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Fabrication and Interfacial Properties of Polymer Brush Gradients by Surface-Initiated Cu(0)-Mediated Controlled Radical Polymerization
Macromolecules ( IF 5.1 ) Pub Date : 2017-03-17 00:00:00 , DOI: 10.1021/acs.macromol.7b00088 Ella S. Dehghani 1 , Yunhao Du 2 , Tao Zhang 2 , Shivaprakash N. Ramakrishna 1 , Nicholas D. Spencer 1 , Rainer Jordan 2 , Edmondo M. Benetti 1
Macromolecules ( IF 5.1 ) Pub Date : 2017-03-17 00:00:00 , DOI: 10.1021/acs.macromol.7b00088 Ella S. Dehghani 1 , Yunhao Du 2 , Tao Zhang 2 , Shivaprakash N. Ramakrishna 1 , Nicholas D. Spencer 1 , Rainer Jordan 2 , Edmondo M. Benetti 1
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Surface-initiated Cu(0)-mediated controlled radical polymerization (Si-CuCRP) can be successfully applied to fabricate poly[(oligoethylene glycol)methyl ether methacrylate] (POEGMA) brushes in one pot, presenting a grafting-density gradient across the surface. This is achieved by continuously varying the distance (d) between a copper plate, used as a source of Cu species, and the initiator-functionalized substrate. X-ray photoelectron spectroscopy (XPS) analysis of monolayers of CuI-selective ligands demonstrates that a higher concentration of activator species diffuses to the initiating substrate in areas closer to the copper plate, a progressive decrease in activator concentration being observed upon increasing the distance between the two surfaces. As confirmed by the SI-CuCRP kinetics measured at different positions along the gradient, radical-termination reactions between propagating chains limit the grafting density of POEGMA grafts where the diffusion of activators is favored (i.e., at d → 0). This effect decreases with increasing d, ultimately yielding a gradual variation of POEGMA grafting density across the substrate. We have investigated the influence of grafting-density variation across the gradient on the swelling of POEGMA brushes as well as on their nanomechanical and nanotribological properties, measured by a combination of variable angle spectroscopic ellipsometry (VASE), colloidal-probe atomic force microscopy (CP-AFM), and lateral force microscopy (LFM). The results of these tests highlight how loosely grafted POEGMA chains incorporating a substantial amount of water can be significantly deformed by a shearing AFM probe, exhibit relatively high friction, and generate friction-vs-load (Ff–L) profiles that follow a sublinear trend described by a Johnson–Kendall–Roberts (JKR) model—typical of deformable films of high surface energy. In contrast, more densely packed POEGMA brushes incorporate less solvent and display very low friction, with Ff–L data following a linear progression according to Amontons’ law.
中文翻译：
表面引发的Cu（0）介导的受控自由基聚合的聚合物刷梯度的制备和界面性质
表面引发的Cu（0）介导的受控自由基聚合（Si-CuCRP）可以成功地应用于制造一锅中的聚[（低聚乙二醇）甲基醚甲基丙烯酸甲酯]（POEGMA）刷子，从而在整个表面上呈现接枝密度梯度。这是通过连续改变用作Cu物种来源的铜板和引发剂官能化的基材之间的距离（d）来实现的。Cu I单层的X射线光电子能谱（XPS）分析选择性配体表明，较高浓度的活化剂物质在更靠近铜板的区域扩散到起始基质，随着两个表面之间距离的增加，活化剂浓度逐渐降低。如通过沿梯度的不同位置处测得的SI-CuCRP动力学所证实的，传播链之间的自由基终止反应限制了POEGMA接枝的接枝密度，其中活化剂的扩散受到促进（即，在d →0时）。该效果随着d的增加而降低，最终在整个基材上产生POEGMA接枝密度的逐渐变化。我们研究了梯度上的接枝密度变化对POEGMA刷膨胀以及它们的纳米机械和纳米摩擦学特性的影响，通过可变角度光谱椭圆偏光法（VASE），胶体探针原子力显微镜（CP）进行了测量-AFM）和横向力显微镜（LFM）。这些测试的结果表明，掺入大量水的POEGMA松散接枝链如何通过剪切AFM探针显着变形，表现出相对较高的摩擦力，并产生摩擦与负载的关系（F f – L）的轮廓遵循Johnson-Kendall-Roberts（JKR）模型所描述的亚线性趋势，该模型通常是高表面能的可变形膜。相反，包装更紧密的POEGMA刷子包含较少的溶剂，并且显示出非常低的摩擦力，根据阿蒙顿定律，F f – L数据遵循线性级数。
更新日期：2017-03-17
中文翻译：
表面引发的Cu（0）介导的受控自由基聚合的聚合物刷梯度的制备和界面性质
表面引发的Cu（0）介导的受控自由基聚合（Si-CuCRP）可以成功地应用于制造一锅中的聚[（低聚乙二醇）甲基醚甲基丙烯酸甲酯]（POEGMA）刷子，从而在整个表面上呈现接枝密度梯度。这是通过连续改变用作Cu物种来源的铜板和引发剂官能化的基材之间的距离（d）来实现的。Cu I单层的X射线光电子能谱（XPS）分析选择性配体表明，较高浓度的活化剂物质在更靠近铜板的区域扩散到起始基质，随着两个表面之间距离的增加，活化剂浓度逐渐降低。如通过沿梯度的不同位置处测得的SI-CuCRP动力学所证实的，传播链之间的自由基终止反应限制了POEGMA接枝的接枝密度，其中活化剂的扩散受到促进（即，在d →0时）。该效果随着d的增加而降低，最终在整个基材上产生POEGMA接枝密度的逐渐变化。我们研究了梯度上的接枝密度变化对POEGMA刷膨胀以及它们的纳米机械和纳米摩擦学特性的影响，通过可变角度光谱椭圆偏光法（VASE），胶体探针原子力显微镜（CP）进行了测量-AFM）和横向力显微镜（LFM）。这些测试的结果表明，掺入大量水的POEGMA松散接枝链如何通过剪切AFM探针显着变形，表现出相对较高的摩擦力，并产生摩擦与负载的关系（F f – L）的轮廓遵循Johnson-Kendall-Roberts（JKR）模型所描述的亚线性趋势，该模型通常是高表面能的可变形膜。相反，包装更紧密的POEGMA刷子包含较少的溶剂，并且显示出非常低的摩擦力，根据阿蒙顿定律，F f – L数据遵循线性级数。
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