Figure 5 Ar permeances through the membrane. Argon permeances
through VACNT/parylene membranes at different temperatures. In general, gas transport through a porous membrane can be described by viscous flow, Knudsen mTOR inhibitor cancer diffusion, and surface diffusion [11, 17, 30, 31]. Knudsen diffusion becomes prominent when the mean free path of the diffusing species is larger than the pore diameter. For most gases, the mean free path is significantly larger than the pore diameter of the CNT membrane (7 nm). Hence, one would expect the gas transport through the CNT membrane to be in the Knudsen regime [30, 32]. The Knudsen permeance could be estimated using the following equation: (1) where P Kn is the Knudsen permeation (mol m-2 s-1 Pa-1), ϵ p is the porosity, τ is the tortuosity, Φ is the inner diameter of CNT (m), L is the layer thickness (m), M is the molecular mass (kg mol-1)
Tanespimycin order of the gas molecule, and T is the absolute temperature (K).The constant experimental permeances of the gases irrespective of the pressure gradient are consistent with the Knudsen model, which provide indirect but important evidence that the gas molecules do transport through the nanoscale interior channel of CNTs rather than the relatively large cracks in the membranes. This finding agrees well with the good impregnation of CNTs with the parylene, which has been demonstrated in Figure 3b. Temperature dependence of the gas permeances across the CNT composite membrane was explored, and the results were presented in Figure 6. According to the Knudsen theory (Equation 1), the gas permeance would decrease with increasing temperature. Surprisingly, our experimental permeances of all the gases firstly increased with raising the temperature up to 50°C and then decreased as the temperature further rose. Ge et al. also found similar dependence of gas permeance
on the temperature in VACNT/epoxy membranes and attributed it to the contribution of both surface diffusion and Knudsen diffusion [11]. Figure 6 Permeability of gases 3-mercaptopyruvate sulfurtransferase at different temperatures. Temperature dependence of the gas permeances across the CNT composite membrane. To investigate the enhancement of experimental permeances over theoretic prediction, the Knudsen permeances were computed using Equation 1. The parameters of the VACNT/parylene membranes are listed in Table 1 for calculating the Knudsen permeance. The membrane porosity ϵ p ~ 0.0008 is estimated from the KCl diffusion experiments [30], as described in Additional file 1. Table 1 Parameters of VACNT/parylene membranes Parameters Values Thickness I (μm) CH5183284 mw Approximately 10 CNT diameter Φ (nm) Approximately 7 CNT tortuosity factor (τ) Approximately 1 Areal porosity (ϵ p) Approximately 0.0008 The permeance enhancement factor is defined as the ratio of experimental permeance to the Knudsen permeance.
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