Department of Applied Physics, National Defense Academy, 1-10-20, Hashirimizu, Yokosuka 239-8686, Japan.
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan.
Langmuir. 2023 May 23;39(20):7063-7078. doi: 10.1021/acs.langmuir.3c00306. Epub 2023 May 9.
The adhesion between silica surfaces and epoxy resins was investigated via molecular dynamics (MD) simulations with stable atomic models of silica substrates prepared by density functional theory (DFT) calculations and reactive force field (ReaxFF) MD simulations. We aimed to develop reliable atomic models for evaluating the effect of nanoscale surface roughness on adhesion. Three consecutive simulations were performed: (i) stable atomic modeling of silica substrates; (ii) network modeling of epoxy resins by pseudo-reaction MD simulations; and (iii) virtual experiments via MD simulations with deformations. We prepared stable atomic models of OH- and H-terminated silica surfaces based on a dense surface model to consider the native thin oxidized layers on silicon substrates. Moreover, a stable silica surface grafted with epoxy molecules as well as nano-notched surface models were constructed. Cross-linked epoxy resin networks confined between frozen parallel graphite planes were prepared by pseudo-reaction MD simulations with three different conversion rates. Tensile tests using MD simulations indicated that the shape of the stress-strain curve was similar for all models up to near the yield point. This behavior indicated that the frictional force originated from chain-to-chain disentanglements when the adhesion between the epoxy network and silica surfaces was sufficiently strong. MD simulations for shear deformation indicated that the friction pressures in the steady state for the epoxy-grafted silica surface were higher than those for the OH- and H-terminated surfaces. The slope of the stress-displacement curve was steeper for surfaces with deeper notches (approximately 1 nm in depth), although the friction pressures for the examined notched surfaces were similar to those for the epoxy-grafted silica surface. Thus, nanometer-scale surface roughness is expected to have a large impact on the adhesion between polymeric materials and inorganic substrates.
采用密度泛函理论（DFT）计算和反应力场（ReaxFF）分子动力学（MD）模拟制备的稳定二氧化硅基底原子模型，通过 MD 模拟研究了二氧化硅表面与环氧树脂之间的粘附。我们旨在开发可靠的原子模型来评估纳米级表面粗糙度对粘附的影响。进行了三个连续的模拟：（i）稳定的二氧化硅基底原子建模；（ii）通过伪反应 MD 模拟对环氧树脂进行网络建模；（iii）通过变形的 MD 模拟进行虚拟实验。我们基于致密表面模型，为考虑硅基底上的天然薄氧化层，制备了 OH-和 H-端二氧化硅表面的稳定原子模型。此外，还构建了稳定的接枝有环氧分子的二氧化硅表面和纳米切口表面模型。通过具有三种不同转化率的伪反应 MD 模拟，在冻结的平行石墨平面之间制备了交联环氧树脂网络。MD 模拟的拉伸试验表明，在接近屈服点之前，所有模型的应力-应变曲线形状相似。这种行为表明，当环氧树脂网络与二氧化硅表面之间的粘附足够强时，摩擦力源于链与链之间的解缠。剪切变形的 MD 模拟表明，对于接枝有环氧的二氧化硅表面，在稳态下的摩擦压力高于 OH-和 H-端表面。尽管考察的切口表面的摩擦压力与接枝有环氧的二氧化硅表面相似，但具有较深切口（约 1nm 深）的表面的应力-位移曲线斜率更陡。因此，纳米级表面粗糙度预计会对聚合物材料和无机基底之间的粘附产生重大影响。
