The children. In 1977 Water-proof sunscreens were produced

The concept of
protecting the skin from the harmful chemicals and bacteria has been used for
centuries. Ancient Egyptians used Olive Oil for the same purpose. Likewise,
pastes of Zinc oxide were also applied on the skin to serve the same purpose.
However, the earliest synthetic sunscreen was not synthesized before 19281. The
importance of sunscreen was slightly heightened in 1936 when this concept was
first industrially used. Sunscreens evolved over time and in 1944, Pharmacist
Benjamin Green was able to formulate a rather more effective Sunscreen formula
for the US military during the World War II. In 19461, the first
effective modern sunscreen was synthesized which has been used till this day.
In addition, sunscreens have just improved as the usage increased among men,
women and children. In 1977 Water-proof sunscreens were produced which Sunscreens
are used to act as a protective layer over1, in order to protect the
skin from the environment. Moreover there are new products being introduced to
the market including Bioadhesive Nanoparticles to increase the chances of
durability of the sunscreen1.  
The concept of SPF (Sun Protection Factor) gave an estimate of how long
the protective layer would last2. Different sunscreens have varying SPF values affects the level of
overall exposure of the skin. A common misconception about sunscreens is that Sun Protection Factor is
the main criteria which affects the UV exposure of the skin. I wanted to
analyze whether this was true. If this was not true, I wanted to find out what
factor affected the protection from UV rays. I inferred
that SPF is not the main factor affecting UV absorption since I used SPF 50++
and my mother used SPF 40++. This was worthy of exploration because I wanted to know the reason behind
the absorption. This eventually led my direction of exploration to find what
would be the best composition of UV absorbing materials in sunscreens that
could provide protection from a wide range of UV radiations. In addition to
this, even though there have been several researches on simply the absorption
of UV by sunscreen, there is very little exploration of how this absorption
could be improved. The fact the Global Warming in increasing day by day,
radiations from the Sun are bound to intensify and cause more forest fires as
well as have side effects on our skin. Since there are various factors

affecting the
absorption, I evaluated and took the cause of this problem, the UV absorption,
to its roots. Based on my extensive research, I found out that there are
various Organic compounds which have Titanium (IV) Oxide and Zinc oxide
suspended in it. Upon further research, I found out that the percentage of the
Organic UV filters was a maximum concentration allowance of 10% by mass. This
was not the case for the ionic compounds. TiO2­ and ZnO have a
maximum allowance of 25%34 by mass.
In some areas of the world such as Japan, there is no limit to the maximum TiO2
and ZnO content. Thus, I concluded that TiO2 and ZnO were the
dominant UV filters in sunscreens. Moreover, UV spectroscopy is used in
determining the concentration of the constituents in a given sample. Sunscreen
samples consist of homogenous mixtures of Organic compounds along with
suspended Titanium (IV) Oxide (TiO2) and Zinc Oxide (ZnO). Even
though the range of TiO2 is given to be a fixed range,
experimentally the same result is not obtained for different concentration of
suspended TiO2 and ZnO. The absorption range of different
concentration sample is for both the ionic compounds. This in return affects
the UV absorption in different concentration mixtures of TiO2 and
ZnO i.e. in sunscreens. Based on the data to be analyzed, I chose to use a UV
spectrometry to determine the UV absorbance of sunscreens, TiO2 and
ZnO. This was repeated with different concentrations of the ionic compounds. After
which, 3 sunscreen samples’ UV absorbance spectrums were recorded and compared
with the pure TiO2 and ZnO absorbance samples to determine the
respective TiO2 and ZnO concentrations.

Research
Question

Hence I derived my
research question: To compare different sunscreen samples and their absorbance
of UVA and UVB based on the composition of Titanium (IV) Oxide and Zinc Oxide
present as compared to Pure Titanium (IV) Oxide and Zinc Oxide samples.

Conceptual Background.

UV Radiation

Ultraviolet radiation is a part of the electromagnetic spectrum and
is classified as the radiation that has a wavelength ranging from 100nm to
400nm, just before the visible spectrum. UV radiation are of 3 main types, UVA,
UVB & UVC. UV radiations are higher in energy and can penetrate the Ozone
layer present in the stratosphere. UVC is usually stopped and minimal amounts
reach the surface of the earth. Most
of us are exposed to large amounts of UVA throughout our lifetime. UVA rays
account for up to 95 percent of the UV radiation reaching the Earth’s surface.
Although they are less intense than UVB, UVA rays are 30 to 50 times more
likely to penetrate the skin.5.

UVA has higher penetration power and can penetrate
to up to the second layer of the skin unlike UVB, which only reaches up to the
first layer. UVA has long been known to play a major part in skin aging and
wrinkling, but until recently it was believed that it was a rather non-dominant.

However, it has been proved that UVA affects the
skin cells called keratinocytes, in return, damaging skin cells called keratinocytes
in the base layer of the epidermis, a centre for development of carcinogenic
cells. Hence, UVA contributes to and may even initiate the development of skin
cancers.

Sunscreen, also known
as sunblock and suntan lotion, is a lotion,
spray, gel or other topical product that absorbs or reflects some of
the sun’s ultraviolet (UV) radiation and thus helps protect
against sunburn.

            Sunscreen
use can help prevent melanoma6 and squamous
cell carcinoma7, two
types of skin cancer. According to recent studies, regular and controlled
usage of sunscreens can temporarily reduce the chances of wrinkling and sagging
of the skin. However there are several potential risks that are associated with
the usage of sunscreens. The potential for TiO2
and ZnO nanoparticles in sunscreens to cause adverse effects
depend primarily upon the ability of the nanoparticles to reach viable skin
cells. To date, the current weight of evidence suggests that TiO2
and ZnO nanoparticles do not reach viable skin cells8. Sunscreen
ingredients typically undergo extensive review by government regulators in
multiple countries, and ingredients that present significant safety concerns
(such as PABA) tend to be withdrawn from the consumer market. Concerns have also been raised about
potential vitamin D deficiency arising from prolonged use of sunscreen.
Typical use of sunscreen does not usually result in vitamin D deficiency;
however, extensive usage may. Sunscreen prevents ultraviolet light from
reaching the skin, and even moderate protection can substantially reduce
vitamin D synthesis. However, adequate amounts of vitamin D can be produced
with moderate sun exposure to the face, arms and legs, averaging 5–30 minutes
twice per week without sunscreen. (The darker the complexion, or the weaker the
sunlight, the more minutes of exposure are needed, approximating 25% of the
time

for minimal
sunburn. Vitamin D overdose is impossible from UV exposure thanks to an
equilibrium the skin reaches in which vitamin D degrades as fast as it is
created

Band Gap & Crystal field theory

The Crystal field theory describes the splitting
of degeneracies of electron orbitals into 2 or more levels of different energies.
 These difference in energies is
equivalent to the energies that lie within the electromagnetic spectrum for
different materials. This is a factor responsible for absorption of UV
radiation in ZnO and TiO29.

Band
gap is an energy range in a solid where no electron states can exist. It also refers to the energy
difference (in electron volts) between
the top of the valence band and
the bottom of the conduction band in insulators and semiconductors. It is the energy required to promote a valence
electron bound to an atom to become a conduction
electron, which is free to move within the crystal
lattice. Sunscreens either absorb UV or
reflect. Likewise, TiO2 and ZnO can scatter light due to its high
refractive index and absorb light of a specific frequency. Light of each
wavelength carries a certain energy. UV light carries energy ranging from 3.1
eV – 12.4 eV (UVA carries energy ranging from 3.10–3.94 eV and UVB
carried energy ranging from 3.94 eV to 4.43 eV. UVC ranges from 4.43 eV – 12.4
eV. However, UVC is not accounted for since it is not the focus of this
exploration.) TiO2 has a band gap of 3.05 eV (TiO2 in the form of
Rutile) and approximately 3.2 eV (TiO2 in the form of Anatase). Likewise, the
band gap of Zinc Oxide is relatively wide at 3.37 eV. The absorption of UV
light has correlates with the energy carried by the UV light and the band gap
of the respective material.

 

Refractive
Index

The refractive
index of a substance is the square root of its permittivity and permeability.
ZnO and TiO2 scatter light to a great extent which is why they
appear colorless or white. Their permittivity and permeability being high,
increases their refractive indices10.
Unlike colored pigments that provide opacity by absorbing visible light,
titanium dioxide and other white

pigments provide opacity by scattering
light. This scattering is possible because the white pigment can bend light. If
there is enough pigment in a system, all light striking the surface, except for
the small amount absorbed by the polymer or pigment, will be scattered outward,
and the system will appear opaque and white. Light scattering is accomplished
by refraction and diffraction of light as it passes through or near pigment
particles. Higher refractive index refers to a higher scattering power. This
means that the penetration of UV will be minimalized and lesser UV will reach
the sensor.