Each soap bubble traps some amount of water in the form of a thin layer between the soap molecules. Adding corn syrup to the dish soap solution prevents the bubbles from drying out as well as from bursting. Therefore, when you combine dishwashing liquid and corn syrup, you are basically making a hybrid between an ordinary soap bubble and a sugar polymer bubble. Glycerine, if used, also decreases the rate of evaporation of the water so the bubbles will last longer.