Coating of Material Surfaces with Layer-by- Layer Assembled Polyelectrolyte Films - Biological and Biomedical Coatings: Processing and Characterization - page 336

ProcessingParametersInfluencingFilmGrowthandStructure
Driving Forces for Film Buildup

Figure 8.2 presents a schematic of all the techniques that can be employed to character-
ize film growth for films deposited on a supporting material. The growth of linearly and
exponentially growing films can indeed be followed by quartz crystal microbalance with
dissipation monitoring (QCM-D). The driving forces behind polyelectrolyte deposition
using the LbL technique in order to form PEM have been already widely described and
reviewed (von Klitzing 2006). These include electrostatic interactions as well as nonelectro-
static interactions, including short-range interactions such as hydrophobicity (Guyomard
et al. 2005), hydrogen bonds (Sukhishvili and Granick 2002), van der Waals forces, charge
transfer halogen interactions (Wang, Ma 2007), and possibly covalent bonds formed by
click chemistry (Kinnane, Wark 2009). Thus, both the intrinsic properties of the polyelec-
trolytes themselves (structure of the polyelectrolyte, charge density, chain stiffness) and
the physical and chemical properties of the suspending medium (presence and type of salt,
pH) are key parameters. Importantly, it is now acknowledged that the driving force behind
multilayer formation is not only of electrostatic origin, but also the gain in entropy due to
the release of counterions (Dubas and Schlenoff 1999; von Klitzing 2006), very similar to
what is observed in the formation of polyelectrolyte complexes (Sukhishvili et al. 2006).

Different Deposition Methods: Dip Coating, Spraying, Spin Coating

Various depositing methods have already been proposed for LbL buildup, including dip
coating (Decher et al. 1992), spin coating (Jiang et al. 2004; Lee et al. 2001), and spraying
(Schlenoff et al. 2000). The most common to date is probably dip coating. Shim et al. (2007)
recently developed a new dewetting method that appears to be efficient, economical,
and fast, and could be used to create unique adsorption topographies, including fractal
networks and aligned fibers. For future use and industrial applications of LbL films, the
total time required for film preparation and the anchorage of the layer to the underlying

AFM (film topography) Top of the film

Fim growth :
- QCM-D
- OWLS
- Ellipsometry
- UV-vis spectrum

5 MHz

ATR-FTIR

Infrared spectroscopy:
Secondary structure

15 MHz

AFM nano, indentation
Film stiffness, E 0 25 MHz

Z-structure

35 MHz

Supporting material (SiO 2 , gold...)

FIGURE 8.2
Scheme of different techniques used to investigate LbL film buildup onto a planar supporting material. Film
growth can be followed by quartz crystal microbalance (QCM-D), optical waveguide lightmode spectros-
copy (OWLS), UV-visible spectrometry, and ellipsometry. Film chemical structure can be probed by Fourier-
transform infrared spectroscopy, and z -structure can be imaged by confocal laser scanning microscopy (CLSM)
for films thicker than ~800 nm. AFM can be used both in topography mode to image film surface and in force
mode to perform nanoindentations (AFM nanoindentation) to determine film Young's modulus, E 0 . E 0 is a
parameter characterizing film's mechanical properties.