Highly Ordered Graphene Oxide and Reduced Graphene Oxide Based Polymer Nanocomposites: Promise and Limits for Dynamic Impacts Demonstrated in Model Organic Coatings

Graphene
oxide (GO) dispersed in water has been combined with a
mixture of aqueous polymer dispersions and melamine formaldehyde resin
(MF). Stable low viscous fluids with no obvious signs of mesoscale
ordering at 0.3 wt % yield transparent films with GO loadings up to
one weight percent in the form of homogeneously aligned double strands,
each comprising few individual layers of the carbon allotrope. While
baking of the films at 160 °C results in minor thermal reduction
of GO, in situ reduction with excess hydroxylamine (HA) in the presence
of the polymer colloids yields stable dispersions in which amphiphilic
graphene like flakes temporarily encapsulate gaseous reaction products.
Depending on the parameters in the time–temperature domain,
the hollow spheres may be transferred into solid material or disassemble
during film formation, the latter case providing black, smooth, and
transparent films with up to eight magnitudes increased electrical
conductivity and an oxygen permeability 30-fold higher compared to
the neat polymer matrix. In contrast, GO reduces oxygen permeability
by that factor, while water permeability stays unchanged. Thermo-mechanical
measurements reveal matrix stiffening by the platelets as well as
by HA, the latter via modifying the MF reactivity. Excellent stone
chip resistance and ballistic impact tests demonstrate efficient energy
dissipation and crack deflection provided by the laminate like morphology
of GO based composite. On the contrary, the same material only provides
moderate substrate protection in rain erosion tests.

将分散于水中的氧化石墨烯（GO）与水性聚合物分散液和三聚氰胺甲醛树脂（MF）的混合体系共混。当流体中GO的含量为0.3 wt%时，具备无明显介观有序特征的稳定低粘度流体，可制备出GO负载量最高达1 wt%的透明薄膜，其中GO以均匀排列的双链形式存在，每条双链包含数个该碳同素异形体的单层结构。在160℃下对薄膜进行烘烤会导致GO发生轻微的热还原；而在聚合物胶体存在下使用过量羟胺（HA）进行原位还原，则可得到稳定的分散体系，此时两亲性类石墨烯薄片会暂时包裹气态反应产物。根据时间-温度域内的工艺参数，空心球可转化为实心材料，或在成膜过程中发生拆解；后者可得到黑色、光滑且透明的薄膜，其电导率提升可达八个数量级，透氧性相较于纯聚合物基体提升30倍。与之形成对比的是，纯GO会使透氧性降低相同倍数，而水渗透率则保持不变。热机械性能测试结果表明，纳米片层与HA均可实现基体增强：HA通过改变MF的反应活性实现增强效果。优异的抗石击性能与弹道冲击试验结果证实，基于GO的层状复合结构可有效实现能量耗散与裂纹偏转。与之相反，该材料在雨水侵蚀试验中仅能为基材提供中等程度的防护。