W. Richard Bowen and Nidal Hilal 4

144 5. AFM AND DEvELOPMENT OF (BIO)FOULINg-REsIsTANT MEMBRANEs
small pieces of membrane are necessary for experiments to be undertaken.
Ultimately the direct measurements of the AFM will help to assist
in the development of new membranes with more fouling-resistant properties.
(Further information on ES 404 and XP 117 is given in Chapter 4.)
5.3 ModIfICAtIon of MEMbrAnES
The development of high-performance membranes involves the
selection of a suitable material and the formation of this material into a
desired membrane structure. However, it is often necessary to modify the
membrane material or the structure to enhance the overall performance
of the membrane. The field of membrane technology is extremely broad,
and the applicability of surface modification for different types of membranes
is equally diverse. Polymeric membranes of nearly every variety
have been utilised in the literature as substrate for polymer modification
by the addition of another polymer.
There are many techniques for the attachment of polymers to membrane
surfaces. Some of these techniques, such as electrochemical and
�-irradiation, require continuous application of current or radiation
throughout the polymerisation process. Others, such as UV-initiation,
electron beam deposition, plasma treatment and silanisation, create reactive
sites for subsequent formation of the polymer in situ, in general by
free radical polymerisation. Whole macromolecules can be incorporated
either by their cross-linking within the pores or by specific attachment of
polymer chains to the membrane pore surfaces. Such modification methods
are commonly applied to improve various membrane properties,
including improvement of their surface-fouling resistance. Rendering the
membrane surface more hydrophilic is a widely used method to reduce
their tendency to become fouled.
Modification by photo-initiated graft polymerisation with various
hydrophilic monomers has been extensively applied to vary the hydrophilicity
of the membrane surface. Acrylic acid, hydroxyethyl methacrylate
(HEMA), poly(ethylene glycol) derivatives and vinyl pyrolidinone are
examples of such hydrophilic monomers. Improvement in membrane fouling
tendency has been reached after modification with such hydrophilic
monomers [16–18].
5.3.1 Modification of Membranes with Quaternary
Ammonium Salts
Quaternary 2-dimethyl-aminoethylmethacrylate (qDMAEMA) was
chosen for the modification of PES and polyvinylidene fluoride (PVDF)
membranes using photo-initiated graft copolymerisation method [1, 19, 20].