In the section on DLS titrations, three-component systems containing two oppositely charged polyelectrolytes and protein molecules will be discussed. This
chapter concludes with a section dedicated to the complex formation of oppositely
charged protein molecules.
Keywords AFM • DLS • Kinetics • PEC • PEM • Relaxation time • Rheology
Contents
1 Kinetics of Polyelectrolyte Complex Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
1.1 Strongly and Weakly Charged Polyelectrolytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
1.2 Polyelectrolyte Multilayer Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
1.3 Influence of Ionic Strength on the Kinetics of Polyelectrolyte Complex Formation 146
1.4 Entropy, Enthalpy and Free Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
2 Experimental Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
2.1 Dynamic Light Scattering Titrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
2.2 Force Measurements . . . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . 162
2.3 Rheology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
3 Protein–Protein Complex Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
1 Kinetics of Polyelectrolyte Complex Formation
When two oppositely charged polyelectrolytes are mixed at equal (stoichiometric)
charge ratio, a neutral complex will form. This process is schematically depicted in
Fig. 1, where one can see that before the reaction a negatively charged polymer with
ten charges is accompanied by ten positively charged counterions, and that the
positively charged polymer (also having ten charges) is accompanied by ten
negatively charged counterions. Basically, polyelectrolyte complex formation can
be regarded as an ion-exchange process where polymer–counterion pairs are
replaced by polymer–polymer ion pairs [2]. The main driving force for this process
at low salt concentrations is an increase in entropy. In Fig. 1 it can be seen that
before the reaction there are two (compound) “particles” and after the reaction there
are 21 particles: The increase in accessible volume to the Na
+ and Cl
À ions is
responsible for this.
Polyelectrolyte complexes consisting of linear polyelectrolytes will phaseseparate into a dense polymeric phase and a dilute aqueous phase. Depending on
the type of polyelectrolytes used and the ionic strength, one finds that this dense
phase is either solid-like or liquid-like. The dynamic state of the complex phase
gives clues about whether the complex is in equilibrium or whether it is likely to be
in a kinetically quenched state.
The reversibility of polyelectrolyte complex formation influences the relaxation
process, which consists of two steps. The first step is the formation of initial
polyelectrolyte complexes, with the simultaneous release of the counterions.
140
S. Lindhoud and M.A. Cohen Stuart
chapter concludes with a section dedicated to the complex formation of oppositely
charged protein molecules.
Keywords AFM • DLS • Kinetics • PEC • PEM • Relaxation time • Rheology
Contents
1 Kinetics of Polyelectrolyte Complex Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
1.1 Strongly and Weakly Charged Polyelectrolytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
1.2 Polyelectrolyte Multilayer Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
1.3 Influence of Ionic Strength on the Kinetics of Polyelectrolyte Complex Formation 146
1.4 Entropy, Enthalpy and Free Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
2 Experimental Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
2.1 Dynamic Light Scattering Titrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
2.2 Force Measurements . . . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . 162
2.3 Rheology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
3 Protein–Protein Complex Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
1 Kinetics of Polyelectrolyte Complex Formation
When two oppositely charged polyelectrolytes are mixed at equal (stoichiometric)
charge ratio, a neutral complex will form. This process is schematically depicted in
Fig. 1, where one can see that before the reaction a negatively charged polymer with
ten charges is accompanied by ten positively charged counterions, and that the
positively charged polymer (also having ten charges) is accompanied by ten
negatively charged counterions. Basically, polyelectrolyte complex formation can
be regarded as an ion-exchange process where polymer–counterion pairs are
replaced by polymer–polymer ion pairs [2]. The main driving force for this process
at low salt concentrations is an increase in entropy. In Fig. 1 it can be seen that
before the reaction there are two (compound) “particles” and after the reaction there
are 21 particles: The increase in accessible volume to the Na
+ and Cl
À ions is
responsible for this.
Polyelectrolyte complexes consisting of linear polyelectrolytes will phaseseparate into a dense polymeric phase and a dilute aqueous phase. Depending on
the type of polyelectrolytes used and the ionic strength, one finds that this dense
phase is either solid-like or liquid-like. The dynamic state of the complex phase
gives clues about whether the complex is in equilibrium or whether it is likely to be
in a kinetically quenched state.
The reversibility of polyelectrolyte complex formation influences the relaxation
process, which consists of two steps. The first step is the formation of initial
polyelectrolyte complexes, with the simultaneous release of the counterions.
140
S. Lindhoud and M.A. Cohen Stuart