Anion - an atom or molecule which has a negative electrical charge.
(see: ion)
Cation - an atom or molecule which has a positive electrical
charge. (see: ion)
Complex - two or more molecules which are associated together by
some type of interaction of electrons, other than a covalent bond. (see:
covalent bond)
Copolymer - A polymer made from more than one kind of monomer.
(see: monomer)
Covalent bond - a joining of two atoms when the two share a
pair of electrons.
Crosslinking - crosslinking is when individual polymer chains are
linked together by covalent bonds to form one giant molecule. (see:
elastomer, thermoset)
Crystal - a mass of molecules arranged in a neat and orderly
fashion. In polymer crystal the chains are lined up neatly like new
pencils in a package. They are also bound together tightly by secondary
interactions. (see: secondary
interactions)
Elastomer - rubber. Hot shot scientists say a rubber or
elastomer is any material that can be stretched many times its original
length without breaking, and will snap back to its original size
when it is released.
Electrolyte - a molecule that separates into a cation and an anion
when its dissolved in a solvent, usually water. For example, salt, NaCl
separates into Na+ and Cl- in water:
Elongation - how long a sample is stretched when it is pulled.
Elongation is usually expressed as the length after
stretching divided by the original length.
Emulsion - a mixture in which two immiscible substances, like
oil and water, stay mixed together thanks to a third substance called an
emulsifier. The emulsifier is usually something like a soap, whose molecules have a water-soluble
end and an organic-soluble end. The soap molecules form little balls
called micelles, in which the water-soluble ends point out into
the water, and the organic-soluble ends point into the inside of the ball.
The oil is stabilized in the water by hiding in the center of the micelle.
Thus the water and oil stay mixed.
Entropy - disorder. Entropy is a measure of the disorder of a
system.
First order transition - a thermal transition that involves both a
latent heat and a change in the heat capacity of the material. (see: heat capacity, latent heat, second order transition,
thermal transition)
Free radical - an atom or molecule which has at least one
electron which is not paired with another electron.
Gel - a crosslinked polymer which has absorbed a large amount of
solvent. Crosslinked polymers usually swell a good deal when they absorb
solvents. (see: crosslinking)
Gem diol - a diol in which both hydroxy groups are on the same
carbon. Gem diols are unstable. Why are they called gem diols?
It's short for geminal, which means "twins". It's related to the
word gemini.
Glass transition temperature - the temperature at which a polymer
changes from hard and brittle to soft and pliable.
Heat capacity - the amount of heat it takes to raise the
temperature of one gram of a material one degree Celsius.
Hydrodynamic volume - the volume of a polymer coil when it is in
solution. This can vary for a polymer depending on how well it interacts
with the solvent, and the polymer's molecular weight.
Hydrogen bond - a very strong attraction between a hydrogen atom
which is attached to an electronegative atom, and an electronegative atom
which is usually on another molecule. For example, the hydrogen atoms on
one water molecule are very strongly attracted to the oxygen atoms on
another water molecule.
Ion - an atom or molecule which has a positive or a negative
electrical charge.
Latent heat - the heat given off or absorbed when a material melts
or freezes, or boils or condenses. For example, when ice is heated, once
the temperature reaches 0 oC, its temperature won't increase
until all the ice is melted. The ice has to absorb heat in order to
melt. But even though it's absorbing heat, its temperature stays the
same
until all the ice has melted. The heat required to melt the ice is called
the latent heat. The water will give off the same amount of latent
heat when you freeze it.
Le Chatelier's principle - this principle states that if a system
is placed under stress, it will act so as to relieve the stress.
Applied to chemical reactions, it means that if product or byproduct is
removed from the system, the equilibrium will be upset, and the reaction
will produce more product to make up for the loss. In polymerizations,
this trick is used to make polymerization reactions reach high conversion.
Ligand - an atom or group of atoms which is associated with a metal
atom in a complex. Ligands may be neutral or they may be ions. (see: complex, ion)
Living polymerization - a polymerization reaction in which there
is no termination, and the polymer chains continue to grow as long as
there are monomer molecules to add to the growing chain.
Matrix - in a fiber reinforced composite, the matrix is the
material in which the fiber is embedded, the material that the fiber
reinforces. It comes from a Latin word which means "mother",
interestingly enough.
Modulus - the ability of a sample of a material to resist
deformation. Modulus is usually expressed as the ratio of stress exerted
on the sample to the amount of deformation. For example, tensile
modulus is the ration of stress applied to the elongation which results
from the stress. (see: elongation, stress)
Monomer - a small molecule which may react chemically to link
together with other molecules of the same type to form a large molecule
called a polymer.
Olefin Metathesis - a reaction between to molecules, both
containing carbon-carbon double bonds. In olefin metathesis, the double
bond carbon atoms change partners, to create two new molecules, both
containing carbon-carbon double bonds.
Oligomer - a polymer whose molecular weight is too low to really be considered a polymer. Oligomers have molecular weights in the hundreds, but polymers have molecular weights in the thousands or higher.
Plasticizer - a small molecule that's added to polymer to lower
its glass transition temperature. (see: glass
transition temperature).
Random coil - the shape of a polymer molecule when its in solution, and it's all tangled up in itself, instead of being stretched out in a line. The random coil only forms when the intermolecular forces between the polymer and the solvent are equal to the forces between the solvent molecules themselves and the forces between polymer chain segments.
Ring-opening polymerization - a polymerization in which cyclic
monomer is converted into a polymer which does not contain rings. The
monomer rings are opened up and stretched out in the polymer chain, like
this:
Secondary interaction - interaction between two atoms or molecules
other than a covalent bond. Secondary interactions include hydrogen
bonding, ionic interaction, and dispersion forces. (see: hydrogen bond)
Second order transition - a thermal transition that involves a
change in heat capacity, but does not have a latent heat. The glass
transition is a second order transition. (see: first order transition, glass transition temperature, heat capacity, latent heat, thermal transition)
Soap - a molecule in which one end is polar and water-soluble and
the other end is non-polar and organic-soluble, such as sodium lauryl
sulfate:
Strain - the amount of deformation a sample undergoes when one puts
it under stress. Strain can be elongation, bending, compression, or any
other type of deformation. (see: elongation, stress)
Strength - the amount of stress an object can receive before it
breaks. (see: stress)
Stress - the amount of force exerted on an object, divided by the
cross-sectional area of the object. The cross-sectional area is the area
of a cross-section of the object, in a plane perpendicular to the
direction of the force. Stress is usually expressed in units of force
divided by area, such as N/cm2.
Termination - in a chain growth polymerization, the reaction that causes the growing chain to stop growing. Termination reactions are reactions in which none of the products may react to make a polymer grow.
Thermoplastic - a material that can be molded and shaped when it's
heated.
Thermal transition - a change that takes place in a material when you heat it or cool it. Examples of thermal transitions include melting, crystallization, or the glass transition. (see: glass transition temperature)
Thermoset - a hard and stiff crosslinked material that does not soften or become moldable when heated. (Compare thermosets with thermoplastics, which do become moldable when heated.) Also, thermosets are different from crosslinked elastomers. Thermosets are stiff and don't stretch the way that elastomers do. (see: elastomer, thermoplastic)
Toughness - a measure of the ability of a sample to absorb mechanical energy without breaking, usually defined as the area underneath a stress-strain curve. (see: stress, strain)
A micelle with the water-soluble ends of the soap molecule on the
outside, and the organic-soluble ends pointing inward, stabilizing a big
brown organic particle on the inside.
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