Counterion Condensation and Electrophoresis of Soft Matter
Date Issued
2012
Date
2012
Author(s)
Hsu, Hsuan-Pei
Abstract
Counterion condensation phenomenon and electrophoretic behabior of soft matter are investigated in this study. General electrokinetic equations including the full nonlinear Poisson-Boltzmann equation are employed as the governing equations which are then solved with a pseudo-spectral method based on Chebyshev polynomials. Counterion condensation phenomenon of a highly charged polyelectrolyte, which is directly related to DNA condensation and RNA folding, has great importance and potential use in biological science, electrokinetic phenomenon, and medical science. To further understand this fascinating phenomenon, the polyelectrolyte particle is modeled as a charged porous sphere based on the experimental observation of the DNA and protein conformations in free solution, both are major polyelectrolytes of interest. The full nonlinear Poisson– Boltzmann equation is used to describe the interaction between the counterions in the electrolyte solution and the backbone macroion of the polyelectrolyte itself. The fraction of total charges condensed is analyzed in particular, with its dependence on the charged condition of the polyelectrolyte as well as the ionic strength of the solution investigated in detail. Comparison with limited experimental data available in the literature for DNA neutralization fraction is excellent in the asymptotic sense, suggesting the reliability of the analysis in this study, as well as the promising possibility of using the charged porous sphere to model a polyelectrolyte. Results presented here provide useful information in biological systems and can be utilized in practical applications such as DNA vaccines and gene delivery. (Chapter 4)
On the other hand, soft sphere, a colloidal particle with a rigid core surrounded by a concentric porous shell, is encountered very often in various colloidal and biocolloidal systems. The fraction of total charges condensed is analyzed in particular, with its dependence on the charged condition of the soft sphere, the thickness of the corona and the ionic strength of the solution investigated in detail. Comparison with experimental data available in the literature for a spherical polyelectrolyte brush (SPB), a special kind of soft particles that has inspired a huge amount of research interest in recent years due to its potential applications, is excellent, indicating the reliability of this analysis, as well as the success of using soft sphere to model an SPB. Results presented here provide crucial information in colloidal/biocolloidal systems and can be utilized in practical applications such as drug delivery, catalyst, functional biomolecules, nanoreactors and carboxylated latex particles. (Chapter 5)
Electrophoresis of a polyelectrolyte in an infinite medium of electrolyte solution is investigated in Chapter 6. The porous sphere is treated as a Brinkman medium with uniformly distributed electric charges. Key parameters of electrokinetic interest are examined for their effects on particle motion. Two major motion-deterring nonlinear effects with Poisson equation which consist of the condensation effect and the double layer polarization effect are separated from each other with an approach, for the first time in the literature, and examined in detail for their respective impact on the particle motion. Convenient charts of correction factors are provided to facilitate the usage by interested experimental researchers. Moreover, an interesting phenomenon is observed that a less charged particle may actually move faster than a highly charged one! This is clearly demonstrated as the dominance of the polarization effect there with strong evidences of corresponding contour plots. Excellent agreement with limited experimental data available in the literature is observed, indicating the reliability of this study.
Electrophoretic behavior of a single polyelectrolyte normal to an air-water interface is investigated in Chapter 7. Two major motion- deterring effects are thoroughly investigated in particular: The boundary effect due to presence of the air-water face, and the double layer polarization effect due to the convection-induced ion flux. The presence of the air–water interface is found to reduce the particle mobility in general, especially when the double layer is very thick or the particle is close to the interface. This boundary effect diminishes as the double layer gets very thin. However, an interesting phenomenon is observed that a particle closer to the interface may actually move faster than a farther one under some circumstances. The reason behind this is the deformation of the double layer surrounding the particle due to the presence of the air-water interface which further weakens the other motion-deterring polarization effect. This is clearly demonstrated with strong evidences of corresponding contour plots. Convenient charts of correction factors are provided to facilitate the usage by interested experimental researchers.
Subjects
Polyelectrolyte
soft sphere
counterion condensation
electrophoresis
boundary effect
polarization effect
SDGs
Type
thesis
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