Transcript G.Cragnolini ITI Malignani - Udine

THE PUZZLE
OF
A LIQUID
ROPE
G.Cragnolini
I.T.I. Malignani - Udine
the transformation from a liquid to a solid
phase is never trivial;
imagine the cooling of a lava stream or
the delicate crystal lattice of frozen water,
where each crystal is different;
solidification processes can be useful or even
lethal (e.g. blood coagulation in-or outside veins);
however, if done by spiders , the solidification
process is simply amazing;
G.Cragnolini
I.T.I. Malignani - Udine
most people ignore
that spiders, often not
greater than a pea,
produce up to 2000 feet
of thread continuously;
where the hell
do they store it ???
G.Cragnolini
I.T.I. Malignani - Udine
The question involves a solidification process;
in general, solidification is due :
-- to temperature drop, as in water freezing;
-- to solvent evaporation, like sodium chloride
in salt works ;
nevertheless, none of these models is fit to explain
the instantaneous solidification of the thread made
up by spiders ;
the answer is that spider’s long, silky string comes
from the solidification of a liquid;
G.Cragnolini
I.T.I. Malignani - Udine
But :
--- spiders live at room temperature,
thereby excluding all freezing processes;
--- the only solvent found inside spiders is
water, but water evaporates slowly at
room temperature, while spider’s thread
solidifies immediately ( it holds the mass
of the insect as soon as produced );
--- besides, if the thread was soluble in water,
then it would be dissolved by rain or dew;
G.Cragnolini
I.T.I. Malignani - Udine
so, what remains ?
The last chance is a kind of polymerisation
process, as for nylon ;
unfortunately nylon melts over 250 °C , that is
much higher than every survival limit;
moreover, polymerisation processes are slow;
anyway, a quick look at polymers may help us
understand spiders’ work :
G.Cragnolini
I.T.I. Malignani - Udine
polymers are buildings with molecular
weights of thousand hundreds ;
atoms that make up the backbone of a
polymer chain come in a regular order;
this pattern is reproduced all along the length
of the chain.
the little recurring structures are called
“ monomers “ ;
G.Cragnolini
I.T.I. Malignani - Udine
G.Cragnolini
I.T.I. Malignani - Udine
G.Cragnolini
I.T.I. Malignani - Udine
most of polymers are linear, that is joined in a long
line to form a huge and flexible chain, often bent in a
tangled mess;
when molten, these chains will act like elastic cooking
“spaghetti” , while cooled in the solid state, they look
more like a ball of string;
all molecules, the small ones as well as the polymer
chains, interact sticking together through forces
placed on the backbone;
G.Cragnolini
I.T.I. Malignani - Udine
when tangled in a ball, polymers set out
a little number of binding forces; when
stretched, many more of them appear and
work:
G.Cragnolini
I.T.I. Malignani - Udine
the yield of spiders
has a variable
composition based on
the amino – acids sequence :
…… ala-ala-gly-ala-ala-gly- ala-ala …..
G.Cragnolini
I.T.I. Malignani - Udine
finally the enigma is puzzled out;
the solution is unbelievably simple,
as it often happens in nature:
spiders excrete a sticky fluid
containing long protein molecules
tangled as a thread ball ;
each chain, when stressed, shows many
chemical structures fit to stick molecules
together , the same way polymers do ;
G.Cragnolini
I.T.I. Malignani - Udine
this way, stretched molecules can join other
ones to form a solid thread;
this is the reason why spiders excrete only
in conditions of traction;
in other words, the protein fluid is drawn
out only in presence of an external force,
such as wind or gravity ;
G.Cragnolini
I.T.I. Malignani - Udine
although hard to agree to, spider’s
filament is one of the strongest
materials in the world (more than
steel) and highly elastic at the same
time :
tensile strength can withstand a weight
of up to 300.000 pounds per square inch
( Nexia Biotechnologies - Montreal ) ;
G.Cragnolini
I.T.I. Malignani - Udine
What about copying spider’s silk ???
--- bridge suspension cables could be modelled
on its molecular structure;
--- car bumpers and bullet-proof vests that
absorb impacts as the spider’s web does;
--- flexible and resistant material for aircraft ......
G.Cragnolini
I.T.I. Malignani - Udine
unfortunately, spider farms are not
possible because spiders tend
to eat one another;
therefore, to get this surprising material
(five times stronger than steel and more
elastic than kevlar ), only industrial
processes can be used;
G.Cragnolini
I.T.I. Malignani - Udine
THIS PROVES AGAIN THAT CHEMISTS
ARE ABSOLUTELY NECESSARY;
spider’s secret being now unveiled, let’s have
a little gossip :
G.Cragnolini
I.T.I. Malignani - Udine
..... Arachne, a pretty maid of
ancient Greece woved
tapestries of such a beauty that
goddess Athena, who fancied
herself superior to any girl ,
became furious and turned
Arachne into a spider ;
now she is living among gods,
but is convicted to spin for
eternity .......
G.Cragnolini
I.T.I. Malignani - Udine
..... natives from the Pacific,
Asia and Australia used
spider silk to weave water
shedding rain gear, make
fishing lines and construct
nets;
..... Gengis khan and his soldiers wore a
leather garment interwoven with spider
silk, to protect them from enemy arrows;
G.Cragnolini
I.T.I. Malignani - Udine
o.k., that’s all;
by the way, a thankful acknowledgement to
all members of the team :
G.Cragnolini
I.T.I. Malignani - Udine