From: The Lahrs (JohnJan@lahr.org)
Date: Thu Sep 16 1999 - 08:16:19 PDT
Message-Id: <3.0.32.19990916091618.008b9ec0@netmail.home.com> Date: Thu, 16 Sep 1999 09:16:19 -0600 From: The Lahrs <JohnJan@lahr.org> Subject: Re: Colour change
This is "out of the blue," so to speak, no pun intended, but I
though this exchange on the color of materials would be interesting
to post. It's from the sciclub-list@eskimo.com that is run by
Bill Beaty. If you haven't seen his web site, it's worth a look:
http://www.eskimo.com/~billb/
The answer below is to the question, why do some materials change
color when being ironed, and then change back when cool again.
>Return-Path: <sciclub-list-request@eskimo.com>
>Resent-Date: Wed, 15 Sep 1999 23:38:21 -0700
>From: michael.foster@excite.com
>To: sciclub-list@eskimo.com
>Subject: Re: Colour change
>
>Yes, Theresa, there is an explanation. I was sort of hoping some kindly
>retired dye chemist would be reading this list and enlighten us. Since that
>hasn't happened yet, I'll have a stab at it.
>
>The part of a dye molecule that gives it its color is called the
>chromophore. Everyone is familiar with the ball-and-stick molecule model.
>In this case, it is useful to replace the sticks with springs to
>conceptualize the mechanism at work here. Most of the "springs" will be
>short and these represent electrons tightly held in covalent bonds. Some
>electrons are held in unsaturated bonds associated with more than one atom
>and these could be thought of as longer, floppier springs. These are the
>chromophores. Now think of picking up this absurd molecule model and
>shaking it. The long spring will resonate with a slower rate of shaking,
>which represents the frequency of visible light. In the actual molecule,
>the light waves which resonate with the chromophore are absorbed into the
>molecule and are distributed as random agitation, in other words, heat.
>
>Now imagine your molecule model as having a greatly increased amount of
>random agitation not caused by by chromophore absorbtion. This would be
>analogous to heating up the actual molecule. As you can imagine, this could
>lead to one or more effects. Depending on the particular dye and the cloth
>or other subtance it is contained in, it could shift the absorbtion toward
>the red end of the spectrum or broaden the absorption or both. Since we see
>the colors which are not absorbed, this would have the effect of making your
>red dye color change to orange or even yellow. Curiously, if the color is a
>deep blue, the color might change in either direction, depending on whether
>the broadening of the absorption or the red shift is the dominant factor.
>In other words the blue colored fabric might tend toward the green or become
>a deeper blue. With a yellow dye, the effect would probably not be
>noticeable.
>This whole thing gets even more complicated with the introduction of other
>atoms and radicals called auxochromes.
>These resonating structures are tacked onto the molecule to modify the
>behavior of the chromophore, but I think you get the general idea.
>
>I hope someone who knows more about this can explain it more clearly, but
>for now, you're kind of stuck with my effort. .
>When I was a little boy, fluorescent colored nylon shirts were popular for
>children. (Kind of dates me, doesn't it?) When my mother first ironed one,
>I was watching because I was anxious put on my new day-glo pink shirt. The
>thing changed color to the most ghastly shade of chartreuse you can imagine.
>I was horrified. I thought my shirt was ruined. It took an amazingly long
>time to return to its orignal color after ironing. These shirts were so
>sensitive to temperature changes you could see noticeable color shifts on a
>hot day. Anyone else remember these things?
>Personally, I prefer the French spelling, couleur, more classy, don't you
>think?
>
>Michael
>
>
John C. Lahr
1925 Foothills Road
Golden, CO 80402
(303) 215-9913
http://lahr.org/john-jan
I am only one, But still I am one.
I cannot do everything, and because I cannot
do everything, I will not refuse
to do the something that I can do.
Edward Everette Hale
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