Structure of materials Flashcards
The properties of solid materials depend on how the particles in these materials are,,,,,,,, and how they are held ……
The properties of solid materials depend on how the particles in these materials are arranged, and how they are held together.
How does a solid melt?
A solid melts when the forces between its particles are broken. This requires energy.
The stronger the forces between the particles, the more energy is needed to break the particles out of the solid structure. The more energy that is needed, the higher the melting point of the solid.
Different polymers have different properties, depending on the small molecules they were made from. But the properties of a polymer can also be changed. How?
Long polymer chains have stronger forces of attraction than shorter ones. By making the chains of a polymer longer, a stronger and less flexible material is produced.
Plasticisers are small molecules that can be added to polymers during their manufacture. How do they make the material more flexible?
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They push the polymer molecules slightly further apart, weakening the forces between them and making the material softer and more flexible. Plasticisers hold the polymer chains apart making it easier for them to slide past each other
Is Unplasticised PVC, usually called uPVC, is hard or soft? What is it used for?
Unplasticised PVC, usually called uPVC, is hard. It is used for pipes and window frames.
Is Plasticised PVC hard or soft. what is it used for?
Plasticised PVC is soft. It is used for clothing and flooring.
Chemical bonds can be formed to link together the chains of some polymers. What do these cross-links do to the material ?
These cross-links make the material tougher and less flexible.
Ethene can be polymerised in slightly different ways to make low-density polyethene (LDPE) and high-density polyethene (HDPE). These polymers have different properties because of the structure of their molecules. Some polymer chains have what ……
Some polymer chains have side branches.
What does LDPE stand for?
Low-density polyethene (LDPE)
The side branches stop the polymer molecules from doing what?
The side branches stop the polymer molecules from lining up regularly. Its structure is not crystalline.
High-density polyethene (HDPE) does not have side branches.
If its structure is not crystalline it means that the material has a lower density than ……
the forces of attraction between polymer molecules are ………………….. , the material is less …………., and has a lower …………. ………………than HDPE
The polymer molecules line up regularly to give a …………. ………….
Its structure is not crystalline. This means that:
the material has a lower density than HDPE
the forces of attraction between polymer molecules are weakened , the material is less strong, and has a lower melting point, than HDPE.
By carefully controlling the amount of branching, it is possible to make polymers with various amounts of crystallinity. This means it is possible to …….
By carefully controlling the amount of branching, it is possible to make polymers with various amounts of crystallinity. This means it is possible to make a polymer with the exact properties that are required for a particular purpose.
What is needed to break the forces between particles in a solid?
Energy is needed to break the forces between particles
A solid has a high melting point if the forces between its particles are?
Large
Increasing the chain length of a polymer makes it?
Increasing the chain length of a polymer makes it less flexible
To make a polymer softer and more flexible we can add:
A plasticiser
Cross linking the chains makes a ………..
Cross linking the chains makes a polymer harder
When the material is stronger, and has a higher melting point, than LDPE , what does that mean for the forces of attraction>
This means that the material has a higher density than LDPE and that the forces of attraction between polymer molecules are strong - the material is stronger, and has a higher melting point, than LDPE.
Various amounts of crystallinity - By carefully …………….. the amount of ……………., it is possible to make polymers with various amounts of crystallinity. This means it is possible to make a polymer with the …… ……………..that are required for a particular purpose.
Various amounts of crystallinity - By carefully controlling the amount of branching, it is possible to make polymers with various amounts of crystallinity. This means it is possible to make a polymer with the exact properties that are required for a particular purpose.
when Polymer chains are represented with wavy lines what does this show?
Polymer chains with no cross-links or plasticisers can be represented with wavy lines
What makes poly(ethene) flexible?
Many polymers, such as poly(ethene), contain long molecules that lie side by side. These can uncoil and slide past each other, making the material flexible.
What is HDPE? Why does it have higher density than LDPE?
High-density polyethene (HDPE) does not have side branches……The polymer molecules line up regularly to give a crystalline structure.
This means that the material has a higher density than LDPE
the forces of attraction between polymer molecules are strong
the material is stronger, and has a higher melting point, than LDPE.
how is it possible to make polymers with Various amounts of crystallinity?
By carefully controlling the amount of branching, it is possible to make polymers with various amounts of crystallinity. This means it is possible to make a polymer with the exact properties that are required for a particular purpose.
How are polymer molecules lined up in HDPE? (High-density polyethene)
The polymer molecules line up regularly
