“Non-Newtonian fluid” experiment

Can a sub­stance be sol­id and liq­uid at the same time? Here’s an ex­per­i­ment to make a non-New­to­ni­an flu­id which doesn’t be­have by the rules!

Warn­ing! Only un­der adults su­per­vi­sion.

Reagents and equip­ment:

• corn starch;
• wa­ter.

Step-by-step in­struc­tions

Sprin­kle 2 parts of corn starch into a glass bowl and grad­u­al­ly add 1 part of wa­ter un­til a vis­cous liq­uid mass forms. Let your imag­i­na­tion run wild as you test the phys­i­cal prop­er­ties of the liq­uid: knead it in your hands, run on it, hit it with your fist or with a ham­mer.

Pro­cess­es de­scrip­tion

Non-New­to­ni­an liq­uids do not obey the laws of or­di­nary liq­uids. They change their den­si­ty and vis­cos­i­ty un­der the im­pact of phys­i­cal force. The stronger the im­pact on an or­di­nary liq­uid, the faster it will flow and change its form. With a non-New­to­ni­an flu­id, we get a com­plete­ly dif­fer­ent ef­fect; it starts to be­have like a sol­id body. The bond be­tween the mol­e­cules of liq­uid will in­crease as the force of the im­pact on it in­creas­es. The vis­cos­i­ty of non-New­to­ni­an flu­ids grows as the liq­uid be­gins to flow more slow­ly. These liq­uids are usu­al­ly high­ly het­ero­ge­neous and con­sist of large mol­e­cules, which form com­plex spa­tial struc­tures.

To put it more sim­ply, a non-New­to­ni­an flu­id is a sub­stance which can be both sol­id and liq­uid, de­pend­ing of the speed of im­pact on it. If we push, knead, throw or hit it quick­ly, it be­haves like a sol­id body, but if we stop, then it turns to a pud­dle in our hands.

Starch par­ti­cles swell in wa­ter and form con­tacts in the form of chaot­i­cal­ly in­ter­laced mol­e­cules. These durable bonds are called mesh­es. Un­der harsh im­pact, durable bonds do not let the mol­e­cules move, and the sys­tem re­acts to ex­ter­nal im­pact like a tight spring. Un­der slow im­pact, the mesh­es spread out and un­tan­gle. The lat­tice tears and the mol­e­cules sep­a­rate.