Center for Molecular and Engineering Thermodynamics & Center for Neutron Science, Department of Chemical and Biomolecular Engineering, University of Delaware , Newark, Delaware 19716, United States.
Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
Langmuir. 2016 Aug 23;32(33):8424-35. doi: 10.1021/acs.langmuir.6b02107. Epub 2016 Aug 5.
Dynamic arrest transitions of colloidal suspensions containing nonspherical particles are of interest for the design and processing of various particle technologies. To better understand the effects of particle shape anisotropy and attraction strength on gel and glass formation, we present a colloidal model system of octadecyl-coated silica rods, termed as adhesive hard rods (AHR), which enables control of rod aspect ratio and temperature-dependent interactions. The aspect ratios of silica rods were controlled by varying the initial TEOS concentration following the work of Kuijk et al. (J. Am. Chem. Soc., 2011, 133, 2346-2349) and temperature-dependent attractions were introduced by coating the calcined silica rods with an octadecyl-brush and suspending in tetradecane. The rod length and aspect ratio were found to increase with TEOS concentration as expected, while other properties such as the rod diameter, coating coverage, density, and surface roughness were nearly independent of the aspect ratio. Ultrasmall angle X-ray scattering measurements revealed temperature-dependent attractions between octadecyl-coated silica rods in tetradecane, as characterized by a low-q upturn in the scattered intensity upon thermal quenching. Lastly, the rheology of a concentrated AHR suspension in tetradecane demonstrated thermoreversible gelation behavior, displaying a nearly 5 orders of magnitude change in the dynamic moduli as the temperature was cycled between 15 and 40 °C. The adhesive hard rod model system serves as a tunable platform to explore the combined influence of particle shape anisotropy and attraction strength on the dynamic arrest transitions in colloidal suspensions with thermoreversible, short-range attractions.
含有非球形颗粒的胶体悬浮液的动态捕集转变对于各种颗粒技术的设计和加工具有重要意义。为了更好地理解颗粒形状各向异性和吸引力强度对凝胶和玻璃形成的影响，我们提出了一种胶体模型体系，即十八烷基包覆的二氧化硅棒，称为粘附硬棒（AHR），它可以控制棒的纵横比和温度相关的相互作用。根据 Kuijk 等人的工作（J. Am. Chem. Soc.，2011，133，2346-2349），通过改变初始 TEOS 浓度来控制二氧化硅棒的纵横比，并用十八烷基刷涂覆煅烧后的二氧化硅棒并悬浮在十四烷中来引入温度相关的吸引力。棒的长度和纵横比随着 TEOS 浓度的增加而增加，这是预期的，而其他性质，如棒直径、涂层覆盖率、密度和表面粗糙度几乎与纵横比无关。超小角 X 射线散射测量表明，在十四烷中，十八烷基包覆的二氧化硅棒之间存在温度相关的吸引力，这表现为在热猝灭时散射强度在低 q 处出现上升。最后，在十四烷中 AHR 悬浮液的流变学研究表明了热可逆凝胶化行为，当温度在 15 和 40°C 之间循环时，动态模量发生了近 5 个数量级的变化。粘附硬棒模型体系是一个可调谐的平台，可以探索颗粒形状各向异性和吸引力强度对具有热可逆、短程吸引力的胶体悬浮液中动态捕集转变的综合影响。
