Experimental solubilities are reported for terephthalic acid (TA) in binary mixtures of N-methyl pyrrolidone (1) + water (2) and N,N-dimethyl acetamide (1) + water (2) in the temperature range of (303.2 to 363.2) K. The mole fraction of water in the N-methyl pyrrolidone + water solvent mixtures x
2 ranges from 0 to 0.5791 and in the N,N-dimethyl acetamide + water solvent mixtures x
2 ranges from 0 to 0.5477. The experimental results show that the solubility of TA increases significantly with an increase in temperature and decreases significantly with an increase in x
2. The solubility data were correlated by a modified Buchowski equation.
TiCl 4 /MgCl 2 catalysts are still the main industrial catalyst for isotactic polypropylene at present. However, the mechanism of isotactic polymerization of propylene has not been fully understood. DFT calculations revealed that the bare Ti active site was regioselective and nonstereoselective in the absence of an electron donor. The role of electron donor ethyl benzoate (EB), diethyl-2,3-diisobutylsuccinate (DiBS), cyclohexylmethyldimethoxysilane (CMDMS), and dicyclopentyldimethoxysilane (DCPDMS) on the active site was investigated. The presence of EB, DiBS, CMDMS, or DCPDMS around the Ti active site can promote the activity and retain the regioselectivity. It is worth noting that in the presence of EB and DCPDMS, the stereoselective behavior can be promoted with the advantage of 1 kcal/mol. The copresence of AlEt 2 Cl species and external donors can increase both the stereoselectivity and regioselectivity.
Raman spectrum, as a kind of scattering spectrum, has been widely used in many fields because it can characterize the special properties of materials. However, Raman signal is so weak that the noise distorts the real signals seriously. Polynomial fitting has been proved to be the most convenient and simplest method for baseline correction. It is hard to choose the order of polynomial because it may be so high that Runge phenomenon appears or so low that inaccuracy fitting happens. This paper proposes an improved approach for baseline correction, namely the piecewise polynomial fitting (PPF). The spectral data are segmented, and then the proper orders are fitted, respectively. The iterative optimization method is used to eliminate discontinuities between piecewise points. The experimental results demonstrate that this approach improves the fitting accuracy.
Ziegler−Natta catalysts are one of the mainly used industrial catalysts for the large-scale production of polyolefins. As one of the important components in a Ziegler−Natta catalyst, the internal donor and external donor pair is responsible for increasing the stereoregularity of polypropylene. In this work, a series of sulfonyl amine internal donors were systematically investigated by density functional theory (DFT) calculations. The adsorption behavior of the sulfonyl aromatic amine BTFMSPA-m-Cl indicates that the O atom exhibited an excellent coordinating affinity to the 4-coordinated Mg atoms on the MgCl 2 (110) surface among the three functional atoms (F, Cl, O). In addition, the substituents have a great influence on the adsorption behavior of the sulfonyl amines. The functional atom of the substituent (Cl or OMe) in the phenyl ring and the oxygen of the sulfonyl group tend to form a more stable bridge-coordination (Cl-Mg1,Mg2-O3, or O-Mg1,Mg2-O3) than the chelate-coordination (O1-Mg2-O2). In all considered internal donors, the stereoselectivity of the Ti active site can be greatly enhanced in the presence of BTFMSPA-m-Cl, which presumably results from the steric hindrance around the Ti active site caused by the bridge-coadsorbed BTFMSPA-m-Cl.
Sensitivity is an important performance index for evaluating surface plasmon resonance (SPR) biosensors. Sensitivity enhancement has always been a hot topic. It is found that the different refractive indices of samples require different combinations of prism and metal film for better sensitivity. Furthermore, the sensitivity can be enhanced by coating two-dimensional (2D) materials with appropriate layers on the metal film. At this time, it is necessary to choose the best film configuration to enhance sensitivity. With the emergence of more and more 2D materials, selecting the best configuration manually is becoming more complicated. Compared with the traditional manual method of selecting materials and layers, this paper proposes an optimization method based on a genetic algorithm to quickly and effectively find the optimal film configuration that enhances sensitivity. By using this method, not only can the optimal number of layers of 2D materials be determined quickly, but also the optimal configuration can be conveniently found when many materials are available. The maximum sensitivity can reach 400°/RIU after optimization. The method provided application value for the relevant researchers seeking to enhance sensitivity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.