Luckham PF, Ukeje MA
Department of Chemical Engineering, Imperial College of Science, Technology and Medicine, Prince Consort Road, London, SW7 2BY, United Kingdom
J Colloid Interface Sci. 1999 Dec 15;220(2):347-356. doi: 10.1006/jcis.1999.6515.
The rheological properties of aqueous polystyrene latex dispersions from three synthetic batches, with nearly the same z-average particle sizes, 400 nm, but varying degrees of polydispersity, 0.085, 0.301, and 0.485, respectively, were systematically investigated using steady-state shear and oscillatory shear measurements. The particles were sized with photon correlation spectroscopy and transmission electron microscopy and were stabilized sterically with PEO-PPO-PEO triblock copolymer (Synperonic F127). Results from steady-state shear measurements show that the viscosities of the systems exhibit shear-thinning behavior at high solid fractions. However, the degree of shear thinning depends on the breadth of particle size distribution, with the narrowest distribution suspension exhibiting the highest degree of shear thinning. The Herschel-Bulkley relationship best describes the flow curves. The relative viscosities as a function of volume fraction data were compared, and it was found that the broadest distribution suspension had the lowest viscosity for a given volume fraction. In addition, the data were fitted to the Krieger-Dougherty equation for hard spheres. A reasonable agreement of theory with experiment is observed, particularly and surprisingly for the very broad distribution. However, when the contribution to the volume due to the adsorbed polymer layer is considered, the agreement between experiment and theory becomes closer for all the suspensions, although the agreement for the broad distribution suspension is now worse. Fitting the Dougherty-Krieger theory to the experimental data based on our experimental maximum packing fractions gives very good agreement for all the systems studied. From oscillatory shear measurements, the moduli were obtained as a function of frequency at various latex volume fractions. The results show general change of the dispersions from viscous (G" > G') at low volume fractions (0.25-0.30) to moderately elastic (G' > G") at moderately high volume fractions (0.41-0.45). The change at this concentration level is likely due to some compression and interpenetration of the stabilizing polymer chain at the periphery, indicating the dominance of the interparticle forces. Overall, the very broad distribution was found to have the lowest elastic modulus for a given volume fraction. Copyright 1999 Academic Press.
对来自三个合成批次的聚苯乙烯胶乳水分散体的流变特性进行了系统研究，这三个批次的胶乳具有几乎相同的z平均粒径（400纳米），但多分散程度不同，分别为0.085、0.301和0.485，采用稳态剪切和振荡剪切测量方法。通过光子相关光谱法和透射电子显微镜对颗粒进行了尺寸测定，并用聚环氧乙烷-聚环氧丙烷-聚环氧乙烷三嵌段共聚物（Synperonic F127）对颗粒进行了空间稳定化处理。稳态剪切测量结果表明，在高固含量下，体系的粘度表现出剪切变稀行为。然而，剪切变稀的程度取决于粒径分布的宽度，粒径分布最窄的悬浮液表现出最高程度的剪切变稀。赫谢尔-布尔克利关系最能描述流动曲线。比较了相对粘度与体积分数数据的函数关系，发现对于给定的体积分数，粒径分布最宽的悬浮液粘度最低。此外，将数据拟合到硬球的克里格-多尔蒂方程。观察到理论与实验有合理的一致性，特别是对于非常宽的分布，这令人惊讶。然而，当考虑到吸附聚合物层对体积的贡献时，所有悬浮液的实验与理论之间的一致性变得更紧密，尽管宽分布悬浮液的一致性现在变差了。根据我们实验得到的最大填充分数，将多尔蒂-克里格理论拟合到实验数据上，对于所有研究的体系都得到了很好的一致性。通过振荡剪切测量，在不同胶乳体积分数下获得了模量随频率的变化关系。结果表明，在低体积分数（0.25 - 0.30）时，分散体总体上从粘性状态（G" > G'）转变为中等弹性状态（G' > G"），在中等高体积分数（0.41 - 0.45）时。在这个浓度水平的变化可能是由于外围稳定聚合物链的一些压缩和相互渗透，表明颗粒间力占主导。总体而言，对于给定的体积分数，发现非常宽的分布具有最低的弹性模量。版权所有1999年学术出版社。
