CD - Bonding and structure *01 Flashcards
How do dyes attach themselves to fibres
intermolecular bonds, ionic bonds, covalent bonding
How do dyes attach themselves to fibres: Hydrogen bonds
functional groups enable dye to attach to fibres
- -NH2, amine group forms hydrogen bonds with fibres
What fibres do dyes that hydrogen bonds, bond well to?
cellulose, cotton, and linen as they contain loads of -OH groups
Are dyes that hydrogen bond colourfast?
no
the hydrogen bonds arent strong enough
How do dyes attach themselves to fibres: ionic interaction
- acidic groups (carboxylic/sulfonic acid), help dyes bind to alkaline -NH- links in fibres
- H+ ions move from dye to fibre molecule and ionic interactions hold them together
DYE-COOH + NH —> DYE-COO-+NH2
- some dyes have ionic salt groups (-SO3-Na+), these can bind to the -NH- links
- the salt group dissociates when you dissolve the dye in water to give -SO3- groups.
- to make -+NH2 groups need to add acid to provide H+ ions to -NH- groups.
- the -SO3- groups then bind to the -+NH2- links
what fibres do dyes have ionic interactions with?
wool, silk, nylon
they have -NH- links
are dyes that have ionic interactions with fibre colourfast
yes
better then hydrogen bonding dyes
How do dyes attach themselves to fibres: covalent bonds
these are fibre reactive dyes
- most permanent
have a functional group that will react with the -OH or -NH- group in the fibre and form strong covalent bonds
what are chromophores?
the structures in the molecules that give them their colour
How do chromophores give colour?
when light hits a chromophore, certain wavelengths are absorbed by electrons in the chromophore.
visible wavelengths not absorbed will be seen as a particular colour
structure of chromophores
tend to contain double or triple bonds, lone pairs of electrons, or benzene rings
these components usually form part of a delocalised system across a large section of the molecule
What happens when you modify a chromophore?
will change the frequency of light that it absorbs and so changes the colour of the molecule
How can you modify a chromophore?
functional groups containing O or N atoms with a lone pair of electrons can be added to a chromophore to adjust the colour of a dye molecule
because the lone pair of electrons become part of the delocalised system responsible for absorbing light
why do dyes need to be water soluble?
the process of dyeing usually involves soaking materials in a solution of the dye compound
ideally dissolves in water as water is cheap, readily available and non-toxic
how do you make dyes more soluble in water?
solubilising functional groups can be incorporated into a dye molecule
often ionic groups (such as the sulfate ions usually in the form of its sodium salt)
- water dissolves ionic substances because of its polar nature.
