Structures and Interactions of Polyelectrolyte Brushes Studied by Surface Forces Measurement

用表面力测量方法直接研究了电离化的聚(L-谷氨酸)和聚(L-赖氨酸)在水中的相互作用。以聚合度PLGA(n=21，44和48)或PLL(n=41和52)为亲水基团的两亲分子通过Langmuir-Blodgett沉积制备刷层。测量和分析了不同pH、盐浓度、聚电解质链长度和链密度时的表面力分布，结果表明，电刷层中几乎所有的电离基团都被偶离子中和。在不同的pH下，电刷层的空间斥力随聚电解质电离度的增加而增大，而在一定的pH范围内(0.43~10 mm)，空间斥力随盐浓度的增加而减小，这可能与…有关空间排斥出现的距离(D_0)相当于扩展聚电解质分子长度的两倍。对于相同聚合度的刷子，在所研究的pH和盐条件下，该距离D_0基本保持不变。L_0是聚电解质链长度的两倍，定义为D_0-6(Nm)，其中6 nm是聚电解质两亲分子中长链长度的两倍，并且与聚电解质的聚合度n成正比。通过微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。基于空间作用力与反离子渗透压关系的模型，推导出描述应力分布的方程，在链密度~0.2链/nm^2处观察到聚电解质刷的密度依赖于密度的转变，并用反离子结合的变化来解释。较少

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