Journal of Modern Physics, 2012, 3, 1878-1881
http://dx.doi.org/10.4236/jmp.2012.312236 Published Online December 2012 (http://www.SciRP.org/journal/jmp)
The Determination of Surface Tension of Traditional
Chinese Medicine Tablet
Xiaolu Zhang, Hao Zhang, Ke Liang, Er’jia Zhu, Ruisi Yan, Hui Yang, Zaiyou Tan*
School of Pharmacy, Guangdong Pharmaceutical University, Guangzhou, China
Received September 27, 2012; revised October 26, 2012; accepted November 4, 2012
ABSTRACT
In this paper we aimed to determine the surface tension of traditional Chinese medicine (TCM) tablet and tried to pro-
vide a key reference parameter to control tablet film coating quality. Using contact angle tester, the Chinese medicine
tablet, a famous Fufang Danshen tablet CP as a model example, was determined by Zisman critical surface tension
method. Our study showed that the critical surface tension of Fufang Danshen tablet CP was determined to be 18.00
dyne/cm. The Zisman method, hence, can determine successfully the critical surface tension of Chinese medicine tablet
and will become an effective manner to control tablet film coating quality.
Keywords: Surface Tension; Contact Angle; The Zisman Critical Surface Tension Method; Fufang Danshen Tablet CP;
Chinese Medicine
1. Introduction
Film coating is a process which involves the deposition
of a membrane consisting of polymer, plasticizer, col-
ourant and possibly other additives onto the surface of a
pharmaceutical dosage form, typical a tablet or a granule.
Over the past two decades, there has been a dramatic
increase in the use of this process in China. The reasons
for file coating are many and varied. They include [1]: 1)
To improve product appearance, odour and taste and to
aid swallowing. 2) To aid identification and hence de-
crease the risk of confusion, especially when patients
have to take several preparations. 3) To protect the active
ingredient against heat, light and moisture. 4) To separate
incompatible active ingredients present in the preparation.
5) To prevent dust formation during subsequent packing
on high-speed packing lines. 6) To control the release of
an active ingredient by use of either a coating with
pH-dependence solubility or a coating that acts as a dif-
fusion membrane. Compared to the conventional sugar
coat, the film coat is relatively thin typically 10 - 100 μm.
Although the technology involved in the application of
such a thin coating to a substrate is not new, having
precedents in both the paints and adhesive technologies,
problems do occur resulting in a number of film defects.
These can either affect the visual appearance of the
coated tablet or, more importantly, result in the loss of
continuity of the film and thus affect the release of the
active ingredient from the preparation. Therefore, look-
ing for the reference factor of quality control of film
coating of tablet is necessary.
One of the requirements of tablet film coating is that
good adhesion of the coat to the tablet must be achieved.
The properties of the coating formulation as well as those
of the tablet can influence adhesion. The prerequisite for
good adhesion is the spreading of the atomized droplets
over the surface of the tablet and limited penetration of
the coating solution into pores of the tablet. Both of these
are controlled by the surface tension of the tablet and the
coating. The surface tension of solid surface can be de-
termined using: Owen’s method [2], Van Oss’s [3] method
and Zisman’s method [4]. The both of Owen’s and Van
Oss’s must depend on accurate interaction energy pa-
rameters of all components to determine the surface ten-
sion of TCM tablet but it is difficult owing to the ingre-
dients of the tablet extracting from various herbs are
complicate. So we make an experiment in order to find
out the surface tension of CTM tablet by Zisman’s me-
thod.
Zisman and his associates found that when the cosine
of the contact angle, was plotted versus the surface ten-
sion for a homologous series of liquids spread on a sur-
face such as Teflon (polytetrafluoroethylene), a straight
line resulted. The line can be extrapolated to cosθ = 1,
that is, to a contact angle of zero, signifying complete
wetting. The surface tension at cosθ = 1 was given the
term critical surface tension and the symbol γc, Zisman
concluded that γc was characteristic for each solid. We
should try to find out such γc of film coating of TCM
*Corresponding author.
C
opyright © 2012 SciRes. JMP

X. L. ZHANG ET AL. 1879
tablet as a characteristic parameter to control tablet coat-
ing quantity. In this paper, we will report the traditional
Chinese medicine tablet, a famous Fufang Danshen tablet
CP [5] as a model example, was determined using contact
angle tester by Zisman critical surface tension method.
2. Instruments and Reagents
2.1. Instruments
The JZ8002 electronic balance (Shanghai Balance In-
strument Factory); GZX-9240MBE significant number of
blast oven (Shanghai Xun Bo Industrial Co., Ltd. Medi-
cal Equipment Factory); JC2000C1 contact angle meas-
uring instrument (Shanghai Zhong Chen Technology Co.,
Ltd.).
2.2. Reagents
Pure water (Guangdong Pharmaceutical University); For-
mamide (Sino Pharmaceutical and Chemical Reagent Co.,
Ltd., AR); Glycol (Guangzhou Chemical Reagent Fac-
tory, AR); Butanol (J & K, AR).
3. The Contact Angle Measurements
3.1. Preparation of Fufang Danshen Tablet CP
and the Test Liquids
We prepare the Fufang Danshen tablet CP by weighing
the formulation 400 mg and Repressing them into 2 mm
thickness and smooth surface tablet for sparing according
to Chinese Pharmacopoeia as a model tablet study and
design several test liquids (pure water, formamide, glycol,
butanol etc.) system.
3.2. Measurements of Contact Angle of Fufang
Danshen Tablet CP
Pretreatment: Place 5 ml water, Butanol, glycol, for-
mamide in the Petri dish, respectively and then put the
Petri dish in closed desiccators. The tablets employed to
test were located in the closed desiccators for 48 h until
the surface was saturated under the steam of the test liq-
uid.
Measure: The measurements were conducted through
the way of sessile drops with a computerized JC2000A
contact angle goniometer (Shanghai Balance Instrument
Factory). When the JC2000A contact angle goniometer
was operated, the production of the sessile drops was
yielded by performing the processes as follows:
1) Control the temperature to be 25˚C.
2) The infusion needle of the instrument was coated
with paraffin to ensure that the droplet is always in the
needle position.
3) Placing the needle near the surface, the correspond-
ing volume of liquid was squeezed out of the syringe.
4) Squeezing a drop of tested liquid on the tablet sur-
face, focusing camera 5 s latter.
5) Recorded every 5 seconds until 30 seconds and test
10 times for each test liquid Contact angle was measured
using the JC2000A, which takes a video image of the
drop and uses goniometer to determine and calculate.
6) Then select the mean value as the θ.
Each measurement should be finished less than 1 min to
minimize the effects of evaporation of the liquids. It was
found experimentally that the contact angle remained
constant within this operating time. An advancing con-
tact angles was measured in this way. Each number in the
Table 1 is the mean value of at least 10 single measure-
ments. The results and images are shown in Figure 1.
4. Results and Discussion
To characterize the TCM tablet, the surface tensions of
several liquids and their contact angles on the model Fu-
fang Danshen tablet CP were determined at 25˚C, as
showed in the following Table 1.
Plot cosθ versus γ, they appear to fit nicely the Zisman
principle, producing a straight line that extrapolates to
cosθ corresponding to a critical surface tension of γc =
18.00 dyne/cm as shown in Figure 1. From the results
obtained, the liquid in the tablet would be expected to the
best wet on the model tablet. For a more exact calcula-
tion of the critical surface tension γc, least-squares linear
regression analysis can be applied to yield:
2
cos0.0029 1.0522,0.9859.
cR



  (1)
According to the above critical surface tension of Fu-
fang Danshen tablet CP which was tested to be 18.00
dyne/cm, we prepared 3 batches of film control release
coated tablets of Fufang Danshen. The results of release
rate and the release profiles of 3 batches of tablets were
exhibited in the Table 2 and Figure 2.
The results showed that the released rate and the veri-
fication of 3 batches which were good agreement on the
quality requirements of control drug release formula-
tions.
5. Conclusion
Although one frequently desires to determine the relative
Table 1. Contact angles of liquids and surface tension of
Fufang Danshen tablets CP at 25˚C.
Surface tension Contact angle cosθ
Water 72.8 31.43 0.845
Formamide 58.2 28.4 0.876
Glycol 48 22.14 0.922
Butanol 24.6 11.6 0.98

X. L. ZHANG ET AL. 1880
Surface Tension of FufangDanshen Tablet CP b
Zisman Method
y = -0.0029x + 1.0522
R
2
= 0.9859
0.82
0.84
0.86
0.88
0.9
0.92
0.94
0.96
0.98
1
1.02
0 102030405060
Surface Tension (Dyne/cm)
cosθ
y
7080
Figure 1. Surface tension of F ufang Danshen tablets CP by Zisman method.
Table 2. Drug release with different batches.
Time (h) 1 2 3
2 21.4 22.7 19.5
4 42.1 45.5 39
6 57.3 62.1 54.2
8 73.6 76.2 70.7
10 83.4 84.9 79.2
12 87.8 89.7 84.1
0
10
20
30
40
50
60
70
80
90
100
0246810
Release Time(h)
Amount Release(%)
1214
Figure 2. Release profile of verification test.
efficiencies of wetting agents, it is difficult to measure
directly the contact angle of a solid surface. As a result of
these difficulties, our experimental tests have indicated
Zisman’ method can be used to measure the critical sur-
face tension of the TCM tablet in industry. To ensure the
quantity control the TCM tablet, we suggest Zisman’s
method can be used for estimating the ability of a wetting
agent or file coating on the surface of the tablet and the
application property of such products are ordinary deter-
mined by subjective evaluation. More importantly, Zis-
man’s method can be applied to the surface tension of
solid which was constituted with various components. It
is difficult for other indirect methods such as the Owen’s
method and Van Oss’s method to determine the surface

X. L. ZHANG ET AL. 1881
tension of solid owing to they must depend on accurate
interaction energy parameters of each component. How-
ever, in order to ensure accessing accurate surface ten-
sion values, the nature of the surface materials should be
poorly hygroscopic. Meanwhile, the humidity of experi-
mental environment must be controlled. The surfaces of
tested samples should be saturated by the tested liquid
during experiment procedure. This job calls for patience.
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