Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM...

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

Transcript of Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM...

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

Copyright © 2005 SRI International

Nano Sunscreen

Adapted from the NanoSense web materials

STEM ED/CHM Nanotechnology 2007

Page 2: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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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

Page 3: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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Why Use Sunscreen?

Too much unprotected sun exposure leads to:

• Premature skin aging (e.g. wrinkles)

• Sunburns

• Skin cancer

Sources: http://www.oasishospital.org/previousnews.html; http://wohba.com/archive/2005_03_01_archive.html

Page 4: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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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 5,0002004 : 1 in 652050 : 1 in 10…

http://www.skincarephysicians.com/skincancernet/whatis.html; http://www.msu.edu/~aslocum/sun/skincancer.htm

Causes of the increase:• Decrease ozone protection• Increased time in the sun• Increased use of tanning beds

Sources: http://www.msnbc.msn.com/id/8379291/site/newsweek/ ;

Page 5: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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

Page 6: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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The Sun’s 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 sun’s radiation is Ultraviolet (UV), Visible & Infrared (IR) :

Source: Adapted from http://www.ucar.edu/learn/imgcat.htm

Page 7: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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Energy Comes in Packets or Photons

• The energy of a photon (E) is determined by the frequency of the radiation (f)

E = h x fE fE

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

Page 8: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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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: http://www.arpansa.gov.au/is_sunys.htm

• As far as we know, visible and IR radiation don’t harm the skin

Page 9: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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• 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; 1997. p. 263-283.

Skin Damage II

Page 10: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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So many sunscreens ….

New and Improved

Now with Nano-Z

SPF 50Goes on Clear

Safe for Children

Broadband Protection

Page 11: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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Sources: http://www.shop.beautysurg.com/ProductImages/skincare/14521.jpg and http://www.shop.beautysurg.com/ProductImages/skincare/14520.jpg

The SPF Rating

• SPF (Sunscreen Protection Factor) Number– Measures the strength of

UVB protection only– Doesn’t 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

Page 12: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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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 yetSource: http://www.cs.wright.edu/~agoshtas/fig8.jpg

Twenty different skin cancer lesions

Page 13: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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Sunscreen Ingredients

• Lotion • Several active

ingredients in colloidal suspension–Organic– Inorganic

Page 14: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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

Octyl methoxycinnamate (C18H26O3)

an organic sunscreen ingredient

Page 15: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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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 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

Page 16: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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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

Page 17: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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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

Page 18: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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How are inorganic sunscreen ingredients different from organic

ones?

Page 19: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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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

Page 20: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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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

• TiO2 always has twice as many O as Ti atoms

~100 nm TiO2 particle ~200 nm TiO2 particle

Source: Images adapted from http://www.cse.clrc.ac.uk/msi/projects/ropa.shtml

Page 21: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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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 http://www.aims.gov.au/pages/research/projects/sunscreens/pages/sunscreens02.html

Page 22: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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Inorganics: Appearance Matters

• Traditional inorganic sunscreens appear white on our skin (not cool!)

• Many people don’t like how this looks, so they don’t use sunscreen with inorganic ingredients

• Of the people who do use them, most apply too little to get full protection

Source: http://www.4girls.gov/body/sunscreen.jpg

Page 23: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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Why Do They Appear White?

• Traditional ZnO and TiO2

clusters are large– (> 200nm)

• Large clusters scatter visible light – (400-700 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

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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

Page 25: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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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?

Page 26: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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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)

Page 27: Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM ED/CHM Nanotechnology 2007.

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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 (320 -280 nm)

Source: http://www.arpansa.gov.au/is_sunys.htm

UV detecting bead wavelengths

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Farewell gift – UV sensitive kit

• ~25 beads, assorted colors

• ~ 1 yard of rawhide

• Make a necklace or bracelet (s)