ITS ALL ABOUT TEXTURE!
The mentos and diet coke and, more importantly, the structure of the mentos, allow carbon dioxide bubbles to form extremely rapidly. When this reaction occurs, it results in a foamy diet coke fountain (its not just diet coke an d mentos that react; other carbonated fizzy drinks will also readily react to the addition of mentos).
Each mentos has thousands of small pores on its surface which disrupt the polar attractions between water molecules, creating thousands of nucleation sites for gas molecules to congregate. In non-science language, this porous surface creates a lot of bubble growth sites, allowing carbon dioxide to rapidly form on the surface of the mentos (if you use smooth surfaced mentos, then to wont get nearly the same reaction). The buoyancy of the bubbles and their growth will eventually cause the bubbles to leave the nucleation site and rise to the surface of the soda. Bubbles wo;; continue to form on the porous surface and the process will repeat, creating a foamy geyser.
In addition to that, the gum arabic and gelatine ingredients of the mentos, combined with the potassium bozoate, sugar or (potentially) aspartame in diet coke, also helps in this process. In these cases, the ingredients end up lowering the surface tension of the liquid, allowing for even more rapid bubble growth on the porous surface of the mentos - higher surface tension would make it a more difficult environment for bubbles to form.
Diet coke produce a bigger reaction than non-diet coke because aspartame lowers the surface tension of the liquid much more than sugar or corn syrup will. You can also increase the effect by adding more surfactants to the fizzy drink when you add the mentos, like an addition of dishwasher soap and water.
The mentos and diet coke and, more importantly, the structure of the mentos, allow carbon dioxide bubbles to form extremely rapidly. When this reaction occurs, it results in a foamy diet coke fountain (its not just diet coke an d mentos that react; other carbonated fizzy drinks will also readily react to the addition of mentos).
Each mentos has thousands of small pores on its surface which disrupt the polar attractions between water molecules, creating thousands of nucleation sites for gas molecules to congregate. In non-science language, this porous surface creates a lot of bubble growth sites, allowing carbon dioxide to rapidly form on the surface of the mentos (if you use smooth surfaced mentos, then to wont get nearly the same reaction). The buoyancy of the bubbles and their growth will eventually cause the bubbles to leave the nucleation site and rise to the surface of the soda. Bubbles wo;; continue to form on the porous surface and the process will repeat, creating a foamy geyser.
In addition to that, the gum arabic and gelatine ingredients of the mentos, combined with the potassium bozoate, sugar or (potentially) aspartame in diet coke, also helps in this process. In these cases, the ingredients end up lowering the surface tension of the liquid, allowing for even more rapid bubble growth on the porous surface of the mentos - higher surface tension would make it a more difficult environment for bubbles to form.
Diet coke produce a bigger reaction than non-diet coke because aspartame lowers the surface tension of the liquid much more than sugar or corn syrup will. You can also increase the effect by adding more surfactants to the fizzy drink when you add the mentos, like an addition of dishwasher soap and water.