Indian Journal of Chemistry
Vol. 39A, June 2000, pp. 589- 597
Effects of additives (NaCl, urea, glucose, guanidine hydrochloride) on the
physico-chemical properties of reverse micelles of Tweens in chloroform
Susantamay Nandi, Subhash Ch Bhattacharya* & Satya P Moulik
Physical Chemistry Section, Chemistry Department, Jadavpur University, Calcutta 700 032
Received 28 June 1999; revised 20 October 1999
The physico-chemical properties, viz, critical micelle concentration (CMC) of reverse micelle(s) and binding of the dye
Safranine T (3,7 diamino-i, 8 dimethyl-5-phenyl phenazinium chloride) with the reverse micelle (RM) of waterffweenChloroform in the presence of varied concentrations of the additives (sodium chloride, glucose, urea and guanidine hydrochloride), have been investigated. While the first reduces the CMC of the studied RM system, the latter three increase it. The
binding efficiency of the dye is likewise affected by the additives. An attempt has been made to rationalize the results on
physico-chemical basis.
Compared to normal micelles (NM), the basics of
reverse micelles (RM) are less explored. The RM
have more application potentials and fundamentals of
their physico-chemical properties should be of significant value. Detailed studies on the physicochemical properties of self-assembling systems using
a great variety of techniques can be found in literature1 -10. Their structural behaviours in solution also
find noteworthy importance4-8. It is known that the
polar/non-polar interface of RM differs from that of
the NM and that the water in the core is considered to
be in a different state compared to the bulk water 11 ·12 •
The oxidation-reduction and acid base equilibria may
. .f 1cant
.
Iy m
. fl uence d m
. RM 13·14 . They are rebe stgnt
ported also to affect the photophysical properties of
certain substances 15-18 . The kinetics of reactions are
observed to be remarkably influenced by the same
micelles 13 ' 14 .
In recent years, formation, thermodynamics and
dye-binding characteristics of both normal and reverse micelles under different conditions have been
reported 9 ·to·19-22 . Th e spec1.f.tc system o f RM very recently studied by us is th at of Tweens in chloroformn. It is known that additives can significantly
affect the micellization characteri stics of surfactants24. Salts and non-ioni c compounds (viz, glucose,
alcohol s, urea, etc. ) have been widely used in thi s
direction . They are found to affect the critical micelle
concentration (CMC) of surfactants and their solubilization capabilities. The effects of additives on the
physico-chemical characteristics of RM have been
scarcely studied. Water soluble compounds are expected to have considerable influence on their formation characteristics. With this end in view, we have
investigated the RM systems of Tweens (Tween 20,
40, 60 and 80) in chloroform in the presence of four
additives, viz, sodium chloride, guanidine hydrochloride, urea and glucose. We have examined how they
compare with respect to the CMC of the RM of
Tweens in chloroform as well as how they influence
the complexing characteristics of the dye Safranine T
(ST) with the RM. The. results have been rationalized
on physico-chemical basis.
Materials and Methods
Safranine T (E Merck) was recry stallized twice
from ethanol-water mixture before use. The surfactants, polyoxyethylene sorbitan monolaurate (Tween
20), polyoxyethylene sorbitan monopalmitate (Tween
40), polyoxyethylene sorbitan monostearate (Tween
60) and polyoxyethylene sorbitan monoo leate (Tween
80), were either BDH or Sigma products. Their characteristics and purity standards were the same as reported previously 19·20 . Glucose ( GR, Qualigens ), sodium chloride (E Merck), urea (BDH) and guanidine
hydrochloride (BDH, England) were used as such.
T he concentration of ST was of the order of I 5 mol
dm- 3 . The concentration of Tweens were 10 mmol
dm- 3 and the concentration of additives varies in the
range from 0.5 mmol dm- 3 to 1.5 mmol dm- 3 . Doubly
distilled (conductivity) water was used for solution
preparation . Spectroscopic grade chloroform from E
o-
590
INDIAN J CHEM, SEC. A, JUNE 2000
Merck was used. Chloroform was dried according to
standard procedures and purified by fractional distillation . The presence of impurities was checked by
emission measurements and they were found to be
absent.
Absorption spectra were recorded using a Shimadzu (Japan) 160 A UV-visible spectrophotometer
with a matched pair of silica cuvettes. Fluorescence
spectra were measured using a Fluorolog F lliA
spectrofluorimeter (Spex . Inc ., NJ , USA) with a slit
width of 2.5 nm. All spectral measurements were duplicated in a constant temperature water bath accurate
to within ± 0.1°C, and the mean values were ]processed for data analysis.
Results
Critical micelle concentration (CMC)
The absorbances of ST at different concentrations
of each of Tween 20, 40, 60 and 80 in chloroform in
the presence of the additives, glucose, sodium chloride, urea and guanidine hydrochloride, were measured. From the plot of the absorbance (520 nrn) vs
[surfactant] (Fig. 1), the CMC values of the RM of
the non-ionic surfac tants (Tweens) in chloroform
were determined at different concentrations of the
additives. The CMC values are presented in Table 1.
The results show the decrease of CMC of the RM in
chloroform in the prese nce of NaCI, and its increase
in the presence of urea, guanidine hydrochloride and
glucose, as summarized in Table I. For a particular
additive, the variation of CMC with the concentration
of additive bears a linear rel ation (Eq. 1), as shown in
Fig. 2. The slope is obviously negative for NaCI and
posi ti ve for the rest of the additives.
.. . (1)
CMC =a+ b [additive]
The intercept (a) and the slope (b) values are presented in the footnote of Table 1. The b values represent the rate of change of CMC with [additive] .
Binding constants of ST with the RM
The formation of 1:1 ST-RM complex has been
reported earlier23 • In the present study , the complexing equilibrium in the presence of different additives
has been investigated. The dye-RM equilibrium
shown in Eq. 2 was considered.
Kc
. . . (2)
Dye+RM :;::::::::::::::::~ D - RM
where RM and D-RM represent the reverse micelle
and dye-RM complex respectively. Kc is the binding
constant. For the determination of Kc, the BenesiHildebrand25 equation was used. In this formalism,
[RM] = Cs In since Cs >> CMC and n is the aggregation number.
n
cd 1
-=-+-'-·- .. . (3)
A
Ec K c Ec Cs
where Cd and Cs are the concentrations of dye and
surfactant, respectively. A and Ec are the absorbance
of the solution and the extinction coefficient of the
complex at Amax = 532 nm. The n values were taken
23
from our earlier report . From the linear plot of Cd I
A vs Cs. 1 (Fig. 3) the values of Kc were evaluated and
given in Table 2. The !<c values for the ST- RM obtained in the presence of different additives follow
(8)
(d)
(a)
(c)
0-3
0·2
0-2
Q.JL-------;:'5'::-0-------..,'1().~0~
[Twun 20)/mmddm3
50
1w~n]fmmot dmJ-
1().0
Fig. !-Absorbance of ST plotted against [Surfactant] at 298 K.
A Observations on Tween 20 in the presence of (a) NaCI, (b) glucose, (c) urea, (d) guanidine hydrochloride.
B. Observations on Tweens in the presence of glucose (a) Tween 20, (b) Tween 40, (c) Tween 60, (d) Tween 80.
591
NANDI et al. : EFFECT OF ADDITIVES ON PROPERTIES OF REVERSE MICELLES
Table I -The CMC' s of the reverse micelle of Tweens in chloroform in presence of additives at 298 K
CMC x 1031mol dm-3
Tween 60
Tween 40
Tween 80
[NaCI] x 104 mol dm-3
Tween 20
2.5
5.0
7.0
8.5
a x l0 3 I mol dm-3
b
2.55
2.30
2.15
2.00
2.70
-0.44
2.30
2.00
1.80
1.70
2.52
-0.50
1.90
1.78
1.60
1.50
2.06
-0.33
1.80
1.60
1.50
1.40
1.90
-0.30
[Glucose] x 104 I mol dm-3
0.5
1.0
1.4
1.6
ax 103 I mol dm·3
b
3.10
3.50
4.00
4.60
2.60
2.10
2.90
3.40
4.00
4.20
2.30
2.10
2.10
2.50
2.90
3.30
1.80
2.00
2.30
2.90
3.40
3.60
1.64
2.40
[Urea] x I 04 I mol dm"3
2.5
5.0
7.0
10.0
a x 103 I mol dm-3
b
3.35
3.80
4.20
4.80
2.80
2.00
3.00
4.00
4.50
5.00
2.20
3.10
2.70
3.00
3.20
4.40
2.00
2.80
2.75
3.80
4.30
5.10
1.80
3.70
[Guanidine hydrochloride] x I04 I mol dm-3
0.3
0.6
0.8
1.1
a x 103 I mol dm-3
b
3.60
4.30
4.60
5.30
3.10
11 .50
3.20
3.90
4.40
5.00
2.88
11 .80
3.00
3.70
3.40
5.00
2.40
13.60
3.00
4.00
4.70
5.60
2.20
17.60
CMC of RM Tween 20 : 2.66, Tween 40 : 2.63, Tween 60 : 1.99, Tween 80: 1.90 in chloroform I mmol dm-3 .
the same trend as obtained in the absence of additives23, i.e. Tween 80 > Tween 60 > Tween 40 >
Tween 20. Compared to Kc values in RM without
additives, the values are higher in the presence of
guanidine hydrochloride, urea and glucose whereas
they are lower in the presence of sodium chloride.
The Kc values in the presence of additives vary linearly with the carbon number (n'c) of the non-polar
tails of the Tweens . The profile is shown in Fig. 4. It
fits the Eq. 4.
logKc = A + B n'c
--- (4)
The A and B values are given in Table 2. The values
of the intercepts refer to logKc at zero carbon number
of the hydrophobic end of the Tweens in the reverse
micelles. This may refer to complexing interaction of
ST with the hydrophilic polyoxyethylene head group
23
of the Tweens as indicated earlier . The magnitude
of this interaction is smaller with NaCI but higher in
the presence of other additives.
Maximum additive concentration
The maximum solubility of an additive (MSA) in
the RM system of constant [H 20] I [Amphiphile] ratio
maintaining a single isotropic solution, has been determined from the plot of absorbance of solutions of a
constant concentration of ST against [additive]. The
MSA values are given in Table 3. For a particular
additive, the MSA values increase with increase in
hydrophobic tail of the Tweens. For a fixed concentration of surfactant (0.01 mol dm·\ the dependence
of MSA on the number of methylene groups in the
Tweens is curvilinear. The behaviour of glucose m
terms of MSA is different from the others (Fig. 5).
Stokes shift and related solvent parameters of RM
In solution the properties of a photoactive molecule
592
INDIAN J CHEM, SEC. A, JUNE 2000
8-0
(a)
d
b
0
c
.....
t
'E
"0
0
E
-2-0
~
0
X
~
u
0 o~~--------~5~----------~,o~
4
3
[Urea]" 10 / mold -
1- 0o!:--------~5---------L,o=-­
m
8-0
4
[Nacl ] x 10 / mol dm-3 - -
5-0
(c)
(d)
a
b
d
d
c
'?
E
0
b
"0
c
0
.....~4.0
Q
u"
~
u
0.6
~anidine-HCl] "lo'+/rnoidm3-
1-2
2
1
[Glucose]
x
lo'+/moldm3 - -
Fig. 2- Plots of CMC vs [additive]
(a) Tween 20, (b) Tween 40, (c) Tween 60, (d) Tween 80.
can be influenced by the molecules of the solvent environm~nt. Th~ measured photophysical characteristics ( 'Ya and 'Yt ) of the molecule decrease with increasing static dielectric constant of the medium. The
hydrogen bond formation or exciplex formation by
the solute solvent interaction may also contribute to
the spectral shift. A generalized dipole-dipole inter26 27
action has been considered by Mataga ' et al. to
explain the spectral red shift for indole.
The stokes shift of a probing solute (for example a
photoactive dye) molecule in different solutions can
thus be exploited to assess the polarity of the solvent
medium. In pure solvents-acetonitrile, ethanol, dioxane, formamide , tetrahydrofuran, ethylene glycol and
acetone, the visible spectral transitions of the dye ST
occur in the region of 524-535 nm, which is 526-530
nm in the RM and 531 -536 nm also in the RM but in
the presence of the additives (NaCl, glucose, urea and
guanidine hydrochloride). The emission maxima in
these three cases occur in the region of 565-587 nm,
577--580 nm and 568- 573 nm respectively.
It is reasonable to consider that the change in the
spectral shift of ST in the RM in the presence of the
additives from that in the pure RM is due to additive
induced change in the polarity of the inner core of the
RM. The spectral shift (.1 y) of ST in the different
solvent systems studied have been linearly correlated
(Fig. 6) with the Kosower z values 28 as well as the
593
NANDI eta/. : EFFECT OF ADDITIVES ON PROPERTIES OF REVERSE MICELLES
Table 2-The additive influenced binding constants of the I : I ST-RM complex at 298 K
Surfactants
n•
NaCI
Tween 20
Tween 40
Tween 60
Tween 80
A (Eq. 4)
B (Eq. 4)
117
153
182
204
0.19
0.31
0.38
0.44
3.74
0.06
Kc X 10"5( mor 1dm 3)
Glucose
0.59
0.98
1.60
2.45
4.08
O.D7
Urea
Guanidine hydrochloride
0.61
1.63
2.78
2.96
3.70
0.11
1.30
2.40
4.40
6.90
4.20
0.10
•, the aggregation number n taken from ref. 23.
10-0
(A)
J'E
"0
(d)
0
E
(c)
........... 5-0
(b)
$2
X
(a)
~<
1-0
2-0
J.O
4-0
5-0
rQx16'lmoC1dm 3100
d
(B)
140
12.0
a
... l,o.o
'E
b
""0
~-
:;--...
w
Q
~&0
40
10
20
1
~/
J.O
-1 ... 1
1Csl•10 mol drrr-
Fig. 3-Plot of CjA vs Cs-1
A. in the presence of urea { [urea]= 0.5 mmol dm-3 ], B. in the presence of NaCI {[NaCI] = 0.6 mmol dm-3 ], [ST] = 1.8 x
dm-3; (a) Tween 20, (b) Tween 40, (c) Tween 60, (d) Tween 80.
w-smol
594
INDIAN J CHEM, SEC. A, JUNE 2000
3-0 r-------------~&0
d
c
b
b
M
f 2-0
4-0
'E
"0
a
0
E
-
M
u
$2
::.::
"
<X:
0'1
0
lfl
~lO
o---0
0
10
0
nc-
10
20
n;:-
20
Fig. 4--Piot of log Kc vs number of C-atoms (n'c) in the hydrophobic tails of the Tweens. (a) NaCI, (b) glucose, (c) urea, (d)
guanidine hydrochloride.
j/-
Fig. 5-Piot of maximum solubility of an additive (MSA) values
vs. the number of C atoms (n' c) in the hydrop hobic tails of
Tweens. (a) NaCI, (b) glucose, (c) urea, (d) guanidine hydrochloride.
Table 3-Maximum solubility of an additive (MSA) at 298 K
Surfactant
Tween
Tween
Tween
Tween
20
40
60
80
3
I0 [NaCI]
0.84
0.98
1.46
1.48
Additive I mol dm-3
I0 3[Urea]
I 0 [Glucose]
4
2.50
3.20
4.20
5.00
transttJOn energies, E/0 for intramolecular charge
transfer. Considering similar correlations of ~ y with
both z and E/0 holding in the RM (pure and additive
loaded), these parameters have been evaluated from
the measured ~ y values and the appropriate calibrating lines in Fig. 6. The results are presented in
Table 4. Since~ y does not bear a linear correlations
with the dielectric constant of the medium, an indirect
method of evaluation has been adopted as has been
done in the past 29 . In this rationale, the linear correla0
tion of dielectric constant 0 with both z and E/ has
30
been exploited (Fig. 7) . The derived z and ET values
of the RM systems have been used to estimate the
corresponding D values . The 0 values are also presented in Table 4.
1.00
1.02
1.05
1.48
10"1[ Guanidine hydrochloride]
1.30
1.38
1.44
1.52
Discussion
The results indicate that the additives (NaCl, glucose, urea and guanidine hydrochloride) appreciably
affect the micellization characteristics of RM of
Tweens in chloroform. Water remains solubilized in
the polar interior of the RM in non-polar solvents.
The MSA v~ues (Table 3) show the accommodation
capacity of the RM interior. Aqueous environments
of varying activities and hydrogen bonding capabilities with [H 20] I [Tween] ratio can be produced from
a low to a high value. The core of RM of Tweens in
chloroform is composed of the polyoxyethylene chain
head group. NaCI undergoes ion-dipole interaction
with the oxyethylene gTOups of the surfactant present
in the mi<;ellar interior. The other additives excepting
NANDI et al.: EFFECT OF ADDITIVES ON PROPERTIES OF REVERSE MICELLES
Table 4-Spectral characteristics of ST in different RM media and the solvent parameters of the waterpool at 303 K
Additive
NaCI
z
E)()T
(em·')
(cm-1)
(~ Y)(cm-1)
(cal mor' )
(cal mor')
Tween 20
Tween 40
Tween 60
Tween 80
18726
18726
18762
18797
17513
17482
17482
17513
1213
1244
1280
1284
70.0
71.0
71.0
71.0
43.0
44.0
44.0
44.0
31.0
32.0
32.0
32.0
Tween
Tween
Tween
Tween
20
40
60
80
18691
18677
18671
18691
17605
17605
17574
17574
1086
1072
1097
1117
66.0
66.0
66.0
67.0
41.0
41.0
42.0
42.0
17.0
17.5
18.0
19.0
Tween 20
Tween 40
Tween 60
Tween 80
18657
18744
18726
18691
17482
17543
17482
17452
1175
1201
1244
1239
69.0
69.0
69.0
69.0
43.0
42.0
43.0
43 .0
28.0
26.0
26.0
26.0
Tween
Tween
Tween
Tween
20
40
60
80
18691
18691
18656
18762
17513
17513
17482
17578
1178
1178
1174
1184
67 .0
67.0
67.0
68.0
43 .0
43.0
43.0
43.0
23 .5
23 .5
23.5
24.0
Tween 20
Tween 40
Tween 60
Tween 80
19011
18957
18921
18857
17361
17331
17331
17331
1650
1626
1590
1526
82.0
81.0
80.0
81.0
44.0
43.5
43 .0
43.5
31.0
27 .0
27 .0
27.0
68.0
68.0
64.0
63 .0
41.0
41.0
37.0
36.0
12.0
12.0
5.0
5.0
Surfactant
'Ya
Yr
'Ya- Yr
D
Glucose
Urea
Guanidine hydrochloride
Absence of Additives•
Normal micellesb
Tween 20
Tween 40
Tween 60
Tween 80
Reference 23 .
b Reference 29.
a
guanidine hydrochloride (which compares with NaCI)
act by way of dipole-dipole interaction . All the MSA
values increase with increase in the number of C atoms in the hydrophobic region of the Tweens (Fig. 5).
The CMC values of the surfactants decrease with increase in concentration of NaCI. For NaCI the b values ofEq. (I) (Table I) are nearly equal for Tween 20
and Tween 40. For Tween 60 and Tween 80, the values are equal but relatively small. This may be due to
the size difference leading to structural difference
between the two sets of amphiphile. The a values i.e.,
intercept of Eq. (l) tally with the CMC of RM in the
absence of NaCI . The reduction of CMC values in the
presence of NaCI is attributed to a salting out type
phenomenon of the Tweens from solution . The Na+
ions of NaCI compete with the Tween for getting the
share of water, the solubility of the amphiphile is thus
decreased and the CMC is lowered by this salting out
phenomenon.
With the addition of urea, guanidine hydrochloride
and glucose, the CMC values of the Tweens increase.
The MSA values also increase with the number of
methylene groups in the surfactants (Table 3). The
additive affected magnitudes of the CMC of the
Tweens follow the order of guanidine hydrochloride
>urea> glucose. The intercept of Eq. (l) which represents the CMC at. zero additive concentration reasonably tallys with the CMC values with minor
variations.
The formation of RM is essentially controlled by
the mutual interactions of the head groups of the amphiphiles and their interaction with the solvent. Factors that influence the amphiphile aggregation and
their solubilization and stabilization should affect the
RM formation . The polyoxyetheylene head groups of
the Tweens remain solubilized and stabilized by
forming hydrogen bonds via dipolar interaction with
water. Both urea and guanidine hydrochloride are
596
INDIAN J CHEM, SEC. A, JUNE 2000
2200
0
1(a) 1(b)
2(a)
2( b )
1)
0
2000
1800
0
1
0
'T
E
~1600
~
40
0 0
0
0
1400
0
20
1200
20
40
60
0
80
100
1
(Z or E{ ) / k Cal mol1000~--J----L----W---~--~~~~~
20
40
60
I
80
100
120
!Z orEr30 ) k Cal mol-1 -
Fig. 6-- -Plot of !:l
various solvents.
y vs Er30 (I)
Fig. 7-Plot of dielectric constant vs Kosower Z values {(2(a)
and 2(b) } and ET 30 {I (a) and I (b)} for various solvents. (viz,
Acetonitrile; acetone; ethanol; ethylene glycol; dioxane; formamide; and tetrahydrofuran)
and Kosower Z value (2) for
protein denaturants and they are also hydrophobic
bond breakers . The phenomenon of normal micelle
(NM) formation is affected by them and the CMC
increases 30 . The reduction in amphiphile aggregation
is expected to be effective in RM formation and the
CMC increase has been consequently observed. In the
case of glucose, hydration of the carbohydrate molecules makes the amphiphile molecules less hydrated ,
and consequently their self-asse mbling potential is
reduced manifesting increased CMC. The efficacy of
the additives can be estimated from the maximum
additive concentrations given in Table 3. For all the
Tweens , the order is guanidine hydrochloride > urea
"" NaCI > glucose. Although the actions of urea and
NaCI are basically different, they end up with comparable effective concentrations. The effect of guanid ine hydrochloride is maximum with respect to the
vari ation of CMC, MSA and Kc. Compared to urea, it
is a better protein de naturant. The present resul ts wit-
ness versatility of th is compound in the process of
self-association of proteins and amphiphiles.
The ST-RM binding constant increases with in23
creasing length of the hydrophobic tail , the order is
Tween 20 < Tween 40 < Tween 60 < Tween 80. For
each case, the effectivity of the additives follows the
order : guanidine hydrochloride > urea > glucose
>NaCI.
It has been observed that the physico-chemical
state of the core water in RM (W= [H 20] I [Tween] =
0 .6) is di stinctly different from the aqueous environment in the interfacial region of the normal micelle
(NM) of the Tweens. The change in stokes shift is a
manifestation of this difference. The polarity of the
aqueous core of the RM (which is greater than that of
the interfacia l region of the NM) is changed in the
presence of the additives. The additive induced polarity of the aqueous core of the RM follows the order
NaCI > urea > guanidine hydrochloride > glucose.
The same order is also followed by the dielectric constant values (D). From the polarity parameters, it is
NANDI et al.: EFFECT OF ADDITIVES ON PROPERTIES OF REVERSE MICELLES
established that the pallisade region of NM (where
the probing dye, ST resides) appears to be less organised compared to the interior water compartment
ofRM.
Based on the above results it can be concluded that
(i) the RM formation of the Tweens in chloroform is
decreased by NaCl and increased by glucose, urea
and guanidine hydrochloride; (ii) among the additives
guanidine hydrochloride is the most effective additive; and (iii) the dye ST forms 1: 1 complex with the
RM which is affected by the additives following the
order; guanidine hydrochloride > urea > glucose >
NaCI.
10
II
12
13
14
15
16
17
18
Acknowledgement
S. Nandi thanks the Physical Chemistry Section of
the Department of Chemistry of Jadavpur University
for laboratory facilities. Financial help from CSIR
[01(1517)/98/EMR-11] is gratefully acknowledged.
References
I
2
3
4
5
6
7
8
9
Desgranges G R, Bordere S & Roux A H, J Colloid Interface
Sci, 162 (1994) 284.
Fendler J H & Fendler E J, Catalysis in micellar and macromolecular systems (Academic Press, New York) 1975.
Attwood D & Florence A T, Surfacrant systems, (Chapman
and Hall, London) 1983.
Bieniecki A, Wilk K A & Gapinski J, J phys Chern B, 101
(1997) 871.
Zhao J & Brown W, J phy Chern 100 (1996) 5908.
Yoshino A, Okabayashi H, Yoshida T & Kushida K, J phy
Chern, 100 (1996) 9592.
Hayashi S & Ikeda S, J phys Chern, 84 (1980) 744.
Roy P, Bhattacharya S C & Moulik S P, J Photochem Photobiol A. Chern, 116 (1998) 85.
Bhattacharya S C, Das H & Moulik S P, J Photochem Photobiol A Chern, 71 (1993) 257.
19
20
21
22
23
24
25
26
27
28
29
30
597
Shinoda K, Nakagawa T, Tamamushi B & Isemura T, Colloidal surfactants (Academic Press, New York), 1963.
Drummond C J, Grieser F & Heaty T W, J chem Soc, Faraday Trans I, 85 ( 1989) 551 .
Moulik S P, Paul B K & Mukherjee DC, J Colloid Interface
Sci, 161 (1993) 72.
Lopez P, Rodriguez A, Gomez C H, Sanchez F & Moya M
L, J chem Soc Faraday Trans , 88 (1992) 2701.
Pileni M P, Structure and reactivity in reversed micelles,
(Elsevier, Amsterdam), 1989.
Thomas 1 K, The Chemistry of excitation at interfaces (ACS
monograph 181 , American Chemical Society, Washington ,
D.C.,) 1984.
Thomas J K, J phys Chern, 91 (1987) 267.
Johannsson R, Almgreen M & Schomacker R, Langmuir 9
(1993) 1269.
Paul B K, Mukherjee D C & Moulik S P, J Photochem
Photobiol A Chern, 94 ( 1996) 53.
Moulik S P, Gupta S & Das A R, Can· J Chern , 67 ( 19S4)
356.
Bhattacharya S C, Das H & Moulik S P, J Photochem Photobiol A Chern, 74 (1993) 239.
Acharya K, Bhattacharya S C & Moulik S P, J Photochem
Photobiol A Chern, I 09 (1997) 29.
Mukhopadhyay L, Mitra N, Bhattacharya P K & Moulik S P,
J Colloid Interface Sci, 186 ( 1997) I.
Bhattacharya S C, Nandi S & Moulik S P, J Photochem
Photobiol A Chern, 97 (1996) 57.
Acharya K, Bhattacharya S C & Moulik S P, Indian J Chern ,
36A (1997) 137.
Benesi H A & Hildebrand J H, JAm chem Soc, 71 (1949)
2703.
Mataga N, Kaifu Y & Koizumi M, Bull chem Soc Japan, 29
(1956) 465.
Mataga N, Toritashi V & Ezumi K, Theor Chim Acta, 2
(1964) 158.
Kosower E M, An introduction to physical organic chemistry, (Wiley, New York) 1968.
Bhattacharya S C, Das H & Moulik S P, J Photochem Photobiol A Chern, 79 (1994) 109.
Kundu S & Chattopadhyay N, Chern Phys Lett, 228 (1994)
79.