Institute of Biophysics and Medical Physics, Faculty of Medicine, University of Leipzig, Leipzig, Germany.
Nanoscale. 2013 Dec 7;5(23):11679-85. doi: 10.1039/c3nr02929h. Epub 2013 Oct 8.
The thickness of a poly(sulfo propyl methacrylate) (PSPM) brush is determined by Atomic Force Microscopy (AFM) imaging as a function of the loading force at different ionic strengths, ranging from Milli-Q water to 1 M NaCl. Imaging is performed both with a sharp tip and a colloidal probe. The brush thickness strongly depends both on the applied load and on the ionic strength. A brush thickness of 150 nm is measured in Millipore water when applying the minimal loading force. Imaging with an 8 μm silica particle as a colloidal probe results in a thickness of 30 nm larger than that measured with the tip. Increasing the ionic strength causes the well known reduction of the thickness of the brush. The apparent thickness of the brush decreases with increasing loading forces. An empirical model analogous to that of a compressible fluid is applied to describe the dependence of the apparent thickness of the brush with loading force. The model comprises three ionic strength dependent parameters for the brush: thickness at infinite compression, energy, and cohesive force. The meaning and significance of these parameters are discussed. A particular advantage of the model is that it allows for determination of the brush thickness at zero loading force.
聚（磺丙基甲基丙烯酸钠）（PSPM）刷的厚度可通过原子力显微镜（AFM）成像来确定，其功能是在不同离子强度下测量加载力，范围从 Milli-Q 水到 1 M NaCl。使用尖锐的针尖和胶体探针均可进行成像。刷的厚度强烈取决于所施加的负载和离子强度。在施加最小负载力时，在 Milli-Q 水中测量到 150nm 的刷厚度。使用 8μm 的二氧化硅颗粒作为胶体探针进行成像，其厚度比用针尖测量的厚度大 30nm。增加离子强度会导致众所周知的刷厚度减小。随着加载力的增加，刷的表观厚度减小。应用类似于可压缩流体的经验模型来描述刷的表观厚度与加载力的关系。该模型包括三个与离子强度相关的刷参数：在无限压缩时的厚度、能量和内聚能。讨论了这些参数的意义和重要性。该模型的一个特别优点是它允许确定零加载力下的刷厚度。
