Effect of Concentration Gradient on the Morphology Development in Polymer Solutions Undergoing Thermally Induced Phase Separation

Abstract

Anisotropic porous polymeric materials fabricated from the phase separation method via spinodal decomposition are used in various practical engineering applications. We studied the formation of anisotropic porous polymeric materials numerically, by imposing an initial linear concentration gradient across a model polymer solution. The initial concentration gradient is placed at three different regions of the polymer sample for comparison purposes. All the simulation results are in good agreement with published experimental observations, which are reported from the applications of porous polymeric membranes. The structure development shows that an anisotropic porous morphology forms when an initial linear concentration gradient is applied to the model polymer solution.magnified image

Computer Simulation of Anisotropic Polymeric Materials Using Polymerization-Induced Phase Separation under Combined Temperature and Concentration Gradients

“…An asymmetric structure was observed along the concentration gradient with larger (smaller) droplets at the lower (higher) concentration side. The results of Figure 2, Figure 3 and Figure 4 are consistent with the results previously obtained for the TIPS process of polymeric solutions under a concentration gradient [31,32]. The phase diagram, however, is fixed in the TIPS studies, and the critical region does not shift, so the study of morphology development is simpler compared to the cases in this paper in which the quench depth and the location of the samples, with respect to the critical point, were continuously changing.…”

“…Increasing the initial concentration of the solvent along the membrane led to the formation of larger particles as well as the decrease of phase separation process time. Jiang and Chan [32] provided a two-dimensional model to determine the effect of the initial concentration of a solvent on the structural feature of polymer/solvent mixtures located at three different regions of the binary phase diagram while undergoing the TIPS process. For the sample located at the left (right) side the critical region, phase separation occurred earlier at the higher (lower) initial concentration edge; in addition, larger solvent-rich (polymer-rich) droplets were observed in this part of the phase-separated mixture.…”

The Ludwig‐Soret Effect on the Thermally Induced Phase Separation Process in Polymer Solutions: A Computational Study

“…[18] Moreover, analyzing the spatial concentration profiles and patterns in Figure 2 to 4, it is interesting to note that the initiation of the phase separation phenomena begins at the low temperature region (i.e., close to x à ¼ 0) of the polymer solution sample at early times and the phase separated regions grow over time increasingly from the region x à ¼ 0 to 1 to occupy the entire solution sample area. This kind of morphological development is due to the externally imposed spatial linear temperature gradient across the polymer solution sample, which induces the effect of differential quench along the x à direction.…”

“…[1][2][3][4][5][6][7][8][9][10] Due to the widespread demand and scope of the unique thermal, mechanical and optical properties of these materials, there has been continuous research and development for the modification of these materials for better properties and functionalities for the last two decades. One of the core areas for research is the introduction of structural anisotropy in these functional polymeric materials for the improvement of their performance, which can be obtained by externally imposing an electrical field, [11,12] a shear flow, [13,14] a concentration gradient, [15][16][17][18] a temperature gradient, [19][20][21][22] or a controlled chemical reaction [23][24][25][26] on a polymer solution sample.…”

Formation of metastable structures by phase separation triggered by initial composition gradients in thin films

“…Related processing has been utilized, for instance, to produce anisotropic microporous polymer membranes (see e.g., Ref. 22), and the theoretical modeling of this processing has been considered, [23][24][25][26] including also an interplay with temperature gradients, 27 but this will be out of consideration here, too.…”