Solid polymer-based materials and devices are inevitably exposed to solvents during their operation [1,2]. In this case, small solvent molecules (e.g. water or alcohol) can diffuse into the polymer material. This holds even if the solvent is considered to be a poor solvent for the polymer. Depending on the solvent the intake is sufficient to lead to swelling up to a certain penetration depth. This rather destructive process is known as “case II diffusion”, and results in interfacial stress buildup and cracks in glassy polymeric materials, thus limiting the life span of the application. Even though this phenomenon has been known for a long time [3], a detailed microscopic understanding is still lacking.   

 

The aim of this project is to study case II diffusion in thin polymer films and its implications for mechanical stability using molecular dynamics simulations. We will begin with computing the kinetics of solvent uptake in commodity polymers that are in itself insoluble in pure water or alcohol, but can marginally swell at intermediate mixing ratios [4]. This effect is shown in Fig. 1 in the infinite dilution limit.

Fig. 1: Swelling of a polymer chain in a mixture of poor solvent

Solvent concentration profiles will be compared and tested against predictions from the continuum diffusion models. Then we will explore the effect of solvent molecules on the mechanical properties by subjecting the polymers to various forms of deformation. The long-term goal of this collaboration is to develop a structure-property relationship for designing better functional materials.

For this purpose, we

− aim to understand the interaction of solvent molecules with polymer this films through
   ­carefully parameterized generic models,

− study key factors governing diffusion of solvents into polymer films,

− study the extent of Case II diffusion effecting materials properties,

− and link the molecular level macromolecular morphologies to mechanical properties.

The ideal candidate will have a background in modeling and simulation of soft materials.

References

[1] M. A. Cohen-Stuart, W. T. S. Huck, J. Genzer, M. Müller, C. Ober, M. Stamm, G. B. Sukhorukov, I. Szleifer, V. V. Tsukruk, M. Urban, F. Winnik, S. Zauscher, I. Luzinov, and S. Minko, Nat. Materials 9, 101 (2010).

[2] D. Mukherji, C. M. Marques, and K. Kremer, Nat. Commun. 5, 4882 (2014).

[3] N.L. Thomas and A.H.Windle, Polymer 4, 429 (1982)
[4] D. Mukherji, C. M. Marques, T. Stuehn, and K. Kremer, Nat. Commun. 8, 1374 (2017).

Principal investigators

Debashish Mukherji (UBC) [Debashish.mukherji@ubc.ca]
Joerg Rottler (UBC) [jrottler@physics.ubc.ca]
Kurt Kremer (Max-Planck-Institut für Polymerforschung) [kremer@mpip-mainz.mpg.de]

 

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