Study of thin liquid film drainage in bubble-liquid-solid systems using integrated thin liquid film force apparatus (ITLFFA)

• Author / Creator

  Zhang, Xurui

• Interactions involving deformable surfaces reveal a number of distinct physicochemical characteristics that do not exist in interactions between rigid solid surfaces. The main focus of this thesis is to develop a unique fully custom-designed instrument, referred to as an integrated thin liquid film force apparatus (ITLFFA) to investigate interactions between a deformable and a solid surface in liquids. Incorporating a bimorph force sensor with interferometry, the ITLFFA allows simultaneous measurement of the time-dependent interaction forces and the corresponding spatiotemporal film thickness of the intervening liquid film. The ITLFFA possesses specific features of measurement under a wide range of hydrodynamic conditions, with a displacement velocity of deformable surfaces ranging from 2 μm/s to 50 mm/s. Equipped with a high speed camera, the results of a bubble interacting with hydrophilic and partially hydrophobic surfaces in aqueous solutions indicated that ITLFFA can provide information on interaction forces and thin liquid film drainage dynamics not only in a stable film but also in films of quick rupture process. The weak interaction force was extracted from a measured film profile. As a result of its well-characterized experimental conditions, ITLFFA permits the accurate and quantitative comparison/validation between the measured and calculated interaction forces and temporal film profiles. Using the ITLFFA, the dynamic drainage process of the liquid film trapped between an air bubble and a flat silica surface over a wide range of hydrodynamic conditions was studied in aqueous solutions of different salt concentrations. Our study demonstrates that increasing the bubble approach velocity has a significant impact on the hydrodynamic pressure and fluid flow within the draining film, promoting the dimple formation and increasing drainage time. The drainage time also depends on the competition between the electrical double-layer and van der Waals interactions, which are repulsive in our system, resulting in a stable liquid film on the hydrophilic surface, with the film thickness being determined by the balance of capillary pressure of the bubbles with the repulsive forces of the film scaled by the electrolyte concentrations. The evolution of the draining film is analyzed using the Stokes-Reynolds-Young-Laplace (SRYL) model. Comparisons between the theory and experimental results indicate that the model captures essential physical properties of the drainage system. Moreover, the thickness of the first occurrence of the dimple can also be precisely predicted from the bubble approach velocity with a simple analytical expression. The dynamic thin liquid film drainage between a bubble and a hydrophobic solid surface of different hydrophobicities with nanoroughness was also studied using this device. For a given bubble approach velocity, the thickness of the first occurrence of the dimple for the hydrophobic surface was much thinner than that of the hydrophilic surface, indicating an apparent surface mobility on the hydrophobic surface. The experimental results were modelled by the SRYL model to obtain the degree of surface mobility for the hydrophobic surface as a function of bubble approach velocity, illustrating a velocity dependent surface mobility. Moreover, the thin film ruptured at thickness as large as hundreds of nanometers. The major contributions to science of this thesis are developing a device-ITLFFA that performs the simultaneous measurement of dynamic forces and spatiotemporal film thickness during thin liquid film drainage between deformable and solid surfaces. It allows measurements over a wide range of hydrodynamic conditions that fills the experimental gap of current techniques. The systematic study of the effect of approach velocity and surface hydrophobicity on the drainage dynamics of thin liquid films appealed us to consider them as vital parameters in the theoretical model that shed light on the problem of boundary condition and hydrophobic interaction.

• Subjects / Keywords

  • Bubble
  • Hydrophobic surface
  • Hydrophilic surface
  • Thin liquid film

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R30G3HC1F

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.