58 Sara Llamas, Laura Fernández-Peña, Ana Mateos-Maroto et al.
Adapted from Reference [26] with permission from The Royal Society of Chemistry.
Figure 8. Charge inversion for (PDADMAC + PSS)n multilayers adsorbed from a NaCl
solution of concentration 50 mM as was obtained by the Kelvin probe.
In this type of applications, the particle is removed after the coating by a
chemical procedure strongly dependent on the particle nature, e.g., polystyrene
latex particles are dissolved in tetrahydrofuran, whereas SiO 2 particles are
removed using HF [203, 204]. It is worth mentioning that the solvent cannot
destroy or modify the multilayers.
5.2. Assembly Driving Forces: Electrostatic vs. Entropic Issues
The fabrication process of LbL polyelectrolyte multilayers involves an
intricate balance between several type interactions in which participate
the different component of the system [205]. The understanding of the role of
the different interactions requires considering the appearance of a complex
interplay between electrostatic and entropic factors that determine the
adsorption, and the final properties of LbL multilayers.
For long time, it was considered that the direct electrostatic interactions
between polyelectrolytes in adjacent layers was the only driving force in the
assembly, with the charge inversion of the surface after each adsorption step
playing a central role. Therefore, it can be expected that the adsorption follows
once the charge neutralization of the surface has been reached, presenting the
final layer a charge of opposite sign than that of the bare surface [76, 206].