Aqueous Bubbles Stabilized with Millimeter-Sized Polymer Plates

Abstract

(Sub)­millimeter-sized hexagonal polymer plates that were monodisperse in shape and size were utilized as stabilizers for aqueous bubbles, and the effects of the hydrophilic–hydrophobic property, size, and solid concentration of the plates on the formability, stability, and shape and structure of aqueous bubbles were investigated. The formability and stability of the bubbles were improved by increasing the hydrophobicity of the plate surface, decreasing the plate size, and increasing the solid concentration of the plates. For plates with suitable water wettability, three-dimensional bubbles with nearly spherical and polyhedral shapes were formed by the adsorption of plates to the bare air bubbles introduced into the continuous water phase by air–water mixing. On the contrary, two-dimensional bubbles with accordion-type structures consisting of alternating layers of plates and entrapped air bubbles were formed by the transfer of multiple plates with poor wettability from the air phase to the water phase by air–water mixing. Furthermore, a correlation was found between the bubble/stabilizer size ratio and bubble shape for plates with the suitable wettability: bubbles with nearly spherical shapes were formed when the bubble/plate size ratios were >2, bubbles with hexahedral, pentahedral, and tetrahedral shapes were formed when the size ratios were approximately 1, and bubbles with triangular and sandwich shapes were formed when the size ratios were <0.8. Additionally, bubbles with similar shapes were formed when the bubble/plate size ratios were close, even when the sizes of the plates and bubbles were different.

Shape design of aqueous bubbles stabilized with millimeter-sized polymer plates

“…Recently, we studied aqueous bubbles stabilized with (sub)millimeter-sized polymer plates and confirmed that polyhedral bubbles with various shapes could be produced when the sizes of the plate and air bubble were comparable. 32 In our previous study, the bubbles were produced simply by handshaking of air, water and plates in one sample bottle, and they were polydispersed in shape and size, which could not be well controlled. Additionally, it was difficult to optimize the size ratios of the plate and air bubble, and therefore the shapes of the polyhedral bubbles were not well defined.…”

“…The size ratio (D b /2S) between the air bubble (diameter, D b ) and the plates (diagonal length, 2S) has been proven to play an important role in predicting the shape and size of the resulting bubbles. 32 In the case of near-spherical bubbles, D b is larger Fig. 1 Schematic representation of the fabrication of polyhedral bubbles stabilized with millimetre-sized polymer plates in a tailor-made manner.…”

“…where D b values were experimentally obtained from our previous study. 32 Here, the D b values were estimated based on Heywood diameters of polyhedral bubbles using the optical microscopy images. The V b values were calculated to be ca.…”

“…where g AS is air-solid interfacial tension (determined by Zisman plot), 32 g AW is the air-water interfacial tension and g WS is the water-solid interfacial tension (determined by Yong's equation). The DG value of the PET plate was calculated to be À7.00 Â 10 13 kT.…”

“…34,47,48 It is noteworthy that the cuboid bubbles could be only realized by the tailor-made method developed in this study, but not by the previous hand-shaking method. 32 The method developed in this study is not at the stage of mass production. Mass production of shape-controlled polyhedral bubbles might be achieved using Shirasu porous glass.…”