A Combined Experimental and Modeling Approach to Study the Sorption and Diffusion Phenomena in Materials

A combined experimental and modeling approach to study the sorption and diffusion phenomena in materials

Hom N. Sharma, Stephen J. Harley, Yunwei Sun, and Elizabeth A. Glascoe

Lawrence Livermore National Laboratory

L288, 7000 East Ave., Livermore, CA 94550

925-423-5368

sharma@llnl.gov

Moisture sorption and diffusion in materials are of great interest in wide range of applications from fuel cells to microfluidics and pharmaceuticals.(1-3) The uptake and outgassing of moisture is also associated with aging and compatibility issues in a system or sub-system, which is important to establishing the lifetimes and viability of current assemblies and screening new materials for future designs. The process is dynamic and consists of different sorption modes and varies dramatically in different materials.(2, 4) Therefore, an in-depth understating of the moisture uptake and outgassing is essential.

In this study, we investigate the moisture sorption and diffusion using a combined experimental and modeling approach. Various materials including polymers are investigated over a wide range of temperature (30 – 70 ^oC) and relative humidities (RH) (0 – 90%) to quantify the moisture transport mechanism as shown Fig. 1. Further, a reactive transport model is developed, which includes (a) a triple-mode sorption model that includes absorption, adsorption, and pooling of species, (b) molecular diffusion, and (c) chemical reaction kinetics. Using a 1D or 3D model, we can simultaneously simulate the transport and chemical reactions of mobile species through materials. The equation of diffusion coupled with Langmuir adsorption and pooling sorption can be given as:

where C, C_H, C_L, C_P, D are the total concentration of sample bulk mass, mass concentration in Henry mode, concentration in Langmuir mode, pooling sorption mode concentration, and effective diffusion coefficient, respectively.

Our results show that the particular mode could become dominant at certain RH regions indicating the material specific diffusion-sorption behavior. For example, Langmuir mode is dominant in Zircar RS1200 at the beginning while Henry mode gradually increases and reaches to its maximum. Above 50% RH, pooling (clustering) starts and becomes dominant sorption mode while Langmuir attains its equilibrium as shown in the figure below. In this presentation, we will discuss our combined experimental and modeling approach using diffusion-sorption mechanisms along with the parameter estimation and uncertainty quantification techniques in various polymeric and non-polymeric materials.

Fig. 1:  Experiments and multi-mode diffusion-sorption modeling results of dynamic moisture uptake by Zircar RS1200 at a range of relative humidities at 50 ^oC.

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Reference:

1.              Harley SJ, Glascoe EA, Maxwell RS. Thermodynamic Study on Dynamic Water Vapor Sorption in Sylgard-184. J Phys Chem B. 2012; 116(48):14183-90.

2.              Harley SJ, Glascoe EA, Lewicki JP, Maxwell RS. Advances in Modeling Sorption and Diffusion of Moisture in Porous Reactive Materials. Chemphyschem. 2014; 15(9):1809-20.

3.              Davis EM, Elabd YA. Water Clustering in Glassy Polymers. J Phys Chem B. 2013; 117(36):10629-40.

4.              Sun YW, Harley SJ, Glascoe EA. Modeling and Uncertainty Quantification of Vapor Sorption and Diffusion in Heterogeneous Polymers. Chemphyschem. 2015; 16(14):3072-83.