Phd in THEORETICAL AND APPLIED MECHANICS

Thesis title: Soft functionalization of surfaces via Coarse-grained Molecular Dynamics simulations

Abstract In modern materials science, the ability to precisely control surface properties has become essential for advancing technologies that rely on interfacial interactions at nanoscale. Functionalized surfaces address this need in a wide spectrum of applications, ranging from electronics to drug delivery. However, despite the significant progress in fabrication, fundamental questions are still not fully elucidated: How do the molecular-level interactions of functionalized surfaces translate into their macroscopic behavior? This thesis addresses this significant question by studying the interfacial be- havior of polymer-grafted surfaces through coarse-grained molecular dynamics simulations, focusing on materials that are paramount for applications such as high-performance liquid chromatography (HPLC), energy damping/storage, and anti-adhesive surfaces. Unraveling the active role of the soft surface functionalization nuances, this work bridges the microscopic molecular interactions with emergent macroscopic behavior, offering valuable insights for both fundamental materials research and technological applications. Two key systems are explored: alkylsilane-grafted nanopores and polydimethylsiloxane (PDMS)- grafted layers. In the case of alkylsilane-grafted nanopores, we find that local grafting heterogeneities crucially influence water intrusion and extrusion pressures. This is attributed to variations in pore radius and surface hydrophobicity caused by specific arrangements of the grafted alkylsilane chains, highlighting the limitations of classical models like the Laplace equation in porosimetry. The molecular-level insights provided here suggest improvements in energy damping and liquid chromatography applications. For PDMS-grafted layers, we developed a coarse-grained model to understand the molecular origins of ultra-low contact angle hysteresis (CAH) in slippery covalently-attached liquid surfaces (SCALS). Simulations, supported by atomic force microscopy (AFM), show that optimal slipper- iness is achieved under specific conditions of chain length, grafting density, and polydispersity, leading to smooth, defect-free surfaces. Notably, a previously unreported microphase separation, caused by chain polydispersity, is linked to the emergence of nanoscale surface undulations. This feature, confirmed by AFM, is linked to surfaces exhibiting high CAH. These insights offer a fresh understanding of the design parameters required for optimizing SCALS properties. In summary, this research contributes novel molecular-level insights that complement experi- mental data, providing a bridge between nanoscale interactions and macroscopic observables. Ad- ditionally, the results suggest guidelines for improving surface functionalization technologies, with broad applications across fields requiring precise control over wetting and interfacial dynamics. Keywords: Coarse-grained molecular dynamics (CGMD), functionalized surfaces, grafting het- erogeneities, nanoporous materials, intrusion-extrusion, wetting and dewetting, contact angle hys- teresis, Slippery covalently-attached liquid surfaces (SCALS), alkylsilanes, polydimethilsiloxane (PDMS)