Adsorption of Polyelectrolytes onto Charged Surfaces 31is possible to highlight: charge density of the polymer chains and of the
surface [13, 22-24], polymer concentration [22, 25], ionic strength [26-32] and
counterion nature [33, 34], pH [35] and temperature [36], as well as solvent
quality for the polymer [37, 38]. A quantitive understanding of the effect of
such parameters is important due to their recognized implication in the control
of the structure of the layer formed. This is strongly dependent on the
conditions and procedures used during the adsorption process. The effect of
the aforementioned variables can be easily understood considering how they
modify the balance between the different forces involved in the system under
study. It is worth mentioning that the contribution of non-electrostatic
interactions, such as entropic contributions or hydration forces [19], must be
taken into account because, in many cases, they become the main driving force
of the adsorption of some polymers. Therefore, the different interactions, and
the balance between them, are essential on the understanding of both the
adsorption processes (adsorption kinetics) and the final properties of the
adsorbed layers (thickness, composition, adsorbed mass, etc.) [39-42].
In recent years, many theoretical approaches, including mean-field
numerical calculations [43, 44] and Monte-Carlo simulations [45-47], and
experimental techniques, such as ellipsometry, quartz crystal microbalance and
different spectroscopy providing information of the thickness of the adsorbed
layers or neutron reflectivity which gives information of the density profile
within the layers [13, 22, 25, 48-50], have been used to deepen on the
understanding of the adsorption processes. However, it is important to stress
that the specific nature of the polymers studied can influence critically in the
adsorption mechanism. This introduces an additional level of complexity on
the study of the adsorption phenomena, being necessary to avoid the
generalization on the study of such systems [51]. Thus, the understanding of
the adsorption of polyelectrolytes onto surfaces has become a challenge not
only for physician or chemistry, but also for biologists, engineers or material
scientifics.
This chapter presents a comprehensive review on the main theoretical
and experimental aspects related to the interaction of polyelectrolytes
and charged surfaces, with the main focus on the description of the a
dsorption processes of polyelectrolyte onto surfaces bearing oppositely
charged, including polyelectrolyte multilayers. Special attention will be paid to
the physico-chemical parameters that allow triggering the adsorption of
polymers onto solid surfaces and the properties of the layers.