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Studies on the cofactor/PEO flocculation systems: In situ structural and viscoelastic analyses of cofactor/PEO complexes by QCM-D

The cofactor/polyethylene oxide (PEO) flocculation systems were studied in terms of in situ interactions between PEO and cofactor molecules on gold surfaces using a quartz crystal microbalance with energy dissipation monitoring (QCM-D). The influence of the initial PEO concentration, the order of sequential injections of PEO and cofactor and the cofactor/PEO mass ratio in mixtures on the obtained QCM-D data were investigated. A condensed polymer between hydroxyldiphenylsulphone monosulphonic acid and formaldehyde (PAL) was used as a cofactor. The frequency shift (∆ƒ) resulting from the PEO injection was not susceptible to the initial PEO concentration in the range from 0.01 to 1 g/L. In contrast, the ∆ƒ value induced by the injection of PAL after the PEO injection was significantly affected by the initial PEO concentration. The absolute values of energy dissipation shift (∆D)/∆ƒ values showed that the viscoelasticity of the PEO layer adsorbed on the gold surface of the QCM-D sensor also increased with increasing the initial PEO concentration. When a PAL/PEO mixture with the mass ratio of 4/1 was used, a remarkable change in ∆ƒ was observed, compared with PAL or PEO only. The minimum |∆D/∆ƒ| value was observed at a PAL/PEO mass ratio around 2. These results indicate that PAL/PEO complexes formed on the gold surface of the QCM-D sensor have more expanded but rigid conformations. These structural changes of the PAL/PEO complexes may bring about the effective flocculation development of colloidal particles present in pulp slurry of papermaking. Thus, even though the present studies of adsorption behavior of PEO and cofactor molecules on the gold surface of QCM-D are just based on model experiments, significant information concerning the practical cofactor/PEO flocculation systems may be obtained from the ∆ƒ and ∆D values.