This paper presents a theoretical formalism for describing systems of semiflexible polymers, which can have density variations due to finite compressibility and exhibit an isotropic-nematic transition. The molecular architecture of the semiflexible polymers is described by a continuum wormlike-chain model. The non-bonded interactions are described through a functional of two collective variables, the local density and local segmental orientation tensor. In particular, the functional depends quadratically on local density-variations and includes a Maier⁻Saupe-type term to deal with the orientational ordering. The specified density-dependence stems from a free energy expansion, where the free energy of an isotropic and homogeneous homopolymer melt at some fixed density serves as a reference state. Using this framework, a self-consistent field theory is developed, which produces a Helmholtz free energy that can be used for the calculation of the thermodynamics of the system. The thermodynamic properties are analysed as functions of the compressibility of the model, for values of the compressibility realizable in mesoscopic simulations with soft interactions and in actual polymeric materials.
The conformational behaviors of charged brushes on a micelle self-assembled by charged-neutral diblock copolymers in salt-free solution are extensively analyzed using a coarse-grained dissipative particle dynamic (DPD) simulation. When only monovalent counterions exist, the brush conformation of the corona in the micelle is exactly consistent with the predictions from the blob-scaling theory based on the spherical polyelectrolyte brush model, which differentiates the system into three distinct regimes: (I) quasi-neutral regime, (II) "Pincus" regime, and (III) osmotic regime. For multivalent counterions such as divalence and trivalence, however, the strong electrostatic correlations lead the micelle structures to deviate obviously from those of scaling predictions. The collapse of the brush appears to be due to the drop in the osmotic pressure inside the corona region of the micelle.
The continuum version of the wormlike chain model (WLC), which was initially developed by Saito, Takahashi and Yunoki in 1967, is particularly suitable for description of polymer conformational properties affected by the chain rigidity. The WLC model is capable of covering an extensive range of chain rigidity, from the flexible chains to the rigid chains, by tuning the persistence length directly. It is widely accepted as a coarse-grained model that can be used to capture the physical properties, such as conformation and structures, of a larger class of real polymers than the Gaussian chain (GSC). Recently, the WLC model attracts increasing interests because of its advantages in studying a variety of polymeric systems, including liquid crystalline polymers and conjugated polymers. This review article focuses on applications of the WLC model, incorporated in the framework of self-consistent field theory, which is an effective method in theoretical exploration of phase separation in polymer systems. The article also pays particular attention to the developments of the numerical schemes to solve the modified diffusion equation governing the probability distribution of polymers. In addition, we summarize recent applications of the self-consistent field theories based on WLC model in the following three areas: phase transitions in liquid-crystalline polymers; the influence of surface curvature on polymeric systems involving the chain orientation effects; self-assembly of wormlike block copolymers. These studies are beyond the scope of self-consistent field theories based on a GSC model, which have been utilized in a large number of theoretical studies in recent years. Finally, we propose the perspectives of theoretical developments in field-theory simulations based on the WLC model for future work. In the polymer literature, it is generally appreciated that chain-rigidity is an important factor that influences the properties of structural stabilities on the meso-scale. The theoretical studies indentify the key physical mechanisms that play crucial roles in many experimental systems with attractively promising applications in practice, for systems such as liquid crystalline polymers and organic solar cell based on the conjugated polymers.
Alkali ion (Li, Na, and K) batteries as a new generation of energy storage devices are widely applied in portable electronic devices and large-scale energy storage equipment. The recent focus has been devoted to develop universal anodes for these alkali ion batteries with superior performance. Transition metal sulfides can accommodate alkaline ions with large radius to travel freely between layers due to its large interlayer spacing. Moreover, the composite with carbon material can further improve electrical conductivity of transition metal sulfides and reduce the electron transfer resistance, which is beneficial for the transport of alkali ions. Herein, we designed zeolitic imidazolate framework (ZIF)-derived hollow structures CoS/C for excellent alkali ion (Li, Na, and K) battery anodes. The porous carbon framework can improve the conductivity and effectively buffer the stress-induced structural damage. The ZIF-derived CoS/C anodes maintain a reversible capacity of 648.9, and 373.2, 224.8 mAh g-1 for Li, Na, and K ion batteries after 100 cycles, respectively. Its outstanding electrochemical performance is considered as a universal anode material for Li, Na, and K ion batteries.
Tea is the second widely consumed beverage next to water. Tea drinking is one of the important pathways for human exposure of organonphosphorus pesticide. Consequently, incidence of organonphosphorus pesticide residues and risk assessment should be clear. In this study, the level of organonphosphorus pesticide residues in 810 Chinese teas manufactured between 2010–2013 was investigated using gas chromatography coupled with tandem mass spectrometry and a flame photometric detector. Incidence of organonphosphorus pesticide residues occurred with a frequency of 29% and the average concentration of 93 μg kg−1. The residue levels varied from tea types, sale spots, and production area. Chlorpyrifos, isocarbophos, and triazophos were the only three organonphosphorus pesticides with detectable residues, and the detectable rates were 13.0%, 13.6%, and 17.4%, respectively. The corresponding average daily intake of chlorpyrifos, isocarbophos, and triazophos by tea drinking was 0.000083 μg kg−1 bw day−1, 0.0036 μg kg−1 bw day−1, and 0.0022 μg kg−1 bw day−1. These results showed that the total hazard quotient of organonphosphorus pesticide pesticides from tea drinking was less than 0.02 and that the tea-drinking originated organonphosphorus pesticide exposure had a little adverse health effect for human being.
The chemical development of a 2,3-disubstituted 4,7-diazaindole is described. The requisite tertiary carbinol substrate was prepared employing in situ-generated CH3TiCl3 as a chemoselective and preferred reagent compared to CH3MgX for methyl addition to an enolizable ketone. The 4,7-diazaindole ring system was efficiently assembled via an intramolecular Chichibabin transformation. The optimized processes were performed on pilot-plant scale to provide kilogram quantities of the target molecule.
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