(346f) 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.