Polymer films confinement effects

Kraus, J., Muller-Buschbaum, P., Kuhlmann, T., Schubert, D. W. and Stamm, M. (2000) Confinement effects on the chain conformation in thin polymer films. Europhys. Lett., 49, 210-216. 

Confinement Effects on the Microphase Separation and Polymer-Solvent Interactions in Swollen Films... 

The current trend towards miniaturization of functional systems and devices has driven the study of confinement effects (finite film thickness and the nature of the binding interfaces) on the fundamental physical properties of soft materials. Rapid developments of novel sensor and lab-on-chip technologies, and of polymer-based stimuli-responsive materials, raise the question of changes in solvent-polymer interactions under confinement. 

We suggest that this approach might be exploited at two levels. Firstly, field assistance of ion transfers (migration) will lead to their being more rapid than neutral species transfers. Secondly, size effects (for ions or neutral species) will lead to a diversity of transport rates. These effects are likely to be more pronounced in the confined geometry of polymer films than for the same species in solution. The extent to which transfer of a given species dominates the net transfer process (on a given time scale) will depend on its availability, i.e. solution concentration. 

Fig.20. Order parameter profiles m(z)=([pA(z)-pB(z)])/([pA(z)+pB(z)]), where pA(z), pB(z) are densities of A-monomers or B-monomers at distance z from the left wall, for LxLx20 films confining a symmetric polymer mixture, polymers being described by the bond fluctuation model with N=32, ab=- aa=- bb=8 and interaction range 6. Four inverse temperatures are shown as indicated. In each case two choices of the linear dimension L parallel to the film are included. While for e/kBT>0.02 differences between L=48 and L=80 are small and only due to statistical errors (which typically are estimated to be of the size of the symbols), data for e/kBT=0.018 clearly suffer from finite size effects. Broken straight lines indicate the values of the bulk order parameters mb in each case [280]. Arrows show the gyration radius and its smallest component in the eigencoordinate system of the gyration tensor [215]. Average volume fraction of occupied sites was chosen as 0.5. From Rouault et al. [56].

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