不同pH条件下木质素磺酸钠的静电逐层自组装研究

以来源于造纸废液中的木质素磺酸钠(SL)为研究对象,利用静电逐层自组装技术,与聚二烯丙基二甲基氯化铵(PDAC)交替吸附,制备木质素磺酸钠的自组装多层吸附膜.研究了不同pH值条件下木质素磺酸钠在固体表面的静电吸附规律.木质素磺酸钠的自组装过程用紫外-可见光吸收光谱来监控,而自组装膜的表面形貌用原子力显微镜来观察.研究表明,SL与PDAC多层吸附膜的紫外-可见光吸收光谱强度随层数增加而线性增长,说明SL/PDAC多层吸附膜的厚度增长是以逐层自组装的方式进行的.木质素磺酸钠浸渍溶液的pH值对多层吸附膜的厚度和表面形貌产生重要的影响.在所研究的pH范围内,pH值越低,越有利于生成吸光度高的自组装膜,而得到的自组装膜的表面粗糙度越大。

pH EFFECT ON ELECTROSTATIC LAYER-BY-LAYER SELF-ASSEMBLY OF SODIUM LIGNOSULFONATE

Sodium lignosulfonate(SL),recovered from spent pulping liquor,has been used as a polyanion to build up multilayer films through an electrostatic sequential adsorption process by using poly(diallyldimethylammonium chloride)(PDAC) as the polycation,and the effect of pH value on the electrostatic layer-by-layer self-assembly has also been studied in this work.The electrostatic sequential adsorption process was monitored by UV-Vis spectrosxopy,and the morphology of the SL/PDAC multilayers was observed by AFM.Results show that during the sequential adsorption process,the UV-Vis absorbance of the SL/PDAC multilayers increases linearly,indicating that the thickness of multilayes increases in a layer-by-layer manner.The solution pH has a significant influence on the thickness and morphology of the SL/PDAC multilayers.In the studied pH value range,the lower is the solution pH,the higher is the UV-Vis absorbance and the larger is the roughness of the multilayer films.This phenomenon is caused by the specific molecular structure of lignosulfonate,and its conformation characteristics in solutions with different pH values.The sodium lignosulfonate exhibits different ionization degrees in the solutions with different pH values,because it includes not only sulfuric groups,but also carboxylic and phenolic groups.Although sulfuric groups can ionize at any pH value,but the ionization degrees of carboxylic and phenolic groups in the solutions increase with increasing pH values.The higher absorbance and the larger roughness of the layer-by-layer films can be attributed to the low ionization degree and the shrinkage conformation of sodium lignosulfonate in the solution with the low pH value.This work is helpful for understanding the adsorption characteristics of SL at a molecular level,and further expanding functionalities of SL through manipulation of the adsorption capacity by changing solution pH values.