Phase state effect on adhesion behavior of self-assembled monolayers.
The effect of phase state of self-assembled monolayers (SAMs) on adhesion behavior was studied using a combination of atomic force microscopy (AFM) and Johnson-Kendall-Roberts (JKR) methods. The phase state of SAMs was controlled by adjusting the reaction temperature. Order-to-disorder structural transitions in monolayers of n-alkyltrichlorosilanes resulted in dramatic increases in adhesion force and adhesion hysteresis, which represents the first report of alterations in adhesion properties due to phase changes of monolayers without any effect of chain length and surface heterogeneity. This increase in mechanical deformation of the disordered monolayer is understood to be caused by increases in (1) molecular contact between the AFM tip and a disordered monolayer due to the more deformable state of the latter and (2) monolayer deformation during unloading by the JKR probe lens. Adhesion hysteresis was found to have greater sensitivity toward the unloading rate for disordered monolayers. The occurrence of maximum hysteresis at faster rates proves that monolayer chain mobility increases with structural disorder, resulting in increased mechanical deformation.
Lee
Dae Ho
DH
Department of Chemical Engineering, School of Environmental Science and Engineering, Polymer Research Institute, Pohang University of Science and Technology, Pohang 790-784, South Korea.
Kim
Dohwan
D
Oh
Taebyoung
T
Cho
Kilwon
K
D000268:Adhesiveness; D008567:Membranes, Artificial; D018625:Microscopy, Atomic Force / Q000379:methods; D049329:Nanostructures / Q000737:chemistry*; D012680:Sensitivity and Specificity; D012821:Silanes / Q000737:chemistry*; D013499:Surface Properties; D013696:Temperature
D008567:Membranes, Artificial; D012821:Silanes