[paulhao]

Hi guys,

I'm doing my lab report and have this question. Why scratching the glass can aid the recrystallization?
I've been searching for the satisfying explanation but there are a lot of explanations online. They talk about the thermodynamics and Oswald theory,etc...
If you have mastered this, please help me. Thanks

[Borek]

Most often it is explained in terms of activation energy required to create crystalization seeds.

[Arkcon]

I've been searching for the satisfying explanation but there are a lot of explanations online. They talk about the thermodynamics and Oswald theory,etc..

Really?  And not one of them considers micro-scratches as nucleation sites, or nucleation seeds from scrapped off glass?

Here's an experiment to try, if you can swing it with the laboratory suppliers -- get two beakers, an old scratched, beaten up one, and a brand new one still from the box (you will have to explain this whole experiment to get them to let you have one.)  See if you can recrystallize easier in the beaten up beaker.

[wildfyr]

I think you two are talking about two sides of the same coin. A nucleation point IS a spot where the activation energy is slightly lower. Thats why it crystallizes first.

[paulhao]

Thank you! I think the explanation about activation energy would be the best !

[Enthalpy]

At the molecular level, I could imagine that a micro-groove (scratch) offers solid surfaces to several sides of a candidate molecule at once, so it catches the molecule more strongly than a smooth glass surface.

It's just an analogy I make with epitaxy on single-crystal semiconductors, where new atoms add with a huge preference to the stairsteps made by the limit of atomic planes.

[Babcock_Hall]

Could the pieces of glass that are scratched off be the sites of heterogeneous nucleation?  One tries to avoid heterogeneous nucleation in some applications, but I don't see why it would matter in the context of an organic recrystallization.