Lecture 6 - Mechanical Properties of Materials Flashcards
Below Tg, why do amorphous solids not undergo plastic deformtion?
No crystalline structure = no dislocations = no plastic deformation
What are polymers?
Materials made up of many repeating units.
What is the molecular weight of a polymer?
The mass of one mole of polymer chains.
What is the difference between weight-average and number-average of a polymer?
The weight-average is calculated by summing the products of each molecular weight (Mi) and the number of molecules (Ni) with that molecular weight, then dividing by the total weight of the sample. Mw = Σ(Mi * Ni) / w_total.
The number-average is calculated by dividing the product by the total number of molecules (N_total). Mn = Σ(Mi * Ni) / Σ(N_total)
What is the degree of polymerization (n)?
The number of repeats within a polymer chain
What is a copolymer?
Polymers that have more than one repeating pattern within the chain.
What are the four types of copolymers?
a) Random
b) Alternating
c) Block
d) Graft
What are the stereoisomer polymers?
Isotactic, Syndiotactic, and Atactic
What is an isotactic polymer?
A polymer with all side chains on the same side of the molecule.
What is a syndiotactic polymer?
A polymer with all side chains on alternating sides of the molecule.
What is an atactic polymer?
A polymer with random position of side chains on the molecule.
What are the geometric isomer polymers?
cis and trans
What is a cis polymer?
A polymer with the R group and hydrogen on the same side.
What is a trans polymer?
A polymer with the R group and hydrogen on opposite sides.
what is a spherulite?
A type of crystalline structure found within polymers.
How does temperature affect the types of bonds within a polymer?
At T>Tg, the polymer is only held together with covalent bonds and the structure is amorphous
At T<Tg, Van Der Waals bonds hold the polymer together more densely and increase density and decrease mobility.
What is a thermoplastic?
A polymer that becomes pliable or moldable when heated and solidifies upon cooling, retaining its shape
ex: polypropylene, polystyrene, polyethylene
What is a thermosetting polymer?
A polymer that becomes hard and brittle at increased temperature (opposite for thermoplastic) and does not melt.
ex: epoxy resins, polyesters, polyurethane…
When subject to a strain force, how do polymers react?
Viscoelastic(ally): they exhibit both flow-like (viscous) and recovery-like (elastic) properties when subject to a deformation
