Department of Chemical Engineering, University of South Carolina, Columbia, SC 29208, United States.
Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, United States.
J Colloid Interface Sci. 2013 Feb 15;392:226-236. doi: 10.1016/j.jcis.2012.09.079. Epub 2012 Oct 12.
This work employs tapping-mode AFM and dynamic light scattering (DLS) to investigate the effects of suspension composition (alkylammonium cation type, concentration) on the degree of exfoliation of a layered perovskite, calcium niobate (HCa(2)Nb(3)O(10), denoted as CNP). It is well known that in aqueous suspensions, tetrabutylammonium (TBA) cations intercalate CNP's layered structure, producing exfoliated platelets. This work shows that tetramethylammonium and tetraethylammonium cations do not produce significant levels of CNP exfoliation. However, TBA leads to complete exfoliation of CNP (>95%) in suspensions prepared with TBA:CNP ratios greater than 1:1. TGA and XRD data indicate that TBA uptake is limited by steric packing constraints. After depositing TBA-CNP platelets on mica surfaces for AFM imaging, quantitative image analysis provides the degree of exfoliation and distributions of platelet thickness, lateral size, and aspect ratio. The aspect ratio of TBA-CNP platelets has a lognormal distribution. Sedimentation of TBA-CNP suspensions under unit gravity removes unexfoliated particles from suspension, and centrifugation leads to differential sedimentation. The lateral size and aspect ratio of residual suspended TBA-CNP platelets decrease with increasing centrifugation speed. For all fractions of TBA-CNP platelets, the number-average lateral size from AFM agrees remarkably well with the effective spherical particle diameter measured by DLS.
这项工作采用敲击模式原子力显微镜和动态光散射（DLS）研究悬浮液组成（烷基铵阳离子类型、浓度）对层状钙钛矿铌酸钙（HCa(2)Nb(3)O(10)，表示为 CNP）剥离程度的影响。众所周知，在水悬浮液中，四丁基铵（TBA）阳离子插入 CNP 的层状结构，产生剥离的薄片。本工作表明，四甲基铵和四乙铵阳离子不会产生显著水平的 CNP 剥离。然而，TBA 导致 CNP 的完全剥离（>95%）在 TBA:CNP 比大于 1:1 的悬浮液中制备。TGA 和 XRD 数据表明 TBA 的摄取受空间位阻的限制。将 TBA-CNP 薄片沉积在云母表面上进行 AFM 成像后，定量图像分析提供了剥离程度以及薄片厚度、横向尺寸和纵横比的分布。TBA-CNP 薄片的纵横比呈对数正态分布。在单位重力下 TBA-CNP 悬浮液的沉降从悬浮液中去除未剥离的颗粒，而离心导致差异沉降。残留悬浮 TBA-CNP 薄片的横向尺寸和纵横比随离心速度的增加而减小。对于 TBA-CNP 薄片的所有级分，从 AFM 获得的数均横向尺寸与 DLS 测量的有效球形颗粒直径非常吻合。
