I have always answered the question "why doesn't Saran Wrap seem to
stick to polyethylene or Styrofoam containers, but does stick very
well to glass?" by invoking the triboelectric series and noting that
polyethylene and Styrofoam are close to Saran Wrap -- in fact, Saran
Wrap is some kind of polyethylene. Glass, on the other hand, tends
to lose electrons more readily while Saran Wrap attracts them, and
these two substances are consequently much farther apart in the
triboelectric series.
As I understand it, the answer has to do with electrostatic
attraction -- the van der Waals force between two surfaces --
positively charged particles on one surface tend to be attracted to
negatively charged particles on the other. But why does Saran Wrap
cling to itself? That has always bugged me and suggests there's more
to this explanation.
The following is from http://www.edgerton.org/kidscorner/staticcling.html . "So if it is
not static, then what makes it cling? .... most kitchen plastic wrap
is made of low density polyethylene, also know as LDPE. This plastic
makes a good barrier to water and air, but it does not stick to
itself. To make it cling, they add another chemical, such as
polyisobutylene or poly(ethylene-vinylacetate). These chemicals do
not mix totally with the LDPE. Instead, they act like the adhesive on
tape, only not as sticky, and it only sticks to certain things. Want
to see? Try sticking it to paper, different plastics, wood and other
substances. Then you will know why the plastic wrap will stick easily
to some containers, but not to others."
It seems to me that adding another chemical doesn't really change the
fundamental argument or answer the question any better. What am I
missing? Thanks in advance -- Wolfgang