Aldakkan Bashayer Saad, Chalmpes Nikolaos, Qi Genggeng, Hammami Mohamed Amen, Kanj Mazen Yousef, Giannelis Emmanuel P
Materials Science and Engineering, Cornell University, Ithaca, New York 14853, United States.
College of Petroleum Engineering & Geosciences, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia.
Langmuir. 2024 Mar 19;40(11):5837-5849. doi: 10.1021/acs.langmuir.3c03713. Epub 2024 Mar 8.
A method to synthesize stable, raspberry-like nanoparticles (NPs), using surface grafting of poly(glycidyl methacrylate) (PGMA) brushes on a polystyrene (PS) core with varying grafting densities, is reported. A two-step functionalization reaction of PGMA epoxide groups comprising an amination step first using ethylene diamine and then followed by a quaternization using glycidyltrimethylammonium chloride generates permanently and positively charged polyelectrolyte brushes, which result in both steric and electrostatic stabilization. The dispersion stability of the brush-bearing NPs is dramatically improved compared to that of the pristine PS core in salt solutions at ambient (25 °C) and elevated temperatures (60 °C). Additionally, the grafted polyelectrolyte chains undergo a reversible swelling in the presence of different ionic strength (IS) salts, which modulate the surface properties, including roughness, stiffness, and adhesion. An atomic force microscope under both dry and wet conditions was used to image conformational changes of the polyelectrolyte chains during the swelling and deswelling transitions as well as to probe the nanomechanical properties by analyzing the corresponding force-sample separation curves. The quaternized polyelectrolyte brushes undergo a conformational transition from a collapsed state to a swelled state in the osmotic brush (OB) regime triggered by the osmotic gradient of mobile ions to the interior of the polymer chain. At IS ∼ 1 M, the brushes contract and the globules reform (salted brush state) as evidenced by an increase in the surface roughness and a reduction in the adhesion of the brushes. Beyond IS ∼ 1 M, quartz crystal microbalance with dissipation monitoring measurements show that salt uptake continues to take place predominantly on the exterior surface of the brush since salt adsorption is not accompanied by a size increase as measured by dynamic light scattering. The study adds new insights into our understanding of the behavior of NPs bearing salt-responsive polyelectrolyte brushes with adaptive swelling thresholds that can ultimately modulate surface properties.
报道了一种合成稳定的覆盆子状纳米颗粒（NPs）的方法，该方法是通过在聚苯乙烯（PS）核上进行不同接枝密度的聚甲基丙烯酸缩水甘油酯（PGMA）刷的表面接枝。PGMA环氧基团的两步官能化反应包括首先使用乙二胺进行胺化步骤，然后使用缩水甘油基三甲基氯化铵进行季铵化，生成永久带正电的聚电解质刷，从而实现空间位阻和静电稳定。与原始PS核相比，在环境温度（25°C）和高温（60°C）的盐溶液中，带有刷的NPs的分散稳定性得到了显著提高。此外，接枝的聚电解质链在不同离子强度（IS）的盐存在下会发生可逆溶胀，从而调节表面性质，包括粗糙度、硬度和粘附力。使用原子力显微镜在干燥和潮湿条件下对聚电解质链在溶胀和去溶胀转变过程中的构象变化进行成像，并通过分析相应的力-样品分离曲线来探测纳米力学性能。季铵化的聚电解质刷在由移动离子向聚合物链内部的渗透梯度触发的渗透刷（OB）区域中经历从塌缩状态到溶胀状态的构象转变。在IS约为1 M时，刷子收缩且小球重新形成（盐刷状态），这通过表面粗糙度的增加和刷子粘附力的降低得以证明。超过IS约为1 M时，带有耗散监测的石英晶体微天平测量表明，盐的吸收主要继续发生在刷的外表面，因为通过动态光散射测量，盐吸附并未伴随着尺寸增加。该研究为我们理解带有具有自适应溶胀阈值的盐响应性聚电解质刷的NPs的行为增加了新的见解，这些阈值最终可以调节表面性质。
