%0 Journal Article
%A Morse, A. J.
%A Armes, S. P.
%A Thompson, K. L.
%A Dupin, D.
%A Fielding, L. A.
%A Mills, P.
%A Swart, R.
%D 2013
%T Novel Pickering Emulsifiers Based on pH-Responsive
Poly(2-(diethylamino)ethyl methacrylate) Latexes
%U https://acs.figshare.com/articles/journal_contribution/Novel_Pickering_Emulsifiers_Based_on_pH_Responsive_Poly_2_diethylamino_ethyl_methacrylate_Latexes/2417866
%R 10.1021/la400786a.s001
%2 https://acs.figshare.com/ndownloader/files/4059433
%K PEGMA
%K CO 2 gas
%K N 2 purge
%K DEA
%K Pickering emulsions
%K Novel Pickering Emulsifiers
%K cationic microgel hydrodynamic diameter
%K background salt
%K solution pH
%K LatexesThe emulsion copolymerization
%X The emulsion copolymerization of
2-(diethylamino)ethyl methacrylate
(DEA) with a divinylbenzene cross-linker in the presence of monomethoxy-capped
poly(ethylene glycol) methacrylate (PEGMA) at 70 °C afforded
near-monodisperse, sterically stabilized PEGMA-PDEA latexes at 10%
solids. Dynamic light scattering studies indicated intensity-average
diameters of 190 to 240 nm for these latexes at pH 9. A latex-to-microgel
transition occurred on lowering the solution pH to below the latex
pKa of 6.9. When dilute HCl/KOH was used
to adjust the aqueous pH, a systematic reduction in the cationic microgel
hydrodynamic diameter of 80 nm was observed over ten pH cycles as
a result of the gradual buildup of background salt. However, no such
size reduction was observed when using CO2/N2 gases to regulate the aqueous pH because this protocol does not
generate background salt. Thus, the latter approach offers better
reversibility, albeit at the cost of slower response times. PEGMA-PDEA microgel does not stabilize Pickering emulsions when homogenized
at pH 3 with n-dodecane, sunflower oil, isononyl
isononanoate, or isopropyl myristate. In contrast, PEGMA-PDEA latex proved to be a ubiquitous Pickering emulsifier at
pH 10, forming stable oil-in-water emulsions with each of these four
model oils. Lowering the solution pH from 10 to 3 resulted in demulsification
within seconds. This is because these pH-responsive particles undergo
a latex-to-microgel transition, which leads to their interfacial desorption.
Six successive demulsification/emulsification cycles were performed
on these Pickering emulsions using HCl/KOH to adjust the solution
pH. Demulsification could also be achieved by purging the emulsion
solution with CO2 gas to lower the aqueous pH to 4.8. However,
complete phase separation required CO2 purging for 4 h
at 20 °C. A subsequent N2 purge raised the aqueous
pH sufficiently to induce a microgel-to-latex transition, but rehomogenization
did not produce a stable Pickering emulsion. Presumably, a higher
pH is required, which cannot be achieved by a N2 purge
alone.
%I ACS Publications