کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5179488 | 1502519 | 2016 | 9 صفحه PDF | دانلود رایگان |
- Elastic modulus of nanometer-sized polymer films can be directly measured by AFM.
- Using sharp probes to minimize the substrate effect on the measured modulus.
- Glassy modulus of PVAc films is independent of film thickness down to 18Â nm.
Probe indentation techniques have been widely used to characterize the stiffness-related properties of polymeric materials over the past two decades. However, it still remains challenging to apply these methods for directly measuring the elastic modulus of nanometer-sized polymer films supported by stiff substrates, primarily due to the convolution between the polymer and substrate moduli. Here, we report on the influence of the probe size on the ability of these methods to directly quantify the elastic modulus of nanometer-sized polymer films supported by a stiff substrate. Particularly, we employ the nanomechanical mapping by atomic force microscopy (AFM) in combination with Johnson-Kendall-Roberts two-point method to measure the elastic modulus of Si-supported ultrathin poly(vinyl acetate) (PVAc) films of thickness ranging from 9Â nm to 610Â nm. For sharp AFM probes of â¼12Â nm in radius, this combination allows us to directly measure the elastic modulus of the polymer films as thin as â¼18Â nm without being affected by the stiff substrate. In contrast, larger probes of â¼150Â nm in radius show an obvious substrate-induced enhancement in the modulus of PVAc films with thickness â¼100Â nm, even when the indentation depth of the probe into the films is kept less than 2-3Â nm.
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Journal: Polymer - Volume 87, 22 March 2016, Pages 114-122