Velocity Dependence of Friction and Hydrogen Bonding Effects

We show that the friction force varies with the sliding velocity in a manner that depends on the chemical nature of the interface. Surfaces terminated with the hydrogen acceptor and donor moieties capable of forming H-bond networks exhibit a friction that decreases with sliding velocity, a behavior that is opposite to that of surfaces where no such networks can form. We explain the results with a model where the domains of glassy H-bond networks are disrupted at a critical applied stress leading to slippage.

Figure 1

Semilog plot of the friction force vs sliding velocity for various applied loads between a ${\mathrm{Si}}_3{\mathrm{N}}_4$ tip and samples of: (a) bare mica surface; (b) monolayer of hexadecylamine with methyl group termination; (c) bare ${\mathrm{SiO}}_2$ surface. For samples A and B the experiments were performed in ambient conditions (Relative humidity: 35%, temperature 22°). For sample (c) the experiment was performed in vacuum (${10}^{-10}\mathrm{\text{torr}}$). Negative loads are used to counteract adhesion requiring pull-off forces of $-45$ to $-50\mathrm{nN}$. The plots have all the same arbitrary friction force scale.

Figure 2

Semilog plot of the friction force vs sliding velocity between a ${\mathrm{Si}}_3{\mathrm{N}}_4$ tip and samples of: (a) APS monolayer on mica; (b) polyethylenimine monolayer on mica; and (c) acid-treated ${\mathrm{SiO}}_2$ to produce a saturated layer of hydroxyl groups. For (a) and (b), the experiments were performed in ambient conditions (Relative humidity: 35%, temperature 22°). (c) was performed in vacuum (${10}^{-10}\mathrm{\text{torr}}$). The plots have the same arbitrary friction force scale.

Figure 3

Semilog plot of the friction force vs sliding velocity between a ${\mathrm{Si}}_3{\mathrm{N}}_4$ tip and the APS coated mica sample after treatment with hydrochloric acid at 0 nN normal force (pull-off force approx. $-50\mathrm{nN}$). The friction-velocity behavior is reversed relative to that of the untreated APS film shown in Fig. 2. Experiment performed in ambient conditions.

Figure 4

Semilog plot of friction force vs sliding velocity between a ${\mathrm{Si}}_3{\mathrm{N}}_4$ tip and an acid-treated ${\mathrm{SiO}}_2$ surface (OH-saturated) at different relative humidity: 50%, 35%, and 12%. The normal force exerted on the cantilever is 40 nN.