Biofouling of polymeric membranes
is a severe problem
in water
desalination and treatment applications. A fundamental understanding
of biofouling mechanisms is necessary to control biofouling and develop
more efficient mitigation strategies. To shed light on the type of
forces that govern the interactions between biofoulants and membranes,
biofoulant-coated colloidal AFM probes were employed to investigate
the biofouling mechanisms of two model biofoulants, BSA and HA, toward
an array of polymer films commonly used in membrane synthesis, which
included CA, PVC, PVDF, and PS. These experiments were combined with
quartz crystal microbalance with dissipation monitoring (QCM-D) measurements.
The Derjaguin, Landau, Verwey, and Overbeek (DLVO) and the extended-DLVO
(XDLVO) theoretical models were applied to decouple the overall adhesion
interactions between the biofoulants and the polymer films into their
component interactions, i.e., electrostatic (El), Lifshitz–van
der Waals (LW), and Lewis acid–base (AB) interactions. The
XDLVO model was found to predict better the AFM colloidal probe adhesion
data and the QCM-D adsorption behavior of BSA onto the polymer films
than the DLVO model. The ranking of the polymer films’ adhesion
strengths and adsorption quantities was inversely proportional to
their γ–values. Higher normalized adhesion
forces were quantified for the BSA-coated colloidal probes with the
polymer films than the HA-coated colloidal probes. Similarly, in QCM-D
measurements, BSA was found to cause larger adsorption mass shifts,
faster adsorption rates, and more condensed fouling layers than HA.
A linear correlation (R2= 0.96) was obtained
between the adsorption standard free energy changes (ΔGads°) estimated for BSA from the equilibrium QCM-D adsorption experiments
and the AFM normalized adhesion energies (WAFM/R) estimated for BSA from the AFM colloidal probe
measurements. Eventually, an indirect approach was presented to calculate
the surface energy components of biofoulants characterized by high
porosities from Hansen dissolution tests to perform the DLVO/XDLVO
analyses.