This paper presents a continuation of our earlier research on the crystallization and solidstate structure of polylactide copolymers. The focus here is on random copolymers containing predominately L-lactide and small amounts (1.5, 3, and 6%) of D-lactide. As expected, degrees of crystallinity and spherulite growth rates decrease substantially with increasing D-lactide content in the copolymers. The importance of defect arrangement (isolated vs paired stereochemical defects) was demonstrated by comparison to our earlier research on L-lactide/meso-lactide copolymers. At a given degree of supercooling, measured lamellar thicknesses decrease significantly with increasing R stereoisomer concentration: e.g., by more than a factor of 2 (compared to poly(L-lactide)) for the 6% D-lactide copolymer. The results of small-angle X-ray scattering experiments indicate that a significant amount of noncrystalline material resides between lamellar stacks. Equilibrium melting points were estimated for the copolymers using the Gibbs-Thomson approach, and the values conform with predictions of the model of Wendling and Suter in the exclusion limit. Taken together with the significant reduction in lamellar thickness and crystallinity, these results point to substantial rejection of D-lactide (and meso-lactide) defects from S stereoisomer crystals. However, experiments by others on similar copolymers suggest that a significant amount of R (or R-R) isomers can be included in S crystals under certain crystallization conditions. Some speculation about the origin of these differences is presented.

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Employing seawater splitting systems to generate hydrogen can be economically advantageous but still remains challenging, particularly for designing efficient and high Cl−‐corrosion resistant trifunctional catalysts toward the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). Herein, single CoNC catalysts with well‐defined symmetric CoN4 sites are selected as atomic platforms for electronic structure tailoring. Density function theory reveals that P‐doping into CoNC can lead to the formation of asymmetric CoN3P1 sites with symmetry‐breaking electronic structures, enabling the affinity of strong oxygen‐containing intermediates, moderate H adsorption, and weak Cl− adsorption. Thus, ORR/OER/HER activities and stability are optimized simultaneously with high Cl−‐corrosion resistance. The asymmetric CoN3P1 structure based catalyst with boosted ORR/OER/HER performance endows seawater‐based Zn–air batteries (S‐ZABs) with superior long‐term stability over 750 h and allows seawater splitting to operate continuously for 1000 h. A self‐driven seawater splitting powered by S‐ZABs gives ultrahigh H2 production rates of 497 μmol h−1. This work is the first to advance the scientific understanding of the competitive adsorption mechanism between Cl− and reaction intermediates from the perspective of electronic structure, paving the way for synthesis of efficient trifunctional catalysts with high Cl−‐corrosion resistance.

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The orientation and crystallization during melt stretching were characterized, and their influence on the lamellar morphology and stretched polypropylene pore structure was clarified. During melt stretching, the MDR range from 40–200 could be divided into two regions. In region I, MDR below 120, the crystalline morphology transformed from ellipsoid spherulites to lamellae structure, and the orientation, elastic recovery, and lamellar lateral dimension were enhanced. The porosity of corresponding stretched microporous membrane was increased from 37.8–45.5%. In region II, with the MDR increasing to 200, the orientation and lamellae lateral dimension were increased, but the elastic recovery did not change much. The porosity of corresponding microporous membrane was improved further to 60.3%. The long period, crystalline phase thickness, crystallinity, and lamellae cluster size were kept constant within the whole MDR range, but the orientation was improved from 0.23 ± 0.02 to 0.41 ± 0.03. Apparently, the orientation induced the increase of lamellar lateral dimension, and it was the main factor deciding the properties of stretched microporous membrane.

The room-temperature stretching process of polypropylene annealed film with rownucleated crystalline structure was studied by in-situ small-angle X-ray scattering (SAXS) setup and off-line wide-angle X-ray scattering (WAXS), temperature-modulated differential scanning calorimetry (TMDSC) and stress-strain curves testing. The formation process of initial connecting bridges and pores was clarified. For the annealed film, except for the initial lamellae structure, the recrystallized part formed by the melting and crystallization of imperfect crystals during annealing, tie chains connecting the lamellae structure among the amorphous region, secondary crystals from the crystallization of tie chains during annealing and daughter crystals from the special cross-hatched crystalline structure of PP coexist. It was found that 10 % stretching lead to the pronounced increase of long period and the appearance of a few initial connecting bridges. The stretching of daughter crystal and recrystallized part contributed to the formation of initial bridges. At stretching ratio of 30 %, uniform distributed connecting bridges were observed and the stretched film showed maximum structure periodicity. At this stretching ratio, except for the stretching of daughter crystal, the stretching of tie chains and secondary crystals within the amorphous region lead to the formation of more connecting bridges. At higher stretching ratios into the strain-hardening region and beyond the second yield point, except for the stretching of the above mentioned crystalline

Herein, polylactic acid cast films were prepared with different melt-draw ratios via an extrusion casting process. The oriented structure appeared at first and then a chi structure crystal was formed at higher MDR.