Collapse of polymer brushes grafted onto planar ... - Wageningen UR

VOLUME FRACTION PROFILES OF ADSORBED POLYMER LAYERS
T. Cosgrove 1) , J. Marshall 1) , J. Hone 1) , F. Leermakers 2) , T.M. Obey 1) , J. Marshall 1)
1) University of Bristol, School of Chemistry,
Cantock’s Close, Bristol BS8 1TS, United Kingdom
2) Laboratory of Physical and Colloid Chemistry, Wageningen University,
Dreijenplein 6, 6703 BC Wageningen, The Netherlands
email: terence.cosgrove@bris.ac.uk
ABSTRACT
Volume fraction profiles for adsorbed polymers are central to the understanding and manipulation of colloidal
dispersions. Small-angle neutron scattering has proven to be an elegant method for determining the shape of
the volume fraction profile though there are some difficulties in dealing with concentration fluctuations. In this
presentation we shall develop the SANS methods for both on and off contrast scattering and use it together
with scaling and mean field theories to provide the most detailed shapes yet for adsorbed polymer layers on
colloidal particles. The improvement in these methods due to better resolution in particle size and momentum
transfer (Q) has made it possible to expand the studies to look at complex formation at interfaces with
surfactants and sugars.
Results and Discussion
-1
I(Q) /cm
1
0.1
0.01
Q /Å -1
0.01 0.1
Figure 1 Figure 2
(z) φ
0.1
0.01
0.001
112.1 K PEO Exponential Profiles
112.1 K PEO Scaling Profiles
112.1 K PEO Scheutjens-Fleer Profiles
0 50 100 150 200 250
Figure 1 shows the scattering obtained from a deuterated polystyrene latex with adsorbed polyethylene oxide
(110K Mw) suspended in water that has the same scattering length density as the latex. Under these
circumstances the latex is essentially invisible. However, unlike earlier data we observe strong oscillation in
the scattering from the polymer layer. This is partly due to preparing a very monodisperse latex (radii
625 ± 20 Ã and 443 ± 10 Ã) and by obtaining higher Q resolution on the D22 camera at Grenoble and NG3 at
NIST. The data have been fitted using an exponential volume fraction profile with fluctuations (solid line) and
without fluctuations (dashed line) both smeared for Q resolution. It is clear that fluctuations do contribute to
the scattering and without suitable safeguards fitting the data without fluctuations can be problematical.
z /Å
R g 112.1 K PEO