School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, West Lafayette, IN 47907, USA.
Printing and Content Delivery Lab, HP Labs, Hewlett-Packard Co., 1501 Page Mill Road, Palo Alto, CA 94304, USA.
J Colloid Interface Sci. 2015 Jul 15;450:434-445. doi: 10.1016/j.jcis.2015.02.051. Epub 2015 Mar 17.
As more sodium dodecylsulfate (SDS) monomers adsorb at the water/titanium dioxide (TiO2) nanoparticles interface, the particles become more stable against agglomeration and sediment more slowly. SDS micelles are not expected to adsorb on the particles and affect the stability against agglomeration or sedimentation. Since micelles are smaller than the 300 nm TiO2 nanoparticles studied, they may introduce depletion forces which may affect the dispersion stability.
Sedimentation times were measured in water and in 100 mM NaCl for SDS concentrations from 0.1 to 200 mM. Adsorption densities of SDS and zeta potentials of particles were measured. Dynamic light scattering was used to measure average diameters of particles or particle agglomerates. Modeling of sedimentation/diffusion was done to predict sedimentation times of particles. Modeling of agglomeration rates was done to help predict sedimentation rates of clusters.
At SDS concentrations close to or above the cmc, up to 60 mM in water or 115 mM in 100 mM NaCl, the nanoparticles sediment most slowly without any agglomeration. At higher micelle concentration, SDS micelle depletion forces are very strong, causing fast flocculation, without coagulation. Then sedimentation occurs much faster. The effective micelle depletant size includes about 4 Debye lengths of the charged micelles or particles.
随着更多十二烷基硫酸钠（SDS）单体在水/二氧化钛（TiO2）纳米粒子界面上吸附，粒子变得更稳定，不易聚集，沉降更缓慢。SDS 胶束不应吸附在粒子上，从而影响抗聚集或沉降稳定性。由于胶束比研究的 300nm TiO2 纳米粒子小，它们可能会引入耗尽力，从而影响分散稳定性。
在水和 100mM NaCl 中测量 SDS 浓度从 0.1 到 200mM 时的沉降时间。测量 SDS 的吸附密度和粒子的动电电位。动态光散射用于测量粒子或粒子聚集体的平均直径。进行沉降/扩散模拟以预测粒子的沉降时间。进行聚集速率模拟以帮助预测聚集体的沉降速率。
在 SDS 浓度接近或高于 cmc（在水中为 60mM，在 100mM NaCl 中为 115mM）时，纳米粒子沉降最慢，没有任何聚集。在更高的胶束浓度下，SDS 胶束耗尽力非常强，导致快速絮凝，而不会发生凝结。然后沉降速度快得多。有效胶束耗尽剂的尺寸包括大约 4 个带有电荷的胶束或粒子的德拜长度。
