Ozone, UV, and Nanoparticles Mort Sternheim STEM Education Institute STEM ED/CHM Nanotechnology 2011.
Presentation on theme: "Ozone, UV, and Nanoparticles Mort Sternheim STEM Education Institute 6/29/2008."— Presentation transcript:
Ozone, UV, and Nanoparticles Mort Sternheim STEM Education Institute 6/29/2008
Todays agenda 1.Ozone and ultraviolet light 2.Nanoparticles and sunscreen 3.Hands on activity Sunscreen PowerPoint and activities based on NanoSense web site: 1.Ozone and ultraviolet light 2.Nanoparticles and sunscreen 3.Hands on activity Sunscreen PowerPoint and activities based on NanoSense web site:
The big ideas Ultraviolet light causes skin damage and cancer Ozone in the stratosphere blocks UV Sunscreen blocks UV, partly Nanoparticles in sunscreen improve blocking
1. What is ozone? Ordinary oxygen gas: O 2 (2 oxygen atoms) Ozone: O 3 (3 oxygen atoms) Polar molecule, like water Ozone is much more reactive, unstable Pale blue, poisonous gas Bad! Absorbs ultraviolet radiation! Good!
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 rays, radio waves. Most of the suns radiation is Ultraviolet (UV), Visible & Infrared (IR) : Source: Adapted from
Some types of electromagnetic radiation The sun emits several kinds of electromagnetic radiation: Visible (Vis), Infrared (IR) and Ultra Violet (UV). Note the split into UVA, UVB, UVC Each kind is distinguished by a characteristic wavelength, frequency and energy Higher energy radiation can damage our skin Source: High Energy Low Energy
What is Radiation? Light radiation is often thought of as a wave with a wavelength ( ), speed (c), and frequency (f) related by Source: Since c (the speed of light) is constant, the wavelength and frequency are inversely related This means that light with a short wavelength will have a high frequency and visa versa.
Radiation energy comes in packets or photons The size of an energy packet or photon (E) is determined by the frequency of the radiation (f) E f E f Radiation with a higher frequency has more energy in each packet The amount of energy in a packet determines how it interacts with our skin
Very high energy radiation (UVC) is currently blocked by the ozone layer 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
Good ozone In the stratosphere, absorbs 97+ % of solar UV, protecting life from harm Produced by solar UV light from O 2 : – O 2 + UV (radiation < 240 nm) 2 O – O + O 2 O 3 Ozone – oxygen cycle: – O 3 + UV (< 320 nm) O 2 + O This cycle heats the atmosphere slightly, so ozone is a minor greenhouse gas
Ozone layer Ozone in stratosphere, 10 to 50 km above surface Ozone Can be depleted by free radical catalysts – NO, OH, Cl, Br – from natural sources Also from chlorofluorocarbons (CFCs) (freons) and bromofluorocarbons (halons) – UV light produces free Cl, Br radicals – Cl, Br catalyze chain reactions destroying ~100,000 ozone molecules Used in aerosols, refrigerators, air conditioners, fire extinguishers
Chemicals that Destroy Stratospheric Ozone Cl is much more abundant than Br Br is about 50 times more effective at O 3 destruction From Ozone FAQ - see
Ozone depletion Stratospheric ozone levels decreasing ~4% per year since 70s More skin cancer? Larger seasonal decrease in lower altitudes (troposphere) in polar regions: the ozone hole CFCs phased out globally by 1996 (Montreal Protocol, 1987) – will take decades to leave atmosphere Ozone levels have stabilized Recovery will take decades
2. Nanoparticles and sunscreen Nanoparticles: 1 to 100 nm in diameter, or about 10 to 1000 atomic diameters Number of products using nanomaterials is growing very rapidly – Doubling every year? Clothing, food and beverages, sporting goods, coatings, cosmetics, personal care Sunscreens: many use nanomaterials – Some labeled as containing nanoparticles – Some not labeled
Why Use Sunscreen? Too much unprotected sun exposure leads to: Premature skin aging (e.g. wrinkles) Sunburns Skin cancer Sources:
Skin Cancer Rates are Rising Fast Skin cancer: Is ~50% of all cancer cases Has > 1 million cases diagnosed each year Causes 1 person to die every hour Probability of getting skin cancer: 1930 : 1 in 5, : 1 in : 1 in 10… Causes of the increase: Decreased ozone protection Increased time in the sun Increased use of tanning beds Sources: ;
Radiation Type Characteristic Wavelength ( Energy per Photon % of Total Radiation Reaching Earth Effects on Human Skin Visible to Human Eye? UVC~ nm (Short-wave UV) High Energy ~0% (<1% of all UV) DNA DamageNo UVB~ nm (Mid-range UV)Medium Energy ~.35% (5% of all UV) Sunburn DNA Damage Skin Cancer No UVA~ nm (Long-wave UV) Low Energy ~6.5% (95 % of all UV) Tanning Skin Aging DNA Damage Skin Cancer No Vis~ nm Lower Energy ~43 %Yes IR~ ,000 nm Lowest Energy ~49%No Sun Radiation Summary Increasing Energy Increasing Wavelength
Which Sunscreen Should You Use??? New and Improved Now with Nano-Z SPF 50 Goes on Clear Safe for Children Broadband Protection
Sources: A Brief History of Sunscreens: The Beginning First developed for soldiers in WWII (1940s) to block sunburn causing rays Shorter wavelengths (more energy) called UVC Longer wavelengths (less energy) called UVA These were called UVB rays WWII soldier in the sun
Sources: and A Brief History of Sunscreens: The SPF Rating SPF (Sunscreen Protection Factor) Number – Measures the strength of UVB protection only – Higher SPF # = more protection from UVB – Doesnt tell you anything about protection from UVA Sunscreens first developed to prevent sunburn – Ingredients were good UVB blockers
A Brief History of Sunscreens: 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
How do you know if your sunscreen is a good UVA blocker?
Know Your Sunscreen: Look at the Ingredients Lotion has inactive ingredients – Dont block UV light UV blocking agents are active ingredients – Usually have more than one kind present Source: Original Image UV blocking agents suspended in a lotion – Colloidal suspension Two kinds of active ingredients – Organic ingredients and inorganic ingredients
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: and original image Octyl methoxycinnamate (C 18 H 26 O 3 ) an organic sunscreen ingredient
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
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
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:
How are inorganic sunscreen ingredients different from organic ones? How might this affect the way they absorb UV light?
Inorganic Ingredients: The Basics Atoms involved – Zinc or Titanium – Oxygen Structure – Ionic molecules: ZnO, TiO 2 – Cluster of ions – Formula unit doesnt dictate size Cluster (particle) 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
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
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
Why not use inorganics? Appearance Matters Traditional inorganic sunscreens have appear white on our skin 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:
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
Organic Sunscreen Molecules are Too Small to Scatter Light ~200 nm TiO 2 particle Methoxycinnamate (Inorganic)(Organic) (Note that these images are not drawn to scale) Source: Images adapted from and
Waves and obstacles Waves go around small obstacles Waves scatter all around from obstacles of sizes comparable to a wavelength Water wave (ripple tank) simulation:
What could we do to inorganic clusters to prevent them from scattering visible light? Source: Adapted from
Nanosized Inorganic Clusters Source: Graph adapted from Maximum scattering occurs for wavelengths twice as large as the clusters – Make the clusters smaller (100 nm or less) and they wont scatter visible light
In Summary… Nanoparticle sunscreen ingredients are small inorganic clusters that: – Provide good UV protection by absorbing both UVB and UVA light – Appear clear on our skin because they are too small to scatter visible light Source:
Essential Questions: Time for Answers 1.What are the most important factors to consider in choosing a sunscreen? 2.How do you know if a sunscreen has nano ingredients? 3.How do nano sunscreen ingredients differ from other ingredients currently used in sunscreens?
3. Testing sunscreen activity Use UV sensitive beads Compare opacity/ transparency of samples for visible light and UV light