Adhesion hysteresis

Yamada S and Israelachvili J N 1998 Friction and adhesion hysteresis of fluorocarbon surfactant monolayer-coated surfaces measured with the surface forces apparatus J. Rhys. Chem. B 102 234-44... 

Chaudhury M Kand Gwen M J 1993 Adhesion hysteresis and friotion Langmuirs 29-31... 

In a separate study using the JKR technique, Chaudhury and Owen [48,49] attempted to understand the correlation between the contact adhesion hysteresis and the phase state of the monolayers films. In these studies, Chaudhury and Owen prepared self-assembled layers of hydrolyzed hexadecyltrichlorosilane (HTS) on oxidized PDMS surfaces at varying degrees of coverage by vapor phase adsorption. The phase state of the monolayers changes from crystalline (solidlike) to amoiphous (liquid-like) as the surface coverage (0s) decreases. It was found that contact adhesion hysteresis was the highest for the most closely packed... 

Fig. 13. Measurement of surface energies of PS and PMMA. It can be seen that there was a finite adhesion hysteresis. At a given load, the contact radius during loading was less than the contact radius during unloading. From the unloading data, we get yi>s = 45 1 mJ/nr, and yi),viMA = 53 1 mj/m . These number are in good agreement with the values of surface energies determined from the pull-off force measured using the SFA.

Fig. 14. Measurement of adhesion between PDMS and PS, and PDMS and PMMA. It can be seen that there was no adhesion hysteresis. The contact radius at a given load, during loading and unloading was the same. From these data, we get WpoMs-ps = 49 3 mJ/m-, and Tfdm.s-fm.ma = 57 1 mJ/m-.

She et al. [128] used rolling contact to estimate the adhesion hysteresis at polymer/oxide interfaces. By plasma oxidation of the cylinders of crosslinked PDMS, silica-like surfaces were generated which could hydrogen bond to PDMS r olecules. In contrast to unmodified surfaces, the adhesion hysteresis was shown to be larger and proportional to the molecular weight of grafted polymer on the substrate. The observed hysteresis was interpreted in terms of the orientation and relaxation of polymer chains known as Lake-Thomas effect. 

Thus this adhesion hysteresis is a result of a time-dependent roughening of the interface. It shows that roughness at an interface may actually develop as a result of bringing the two phases together as a result of the intrinsic properties of the surface molecules. 

The adhesion hysteresis and its contribution to the friction have been studied extensively by means of SFA [39], which leads to an important conclusion that it is the adhesion hysteresis or the energy loss during the process of approach/separation, rather than the surface energy itself, that dominates the frictional behavior of boundary films. 

The dynamical adhesion process described in this section is also referred to as adhesion hysteresis. We will come back to this subject in later sections when discussing the correlation between adhesion and friction. 

Fig. 26—Connections between adhesion hysteresis and friction on the left the hysteresis results in a relatively large friction, on the right the hysteresis disappears due to introducing decane vapor, which leads to a smaller friction (from Ref. [21]).

Two conclusions can be drawn from Eqs (24) and (25). First, friction is in direct proportion to the energy difference Ay in the adhesion hysteresis, which is consistent with the experimental results presented in the last section. Secondary, an increase in Dq, namely the mean separation or film thickness, will lead to decrease in friction, which agrees well with the observation in boundary lubrication. If the coefficient s somehow remains fixed, it can be deduced from Eq... 

Amongst different channels of the energy dissipation, the most relevant are the sample viscosity, the contact friction, and the adhesion hysteresis. When the drive frequency is chosen to be CQ0, the power that is dissipated when the tip periodically interacts with the sample can be written as... 

Fig. 4.9 CFM of droplets appearing with time after 30 min of UV/ozone exposure (a) height, (b) maximum adhesive forces, and (c) adhesion hysteresis. The color scales indicate the height [bright (0 nm) to dark (10 nm] maximum adhesive force [dark (6 nN) to bright (17 nN)] and hysteresis [dark (0.2 x 10-17 J) to bright (1.2 x 10-17 J)]. (d) Representative force-distance curves. Adapted with permission from [28]. Copyright 2004. American Chemical Society.

Using the SFA technique, it could be demonstrated that there is an intimate relationship between adhesion hysteresis and friction [28, 29, 77]. Both processes dissipate energy through non-equilibrium mechanisms... 

Figure 10 Effect of temperature on adhesion hysteresis (after Ref. 79).

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