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22 results on '"He, Yanping"'

12. A study on the nucleation mechanisms under critical micelle concentration (CMC) in emulsion polymerization of methyl methacrylate (MMA)

Author

Si Tian, Yan Lin Sun, Xiaoqin Xiao, He Yanping, Zhu Linhua, Hong Wang, and Bingwen Xu

Subjects
Flocculation, education.field_of_study, Materials science, Polymers and Plastics, General Chemical Engineering, Population, Nucleation, Emulsion polymerization, Pulmonary surfactant, Chemical engineering, Critical micelle concentration, Polymer chemistry, Materials Chemistry, Particle, Particle size, education
Abstract

In this study, formulation of latex with methyl methacrylate (MMA) as a function of surfactant concentration ([S]) under critical micelle concentration (CMC) was investigated to explore the nucleation mechanism and the key to control the particle number (N p) of latex in emulsion polymerization. Influences of surfactant concentration [S] on the conversion of monomer, particle size (PS), N p, and surfactant surface coverage (θ) were studied, as well. Flocculation nucleation was considered as the main mechanism to generate particle nuclei when [S] was much less than CMC. The nucleation mechanism experienced an evolution of a flocculation nucleation-dominated region ([S] 3.3 mmol L−1). The contribution ratio of the flocculation nucleation was 86 % compared with the micellar nucleation. The particle number (N p) was found to be controlled by the combination of micellar and flocculation nucleation-dominated regions under CMC, and the regulation range was about 1–6. The results can be used to guide the preparation of a bimodal high solid content (HSC) latex by creating a population of small particles in the presence of an initial population of larger ones in a controllable way. In this way, a controllable amount of large latex particles were prepared using a high emulsifier concentration, at first, and then the second population of small particles was formulated by secondary nucleation at a proper time through controlling surfactant concentration at a low level, followed by the growth of the two groups of the particles, and then the bimodal HSC latex can be prepared at low viscosity.

Published
2015

16. Photophysical and photosensitive properties of Elsinochrome A

Author

He Yanping, Ou Lingcheng, Zhikun Yao, Mengbi Guo, Maojun Tian, and Cong Li

Subjects
chemistry.chemical_compound, Multidisciplinary, Absorption spectroscopy, Cyclohexane, Semiquinone anion, Chemistry, Singlet oxygen, Quantum yield, Hypocrellin A, Triplet state, Nanosecond, Photochemistry
Abstract

In this paper, the photophysical and photosensitive properties of Elsinochrome A (EA), another member of perylenequinone photosensitizers derived via artificially biological synthesis, were studied by taking hypocrellin A (HA) and hypocrellin B (HB) as the references. It was found that the quantum yield of singlet oxygen produced via the photosensitization of EA was 0.98 with HB (0.84) as a reference. Furthermore, the semiquinone anion could be produced via photosensitization of EA in oxygen-free solution. Besides, taking advantage of nanosecond time-resolved spectral technique, the transient triplet absorption spectra and the lifetime of EA in cyclohexane were determined by the use of the ground-state depletion method.

Published
2006

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