National Institute of Standards and Technology, Materials Science and Engineering Division, Gaithersburg, MD 20899, USA.
Soft Matter. 2017 Oct 4;13(38):6743-6755. doi: 10.1039/c7sm01035d.
Mixtures of fumed fractal metal oxide nanoparticles (np's) dispersed in water, at a solution pH where one species is positively charged and the other is negatively charged, form yield stress gels at volume fractions as low as 1.5%, due to electrostatic heteroaggregation into networks as confirmed by small-angle neutron scattering. These gels exhibit a measurable yield stress and an apparent viscosity that follows a power law relationship with shear rate. Rotational and oscillatory shear rheology is presented for binary mixtures of fumed silica, fumed alumina, and fumed titania in aqueous dispersions. Gels were characterized at various particle concentrations, solution pHs, mixture ratios, and salt concentrations. The strength of the gel network, as evaluated by the storage modulus and yield stress, is maximized when the mixture contains a mixture of particles with an approximately equal, but opposite, number of charged groups.
分散在水中的烟雾状分形金属氧化物纳米粒子（np）混合物，在溶液 pH 值下，一种物质带正电荷，另一种带负电荷，由于静电异质聚集形成网络，在体积分数低至 1.5%时形成屈服应力凝胶，这一点已通过小角中子散射得到证实。这些凝胶表现出可测量的屈服应力和表观粘度，与剪切速率呈幂律关系。旋转和振荡剪切流变学呈现了烟雾状二氧化硅、氧化铝和二氧化钛在水基分散体中的二元混合物。在不同的颗粒浓度、溶液 pH 值、混合比和盐浓度下对凝胶进行了表征。通过储能模量和屈服应力评估的凝胶网络强度在混合物中包含带等量但相反电荷的颗粒混合物时达到最大值。
