Bayat Haider, Raoufi Mohammad, Zamrik Imad, Schönherr Holger
Physical Chemistry I & Research Center of Micro and Nanochemistry and Engineering (Cμ), Department of Chemistry and Biology, School of Science and Technology, University of Siegen, Adolf-Reichwein-Str. 2, 57076 Siegen, Germany.
Langmuir. 2020 Mar 17;36(10):2663-2672. doi: 10.1021/acs.langmuir.9b03700. Epub 2020 Mar 2.
We report on the synthesis and characterization of poly(diethylene glycol methylether methacrylate) (PDEGMA) brushes by surface-initiated atom transfer radical polymerization inside ordered cylindrical nanopores of anodic aluminum oxide with different pore radii between 20 and 185 nm. In particular, the dependence of polymerization kinetics and the degree of pore filling on the interfacial curvature were analyzed. On the basis of field emission scanning electron microscopy data and thermal gravimetric analysis (TGA), it was concluded that the polymerization rate was faster at the pore orifice compared to the pore interior and also as compared to the analogous reaction carried out on flat aluminum oxide substrates. The apparent steady-state polymerization rate near the orifice increased with decreasing pore size. Likewise, the overall apparent polymerization rate estimated from TGA data indicated stronger confinement for pores with increased curvature as well as increased mass transport limitations due to the blockage of the pore orifice. Only for pores with a diameter to length ratio of ∼1, PDEGMA brushes were concluded to grow uniformly with constant thickness. However, because of mass transport limitations in longer pores, incomplete pore filling was observed, which leads presumably to a PDEGMA gradient brush. This study contributes to a better understanding of polymer brush-functionalized nanopores and the impact of confinement, in which the control of polymer brush thickness together with grafting density along the nanopores is key for applications of PDEGMA brushes confined inside nanopores.
我们报道了通过表面引发的原子转移自由基聚合，在孔径为20至185nm的有序圆柱形阳极氧化铝纳米孔内合成和表征聚（二甘醇甲基醚甲基丙烯酸酯）（PDEGMA）刷。特别地，分析了聚合动力学和孔填充程度对界面曲率的依赖性。基于场发射扫描电子显微镜数据和热重分析（TGA），得出结论：与孔内部相比，以及与在平坦氧化铝基板上进行的类似反应相比，孔口处的聚合速率更快。孔口附近的表观稳态聚合速率随孔径减小而增加。同样，从TGA数据估计的总体表观聚合速率表明，随着曲率增加，孔的限制更强，并且由于孔口堵塞，传质限制增加。仅对于直径与长度比约为1的孔，得出结论PDEGMA刷以恒定厚度均匀生长。然而，由于较长孔中的传质限制，观察到孔填充不完全，这可能导致PDEGMA梯度刷。这项研究有助于更好地理解聚合物刷功能化纳米孔以及限制的影响，其中控制聚合物刷厚度以及沿纳米孔的接枝密度是限制在纳米孔内的PDEGMA刷应用的关键。
