A series of semifluorinated alkanes (C n F 2n+1 C m H 2m+1 diblocks, FnHm, n = 6, 8, 10; m = 16, 18, 20), when cast as films onto solid substrates, were found to form ring-banded or radial spherulites when heated above their isotropic temperature and subsequently cooled down to room temperature, demonstrating that the formation of two-dimensional (2D) spherulites is a general feature of molecular fluorocarbon−hydrocarbon diblocks. These spherulites are not birefringent, a seldom encountered feature for such structures (never, so far, for spherulites made of small molecules). They also provide examples of fluorinated 2D spherulites. Film morphology was analyzed by optical microscopy, interferometric profilometry, atomic force microscopy (AFM), and scanning electron microscopy. Increasing the length of the Fn segment favors the formation of ring-banded spherulites, whereas short Fn segments tend to favor extended radial stripes. Variation of the cooling rate provides control over the size and morphology of the spherulites: slow cooling promotes fibers and radial spherulites, whereas fast cooling fosters ring-banded spherulites. The AFM studies of F10H16 films revealed that the latter consist of stacks of regularly spaced lamellae. We also observed that, remarkably, stacked lamellae (repeating distance ∼6 nm) can coexist with a layer of close-packed monodisperse circular self-assembled surface nanodomains of FnHm diblocks (∼30 nm in diameter); the latter are known to form from such diblocks at interfaces at room temperature. Substrates partially covered with F10H16 contain incomplete ring-banded spherulites and smaller objects in which the lamellae and circular nanodomains coexist. ■ INTRODUCTION Two-dimensional spherulites are generated on solid surfaces by solvent evaporation or melting of a variety of compounds. 1 Many polymers [e.g., polyethylene, polypropylene, and poly-(ethylene adipate)] form ring-banded patterns that exhibit optical birefringence under polarized light. 2−5 Several small inorganic or organic molecules also produce ring-banded spherulites (e.g., phthalic acid, 6,7 aspirin, 8 hippuric acid, 9 mannitol, 10 and testosterone propionate 11), sometimes in the presence of additives. Despite sustained investigation, the mechanism of formation of spherulites is still being debated. Concentric ring bands were proposed to be due to either a twisting of crystals, which results in periodic and continuous changes in crystallite orientation from edge-on to flat-on lamellae visible under polarized light, or to a rhythmic crystallization, the latter being essentially encountered for small molecules that do not have a helical structure. For some blends of polymers, for example, poly(aryl ether ketone) and poly(aryl ether ether ketone), 12 phase separation occurred and induced the rhythmical crystallization growth. Reports of nonbirefringent spherulites are scarce, 13−15 and we found no examples of nonbirefringent spherulites of small molecules. Poly(L-lactide) undergoes an alternation between birefringence and nonbirefringence when film thickness increases. 16 The formation of spherulites from polymers was usually ascribed to the rhythmical precipitation mechanism. Highly fluorinated spherulites are also uncommon and concern polymers, 17 and there does not appear to be any mention yet of fluorinated two-dimensional (2D) spherulites. The modification of surface properties (e.g., wettability) might be achieved using such fluorinated spherulites. Examples of nanohybrids consisting of nanoparticle-loaded fluorinated polymeric spherulites have been proposed. 18 Semifluorinated alkanes (C n F 2n+1 C m H 2m+1 , FnHm diblocks) are being extensively studied because of their unique combination of hydrophobic, amphiphilic, amphisteric, and amphidynamic properties, 19 and their aptitude to act as cosurfactants with phospholipids. 20,21 Earlier this year, we reported the unexpected first examples of spherulite formation from a diblock, F10H16. 22 It therefore became mandatory to determine whether this was a common feature for FnHm diblocks and how the diblock structure affected the spherulite