軟球層密度分布對密集軟球膠體粒子溶液振盪電泳行為之影響

Dynamic Electrophoresis of Concentrated Soft Particles with Soft Layer Density Distribution

林佳翰(Chia-Han Lin)

指導教授 ： 李克強

國立臺灣大學/工學院/化學工程學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.10520

摘要

本研究中將探討軟球層分布對密集軟球懸浮液振盪電泳動度的影響，軟球粒子內為一不可穿透的硬球核，外面包覆一層離子可穿透的高分子層，常用來模擬生物分子或經表面處理後的高分子粒子。
過去研究多半為了方便計算與討論，將軟球層內高分子層體積密度分布假設為均勻，但隨著對於真實系統的了解以及運算處理的進步，高分子軟球層的結構複雜，為了能夠更加貼近真實系統，應該考慮軟球層內隨位置不同的不均勻分布，根據不同的系統分布的情形將會有所不同。由Duval, Ohshima和Ballauff等學者過去的研究指出，因為立體結構與人工製造等原因，1/r2的體積密度分布函數最適合用來描述SPB系統 (以人工方式於膠體粒子表面密集種植高分子鏈，形成SPB粒子)。因此本研究中我們使用1 /r2的體積密度分布函數，即體積電荷密度與摩擦係數將同時隨著離粒子表面越遠而呈現1/r2的遞減來描述SPB系統之軟球層的分布。
在此研究中，我們同時將電雙層極化效應以及電雙層動態平衡的因素納入考慮，並採用Brinkman模型來描述高分子層，Kuwabara單位晶格模型來模擬密集溶液的情形，為了適當的描述系統，我們使用球座標進行多區聯解，在弱外加交流電場假設下，將相互耦合的電動力學方程組線性化，以Chebyshev擬譜方法求解線性化後的方程組解。
我們針對軟球層均勻分布與不均勻分布的泳動度結果作比較，發現軟球層不均勻分布將同時造成軟球總帶電量與所受流體摩擦力下降，因此同時影響粒子所受的電驅動力和摩擦阻力的結果，也造成極化效應的程度有所不同，電力與流力的交互作用下，決定了均勻與非均勻軟球層振盪電泳動度的差別。最後我們比較相關文獻的SPB實驗，能有效且合理的預測實驗的結果和趨勢，也驗證了我們理論的正確性以及考慮軟球層分布的重要性。

關鍵字

軟球粒子 ； 振盪電泳 ； 電雙層 ； 極化效應 ； 電雙層動態平衡 ； 軟球層密度分布 ； 人造球型聚電解質

並列摘要

In this study, the influences of soft layer segment distribution on the dynamic electrophoresis of concentrated suspensions of soft particles, that is, particles consisting of a rigid core and an ion-penetrable layer of polyelectrolyte are investigated. The electrokinetic theory of soft particles has been employed to analyze experimental data of various polyelectrolyte-coated particles such as biological cells.
In the previous research, the polyelectrolyte layer (soft layer) of soft particle is usually modeled as a homogeneous distribution, that is, the soft layer is assumed to have a uniform segment distribution. However, the polyelectrolyte layer is originated form polymer adsorption, in which the effect of segment density distribution becomes important. In this study, we modify the soft layer segment density distribution as an 1/r2 distribution provided by previous workers: Duval, Ohshima and Ballauff. Both the distribution of volume charge density and the friction coefficient of the soft layer follow the 1/r2 decay. This model is found to match the spherical polyelectrolyte brushes (SPBs) systems very well according to experimental results. The SPBs systems consist of long polyelectrolyte chains that are densely grafted to the surface of core particle and are widely used in nanotechnology, functional biomolecules and drug delivery.
In this study, the effect of double-layer polarization, double-layer relaxation and volume fraction are taken into account. Brinkman model are adopted to simulate the polyelectrolyte layer, and Kuwabara unit cell model is used for concentrated suspensions. We treat the problem by separating the physical region into two domains using spherical coordinates. The coupled electrokinetic equations are linearized assuming the applied alternating electric field is weak. General electrokinetic equations are employed and solved with pseudo-spectral method based on Chebyshev polynomials and Newton-Raphson schemes.
We focus on the electrokinetic behavior of concentrated suspensions of soft particles under the action of alternating electric fields. Comparison between uniform and non-uniform soft layer distribution was made in our study. We found, among other things, non-uniform soft layer distribution quantitatively reduced the total charge (electrical driving force) and drag force (hydrodynamic retarding force) of the particles simultaneously, which are important in determine the dynamic mobility. In the final part, we compare our results to experimental data. Our results fit the data reasonably, indicating the reliability of this analysis, as well as the significantly importance of considering soft layer distribution.

並列關鍵字

soft particle ； dynamic electrophoresis ； electric double layer ； double layer polarization ； double layer dynamics ； soft layer segment density distribution ； spherical polyelectrolyte brushes (SPB)

參考文獻

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