Co-existing handednesses of lamella twisting in one spherulite observed with scanning microbeam wide-angle X-ray scattering

Chiral Nucleating Agents Affecting the Handedness of Lamellar Twist in the Banded Spherulites in Poly(ε-Caprolactone)/Poly(Vinyl Butyral) Blends

Chiral silica, which acts as a nucleating agent of poly(ε-caprolactone) (PCL), was demonstrated to induce excess handedness of lamellar twist in the banded spherulites of PCL blended with poly(vinyl butyral). The d- and l-forms of silica enhanced the right- and left-handed twists, respectively. The influences of chiral silica on the twist handedness were statistically significant. These results indicate that the handedness of twisting can be controlled upon primary nucleation. The organic substances used as chiral templates of silica had no effect on the handedness; silica was shown to govern the handedness. The possible mechanisms of the chirality transfer are discussed.

Temperature-dependent IR-transition moment orientational analysis applied to thin supported films of poly-ε-caprolactone

A novel experimental setup is described which enables one to carry out infrared transition moment orientational analysis (IR-TMOA) depending on temperature. By this, three dimensional molecular order parameter tensors of IR-active transition dipole moments with respect to the sample coordinate system can be determined in their thermal evolution (35 °C < T < 59 °C). As an example crystallinity and macroscopic order of poly-ε-caprolcatone are monitored. Both remain largely unaltered up to T ∼ 50 °C, above which they decrease. These reductions are explained as the melting of flat-on crystalline lamellae that make up about 34% of the crystalline material. The remaining crystallites are arranged into bulk-like, confined spherulitic structures and do not melt by more than (3 ± 3)%. Therefore, flat-on oriented lamellae are supposed to be kinetically favored by confinement during melt crystallization but are thermodynamically less stable than two-dimensionally confined bulk-like spherulites.

Organization of Twisting Lamellar Crystals in Birefringent Banded Polymer Spherulites: A Mini-Review

In this mini-review, we summarize the evidences of lamellar twisting in the birefringent banded polymer spherulites demonstrated by various characterization techniques, such as polarized optical microscopy, real-time atomic force microscopy, micro-focus wide angle X-ray diffraction, etc. The real-time observation of lamellar growth under atomic force microscopy unveiled the fine details of lamellar twisting and branching in the banded spherulites of poly(R-3-hydroxybutyrate-co-17 mol% R-3-hydroxyhexanoate). Organization of the twisting lamellar crystals in the banded spherulites was revealed as well. The lamellar crystals change the orientation via twisting rather than the macro screw dislocations. In fact, macro screw dislocation provides the mechanism of synchronous twisting of neighboring lamellar crystals. The driving force of lamellar twisting is attributed to the anisotropic and unbalanced surface stresses. Besides molecular chirality, variation of the growth axis and the chemical groups on lamellar surface can change the distribution of the surface stresses, and thus may invert the handedness of lamellar twisting. Thus, based on both experimental results and physical reasoning, the relation between crystal chirality and chemical molecular structures has been suggested, via the bridge of the distribution of surface stresses. The factors affecting band spacing are briefly discussed. Some remaining questions and the perspective of the topic are highlighted.

Growth actuated bending and twisting of single crystals

Crystals of a variety of substances including elements, minerals, simple salts, organic molecular crystals, and high polymers forgo long-range translational order by twisting and bending as they grow. These deviations have been observed in crystals ranging in size from nanometers to centimeters. How and why so many materials choose dramatic non-crystallographic distortions is analyzed, with an emphasis on crystal chemistries that give rise to stresses operating either on surfaces of crystallites or within the bulk.