School of Pharmacy, University of Reading, Whiteknights, Reading, RG6 6AD Berkshire, United Kingdom.
Pharmaceutical Sciences Laboratory, Faculty of Science and Engineering, Åbo Akademi University, 20520 Turku, Finland; Department of Chemistry and Chemical Technology, Al-Farabi Kazakh National University, 050040 Almaty, Kazakhstan.
J Colloid Interface Sci. 2021 May 15;590:249-259. doi: 10.1016/j.jcis.2021.01.044. Epub 2021 Jan 27.
Temperature-responsive nanomaterials have gained increasing interest over the past decade due their ability to undergo conformational changes in situ, in response to a change in temperature. One class of temperature-responsive polymers are those with lower critical solution temperature, which phase separate in aqueous solution above a critical temperature. When these temperature-responsive polymers are grafted to a solid nanoparticle, a change in their surface properties occurs above this critical temperature, from hydrophilic to more hydrophobic, giving them a propensity to aggregate. This study explores the temperature induced aggregation of silica nanoparticles functionalised with two isomeric temperature-responsive polymers with lower critical solution temperature (LCST) behavior, namely poly(N-isopropyl acrylamide) (PNIPAM), and poly(2-n-propyl-2-oxazoline) (PNPOZ) with similar molecular weights (5000 Da) and grafting density. These nanoparticles exhibited striking differences in the temperature of aggregation, which is consistent with LCST of each polymer. Using a combination of small-angle neutron scattering (SANS) and dynamic light scattering (DLS), we probed subtle differences in the aggregation mechanism for PNIPAM- and PNPOZ-decorated silica nanoparticles. The nanoparticles decorated with PNIPAM and PNPOZ show similar aggregation mechanism that was independent of polymer structure, whereby aggregation starts by the formation of small aggregates. A further increase in temperature leads to interaction between these aggregates and results in full-scale aggregation and subsequent phase separation.
在过去的十年中，由于温度响应纳米材料能够在原位发生构象变化，因此它们受到了越来越多的关注。一类温度响应聚合物是那些具有较低临界溶液温度的聚合物，它们在临界温度以上的水溶液中会发生相分离。当这些温度响应聚合物接枝到固体纳米颗粒上时，它们的表面性质会在高于这个临界温度的情况下发生变化，从亲水性变为更疏水性，从而使它们倾向于聚集。本研究探索了两种具有较低临界溶液温度（LCST）行为的同系物温度响应聚合物接枝的二氧化硅纳米颗粒的温度诱导聚集，即聚（N-异丙基丙烯酰胺）（PNIPAM）和聚（2-正丙基-2-恶唑啉）（PNPOZ），它们具有相似的分子量（5000 Da）和接枝密度。这些纳米颗粒在聚集温度上表现出显著的差异，这与每种聚合物的 LCST 一致。通过小角中子散射（SANS）和动态光散射（DLS）的结合，我们探测了 PNIPAM 和 PNPOZ 修饰的二氧化硅纳米颗粒的聚集机制中的细微差异。用 PNIPAM 和 PNPOZ 修饰的纳米颗粒表现出相似的聚集机制，这种机制与聚合物结构无关，即聚集首先通过小聚集体的形成开始。进一步提高温度会导致这些聚集体之间的相互作用，从而导致全面聚集和随后的相分离。
