Effect of Wettability on Adhesion Force between Silica Particles Evaluated by Atomic Force Microscopy Measurement as a Function of Relative Humidity

Abstract

Wettability and the adhesion force between two silica particles were measured as a function of relative humidity. The wettability of silica particles was controlled by rehydroxylation and modification by hexamethyldisilazane and evaluated by a preferential dispersion test, heat of immersion, and water adsorption. The adhesion force between two particles was measured by atomic force microscopy using a "colloidal technique". The wettability varied from hydrophilic to hydrophobic at trimethylsilyl density ) 1.0 nm -2 as modified groups shielded the residual silanol groups and hindered the formation of a capillary bridge between the two particles. This "hindrance effect" is thought to result in the absence of a critical increase in adhesion force at high relative humidity and also the reduction of surface energy at low humidity where hydrogen bonding dominated the adhesion force.

On the Adhesion between Fine Particles and Nanocontacts: An Atomic Force Microscope Study

“…No significant dependence of the adhesion force on humidity was observed on HOPG (Fig.4.26). This agrees with previous results, where a significant influence of humidity was observed only for the adhesion between hydrophilic surfaces, while forces on hydrophobic surfaces showed no dependency [42,58,190]. …”

“…Water condenses into the gap at the contact region between hydrophilic particles. This is with AFM [69,119,[190][191][192][193][194][195][196][197][198]. Many experiments showed a significant dependency of the adhesion force on the relative humidity [40,52,54,56,57,183].…”

“…A continuous increase humidity was, for example, observed for the interaction of a silicon nitride tip with mica [194], between silica particles [199], a silica particle and a silicon wafer [200], or between a silicon nitride tip and molybdenum trioxide [201]. The adhesion force between particles or particle surface by using AFM colloidal probe technique depending on relative humidity [190,202,203]. Jones et al study of adhesion between flat surfaces of glass or silicon and silicon AFM tip or glass microspheres [204].…”

Force measurements with the atomic force microscope: Technique, interpretation and applications

“…(7.8), meniscus forces are expected to be maximal for hydrophilic surfaces (small contact angle) and to vanish for very hydrophobic surfaces. The expected decrease of the adhesion force with increasing hydrophobicity has indeed been observed by several authors [682][683][684][685][686][687][688]. An obvious limitation of Eq.…”

The Colloidal Probe Technique and its Application to Adhesion Force Measurements

“…When increasing the relative humidity to 70% ± 80% a steep increase of adhesion was observed (from $ 50 mN/m to $ 500 mN/m), indicating capillary condensation. In a further study [73], the wettability of the nonporous silica particles was controlled by rehydroxilation or modification with hexamethyldisilazane that introduced trimethylsilyl (TMS) groups on the surface of the particles. For TMS densities of > 1.0 TMS/nm 2 , particles were hydrophobic as proved by dispersion tests, heat of immersion and water adsorption isotherms.…”