Molecular Characterization of Bonding Interactions at the Buried Steel Oxide–Aminopropyl Triethoxysilane Interface Accessed by Ar Cluster Sputtering

The
overall performance of any organic coating system on a metal
is largely dependent on the primer coating which has the crucial function
to ensure adhesion to the metal substrate. Although performance in
terms of adhesion can be empirically measured, the underlying chemical
adhesion mechanism is difficult to unravel. A detailed molecular characterization
of interfacial chemistry is required for this purpose, but brings
up the challenge to reach the buried interface without inducing excessive
damage to its molecular structure. In this work, argon gas cluster
ions are being applied to sputter through an aminosilane coating on
steel, in order to access the steel oxide–silane interface
with time-of-flight secondary ion mass spectrometry (ToF-SIMS). In
situ atomic force microscopy measurements during the sputter process
demonstrate the importance of optimizing the Ar gas cluster ion beam
in order to minimize sputter-induced roughness and molecular damage.
ToF-SIMS spectra obtained at the buried steel oxide–aminosilane
interface accessed by sputtering were compared to spectra from a steel
oxide–aminosilane interface that was directly accessible without
the need for sputtering. This comparison allowed us to identify contributions
from sputter-induced damage in the buried interface spectra. Fragments
characteristic for interfacial bonding interactions could be extracted,
although there is a significant loss of molecular information because
of sputtering. Nevertheless, insights into the role of steel surface
hydroxyl groups in the adsorption mechanism of aminosilanes could
be obtained through deuteration of the steel substrate.

金属表面任意有机涂层体系的整体性能，在很大程度上取决于底漆涂层——其核心功能是确保与金属基底的粘附结合。尽管粘附性能可通过经验方式进行测量，但其背后的化学粘附机理却难以厘清。为此需对界面化学开展详细的分子表征，但这一过程面临一项挑战：需在不对掩埋界面的分子结构造成过度损伤的前提下，抵达该界面。本研究采用氩气团簇离子（argon gas cluster ions）对钢材表面的氨基硅烷涂层进行溅射，以借助飞行时间二次离子质谱（time-of-flight secondary ion mass spectrometry，ToF-SIMS）抵达氧化钢-硅烷掩埋界面。溅射过程中的原位原子力显微镜（in situ atomic force microscopy）测量结果证实，优化氩气团簇离子束对于最小化溅射诱导的粗糙度与分子损伤至关重要。将通过溅射获取的掩埋式氧化钢-氨基硅烷界面的ToF-SIMS谱图，与无需溅射即可直接接触的氧化钢-氨基硅烷界面的谱图进行对比。该对比分析使得我们能够识别出掩埋界面谱图中由溅射诱导损伤所带来的信号贡献。尽管因溅射导致分子信息出现显著丢失，但我们仍可提取出界面键合相互作用的特征碎片。尽管如此，通过对钢材基底进行氘代（deuteration）处理，我们仍得以揭示钢表面羟基在氨基硅烷吸附机理中的作用。