1. Intermolecular interactions Binders Molecule type Gum arabic polysaccharide H-bonding Drying oils Lipids (oils) hydrophobic Acrylics polymers hydrophobic Tempera (egg yolk) Protein, fat/oil, lecithin Mixed (H-bonding, dipole interactions, hydrophobic interactions)

2. Gum Arabic: A polysaccharide: “poly –sugar” Gum on acacia tree These –OH groups bond with water A polysaccharide: “poly –sugar” Gums: soluble in water; form viscous (mucilinous) "solutions"; of C, H and O only. Are typically organic carboyhydrate acids as Ca, Mg or K salts.

3. Drying oils: lipids 5 Views of Linoleic Acid = C18H32O2 2 unsaturated bonds (2 double bonds) Carbons only Note bend: due to Double bond Carbons and Hydrogens

4. Other drying oils: Linoleic Acid = C18H32O2: 2 unsaturated bonds (2 double bonds) Oleic = C18H34O2 Linolenic= C18H30O2 1 unsaturated bonds (1 double bonds) 3 unsaturated bonds (3 double bonds)

5. The “drying” reaction: • Drying is not just evaporation of solvent (like fresco drying wasn't). • Is a chemical reaction: oxidation (here, addition of O2); • Double bonds are reactive (unstable) and that is where O2 adds • Oxidation by O2 can be catalyzed by Co, Mn other metals (siccants)

6. Acrylics: are polymers monomer unit = Acrylic Acid: CH2=CHOOH picture of polymer Methyl Methacrylate: monomer unit CH2=C(CH3)COOCH3

7. Tempera (egg yolk): Protein, fat/oil, lecithin Oil / fat

8. Tempera (egg yolk): Protein, fat/oil, lecithin lecithin Fatty acid

9. Tempera (egg yolk): Protein, fat/oil, lecithin lecithin Fatty acid Example of protein

10. So what’s the bottom line regarding binders? They’re all BIG molecules They’re all organic molecules They’re most often biomolecules They bind using Intermolecular Forces