Tiancheng Mu

Nanosized poly(ethylene glycol) domains within reverse micelles formed in CO2.

The liquid at nanometer scale differs substantially from bulk liquid, which is of particular significance for different applications. As one of the most efficient ways, reverse micelles have been widely utilized in forming liquid domains at the nanometer scale. For example, nanosized water domains are formed in reverse micelles, which can be used as nanoreactors for chemical reactions, material synthesis, extraction, and biochemistry research. Recently, roomtemperature ionic liquids (ILs) have been reported to form nanosized domains in reverse micelles, which have found applications in material synthesis and chemical reactions. Poly(ethylene glycol) (PEG) with a small molecular weight (< 800 g mol ) is in the liquid state at room temperature. Liquid PEG is usually regarded as green solvent, because it is economical, environmentally benign, biocompatible, and its properties are tunable by changing the molecular weight. Owing to these special properties, liquid PEGs have been widely used in various fields, such as materials science, chemical reactions, electrochemistry, pharmaceutical industry, and others. Herein we report for the first time the formation of nanosized PEG domains in reverse micelles by using supercritical CO2 as the continuous phase. Supercritical CO2 is readily available, inexpensive, nontoxic, nonflammable, and the physical properties can be adjusted continuously by pressure and temperature. Therefore, the system combines the advantages of both PEG and supercritical CO2. With the aid of surfactant N-EtFOSA (C2H5NHSO2C8F17, see Figure S1 in the Supporting Information for its molecular structure), the nanosized PEG domains are formed in CO2. The PEG domains are “tunable”, because their size and property can be easily changed by controlling the PEG content. Furthermore, to demonstrate their potential applications, the nanosized PEG domains have been utilized as nanoreactors to synthesize highly dispersed gold nanocrystals. The phase behavior of the PEG-400/N-EtFOSA/CO2 systems was observed at different pressures and temperatures. The surfactant concentration was fixed at 0.05 g mL . The cloud-point pressure is the minimum pressure at which the PEG-400/N-EtFOSA/CO2 system keeps in one phase region. In other words, when the pressure is lower than the cloudpoint pressure, phase separation occurs. The dependence of the cloud-point pressure of the PEG-400/N-EtFOSA/CO2 system on the molar ratio of PEG-400 to surfactant (W0 ) at different temperatures is shown in Figure S2 in the Supporting Information. It is known that a small amount of PEG can be solubilized in CO2 at high pressure. [16] In this work the amount of PEG-400 solubilized in pure CO2 at different pressures and temperatures was determined (Table S1 in the Supporting Information), and a comparison for the PEG solubility in pure CO2 and in the N-EtFOSA/CO2 system is shown in Figure S3 in the Supporting Information. It is clear that the PEG solubility is enhanced significantly with the addition of surfactant N-EtFOSA. This enhanced solubility indicates that a sufficient amount of PEG is solubilized in reverse micelles, that is, PEG-in-CO2 microemulsions are formed. The molar ratio of PEG solubilized in reverse micelles to surfactant is denoted as W0 , which is obtained by subtracting the amount of PEG in bulk CO2 from the total amount of loading PEG. Figure 1 shows the dependence of cloud-point pressure of the PEG-400/N-EtFOSA/CO2 system on W0 corr at different temperatures. Evidently, the cloud-point pressure increases with increasing ratio W0 . The cloudpoint pressure increases, because with a higher concentration

Synthesis and characterization of polyether structure carbon nitride

Carbon nitride powder with an atomic N/C ratio of 1 has been prepared by reaction of cyanuric chloride with sodium metal. X-ray diffraction, Fourier transform infrared spectra, and x-ray photoelectron spectroscopic data provide substantial evidence for a graphite-like sp 2 -bonded structure composed of building blocks of s-triazine rings bridged by carbon-carbon atoms in the bulk carbon nitride. The electron-microscopy results reveal that the material is spherical particles with an average diameter of 50 nm. The optical properties and thermal stability are also characterized. Based on the experimental results, it is deduced that the structure of as-prepared material carbon nitride has polyether structure.

Effect of compressed CO2 on the properties of AOT reverse micelles studied by spectroscopy and phase behavior

Combination of reverse micellar solutions and supercritical or compressed carbon dioxide (CO2) is a new and interesting topic. This work conducted the first study on the effect of compressed CO2 on the micro-properties (e.g., micropolarity, ionic strength, pH) of the sodium bis(2-ethylhexyl) sulfosuccinate reverse micelles in isooctane by phase behavior measurement, Fourier transform infrared and UV–vis spectroscopic techniques. The results show that CO2 can dissolve in both the organic-continuous phase and the water cores of the reverse micelles. The properties of the reverse micelles can be tuned continuously by changing the pressure of CO2 because the solubility of CO2 in the solution and in the water cores depends on the pressure. CO2 in the water cores can be ionized to produce HCO3−1 and H+. The micropolarity and ionic strength of the water cores increase with the pressure of CO2. Accordingly, the pH is reduced as the pressure and water-to-surfactant molar ratio (w0) are increased.

Effects of ultrasound on the microenvironment in reverse micelles and synthesis of nanorods and nanofibers

FTIR and UV-vis techniques were used to investigate the effect of ultrasound on the microenvironment of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelles in iso-octane. The studies revealed that ultrasound resulted in re-aggregation of the reverse micelles and thus enlarged the water core of the micelles. On the basis of these investigations, ZnS nanorods and nanofibers were synthesized in the reverse micelles by the ultrasound-induced method. A possible mechanism for ultrasound-induced formation of nanorods and nanofibers in reverse micelles is discussed.

An investigation of non-fluorous surfactant Dynol-604 based water-in-CO2 reverse micelles by small angle X-ray scattering

Synchrotron radiation small-angle X-ray scattering (SAXS) technique was used to quantitatively derive structural information of the Dynol-604 (a surfactant) based water-in-CO2 reverse micelles. By using the Guinier plot (In I(q) vs. q(2)) on the data sets in a defined small q range (0.025 -0.040 Angstrom(-1)), the radii of the reverse micelles at different pressures and loading water were estimated, which were in the range of 73.8 to similar to 78.1 Angstrom

Effect of cosolvent on the phase behavior of non-fluorous Ls-54 surfactant in supercritical CO2

Abstract The effect of 1-propanol, n -pentanol, n -heptanol, and benzyl alcohol on the phase behavior of CO 2 /Ls-54 system has been investigated. The results indicate that the alkyl chain alcohols can reduce the cloud point pressure (CPP) considerably, and the smaller alcohols are more effective. However, addition of benzyl alcohol leads to increase in CPP. In addition, the phase behavior study of Ls-54 surfactant in supercritical (SC) CO 2 with different n -heptanol concentration was also carried out. The results showed that the CPP increases with increasing temperature and decreases with increasing n -heptanol concentration.

Tautomeric equilibrium of ethyl acetoacetate in compressed CO2+ethanol and CO2+methanol mixtures

Tautomerism equilibrium of ethyl acetoacetate (EAA) in compressed CO2 + methanol and CO2 + ethanol mixtures was studied by UV-Vis spectroscopy at 308.15 K and different pressures. The volume expansion coefficient (alpha) of the solvents at different pressures was also determined. The relative permittivity (epsilon) of CO2 + methanol and CO2 + ethanol mixtures at different conditions was calculated using the Kc and Onsager solvent parameter. The equilibrium constant (Kc) of EAA in the binary mixtures increases considerably with increasing pressure or volume expansion coefficient. The relative permittivity or the polarity of the binary mixtures decreases sharply with increasing volume expansion coefficient in the range of 0 < alpha < 1.5. However, as the volume expansion coefficient exceeds 1.5, the relative permittivity decreases slowly. In other words, the dissolution of CO2 in the polar solvents can reduce the polarity of the solvents significantly in the low volume expansion coefficient range, and the polarity of the solution is not sensitive to the volume expansion coefficient as its value is large enough. The difference in polarity of the two solvents reduces with increasing pressure and becomes negligible after volume expansion coefficient exceeds about 2.5.