The surface forces measurement was employed to study interactions between monolayers of an anionic polyelectrolyte using chain-end-anchored poly(methacrylic acid). The polyelectrolyte layers were prepared by depositing monolayers of the poly(methacrylic acid) amphiphile onto mica. The force was repulsive and was altered by ionization and structural changes of the polyelectrolyte layers at different pH values and NaBr concentrations. The majority of negative charges was insulated by counterions, resulting in saturation of repulsion at shorter distances. The thickness of the polyelectrolyte layer was determined from the force measurement. When the carboxylic acid group was ionized by more than 10%, the polyelectrolyte chain was extended to a length about 6 times greater than that of its hypercoiled form.
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