Biomedical subjects

Chenhang Sun

Publications and source records attributed to Chenhang Sun.

5 recordsLinked to original sources

PubMed2004

Concentrating solutes and nanoparticles within individual aqueous microdroplets.

This paper describes a method to concentrate solutes and colloidal entities, from small ions and molecules to proteins and nanoparticles, within individual aqueous microdroplets in oil. The mechanism lies in the entrapment of the solutes within an aqueous microdroplet, while the water molecules from the droplet slowly dissolve into the organic phase. Because the rate of change in concentration scales as the fifth power of the surface-area-to-volume ratio of the droplet, this phenomenon is prominent mostly in the micrometer-length scale. This paper presents measurements that quantify the degree of solute entrapment within the microdroplet and further describes the dynamics of droplet shrinkage and the factors that influence the rate of shrinkage. In addition, this paper explains why this concentration effect does not occur for certain organic microdroplets in aqueous solutions.

Journal Article↗

PubMed2003

A review of the different techniques for solid surface acid-base characterization.

In this work, various techniques for solid surface acid-base (AB) characterization are reviewed. Different techniques employ different scales to rank acid-base properties. Based on the results from literature and the authors' own investigations for mineral oxides, these scales are compared. The comparison shows that Isoelectric Point (IEP), the most commonly used AB scale, is not a description of the absolute basicity or acidity of a surface, but a description of their relative strength. That is, a high IEP surface shows more basic functionality comparing with its acidic functionality, whereas a low IEP surface shows less basic functionality comparing with its acidic functionality. The choice of technique and scale for AB characterization depends on the specific application. For the cases in which the overall AB property is of interest, IEP (by electrokinetic titration) and H(0,max) (by indicator dye adsorption) are appropriate. For the cases in which the absolute AB property is of interest such as in the study of adhesion, it is more pertinent to use chemical shift (by XPS) and the heat of adsorption of probe gases (by calorimetry or IGC).

Acids↗

PubMed2003

The effective surface energy of heterogeneous solids measured by inverse gas chromatography at infinite dilution.

Inverse gas chromatography (IGC) at infinite dilution has been widely used to access the nonspecific surface free energy of solid materials. Since most practical surfaces are heterogeneous, the effective surface energy given by IGC at infinite dilution is somehow averaged over the whole sample surface, but the rule of averaging has thus far not been established. To address this problem, infinite dilution IGC analysis was carried out on mixtures of known heterogeneity. These materials are obtained by mixing two types of solid particles with significantly different surface energies as characterized individually with IGC, and results are obtained for binary combinations in varying proportions. It is found that when all surface components have the same accessibility by probe molecules, the effective surface energy of such a heterogeneous surface is related to the surface energy distribution by a square root linear relationship, square root sigma(eff)(LW)= summation operator (i)phi(i) square root sigma(i)(LW), where sigma(i)(LW) refers to the nonspecific (Lifshitz-van der Waals) surface energy of patches i, and phi(i) to their area fraction.

Journal Article↗

PubMed2002

Effect of moisture on the surface free energy and acid-base properties of mineral oxides.

Surface energetic properties of mineral oxides are important in many applications. Since oxide surfaces in practice have generally come in contact with water molecules, it is important to know how water coverage affects the surface properties. In this work, five oxide samples, namely MgO, Al2O3, TiO2, SnO2 and SiO2 are heat-treated to various extents, to produce different degrees of hydration, and characterized thereafter by inverse gas chromatography. Water contents of the treated samples are determined independently by Karl Fischer titration, and specific surface areas are measured by the BET method. The results show that in general as water coverage decreases, the Lifshitz-van der Waals component of the specific surface free energy (sigma(S)LW) increases, but the acid-base interaction potential (-deltaG(AB)) decreases. These attributes are more sensitive to changes in water coverage at lower coverages, where the surface is presumed to consist of patches of molecular water and unhydrated hydroxyl groups.

Chromatography, Gas↗

PubMed2002

Structural evolution of octyltriethoxysilane films on glass surfaces during annealing at elevated temperature.

Glass samples treated by octyltriethoxysilane were annealed for times ranging from 0 to 16 h, and their topography, adhesion, and stiffness properties were examined using pulsed-force mode (PFM) atomic force microscopy. While the surfaces of samples dried at room temperature were structurally featureless, those annealed at 145 degrees C showed formation of islands, increasing in size and number with heating time. PFM adhesion and stiffness maps suggested that the glass substrate remained at least partially covered by silanes even after island formation.

Glass↗