Microstructure and Chirality: The Impact on Twisted or Tilted Crystals in Ring-Banded (R)/(S)-Mandelic Acids with Complex Assembly Structures

This study explores the crystallization and self-assembly behavior of spherulites formed from blends of (S)-mandelic acid (MA) and (R)-MA, modulated with poly(ethylene oxide) (PEO) into various periodic morphologies. Unique morphologies emerge: ginger-root-like spherulites at 25–35 °C and well-defined ring-banded structures at 40–50 °C, but corrupted at 60 °C. Precise adjustments in crystallization temperatures yield tailored microstructures. Analysis of (S)-MA/(R)-MA/PEO blends at 40 °C reveals chiral ratio impacts on ring-banded spherulites, with nonracemic and reversed blends showing similar textures but distinct crystal orientations. Scanning electron microscopy (SEM) images highlight specific lamellar arrangements in fractured 3D interiors, emphasizing chirality’s role in crystal growth. Synchrotron microbeam X-ray diffraction analysis (both small- and wide-angle) provides insights into lamellar orientation and structure. The microbeam X-ray results reveal monoclinic crystals for (R)-MA and (S)-MA, while (R/S)-MA forms orthorhombic crystals; blends exhibit mixed structures. Microbeam X-ray results also show vertical lamellae in ridges and horizontal ones in valleys, in alternate cycles, highly modulated by PEO. This study underscores stereochemistry’s influence on the macroscopic lamellar assembly of spherulitic morphology, revealing insights into formation mechanisms and stability.