Pakzad A, Simonsen J, Yassar R S
Mechanical Engineering-Engineering Mechanics, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA.
Nanotechnology. 2012 Feb 1;23(8):085706. doi: 10.1088/0957-4484/23/8/085706.
In spite of extensive studies on the preparation and characterization of nanocomposite materials, the correlation of their properties at the nanoscale with those in bulk is a relatively unexplored area. This is of great importance, especially for materials with potential biomedical applications, where surface properties are as important in determining their applicability as bulk characteristics. In this study, the nanomechanical characteristics of thin poly(vinyl alcohol) (PVOH)-poly(acrylic acid) (PAA)-cellulose nanocrystal (CNC) membranes were studied using the nanoindentation module in an atomic force microscope (AFM) and the properties were compared with the macro-scale properties obtained by tensile tests. In general, the elastic properties measured by nanoindentation followed the same trend as macro-scale tensile tests except for the PVOH 85-PAA 0-CNC 15 sample. In comparison to the macro-scale elastic properties, the measured elastic moduli with AFM were higher. Macro-scale tensile test results indicated that, in the presence of PAA, incorporation of CNCs up to 20 wt% improved the elastic modulus of PVOH, but when no PAA was added, increasing the CNC content above 10 wt% resulted in their agglomeration and degradation in mechanical properties of PVOH. The discrepancy between macro-scale tensile tests and nanoindentation in the PVOH 85-PAA 0-CNC 15 sample was correlated to the high degree of inhomogeneity of CNC dispersion in the matrix. It was found that the composites reinforced with cellulose nanocrystals had smaller indentation imprints and the pile-up effect increased with the increase of cellulose nanocrystal content.
尽管对纳米复合材料的制备和表征进行了广泛研究，但它们在纳米尺度上的性质与宏观性质之间的相关性仍是一个相对未被探索的领域。这一点非常重要，特别是对于具有潜在生物医学应用的材料，其表面性质在决定适用性方面与宏观特性同样重要。在本研究中，使用原子力显微镜（AFM）中的纳米压痕模块研究了聚（乙烯醇）（PVOH）-聚（丙烯酸）（PAA）-纤维素纳米晶体（CNC）薄膜的纳米力学特性，并将这些性质与通过拉伸试验获得的宏观尺度性质进行了比较。总体而言，除了PVOH 85-PAA 0-CNC 15样品外，通过纳米压痕测量的弹性性质与宏观尺度拉伸试验遵循相同的趋势。与宏观尺度弹性性质相比，用AFM测量的弹性模量更高。宏观尺度拉伸试验结果表明，在存在PAA的情况下，加入高达20 wt%的CNC可提高PVOH的弹性模量，但当不添加PAA时，将CNC含量增加到10 wt%以上会导致其团聚并使PVOH的机械性能下降。PVOH 85-PAA 0-CNC 15样品中宏观尺度拉伸试验与纳米压痕之间的差异与CNC在基体中的高度不均匀分散有关。发现用纤维素纳米晶体增强的复合材料具有较小的压痕印记，并且堆积效应随着纤维素纳米晶体含量的增加而增加。
