PH-Responsive Aqueous Bubbles Stabilized With Polymer Particles Carrying Poly(4-vinylpyridine) Colloidal Stabilizer.

Masaya Ito,Yoshinobu Nakamura,Shin-Ichi Yusa,Haruka Hanochi,Syuji Fujii,Yuta Asaumi,Koki Takano

doi:10.3389/fchem.2018.00269

Abstract

Free radical dispersion polymerization was conducted to synthesize near-monodispersed, micrometer-sized polystyrene (PS) particles carrying pH-responsive poly(4-vinylpyridine) (P4VP) colloidal stabilizer (P4VP-PS particles). The P4VP-PS particles were extensively characterized in terms of morphology, size, size distribution, chemical composition, surface chemistry, and pH-response using optical and scanning electron microscopies, elemental microanalysis, X-ray photoelectron spectroscopy, laser diffraction particle size analysis, and zeta potential measurement. The P4VP-PS particles can work as a pH-responsive stabilizer of aqueous bubbles by adsorption at the air-water interface. At and above pH 4.0, where the particles have partially protonated/non-protonated P4VP stabilizer with relatively hydrophobic character, particle-stabilized bubbles were formed. Optical and scanning electron microscopy studies confirmed that the P4VP-PS particles were adsorbed at the air-water interface of the bubbles in aqueous media. At and below pH 3.0, where the particles have cationic P4VP stabilizer with water-soluble character, no bubble was formed. Rapid disruption of the bubbles can be induced by decreasing the pH; the addition of acid caused the in situ protonation of pyridine groups in P4VP, which impart water-soluble character to the P4VP stabilizer, and the P4VP-PS particles were desorbed from the air-water interface. The bubble stabilization/destabilization cycles could be repeated at least five times.

Highlights

For a long time, it has been known that gas bubbles can be stabilized solely by solid colloidal particles in aqueous media (Ramsden, 1903; Binks and Horozov, 2006; Studart et al, 2006; Fujii and Murakami, 2008; Hunter et al, 2008; Kruglyakov et al, 2011; Stevenson, 2012; Pugh, 2016; Fujii and Nakamura, 2017)
These results indicated that the threshold pH value which determines bubble stability depends on the pH-responsive nature of the colloidal stabilizer on the particle surfaces
We demonstrated that PS particles carrying poly[2-(dimethylamino)ethyl methacrylate] (PDMA) colloidal stabilizer can work as the pH-responsive particulate bubble stabilizer

Summary

Introduction

It has been known that gas bubbles can be stabilized solely by solid colloidal particles in aqueous media (Ramsden, 1903; Binks and Horozov, 2006; Studart et al, 2006; Fujii and Murakami, 2008; Hunter et al, 2008; Kruglyakov et al, 2011; Stevenson, 2012; Pugh, 2016; Fujii and Nakamura, 2017). These results indicated that the threshold pH value which determines bubble stability depends on the pH-responsive nature (pKa value) of the colloidal stabilizer on the particle surfaces. There are two objectives: (i) synthesis and characterization of near-monodispersed, micrometer-sized PS particles carrying poly(4-vinylpyridine) (P4VP) colloidal stabilizer on their surfaces (P4VP-PS particles) by free radical dispersion polymerization, and (ii) investigation of their ability as a pH-responsive particulate bubble stabilizer (Figure 1).

Results

Conclusion