Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, 30-239 Cracow, Poland.
Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, 30-239 Cracow, Poland.
J Colloid Interface Sci. 2015 Jan 15;438:249-258. doi: 10.1016/j.jcis.2014.09.071. Epub 2014 Oct 5.
Physicochemical characteristics of tannic acid (tannin) suspensions comprising its stability for a wide range of ionic strength and pH were thoroughly investigated using UV-vis spectrophotometry, dynamic light scattering and microelectrophoretic measurements. These studies allowed to determine the hydrodynamic diameter of the tannic acid that was 1.63 nm for the pH range 3.5-5.5. For pH above 6.0 the hydrodynamic diameter significantly decreased as a result of the tannin hydrolysis. The electrophoretic mobility measurements confirmed that tannic acid is negatively charged for these values of pH and ionic strength 10(-4)-10(-2) M. Therefore, in order to promote adsorption of tannin molecules on negatively charged mica, the poly(allylamine hydrochloride) (PAH) supporting monolayers were first adsorbed under diffusion transport conditions. The coverage of polyelectrolyte monolayers was regulated by changing bulk concentration of PAH and the adsorption time. The electrokinetic characteristics of bare and PAH-covered mica were determined using the streaming potential measurements. The zeta potential of these PAH monolayers was highly positive, equal to 46 mV for ionic strength of 10(-2) M. The kinetics of tannin adsorption on these PAH supporting monolayers was evaluated by the in situ the streaming potential measurements. The zeta potential of PAH monolayers abruptly decreases with the adsorption of tannin molecules that was quantitatively interpreted in terms of the three-dimensional electrokinetic model. The acid-base characteristics of tannin monolayers were acquired via the streaming potential measurements for a broad range of pH. The obtained results indicate that it is possible to control adsorption of tannin on positively charged surfaces in order to designed new multilayer structures of desirable electrokinetic properties and stability.
使用紫外-可见分光光度法、动态光散射和微电泳测量技术，深入研究了单宁酸（单宁）悬浮液的物理化学特性，包括其在广泛的离子强度和 pH 值范围内的稳定性。这些研究确定了单宁酸的水动力直径在 pH 值为 3.5-5.5 范围内为 1.63nm。对于 pH 值高于 6.0 的情况，由于单宁酸的水解，水动力直径显著减小。电泳迁移率测量证实，对于这些 pH 值和离子强度 10(-4)-10(-2)M 的值，单宁酸带负电荷。因此，为了促进单宁分子在带负电荷的云母上的吸附，首先在扩散传输条件下吸附聚（盐酸烯丙胺）（PAH）支撑单分子层。通过改变 PAH 的体相浓度和吸附时间来调节聚电解质单分子层的覆盖率。使用流动电势测量法确定裸云母和 PAH 覆盖云母的电动特性。这些 PAH 单层的动电电位非常正，对于离子强度为 10(-2)M 时等于 46mV。通过原位流动电势测量评估单宁酸在这些 PAH 支撑单分子层上的吸附动力学。PAH 单层的动电电位随着单宁酸分子的吸附而急剧下降，这可以根据三维动电模型进行定量解释。通过流动电势测量获得了单宁酸单分子层的酸碱特性，涵盖了广泛的 pH 值范围。所得结果表明，有可能控制单宁酸在带正电荷表面上的吸附，以设计具有理想动电特性和稳定性的新多层结构。
