Colloidal Stability of Graphene Oxide: Aggregation in Two Dimensions
Colloidal Stability of Graphene Oxide: Aggregation in Two Dimensions
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DOI：
10.1021/acs.langmuir.6b01012
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发表时间：
2016-05-24
期刊：
影响因子：
3.9
通讯作者：
Gudarzi, Mohsen Moazzami
中科院分区：
文献类型：
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作者：
Gudarzi, Mohsen Moazzami
采用基于Derjaguin-Landau-Verwey-Overbeek（DLVO）理论的改进聚集模型，研究了氧化石墨烯（GO）在水和有机介质中的胶体稳定性.结果发现，无论是大小和缩放法律的货车范德华力的影响显着的二维（2D）性质的GO。GO在一价盐溶液中的实验临界混凝浓度（CCC）与DLVO理论预测一致。GO的表面电荷密度在很大程度上受pH的影响。然而，理论计算和实验观察表明，与3D胶体的经典图片相比，2D胶体的胶体稳定性对表面电荷密度的变化不太敏感。DLVO理论还定量预测了还原GO（rGO）的胶体稳定性。与GO相比，rGO的稳定性较低的根源在于rGO片层之间较高的货车德瓦尔斯力，特别是在还原过程中去除带负电荷的基团以及可能形成一些阳离子基团。GO还在极性有机溶剂中剥离并产生稳定的分散体。然而，在临界体积分数下，添加非极性溶剂会干扰胶体稳定性。分析GO在不同非极性溶剂和N-甲基-2-吡咯烷酮的混合物中的聚集提出，具有小于24的介电常数的溶剂不能承载稳定的GO胶体。然而，GO在极极性溶剂中的分散体在高浓度（>1 M）的盐和酸下显示出出乎意料的稳定性。这种稳定性的来源很可能是溶剂化力。影响极性溶剂赋予GO高稳定性的能力的关键参数是它们的分子尺寸：它们越大，稳定化的机会越高。
Colloidal stability of graphene oxide (GO) is studied in aqueous and organic media accompanied by an improved aggregation model based on Derjaguin-Landau-Verwey-Overbeek (DLVO) theory for ultrathin colloidal flakes. It is found that both magnitude and scaling laws for the van der Waals forces are affected significantly by the two-dimensional (2D) nature of GO. Experimental critical coagulation concentrations (CCC) of GO in monovalent salt solutions concur with DLVO theory prediction. The surface charge density of GO is largely affected by pH. However, theoretical calculations and experimental observations show that the colloidal stability of the 2D colloids is less sensitive to the changes in the surface charge density compared to the classical picture of 3D colloids. The DLVO theory also quantitatively predicts the colloidal stability of reduced GO (rGO). The origin of lower stability of rGO compared to GO is rooted in the higher van der Waals forces among rGO sheets, and particularly, in the removal of negatively charged groups, and possibly formation of some cationic groups during reduction. GO also exfoliates in the polar organic solvents and results in stable dispersions. However, addition of nonpolar solvents perturbs the colloidal stability at a critical volume fraction. Analyzing the aggregation of GO in mixtures of different nonpolar solvents and N-methyl-2-pyrrolidone proposed that the solvents with dielectric constants of less than 24 are not able to host stable colloids of GO. However, dispersions of GO in very polar solvents shows unexpected stability at high concentration (>1 M) of salts and acids. The origin of this stability is most probably solvation forces. A crucial parameter affecting the ability of polar solvents to impart high stability to GO is their molecular size: the bigger they are, the higher the chance for stabilization.