Encapsulation of Amphoteric Substances in a pH-Sensitive Pickering Emulsion

Haase, Martin F.; Grigoriev, D. O.; Moehwald, Helmuth; Tiersch, Brigitte; Shchukin, Dmitry G.

doi:10.1021/jp104052s

Cited by 60 publications

(44 citation statements)

References 33 publications

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“…13, 33 To further investigate the interfacial structure, CLSM measurements were performed. 33,36 This was consistent with the droplet diameter data listed in Table 1. Typical droplet images revealed that the aggregated microspheres adsorbed at the oil/water interface, rather than single microspheres.…”

Section: Resultssupporting

confidence: 89%

Color changing Pickering emulsions stabilized by polysiloxane microspheres bearing phenolphthalein groups

et al. 2015

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The benzoxazine monomer bearing phenolphthalein and alkoxysilane groups was synthesized using phenolphthalein, 3-aminopropyltriethoxysilane, and paraformaldehyde as raw materials via Mannich reaction. After hydrolysis and condensation of alkoxysilane groups, the novel polysiloxane microsphere bearing phenolphthalein groups (PMP) was synthesized.Furthermore, toluene-in-water Pickering emulsion using PMP as particulate emulsifier was prepared. The existence of phenolphthalein and oxazine structures in PMP were confirmed by Fourier transform infrared (FTIR) spectroscopy. The average diameter of PMP was 208 nm as indicated by Dynamic light scattering (DLS), and the PMP shape was spherical as revealed by transmission electron microscopy (TEM). Due to the introduced phenolphthalein structure, stable toluene-in-water Pickering emulsion presented a color changing behavior within the pH range from 9 to 12. It also exhibited doubly pH-responsive property: two emulsification/demulsification processes occurred at pH 9 and 12, respectively. Moreover, these processes were verified to be reversible: five and three demusification/emulsification cycles were repeated with the aid of homogenization.phenolphthalein solution (see Figure 3a). This was explained by the structural change of phenolphthalein. It changed from the colorless non-conjugated lactone form (I) to the red conjugated quinonoid form (II). 26 As the pH increased from 9 to 13, the color of the dispersion turned gradually to deep red, similar to that of phenolphthalein solution. This was attributed to the increasing concentration of conjugated quinonoid form (II). When the pH reached 14, the dispersion color partially faded. This was because that the phenolphthalein structure changed from conjugated quinonoid form (III) to the non-conjugated carbinol form (IV). 26It should be noted that the color window of PMP dispersions moved to slightly higher pH value than that of phenolphthalein solutions. This might be due to the relatively low phenolphthalein concentration on the surface of PMPs, despite of the fact that the concentration of phenolphthalein in PMP dispersions (0.5 wt %) was equal to that of the phenolphthalein solutions (0.21wt %).indicated that the lactone rings of phenolphthalein were opened and anionic carboxylic acid groups (-COO -) were generated. Both factors lowered the positive charges at the particle surfaces, and reduced the excessively high hydrophilicity of PMPs. As a result, the PMPs' surface wettability became appropriate to stabilize Pickering emulsion. 18,32 This was evidenced by the decreasing of zeta potential for PMPs from 46.1mV to 28.4 mV as the pH increased from 8.0 to 9.0 (see Figure 5), indicating the increasing emulsifying capacity of PMPs.When the pH increased from 9.0 to 12.0, the emulsion color changed from pink to deep red, exhibiting the similar color changing property to PMP dispersions. Optical micrographs of Pickering emulsions at pH 9.0-12.0 revealed the spherical dispersed droplets which existed in the typical emulsion (see Fi...

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Section: Resultssupporting

confidence: 89%

Color changing Pickering emulsions stabilized by polysiloxane microspheres bearing phenolphthalein groups

et al. 2015

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“…However, several limitations and disadvantages have been reported for water-borne coatings [70][71][72][73][74][75] including:…”

Section: Water-borne Smart Coatingsmentioning

confidence: 99%

Techniques for synthesizing and applying smart coatings for material protection

Makhlouf¹

2014

Handbook of Smart Coatings for Materials Protection

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“…10,11 We are aware of some literature describing the use of pH-sensitive inorganic particles (e.g., silica). 5,12,13 However, polymer latexes have become widely used as Pickering emulsifiers since they provide an opportunity to tailor surface properties via synthesis. It is also noteworthy that Dai's group reported the production of stable Pickering emulsions at submonolayer coverages using micrometer-sized polystyrene latex particles.…”

Section: ■ Introductionmentioning

confidence: 99%

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

et al. 2012

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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.

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Encapsulation of Amphoteric Substances in a pH-Sensitive Pickering Emulsion

Cited by 60 publications

References 33 publications

Color changing Pickering emulsions stabilized by polysiloxane microspheres bearing phenolphthalein groups

Color changing Pickering emulsions stabilized by polysiloxane microspheres bearing phenolphthalein groups

Techniques for synthesizing and applying smart coatings for material protection

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

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