The adsorption of a strong, highly charged cationic polyelectrolyte to a kraft lignin thin film was investigated as a function of the adsorbing solution conditions using the quartz crystal microbalance. The polyelectrolyte, PDADMAC, with a molecular weight of 100 kDa and one cationic charge group per monomer, was adsorbed to the anionically charged lignin film in the pH range 3.5—9.5 in electrolyte solution of 0.1 to 100 mM NaCl. At low pH, the adsorbed amount of PDADMAC was minimal, however, this increased as a function of increasing pH. Indeed, the surface excess increased significantly at about pH 8.5, where ionization of the phenolic groups on the lignin macromolecule may be expected. Furthermore, at this elevated pH, the adsorbed amount of PDADMAC decreased as the ionic strength of the solution increased above 1 mM. This is due to the competitive adsorption of counterions to the lignin surface and indicates that the adsorption of PDADMAC to lignin is of a pure electrosorption nature.
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机译：使用石英晶体微量天平，研究了强力，高电荷的阳离子聚电解质在牛皮纸木质素薄膜上的吸附情况，这与吸附溶液的条件有关。在0.1至100 mM NaCl的电解质溶液中，分子量为100 kDa且每个单体一个阳离子电荷基团的聚电解质PDADMAC被吸附到pH范围为3.5-9.5的带阴离子的木质素膜上。在低pH下，PDADMAC的吸附量很小，但是，随着pH的增加，吸附量增加。实际上，表面过量在约pH 8.5时显着增加，其中可预期木质素大分子上酚基的电离。此外，在该升高的pH下，随着溶液的离子强度增加至1mM以上，PDADMAC的吸附量降低。这是由于抗衡离子在木质素表面上的竞争性吸附，表明PDADMAC对木质素的吸附具有纯电吸附性质。
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