1Þ where P(q) is the form factor of the particles, S(q) is an approximate interference factor and K is a constant in terms of Δb, n and v. We assume that the number of the particles per volume is high that S(q) must be considered despite the random arrangement of the particles. The contrast Δb¼b p À b m is defined by the difference between the scattering length density (SLD) of the particle phase, b p , and that of the matrix phase, b m . Thus, Δb is computable as long as the shape and composition of the particle phase and the matrix phase are well determined, and their SLDs are theoretically estimated below. SLD of a molecule of i atoms is related to its molecular structure and may be readily calculated from the simple expression given by Mw where b i is the scattering length of ith atom, d is the mass density of the scattering body, M w is the molecular weight, and N A is the Avogadoro constant [6].
Let us consider an ensemble of spheres with varying sizes that can be described by a Gaussian size distribution: with R being the average radius, and σ R being its standard deviation. Thus v ¼ 4πR 3 3 . We consider Percus-Yevick expression to account for interparticle interference [2,7], then S(q) is the interference factor, described for a random arrangement of spheres by the following expression: here A¼2qR and ϕ is the hard sphere volume fraction. F(A) is a trigonometric function of A and ϕ given by The distribution of the ionic clusters at high-q range can be fitted well by Gaussian distribution function, where the scattering intensity around the ionomer peak at 0.08 Å À 1 oq o0.45 Å À 1 , I ion (q), can be expressed by where I m,ion is the ionomer peak height, G(q) is Gaussian distribution function about the ionomer peak at q m,ion , given by G q ð Þ ¼ 1 ð2πÞ 1=2 σq exp À q À q m;ion À Á 2 =ð2σ q 2 Þ h i , with σ q being the standard deviation of q m,ion , and I inc is the incoherent scattering intensity, which can be determined by the average intensity of the flat part of the profile at q 40.4 Å À 1 in the high-q region. Eq. (6) is used to fit profiles in Fig. 1a and b and the fitting parameters are listed in Tables 1 and 2.