Applying the string method to the self-consistent field theory (SCFT) of ABC linear triblock copolymers, we developed a new strategy to design kinetic pathways for the formation of stable or metastable network mesophases in order-order transition (OOT) processes. The design principle regarding the kinetic pathways between distinct mesophases is based on the matching relationships of both domain spacing and dominant Fourier components of the density distributions. The results suggest that complex ordered network mesophases, such as alternating diamond (D) and alternating plumber's nightmare (P) could be obtained in kinetic pathways between simple phases covering lamellae, cylinders and spheres. By virtue of the minimal free energy pathway (MEP) obtained, we could acquire the epitaxial relationship and phase transition mechanism. Furthermore, we managed to regulate the MEP by changing the block composition to adjust packing frustration. Two new metastable networks, core-shell five-pronged and six-pronged morphologies, were found in the kinetic pathways, further demonstrating the regulating mechanism. The results will contribute to a better understanding of the kinetic relationship between simple phases and complex networks, thus providing a platform for soft materials design via the OOT route and guiding experimental procedures to fabricate ordered network mesophases.

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The kinetics for the formation of the single gyroid (SG) nanostructure in ABC triblock terpolymers is investigated using the self‐consistent field theory combined with the string method. Both simple phases (lamellae, cylinders, and spheres) and networked double diamonds (DD) can transform into SG through order–order phase transition (OOT). In particular, a packing frustration‐induced variation in the epitaxial relationship between DD and SG is demonstrated. By regulating the block interaction, an expected epitaxial phase transition between these two networks without any rotation of the crystallographic directions can be achieved. Interestingly, the hexagonally perforated lamellae (HPL) are encountered in all identified transition pathways to SG. Nucleation kinetics investigation shows that the HPL tends to nucleate from SG easily, which confirms the kinetic origins of the instability of SG in experiments. Therefore, several strategies of preventing the SG being bypassed, such as controlling annealing time and rates during the morphology evolution, are proposed to promote the stabilizing of the SG in kinetic pathways. The findings reported here provide a novel route for fabrication of SG structured materials by manipulating both the epitaxial relationship and the nucleation kinetics in OOT pathways.

We employ a rod-coil multiblock molecular chain model to investigate chain folding behavior, which is a significant characteristic in semicrystalline polymers, by using the method of self-consistent field theory (SCFT). Polymer chains with different conformations in crystalline and amorphous regions are described by rigid rod chains and flexible Gaussian chains, respectively. At present, we concentrate on the thermodynamic behaviors of polymer semi-crystals after the formation of the initial lamellar crystals. A new mechanism for lamellar thickening is proposed to realize that the end of lamellar thickening depends on the crystallinity degree. In other words, it is impossible for lamellae to develop into extended-chain crystals by means of lamellar thickening if crystallinity is limited to a certain degree. We further discuss the competition between crystalline and amorphous regions and its influence on crystallization behaviors, such as the formation of double lamellae, chain tilt, the anomalies and adjacent re-entry. The synergistic influences of the driving force of crystallization, interfacial energy and crystallinity degree on chain folding behavior are also investigated when the density anomalies in amorphous regions are excluded. Our model demonstrates advantages in accurately describing the mesoscopic layered structures of semicrystalline polymers based upon a microscopic chain model and provides at least a semi-quantitative thermodynamic picture for chain folding.