Master Assignment

Polyelectrolytes for an improved aquaporin embedded top layer for next generation

An emerging separation and desalination technology that shows great potential is forward osmosis
(FO). FO uses osmotic pressure gradients to transport water across a semipermeable membrane. These
membranes are usually based on reverse osmosis (RO) membranes, which lack, however, suitability for
FO applications [1]. A way to create new membranes truly optimized for FO, is by self-assembly of
oppositely charged polyelectrolytes (PEs) on the surface of a porous ultrafiltration support
membrane. In this so-called Layer-by-Layer (LbL) assembly, the support membrane is alternatively
exposed to polycations and polyanions [3]. Such a PEM coating is easily applied on all geometries.
In this study, the focus will be to create a PEM based membrane suitable for FO. PEMs will be made
as dense as possible by means of crosslinking and the use of different kinds of PEs. Subsequently
the layer will be characterized and tested on its FO performance. To make these membranes more even
more suitable, aquaporin containing vesicles can be incorporated within the PEM layer to enhance
the permeation and rejection properties [2].

Creating more intrinsic bonds will increase the rejection properties of an active membrane layer.
Crosslinking is a manner to create more intrinsic bonds and can easily be done by heat or a
catalyst. Many moieties of PEs are amines or carboxylic acids which can easily be crosslinked, as
shown in Figure 1.
Crosslinking of PEMs has already shown to be a promising way to create an active layer capable of
retaining salts [4]. For FO purposes, the layer has to be as dense as possible in order to cope
with highly concentrated saline streams. In order to control the layer density, different materials
can be used that influence the intermolecular distance.
In this MSc project, different types of crosslinking techniques and materials will be evaluated.
Materials will vary from aliphatic, branched, to aromatic structures while controlling and
monitoring the performance of the membrane.

PEMs can be made by dip-coating silicon wafers or membranes in a solution containing a certain
polyelectrolyte. The growth and properties of these multilayers can be monitored by using
techniques like reflectometry, ellipsometry, contact angle, and

Crosslinking can be done catalyzed or non- catalyzed. Non-catalyzed reactions take place under the
influence of heat. To see if crosslinking has  taken  place,  the  layer  will  be  characterized
using FTIR and NMR measurements.
The knowledge obtained from model surfaces (silicon wafers) will be translated to hollow fiber
membranes. The membranes will be coated and crosslinked under the same conditions as the model
surfaces and will be tested on their performances in forward osmosis operating conditions.

Figure 1: Crosslinking of polyelectrolyte multilayers [5].

 zeta potential measurements.                                                                      
1.          Shaffer, D.L., et al., Forward osmosis: Where are we now?, Desalination, 2015. 356.
2.          Tang, C., et al., Biomimetic aquaporin membranes coming of age, Desalination, 2015. 368.
3.          Decher, G., Fuzzy Nanoassemblies: Toward Layered Polymeric Multicomposites, Science, 1997. 277(5330).
4.          Park, J., et al., Desalination membranes from pH‐controlled and thermally‐crosslinked layer‐by‐layer assembled multilayers, Journal of Materials Chemistry, 2010. 20(11).
5.          Sullivan, D.M. and M.L. Bruening, Ultrathin, cross‐linked polyimide pervaporation membranes prepared from polyelectrolyte multilayers, Journal of Membrane Science, 2005. 248(1‐2).