Diffusion and Deuteron Nuclear Magnetic Resonance Study of the Distribution of Water Molecules in Polyimide Films

Abstract

The nature and distribution of water molecules in polyimide (KAPTON) films of varying thickness is studied by diffusion and deuteron (2H) nuclear magnetic resonance spectroscopy with complementary studies of IR absorption and differential scanning calorimetry. The results supports the conclusion, drawn from a previous study, that water exists in two distinct sites called ~ and ~2, neither of which is strongly bound to the host polymer nor is isotropically free. The water molecules in the ~ site are distributed uniformly throughout the volume of the film, while those in the ~2 site (which are filled only at higher values of relative humidity) appear to be in small molecular clusters.ABSTRACT Cathode dissolution is a major problem for the development of the molten carbonate fuel cell. In order to evaluate the stability of the cathode, the solubility of NiO has been measured for several Compositions of molten alkaline carbonates in the COs pressure range from 10 .5 to 1 atm and the temperature range from 873 to 1023 K. The solubility depended on the CO, pressure, although the solubility of NiO was independent of either O2 or H20 pressure. In any composition of the Li/K and LENa carbonate melts, the acid dissolution has been observed at higher COs pressure and the basic dissolution has been observed at low COs pressure. NiO was found to be more stable in Li rich or Li/Na melts than in the Li/K eutectic melt.

A molecular dynamics simulation study of three polysulfones in dry and hydrated states

“…However, it is clear that, for all types, the correlation lifetimes of the H‐bonds are about twice as long in these polysulfones than in PMDA–ODA 156. We can note here that the averages of experimentally determined diffusion coefficients of water in PMDA–ODA, PESU and PSU between 23 and 50 °C are ∼0.27 × 10 −8 cm 2 s −1 ,75, 105, 243–248 ∼8 × 10 −8 cm 2 s −1 ,64, 199, 200, 249 and ∼9 × 10 −8 cm 2 s −1 , respectively 9, 16, 29, 64, 199, 213. This would suggest that the H‐bond lifetime is not the critical parameter for defining water diffusion if the models reproduced the same tendencies for the diffusion coefficients.…”

“…Hydrolysis of polymers by water is also a well‐known phenomenon 3, 18, 43, 49–61. For all these reasons, water sorption has been studied for many years mainly using techniques such as sorption isotherms,24, 50, 62–76 density or swelling measurements,1, 11, 22–35, 49, 77 differential scanning calorimetry (DSC),12, 78–81 infrared experiments,6, 28, 81–100 dielectric measurements24, 98, 101, 102 or nuclear magnetic resonance (NMR) 12, 78, 79, 102–106. Other specific experimental techniques have also been applied.…”

Molecular Dynamics Simulation Study of Water in Amorphous Kapton

“…Experimental measurements of the limiting weight percentage of water uptake by amorphous Kapton in contact with water vapor at its saturation pressure in the temperature range from 25 to 80 °C vary between ∼2% and ∼6%. 3,16,[23][24][25][26][28][29][30]124,[150][151][152][153][154][155] The scatter in experimental data is thought to be related to the film preparation history, the measurement technique, and in some cases the thickness of the films. 16,24,26,150 For example, Ree et al 26 It should be recalled here that, in a periodic model system, we are not limited to the amount of water that can be added to the polymer system, although phase separation is expected at very high water contents.…”

“…27 However, dielectric measurements, NMR, and infrared attenuated total reflection (ATR) studies suggest the existence of water clusters at lower activities. 25,[28][29][30][31] In addition, Yang et al studied hygrothermally aged Kapton and found that it did not display the upwardly curving shape at high activities, which was interpreted by the authors as "the absence of clustering in the aged film" and was attributed to chemical modifications giving rise to more hydrophilic films. 18 This is difficult to understand as, at high activities, there is a lot of water to accommodate in the dense polyimide.…”

Surface-Influenced Phase Separation in Organic Thin Films on Drying

“…This is instantaneous compared to the induction time of t i ∼ 8 s (at least) before any lateral phase separation is observed by AFM . Conservatively, for t i = 5 s (time before phase separation) and solvent diffusion coefficient, D ∼ 10 -9 cm 2 /s at 70 °C, the DTL thickness, l ∼ 1.5( Dt i ) 1/2 / S ∼ 170−200 nm for c 0 in the 0.920−0.950 range. S is the shrinkage given by {[(1 − c 0 )/ρ] + [ c i /ρ s ]}/{[(l − c 0 )/ρ] + [ c 0 /ρ s ]}, where ρ ∼ l.2 and ρ s = 1.033 g/cm 3 are densities of the polymer and NMP.…”