尼龙6/季铵盐/蒙脱土纳米复合材料的分子动力学模拟

Molecular Dynamics Simulation of the Nylon-6/Quaternary Ammonium Salt/Montmorillonite Nanocomposites

通过分子动力学(MD)模拟方法对十六烷基三甲基氯化铵(CTAC)、十六烷基三甲基溴化铵(CTAB)和十八烷基三甲基氯化铵(OTAC)改性蒙脱土(MMT)的尼龙6(PA6)/季铵盐/MMT纳米复合材料共混体系的微观分子结构进行了研究。结果表明,MD模拟平衡后季铵盐分子平铺在MMT上,几乎覆盖了MMT的整个表面,PA6塌缩在季铵盐分子上,没有直接与MMT表面相接触;季铵盐与MMT之间存在强烈的相互作用,季铵盐中的非极性长链烷基通过范德华力与高分子链发生作用,烷基链数越少作用越强;季铵盐中的极性基团(卤素取代基)通过静电力与MMT相作用,取代基电负性越大,作用越强;烷基链数越多,高分子链越容易插入MMT片层中;10 nm^25 nm为季铵盐和PA6相互作用的界面区。

The atomistic structures of nylon-6 （PA6）/quaternary ammonium salt/montmorillonite （MMT） nanocomposites, which were modified by cetyltrimethylammonium chloride （CTAC）, cetyl- trimethylammonium bromide （CTAB） and octadearyl dimethyl ammonium chloride （OTAC）, were investigated by molecular dynamics （MD） simulations. The equilibrium conformations obtained by MD simulations show that the quaternary ammonium salt chains are flatten onto the MMT, covering almost the entire surface, and the polymer molecules collapse onto the quaternary ammonium salt themselves rather than directly on the MMT surface. The binding energy between nylon- 6, the quaternary ammonium salt and MMT is favorable, and provides an efficient composite interface. Strong favorable interactions between MMT and the quaternary ammonium salt exist. The apolar long-chain alkyl groups of the quaternary ammonium salt interact with polymer chain mainly via van der Waals （vdW） forces. The interaction energy increases with decrease of the number of alkyl group. While the polar groups positively interact, mainly via a strong electrostatic attraction, with the MMT layer. The higher electronegativity of the polar group is, the stronger the attraction between them becomes. It is turned out that polymer chain is more easily intercalated in the clay structure, with increasing of the number of alkyl group. The thickness of interface of polymer chain and quaternary ammonium salts is 1 nm-2.5 nm.