Maliba Pharmacy College, UKA Tarsadia University, Gopal-Vidyanagar Campus, Surat 394350, India.
Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
Langmuir. 2021 Jan 19;37(2):867-873. doi: 10.1021/acs.langmuir.0c03206. Epub 2021 Jan 5.
Graphene oxide (GO) nanosheet suspension is not stable in physiological ionic fluids. To improve stability, surfactants such as Pluronic 103 (P103) have been tested. Going further, this work investigated whether conferring positive surface charge to the surfactant may improve the adsorption ability of P103 micelles on GO sheets. Positive charge on the surfactant was induced by adding dodecyltrimethylammonium bromide (DTAB, a cationic surfactant) in P103 micelles. Subsequent changes in aggregation parameters were investigated through dynamic light scattering and small-angle neutron scattering studies. DTAB incorporation was accompanied by a steady increase in the ζ potential and mixed micelle formation. At high surface charge density, the interaction between adjacent head groups was distorted, which led to dissociation of mixed micelles. Structural developments during the adsorption of mixed micelles on the sheet surface (mass fractal formation) were monitored in terms of changes in the scattering features of aggregates. These fractals emerged as a result of electrostatic interactions. Our observations point toward the existence of small-sized building blocks at low DTAB concentration (≤4 mM). With a superior adsorption, mixed micelles are expected to occupy the intersheet space and maintain a hydration layer. However, at a higher DTAB concentration (≥10 mM), micelles dissociate to produce DTAB-rich unimers and P103-rich loose aggregates. At this point, sheets tend to aggregate in the solvent, regardless of fractal formation.
氧化石墨烯（GO）纳米片悬浮液在生理盐水中不稳定。为了提高其稳定性，研究人员测试了表面活性剂，如 Pluronic 103（P103）。更进一步，本工作研究了赋予表面活性剂正电荷是否可以提高 P103 胶束在 GO 片上的吸附能力。通过在 P103 胶束中添加十二烷基三甲基溴化铵（DTAB，一种阳离子表面活性剂）来诱导表面活性剂带正电荷。通过动态光散射和小角中子散射研究研究了聚集参数的后续变化。DTAB 的加入伴随着 ζ 电位的稳定增加和混合胶束的形成。在高表面电荷密度下，相邻头基之间的相互作用被扭曲，导致混合胶束解离。通过监测聚集物散射特征的变化，从结构上跟踪了混合胶束在片层表面上吸附过程中的发展（质量分形形成）。这些分形是由于静电相互作用而出现的。我们的观察结果表明，在低 DTAB 浓度（≤4 mM）下存在小尺寸的构建块。由于具有优越的吸附能力，混合胶束有望占据层间空间并保持水合层。然而，在较高的 DTAB 浓度（≥10 mM）下，胶束解离产生富含 DTAB 的单分子和富含 P103 的松散聚集物。此时，无论分形形成如何，片层都倾向于在溶剂中聚集。
