Reversibly controlling the rigidity of adsorbed polycations

Changes in the properties of an adsorbed layer at a solid-liquid interface are extensively used as controllable surfaces. A gold coated quartz crystal was oxidized in an UV/O3 chamber for 15 minutes to clean the surface before conducting the QCM-D experiment About 250μL of 300μg/mL PLL hydrobromide in 100 mM NaBr solution at pH 7.4 was absorbed onto a gold coated quartz crystal using a QCM-D for 30 minutes. The rigidity of an adsorbed polyelectrolyte layer can also be controlled by changing the pH of a solution and will depend on the pKa of the functional group of the polymer. The properties of PLL at a solid-liquid interface were studied using ATR/FTIP and spectra were collected at a gain of 8 and resolution of 2 cm-1 with 50 scans of each sample. The divalent SO4-2 ion cross linked the adsorbed polycationic chain via electrostatic interactions and resulted in more rigid layer.