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Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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Presentation on theme: "Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007."— Presentation transcript:

1 Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007

2 2 Nano Products Number of products using nanomaterials is growing very rapidly – Doubling every year? Clothing, food and beverages, sporting goods, coatings, cosmetics, personal care Sunscreens: today many (most?) use nanomaterials – Some labeled as containing nanoparticles – Some not labeled

3 3 Why Use Sunscreen? Too much unprotected sun exposure leads to: Premature skin aging (e.g. wrinkles) Sunburns Skin cancer Sources:

4 4 Skin Cancer Rates are Rising Fast Skin cancer: ~50% of all cancer cases > 1 million cases each year (US) Causes 1 person to die every hour (US) Probability of getting skin cancer: 1930 : 1 in 5, : 1 in : 1 in 10… Causes of the increase: Decrease ozone protection Increased time in the sun Increased use of tanning beds Sources: ;

5 wavelength Frequency = number of waves per second Wavelength = distance from one wave peak to the next Frequency x wavelength = speed of light About Light Waves Higher frequency shorter wavelength

6 6 The Suns Radiation Spectrum ~ 43% is in the visible range ~ 49% is in the near infrared range ~ 7% is in the ultraviolet range < 1% is x-rays, gamma waves, and radio waves. Most of the suns radiation is Ultraviolet (UV), Visible & Infrared (IR) : Source: Adapted from

7 7 Energy Comes in Packets or Photons The energy of a photon (E) is determined by the frequency of the radiation (f) E = h x f E f E f Radiation with a higher frequency has more energy in each photon The amount of energy in a photon determines how it interacts with our skin The total light energy is determined by the number of photons

8 8 Skin Damage The kind of skin damage is determined by the size of the photon ( E = h x f) The UV spectrum is broken into three parts: – Very High Energy (UVC) – High Energy (UVB) – Low Energy (UVA) High Energy Low Energy Source: As far as we know, visible and IR radiation dont harm the skin

9 9 Very high energy radiation (UVC) is currently blocked by the ozone layer (ozone hole issue) High energy radiation (UVB) does the most immediate damage (sunburns) But lower energy radiation (UVA) can penetrate deeper into the skin, leading to long term damage Source: N.A. Shaath. The Chemistry of Sunscreens. In: Lowe NJ, Shaath NA, Pathak MA, editors. Sunscreens, development, evaluation, and regulatory aspects. New York: Marcel Dekker; p Skin Damage II

10 10 So many sunscreens …. New and Improved Now with Nano-Z SPF 50 Goes on Clear Safe for Children Broadband Protection

11 11 Sources: and The SPF Rating SPF (Sunscreen Protection Factor) Number – Measures the strength of UVB protection only – Doesnt tell you anything about protection from UVA – Most (all?) now claim UVA/B protection Sunscreens first developed to prevent sunburn – Ingredients were good UVB blockers

12 12 The UVA Problem UVA rays have no immediate visible effects but cause serious long term damage – Cancer – Skin aging Sunscreen makers working to find UVA blockers – No official rating of UVA protection yet Source: Twenty different skin cancer lesions

13 13 Sunscreen Ingredients Lotion Several active ingredients in colloidal suspension – Organic – Inorganic

14 14 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 – Typically a few to several dozen Å (<10 nm) Sources: and original image Octyl methoxycinnamate (C 18 H 26 O 3 ) an organic sunscreen ingredient

15 15 Organic Ingredients: UV Absorption 1.Electrons capture the energy from UV rays 2.They jump to higher energy levels 3.The energy is released as infrared rays which are harmless (each ray is low in energy) Source: Adapted from hf=2.48 eV3hf=2.48 eV

16 16 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

17 17 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:

18 18 How are inorganic sunscreen ingredients different from organic ones?

19 19 Inorganic Ingredients: The Basics Atoms Involved – Zinc or Titanium – Oxygen Structure – Ionic attraction – Cluster of ions – Formula unit doesnt dictate size Size – Varies with # of ions in cluster – ~10 nm – 300 nm Source: and image adapted from Group of TiO 2 particles Detail of the ions in one cluster

20 20 Inorganic Ingredients: Cluster Size Inorganic ingredients come in different cluster sizes (sometimes called particles) – Different number of ions can cluster together – Must be a multiple of the formula unit ZnO always has equal numbers of Zn and O atoms TiO 2 always has twice as many O as Ti atoms ~100 nm TiO2 particle ~200 nm TiO 2 particle Source: Images adapted from

21 21 Inorganic Ingredients: UV Absorption Inorganics have a different absorption mechanism than organics Absorb consistently through whole UV range up to ~380nm Source: Graph adapted from

22 22 Inorganics: Appearance Matters Traditional inorganic sunscreens appear white on our skin (not cool!) Many people dont like how this looks, so they dont use sunscreen with inorganic ingredients Of the people who do use them, most apply too little to get full protection Source:

23 23 Why Do They Appear White? Traditional ZnO and TiO 2 clusters are large – (> 200nm) Large clusters scatter visible light – ( nm) – Maximum scattering occurs for wavelengths twice as large as the clusters The scattered light is reflected to our eyes, appearing white Source: Original image

24 24 Waves and obstacles Waves go around small obstacles Waves scatter all around from obstacles of sizes comparable to a wavelength – Ocean waves scatter off big rocks, go around small ones Nano size particles (< 100 nm) will not scatter visible light and nano sunscreen appears clear Nanosized ZnO particles Large ZnO particles

25 25 Questions to investigate 1.Does the opacity of a substance (to visible light) relate to its ability to block UV light? 2.Does a particular sunscreen block UV A? 3.How do you know if a sunscreen has nano ingredients?

26 26 UV experiments 2 setups at each table UV sensitive testers (flattened beads) sensitive to 360 – 300 nm light UV A lamps Share some test materials (see list in handout)

27 27 UV Detecting Beads Absorb 360 – 300 nm light Includes high energy end of UV A (400 – 320 nm) and low energy part of UV B ( nm) Source: UV detecting bead wavelengths

28 28 Farewell gift – UV sensitive kit ~25 beads, assorted colors ~ 1 yard of rawhide Make a necklace or bracelet (s)

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