Cuba-Chiem Linh T, Huynh Le, Ralston John, Beattie David A
Ian Wark Research Institute, University of South Australia, Mawson Lakes, Adelaide, South Australia 5095, Australia.
Langmuir. 2008 Aug 5;24(15):8036-44. doi: 10.1021/la800490t. Epub 2008 Jun 26.
Carboxymethyl cellulose (CMC), in solution and adsorbed on the surface of talc, has been studied with ATR FTIR spectroscopy as a function of the solution pH. The solution spectra enable the calculation of the extent of ionization of the polymer (due to protonation and deprotonation of the carboxyl group) at various pH values, yielding a value of 3.50 for the pK(app)(1/2) (pH at which half of all carboxyl groups are ionized) in a simple electrolyte solution and a value of 3.37 for the pK(app)(1/2) in solutions containing magnesium ions (3.33 x 10(-4) M). The spectra of the adsorbed layer reveal that CMC interacts with the talc surface through a chemical complexation mechanism, via the carboxyl groups substituted on the polymer backbone. The binding mechanism is active at all pH values down to pH 2 and up to pH 11. The adsorbed layer spectra reveal that protonation and deprotonation of the polymer are affected by adsorption, with an increase in the pK(app)(1/2) to a value of 4.80. Spectra of the adsorbed polymer were also acquired as a function of the adsorption time. Adsorption kinetic data reveal that the polymer most likely has two different interactions with the talc surface, with a stronger interaction with the talc edge through chemical complexation and a weaker interaction with the talc basal plane presumably through the hydrophobic interaction.
羧甲基纤维素（CMC）溶解于溶液中并吸附在滑石表面，已通过衰减全反射傅里叶变换红外光谱（ATR FTIR）对其进行了研究，考察其作为溶液pH值的函数关系。溶液光谱能够计算出聚合物在不同pH值下的电离程度（由于羧基的质子化和去质子化），在简单电解质溶液中，表观解离常数pK(app)(1/2)（所有羧基一半电离时的pH值）为3.50，在含有镁离子（3.33×10⁻⁴ M）的溶液中，pK(app)(1/2)为3.37。吸附层的光谱表明，CMC通过聚合物主链上取代的羧基，通过化学络合机制与滑石表面相互作用。这种结合机制在低至pH 2至高至pH 11的所有pH值下均有效。吸附层光谱表明，聚合物的质子化和去质子化受吸附影响，pK(app)(1/2)增加到4.80。还获取了吸附聚合物的光谱作为吸附时间的函数。吸附动力学数据表明，聚合物与滑石表面最可能存在两种不同的相互作用，通过化学络合与滑石边缘的相互作用更强，而与滑石基面的相互作用较弱，推测是通过疏水相互作用。
