Counterions in poly(allylamine hydrochloride) and poly(styrene sulfonate) layer-by-layer films.
The amount of counterions in layer-by-layer (LBL) films of poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS) has been determined with X-ray photoelectron spectroscopy (XPS) for films prepared from solutions with various NaCl concentrations. Sodium and chloride counterions are present in LBL films produced from salt solutions, which are located at the surface and in the bulk of the films. The percentage of bulk counterions increases with the ionic strength of the polyelectrolyte before reaching a constant value. The bulk sodium/sulfur percentage ratios tend to 0.8 for samples washed with pure water and for samples washed with NaCl aqueous solutions, while the bulk chlorine/nitrogen percentage ratios tend to 0.5 for the same samples. The ratio between the percentages of polyelectrolyte ionic groups lies close to unity for all samples, indicating that counterions do not contribute to charge compensation in the polyelectrolyte during the adsorption process. The presence of counterions in LBL films is explained by Manning condensation near the polyelectrolyte ionic groups, leading to inter-polyelectrolyte ionic bondings via ionic networks. It is believed that condensation leads to the formation of NaCl crystallites in these LBL films, which was confirmed by X-ray diffraction measurements.
Lourenço
João M C
JM
CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal.
Ribeiro
Paulo António
PA
Botelho do Rego
Ana Maria
AM
Braz Fernandes
Francisco M
FM
Moutinho
Augusto M C
AM
Raposo
Maria
M
D003460:Crystallization; D006851:Hydrochloric Acid / Q000737:chemistry*; D008567:Membranes, Artificial; D011073:Polyamines / Q000737:chemistry*; D011137:Polystyrenes / Q000737:chemistry*; D012680:Sensitivity and Specificity; D012965:Sodium Chloride / Q000737:chemistry; D013052:Spectrometry, X-Ray Emission / Q000379:methods; D013499:Surface Properties; D014961:X-Ray Diffraction
D008567:Membranes, Artificial; D011073:Polyamines; D011137:Polystyrenes; C063994:polyallylamine; D012965:Sodium Chloride; C003321:polystyrene sulfonic acid; D006851:Hydrochloric Acid