Zeta Potential of Poly(methyl methacrylate) (PMMA)
in Contact with Aqueous Electrolyte–Surfactant Solutions
Posted on 2017-09-15 - 00:00
The
addition of surfactants can considerably impact the electrical
characteristics of an interface, and the zeta potential measurement
is the standard method for its characterization. In this article,
a comprehensive study of the zeta potential of poly(methyl methacrylate)
(PMMA) in contact with aqueous solutions containing an anionic, a
cationic, or a zwitterionic surfactant at different pH and ionic strength
values is conducted. Electrophoretic mobilities are inferred from
electrophoretic light scattering measurements of the particulate PMMA.
These values can be converted into zeta potentials using permittivity
and viscosity measurements of the continuous phase. Different behaviors
are observed for each surfactant type, which can be explained with
the various adsorption mechanisms on PMMA. For the anionic surfactant,
the absolute zeta potential value below the critical micelle concentration
(CMC) increases with the concentration, while it becomes rather constant
around the CMC. At concentrations above the CMC, the absolute zeta
potential increases again. We propose that hydrophobic-based adsorption
and, at higher concentrations, the competing micellization process
drive this behavior. The addition of cationic surfactant results in
an isoelectric point below the CMC where the negative surface charge
is neutralized by a layer of adsorbed cationic surfactant. At concentrations
near the CMC, the positive zeta potential is rather constant. In this
case, we propose that electrostatic interactions combined with hydrophobic
adsorption are responsible for the observed behavior. The zeta potential
in the presence of zwitterionic surfactant is influenced by the adsorption,
because of hydrophobic interactions between the surfactant tail and
the PMMA surface. However, there is less influence, compared to the
ionic surfactants. For all three surfactant types, the zeta potential
changes to more-negative or less-positive values for alkaline pH values,
because of hydroxide adsorption. An increase of the ionic strength
decreases the absolute value of the zeta potential, because of the
shielding effects.
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Khademi, Mahmoud; Wang, Wuchun; Reitinger, Wolfgang; P. J. Barz, Dominik (2017). Zeta Potential of Poly(methyl methacrylate) (PMMA)
in Contact with Aqueous Electrolyte–Surfactant Solutions. ACS Publications. Collection. https://doi.org/10.1021/acs.langmuir.7b02487
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AUTHORS (4)
MK
Mahmoud Khademi
WW
Wuchun Wang
WR
Wolfgang Reitinger
DP
Dominik P. J. Barz