Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB, Canada; National Institute for Nanotechnology, National Research Council of Canada, Edmonton, AB, Canada.
Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB, Canada.
J Colloid Interface Sci. 2014 Sep 15;430:157-65. doi: 10.1016/j.jcis.2014.05.011. Epub 2014 May 19.
Thermo-responsive poly(N-isopropylacrylamide) (poly(NIPAAm)) brushes were grafted from the surface of cellulose nanocrystals (CNC) via living radical polymerization (LRP) using different initiator and monomer concentrations. The dry film thickness of the poly(NIPAAm) layer around CNC was calculated based on Scanning Electron Microscopy (SEM) and dynamic light scattering (DLS) measurements. The wet film thicknesses of grafted poly(NIPAAm) brushes in water were calculated to be 15 and 9nm for NIPAAm-CNC-1 and NIPAAm-CNC-2, respectively. Grafted chain densities and wet film thicknesses at below and above the critical temperature (T=34°C) of polyNIPAAm were calculated by applying mean-field analytical theory. The non-ionic poly(NIPAAm) brushes screened the surface charges of CNC particles, leading to a significant decrease in the absolute zeta potential values for the poly(NIPAAm) grafted CNCs compared to the unmodified and initiator modified CNC samples. Nevertheless, the colloidal stability of poly(NIPAAm) grafted CNC particles were still maintained by steric stabilization below the critical temperature On the other side, hydrophobic attractions among poly(NIPAAm) grafted CNC rods above 34°C lead to coagulation and phase separation. While both poly(NIPAAm) grafted CNC samples showed thermo-responsive behavior, the reversibility of this temperature triggered property was dependent on grafting density.
通过使用不同的引发剂和单体浓度，通过活性自由基聚合（LRP）从纤维素纳米晶体（CNC）表面接枝温敏性聚（N-异丙基丙烯酰胺）（poly（NIPAAm））刷。基于扫描电子显微镜（SEM）和动态光散射（DLS）测量，计算了 CNC 周围聚（NIPAAm）层的干膜厚度。接枝的聚（NIPAAm）刷在水中的湿膜厚度分别为 15nm 和 9nm，对于 NIPAAm-CNC-1 和 NIPAAm-CNC-2。通过应用平均场分析理论，计算了低于和高于聚 NIPAAm 的临界温度（T=34°C）时接枝链密度和湿膜厚度。非离子型聚（NIPAAm）刷屏蔽了 CNC 颗粒的表面电荷，导致接枝 CNC 的聚（NIPAAm）的绝对zeta 电位值与未改性和引发剂改性的 CNC 样品相比显着降低。然而，在临界温度以下，聚（NIPAAm）接枝 CNC 颗粒的胶体稳定性仍通过空间稳定来维持。另一方面，在 34°C 以上，聚（NIPAAm）接枝 CNC 棒之间的疏水力导致凝聚和相分离。虽然两种聚（NIPAAm）接枝 CNC 样品都表现出温度响应行为，但这种温度触发特性的可逆性取决于接枝密度。
