Bubble Attachment to Cellulose and Silica Surfaces of Varied Surface Energies: Wetting Transition and Implications in Foam Forming.

Annika E Ketola,Orlando J Rojas,Wenchao Xiang,Tekla Tammelin,Jukka A Ketoja,Tuomo Hjelt,Heikki Pajari

doi:10.1021/acs.langmuir.0c00682

Abstract

To better understand the complex system of wet foams in the presence of cellulosic fibers, we investigate bubble–surface interactions by following the effects of surface hydrophobicity and surface tension on the contact angle of captive bubbles. Bubbles are brought into contact with model silica and cellulose surfaces immersed in solutions of a foaming surfactant (sodium dodecyl sulfate) of different concentrations. It is observed that bubble attachment is controlled by surface wetting, but a significant scatter in the behavior occurs near the transition from partial to complete wetting. For chemically homogeneous silica surfaces, this transition during bubble attachment is described by the balance between the energy changes of the immersed surface and the frictional surface tension of the moving three-phase contact line. The situation is more complex with chemically heterogeneous, hydrophobic trimethylsilyl cellulose (TMSC). TMSC regeneration, which yields hydrophilic cellulose, causes a dramatic drop in the bubble contact angle. Moreover, a high interfacial tension is required to overcome the friction caused by microscopic (hydrophilic) pinning sites of the three-phase contact line during bubble attachment. A simple theoretical framework is introduced to explain our experimental observations.

Highlights

Cellulosic microfibrils are versatile biobased materials possessing high strength and relatively low density
In agreement with earlier measurements,[35,51] we found a similar difference between dispersive components of hydrophilic and hydrophobic silica
Bubble attachment on regenerated cellulose and modified silica surfaces of different degrees of hydrophobicity was studied to reveal the key mechanisms involved in complex bubble−fiber interactions

Summary

Introduction

Cellulosic microfibrils are versatile biobased materials possessing high strength and relatively low density. They are the reinforcing structural component of plant cell walls, making cellulose the most abundant biomolecule in the biosphere. The wet foam is guided onto a wire, and the liquid in the foam is removed by vacuum drainage and drying with heat, leaving a self-standing dry fiber structure As this technology is relatively new, research has focused on a better understanding of the fundamentals of the wet fiber foam system (drainage rate, bubble size distribution, coarsening rate)[7−10] and its effects on dry material properties.[11−14]

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Results

Conclusion