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

Figure 2 show a semi-log comparison of volume fraction profiles obtained from fits to the on-contrast layer
scattering (black lines) and interference scattering (red lines) for 112 kD PEO at full surface coverage. The
calculated radius of gyration (Rg) for 112 kD PEO is also shown. Three different functional forms have been
chosen to fit the data, an exponential (as in Figure 1), a scaling profile and a profile generated by a modified
Scheutjens Fleer (SF) theory. The profiles in the last case overlap completely. Further examples will be
shown and the results indicate that up to ca 100k Mw the SF model can quantitatively predict the scattering
data. Beyond this molecular weight as tails become progressively more extended and dilute the scattering
becomes progressively less sensitive to the layer extent.
Other systems that will be discussed include grafted and physically adsorbed PEO layers complexing with
surfactants and cyclodextrins. Figure 3 below shows the volume fraction profiles for a grafted PEO layer and
the effect of addition of α-cyclodextrin. Cyclodextrin forms spontaneous inclusion complexes with PEO in
solution that are insoluble and precipitate. In the case of a grafted layer geometric constraints would prevent
a complete complexation( the cyclic sugar threads on to the chain starting at one end). The data here show
that these complexes can form at interfaces, causing the chains to stiffen and expand.
Volume fraction
0.4
0.3
0.2
0.1
0.0
Increased CD
concentration
5.7Å αααα cyclodextrin
0 100 200
z/Å
300 400
References
1. Fleer, G.J., Cohen Stuart, M.A., Scheutjens, J.M.H.M., Cosgrove, T., Vincent, B. Polymers at Interfaces,
Chapman and Hall, London, 1993.
2. Auvray, L., Auroy, P. Neutron, X-Ray and Light Scattering; Linder, P. and Zemb, T., Eds., Elsevier
Science Publishers, B.V., Amsterdam, 1991.
3. Hone, J.H.E., Cosgrove, T., Saphiannikova, M., Obey, T.M., Crowley, T.L., 2002. Langmuir 18, 855-864.