This work reports a systematic study of the aggregation behavior and structural properties of micelles formed by a selectively deuterated h-polystyrene-d-polybutadiene (h-PS10-d-PB10, where 10 denotes the approximate block molecular weight in kilograms per mole) block copolymer in a series of n-alkanes, CnH2n+2, where n = 7, 10, 12, 14, 16. By applying small-angle neutron scattering (SANS) in combination with contrast variation, very detailed aspects of the micellar structure are resolved. The results show that the micelles are rather poorly segregated with a large quantity of solvent (approximately 35-55%) penetrating the core and a smaller compact corona. Interestingly, the solvent fraction in the core decreases, and the overall aggregation number increases with the size of the solvent molecules. At first sight, this is not intuitively expected because the Flory-Huggins interaction parameter, chi, or the interfacial tension, gamma, stay constant or are even slightly decreasing, thus suggesting that the enthalpic interactions between the core-forming PS segments and the n-alkanes remain unchanged or decrease. However, this behavior can be understood semiquantitatively by applying a modified mean field theory where the solvent entropy effects in both core and corona are properly taken into account. This work thus directly demonstrates that contributions of the solvent entropy to the overall free energy are important whenever the interfacial tension is low.