Effects of copper ions on dissolution mechanism of marmatite

The dissolution mechanism of marmatite in the presence of Cu^(2+)was intensively studied by experiments and density functional theory(DFT) calculations. Leaching experiments showed that Cu^(2+)accelerated marmatite dissolution at high temperatures(above 55 ℃), but the trend was reversed at low temperatures(below 45 ℃), which may be because the reaction mechanism between Cu^(2+)and marmatite changed from surface adsorption to bulk substitution with increasing temperature. The substitution reaction caused more zinc atoms in the marmatite crystal lattice to be released and enhanced the electrochemical reactivity, while the adsorption of copper ions at low temperatures would passivate marmatite, thus inhibiting the reaction process. DFT calculations showed that the energy of the substitution reaction was more negative than that of the adsorption reaction at high temperatures, which further verified the proposed mechanism.

Unusual Spherulitic Morphology of Poly(propylene fumarate)

Spherulites are the most common crystalline morphology and thus the visual expression of crystal structures for polymers.The diversified patterns have provided intuitive morphology probes for various crystallization behaviors,while the correlations between them are still needed to be enriched.In this work,the complicated spherulitic morphology of poly(propylene fumarate)(PPF),which is sensitive to crystallization temperature,is investigated.PPF melt,respectively,crystallizes into rough spherulites,regularly banded spherulites,and spherulites containing both two kinds of morphology at low,high,and mediate temperatures.By systematically assaying,it is clear that the growth axis along the radial direction changes from a-axis to b-axis as the crystallization temperature increases,which leads to the formation of unique crystallization-temperature-dependent spherulites.Based on detailed characterization of Fourier transform infrared spectroscopy,the packing state of the specific hydrogen bonds of"C=C-H…O=C-C=C"in PPF crystal lattices is determined,and furthermore,the mechanism for temperature-dependent selection of growth axes for PPF spherulites in melt is reasonably speculated.

Distinctive Polymorphism-like Isodimorphism in Poly(propylene succinate-ran-propylene fumarate)

Co-crystallization of different monomeric units fundamentally contributes to the versatile and tunable performance of random copolymers.At present,the crystallization manners of random binary copolymers have been divided into three categories:isomorphism,isodimorphism and comonomer exclusion.Each category,however,has its own advantages and disadvantages.Therefore,it is challenging to design and prepare random copolymer sharing the advantages of isomorphism and isodimorphism through a new co-crystallization manner beyond the ones already exist.On the basis of previous study on poly(alkylene succinate-ran-alkylene fumarate)whose co-crystallization can be extensively and finely regulated by simply varying the chemical structure of alkylene,random copolymers of poly(propylene succinate-ranpropylene fumarate)(PPSF)are synthesized using 1,3-propanediol as the diol source.The thermal properties and crystal structure of PPSF are investigated,and,intriguingly,it is proved that PPSF is an isodimorphism system while displays similar composition-dependent thermal properties and crystallinity as isomorphism.That is,PPSF exhibits a novel co-crystallization behavior that has rarely been discovered,which would combine the advantages of both isomorphism and isodimorphism.Consequently,PPSF could be termed as a new-type,special compositiondependent polymorphism.Besides,the altering of PPS-like to PPF-like crystal structure of PPSF when changing chain composition has been proved to originate from the shift of dominant inter-segment interaction from van der Waals forces to strong hydrogen-bonding interaction.This work enriches the co-crystallization manner of random copolymers,leading to more diverse performance design of polymer materials.