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Study on polystyrene conformational changes in supercritical fluid anti-solvent process by small angle X-ray scattering
| Content Provider | Semantic Scholar |
|---|---|
| Author | Huo, Qiji Li, Dong |
| Copyright Year | 2018 |
| Abstract | In recent years, more and more emphasis is put on supercritical fluid technology. There are two main reasons: first, supercritical fluids have many unique properties; second, this technique causes little or no pollution [1-3]. Supercritical fluids (SCFs) have many unique properties near the critical point; the fluid physical and chemical properties such as viscosity, density, diffusion coefficient, solvation capability, dielectric constant are sensitive to changes in temperature and pressure. Viscosity and diffusion coefficients are close to those of gases, the density and the solvation ability are close to those of liquids. So far, supercritical fluid technology has been applied in many areas such as extraction and separation technology [4], petrochemistry [5], analytical techniques [6], chemical reaction engineering, materials science, biotechnology, etc. [7, 8], and has broad prospect. Preparation of particles is an important part of the chemical industry. Particles which have different properties can be used as stationary phases, adsorbents, catalyst carriers, etc., supercritical fluid anti-solvent process technology applications have attracted attention in this regard [9, 10]. The principle of the anti-solvent process (SAS) is: Many substances are soluble in organic solvents, but insoluble in a certain gas or a supercritical fluid. Meanwhile, under high pressure, the solubility of CO2 and other gases in many organic solvents is high, resulting in volume expansion of the solvent, therefore, when the gas or supercritical fluid is dissolved in the solvent, the solvent capacity for dissolving the solute decreases, and under appropriate conditions part or all of the solute can be precipitated which is called antisolvent process (SAS). In the anti-solvent process, the nature of the precipitate (particle size, crystal type, etc.) can be adjusted by pressure, temperature and speed of the gas dissolution. SAS techniques have applications in many areas such as natural products isolation, explosive fragmentation [11], preparation of drug particles [12], recrystallization of inorganic substances [11], etc. Small angle X-ray scattering (SAXS) originates from spatial fluctuations of the electronic density within a material. It is ideally suitable for investigating the geometric structure of inhomogeneous materials containing regions in which fluctuation or variation in electron density extends over distances of about 0.4 nm to 200 nm (e. g., nanomaterials or porous materials). The Xray intensity emitted from a common X-ray source is always very low, so that the application of SAXS is limited. By using synchrotron radiation with high intensity as X-ray source, SAXS measurement can be well improved [13, 14]. Our work is to make use of small angle x-ray scattering (SAXS) study of polystyrene conformational changes in the supercritical fluid anti-solvent process. X-ray scattering like other light scattering is caused by the unevenness of the system. For example, there are particles of dust and water vapor in the atmosphere, the electron densities of the atmospheric dust and water vapor are different. When the light illuminates the subject, they produce scattered light. If the size of the particles (as the polymer solution) dispersed in uniform media is a few microns, because the X-ray waves are much smaller than visible light, only a small range of angles (θ<2o) of the scattered light can be observed [15]. The intensity of the scattered *To whom all correspondence should be sent: E-mail: huo_q2002@aliyun.com |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.bcc.bas.bg/BCC_Volumes/Volume_49_Special_K_2017/BCC-NC14794-49-SI-K1-220-223.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
