A vapor-chamber that includes a porous microstructure sheet with varying surface energy across different regions to optimize utilization of a working fluid. Modulating the surface energy of the porous microstructure sheet can minimize the amount of the working fluid that becomes trapped in the condenser region(s) and maximize an aggregate thin-film evaporation area of the working fluid in the evaporator region(s). The condenser region of the vapor-chamber is treated so that the internal surfaces have low surface energy. For example, the treatment may cause the condenser region to become hydrophobic to minimize the amount of fluid that becomes trapped in the condenser. The evaporator region is treated so that the internal surfaces have high surface energy. For example, the treatment may cause the evaporator region to become hydrophilic to induce the formation of large numbers of robust (e.g., dry-out resistant) thin-film evaporation sites.
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