Woah! Glow!

There’s already been a few posts on glow in the dark materials, but I investigated the specific mechanism behind what produces a glow. Specifically, what makes things glow in the dark?

Most glow in the dark items are made with phosphors. A phosphor is any substance that releases visible light in response to radiation. An incoming radiation particle collides with an atom or molecule, exciting an electron. The electron then emits the extra energy as a photon (the most elementary particle of light, a particle with zero mass.) This property of an object, by the way, is known as luminescence, the emission of light not resulting in heat, which itself is a form of cold body radiation.

 

Radiation probably sounds scary to you, because some types are dangerous, but not all types of radiation will set your spidey senses tingling. Radiation is simply the term for the emission of energy in electromagnetic waves or as subatomic particles. Those particles often cause ionization, as described above. In the case of glow in the dark materials, that ionization is occuring when incoming light excites an electron.

 

Often the radiation that allows glow in the dark items to glow is the same radiation we’re exposed to on a daily basis – UV rays from the sun. Two materials most often used are Zinc Sulfide and Strontium aluminate.

 

Zinc Sulfide is a common pigment. When combined with a bit of activator, it is used as a phosphor in many products. Different activators produce different colored glows – silver results in a bright blue, manganese an orange-red, and copper produces the most familiar greenish glow, which, incidentally, is the longest lasting of the three.

 

Here’s a cool video on how to make your own!

https://www.youtube.com/watch?v=r_6V72zB0L8

 

Strontium aluminate is widely considered superior to Zinc Sulfide. It’s a newer development that produces a brighter and longer lasting glow, though it’s slightly more expensive to manufacture. Strontium aluminate glows green or aqua, and the type of glow can be modified by changing its crystal structure. When manufactured to glow brighter, the glow is typically shorter lasting. The relationship is shown in this nifty graph:

c0jm02851g-f11

 

Neat.

Sources:

http://science.howstuffworks.com/innovation/science-questions/question388.htm

Wikipedia

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Glow Sticks

How Glow Stick Work:

A typical commercial light stick holds a hydrogen peroxide solution and a solution containing a phenyl oxalate ester and a fluorescent dye. Here’s the sequence of events when the two solutions are combined:

  1. The hydrogen peroxide oxidizes the phenyl oxalate ester, resulting in a chemical called phenol and an unstable peroxyacid ester.
  2. The unstable peroxyacid ester decomposes, resulting in additional phenol and a cyclic peroxy compound.
  3. The cyclic peroxy compound decomposes to carbon dioxide.
  4. This decomposition releases energy to the dye.
  5. The electrons in the dye atoms jump to a higher level, then fall back down, releasing energy in the form of light.

(HowStuffWorks.com)

After understanding the mechanism of glow sticks, Victor and I conducted an experiment in which we vary the temperature of phenol oxalate ester and hydrogen peroxide to see how temperature affects the reaction speed and the ‘glowing length’ of a glow stick.

We conducted two sets of experiment: one in root temperature and one below freezing point (0 Celsius). We had 60 samples per hour for 18 hours. Following chart records the result of these two experiment sets.

Screen Shot 2014-04-12 at 2.12.32 PM

 

As the chart shows, glow stick materials in room temperature reacted much faster than those under the freezing point. In fact, the reaction time for the RT set was so fast that the probe did not catch it.

As the chart shows, the RT glow stick only lasted about 20-30 minutes and the glow stick below 0 Celsius lasted about 4 hours. It appears that cold temperature slowed down the reaction process. For this reason, the cold glow was able to last much longer than the RT one. However, the cold glow stick took much more time to reach its peak brightness.

The data that we have appears to be somewhat flawed since the range of brightness should be between 0-3 (0 being very bright and 3 being complete dark). One of the data set had range of 0 ~ 4 which appears to be technical error of the labprobe. For this reason, we could not do any interesting calculation about the slope of these chemical process since the data was not perfect.

After all, one more trial of the same experiment will help us to understand more about the reaction speed and its ‘glowing time length’.

 

Sangwon & Victor

Glowing Flowers

glowing flower

Have you seen this lovely glowing flower before?

Since our class has been exploring a topic of “translucent” materials, I decided to post something related. And I remembered an experiment I did when I was 4th grade in school, which was putting a white flower into dyed water (red and blue) and observing the change in color of petals. When I came across this photo, it stimulated my nostalgic memory, so I had to replicate a similar experiment with three different types of liquids.

photo

The flower at left is placed in the bleach, the middle one in the pink highlighter, and the right one in the regular blue dye. (Bear with me, a white flower was nowhere to be found on this campus :() Anyways, I waited for about 3 days to observe the change in colors. And this is what I found after 72 hours:

photo 4

Very small change. The flower at the left is almost dead, while the one at the right is partially dyed into blue. However, the one in the middle has not changed at all. Would this mean that it has not absorbed the liquid at all? To find out, we decided to use black light, to see whether the stem actually sucked the highlighter all the way up to the petals.

photo 1 photo 3

This is a flower that has been placed in the pink highlighter. As you can see, under the black light, the tip of the stem glows, which indicates that it did suck up the liquid. Thus, I began to cut away the stem little by little to find out how high did the highlighter reach up the stem. Surprisingly, it had only traveled 1/3 of the entire stem. How does this happen, while the other flowers were able to absorb blue dye and bleach all the way up to the petals?

But first, let us learn about the mechanism of water absorption of plants.

addgateway_plant_stem

This is a diagram of a stem. Usually, plants absorb water through their roots and transport it through the tissue called, “xylem”. This process is also called “transpiration”. If you had taken intro chemistry, you should know that there is “hydrogen bond” in water molecules. these molecules are attracted to xylem and gradually travel up the stems, while the other molecules follow traveling molecules. Eventually, they reach to cells in the petals. Perhaps, we may be able to provide an answer to the question above, through studying the strength of attraction for each liquid.

Highlighters usually use compound called “pyranine”(C16H7Na3O10S3) When pyranine dissolves in water, the intermolecular force (hydrogenbonding) is no longer as strong. 712px-Pyranine.svg

Considering the fact that hydrogen bonding is second-strongest IMF after ionic bond, the weakening of HB should result in decrease in IMF. Thus, it may be concluded that the capillary action, the process in which water climbs the narrow tube, is discouraged, resulting in a failure for pyranine solution to transpire.

Although I have not had a chance to learn more about properties of blue-dye or bleach, due to shortage of time, I will later come back to do further study on this topic.

 

Thanks.

Black Light!

Black lights are used for many purposes today. They can be seen everywhere; from amusement parks to Halloween displays. The name of it is something of a misnomer as it actually tends to make things light up and fluoresce. When it is turned on, it makes white things glow in the dark.

You actually can not see the entirety of Black Light. When black light is turned on, people only see a purplish grow. They are unable to see the ultraviolet light that is also produced. Image

So the Black Light bulbs produce UVA light. There is UVB light but it is more harmful.

 

Anyway, what glows in the dark when shone by black light is a substance called PHOSPHORS. 

It is a substance that emits visible light when exposed to some sort of radiation. It converts the black light (the invisible light) of the Black Light Bulb into a color that is visible by the human eye. 

 

There are many questions as to the safety of black lights or UVA lights in general. UVA lights, as said before, are less harmful than UVB. In fact, UVA is even used to treat certain disorders. It is also used in tanning booths. UVA is the majority of the light reaching Earth, about 95 %. But UVA isn’t all good. UVA is known to play a major role in skin aging and wrinkling. In fact, it is even known to play a role in causing skin cancer. This is mainly due to the fact that UVA penetrates the skin very deeply, even deeper than UVB, which is much more intense. 

 

A warning to people that use tanning booths frequently. Tanning booths emit UVA levels 12 times that of the sun. That is a tremendous amount of UVA. People who use tanning salons frequently are 2.5 times more likely to develop squamous cell carcinoma and 1.5 times more likely to develop basal cell carcinoma.

GLOW Pt. 1

Just to begin, this is a very basic informative snapshot of Dr. Edith Widder’s TED Talks on bio-luminescence. Check it out:

<http://www.ted.com/talks/edith_widder_the_weird_and_wonderful_world_of_bioluminescence&gt;

This blog post will just be a basic introduction of bio-luminescence. I will follow-up with specific examples in the future blogs about specific examples, for instance, how bio-luminescence occurs in lantern fish, fireflies, and plankton.

What is Bio-Luminescence?

Bio-Luminescence is the “light produced by a chemical reaction within a living organism” (National Geographic Education). Bio-Luminescence is “cold-light”, which means that less than 20% of the energy is produced by thermal heat. Ninety-percent of marine animals are seen to use bio-luminescence in one way or another.

How does Bio-Luminescence Work?

The two chemicals of luciferin/luciferase or photoprotein are involved in the process. The luciferin/luciferase is actually the chemical that produces light. Some bio-luminescent organisms that do not synthesize luciferin tend to absorb it through other organisms. Here are some various pictures of different types of luciferins:

Screen shot 2014-03-27 at 10.19.12 AM Screen shot 2014-03-27 at 10.19.20 AM Screen shot 2014-03-27 at 10.19.26 AM Screen shot 2014-03-27 at 10.19.32 AMScreen shot 2014-03-27 at 10.19.37 AM

Each of these luciferins are found in various bio-luminescent organisms and occur using the luciferin-luciferase system. In contrast to the commonality of luciferins found, photoproteins were only recently discovered. Unlike luciferins, which can produce light by its own, photoproteins need both oxygen, luciferins, and another agent to produce light. The variety of color that the organisms can display can vary, some creatures can even emit a different shade of light in one body! Most organisms however, usually flash for about 10 seconds in a yellow or blue-green light.

Thanks for reading!