a) b - École Polytechnique de Montréal

2.4.1.1.9 LbL Deposition on Curved Surfaces
Numerous investigations for adsorption of polymer on rough and corrugated(Blunt, Barford, &
Ball, 1989) or sinusoidal(Hone, Ji, & Pincus, 1987) substrate surfaces have been performed. The
first investigations on macroscopically curved bodies was carried out by Alexander(Alexander,
1977). Of considerable interest is the adsorption of strongly charged polymers on oppositely
charged spheres(Golestanian & Sens, 1999; Gurovitch & Sens, 1999; Wallin & Linse, 1996) and
cylinders(Kunze & Netz, 2002; Odijk, 1980). It has been found that when the radius of the
curved surface is much larger than the polymer size, this effect can be neglected. But when the
polymer size is large enough, surface curvature has a great effect on polyelectrolyte adsorption
on the substrate, whereas the electrostatic energy of the adsorbed polyelectrolyte layer depends
strongly on curvature. Very small spherical substrates need a large amount of electrostatic energy
to bend a charged polymer around them(Mateescu, Jeppesen, & Pincus, 1999; Nguyen &
Shklovskii, 2001). Curvature disfavors adsorption of long, strongly charged polyelectrolytes at
too low salt concentration, due to self-repulsion of the charged chains.
2.4.1.1.10 Effect of Roughness on the Multilayer Thickness
The adsorbed polymer layer can be described in terms of loop and tail size distributions (Figure
2-37). It has been observed that the thickness of the adsorbed layer increases with an increase in
the adsorption of loopy structures, leading to the deposition of correspondingly large amounts of
polyelectrolyte. The relative weight of loops and tails in an adsorbed layer is a measure of
entanglement of free polymers to this layer. Loops due to binding to the substrate at both ends
are more prone to entanglements than tails. On the other hand, polymer loops dangling from the
surface into the solution may entangle with free chains. Consequently, loop size distribution
governs coupling between the bulk and the interface(Adjari et al., 1994). The monomers close to
the wall mainly belong to loops, whereas the external part of the layer is mostly built up by the
tails. This fold-forming of polymer chains (loops and tails) leads to an increase in film
roughness. As the polymer concentration increases, the film surface roughness increases due to
entangling more polymer chains to loops and tails. Surface roughness is also enhanced by
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