Nano Sunscreen

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Organic ingredients and inorganic ingredients

Slide 24

Organic Ingredients: The Basics

Organic = Carbon Atoms

Hydrogen, oxygen & nitrogen atoms are also often involved

Structure

Covalent bonds

Exist as individual molecules

Size

Molecular formula determines size

Typical a few to several dozen Å (<10 nm)

Sources: http://www.3dchem.com/molecules.asp?ID=135# and original image

Octyl methoxycinnamate (C18H26O3)

an organic sunscreen ingredient

Slide 25

Organic Ingredients: UV Absorption

Electrons capture the energy from UV rays

They jump to higher energy levels

The energy is released as infrared rays which are harmless (each ray is low in energy)

Source: Adapted from http://www.3dchem.com/molecules.asp?ID=135#and http://members.aol.com/WSRNet/tut/absorbu.htm

hf=2.48 eV

3hf=2.48 eV

Slide 26

Organic Ingredients: Absorption Range

Organic molecules only absorb UV rays whose energy matches difference between electron energy levels

Different kinds of molecules have different peaks and ranges of absorption

Using more than one kind of ingredient (molecule) gives broader protection

One Ingredient Two Ingredients Three Ingredients

Source: Graphs adapted from http://www.aims.gov.au/pages/research/projects/sunscreens/pages/sunscreens02.html

Slide 27

Organic Ingredients: Absorption Range cont.

Most organic ingredients that are currently used were selected because they are good UVB absorbers

The FDA has approved 15 organic ingredients

Sunscreen makers are trying to develop organic ingredients that are good UVA blockers

Avobenzone (also known as Parasol 1789) is a new FDA approved UVA blocker

Source: http://jchemed.chem.wisc.edu/JCEWWW/Features/MonthlyMolecules/2004/Oct/JCE2004p1491fig4.gif

Slide 28

How are inorganic sunscreen ingredients different from organic ones?

How might this affect the way they absorb UV light?

Slide 29

Inorganic Ingredients: The Basics

Atoms Involved

Zinc or Titanium

Oxygen

Structure

Ionic attraction

Cluster of ions

Formula unit doesn’t dictate size

Size

Varies with # of ions in cluster

~10 nm – 300 nm

Source: http://www.microspheres-nanospheres.com/Images/Titania/TIO2%20P7.jpg and image adapted from http://www.cse.clrc.ac.uk/msi/projects/ropa.shtml

Group of TiO2 particles

Detail of the ions in one cluster