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UV Lensing of Water Droplets Facilitated by Topical Skin Agents
Abstract
Previous experiments have demonstrated the optical properties of water droplets. Likewise,
water droplets have been shown to focus ultraviolet (UV) rays, thus increasing UV radiation
transmitted to the surface below the water droplets. This experiment involved determining the
influence of topical skin agents on the optical properties of water droplets through the simulation
of water droplets on lotion-covered skin. UV radiation transmitted through 0.5 mL water droplets
above various commercial skin agents was measured and compared with UV radiation
transmitted through solely water droplets and solely topical skin agents. Results indicate that
highly hydrophobic substances creating spherical droplets with the biggest critical angles had the
greatest amount of UV transmission thereby the most intensified UV radiation beneath the water
droplets. These results suggest that the hydrophobic topical skin agents applied to human skin
might be responsible for increased UV absorption.
Primary Discipline: Interfacial Chemistry
Sub-Discipline: Biomedical Application
UV Lensing of Water Droplets
Facilitated by Topical Skin
Agents
TABLE OF CONTENTS
Introduction………………………………………………………………………………Page 1
Materials and Methods...…………………………………………………………………Page 3
Results……………………………………………………………………………………Page 5
Discussion………………………………………………………………………………..Page 8
Acknowledgements………………………………………………………………………Page 10
Literature Cited…………………………………………………………………………..Page 10
INTRODUCTION
Numerous research and experiments have been conducted on ultraviolet (UV) radiation’s
effect on various substances and materials. Previous research by this author (Aridegbe 2009)
tested the effectiveness of UV reactive pigments in contact lens design. It was concluded that
contact lenses could magnify UV transmission through the lens due to its convex shape thereby
creating a microscopic lensing effect. On the other hand, when the contact lenses were
impregnated with UV reactive pigments, UV transmission decreased, showing that the color
changing ability of the pigments played a role in the decline in UV radiation transmission.
Additional experimental research conducted by Allen H. Conney and his team (2008)
demonstrated tumorigenic effect of certain moisturizing creams when applied topically to UVBpretreated high-risk mice. The research showed that when skin lotion was applied to the skin of
laboratory rats that were then exposed to UV radiation, a formation of cancerous tumors
appeared in the rats (Heffernan 2008). In another experiment, Paul Forbes (2009) showed that
topically applied creams can influence the optical physics of skin and consequently alter UV
transmission.
Furthermore, water droplets are widely known in the science field for their optical
properties due to their convex shape. Water, being polar, has a molecular attraction to polar
surfaces, also known as adhesion. When water is placed on a non-polar surface, its molecules
have a greater attraction to each other, cohesion, than to the surface to which they were placed
on. This cohesion of water molecules results in visible beading of water droplets. Accordingly,
non-polar, hydrophobic, surfaces have greater wettability than polar, hydrophilic, surfaces
(Huang 2006).
Current research involving the interaction between leaf trichomes, leaf wettability and
the optical properties of water showed that lensing effects of water droplets on leaf surfaces
increased the sunlight transmitted directly under the water droplet-covered leaf trichomes by 20
fold (Brewer 2006). Similar research conducted by Jeremy D. Barnes (1995) and his team
showed that wettability of tobacco leaves positively correlated to its epicuticular wax chemical
composition and trichome densities. The results of these experiments may have important
implications for many processes of plants such as photosynthesis, stomatal function and
transpiration (Brewer 2006). Since interfacial chemistry between water droplets and leaf surfaces
may be similar to the interfacial chemistry between water droplets and human skin surfaces, the
optical water properties may have a negative effect on the surface of human skin.
The human skin is often at high risk for excessive exposure to radiation. One type of
radiation, ultraviolet (UV) radiation consists of invisible rays emitted from the sun. UV radiation
is a major concern for scientists as well as humans who continuously expose themselves to the
harmful rays of the sun since it is the main cause of skin cancer (<http://cancer.stanford.edu/skin
cancer/skin/causes/uvrad.html>).
In this experiment, a study on the influence of topical skin agents on the optical
properties of water droplets was conducted through the simulation of water droplets on lotioncovered skin. Based on the results of Conney’s research showing the tumorigenic effect of
moisturizing creams on the skin of UVB-pretreated high-risk mice, it was hypothesized that
water droplets scattered above topical skin agents would have a greater amount of UV radiation
transmission when exposed to UV light than solely topical skin agents.
MATERIALS AND METHODS
Prior to experimentation, equipment was set up on a secluded table. A cardboard shield
was situated to surround the apparatus to prevent excessive UV exposure. First, a UV radiation
Vernier sensor was positioned seven measured centimeters directly above a UV radiating lamp
already clamped to a ring stand on the table. A hollowed wooden block-like apparatus, placed
between the UV radiating lamp and UV radiation Vernier sensor, functioned as a stationary
platform for the microscope slides covered in water droplets, topical skin agents, skin agents and
water droplets or nothing at all. The UV radiating lamp and UV radiation Vernier sensor were
both secured to a ring stand by a tightened ring stand clamp (Figures 1 and 2)
Figure 1: Full view of experiment apparatus and a diagram of experiment apparatus
Figure 2: Close up view of apparatus
Initially, all microscope slides, rectangular in shape, that were used were divided into
three equally spaced sections; section one left blank, section two holding a 0.5 mL water droplet
and section 3 holding a 0.5 mL water droplet over a thin layer of one of the three skin agents
used (Figure 4).
Figure 3: Diagram of 3-sectioned microscope slide
Also, each trial of the experiment was divided into three phases; in phase one, section
three of the microscope slide contained a thin layer of Vaseline and a 0.5 mL water droplet, in
phase two, section three of the microscope slide contained a thin layer of Olay Ultra Moisture
Lotion with Shea Butter and a 0.5 mL water droplet, and in phase three, section three of the
microscope slide contained a thin layer of Garnier Nutritioniste Skin Renew Daily Regenerating
Moisture Lotion with SPF 15 sunscreen and a 0.5 mL water droplet. Ten trials, each with three
phases were conducted.
Next, another set of trials were conducted in which the same 3-sectioned microscope
slide setup was used but with different methods. For the first trial set, nothing was placed in
section one of the microscope slides, a 0.5 mL water droplet was pipetted onto section two and a
0.5mL water droplet was pipetted onto a thin layer of skin agent on the third section of the
microscope slides and then UV radiation transmitted was recorded. For the second trial set,
nothing was placed in section one of the microscope slides, a 0.5 mL water droplet was pipetted
onto section two of the microscope slides and a thin layer of skin agent was evenly distributed on
the third section. After the amount of UV radiation transmitted was recorded for each section of
the microscope slide, a 0.5mL water droplet was pipetted on top of the thin layer of skin agent on
section three of the microscope slide and UV radiation transmission was recorded for section
three. Five trials, each with three phases were conducted.
For each trial and its phases, the prepared microscope slide was placed in the slotted
opening of the hollowed wooden block and the UV radiation transmitted through the microscope
slide was measured by the UV radiation Vernier sensor (Figures 2 and 3). To allow stabilization
of the emitted UV radiation from the lamp, the UV light was left on throughout the data
collection phase of this experiment. Subsequent to the completion of data collection, the 0.5 mL
water droplets on the four different microscope surfaces were photographed with a Sony 10
Mega-pixel Digital Camera and contact angles for each droplet were calculated using the
formula,
.
Materials used to conduct this experiment were either commercially available or hand
made and all non-reusable materials were disposed of as per the Woodbridge Chemical Hygiene
Plan. Goggles and gloves were worn during experimentation. All experimental data was
collected by a Vernier LabQuest and manually recorded.
RESULTS
According to the averages of the amounts of UV radiation transmitted, a 0.5 mL water
droplet on a Vaseline surface produced a significantly greater amount of UV radiation
transmission than a 0.5 mL water droplet on a cream, Olay Ultra Moisture Lotion with Shea
Butter, surface which produced a greater amount of UV radiation transmission than a 0.5 mL
water droplet on a SPF 15 sunscreen containing cream, Garnier Nutritioniste Skin Renew Daily
Moisture Lotion with SPF 15 Sunscreen (Figure 5).
According to this experiment’s second data set, the addition of a 0.5 mL water droplet to
a Vaseline surface caused an increase in the amount of UV radiation transmitted. On the other
hand, the addition of a 0.5 mL water droplet to the cream, Olay Ultra Moisture Lotion with Shea
Butter, caused a decrease in the amount of UV transmitted (Figure 6). Results also indicate that
the addition of a 0.5 mL water droplet to the SPF 15 sunscreen-containing lotion did not alter the
0 mW/m2 of UV radiation that was transmitted through the SPF 15 lotion (Figure 6).
Figure 4: Averages of UV transmission through blank, water droplet-covered, cream and water
droplet-covered 3-sectioned microscope slides in first trial set
Figure 5: Averages of UV transmission through blank, water droplet-covered, cream-covered,
and cream and water droplet-covered 3-sectioned microscope slides in first trial set
Using the formula,
, the contact angles for water droplets
formed on each surface of the four various surfaces was calculated. The contact angles for the
water droplet on Vaseline, the water droplet on a bare microscope slide, the water droplet on the
cream, Olay Ultra Moisture Lotion with Shea Butter, and the water droplet on the SPF 15 cream,
Garnier Nutritioniste Skin Renew Daily Moisture Lotion with SPF 15 sunscreen were 99.3
degrees, 58.9 degrees, approximately 0 degrees, and close to 0 degrees. The contact angle of the
SPF 15 cream was close to 0 degrees due to its large radius, r value, and small height, b value.
Figure 6: Contact angle of water droplet
on Vaseline
Figure 7: Contact angle of water droplet on bare
microscope slide
Figure 8: Contact angle of water droplet
on Olay Ultra Moisture Lotion with Shea
Butter
Figure 9: Contact angle of water droplet on
Garnier Nutritioniste Skin Renew Daily Moisture
Lotion with SPF 15 sunscreen
DISCUSSION
According to the results of trial set one, water droplets alone, increased UV transmission,
as was expected. On the other hand, the combination of each skin cream with the 0.5 mL water
droplet decreased UV radiation transmission, compared to solely the 0.5 mL water droplet.
Specifically, UV radiation transmission through Vaseline and water drop was the highest,
followed by the UV radiation transmission through the cream and water drop, which is then
followed by the UV radiation transmission through the cream with SPF 15 sunscreen and water
droplet. Although sample size was sufficient, statistical tests for significance such as Analysis of
Variance were not performed.
From a molecular standpoint, the results indicate that the Vaseline caused more beading
than the regular cream and the cream with SPF 15 sunscreen because of its polarity. Vaseline,
being non-polar was not as attracted to the polar water molecules as the regular cream and the
cream with SPF 15 sunscreen. Results in the contact angle measurements, can be explained with
the same reasoning. The water droplet on top of the Vaseline had a greater contact angle than the
water droplets above the cream and cream with SPF 15 sunscreen because of the water droplets
polarity and the hydrophobic nature of the Vaseline. The cream and the sunscreen cream, being
less hydrophobic, had significantly smaller contact angles which resulted in the significantly
lower UV radiation transmission. Results of this experiment indicate that the correlation between
contact angles and UV transmission is that the greater the contact angle, the greater the amount
of UV radiation transmitted through the water droplet becomes (<http://www.eng.yale.edu/
design/ContactAnglePrinciples.pdf>) (Figure 15).
Figure 10: Polarity of Test Surface vs. Beading of Water Droplet
Conney’s (2008) research uncovered the possible tumorigenic effect of some commonly
used moisturizing creams. It is possible that his results were caused by the UV radiation’s
chemical alteration of the topically-applied skin cream. This experiment’s results uncovered an
additional possible mechanism of increased tumorgenicity resulting from application of skin
products. The ability of extremely hydrophobic skin agents, such as the Vaseline used in this
experiment, to enhance the UV radiation lensing ability of water droplets might play a role in the
formation of human skin cancer.
As a substitute for skin lotion, baby oil is widely used as a skin moisturizer. Baby oil,
similar to Vaseline in that it is extremely hydrophobic, can also act as Vaseline did in this
experiment and enhance the UV radiation lensing ability of water droplets. It is possible that this
enhancement in the optical properties of water droplets on the human skin can be an important
factor in the development of skin cancer. The previously discussed experiment conducted by
Brewer (2006) indicated the facilitation of leaf trichomes in the lensing properties of water
droplets. Could hair naturally found on the human skin have a similar effect on the lensing
properties of water droplets? For future research, studies on human and animal skin should be
conducted to test the role of baby oil and skin hair in the UV lensing properties of water droplets.
ACKNOWLEDGEMENTS
The author would like to thank her science teacher for his expertise as well as members
of her high school science faculty department who provided the time and resources needed to
conduct and analyze her research and her parents for their patience and support.
LITERATURE CITED
Aridegbe, Ife. “The Effectiveness of UV Pigments in Contact Lens Design.” 2009. Print.
Barnes, Jeremy D., Kevin E. Percy, Nigel D. Paul, Pam Jones, Chris K. McLaughlin, Phil M.
Mullineaux, Gary Creissen, and Alan R. Wellburn. "The Influence of UV-B Radiation on
the Physicochemical Nature of Tobacco (Nicotiana Tabacum L.) Leaf Surfaces — J Exp
Bot." Oxford Journals | Life Sciences | Journal of Experimental Botany. Web. 30 Nov.
2010.
<http://jxb.oxfordjournals.org/content/47/1/99.short>.
Brewer, C. A., W. K. Smith, and T. C. Vogelmann. "Functional Interaction between Leaf
Trichomes, Leaf Wettability and the Optical Properties of Water Droplets - BREWER -
2006 - Plant, Cell & Environment." Wiley Online Library. Web. 30 Nov. 2010.
<http://onlinelibrary.wiley.com/doi/10.1111/j.1365-3040.1991.tb00965.x/abstract>.
Forbes, Paul Donald. "Moisturizers, Vehicle Effects, and Photocarcinogenesis." Journal of
Investigative Dermatology. (2009): 261-62. Print.
Heffernan, Timothy, Masaoki Kawasumi, Allessandra Blasina, Kenna Anderes, and Allan
Conney. "ATR-Chk1 Pathway Inhibition Promotes Apoptosis after UV Treatment in
Primary Human Keratinocytes: Potential Basis for the UV Protective Effects of
Caffeine." Journal of Investigative Dermatology 129.7 (2009): 1805-1815. Web. 10 Dec
2009.
Huang, Scott. "Scott Huang - Liquid Lens Project." Stony Brook Laser Teaching Center. Web.
30 Nov. 2010. <http://laser.physics.sunysb.edu/~scott/liquid-lens/>.
Myint, H. H., A. M. Marpaung, H. Kurniawan, H. Hattori, and K. Kagawa. "Water Droplet
Lens Microscope and Microphotographs." IOPscience: Physics Education. Web. 30 Nov.
2010.
<http://iopscience.iop.org/0031-9120/36/2/301>.
"Principles of Contact Angle Analysis." AST Products, Inc. Web. 21 Sept. 2010.
<http://www.eng.yale.edu/design/ContactAnglePrinciples.pdf>.
"Ultraviolet Radiation." Ultraviolet Radiation- Causes of Skin Cancer- Stanford Cancer Center.
Stanford Medicine. Web. 0 Sept. 2010.
<http://cancer.stanford.edu/skincancer/skin/causes/uvrad.html>.