Elasticity Dominated Surface Segregation of Small Molecules in Polymer Mixtures

Abstract

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. We study the phenomenon of migration of the small molecular weight component of a binary polymer mixture to the free surface using mean field and self-consistent field theories. By proposing a free energy functional that incorporates polymer-matrix elasticity explicitly, we compute the migrant volume fraction and show that it decreases significantly as the sample rigidity is increased. A wetting transition, observed for high values of the miscibility parameter can be prevented by increasing the matrix rigidity. Estimated values of the bulk modulus suggest that the effect should be observable experimentally for rubberlike materials. This provides a simple way of controlling surface migration in polymer mixtures and can play an important role in industrial formulations, where surface migration often leads to decreased product functionality. In this Letter we ask how the elasticity of the polymer matrix influences surface migration of small molecules in polymer mixtures. We propose a free energy functional that incorporates elasticity of the polymer mixture explicitly, a feature that has been ignored in previous surface segregation studies. Using a Schmidt-Binder mean field theory (SB) and self-consistent field theory (SCFT) we show that as the sample rigidity is increased (i) the migrant fraction decreases, and (ii) a wetting transition can be avoided (demonstrated by a geometric construction [8,9]). These results are of paramount importance in industrial product formulations where surface migration of small molecular weight component results in decreased functional performance of the product.Surface migration.-For a binary mixture, the component with the lower surface energy will migrate to the interface. A balance between loss of translational entropy and gain in surface energy dictates the equilibrium morphology of such systems. This is shown in Fig. 1 with a high migrant (black) concentration close to the interface (z ¼ 0) of a mixture of low and high (red) molecular weight polymers. The migrant concentration decreases

Predicting oligomer/polymer compatibility and the impact on nanoscale segregation in thin films

“…We consider the main factors driving surface segregation to be (i) disparity in molecular weight, (ii) difference in surface energy and (iii) incompatibility between components. Other factors such as elasticity, 48 crystallization 12 or deformation may be relevant to more complex matrices, but are not considered here since all of the components are amorphous and have shorter relaxation times than the timescale of observation.…”

Phase separation in swelling and deswelling hydrogels with a free boundary

“…The transport of solvent into and out of the network leads to the swelling and drying of the hydrogel, thereby introducing large deformations of the polymer network. Since hydrogels are omnipresent in nature, in innumerable biological processes, but also in many smart soft-matter as well as medical applications, there have been a large number of theoretical and experimental studies aiming at understanding the dynamic behavior and pattern formation during swelling and drying processes [1][2][3][4][5][6][7][8][9]. Fundamental phenomena include the formation of a core-shell structure for the swelling of beads [1,10], or the appearance of wrinkling instabilities, such as those described in the seminal work by Tanaka et al [11] and others [1,12].…”

Gelation Impairs Phase Separation and Small Molecule Migration in Polymer Mixtures

“…The precise connection between the bulk modulus and the microscopic gel architecture is not known, to the best of our knowledge. Therefore, we use values of the bulk modulus which are similar to those used in earlier calculations on the thermodynamics of phase separation in mixtures of small molecules and gels [ 31 ]. In an ongoing work, we are investigating the effects of gel elasticity on the domain coarsening length scale and how this depends on the gel fraction or the cross-link density of the mesh structure.…”

“…This is an exciting recent area with lots of experimental activity [ 29 , 30 ] but relatively scant theoretical understanding. In an earlier theoretical study [ 31 ], we showed that increasing the bulk modulus of a gel–oligomer mixture causes a dramatic reduction in the surface fraction of migrant molecules. The wetting transition observed for de-mixed systems can also be avoided.…”