Premelting at Defects Within Bulk Colloidal Crystals

Abstract

Premelting is the localized loss of crystalline order at surfaces and defects at temperatures below the bulk melting transition. It can be thought of as the nucleation of the melting process. Premelting has been observed at the surfaces of crystals but not within. We report observations of premelting at grain boundaries and dislocations within bulk colloidal crystals using real-time video microscopy. The crystals are equilibrium close-packed, three-dimensional colloidal structures made from thermally responsive microgel spheres. Particle tracking reveals increased disorder in crystalline regions bordering defects, the amount of which depends on the type of defect, distance from the defect, and particle volume fraction. Our observations suggest that interfacial free energy is the crucial parameter for premelting in colloidal and atomic-scale crystals.

Melting of Colloidal Crystal Films

“…Their melting transitions, however, have not been measured because it is difficult to drive the melting transition in situ using conventional colloids. The present melting experiments are facilitated by novel N-isopropylacrylamide (NIPA) colloidal microgel spheres whose diameter can be tuned by temperature [13] to drive volume-fraction dependent melting transitions [14][15][16]. Interestingly, we find that thick films (>4 layers), thin films ( 4 layers), and monolayers exhibit different melting behaviors.…”

“…[18]). The effective diameter, , at uð Þ ¼ 1k B T, varied linearly from 1:27 m at 24:1 C to 1:14 m at 28:0 C. Many colloidal layers can be observed, even with bright-field microscopy [15]. Very thick samples with more than 20 layers were loaded into 18 Â 3 Â H mm 3 glass channel samples, where H is the channel thickness.…”

Slow dynamics, aging, and glassy rheology in soft and living matter

“…For example, recent work on melting of colloidal crystals has elucidated the importance of pre-melting at grain boundaries [11]. Another example is the mode coupling theory (MCT).…”

Non-equilibrium melting of colloidal crystals in confinement

“…Still open issues are e.g. the role of dislocations, grain boundaries and free surfaces [22,23,24,25] favouring either randomly distributed global or local initiation of the melting process. Second, stationary gradients of interaction strength had been introduced in various ways [14,15].…”