PS-b-PAA两亲性嵌段聚电解质在水溶液中的聚集行为及其流变特性

以两嵌段共聚物聚苯乙烯-b-聚丙烯酸(PS-b-PAA)为研究对象,采用动态光散射(DLS)及透射电镜(TEM)表征了胶束及聚集体的结构,采用应力控制型旋转流变仪AR-G2研究了体系的流变特性.着重考察了聚电解质浓度、pH值以及外加盐(KBr)浓度对其在水中聚集行为的影响及对体系流变特性的影响.发现随着外加盐和聚电解质浓度的增高,体系中的胶束发生聚集,形成更大的聚集体.而pH值对胶束的聚集形态无明显的影响.胶束乳液均呈现明显的剪切变稀特征.然而,随着聚电解质浓度增加,低剪切速率下体系的表观粘度增高;高剪切速率时体系粘度趋于同一值(0.01Pa·s).与纯胶束乳液相比,外加盐的存在导致体系粘度增加;当外加盐浓度增加至4.31g/L,在低剪切速率下,体系出现牛顿平台区.溶液pH值对体系粘度无显著影响.

The Association Behavior and Rheological Properties of PS-b-PAA Amphiphilic Diblock Copolymer Polyeletrolyte Micelles in Water

Relationships between solution parameters including concentration of polyeletrolyte and potassium bromide (KBr),pH value of solution and the aggregation behavior for the micelles formed by the amphiphilic diblock polyeletrolyte,poly(styrene-b-acrylate acid) (PS-b-PAA) were studied.The effect of the micellar aggregation behavior on the rheological properties of the micellar latex was examined.Results revealed that increasing the copolymer concentration and salt concentration led to formation of greater irregular structure in polyelectrolyte micelles due to the aggregation of them,while the effect of pH value can be negligible due to the higher composition of PS block in the copolymer composed of a long hydrophobic block (PS) and a comparable short amphiphilic block (PAA).The aggregation structures were characterized through dynamic light scattering (DLS),transmission electron microscopy (TEM),and rheological properties of the micellar latex were tested using the stress-control rheometer AR-G2.All of the micellar latex exhibit shear thinning behavior,while the apparent viscosity increases with increasing copolymer concentration at lower shear rates,and approaches a constant value (0.01 Pa·s) of ten times of magnitude greater than that of water.Furthermore,the presence of potassium bromide remarkably increases the latex viscosity,comparable with that without added salt,and newtonian plateaus at lower shear rates appeared when the salt concentration reached 4.31 g/L.It is suggested this phenomenon is resulted from the effect of corona expansion involving in the charges-shielding by the added ions.The obvious effect of pH value on the latex viscosity could hardly be observed due to the comparable short amhpihpilic block.