Monthly Archives: October 2001

Why does glue not stick to its container?

 

      Have you ever wondered why glue does not stick inside its own tube?

Glue as we know comes out so nice and liquid and then sticks to any surface you apply it to. And then there is insta glue or the crazy glue that sticks seconds after it comes out of its tube. And it always ALWAYS sticks to your fingers and there is a horrible mess.

      To answer these questions the VERITAS team travelled all the way to the Andes mountains, crossed the Amazon and came back to Noida and found the answer in the Scientific American ( Just joking).

      Lets see how glues and adhesives actually work. There are two forces that are involved here: adhesion and cohesion. Cohesion is when molecules of the same substance bind together. Adhesion is when molecules of two different substance bind together. In glue both the forces are strong. So glue sticks to itself and to other surfaces too. And the binding properties of glue are because of both these properties. The glue binds to any surface and then binds togther with its own kind to form a strong bond.

        Glue molecules are giant plastic polymers. Now there are two kinds of glues :

1) Normal ones( less sticky, used in offices etc): This glue has lots of giant plastic molecules floating about in water. So when you apply it to a surface and dry it then all the water evaporates. All that is left is the sticky glue molecules that sticks. So the point is that it contains water so you have to dry it to remove water.

 

   This kind of glue does not stick inside the tube because it cannot dry inside the closed tube. However if you keep the tube open then the mouth of the tube dries and the lil bit of glue near the mouth will dry . And you will have to puncture it again.

 

2) Insta glue, crazy glue, super glue( very sticky, used to really STICK): This kind of glue is the one that sticks IMMEDAITELY on contact with a surface. This glue is usually made of lots of small molecules of ethyl-2-cyanoacrylate. THis molecule is a small one. But on coming in contact with water it IMMEDIATELY joins together to form a HUGE, LONG chain. i.e it polymerises on contact with water. Now all surfaces and air contain some moisture. So as soon as it comes out of the tube it polymerises to form a hard brittle substance, sticking anything it finds on the way. Inside the tube there is no moisture so no sticking.

 

  Another reason which does not let glues stick to their tubes is that the insides of the tubes have a single charge on them and glues work best on polar substances( both charges + and – separated by a distance) .

Book Review: The Double Helix

 

      Today’s VERITAS is a book review. A few days back I finished reading a wonderful book and I strongly recomment it to the VERITAS folks.

      We all know that the structure of DNA was discovered by Watson and Crick. They received a Nobel prize in in 1962 for their discovery. One point must be noted here: DNA was NOT discovered by Watson and Crick. The structure of DNA was discovered by them .

      James Watson wrote a very personal account of the discovery in a book called : The Double Helix. And this is a wonderful book .

It only has only 131 pages. And if you think that these pages are full of biology and chemistry … you are so wrong. These 131 pages are one of the most honest accounts of how Scientists actually discover things. It is a book about competition, hitting below the belt, jealousy, ambition and above all fun that one has in doing Science.

 

      This book describes in detail the story of the discovery of the structure of DNA. The ideas that worked and the ideas that did not.

The scientists that got close and the scientists that were way off. The fact that science is sometimes a set of lucky guesses. 

      Watson has no respect for any scientist in the book. But it describes the competition with the great chemist Linus Pauling in detail. Linus Pauling was way ahead of Watson and Crick in the race to discover the structure. In fact he even published a paper in which he thought he had discoved the structure. But this paper had an error and Watson was happy. And he did not tell Pauling about the error. He was worried that someone else would tell Pauling about his error, and then Pauling, in a week would discover the correct structure and the Nobel prize would be his.

      And this book is very entertaining. Watson writes :” As an undergraduate I was mainly interested in birds. I avoided taking any Chemistry or Physics .. even of medium difficulty” .

      And it tells you a very important thing : If Watson and Crick had not discovered the structure , someone else would have. And the discovery ( if Watson and Crick had not done it ) would not have been delayed by more than a year. Scientists just represent mankind’s attempt to understand nature. The attempt yields fruit. And this fruit does not belong to any individual.

 

      Overall a very interesting book, a book that shows the human aspect of Science. A book that is racy and lucid. A book that is honest. I statement that deserves one line does not get two. A book that has no problems with being short 🙂 . A must read !