However, sample C with $\sim 1.4 \;\text{mg cm}^{-1} $ of polymer completely crystallized in 1 day. This means the glass transition line has moved to higher $\phi$. Failure to crystallize was seen again for samples with polymer concentration above $\sim 2.5 \;
\text{mg cm}^{-1}$ (samples F,G,H). The behavior of all the samples in this region taken together show that the line of failure to crystallize had a re-entrant shape.

In pure hard-spheres, crystallization ceases at essentially the same volume fraction as where $f(q,\infty)$ first becomes non-zero, i.e. at the glass transition [@HSNature; @HSglass]. If this coincidence still holds for attractive hard-spheres systems, then we have observed a re-entrant glass transition in hard spheres with short-range attraction.

Previous studies of sticky hard spheres by MCT [@glassMCT; @gelMCTHiPhi] and computer simulation [@reentrantGlass; @reentrantSim] suggest that the re-entrant behavior is due to two different mechanisms of glassy arrest. The heuristic picture is as follows. In the ‘repulsion-dominated’ hard-sphere glass, particles are caged by their neighbors at high enough volume fraction. Short-range attraction clusters the particles of the cage and opens up holes, ultimately melting the glass. However, increasing the attraction further leads to an ‘attraction-dominated’ glass where particles stick to their neighbors with 