This thesis describes the development of in-situ cinematographic recording techniques for investigating phase dynamics using nanoparticles (NPs) as model systems. The suitable experimental platform realized the simultaneous high spatial and temporal resolution for in-situ observations of phase transitions. The impact of increased surface energy on phase stability in NPs drives phase dynamics under ambient conditions. By leveraging this, nano-specific polymorphs and the energy profile of structural fluctuation on NPs of inorganic compounds were identified at atomic resolution in real space. The surface energy-driven phase dynamics revealed here provide new guidelines for controlling nanomaterial structures and expanding the scope of future material exploration.