We investigate the expansion dynamics of two-dimensional colloidal assemblies interacting through a competing potential that supports unconventional local ordering. The systems are initially prepared under logarithmic confinement and subsequently released, generating a nonequilibrium decompression process. We show that expansion is not a simple disordering mechanism. Instead, the system undergoes a rich structural reorganization in which an initially dominant hexagonal core progressively shrinks while square local environments emerge and proliferate in the surrounding region. By combining real-space analysis, structure factors, bond-orientational order parameters, mean-square displacement, and dynamic exponents, we demonstrate that the expansion process promotes the formation and reorganization of square domains whose orientations initially reflect the sixfold geometry of the central hexagonal nucleus. This orientational-domain organization strongly influences the evolution of global order through cancellation effects between domains with different orientations. Finite-temperature simulations and independent thermal realizations further show that the structural conversion is robust, whereas the detailed late-time mobility events are trajectory dependent. As a consequence, substantial amounts of square local order may remain hidden from conventional global order parameters, demonstrating that local and global measures of structural order can become strongly decoupled during nonequilibrium expansion.

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• Pattern formation
• Self-assembly
• Colloids
• Nonequilibrium systems
• Brownian dynamics