Surface chemistry of paper is just like how a cookie tastes different if it is dipped in milk or not. Paper has a surface too and when we touch it, it feels like it can absorb ink or water. This is because the surface of the paper has small structures on it called fibers. These fibers are like tiny sticks sticking out of the paper.
These fibers are not just plain sticks, they have different kinds of chemicals on them. Just like some sticks are sticky and some are not, some fibers attract water and are called hydrophilic, while others repel water and are called hydrophobic.
The chemicals present in these fibers help to determine how the paper will interact with ink or water. If the fibers on the surface of the paper are hydrophilic, then it will absorb the water or ink that is applied to it. If they are hydrophobic, then they will not absorb it and will repel it.
Therefore, the surface chemistry of paper plays an important role in determining how the paper will be used. For example, if we want to print on the paper then it should have hydrophilic fibers so that the ink is absorbed, and if we want to protect the paper from water, it should have hydrophobic fibers, which will prevent the water from penetrating the surface of the paper.
In conclusion, surface chemistry of paper is just like a cookie and milk. Just like dipping a cookie in milk changes its taste, the chemicals present on the surface of paper can determine how it will interact with ink or water.