The Direct Cause of Amplified Wettability: Roughness or Surface Chemistry?

Emmanuel E Ubuo,Andrew T Tyowua,Inimfon A Udoetok,Ifiok O Ekwere,Hamza S Al-Shehri

doi:10.3390/jcs5080213

Emmanuel E Ubuo, Andrew T Tyowua + Show 3 more

Open Access

https://doi.org/10.3390/jcs5080213

Copy DOI

Abstract

Higher contact angles or amplified wettability observed on surfaces of rough solid materials are typically expressed as a function of a physical dimension (roughness factor). Herein, we present a simple experimental approach that demonstrates that roughness may only magnify the inherent surface chemistry that seems to have direct influence on surface wettability. We investigate gradual change in surface chemistry (hydrophobisation) of rough and smooth glass surfaces, from a very low concentration (10−7 M) of dichlorodimethylsilane, DCDMS through various intermediate hydrophilic/hydrophobic states to when the surfaces are maximally hydrophobised with DCDMS at 0.1 M. The wettability of the modified glasses was studied by water contact angle measurements using drop shape analysis system (DSA). The data obtained indicate a deviation from Wenzel model, with the functionalized rough glass surfaces showing higher reactivity towards DCDMS when compared to the smooth glass surfaces, indicating that the two surfaces are not chemically identical. Our study reveals that just like transforming a solid material to powder, a well-divided glass (rough) surface may not only exhibit a greater surface area than the smooth counterpart as rightly predicted by the Wenzel model, but seems to be bloated with functional groups (–OH or –CH3) that can amplify surface interaction when such functional species dominate the solid surface.

Highlights

Though direct measurement of the surface energy of solid materials is difficult, it may be indirectly determined through measurement of the contact angle of liquid droplets on the solid materials [8,9]
To further throw more light on the wettability of rough surfaces, we simultaneously study the hydrophobisation and wettability of smooth and rough surfaces of a particular glass material using different concentrations of dichlorodimethylsilane (DCDMS) and contact angle measurements, respectively
Glass slides with rough surfaces exhibit higher rates of hydrophobisation than the corresponding slides with smooth surfaces

Summary

Introduction

The reports reveal that surface texture and surface energy play significant roles in determining the extent of surface wettability [4,5,6]. Surface energy is directly related to surface chemistry and depends on the type of chemical bonds on the material’s surface [7]. Though direct measurement of the surface energy of solid materials is difficult, it may be indirectly determined through measurement of the contact angle of liquid droplets on the solid materials [8,9]. Contact angles of liquid droplets on solid materials have been employed in the prediction of wettability and surface energies of different materials. Materials with high surface energy are hydrophilic and water droplets over their surfaces exhibit contact angles below 90◦

Objectives

Methods

Results

Conclusion