pH-responsive disruption of ‘liquid marbles’ prepared from water and poly(6-(acrylamido) hexanoic acid)-grafted silica particles

Abstract

A chain transfer agent was immobilized onto the surface of 11-lm diameter silica particles (CPD-SiO 2 ) for use in reversible addition-fragmentation chain transfer (RAFT)-controlled radical polymerization. pH-responsive poly(6-(acrylamido)hexanoic acid) (PAaH)-grafted silica particles (PAaH-SiO 2 ) were prepared via RAFT-controlled radical polymerization using CPD-SiO 2 . Immobilization of the PAaH chains onto the surface of silica particles was confirmed by thermogravimetric analysis, attenuated total reflection-Fourier transfer infrared and scanning electron microscopy measurements. The solubility of PAaH in water is strongly dependent on the pH of the solution. PAaH-SiO 2 was flocculated at pH 3 because of the hydrophobic interaction of the grafted PAaH chains with protonated carboxyl pendant groups. In contrast, PAaH-SiO 2 was dispersed at pH 10 because of electrostatic repulsion between the grafted PAaH chains with pendant carboxylate ions. Millimeter-sized 'liquid marbles' can be prepared using the pH-responsive PAaH-SiO 2 particles. The 'liquid marble' can be transferred intact onto the surface of a neutral or acidic water pool and exhibit long-term stability. When the pH of the water pool becomes alkaline, the 'liquid marble' immediately bursts on the surface of the water pool.

pH-responsive Liquid Marbles Prepared Using Fluorinated Fatty Acid

“…The pH-responsive liquid marble disintegrates on addition of NaOH aqueous solution to the bulk aqueous phase because the particle surface becomes hydrophilic, owing to the ionization of the pendant hexanoic acid groups in the grafted polymer chains. 6,7 In this study, pH-responsive liquid marbles were prepared using a hydrophobic fluorinated powder, 2H,2H,3H,3H-heptadecafluoroundecanoic acid (HFUA). To prepare pH-responsive liquid marbles without much time and labor, we used HFUA as a pH-responsive powder (Figure 1).…”

“…The liquid marble was floated on the bulk phase containing luminol and H 2 O 2 ( Figure 6 and Video S3). For the reaction, luminol was activated with H 2 O 2 , and K 3 [Fe(CN) 6 ] was the catalyst. When the liquid marble was broken by adding NaOH, the activated luminol came in contact with the K 3 [Fe(CN) 6 ] catalyst, causing it to exhibit luminescence.…”

“…For the reaction, luminol was activated with H 2 O 2 , and K 3 [Fe(CN) 6 ] was the catalyst. When the liquid marble was broken by adding NaOH, the activated luminol came in contact with the K 3 [Fe(CN) 6 ] catalyst, causing it to exhibit luminescence. Various chemical reactions with a mix of two solutions can be initiated by triggering liquidmarble disintegration due to a pH change.…”

“…Therefore, the two reactants come in contact to start the chemical reaction. The pH-responsive liquid marble was used in a pH-triggered chemical reaction of aqueous solutions of luminol and K 3 [Fe(CN) 6 ]. 11 The aqueous solution containing luminol (0.1 wt %) and H 2 O 2 (1.5 wt %) was used as the bulk phase.…”

Near-infrared-responsive Liquid Marbles Stabilized with Carbon Nanotubes

“…7 There have recently been reports of liquid marbles whose stability can be controlled by external stimuli; these are known as stimuli-responsive liquid marbles. Liquid marbles stabilized by particles containing pH-responsive polymers, such as deprotonated hydrophobic poly[2-(dimethylamino)ethyl methacrylate], 8 poly(2-vinylpyridine) (P2VP), 9 or protonated hydrophobic poly [6-(acrylamide)hexanoic acid], 10 which can float on the surface of bulk water, disintegrate upon addition of acid or base to the bulk water, because the particle surface becomes hydrophilic due to ionization of the pH-responsive polymers. Recently, Wang et al 11 reported the preparation of magnet-and UV-responsive liquid marbles using Fe 3 O 4 /SiO 2 particles with a pH-responsive block copolymer containing P2VP and a photo acid generator (PAG).…”