Lamellar Orientation Inversion under Dynamic Interplay between Crystallization and Phase Separation

Risk evaluation and prevention of China’s investment in countries along the belt and road

The Belt and Road Initiative is a major Initiative proposed by Chinese President Xi Jinping in 2013. Research on the risk prevention and control of China’s financial investment in countries along the Belt and Road has become a very hot topic in the world. This research focuses on the risk evaluation methods and prevention and control countermeasures of China’s foreign investment under the Belt and Road Initiative. First, based on the analysis of the existing studies on economic investment evaluation, an intuitionistic fuzzy multi-attribute evaluation method based on entropy method and G1 method is proposed. The essence of the proposed method is to combine the intuitionistic fuzzy set theory with subjective and objective evaluation methods, which improves the disadvantage of the original evaluation method taking too much subjective factors into consideration. This study applies the proposed method to the economic risk evaluation of China’s outward foreign direct investment (OFDI), constructs a 17-indicator economic risk system, and uses this method to rank the importance of the 17 indicators. The more important contribution is that this paper not only achieves improvements at the theoretical level and innovation at the practical level, but also condenses the research conclusions into three pieces of countermeasures and suggestions on China’s investment in countries along the Belt and Road. This research can provide theoretical support for Chinese government to make financial investment decisions in countries along the Belt and Road, and can also help countries along the Belt and Road to actively integrate into the Belt and Road Initiative, and promote the high-quality social and economic development of the countries along the Belt and Road.

Spontaneous Creation of Anisotropic Polymer Crystals with Orientation-Sensitive Birefringence in Liquid Drops

It remains a grand challenge to prepare anisotropic crystal superstructures with sensitive optical properties in polymer science and materials field. This study demonstrates that semicrystalline polymers develop into anisotropic hollow spherulitic crystals spontaneously at interfaces of liquid drops. In contrast to conventional spherulites with centrosymmetric optics and grain boundaries, these anisotropic spherulitic crystals have vanished boundary defects, tunable aspect ratios, and noncentrosymmetric, orientation-sensitive birefringence. The experimental finding is elaborated in poly(l-lactic acid) crystals and is further verified in a broad class of semicrystalline polymers, irrespective of molecular chirality, chemical constitution, or interfacial modification. The facile methods and general mechanism revealed in this study shed light on developing new types of optical microdevices and synthesis of anisotropic semicrystalline particles from liquid emulsions.

Unexpected Tribological Synergy in Polymer Blend Coatings: Leveraging Phase Separation to Isolate Domain Size Effects and Reduce Friction

We employed a systematic processing approach to control phase separation in polymer blend thin films and significantly reduce dynamic friction coefficients (μ)s. We leveraged this modulation of phase separation to generate composite surfaces with dynamic friction coefficients that were substantially lower than expected on the basis of simple mixing rules, and in several cases, these friction coefficients were lower than those of both pure components. Using a model polyisoprene [PI]/polystyrene [PS] composite system, a minimum μ was found in films with PS mass fractions between 0.60 and 0.80 (μ_blend = 0.11 ± 0.03); that value was significantly lower than the friction coefficient of PS (μ_PS = 0.52 ± 0.01) or PI (μ_PI = 1.3 ± 0.09) homopolymers and was comparable to the friction coefficient of poly(tetrafluoroethylene) [PTFE] (μ_PTFE = 0.09 ± 0.01) measured under similar conditions. Additionally, through experiments in which the domain size was systematically varied at constant composition (through an annealing process), we demonstrated that μ decreased with decreasing characteristic domain size. Thus, the tribological synergy between PS and PI domains (discrete size, physical domain isolation, and overall film composition) was shown to play an integral role in the friction and wear of these PS/PI composites. Overall, our results suggest that even high friction polymers can be used to create low friction polymer blends by following appropriate design rules and demonstrate that engineering microstructure is critical for controlling the friction and adhesion properties of composite films for tribologically relevant coatings.

Tuning the crystalline and mesophase structure of olefin block copolymer through self-nucleation and annealing treatments

As a type of novel semi-crystalline block copolymers, the final properties of olefin block copolymers (OBCs) greatly depend on the crystalline and phase-separated structures. In the present work, we systematically investigated the influence of self-nucleation and annealing on the lamellar and mesophase-separated structure of OBCs. According to the crystalline and melting behavior after self-nucleation and annealing treatments, four different regimes can be recognized with the self-seeding temperature Ts varying from 125 to 109 °C. In regime A, only self-nucleation occurs, while it coexists with lamellar thickening in regime B. In regime C, there is only lamellar thickening behavior. The lamellar thickening induced inconsecutive lamellar crystals observed revealed that the rearrangement of the hard blocks, which are next to the soft blocks and trapped in the intermediate regime between crystalline and amorphous phases, into neighboring lamellar crystals should be the mechanism for the lamellar thickening of the OBCs. Surprisingly, no lamellar thickening occurs and a new small melting peak appears at lower temperatures in regime D. Considering the block dispersity of OBCs, the emergence of a small melting peak at lower temperatures can be attributed to the crystallization of the ethylene sequence with relatively weaker crystallization abilities, which are not able to crystallize in a standard crystalline state. Based on these findings, we gained some new understandings on lamellar thickening behavior of OBCs and established the self-nucleation and annealing process as a powerful tool for tuning the crystalline and phase-separated structures of OBCs.

Hierarchical coarsening in the late stage of viscoelastic phase separation

Coarsening is a general phenomenon in phase separating mixtures. In this study, we report a hierarchical coarsening at different length scales. Dispersed domains grew by direct combination of two/three small ones while some small domains can survive for a long time. The small angle laser light scattering showed that the scattered intensity exhibited multiple "decay-growth" transitions in the coarsening process. The evolution of the main peak gave a characteristic power law index of about -3/4, which is much faster than the -1/3 relationship from the traditional theories. We propose that relaxation and hydrodynamic flow play important roles in this process.

Ultraporous interweaving electrospun microfibers from PCL-PEO binary blends and their inflammatory responses

Production of one dimensional nanomaterials with secondary morphology exhibiting unique functions is challenging. Here we report for the first time that a nanoscale immiscible polymer blend solution electrojet can assemble into ultraporous interweaving microfibers. This intriguingly novel morphology originated from a blend of polycaprolactone (PCL) and polyethylene oxide (PEO) in a DCM-DMF mixed solution when the ratio between each component reached a threshold and when the electrospinning parameters were delicately controlled. The morphology, crystallinity, surface chemistry and wettabilities were characterized to understand the mechanism of formation. The interplay of the two semi-crystalline polymers and the pair of solvents/non-solvents with the electrospinning processing parameters was found to be critical for the formation of the unique structure. Furthermore, the interesting combination of biocompatible, biodegradable PCL with protein-resistant PEO motivated us to assess its inflammation responses on the RAW 264.7 macrophage cell line. All fibers were found to be biocompatible with low inflammation potential upon incubation, while compared with pure PCL nanofibers; the unique interweaving microfibers induced a slightly higher inflammatory reaction.

Single-Walled Carbon Nanotube-Induced Orthogonal Growth of Polyethylene Single Crystals at a Curved Liquid/Liquid Interface

We report herein single-walled carbon nanotube-induced polyethylene crystallization at the curved liquid/liquid interface. A Pickering emulsion system comprised of polyethylene (PE)/single-walled carbon nanotubes (SWCNTs)/1,2-dichlorobenzene (DCB)/water is formed using probe sonication at an elevated temperature. SWCNTs are used as the Pickering agents, and they are bent into nanosized rings by the curved DCB/water interface. Upon cooling, PE crystallizes onto SWCNTs, forming kebab single crystals, and the PE lamellae are orthogonal to the DCB/water interface. The unique structure resembles nanohybrid shish kebab (NHSK) rings.

Viscoelastic Phase Separation and Interface Assisted Crystallization in a Highly Immiscible iPP/PMMA Blend

Polymer blends with dynamic asymmetry have attracted much interest recently. In this study, we report a more typical case where the dynamically asymmetric system is highly immiscible. We find that there is a transient network growth and phase inversion for the slow minor component. The network structure shows a hierarchical growth behavior, which is the result of competition between a slow relaxation-controlled concentration growth on local scale and a fast hydrodynamic growth on large scale. When phase separation couples with a subsequent crystallization, the interfacial boundary may assist lateral crystallization and irregular spherulites would grow epitaxially around the amorphous component-rich domains. The interface may play the role of substrates for heterogeneous nucleation. These phenomena may help us with morphological control in material processing.