Hong Huo

Effects of lithium perchlorate on the nucleation and crystallization of poly(ethylene oxide) and poly(ε-caprolactone) in the poly(ethylene oxide)–poly(ε-caprolactone)–lithium perchlorate ternary blend

The effects of lithium perchlorate (LiClO4) on the nucleation and crystallization of poly(ethylene oxide) (PEO) and poly(e-caprolactone) (PCL) in the PEO–PCL–LiClO4 ternary blend were studied by using a polarizing optical microscope (POM), differential scanning calorimetry (DSC) and Fourier transformation infrared spectroscopy (FTIR). LiClO4 has a heterogeneous nucleation effect on PEO in the blend, irrespective of the presence of PCL. The coordination interaction between PEO and LiClO4 decreases with the increase of the PCL content, so the heterogeneous nucleation ability of LiClO4 on PEO decreases with the increase of the PCL content in the ternary blends. LiClO4 has no heterogeneous nucleation effect on PCL. In the ternary blend, the heterogeneous nucleation effect of PEO on PCL is remarkably promoted with the addition of LiClO4. POM observations show that the miscibility of PEO and PCL improves after the addition of LiClO4, leading to an increase in the interface volume of PEO and PCL phase domains. The increased concentration-fluctuation at the interface promotes the interfacial nucleation of PCL in the ternary blend. The combination of “fluctuation-assisted crystallization” and “interface-assisted crystallization” mechanisms of the interfacial nucleation of PCL in the PEO–PCL binary blend is also suitable for the interfacial nucleation of PCL in the PEO–PCL–LiClO4 ternary blend.

Crystallization behavior of poly(ε-caprolactone) and poly (ε-caprolactone)/LiClO4 complexes from the melt

The crystalline structures and isothermal crystallization behavior of poly(e-caprolactone) (PCL) and PCL/LiClO4 complexes from the melt were investigated via time-resolved simultaneous synchrotron small-angle and wide-angle X-ray scattering (SAXS/WAXS) measurements in this paper. The influences of Li salts and crystallization temperature on the isothermal crystallization behavior and structural evolution dynamics of PCL were discussed. The results indicated that Li salts affected the crystallization behavior of PCL without changing the structure of the crystalline. It was also shown that the formation of pre-ordered phase (according to SAXS) in the induction stage prior to the appearance of crystalline peaks (according to WAXS) during the isothermal crystallization of PCL and PCL/LiClO4 complexes. The collected SAXS data were analyzed according to Guinier plot and correlation function. By comparing the average radius size of isolated domains formed in the melt obtained from the Guinier plot in the early stage of crystallization with the crystalline lamellar thickness calculated according to the correlation function in the later stage of crystallization, it is concluded that the final crystalline structure may evolve from pre-ordered phase in the initial stage of the melt. Through accurate analysis the PCL and PCL/LiClO4 complexes depicted invariant SAXS intensities, it is found that the LiClO4 coordinated PCL chains mainly locate at the interphase between the crystalline lamellae and amorphous layer. The structural evolution during crystallization in the induction period and subsequent stages of PCL and PCL/LiClO4 were analyzed according to a proposed model.

Hydrodynamic behaviors of amphiphilic dendritic polymers with different degrees of amidation

A series of amphiphilic dendritic copolymers (ADPs) with different degrees of amidation (DA) were synthesized by the amidation reaction of polyethyleneimine (HPEI) with dendritic palmitate tails. The hydrodynamic radii (Rh) of the polymers were investigated via dynamic light scattering (DLS). It was found that Rh increased with increasing DA, and a sharp increase was noted when DA was near 51 percent. The intrinsic viscosity was measured using an Ubbelohde capillary viscometer to understand the structure evolution of the ADPs. The results showed that the intrinsic viscosity decreased slowly with increasing DA. The Fox–Flory formula was employed to calculate the radius of gyration (Rg). The ratio of Rg and Rh was around 0.77, which indicated that the ADPs were compact. The solvent effects on Rh were investigated which showed that the Rh in chloroform was bigger than that in a poor solvent for HPEI. However, Rh remained unchanged with the increasing volume fraction of poor solvent for HPEI from twenty percent to eighty percent. The solvent quality has no obvious influence on the relationship between Rh and Mn before DA = 51 percent, but a sharper slope is noted after DA = 51 percent. This phenomenon can be explained by the compact structure of the ADPs. The Rh values remained constant for the synthesized DA within the measured temperature range in chloroform and glycol dimethyl ether.

Effects of ultrasonication on the interfacial interactions between poly(3-hexylthiophene) and graphene oxide

The interactions between poly(3-hexylthiophene) (P3HT) and graphene oxide (GO) have endowed the P3HT/GO composite with excellent properties. Controlling these interactions is important to improve the performance of P3HT-based devices. In this work, ultrasonication was used to regulate the nanostructures of P3HTs (high Mw and low Mw), and further strongly affected the interactions between P3HTs and GO. Atomic force microscopy (AFM), UV-vis absorption spectroscopy, Raman spectroscopy, and grazing incidence X-ray diffraction (GIXRD) were used to study the effects of ultrasonication on the interfacial interactions between P3HTs and GO. With prolonged ultrasonication time, the molecular order of high Mw P3HT nanofibers increased, but that of low Mw P3HT nanofibers decreased. Molecular order is a crucial factor affecting the interfacial interactions between P3HTs and GO, and the amounts of P3HT nanofibers absorbed onto the GO surface increased with the decreased molecular order of the nanofibers. After absorption, the overall molecular order of P3HT/GO composite nanofibers was determined by the nanofibers absorbed onto the GO surface and the nanofibers nucleated by GO. Compared with the molecular order of the nanofibers before absorption, the overall molecular order of the composites with high Mw P3HT increased, but that of composites with low Mw P3HT decreased. These findings can help to understand and modulate the interactions between P3HT nanofibers and GO to provide more information in the field of interfacial engineering of conjugated polymers in polymer-based devices.

Effects of isomorphic poly(butylene succinate-co-butylene fumarate) on the nucleation of poly(butylene succinate) and the formation of poly(butylene succinate) ring-banded spherulites

The nsucleation effects of isomorphic poly(butylene succinate-co-butylene fumarate)s (PBSFs) on poly(butylene succinate) (PBS) were investigated using differential scanning calorimetry (DSC) and polarized optical microscopy (POM). When the content of PBSF is fixed at 2.0 wt% in the PBSF/PBS blends, the nucleation efficiency of PBSF is related to the BF molar ratio in PBSF. Nucleation efficiency is not observed when the molar ratio of BF is ≤5%; the nucleation efficiency is weak when the molar ratio of BF is between 10% and 30% and the nucleation efficiency is strong when the molar ratio of BF is ≥40%. In fixing the nucleating agent as PBSF-5 (the BF molar ratio of PBSF is 5%), the nucleation efficiency of PBSF-5 is related to its content in the PBSF-5/PBS blends. Nucleation efficiency is not observed when the content of PBSF-5 is ≤2.0 wt% and the nucleation efficiency strengthens dramatically when the content of PBSF-5 is ≥5.0 wt%. POM images reveal the changes of PBS ring-banded spherulites in the PBSF/PBS blends. The band spacing of PBS in the PBSF/PBS blends decreases with the increase of the BF molar ratio of PBSF or the content of PBSF-5. The cell parameters of the PBSF nucleating agent are important in the formation of PBS ring-banded spherulites. No PBS ring-banded spherulite forms when the BF molar ratio of PBSF is ≥40%. In the PBSF-5/PBS blends, the crystallization temperature range of the ring-banded spherulite formation gradually narrows when the content of PBSF-5 is ≥5.0 wt%. In this work, clarifying the slight structure difference of isomorphic PBSFs on the epitaxial nucleation and the formation of PBS ring-banded spherulites is advantageous.