Structures and Interactions of Polyelectrolyte Brushes Studied by Surface Forces Measurement

采用表面力测量法直接研究了聚电解质（离子化聚（L-谷氨酸）（PLGA）或聚（L-赖氨酸）（PLL））在水中相对刷层之间的相互作用。通过Langmuir-Blodgett沉积带有PLGA（聚合度，n = 21、44和48）或PLL（n = 41和52）作为亲水基团的两亲物来制备刷层。通过改变pH值、盐浓度、碳链长度和碳链密度，测量和分析了刷层表面力分布，包括长程双电层排斥和短程空间排斥，由双电层排斥得到的表面电势表明刷层中几乎所有的离子基团都被反离子中和.刷层的空间排斥力随着聚电解质的电离度的增加而增加，通过改变pH值，而在固定pH值下，随着盐浓度的增加（0.43 × 10 mM）而降低，可能是由于 ...更多信息 空间位阻出现的距离（D_0）相当于伸展的双链分子长度的两倍。对于相同聚合度的刷，在所研究的pH和盐条件下，该距离D_0实际上保持相同。L_0为双链长的2倍，定义为D_0 - 6（nm），其中6 nm为双链两亲分子长链长度的2倍，并与双链聚合度成正比。通过区分力曲线获得的应力曲线根据距离缩放，以提供不同聚合物链长度的相同曲线。基于将空间位阻力归因于反离子渗透压的模型，我们推导出了描述应力分布的方程，在链密度大于等于0.2 chain/nm^2时，观察到了反离子刷的密度依赖性转变，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