Charge dispersity of size disperse colloidal spheres

合成胶体不可避免地在大小和形状上表现出一些铺展。此外，它们的电荷是不一致的。理论和实验表明，这两种分散性对胶体悬浮液的结构、相行为和动力学以及对材料性能(如保质期和流变学)都有多方面和显著的影响。大小和形状实际上是通过合成来固定的。相比之下，充电是一个复杂的过程，取决于颗粒化学、盐浓度、pH、颗粒浓度和颗粒大小。这样调整的裸表面电荷以一种已知的方式与不同的实验可获得的有效电荷有关。这些反过来决定了系统的属性和行为。然而，尺寸与有效电荷、尺寸分散度与电荷分散度之间的关系以及它们对实验条件的依赖关系仍未得到很好的理解。虽然在不同的理论方法中对这些进行了讨论，但主要的障碍似乎是缺乏可靠的途径和有效电荷分散性的表征。如果可用，它可以与容易获得的大小分散性进行比较。这将更详细地揭示这两个分散体之间的联系。它还将有助于区分这两种分散体对悬浮行为的影响和相对重要性。在此，我们建议在实验边界条件的系统变化下，研究具有良好尺寸分散性的粒子的电荷分散性。我们将把已建立的光散射技术(超外差动态光散射，SH-DLS)与在电导控制下精确调整实验参数相结合。SH-DLS记录了均匀直流电场作用下胶体颗粒的速度分布的多普勒谱。这些谱不仅表现为扩散线展宽，而且还表现为场相关展宽。后者与迁移率的分散性直接相关，从而与电荷分散性直接相关。其他额外的加宽机制将被避免(例如，通过使用抑制溶剂流动的特殊电池设计来进行泰勒分散)，或者在评估中独立表征和考虑(如中等相互作用强度下的时间速度波动)。我们将研究不同平均尺寸、不同尺寸分布宽度和不同表面化学的球体。在实验边界条件的系统变化下的补充实验将提供尺寸和电荷分散性之间的耦合。然后，可以将获得的数据集与理论模型进行比较。这将加深我们对电荷分散性及其与尺寸分散性的关系的理解。从长远来看，我们的研究可能有助于通过尺寸和电荷分散性来有针对性地控制体系的性质。

Synthetic colloids inevitably show some spread in size and shape. Further their charge is non-uniform. Theory and experiment reveal a manifold and pronounced influence of both dispersities on the structure, phase behaviour and dynamics of colloidal suspensions aswell as on material properties like shelf life and rheology. Size and shape are practically fixed by synthesis. By contrast, charging is a complex process depending on the particle chemistry, on salt concentration, pH, particle concentration, and particle size. The thus adjusted bare surface charge is related in a known way to different experimentally accessible effective charges,. These in turn determine the system properties and behaviour. However, the relations between size and effective charge, between size dispersity and charge dispersity as well as their dependence on the experimental conditions are still poorely understood. While these are discussed in various theoretical approaches, the main obstacle appears to be a lack of a reliable access and characterization of effective charge dispersity. If available, it could be compared to the easily accessible size dispersity. This would reveal the connection between the two dispersites in much detail. It further will assist the discrimination of the influences and the relative importance of the two dispersities on suspension behaviour. Here we suggest to study on the charge dispersity of particles with well-characterized size dispersity under systematic variation of experimental boundary conditions. We willcombine an established light scattering technique (super-heterodyne dynamic light scattering, SH-DLS) with the precise adjustment of experimental parameters under conductometric control. SH-DLS records Doppler spectra corresponding to the velocity distribution of colloidal particles subjected to a homogeneous DC electric field. Thespectra show a diffusive line broadening but also a field-dependent broadening. The latter is directly related to the dispersity of mobilities and hence the charge dispersity. Other additional broadening mechanisms will be either avoided (e.g. taylor dispersion by working with a special cell design suppressing solvent flows) or independently characterized and accounted for in evaluation (like temporal velocity fluctuations at moderate interaction strength). We will study spheres of diferent average size, different size distribution widths, and different surface chemistry. Complementary experiments under systematical variation of experimental boundary conditions will provide access to the coupling between size and charge dispersity. The obtained datasets can then be compared to theoretical models. This shall deepen our understanding of chargedispersity and its relation to size dispersity. In the long run, our studymay assist the targeted control of system properties via size andcharge dispersity.