Starches are more than chains of sugar granules strung together. In the case of corn starch, it is actually millions of these molecules packed into very discrete granules, which cannot be seen by the naked eye. Putting corn starch into cold water, nothing happens because cold water does not dissolve these granules. Putting it into hot water (like cooking gravy) however, these granules dissolve and create bonds between the water and the starch.
