Determination of Solvation Layer Thickness by a Magnetophotonic Approach
ABSTRACT Derjaguin-Landau-Verwey-Overbeek (DLVO) theory fails in explaining the superior stability of colloid particles in aqueous suspensions under conditions of high ionic strengths where electrostatic forces are effectively screened. Accumulating evidence shows that the formation of a thin rigid layer of solvent molecules in the vicinity of a colloidal particle surface provides an additional repulsive interaction when the interparticle distance is reduced to several nanometers. The effective determination of the thickness of the solvation layer however remains a challenge. Here, we demonstrate a simple yet powerful magnetophotonic technique that can be used to study the thickness of the solvation layers formed on the colloidal silica surface in various polar solvents. A relationship between the hydrogen-bonding ability of the solvents and the thickness of solvation layer on colloidal silica surfaces has been identified; this observation is found to be consistent with the previously proposed hydrogen-bonding origin of the solvation force.
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ABSTRACT: The effects of two amphiphiles, DBSA and LA, on the associating state and viscosity of three heavy oils with different resin/asphaltene (R/A) mass ratios were investigated through DSC analysis, rheological test and electrical conductivity measurement. The wax appearance temperatures of the three heavy oils are lower than 40 °C. The viscosity of heavy oils at temperature range 50~70 °C increases with increasing DBSA concentration but decreases with increasing LA concentration. Addition of DBSA increases the electrical conductivity of heavy oils, which implies that the DBSA acts as asphaltene dispersants; the electrical conductivity of heavy oils decreases after LA addition, which implies that the LA acts as asphaltene flocculants. The addition of DBSA decreases the size of asphaltene particles and generates new solvation layers, both of which favor the increase of heavy oil viscosity; the addition of LA increases the size of asphaltene particles and releases some liquid oils bounded by asphaltene particles, both of which favor the decrease of heavy oil viscosity. With the increase of R/A mass ratio, the stability of heavy oils increases while the viscosity enhancing/reducing efficiency of DBSA/LA decreases.Journal of Petroleum Science and Engineering 12/2014; DOI:10.1016/j.petrol.2014.10.004 · 1.10 Impact Factor
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ABSTRACT: We analyze the existence of non-uniformity at the boundary of turbid media, and develop a gradient complex refractive index multilayered model in terms of this fact. Our model reveals the physics mechanism of the discrepancies between experimental data above the critical angle and the fitting curve with Fresnel’s Formula. Also, from the perspective of the energy flow, reflectance R is obtained by the simplified models. We get complex refractive indexes and reflectance curves by fitting experimental data of 20% and 30% Intralipid solutions and rutile Ti O 2 powder suspension with two different methods. Compared with Fresnel’s Formula, our model can fit experimental data better.Optics Express 03/2015; 23(6). DOI:10.1364/OE.23.007320 · 3.53 Impact Factor
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ABSTRACT: Exosomes are stable nanovesicles secreted by cells into the circulation. Their reported sizes differ substantially, which likely reflects the difference in the isolation techniques used, the cells that secreted them, and the methods used in their characterization. We analyzed the influence of the last factor on the measured sizes and shapes of hydrated and desiccated exosomes isolated from the serum of a pancreatic cancer patient and a healthy control. We found that hydrated exosomes are close-to-spherical nanoparticles with a hydro-dynamic radius that is substantially larger than the geometric size. For desiccated exosomes, we found that the desiccated shape and sizing are influenced by the manner in which drying occurred. Isotropic desiccation in aerosol preserves the near-spherical shape of the exosomes, whereas drying on a surface likely distorts their shapes and influences the sizing results obtained by techniques that require surface fixation prior to analysis.Analytical and Bioanalytical Chemistry 03/2015; 407(12):3285-3301. DOI:10.1007/s00216-015-8535-3 · 3.58 Impact Factor