Fluorocarbons (CnF2n+2) and hydrocarbons (CnH2n+2) are mutually immiscible at room temperature, while they form clear and homogeneous mixtures at high temperatures. Tile phase separation curves of these systems show upper critical solution temperatures (UCST), which depend on the chemical formulas of the two liquids. In this paper we report the first observation of the mixing between perfluorooctane (PFO) and isooctane (i-OCT) at low temperature upon addition of a semifluorinated diblock copolymer (F8H16) Further cooling results in phase separation or formation of solid gels, depending on the amount of copolymer added to the mixture. Phase diagrams, light-scattering, birefringence, and small-angle X-ray-scattering measurements indicate the presence of microdomains in the gel and in the liquid phase, depending on the temperature and on the copolymer volume fraction.