Supporting Information

Transcription

1 Supporting Information Effects of Interphase Modification and Biaxial Orientation on Dielectric Properties of Poly(ethylene terephthalate)/poly(vinylidene fluoride-co-hexafluoropropylene) Multilayer Films Kezhen Yin, Zheng Zhou, Donald E. Schuele, Mason Wolak, Lei Zhu,,* and Eric Baer,* Center for Layered Polymeric Systems (CLiPS) and Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio , United States Department of Physics, Case Western Reserve University, Cleveland, Ohio , United States U.S. Naval Research Laboratory, Washington, D.C , United States * Corresponding authors. s: lxz121@case.edu (L.Z.) and exb6@case.edu (E.B.) S-1

2 I. Comparison of Breakdown Strength Measured by Needle- and Plane-Electrode Methods In addition to the needle-electrode method, breakdown strength was also measure by the plane-electrode method. The multilayer films were coated with gold electrode on both sides. The diameter of the electrodes was 2.5 mm and the thickness of the electrodes was ca. 10 nm. Unlike the needle-electrode method, this type of electrode set-up ensured a more uniform electric field. A voltage ramp of 500 V/s was applied to the multilayer films until electrical breakdown. Fifty repeats were measured for each sample and the breakdown field was plotted using Weibull analysis (Figure S1A). From the analysis, the breakdown value (α) at 63.2% failure probability was taken as the breakdown strength and the Weibull slope (β) was also obtained. Comparison of the breakdown strengths measured by the plane- and needle-electrode methods are shown in Figure S1B. Both methods exhibited similar trends for as-extruded and biaxially oriented PET/P(VDF-HFP) films with different amounts of PMMA, although the needle-electrode results showed consistently higher values. Therefore, we consider that the needle-electrode method is valid to compare breakdown strengths for different films. Figure S1. (A) Weibull analysis plot of breakdown strength measured by the plane-electrode method for 0% and 8% PMMA multilayer films with and without biaxial orientation. (B) Comparison of breakdown strengths measured by the needle- and plane-electrode methods. S-2

3 II. Electrical Conductivity for PVDF and Dissipation Factor at Different Temperatures for the PET/PMMA/P(VDF-HFP) 65-Layer Film with 8% PMMA The real part of electrical conductivity is defined as: σ = 2πfε0εr, where f is frequency, ε0 vacuum permittivity, and εr imaginary part of the relative permittivity. From Figure 2D in ref. 14, the σ at 1 Hz can be plotted as a function of temperature in Figure S2A. At low frequencies (e.g., 1 Hz) and above the Tg, the σ is mainly resulted from ionic conduction in PVDF. As we can see, the conductivity is as low as S/m, whereas it increases above S/m around 100 C. Therefore, the ionic conduction at room temperature can be neglected. Figure S2. (A) σ as a function of temperature at 1 Hz for a biaxially oriented PVDF film. S1 (B) Dissipation factor, tanδ, as a function of frequency for the as-extruded PET/PMMA/P(VDF- HFP) 65-layer film with 8% PMMA at various temperatures. Assignment of various relaxation processes can be obtained from the frequency-scan BDS results at various temperatures in Figure S2B. Upon increasing temperature, the αc relaxation gradually shifts to higher frequencies. Below 40 C, loss from impurity ions does not exist at low frequencies (i.e., Hz). At 60 C, an upturn is observed at low frequencies, which can be assigned to the migrational loss from impurity ions. Note that the migrational loss of impurity ions usually shows a peak, rather than a plateau, in both εr and tanδ in the frequency domain. Therefore, the upturn at low frequencies is part of the ionic loss peak (i.e., the high frequency part). With increasing temperature, the ion relaxation peak should shift to higher frequencies due to an enhanced diffusion coefficient at a higher temperature. This is seen when the temperature increases to 80 C. However, at 100 C, the low frequency upturn shifts to lower frequencies as compared with the result at 80 C. This is totally out of expectation. Meanwhile, a new relaxation peak appears around 300 Hz. Given different impurity ions (including cations and anions with different sizes) in the sample, we can explain this as the following. The relaxation peak around 300 Hz and 100 C should be attributed to fast ions (e.g., cations with a smaller size). The relaxation below 10-1 Hz at 100 C should be attributed to slow ions (e.g., cations with a larger size). S-3

4 III. Estimation of Mutual Diffusion Coefficient for PMMA and P(VDF-HFP) In order to calculate mutual diffusion coefficient, D0, 33 layers of PMMA/P(VDF-HFP) films was coextruded using forced assembly technique at 260 C. Seven PMMA/P(VDF-HFP) multilayer films with different compositions were extruded, 0/100, 20/80, 35/65, 50/50, 65/35, 80/20, and 100/0. The interdiffusion model S2 was applied to this system as described in the main text. The composition of PMMA and P(VDF-HFP) as a result of interdiffusion can be obtained from Eqn. 4 in the main text:, sin cos exp.... (S1) where L1 and L2 are layer thicknesses for PMMA and P(VDF-HFP) in the multiplier and can be calculated based on the width of the multiplier channel (25.4 mm) and the number of layers. The weight fraction profile of each PMMA/P(VDF-HFP) films was converted to a water vapor permeability profile using a miscible blends model: S3 ln, 1 (S2) where ϕ is volume fraction and P is water vapor permeability of the pure polymer. This profile was further sliced into q equal layers and the total permeability profile can be calculated using a series model: S4 / (S3), Based on previous publication, S5 q was selected to be 41 to achieve error less than 2%. Water vapor permeability (P) was measured by MOCON (Minneapolis, MN, Permantran W 3/33 unit) at 1 atm and 23 C, and the result is shown in Figure S2. Mutual diffusion coefficient, D0, was varied to fit the measured water vapor permeability values. From the best fitting, the D0 for PMMA/P(VDF-HFP) at 260 C is m 2 /s, and this values is used to calculated interdiffusion of PMMA and P(VDF-HFP) in PET/PMMA/P(VDF-HFP) multilayer films. Figure S3. Water permeability of PMMA/P(VDF-HFP) films as a function of PMMA composition. Red symbols are experiment data. S-4

5 References S1. Yang, L.; Ho, J.; Allahyarov, E.; Mu, R.; Zhu, L. Semicrystalline Structure - Dielectric Property Relationship and Electrical Conduction in a Biaxially Oriented Poly(vinylidene fluoride) Film Under High Electric Fields and High Temperatures. ACS Appl. Mater. Interfaces 2015, 7, S2. Pollock, G.; Nazarenko, S.; Hiltner, A.; Baer, E., Interdiffusion in Microlayered Polymer Composites of Polycarbonate and a Copolyester. J. Appl. Polym. Sci. 1994, 52, S3. Robeson, L. M. Polymer Blends: A Comprehensive Review; Carl Hanser Verlag: Munich, S4. Khariwala D. Structure-Property Relationships in Multilayered Polymeric System and Olefinic Block Copolymers. Ph.D. thesis: Case Western Reserve University; S5. Lai, C.; Ponting, M.; Baer, E. Influence of Interdiffusion on Multilayered Gradient Refractive Index (GRIN) Lens Materials. Polymer 2012, 53, S-5