rheology

School of Pharmaceutical Sciences

FAR 223/3

Physical Pharmacy II

Experiment 3

Rheological Properties of Liquids and Ointments

Names : Tan Lee Khing 103621

: Thai Gaik Lee 103628

: Wong Jen Yie 103634

: Yap Yae Tyug 103638

Date : 25 February 2011

Coordinator: Mr. Samer Al-Dhalli

Objectives

a) To study the rheological properties of Bephanten, Vaseline and Nivea cream, including viscosity,

flowability and thixotropy.

b) To study type of flow of medicated ointment, Vaseline and Nivea cream.

c) To access customers’ acceptability towards medicated ointment, Vaseline and Nivea cream using

a ranking system.

d) To correlate patients’ acceptance with the rheological properties of the preparations.

Introduction

Rheology is the study of the deformation and flow of matter under the influence of an

applied stress. Rheology can also be defined as a study of the change in form and flow of matter,

embracing elasticity, viscosity, and plasticity. Basically, liquids can be divided into Newtonian fluids

and non- Newtonian fluids according to their flow properties.

The behavior of Newtonian liquids at constant temperature and pressure has the following

features:

1. The change in the shear rate is proportional to and at a constant rate to the change in the

shear stress applied. Thus the relationship between shear rate and shear stress is linear.

2. The shear viscosity doesn't vary with shear rate.

3. The viscosity is constant with respect to the time of shearing.

4. The viscosities measured in different types of deformation are always in simple proportion

to one another.

A liquid showing any deviation from the above features is non-Newtonian.

The following diagram shows the typical rheograms (flow curves) for Newtonian liquid

rate of shear

(sec -1 )

Shearing stress (dynes/cm)

http://en.wikipedia.org/wiki/Stress_(physics)

http://en.wikipedia.org/wiki/Matter

Non- Newtonian liquid is defined as one for which the relationship between shear rate and

shear stress is not constant. The viscosity of non-Newtonian fluids changes as the shear rate is

varied. Thus, the parameters of viscometer model, spindle and rotational speed all have an effect on

the measured viscosity. This measured viscosity is called apparent viscosity and is accurate when

explicit experimental parameters are adhered to. There are several types of non-Newtonian flow

behavior, characterized by the way a fluid's viscosity changes in response to variations in shear rate.

Pseudoplastic

Fluid displays a decreasing viscosity with an increasing shear rate, some examples include paints and

emulsions.

Dilatant

The fluid is characterized by an increasing viscosity with an increase in shear rate, some examples

include clay slurries, candy compounds, corn starch in water, and sand/water mixtures.

Plastic Flow (Bingham)

Liquid behaves like solid under static conditions. A certain amount of force must be applied to the

fluid before any flow is induced. This force is called yield value. Tomato catsup is an example of such

fluid. Once the yield value is exceeded and flow begins.

Some fluids display a change in viscosity with time under conditions of constant shear rate.

Tixotropic

Fluid undergoes a decrease in viscosity with time, while it is subjected to constant shearing

Rheopexic

Fluid's viscosity increases with time as it is sheared at a constant rate.

Experimental Procedure

Please refer to practical manual FAR223/3 Physical Pharmacy II, pages 13-18.

Result& Calculation

A. Vaseline

Shear stress, Pa Average shear rate 1/s log10 shear rate log10 (S-F)0.05006 0.00002422 -4.616 -

10.05000 0.00181850 -2.740 -20.05000 0.00689400 -2.162 -30.05000 0.01435500 -1.843 -40.05000 0.02464000 -1.608 -50.05000 0.03814500 -1.419 -60.05000 0.05612500 -1.251 -70.05000 0.08174000 -1.088 -80.05000 0.11939500 -0.923 -90.05000 0.18900000 -0.724 -

100.00000 0.32350000 -0.490 -110.00000 0.58715000 -0.231 0.301029996120.00000 0.95490000 -0.020 1.079181246130.10000 1.51145000 0.179 1.344392274140.10000 2.33150000 0.368 1.506505032150.10000 3.14250000 0.497 1.624282096160.10000 3.88600000 0.590 1.716837723170.10000 4.59750000 0.663 1.7930916180.10000 5.26000000 0.721 1.857935265190.10000 5.85800000 0.768 1.914343157200.10000 6.38750000 0.805 1.96425963210.10000 6.93800000 0.841 2.009025742220.10000 7.48650000 0.874 2.049605613230.10000 8.04200000 0.905 2.086715664240.10000 8.65600000 0.937 2.120902818250.00000 9.29100000 0.968 2.152288344250.00000 9.51900000 0.979 2.152288344240.00000 9.30100000 0.969 2.120573931230.00000 9.21050000 0.964 2.086359831220.00000 9.04900000 0.957 2.049218023210.00000 8.81750000 0.945 2.008600172200.00000 8.61350000 0.935 1.963787827190.00000 8.29850000 0.919 1.913813852180.00000 7.92250000 0.899 1.857332496170.00000 7.54500000 0.878 1.792391689160.00000 7.10850000 0.852 1.716003344150.00000 6.66750000 0.824 1.62324929140.00000 6.26000000 0.797 1.505149978130.00000 5.73550000 0.759 1.342422681120.00000 5.24200000 0.719 1.079181246

110.00000 4.72900000 0.675 0.301029996100.00000 4.15050000 0.618 -90.00000 3.58800000 0.555 -80.00000 3.02900000 0.481 -70.00000 2.50050000 0.398 -60.00000 1.97750000 0.296 -50.00000 1.46150000 0.165 -40.00000 0.99620000 -0.002 -30.00000 0.58235000 -0.235 -20.00000 0.27060000 -0.568 -10.00000 0.06701000 -1.174 -0.05006 -0.00317850 - -

0.00 50.00 100.00 150.00 200.00 250.00 300.00

-2.00

0.00

2.00

4.00

6.00

8.00

10.00

12.00

Average Shear Rate 1/s vs Shear Stress (Pa)

Shear Stress ( Pa )

Aver

age

Shea

r rat

e 1/

s

Initial Yield Value

Yield Value

From graph of Average Shear Rate Vs Shear Stress,

Initial Yield value for Vaseline = 60 PaActual Yield value for Vaseline = 108 Pa

0.00 50.00 100.00 150.00 200.00 250.00 300.00

-2.00

0.00

2.00

4.00

6.00

8.00

10.00

12.00

Average Shear Rate 1/s vs Shear Stress (Pa)

Shear Stress ( Pa )

Aver

age

Shea

r rat

e 1/

s

C

D

EF

The Viscosity , ŋ =

1gradient

Based on the graph, gradient = (9.2-0.6)/(250-120) = 0.066Thus, the viscosity = 1 / 0.066 = 15.12 Pa /s

Thixotropy is determined through the area between the 2 curves of the graphArea A: ½ x 4.0 x 80 = 160Area B: ½ x 4.4 x 80 = 176Area C: ½ x 3.2 x 70 = 112Area D: ½ x 3.2 x 50 = 80Area E: ½ x 0.8 x 70 = 28Area F: ½ x 1.2 x 30 = 18Total = Area A + Area B + Area C+ Area D + Area E + Area F = 574 Pa/ s

Thus, degree of thixotropy is 574.

0.00 0.50 1.00 1.50 2.00 2.50

-0.40

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

1.20Log10 Average Shear Rate vs Log10 (S-F)

Log10 (S-F)

Log1

0 Av

erag

e Sh

ear R

ate

From graph of Log10 Average Shear Rate Vs Log10 (S-F),

Constant, n = gradient of graph = (1.00-0.48)/(2.18-1.60) = 0.9

Terminal viscosity =1/gradient = 1/0.9 = 1.11

From the formula ,Log G = N log (S-F) – log (intrinsic viscosity) log γ = n log (x – ƒ ) - log ŋ’ Y = m x + c C = Y intercept = -0.32 C = - log ŋ’

-log ŋ’ = -0.32ŋ’ = 2.09 Pa/s

n=0.9, ≈ 1Therefore, the plastic flow of Vaseline can be categorized as plastic Bingham flow.

B. Nivea

Shear stress, Pa Average shear rate 1/s log10 shear rate log10 (S-F)0.05 -0.00011565 - -10.05 -0.00006748 - -20.05 -0.00008759 - -30.05 -0.00009499 - -40.05 0.0003347 -3.475459938 -50.05 0.0001825 -3.738852781 -60.05 0.0003233 -3.490509945 -70.05 0.0002841 -3.546644416 -80.05 0.0003882 -3.411060119 -90.05 0.0006621 -3.179192062 -100.00 0.0006516 -3.186134574 -110.00 0.0009936 -3.002904067 -120.00 0.0016554 -2.781212699 -130.10 0.0028301 -2.548313869 -1140.10 0.0086651 -2.062342071 1.004321374150.10 0.01876 -1.726882816 1.303196057160.10 0.034295 -1.464884843 1.478566496170.10 0.052105 -1.28323625 1.603144373180.10 0.074245 -1.129448438 1.699837726190.10 0.104264 -0.981981268 1.778874472200.10 0.134161 -0.872489363 1.845718018210.10 0.174025 -0.759504008 1.903632516220.10 0.212296 -0.673173839 1.954724791230.10 0.25545 -0.592809743 2.000434077240.10 0.29875 -0.524807736 2.041787319250.00 0.36633 -0.436243164 2.079181246250.00 0.38019 -0.42011496 2.079181246240.00 0.3628 -0.440448372 2.041392685230.00 0.34735 -0.459348347 2220.00 0.3341 -0.476239174 1.954242509210.00 0.31725 -0.498714019 1.903089987200.00 0.29678 -0.52768102 1.84509804190.00 0.27605 -0.559127899 1.77815125180.00 0.25405 -0.595196451 1.698970004170.00 0.23235 -0.633972973 1.602059991160.00 0.2048 -0.688785698 1.477121255150.00 0.1797 -0.745567573 1.301029996140.00 0.1497 -0.82489385 1130.00 0.1275 -0.894605465 -120.00 0.10407 -0.982790095 -110.00 0.081135 -1.09090741 -100.00 0.059605 -1.224832958 -

90.00 0.042625 -1.370451258 -80.00 0.030665 -1.513472681 -70.00 0.02059 -1.686459303 -60.00 0.008745 -2.058355836 -50.00 0.0017317 -2.761642993 -40.00 -0.0002614 - -30.00 -0.0002805 - -20.00 -0.0003677 - -10.00 -0.0003236 - -0.05 -0.0004428 - -

0 50 100 150 200 250 300-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Graph of Average Shear Rate (1/s) vs Shear Stress (Pa)

Shear Stress (Pa)

Ave

rage

She

ar R

ate

(1/s

)

Actual Yield Point

Initial Yield Point


Initial Yield value for Nivea cream = 130 PaActual Yield value for Nivea cream = 170 Pa

The Viscosity, ŋ =

1gradient

Based on the graph, gradient = (0.39-0.02) / (270-170) = 0.0037

Thus, the viscosity = 1 / 0.0037 = 270.27 Pa /s

Thixotropy is determined through the area between the 2 curves of the graphArea A: ½ x 0.15 x 90 = 6.75Area B: ½ x 60 x 0.15 = 4.5Area C: ½ x 70 x 0.16 = 5.6Area D: ½ x 30 x 0.14 = 2.1Area E: ½ x 40 x 0.07 = 1.4Total = Area A+Area B +Area C+ Area D+ Area E= 20.35 Pa/ s

Thus, the degree of thixotropy is 20.35 Pa/s .

From graph of Log10 Average Shear Rate Vs Log10 (S-F),

The gradient = ( 3-0.5 ) / ( 2.2-0.5 ) = 1.471Terminal viscosity = 1/gradient = 1/1.471 =0.6798From the formula, log γ = n log ( σ – ƒ ) - log ŋ’ Y = m X + CC= Y intercept = -2.3C = - log ŋ’ -log ŋ’ = -2.3ŋ’ = 199.53 Pa/s

The gradient, n= 1.471n>1, thus the plastic flow of Nivea cream an be categorized as Casson model. It is also because up-curve and down-curve are not superimposed.

C. Bephanten Cream

Stress (Pa) Shear Rate (Pa/s)Average

Shear Log10 Stress Log10

Average Log10 S-F Rate (1/s) Shear Rate

5.01E-02 1.93E-05 -8.25E-06 5.53E-06 -1.30E+00 -5.26E+00 -1.01E+01 1.69E-03 1.69E-03 1.69E-03 1.00E+00 -2.77E+00 -2.01E+01 3.15E-03 2.92E-03 3.04E-03 1.30E+00 -2.52E+00 -3.01E+01 2.11E-01 5.16E-03 1.08E-01 1.48E+00 -9.67E-01 -4.01E+01 4.28E-01 1.73E-01 3.00E-01 1.60E+00 -5.22E-01 -5.01E+01 6.72E-01 4.64E-01 5.68E-01 1.70E+00 -2.46E-01 -6.01E+01 1.02E+00 8.01E-01 9.12E-01 1.78E+00 -4.01E-02 -7.01E+01 1.43E+00 1.12E+00 1.28E+00 1.85E+00 1.06E-01 -8.01E+01 1.91E+00 1.53E+00 1.72E+00 1.90E+00 2.34E-01 -9.01E+01 2.51E+00 2.03E+00 2.27E+00 1.95E+00 3.56E-01 -1.00E+02 3.38E+00 2.94E+00 3.16E+00 2.00E+00 5.00E-01 -1.10E+02 5.07E+00 4.89E+00 4.98E+00 2.04E+00 6.97E-01 -1.20E+02 9.15E+00 1.01E+00 5.08E+00 2.08E+00 7.05E-01 -1.30E+02 2.11E+01 2.94E+00 1.20E+01 2.11E+00 1.08E+00 0.785331.40E+02 5.41E+01 7.83E+00 3.10E+01 2.15E+00 1.49E+00 1.2072751.50E+02 1.05E+02 1.36E+00 5.30E+01 2.18E+00 1.72E+00 1.4173331.50E+02 1.35E+02 1.63E+00 6.85E+01 2.18E+00 1.84E+00 1.4173331.40E+02 1.30E+02 1.47E+00 6.56E+01 2.15E+00 1.82E+00 1.2072751.30E+02 1.10E+02 1.26E+00 5.58E+01 2.11E+00 1.75E+00 0.785331.20E+02 9.08E+01 1.04E+00 4.59E+01 2.08E+00 1.66E+00 -1.10E+02 7.01E+01 8.22E+00 3.92E+01 2.04E+00 1.59E+00 -1.00E+02 5.07E+01 6.01E+00 2.84E+01 2.00E+00 1.45E+00 -9.01E+01 3.31E+01 4.11E+00 1.86E+01 1.95E+00 1.27E+00 -8.01E+01 1.75E+01 2.31E+00 9.88E+00 1.90E+00 9.95E-01 -7.01E+01 7.69E+00 1.05E+00 4.37E+00 1.85E+00 6.40E-01 -6.01E+01 3.18E+00 4.01E+00 3.60E+00 1.78E+00 5.56E-01 -5.01E+01 1.49E+00 1.33E+00 1.41E+00 1.70E+00 1.50E-01 -4.01E+01 8.57E-01 6.49E+00 3.67E+00 1.60E+00 5.65E-01 -3.01E+01 4.37E-01 2.57E+00 1.50E+00 1.48E+00 1.77E-01 -2.01E+01 1.64E-01 -2.29E+00 -1.06E+00 1.30E+00 - -1.01E+01 -4.26E-03 -4.26E+00 -2.13E+00 1.00E+00 - -5.01E-02 -5.84E-03 -1.16E+00 -5.83E-01 -1.30E+00 - -

0.00E+00 2.00E+01 4.00E+01 6.00E+01 8.00E+01 1.00E+02 1.20E+02 1.40E+02 1.60E+02-1.00E+01

0.00E+00

1.00E+01

2.00E+01

3.00E+01

4.00E+01

5.00E+01

6.00E+01

7.00E+01

8.00E+01

Graph of Average Shear Rate vs Shear Stress (Bephanten)

Shear Stress

Aver

age

Shea

rRat

e (1

/s)


Initial yield value: 50 PaActual yield value: 125 Pa

0.00E+00 2.00E+01 4.00E+01 6.00E+01 8.00E+01 1.00E+02 1.20E+02 1.40E+02 1.60E+02-1.00E+01

0.00E+00

1.00E+01

2.00E+01

3.00E+01

4.00E+01

5.00E+01

6.00E+01

7.00E+01

8.00E+01

Graph of Average Shear Rate vs Shear Stress (Bephanten)

Shear Stress

Aver

age

Shea

rRat

e (1

/s)

C

Initial Yield Value Actual Yield Value


The Viscosity , ŋ =

1gradient

Based on the graph, gradient = (80-0) / (160-126) = 2.35Thus, the viscosity = 1 / 2.35

= 0.43 Pa /s

Thixotropy is determined through the area between the 2 curves of the graphArea A: ½ x 32x 28= 448Area B: ½ x 32x36 = 576Area C: ½ x 37x38 = 703Total = Area A+Area B +Area C= 1727 Pa/ s

Thus, the degree of thixotropy is 1727.

From graph of Log10 Average Shear Rate Vs Log10 (S-F),The gradient = (1.84-(-0.18) ) / ( 1.4-0 ) = 1.443

Terminal viscosity = 1/gradient = 1/1.443 =0.693

From the formula, log γ = n log ( σ – ƒ ) - log ŋ’ Y= mX + C

C= Y intercept = -0.18C = - log ŋ’ -log ŋ’ = -0.18ŋ’ =1.51 Pa/s

The gradient, n= 1.443n>1, thus the plastic flow of Bepanthen cream can be categorized as Casson model.

CUSTOMER ACCEPTABILITY ASSESSMENT

One Way ANOVA

Step 1:

Step 2:

Step 3:

Step 4:

Step 5:

Step 6:

Step 7:

If F value > critical value, the difference is statistically significant. Tukey HSD test is carried out to determine which of the groups are statistically different.

Dear junior, to make the calculation for ANOVA easier you can use the excel worksheet title ANOVA worksheet. Just replace the raw data values in the highlighted columns =)

CF=(Σx total )2

n total

SStotal=∑ x2total−CF

SSbetween=(∑ xNivea )

2

nNivea+

(∑ xBephanten )2

nBephanten+

(∑ xVaseline )2

nVaseline−CF

SSwithin=SS total−SSbetween

S2between=SSbetweend . f .between

S2within=SSwithind . f .within

F=S2betweenS2within

1)Thickness

One-way ANOVA test of customer acceptability assessment towards thickness

HO : The difference in thickness of the ointments is not significant.

HA : The difference in thickness of the ointments is significant.

Ranking, x

Frequency, f fx fx²

Nivea

Bephanten

Vaseline Nivea

Bephanten

Vaseline

Nivea

Bephanten

Vaseline

1 2 5 0 2 5 0 2 5 0

2 5 14 4 10 28 8 20 56 16

3 10 7 4 30 21 12 90 63 36

4 6 1 5 24 4 20 96 16 80

5 3 0 4 15 0 20 75 0 100

6 1 0 10 6 0 60 36 0 360

Total, ∑ 27 27 27 87 58 120 319 140 592

NiveaBephant

enVaselin

e

mean3.2222

222.14814

84.4444

44

Variance

1.196703 0.75541

1.474055

CF = 866.9753SStotal =184.0247SSbetween = 71.28395SSwithin = 112.7407

d.f. SSbetween= k-1 = 3-1 = 2d.f. SSwithin = nTotal-k = 81-3 = 78d.f SStotal = nTotal-1= 81-1= 80

S2 between = 35.64198

S²within = 1.445394F= 24.659

At the 5% significance level,

Fcrit(2,78) = 3.114 at α = 0.05

From the test, F= 24.659> 3.114 Thus, the difference in thickness of the ointments is significant.

∴HA is accepted

Tukey Test

From table of q (0.05 level)

k = 3, d.f. = 78q = 3.38

HSD = q x √ within−groupsmean squaresn

= 3.38 x √ 1.44539427

=0.782038

Type of ointment Mean (x) Difference of mean, Δ HSD Conclusion

Vaseline 4.444444 |xV - xB|=2.296296 0.782038 Δ> HSD, p < 0.05

Bephanten 2.148148 |xV - xN|=1.222222 0.782038 Δ>HSD, p < 0.05

Nivea 3.222222 |xB - xN|=1.074074 0.782038 Δ> HSD, p < 0.05

- Difference between Vaseline and Bephanten is significant.

- Difference between Vaseline and Nivea is significant.

- Difference between Bephanten and Nivea is significant.

2)SpreadibilityOne-way ANOVA test of customer acceptability assessment towards spreadibility HO : The difference in spreadibility of the ointments is not significant.HA : The difference in spreadibility of the ointments is significant.

Ranking, x


NiveaBephanten

Vaseline

Nivea

Bephanten

Vaseline

Nivea

Bephanten

Vaseline

1 2 7 3 2 7 3 2 7 3

2 6 8 4 12 16 8 24 32 16

3 6 4 10 18 12 30 54 36 90

4 5 4 4 20 16 16 80 64 64

5 8 0 4 40 0 20 200 0 100

6 0 4 2 0 24 12 0 144 72 Total, ∑

27 27 2792 75 89 360 283 345

NiveaBephanten

Vaseline

mean3.407407

2.777778

3.296296

Variance

1.312596

1.662959

1.382826



S2 between = 3.049393S²within = 2.215574F= 1.376344

At the 5% significance level,Fcrit(2,78) = 3.114 at α = 0.05

From the test, F= 1.376344< 3.114 Thus, the difference in spreadibility of the ointments not significant.

HA is rejected.3)PreferenceOne-way ANOVA test of customer acceptability assessment toward preference HO : The difference in preference of the ointments is not significant.HA : The difference in preference of the ointments is significant.

Score, x


NiveaBephanten

Vaseline

Nivea

Bephanten

Vaseline

Nivea

Bephanten

Vaseline

1 3 8 4 3 8 4 3 8 4

2 9 7 5 18 14 10 36 28 20

3 4 4 9 12 12 27 36 36 81

4 4 5 6 16 20 24 64 80 96

5 5 1 2 25 5 10 125 25 50

6 2 2 1 12 12 6 72 72 36 Total, ∑

27 27 2786 71 81 336 249 287

NiveaBephanten

Vaseline

mean3.185185

2.629630

3.000000

Variance

1.516258

1.518970

1.276569



S2 between = 2.160494S²within = 2.158594F= 1.00088

At the 5% significance level,Fcrit(2,78) = 3.114 at α = 0.05From the test, F= 1.00088< 3.114 Thus, the difference in preference of the ointments not significant.

HA is rejected.

Discussion :

A) Product Assessment

i. Characteristic of flow

All the 3 ointments ( Vaseline, Nivea cream and Bephanten) in this experiment are non-

Newtonian liquids as all the curves obtained from the plotted graphs (shear strain,G vs shear

stress,S) are not linear. Instead of that, straight line will be obtained from the graph since Newtonian

liquid exhibits a constant ratio between shear stress and shear rate.

Vaseline, Nivea cream and Bephanten are non- Newtonian liquids with plastic flows since

the curves intercept with the x-axis and not passing through the origin of the graphs ( G vs. S).

Fluidity of all the 3 ointments increases with the shear stress that applied to each of them. Shear

stress applied to the systems should exceed the yield value so that elastic strength can be overcome

in order to produce flows of ointments.

Types of plastic flows can be further determined using the graph log G versus log (S-F) and

the equation of Log G = N log (S – F) – log n’. Vaseline shows a plastic flow that follow Bingham

model as the gradient of the slope, N is nearly 1. Besides, Nivea cream and Bephanten show plastic

flows that follow Casson model since both of their N is greater than 1.

ii. Yield value

Yield value is the minimum shear stress which is required to be applied to the system to

cause measurable shear rate and produce flow. The bonds between the ointments particles must

first be broken to initiate flow. In other word, the ointments does not flow but deforms elastically or

reversibly if the shear stress applied to each of them lower than initial yield value. In this

experiment, Vaseline possesses the lowest yield value followed by Bethanpen and Nivea. The least

stress is needed to cause flow of Vaseline compared to other 2 ointments.

The sequence of yield values : Vaseline < Bephanten < Nivea cream

iii. Plastic viscosity

Apparent viscosities of each ointment can be determined by dividing the gradient of slope

from graph (1/s vs S ) by 1. Nivea cream shows the highest apparent viscosity with 270.27Pa/s,

followed by Vaseline (15.12Pa/s) and Bephanten (0.43Pa/s). Increasing of shear stress can break the

bond between droplets of ointments to reduce the viscosities of ointments. At the same time, the

fluidities of ointments are increased, which mean that the ointment has higher ease of flow.

iv. Thixotropy

Thixotropy can be defined as a reversible, time-dependent decrease in viscosity at a constant

shear rate. All 3 ointments show thixotropic properties as there are shift of the down-curve to the

left when stress is gradually decreases in the graphs of (G vs. S). G increase with S in this experiment.

When S is keep constant, G will still increase with time. At this point, the viscosities of the ointments

keep on decreasing. However, the ointments will gradually return to their original shape and

viscosities increase again when S is removed.

Degree of thixotropy can be related to the concentration of the ointment. Higher viscosity

will be produced when concentration of ointment used is high. There are more bonds or network

between particles to be formed in the system. This results in a more viscous system and stronger

three dimensional structures. Hence, ointment with higher viscosity needs a longer time to re-form

into its initial structure, resulting in higher degree of thixotropy.

In this experiment, the thixotropic value obtained for Vaseline is 574 Pa/s, Bephanten is

1727 Pa/s, and Nivea cream is 20.35 Pa/s. Therefore we can conclude that the Nivea cream can

return to its initial structure easily after a flow has occurred due to its lowest thixotropic value.

B) Customer Acceptability Assessment

27 students are enrolled in this experiment to evaluate 3 samples, which are Vaseline,

Bephanten and Nivea cream based on their thickness, spreadibiliy and customer preference. . The

three characteristics are compared and ranked individually. One-way ANOVA test has been carried

out to study whether there is any significant difference between the 3 samples. Tukey Test is further

carried out to determine where the difference occurs due to the limitation of One-way ANOVA test

which unable to determine such difference.

I. Thickness

From the data showed by one-way ANOVA, there is significant difference among the three

samples if is more than 0.05, which means that F is more than critical value of 3.114. and Tukey

Test is further carry out to determine where the significant differences occurs. If the difference of

mean, is more than T (obtained from calculation) which is 0.782, the difference is significant and

vice versa. The thickness of the three samples can be show as below:

Vaseline < Nivea cream < Bephanten

From one-way ANOVA, F is 24.659 which is more than 3.114, so there is significant

difference in thickness. Tukey test results show that the difference of mean in thickness between

Vaseline and Nivea cream, Vaseline and bephanten , Nivea cream and Bephanten are significant.

Differences of mean between all these 3 samples are more than 0.782.

II. Spreadibility

From the data showed by one-way ANOVA, there is no significant difference in spreadibility

of these three samples since F is 1.376 which is less than 3.11. It means that the 3 samples have

almost similar spreadability.

III. Preference

There is no significant difference in term of customer preference of these three samples

since. F obtained is 1.000 which is less than 3.11 in one-way ANOVA. This may be due to the similar

materials present in the three samples. The three samples are quite oily and very viscous.

Although there are some significant differences in term of thickness, there are no significant

difference in term of customer preference and spreadibility. So, we conclude that thickness of

samples will not affect spreadibility and preference of customers. However, the results we get from

the experiment seem to be not accurate enough due to the sample size is too small. Bias may occur

as the decisions of students may influence by other students.

Conclusion

1. From the graph rates of shear versus shearing stress, we found that the actual yield value of

preparations is in order of:

Vaseline < Bephanten < Nivea cream

2. From experiment, we found that the viscosity of the ointment is in the order of:

Bephanten < Vaseline < Nivea cream

3. From the ANOVA and Turkey Test done, we can summarize the acceptability of customers

towards the Vaseline, Nivea cream and Bephanten:

-There is significant difference among the thickness of three samples.

-There is no significant difference among the spreadibility and customers’ preferences of the

three samples.

-Thickness of the samples will not affect spreadibility and preference of customers towards

the samples.

References

1. S. Balakrishnan. PharmaExpress. Characterisings pharmaceutical lotions by rheology

[Online]. [2001]; Available

from:http://www.expresspharmaonline.com/20061215/ipcspecial04.shtml

2. Ian Scott and Debbie Mazhindu. Statistics for healthcare professionals. An Introduction.

SAGE Publications Ltd; 2005

3. Physical Pharmacy Practical Manual FAR223/3 page 13-18

4. Dr Toh Seok Ming’s Rhelogy lecture notes 2011

rheology

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