Duangrut Julthongpiput

Effects of Surface Functionality and Humidity on the Adhesion Force And Chemical Contrast Measured with AFM

The ability to probe chemical heterogeneity with nanometer scale resolution is essential for developing a molecular–level understanding of a variety of phenomena occurring at surfaces of materials. One area that could benefit greatly from nanoscale chemical measurement is an understanding of the degradation mechanisms of polymeric materials exposed to the environment. For example, the degradation (photo and hydrolytic) of polymers and polymeric materials has been observed to occur non-uniformly in which nanometer pits form locally, which deepen and enlarge with exposure (1, 2). The pitting has been postulated to initiate in the hydrophilic degradation-susceptible regions of the films (3). However, due to the lack of spatial resolution of the most current surface analytical techniques, the chemical nature of the degradation-initiated locations has not been identified. The use of a chemically-functionalized probe in an AFM (chemical force microscopy CFM) (4) has been shown to be capable of discriminating chemically-different domains of self-assembled monolayer (SAM) surfaces at the nanoscale spatial resolution. This study provides data to demonstrate that, by using proper RH at the tip-sample environment, the contrast between the hydrophilic and hydrophobic domains in SAM and polymer samples can be discerned, and presents results on the effects of RH on tipsample adhesion forces for different substrates.

Effect of Relative Humidity on Chemical Heterogeneity Imaging with Atomic Force Microscopy

In this study, a well-controlled humidity system is used to enhance the sensitivity of AFM for characterizing surface chemical heterogeneity of patterned self-assembled monolayers (SAMs) and hydrophilic-hydrophobic polymeric brush specimens. Dependence of the AFM friction contrasts on the surface energy differences between the hydrophilic regions and hydrophobic regions of the chemically heterogeneous samples has been investigated as a function of relative humidity (RH). Effects of RH and surface chemistry on tip-sample adhesion are also investigated. Both AFM image contrast and tip-sample adhesion forces between the hydrophilic and hydrophobic regions significantly depend on RH and follow the similar trend as a function of RH. The results clearly demonstrate that, by using proper RH at the tip-sample environment, chemically heterogeneous regions can be distinguished with the AFM.