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Analysis and manipulation of solid particles
Published in Michael Pycraft Hughes, Nanoelectromechanics in Engineering and Biology, 2018
Consider the predicted dielectrophoretic response of a homogeneous latex sphere of diameter 200 nm. We can determine this by inserting values for the conductivity and permittivity of the sphere (conductivity 10–6 S m–1, relative permittivity 2.55) and the suspending medium (say, conductivity 10–3 S m–1, relative permittivity 78) into Equation 4.2 and calculating values of Re[K(ω)] over a range of frequency. If we consider the mechanism described earlier where the plot of polarizability is gradually reduced, we would expect that the crossover would start at a given value and remain at approximately that value as the conductivity increases, until a threshold is reached where the crossover frequency drops. Above that threshold conductivity, the crossover frequency drops sharply, and above the threshold, the particle exhibits only negative dielectrophoresis; this is the profile shown by the black line in Figure 4.4b. For micrometer-scale homogeneous particles, the observed dielectrophoretic response closely matches the crossover spectrum. However, as the diameter of the particle under study is reduced past 1 μm, this model becomes increasingly inaccurate. The crossover is found to rise with increasing medium conductivity, and above the threshold where the crossover drops rapidly and only negative dielectrophoresis should be seen, the particle still exhibits a crossover but at a lower frequency. The reason for this change in behavior is the increasing effect of the surface charge, and more specifically the electrical double layer.
Role and importance of surface heterogeneities in transport of particles in saturated porous media
Published in Critical Reviews in Environmental Science and Technology, 2020
Chongyang Shen, Yan Jin, Jie Zhuang, Tiantian Li, Baoshan Xing
Various methods have been developed to measure surface charge such as potentiometric titration, ion retention, and electrokinetic potential techniques (Bolan, Naidu, Syers, & Tillman, 1999; Tan, Sherman, Qin, & Ford, 2005). The potentiometric titration is used to determine net proton surface charge for particles in aqueous solutions which is proportional to the difference between the amounts of H+ and OH− adsorbed by surface functional groups. The ion retention technique, developed by Schofield (1950), measures net surface charge for soil particles through saturation of particle surface sites with a nonspecifically adsorbed cation and anion using an index indifferent-electrolyte solution. The particle surface charge can then be estimated by calculating the amount of adsorbed cation and anion on the particle surfaces. Electrokinetic techniques include electro-osmosis, streaming potential, and electrophoretic mobility, which measure the electric potential that is developed when the charged particles and the liquid move in relation to each other. The measured electric potential can be converted to surface charge using the well-known Gouy-Chapman model and Boltzmann’s theory (Verwey & Overbeek, 1948). Other examples of the methods used to determine surface charge include electroacoustic techniques, salt titration, mineral addition, electrostatic interaction chromatography, aqueous two-phase partitioning, and redox potential measurements. Details about using these methods to measure surface charge can be referred to previous studies (Bolan et al., 1999; Kosmulski, 2009; Tan et al., 2005).
Preparation and application of uniform TiO2 electrospun nanofiber based on pickering emulsion stabilized by TiO2/amphiphilic sodium alginate/polyoxyethylene
Published in Journal of Dispersion Science and Technology, 2022
Houkui Gong, Qichang Zhou, Feilin Lin, Wenqi Qin, Siqi Zhang, Shujuan Yang, Jiacheng Li, Yuhong Feng
The TEM images of emulsion and non-emulsion electrospun composite fiber films are shown in the Figure 8a, b. TEM images of the embedded TiO2 that are well-oriented along the nanofiber axis. It should be noted that the TiO2 well dispersed within the nanofiber individually. The embedded TiO2 within the nanofibers could be identified, and their alignments could also be investigated by TEM images. It is similar to the distribution of CNTs in nanofibers.[53] The nanofibers produced by the emulsion electrospinning exhibited more uniform thickness and excellent network structure compared with that prepared by the non-emulsion electrospinning. It is commonly recognized that the enhancement of the surface areas by micro/nanostructures enhances the effective surface charge density. However, the interfaces require numerous volatile organic solvents, resulting in environmental concerns and hampering widespread utilization. Therefore, it is highly anticipated that the environmentally friendly reaction media and interfaces are expected to be utilized for fabricating multifunctional fibrous nanomaterials. The black parts attached to nanofibers are TiO2, whose dispersion in the product prepared by emulsion electrospinning is more uniform than that prepared by non-emulsion electrospinning, and the nanofiber is tenuous in diameter. As can be seen from the results in the Figure 8a1, a2 TiO2 is homogeneously dispersed and does not agglomerate with emulsification by using Ugi–Alg. By contrast, nanofibers produced by the non-emulsion electrospinning are crassi and TiO2 is aggregated.
Zone-specific temperature distribution, densification trajectory and grain-growth kinetics of microwave-hybrid-sintered and conventionally sintered Al2O3 slip casts
Published in Journal of Asian Ceramic Societies, 2022
Muhammad Waqas Khalid, Young Il Kim, Muhammad Aneeq Haq, InYeong Kim, Dongju Lee, Bum Sung Kim, Bin Lee
Another means of explaining these results was suggested by Becker et al. [43]. They proposed that during electric-field-assisted sintering of ceramics, there exists a high surface area of material if there is no plastic deformation. The high surface area causes buildup and discharge of the surface charge. As a result, particle sliding occurs due to surface softening, which speeds up densification. If there is no plastic deformation, the electric field also affects the grain-growth mechanisms. The charged defects that move to the particle surface also affect the grain-boundary mobility, influencing the grain growth.