Novel Pickering Emulsifiers based on pH-Responsive Poly(tert-butylaminoethyl methacrylate) Latexes

Abstract

Emulsion copolymerization of 2-(tert-butylamino)ethyl methacrylate in the presence of divinylbenzene (DVB) cross-linker and monomethoxy-capped poly(ethylene glycol) methacrylate (PEGMA) macromonomer at 70 °C afforded sterically-stabilized latexes at approximately 10% solids at pH 9. Dynamic light scattering and scanning electron microscopy (SEM) confirmed that relatively narrow size distributions were obtained. SEM confirmed the formation of spherical particles in the absence of any DVB cross-linker using a simple batch protocol, but in the presence of DVB it was necessary to use seeded emulsion polymerization under monomer-starved conditions to prevent the formation of latexes with ill-defined non-spherical morphologies. Lightly cross-linked latexes acquired cationic microgel character upon lowering the solution pH due to protonation of the secondary amine groups. Increasing the degree of cross-linking led to a progressively lower effective pK(a) of the copolymer chains from 8.0 to 7.3, which implies a gradual reduction in their basicity. Poly(tert-butylamino)ethyl methacrylate latex proved to be an effective Pickering emulsifier at pH 10, forming stable oil-in-water emulsions when homogenized with either n-dodecane or sunflower oil at 12,000 rpm for 2 min. These Pickering emulsions exhibited pH-responsive behavior: lowering the solution pH to 3 resulted in immediate demulsification due to the spontaneous desorption of the cationic microgels from the oil/water interface. Following rehomogenization at high pH, four successive demulsification/emulsification pH cycles could be achieved without a discernible loss in performance. However, no demulsification occurred on acidification of the fifth cycle, due to the progressive build-up of background salt.

Polymerization-induced self-assembly of block copolymer nanoparticles via RAFT non-aqueous dispersion polymerization

“…The use of various latex or microgel particles as Pickering emulsifiers to stabilize either oil or water droplets has been widely reported [104][105][106][107]. It is well known that the Pickering emulsion type is dictated primarily by the particle contact angle or surface wettability.…”

A pH responsive Pickering emulsion stabilized by fibrous palygorskite particles

“…Traditional Pickering emulsions have been mainly stabilized by uniform spherical particles such as silica Lumsdon, 1999, 2000;Binks and Clint, 2002;Aveyard et al, 2003), BaSO 4 (Schulman and Leja, 1954), CaCO 3 (Zhu et al, 2013), iron oxide (Melle et al, 2005;Zhou et al, 2011), TiO 2 (Stiller et al, 2004), and polymer latex (Morse et al, 2012). Another class of Pickering emulsions is stabilized by plateshaped particles, such as montmorillonite (MMT) (Lagaly et al, 1999a, b;Thieme et al, 1999;Nciri et al, 2009), aluminum silicate dehydrate (kaolinite powder) (Yan and Masliyah, 1995), Laponite clay (Ashby and Binks, 2000), and layered double hydroxides particles (LDHs) (Yang et al, 2006).…”

Microgel Colloidosomes Based on pH-Responsive Poly(tert-butylaminoethyl methacrylate) Latexes

“…The PEGMA-stabilized PTBAEMA latex syntheses have been described elsewhere. 19 Full details of these can be found in Supporting Information. Chargestabilized PTBAEMA latexes were produced in both the absence and presence of a Nile blue-functionalized methacrylamide (NBM; 0.001 wt % based on monomer) comonomer recently synthesized within our group.…”

“…It is worth briefly commenting on the series of sterically stabilized lightlycross-linked PEGMA−PTBAEMA latexes that have been reported previously. 19 These syntheses were conducted via aqueous emulsion copolymerization of TBAEMA with DVB cross-linker in the presence of a hydrophilic PEGMA macromonomer at approximately 10% solids (see Figure 1). Mean latex diameters ranged from 150 to 220 nm depending on the initial DVB cross-linker concentration.…”

“…In this sense, the spatial location of the cross-linking reaction described herein is similar to that described by Croll et al 21 The mechanical integrity of these colloidosomes can be readily tested by an acid challenge. Unlike PTBAEMAstabilized Pickering emulsions that readily demulsify upon addition of acid 19 (see route A, Figure 3), such cross-linked PTBAEMA-based colloidosomes were expected to survive the addition of excess acid or ethanol. In the former case, a latex-tomicrogel transition was expected, but the swollen cross-linked microgel layer should remain intact to produce a microgel colloidosome (see route B, Figure 3).…”