Biennial Report 2016/2017

Selected Results
Tailoring Membrane Surface Charges: How Electrostatic Interactions
Dominate Membrane Fouling
D. Breite, M. Went, A. Prager, I. Thomas, A. Schulze
A major problem that affects membranes in an
aqueous environment is fouling. Material from the
surrounding media is adsorbed to the membrane.
The porous structure of the membranes is
therefore blocked and the permeability and the
overall performance of the membrane decrease.
According to literature the cause of these
adsorption processes are hydrophobic and
electrostatic interactions.
To further investigate the fouling caused by
electrostatic interactions a new fouling test system
was developed [1-3]. Anionic, neutral, and
cationic polystyrene particles were synthesized
and utilized for the investigation of fouling of
polyvinylidene fluoride and polyethersulfone
membranes. To identify the dominant interaction
during fouling, the membranes were also modified
using electron beam technology to gain anionic,
Figure 1: a) Zeta potential vs. pH curves of membranes with
cationic (TEPA), anionic (PSS), and zwitterionic (Lysine)
surface modifications, and b) chemical structures of the
respective charged moieties.
cationic, or zwitterionic moieties on the membrane
surface (Figure 1).
It was possible to show that fouling of anionic and
cationic membrane surfaces is dominated by
electrostatic interactions. When membrane
surface and particles were oppositely charged,
electrostatic attractive interactions occurred and
heavy fouling was observed. On the other hand,
when both surfaces were evenly charged,
electrostatic repulsive interactions occurred and
no fouling was detected.
In the case of the zwitterionic membrane surfaces
fouling was found to be pH dependent (Figure 2).
When the pH of the surrounding solution was
adjusted to be acidic or alkaline, the membrane
surface was either negatively or positively
charged, respectively. Membrane fouling was
then observed as described above when
electrostatic interactions were dominant. By
determining the zeta potential at the pH value
which was critical for membrane fouling, an
according critical zeta potential could be obtained.
This work demonstrated that electrostatic
interactions considerably impact the fouling of
polymer membranes, especially when charged
surfaces are involved.
Literature
[1] D. Breite, M. Went, A. Prager, A. Schulze, Polymers 7
(2015) 2017-2030.
[2] D. Breite, I. Thomas, M. Went, A. Prager, A. Schulze,
RSC Advances 6 (2016) 65383–65391.
[3] D. Breite, M. Went, A. Prager, A. Schulze, RSC
Advances 6 (2016) 98180-98189.
42