Departamento de Química Física I, Facultad de Química, Universidad Complutense de Madrid, 28040 Madrid, Spain.
J Colloid Interface Sci. 2013 Jun 15;400:49-58. doi: 10.1016/j.jcis.2013.03.015. Epub 2013 Mar 22.
Lithium cations are known to form complexes with the oxygen atoms of poly(oxyethylene) chains. The effect of Li(+) on the surface properties of three block-copolymers containing poly(oxyethylene) (PEO) have been studied. Two types of copolymers have been studied, a water soluble one of the pluronic family, PEO-b-PPO-b-PEO, PPO being poly(propyleneoxyde), and two water insoluble ones: PEO-b-PS and PEO-b-PS-b-PEO, PS being polystyrene. In the case of the pluronic the adsorption kinetics, the equilibrium surface tension isotherm and the aqueous/air surface rheology have been measured, while for the two insoluble copolymers only the surface pressure and the surface rheology have been studied. In all the cases two different Li(+) concentrations have been used. As in the absence of lithium ions, the adsorption kinetics of pluronic solutions shows two processes, and becomes faster as [Li(+)] increases. The kinetics is not diffusion controlled. For a given pluronic concentration the equilibrium surface pressure increases with [Li(+)], and the isotherms show two surface phase transitions, though less marked than for [Li(+)]=0. A similar behavior was found for the equilibrium isotherms of PEO-b-PS and PEO-b-PS-b-PEO. The surface elasticity of these two copolymers was found to increase with [Li(+)] over the whole surface concentration and frequency ranges studied. A smaller effect was found in the case of the pluronic solutions. The results of the pluronic solutions were modeled using a recent theory that takes into account that the molecules can be adsorbed at the surface in two different states. The theory gives a good fit for the adsorption kinetics and a reasonably good prediction of the equilibrium isotherms for low and intermediate concentrations of pluronic. However, the theory is not able to reproduce the isotherm for [Li(+)]=0. Only a semi-quantitative prediction of the surface elasticity is obtained for [pluronic]≤1×10(-3) mM.
锂离子与聚（氧乙烯）链的氧原子形成配合物。研究了锂（+）对三种嵌段共聚物的表面性质的影响，这三种嵌段共聚物含有聚（氧乙烯）（PEO）。研究了两种类型的共聚物，一种是水溶性的 Pluronic 家族，PEO-b-PPO-b-PEO，PPO 是聚（丙烯氧基），另外两种是不溶于水的：PEO-b-PS 和 PEO-b-PS-b-PEO，PS 是聚苯乙烯。对于 Pluronic，测量了吸附动力学、平衡表面张力等温线和水/空气表面流变学，而对于两种不溶性共聚物，仅研究了表面压力和表面流变学。在所有情况下，都使用了两种不同的 Li（+）浓度。由于在没有锂离子的情况下，Pluronic 溶液的吸附动力学显示出两个过程，并且随着[Li（+）]的增加而加快。动力学不是扩散控制的。对于给定的 Pluronic 浓度，平衡表面压力随[Li（+）]的增加而增加，并且等温线显示出两个表面相转变，尽管比[Li（+）]=0 时的转变不那么明显。对于 PEO-b-PS 和 PEO-b-PS-b-PEO 的平衡等温线也发现了类似的行为。发现这两种共聚物的表面弹性随[Li（+）]的增加而在整个表面浓度和频率范围内增加。在 Pluronic 溶液的情况下，发现的效果较小。使用最近的理论对 Pluronic 溶液的结果进行了建模，该理论考虑了分子可以在表面上以两种不同的状态被吸附。该理论很好地拟合了吸附动力学，并很好地预测了 Pluronic 的低浓度和中等浓度的平衡等温线。然而，该理论无法重现[Li（+）]=0 的等温线。仅对于[Pluronic]≤1×10（-3）mM，才能获得表面弹性的半定量预测。
