Structures and Interactions of Polyelectrolyte Brushes Studied by Surface Forces Measurement

利用表面力测量直接研究了聚l -谷氨酸（PLGA）和聚l -赖氨酸（PLL）在水中的相互作用。采用Langmuir-Blodgett沉积法制备了两亲分子，分别含有PLGA（聚合度，n = 21、44和48）或PLL （n = 41和52）作为亲水性基团。在不同的pH值、盐浓度、聚电解质链长和链密度下，测量并分析了由远程双电层斥力和短程立体斥力组成的表面力分布。由双层斥力得到的表面电位表明，电刷层中几乎所有的电离基团都被反电势中和。电刷层的位阻斥力随pH值的变化而增大，随盐浓度（0.43 ~ 10 mM）的增加而减小，这可能是由于反离子渗透压的降低。空间排斥力出现的距离（D_0）对应于扩展的聚电解质分子长度的两倍。对于相同聚合度的电刷，在pH和盐条件下，该距离D_0几乎保持不变。作为聚电解质链长度的两倍，L_0定义为D_0 - 6 (nm)，其中6 nm是聚电解质两亲体中长烷基链长度的两倍，并发现L_0与聚电解质的聚合程度n成正比。通过区分力分布得到的应力分布，根据距离进行缩放，以提供不同聚合物链长度的相同分布。根据一个将空间作用力归因于反离子渗透压的模型，推导出了描述应力分布的方程。在约0.2链/nm^2的链密度下观察到聚电解质电刷中的密度依赖性转变，这可以通过反离子结合的变化来解释。少

Interactions between opposed brash layers of polyelectrolytes, ionized poly(L-glutamic acid) (PLGA) or poly(L-lysine) (PLL), in water were directly investigated using the surface forces measurement. The brush layers were prepared by the Langmuir-Blodgett deposition of amphiphiles bearing PLGA (degree of polymerization, n = 21,44 and 48) or PLL (n = 41 and 52) as hydrophilic groups. Surface force profiles, consisting of a long-range electrical double layer repulsion and a short-range steric repulsion, were measured and analyzed with varying pH, salt concentration, and polyelectrolyte chain length and chain density.The surface potential obtained from the double layer repulsion indicated that nearly all of the ionized groups in the brush layers were neutralized by couterions. The steric repulsion of the brush layer increased with increasing the ionization degree of polyelectrolytes by varying pH, while it decreased with increasing salt concentration (0.43 〜 10 mM) at a fixed pH likely due … More to a decrease in the osmotic pressure of the counterions.The distance at which the steric repulsion appeared (D_0) corresponded to twice the length of an extended polyelectrolyte molecule. This distance D_0 remained practically the same under the pH and salt conditions studied for the brush of an identical polymerization degree. Twice the length of polyelectrolyte chains, L_0 was defined as D_0 - 6 (nm) where 6 nm was twice the length of the long alkyl chains in polyelectrolyte amphiphiles, and found to be proportional to the polymerization degree of polyelectrolyte n. The stress profiles, obtained by differentiating the force profiles, were scaled according to the distance to provide identical profiles for different polymer chain lengths. An equation describing the stress profiles was derived based on a model that attributed the steric force to the osmotic pressure of the counterions.The density-dependent transition in polyelectrolyte brushes was observed at a chain density 〜 0.2 chain/nm^2, which was interpreted by the change in the counterion binding. Less