Rotureau Elise, Thomas Fabien, Duval Jérôme F L
Laboratory Environment and Mineral Processing, Nancy-University, CNRS, BP 40-F-54501 Vandoeuvre-lès-Nancy Cedex, France.
Langmuir. 2007 Jul 31;23(16):8460-73. doi: 10.1021/la700427p. Epub 2007 Jul 10.
The electrostatic, hydrodynamic, and swelling properties of a well-defined, functionalized carboxymethyldextran (CMD) polysaccharide are investigated in aqueous NaNO3 solution over a broad ionic strength range. The impact of the polycarboxylate charge and molar mass of the CMD macromolecules on their electrohydrodynamic features is thoroughly examined by combined protolytic titration, dynamic light scattering, and electrokinetic analyses. Electrophoretic mobility data obtained for sufficiently high electrolyte concentrations reveal a typical soft particle behavior. Upon decrease of the ionic strength, mobilities strongly increase in magnitude while significant electrostatic swelling takes place, as reflected in a decrease in the diffusion coefficients. CMD entities undergo conformational transitions from compact random coil at large ionic strengths to swollen coil and possibly a wormlike structure at lower NaNO3 concentrations. The magnitude of the variations in size and mobility with electrolyte concentration strongly depends on the overall charge of the CMD entity as well as on its molar mass. These factors control the stiffness of the constituent polymer chains and thus the degree of macromolecular permeability ("softness"). Using the soft-diffuse interface formalism previously developed for the electrohydrodynamics of charged permeable macromolecules, a quantitative analysis of the electrophoretic mobility data is presented. The measured values of the diffusion coefficient and space charge density Gamma degrees, as evaluated independently from the modeling of potentiometric titration curves, are taken into account in a self-consistent manner. It is found that large CMD entities of low charge densities are the most permeable to flow penetration with a limited heterogeneous electrostatic stiffening of the chains, whereas small CMD entities of larger Gamma degrees significantly expand upon lowering the ionic strength, giving rise to a strong anisotropy for the spatial distribution of polymer chain density.
在较宽的离子强度范围内，研究了一种定义明确的功能化羧甲基葡聚糖（CMD）多糖在硝酸钠水溶液中的静电、流体动力学和溶胀特性。通过酸碱滴定、动态光散射和电动分析相结合的方法，全面研究了CMD大分子的聚羧酸盐电荷和摩尔质量对其电流体动力学特征的影响。在足够高的电解质浓度下获得的电泳迁移率数据显示出典型的软颗粒行为。随着离子强度的降低，迁移率的大小显著增加，同时发生明显的静电溶胀，这反映在扩散系数的降低上。CMD实体经历从高离子强度下的紧密无规线团到较低硝酸钠浓度下的溶胀线团以及可能的蠕虫状结构的构象转变。尺寸和迁移率随电解质浓度变化的幅度强烈取决于CMD实体的总电荷及其摩尔质量。这些因素控制着组成聚合物链的刚度，从而控制大分子的渗透程度（“柔软度”）。使用先前为带电可渗透大分子的电流体动力学开发的软扩散界面形式，对电泳迁移率数据进行了定量分析。从电位滴定曲线建模中独立评估得到的扩散系数和空间电荷密度Γ°的测量值以自洽的方式被考虑在内。结果发现，低电荷密度的大CMD实体对流动渗透的渗透性最强，链的非均匀静电硬化有限，而较大Γ°的小CMD实体在降低离子强度时会显著膨胀，导致聚合物链密度的空间分布具有很强的各向异性。
