N2: number of drops of shampoo
solution.
R1: surface tension of distilled
water at room temperature.
R2: surface tension of shampoo
solution (39).
A good shampoo preparation can
reduce the surface tension of pure
water from 72 to less than 40
dyne/cm 25°C. Surfactants and
other compounds that diminish the
surface tension of the air have an
effect on its effectiveness.
Therefore, shampoos that diminish
water's surface tension have strong
detergency (cleansing ability) (27).
9. Wetting ability
Shampoo's wetting ability is
depending on the concentration of
surfactant in the formulation. A
higher surfactant concentration will
result in better wetting ability. The
shampoos with highest demand are
those with the shortest wetting time.
Shampoo formulations with shorter
wetting times contain more
detergent (27). Thus, the lesser time
it takes to remove the shampoo from
the hair, the better cleansing ability
the shampoo has (40). Wetting time
is calculated by timing how long it
takes for the shampoo to completely
wet the canvas paper. Then weigh
the canvas before cutting it into 1-
inch-diameter discs. After that,
place a disc of canvas paper on the
surface of the shampoo (1% v/v)
and time how long it takes for the
paper to absorb the shampoo using
a stopwatch (41).
10. Conditioning performance
The conditioning performance of
shampoo depends on its chemical
properties. Shampoos generally
contain conditioning polymers that
deposit, adhere to, or absorb into
hair proteins. The polymer
increases the ease of styling,
reduces static, and makes hair soft
and smooth. The shampoo's
conditioning effect was evaluated
by first washing the cut hair mass
with the shampoo preparation and
then performing physical
observations (27). Conditioning
performance criteria are graded on a
scale of 1 to 4, with 4 being very
good, 3 being good, 2 being
satisfactory, and 1 being poor (42).
11. Specific gravity
One of the physical analyses
performed to determine the stability
of the shampoo during storage is
specific gravity, because knowing
the specific gravity may also
establish the purity value of the
shampoo (43). The specific gravity
measurement is carried out using a
pyrex pycnometer. The pycnometer
is cleaned first, then dried and
allowed to cool. Then, weigh and
record the weight of the empty
pycnometer (A). The pycnometer is
then filled with water until it is
completely full and no air remains.
Clean the pycnometer's neck with a
clean towel before weighing it.
Next, record the weight of a
pycnometer filled with water (B).
Following that, the pycnometer is
cleaned and dried. Then, pour a
sample of the shampoo preparation
into the pycnometer. Weigh and
record the weight of the sample-
containing pycnometer (C). Set the
measurement conditions to a
temperature of 25°C (21).
12. Microbial examination
Mix 100 microliters of shampoo
preparation with liquid Mueller
Hinton agar and pour it into sterile
petri dishes under aseptic
conditions. The container is rotated
to thoroughly mix the contents
before it starts to harden. Following
that, the plate was incubated at 37°C
for 24 hours and the microbial
growth was detected (44).
13. Antimicrobial activity