The science — how it actually works
SiO₂ is silicon dioxide — silica. In a spray sealant it's carried as a silane/siloxane resin that cross-links as it cures, forming a thin, hard, sacrificial film that chemically bonds to your clear coat rather than just sitting on it like a wax.
Why water beads: the cured layer has very low surface energy. Water can't spread across a low-energy surface, so it pulls itself into beads (high contact angle) and sheets off, taking dirt with it. That's hydrophobicity — and it's not just for the photos: less water sitting on the panel means less dwell time for contaminants and far easier washing.
Why prep is everything: the resin bonds to whatever surface it meets. If that surface has iron fallout, tar or old wax on it, you have chemically bonded a sealant on top of contamination — and locked it in for months.