Adsorption Of Ionic And Nonionic Polymers
ADSORPTION OF IONIC AND NONIONIC POLYMERS
AT METAL OXIDE/SOLUTION INTERFACE; STRUCTURE
OF THE ADSORPTION LAYERS
S. Chibowski, M. Wiśniewska, M. Paszkiewicz
Faculty of Chemistry, Maria Curie-Sklodowska University,
Maria Curie-Sklodowska sq. 3, 20-031 Lublin, Poland
e-mail:schibows@hermes.umcs.lublin.pl
An influence of the molecular weight of the polymer, its functional groups and pH of the solution was studied on the adsorption and structure of adsorption layers at metal oxide – solution interface. Two ionic polymers were used: polyacrylic acid (PAA) and polyacrylamide (PAM) and two nonionic polymers: polyvinyl alcohol (PVA) and polyethylene glycol (PEG). MnO2 was used as an adsorbate for the polyelectrolytes and Al2O3 for nonionic polymers.
For more detailed characteristics of the studied systems (PAA‑MnO2‑NaCl, PAM-MnO2-NaCl, PVA-Al2O3-NaCl, PEG‑Al2O3‑NaCl) surface charge and dzeta potential of oxides were measured, with and without the mentioned polymers. A thickness of the adsorption layer (d) was calculated from the viscosity measurements [1].
From the obtained data, the main factors were determined which influence changes in the amount of the adsorbed polymer, its conformation on the surface of the solid, thickness and the structure of the adsorption layers.
The analysis of these data proved that the pH the solution has crucial meaning for polyelectrolyte adsorption and their electrokinetical properties. It influences the number of dissociated carboxyl groups in PAA and PAM macromolecules. These groups are responsible for bonding of polymer chains to MnO2 surface by hydrogen bridges.
The behavior of polyvinyl alcohol at metal oxide-solution interface is ruled by acetate groups, presented in its macromolecules. It was also demonstrated that the change of ionic structure of the Stern layer, depends on molecular weight of the polymer, as well as on number of acetate groups (degree of hydrolysis) in PVA chain as well as number and distribution of the
carboxyl group in PAA and PAM macromolecules.
Determined thickness of the adsorption layer is listed in Table 1.
Table1.Thickness of the adsorption layer determined for the systems: PAA‑MnO2-NaCl, PAM-MnO2-NaCl, PVA-Al2O3-NaCl, PEG‑Al2O3-NaCl; (pH=6, Cp=100ppm)
System
Molecular weight of the polymer
d [nm]
PAA-MnO2-NaCl
2000
2.72
170000
8.41
240000
11.85
PAM-MnO2-NaCl
1500
2.05
10000
4.1
PVA-Al2O3-NaCl
16000 (hyd. deg. 87%)
5.8
16000 (hyd. deg. 98%)
6.7
PEG‑Al2O3-NaCl
2000
4.8
20000
6.4
References
1. A.M’Pandou, B. Siffert, Colloids Surf., 24(1987)159.
Related articles::