Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
The Adsorption and Conformational Properties of Polyelectrolyte Complexes on the Oppositely
Charged Surface
Sedat Ondaral 1 *, Caroline Bergholtz Ankerfors 2,3 , Lars Wågberg 2
1 Department of Pulp and Paper Technology, Karadeniz Technical University, 61080 Trabzon, Turkey
2 Fibre and Polymer Technology, Royal Institute of Technology, SE-100 44 Stockholm, Sweden
3 Eka Chemicals AB, 445 80 Bohus, Sweden
Abstract-We investigated how PEC’s adsorption properties and conformation behaviors change on silicon o xide surface depending on the
molecular weight of polyelectrolytes. The findings of the present study are remarkably giving a new insight about the PEC’s properties related
to their use and performance.
By mixing oppositely charged polyelectrolytes in water,
polyelectrolyte complexes can be formed, which is driven by
the increase of entropy due to the release of small ions from
the double layers around the individual polyelectrolytes. The
main interaction force for complexation of two oppositely
charged polyelectrolytes is Columbic forces. Additionally,
hydrogen bonding, charge transfer, dipole-dipole and
hydrophobic forces play role in the different complexation
system. 1-2 Co mplexation can result in the three different form,
soluble, colloidaly stable and coacervate complexes,
depending on the factors such as mixing ratio, polyelectrolyte
concentration, pH, electrolyte concentration, nature of ionic
groups, temperature and preparation conditions. 3-5 Their uses
have grown rapidly in the large scale industrial applications,
such as coatings, binders, flocculants, as well as in
biotechnical and biomedical applications, for few decades. 6-9
For these application, it is very important to determine how
the properties of PEC change with such factors mentioned
before as well as adsorption and conformational behaviors of
PEC in both solution and on the surface.
In the present study, we mainly focused on the adsorption
properties and conformational behaviors of PECs prepared by
combining poly(allylamine hydrochloride) (PAH) and
poly(acrylic acid) (PAA) by using a confined impinging jet
(CIJ) mixer. The adsorption properties of PECs were
investigated with the aid of Stagnation Point Adsorption
Reflectometry (SPAR) and Quartz Crystal Microbalance with
Dissipation (QCM-D) using SiO2 surfaces. We found that the
PEC-A, which prepared with higher molecular weight
PAH/PAA, showed a higher adsorption to the SiO 2 surfaces
compared to the PEC-B, which prepared with lower molecular
weight PAH/PAA. The adsorption of the PEC-A also showed
a larger change in the dissipation (D), fro m the QCM -D
measurements, indicating that the adsorbed layer had a
relatively lower viscosity and a lower shear modulus for the
PEC-A. We also determined that “how PEC’s conformation
changes on the oppositely charged surface” by means of
Atomic Force Microscope (AFM). Complementary
investigations of the adsorbed layer using AFM showed that
the adsorbed layer was significantly different for PEC-A and
PEC-B and that the change in properties with adsorption time
was very different for the two types of PECs. PEC-A showed
a coalescence type of behaviour whereas this was not detected
for the PEC-B, as shown in Figure 1. The exact reason to this
difference in behaviour is not known but size determinations
of the complexes in solutions showed that they were very
stable over time and therefore, the coalescence behaviour was
concluded to be initiated by the interaction between the
complexes and the surface. AFM results for the PEC-A
showed the existence of two types of complexes with similar
size but different mechanical properties, i.e. collapsing
behaviour, when in contact with the surface. This could most
probably be linked to the phase separation of the complexes
during their preparation.
Figure 1. AFM images (amplitude mode) of PEC-A and PEC-B on
silicon oxide surface after different adsorption periods (image size
5x5 m).
In summary, these results show that the higher adsorption
amount and higher surface coverage of PECs can be achieved
by increasing molecular weight of polyelectrolytes used for
preparation of PEC. That is promising for the future
application studies related to enhancing the PEC’s
performance especially as a binder. This study was conducted
in the laboratories of Fibre Technology Department (Royal
Institute of Technology, Stockholm-Sweden).
*Corresponding author: 2Tondaral@ktu.edu.tr
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