Bhairamadgi Nagendra S, Pujari Sidharam P, van Rijn Cees J M, Zuilhof Han
Laboratory of Organic Chemistry, Wageningen University , Dreijenplein 8, 6703HB, Wageningen, The Netherlands.
Langmuir. 2014 Oct 28;30(42):12532-40. doi: 10.1021/la501802b. Epub 2014 Oct 14.
The effects of fluorination on the adhesion and friction properties of covalently bound poly(fluoroalkyl methacrylate) polymer brushes (thickness ∼80 nm) were systematically investigated. Si(111) surfaces were functionalized with a covalently bound initiator via a thiol-yne click reaction to have a high surface coverage for initiator immobilization. Surface-initiated atom-transfer radical polymerization (SI-ATRP) was employed for the synthesis of four different fluoropolymer brushes (SPFx, where x = 0, 3, 7, or 17 F atoms per monomer), based on fluoroalkyl methacrylates. All polymer brushes were characterized with static contact angle measurements, X-ray photoelectron spectroscopy (XPS), and infrared absorption reflection spectroscopy (IRRAS). The polymer brushes exhibited an excellent hydrophobicity, with static water contact angles of up to 121° depending on the number of fluorine atoms per side chain in fluoroalkyl methacrylate. The degree of swelling was precisely studied by using ellipsometry in different solvents such as acetone, hexadecane, hexafluoroisopropanol, nonafluorobutyl methyl ether, and Fluorinert FC-40. The polymer brushes have shown nanoscale swelling behavior in all solvents except hexadecane. The grafting density decreased upon increasing fluorine content in polymer brushes from 0.65 chains/nm(2) (SPF0) to 0.10 chains/nm(2) (SPF17) as observed in Fluorinert FC-40 as a good solvent. Adhesion and friction force measurements were conducted with silica colloidal probe atomic force microscopy (CP-AFM) under ambient, dry (argon), and lubricating fluid conditions. SPF17 showed the lowest coefficient of friction 0.005 under ambient condition (RH = 44 ± 2%) and a further decrease with 50% under fluidic conditions. These polymer brushes also showed adhesion forces as low as 6.9 nN under ambient conditions, which further went down to 0.003 nN under fluidic conditions (Fluorinert FC-40 and hexadecane) at 10 nN force.
系统研究了氟化对共价键合的聚（甲基丙烯酸氟烷基酯）聚合物刷（厚度约80 nm）的粘附和摩擦性能的影响。通过硫醇-炔点击反应，用共价键合的引发剂对Si(111)表面进行功能化，以使引发剂固定化具有高表面覆盖率。采用表面引发原子转移自由基聚合（SI-ATRP）合成了四种不同的含氟聚合物刷（SPFx，其中每个单体含x = 0、3、7或17个氟原子），其基于甲基丙烯酸氟烷基酯。所有聚合物刷均通过静态接触角测量、X射线光电子能谱（XPS）和红外吸收反射光谱（IRRAS）进行表征。聚合物刷表现出优异的疏水性，根据甲基丙烯酸氟烷基酯中每个侧链的氟原子数，静态水接触角高达121°。通过椭偏仪在丙酮、十六烷、六氟异丙醇、九氟丁基甲基醚和氟化物FC-40等不同溶剂中精确研究了溶胀程度。除十六烷外，聚合物刷在所有溶剂中均表现出纳米级溶胀行为。在作为良溶剂的氟化物FC-40中观察到，随着聚合物刷中氟含量从0.65链/nm²（SPF0）增加到0.10链/nm²（SPF17），接枝密度降低。在环境、干燥（氩气）和润滑液条件下，使用二氧化硅胶体探针原子力显微镜（CP-AFM）进行粘附和摩擦力测量。在环境条件（相对湿度 = 44 ± 2%）下，SPF17的摩擦系数最低，为0.005，在流体条件下进一步降低50%。这些聚合物刷在环境条件下的粘附力也低至6.9 nN，在10 nN力下，在流体条件（氟化物FC-40和十六烷）下进一步降至0.003 nN。
