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Substance Property and Structure
Name: Brisham
Status: student
Grade: other
Country: Mauritius
Date: Summer 2009
Question:
How do the properties of polymers, amorphous substances and
crystalline materials relate to their structure?
Replies:
Brisham,
Generally speaking, "crystalline" refers to materials with regular,
repeating structures, while "amorphous" refers to materials that are
not crystalline. Technically speaking, crystallinity is better defined
by its (x-ray) diffraction pattern rather than purely by arrangement
of atoms. I am unsure of your grade level, so let me know if you need a
little more explanation or if you want more detail on this. In any
case, a polymer could be crystalline, or it could be amorphous (and in
fact many polymers are both) -- and is the case with many other
materials.
Hope this helps,
Burr Zimmerman
Hi Brisham,
I am not sure I understand your question. The naming of a substance as
either amorphous or crystalline, is based only on its molecular
structure. So in stating a material is either crystalline, or
amorphous, you have already classified its molecular structure to a
large degree.
Plastics are all either amorphous, or at best, exhibit a very limited
amount of crystalline structure. Those plastics that exhibit a limited
amount of crystalline structure, such as the polyacetal family
(commonly referred to as Delrin), have a tendency to be somewhat more
rigid than many amorphous plastics. Semicrystalline plastics also
present greater difficulties in molding, because shrinkage upon
cooling, tends to be different in different directions of the plastic
part, depending on the orientation of the crystals formed when
cooling. Amorphous plastics tend to shrink equally in all directions
when cooling.
Regards,
Bob Wilson
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