Ind. Eng. Chem. Prod. Res. Dev. 1900, 79, 136-142
136
11. Developments in Dyeing and Finishing G. 0. Phillips and H. Tonami ACS/CSJ Chemical Congress, Honolulu, Hawaii, April 1979 (Continued from March 1980 issue)
The Interaction between Dyes and Nonionic Surfactants: the Mode of Action of Nonionic Surfactants in Dyeing Yoshio Nemoto" and Hlroyuki Funahashi Nagoya Municipal Industrial Research Institute, 3-24 Rokuban-cho, Atsuta-ku, Nagoya, Japan
It has been known that the nonionic surfactant having good affinity for acid dye forms a complex which controls both the rate of adsorption and the affinity of the dye for wool or nylon. Thus, the investigation of the interaction between acid dye (D) and nonionic surfactant (S) is very important in clarifying the behavior of the latter in dyeing. Several kinds of interaction and complex formation between acid dye and nonionic surfactant were found: (1) the formation of hydrophilic small complexes (e.g., DS, DS2, DS3), estimated by spectrophotometric method, (2) the formation of hydrophilic large complexes (DS10-30)and hydrophobic ionic bonding complex, estimated by surface tension method, and (3) the formation of mixed micelle of dye and nonionic surfactant, established by the measurements of cloud point.
Introduction In the field of textiles, however, many kinds of surfactants are used in dyeing or finishing processes; the way of using them depends usually upon previous experience. In dyeing processes, the roles of surfactant are especially very important. The main interest is the characteristic behaviors of surfactants which give a good level of dyeing and increase fastness of dye on fiber. Main roles of the surfactant used in dyeing as auxiliary product can be classified into four types of actions: (1) as surface active compound, namely, solubilizing, dispersing and wetting; (2) as fiber affinity compound, similar to colorless dye; (3) as dye affinity compound; and (4) as both fiber and dye affinity compound. In order to understand the roles of surfactants in dyeing, it is necessary to study the interactions among fiber, dye, and surfactant dye
fiber
surfactant
In this paper, the interaction between acid dye and surfactant, especially a nonionic surfactant, will be discussed.
Formation of Hydrophilic Small Complex Estimated by Spectrophotometric Method It has been noticed that color change occurs on addition of a certain nonionic surfactant to an aqueous solution of some dyes. Figure 1 shows the color change of C.I. Acid Blue 116 01 96-4321 / 8 0 / 1219-0136$01 .OO/O
\
S03Na
by the addition of poly(oxyethy1ene)octadecyl alcohol (OAL29.0);the absorption spectra are found to be shifted to longer wavelengths with increasing amounts of OAL29.0. It is known that in most cases such spectral changes might occur suggesting the formation of complexes resulting from the interaction between dye and surfactant molecules. Further, in Figure 1, a well-defined isosbestic point can be seen a t 575 nm, which may generally be taken as confirmed formation of only one species of complex in the interaction system. So it is assumed that a reversible stoichiometric equilibrium mD + nS D,S, (1) exists in a dye solution containing surfactant, where D, S, and D,S, represent dye, nonionic surfactant, and complex molecules, respectively. In order to calculate the equilibrium constant ( K ) ,it is necessary to determine the values of m and n in eq 1; they are usefully determined by the continuous variation method (Nemoto, 1958, 1959, 1967), in which, for determination, each solution is prepared at a constant total number of moles of dye and surfactant, varying their compositions. For example, in the interaction between C.I. Acid Blue 116 and OAL(EO),, the following experiment, as shown in Figure 2, was carried out for the determination of the numbers of m and n. Figure 2 shows that there is
0 1980 American
Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 2, 1980
137
Table I. Values of n / m , K , and -Ape for t h e Interaction between C.I. Acid Blue 1 2 0 and Various Nonionic Surf act ants nonionics
C
NP9.0
16 25 41 20 25 41 19 25 39 18 25 39 18 25 41 18 26 41 16 26 41 17 26 41
NP19.3 DAL1O.O DAL19.7 OAL21.6 5'40
500
660
620
580
Wave Length (mi)
OAL29.0
Figure 1. Absorption sptxtra of solutions containing (2.1. Acid Blue 116 and OAL29.0. --.-oAL
8.2 21.6
-0-OAL -x-OAL
OAM19.9 OAM29.8
29.0
n/m
K 1.28 x 5.98 X 2.40 X 3.57 x 2.37 x 1.79 x 9.93 x 4.97 x 2.91 X 2.02 x 1.57 X 1.43 X 1.36 x 8.31 x 3.89 X 9-27 x 6.64 x 3.89 x 1.24 X 4.71 x 4.00 x 2.00 x 9.79 x 7.80 x
kcallmol 17.4 17.4 17.8 11.5 11.4 11.9 17.4 17.3 17.8 11.1 11.2 11.7 18.8 19.0 19.5 18.6 18.8 19.5 18.7 18.7 19.6 19.0 19.2 20.0
1013 10" 10''
lo8
lo8 lo8 10l2 l0lZ
lo'*
lo8 lo8 10' lox4 10l3 10l3 1013 1013 1013 10'' 1013 1013 1014 1013 1013
NP, nonyl phenol; DAL, dodecyl alcohol; OAL, octadecyl alcohol; OAM, octadecyl amide.
Y
Table 11. Thermodynamic Parameters for t h e Interaction between C.I. Acid Blue 120 and Various Nonionic Surfactants o
0.2
0.4
0.6
1.0
0.8
Molar Fraction of rye
Figure 2. Values of n / m of the complex formed in the interaction between (2.1.Acid Blue 116 and OAL(EO),, estimated by the continuous variation method.
a maximum of Y a t 0.25 mole fraction of the dye in the curves. From this fact, it is found to be m = 1 and n = 3; the complexes DS3 are formed. The values of Y in Figure 2 are defined 'by the difference in the spectrophotometric absorbances for two solutions; one of them contains both dye and surfactant and the other contains dye alone, where each solution contains the same amount of dye. From the above definition, the value of Y can be expressed in terms of the molar extinction coefficients, e and e', of the dye anld complex, respectively, as
Y = X ( E ' - me)
(2)
where x (= [D,Sn]) is the molar concentration of complex. The value of E' can be determined by the addition of surfactant in larger excess to a dye solution so that equilibrium 1 may be transferred almost completely to the complex side. According to eq 2, the value of Y is proportional to the amount of complex in the solution; when the value of m has been determined, therefore, the complex concentration x can be found in any solution a t once. Since equilibrium I is assumed to hold in solution, it follows that
K = - - EDrnsnl Plm[Sln
-
-(a
X -
mx)"(b - n
~
)
~
t 3)
provided that the value of activity coefficient is unity,
-AH", kcallmol
AS",
nonionics NP9.0 NP19.3 DALl 0.0 DAL19.7 OAL21.6 OAL29.0 0AM1 9.9 OAM29.8
12.1 6.1 11.1 3.0 10.0 7.0 8.1 7.0
18 19 22 28 30 40 36 41
eu
where a and b represent the initial concentration of dye and surfactant, respectively. When the numbers of m, n, and the value of x have been determined, K can be calculated from eq 3, so that the standard affinity can be estimated -Apo =
RT In K
(4)
where R represents the gas constant and T the absolute temperature. Table I shows the values of n l m , K , and -Ape, and Table I1 shows the thermodynamic parameters for the interaction between C.I. Acid Blue 120 Na03S,
and various nonionic surfactants. The results lead to the following conclusions. (1)The value of n l m is lower with the surfactants of larger ethylene oxide adduct. (2) K and -Ape are greater as the ethylene oxide adduct is larger or as the hydrophobic alkyl chain of surfactant is longer; however, if ethylene oxide adduct chains are lengthened too much, a decrease in the value of n l m occurs, which is
138
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 2, 1980
Table 111. Values of n / m , K , and Thermodynamic Parameters Determined by Surface Tension, Compared with the Results of Spectroscopic Determination method
nonionics
surface tension
NP10 NP20
spectrometry
NP9.0 NP19.3
"C
nlm
10 15 20 10 15 20 16 25 41 20 25 41
3 2 3
2
3.39 x 2.22 x 1.66 x 1.33 x 1.09 x 8.98 X 1.28 x 5.98 X 2.40 A 3.57 X 2.37 X 1.79 X
1013 1013 1013 109 109 10' 101~ 10"
10"
lo6 10' 10'
AS",
-AH",
-A!J0,
K
kcalimol
kcallmol
eu
17.5 17.6 17.7 11.8 11.9 12.0 17.4 17.4 17.8 11.5 11.4 11.9
11.9
20
6.2
20
12.1
18
6.1
19
C . I . A c i d Blue 120 - NPlO
0
C
r
z
"'-,.p\,
\.
9 401 '&,;.& 0
~
LL1
+
$1
1
E
3 VI
30Lp-.---I Os
3 5
3
7 x 105
\o+:-x.x.
~ . x - ~
16 16
A
\ O \ ~ ' X P ~ - ~ ~ . ,
'0,.
[Dl ( M I 0 2 lo5
-o:p:-o-
'.\_...__ ".,p,'-xp. *-.5::%::2?*n.D-x+.. o:n,*-xPY
--lo3
IOL
NPlO
1 o2
(M)
[SI* [SI tS$mc
[Slcmc
SURFACTANT (MI
Figure 4. Surface tension vs. log [SI (M), drawn schematically.
Figure 3. Surface tension vs. log [NPlO] (M)at various constant concentrations of C.I. Acid Blue 120.
followed by a decrease of K and -Aho. (3) The interaction is exothermic, since the enthalpy is negative. (4)The interaction would be due to hydrophobic bonding, since the entropy is positive. The positive entropy suggests that the iceberg structure water in the neighborhood hydrophobic parts of dye and surfactant molecules is destroyed. Furthermore, the hydrophobic bonding is confirmed by the fact that K and -&LO are greater as the hydrophobic alkyl chain of surfactant is longer, as mentioned above. ( 5 ) Affinity is greater with OAL21.6, OAL29.0, OAM19.9, and OAM29.8, which may be expected to be effective as a dyeing assistant. Formation of Hydrophilic Large Complex and Hydrophobic Ionic Bonding Complex Estimated by Surface Tension Method The evaluation of surface tension (Nemoto and Funahashi, 1977) can be applied for the investigation of the acid dye-surfactant interaction. For example, when the surface tension of poly(oxyethy1ene)nanyl phenyl ether (NP10) in the presence of C.I. Acid Blue 120 is measured a t various constant concentrations of the dye and plotted as a function of NPlO concentration, a multiplicity of inflections is observed, as shown in Figure 3, where for the comparison, the curve for NPlO alone is also shown. In the presence of the dye, when the concentration of NPlO increases, the surface tension initially decreases, reaches a short plateau through the first transition, decreases again, and finally attains a constant value through the second transition, where the surface tension is identical with that a t the cmc of NPlO solution in the absence of dye. Such a multiplicity of inflections has also been observed by Jones (1967) in the interaction of sodium dodecyl sulfate with polyethylene oxide. In order to explain the results in Figure 3 conveniently, they have been drawn schematically, as shown in Figure 4. It is assumed that the surface tension of the solution containing both surfactant and dye would be a measure of the amount of free surfactant in the solution through
0 NPZO x
20
40
lo5 ( M )
Figure 5. Values of Y from spectroscopy and [XI from surface tension vs. [NP20], measured with solutions containing 2 x M of C.I. Acid Blue 120. The scale of [NP20] is different above and below the first transition; relevant figures above the first transition are five times as large as those below.
adsorption equilibrium of the free surfactant molecules to the surface of the solution, provided that complexes are not adsorbed to the surface. This assumption is reasonable, since the surface tension a t [S]*,,, in Figure 4 is identical with that at [S],,,. The assumption would further be supported reasonably in view of the properties of the complex, in that the complex would be more hydrophilic than the surfactant itself, complex formation being chiefly due to hydrophobic bonding (Craven and Datyner, 1961, 1963, 1967; Nemoto and Imai, 1959). In Figure 4, therefore, the difference in the surfactant concentration, [XI = [SI -- [SI*,represents the amount of the surfactant interacting with dye, since [SI* is the amount of the free surfactant in the solution containing dye; the values of [XI are proportional to the amount of complex in the solution as well as the values of Y in spectrometry, and consequently, even in the surface tension method, the values of n/ m and thermodynamic parameters can be determined by use of the value of [XI, as shown in Table 111, where
Ind. Eng. Chern. Prod. Res. Dev., Vol. 19, No. 2, 1980 100,
Large Complex
(Single Ion)
I1
%
(Aggregate)
(DS2
,
DS3)
139
(Single Molecule)
(surface)
1
60
e e 40
sq
(Micelle)
Figure 6. Possible processes of equilibria in solution of nonionic surfactant with acid dye.
the data determined hy spectrometry are summarized, too. In Table 111, it is found that the values obtained from the surface tension method agree well with those from the spectroscopic method. Figure 5 also shows an increasing amount of complexes formed in the solution of C.I. Acid Blue 120 with poly(oxyethy1ene)nonyl phenyl ether (NP20), in which the measurements are made by the two methods. The values of Y increase with the concentration of “20 and approach a constant value above the NP20 concentration, 2.75 X lo4 M, which corresponds to [SI,,, observed by the measurement of surface tension. It is therefore assumed that there may be little free dye in the solution above the [S],, and that ordinary micelles would be formed in the region of the concentrations above the [SI,,,. Moreover, in Figure 5 , transition points are shown in the curves and they correspond to the short plateau, exactly the first transition point, observed in Figure 4. The values of [XI and Y gradually increase below these points, whereas they rise rapidly above. This implies that another complex DSI different from DS, ( n = 2 or 3) would be formed above the first transition point, and the formation of DSLcauses the increase of the values of [XI or Y. It is supposed that there is no more formation of DSI above the second transition point ([S],,,), due to little free dye a t the point, as discussed above. The number of 1 would be determined by the difference, [SI,,, - [SI*,,,, assuming that [DS,]
o
Y
100/
B’
I
I
90
Y
/
I
O’
o
500rrrn
I
02
141
1
-
to -
//O
lo
cmc
~
c
>,D’
70
0 ’
dL.-_------
10
IO3
NP
IO(M)
Figure 11. Values of Y from spectroscopy, measured wlth solutions containing 6 x 10-j mol ‘I2 of dye 3.
104
lo2
lo3
101
KCI (M) 100
NP
io
5x ~o-~(M)
,
90
Figure 13. Effect of electrolyte on cloud point (CP), at constant concentration of acid dye and nonionic surfactant. Table IV. Structures of Acid Dyes
Y .-
0
YPR
a ‘0 I
+-W
70
1
2
DYE
x104 (h.o
3
Figure 12. Effect of wid dye on cloud point of NPlO solutions.
crease above the cmc of NPlO. Figure 12 shows the effect of the dyes on the cloud point of the NPlO solutions. It is to be noted that the cloud point increases with the addition of acid dye (Craven and Datyner, 1967) or anionic surfactant (Maclay, 1956). Among these three dyes adopted here, dye 1 is the most hydrophobic and the cloud point of the solution containing dye 1 is found to be most significantly increased. It is important to recognize that even in this case, the hydrophobic interaction takes place. Figure 13 shows the effect of electrolyte, potassium chloride, on the cloud point at the constant concentration of dye and surfactant. In region I, below the cloud point, the solution, in which mixed micelles consisting of dye and surfactant are formr.d, remains clear. Above the cloud point, first the solution clouds due to the separated particles in the soluticn and then the appearance of the clouded solution undergoes a change, depending upon the concentrations of potassium chloride after standing for about 30 min, as shown in Figure 13. In region 11, the particles are quite stable even after standing for a long time. This might be due to the electronic repulsion which results from the negative charges, sulfonic anions, of acid dye in the mixed micelles. In region 111, where the concentrations of potassium cation are considerably high, the charges of the mixed micelles would be decreased and the particles in the solution become unstable. As a result, the particles coagulated, namely a separated layer is obtained in the solution after c tanding. In addition, it is to be noted from Figure 13 that in higher concentrations of potassium chloride, region 111 can be achieved directly from region I by just raising the temperature. The analysis of the layer obtained in the solution by means of a polarizing microscope showed this product to be a liquid crystal. This liquid crystal, which might be formed in a dye bath, is thought to be very important in dyeing; fiber would h t covered with it and the dyeing might
I
H
H S03Na
‘I
R’
R4
SO’Na
S0,Na
H
H
R2
R’
dye 60 0
SO$n &5H,
SO,Na
VI1 H S03Y0
VI11 H
OC,,H,, €I
proceed through the liquid crystal layer.
Conclusion In practical dyeing, sufficient considerations are required for the selection of surfactants. However, it is difficult to understand correctly what kinds of surfactants are suitable for a dyeing system because, in practical dyeing, the dyeing processes are quite complicated. For example, dyeing temperature is not constant but changes during the dyeing. Surfactants must therefore be selected in consideration of the effect of temperature. As another example, with acid dye, it might be necessary to take into account the effect of pH. Moreover, surfactants should be selected in conjunction with the molecular structure of dye. For this subject, several papers have been published. For example, the following report was presented by Craven and Datyner (1961), using NPlO and NP30 as surfactants and some kinds of dyes listed in Table IV. The results are shown
142
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 2, 1980
Table V. Dyeing Behavior of Acid Dye in Presence of Surfactants
I
-
interaction
dyeing
A; no B; yes, at low temp. no, at high temp. C; yes
rapid retard rapid retard
interaction and dyeing rate dye
I I1 I11 IV V VI VI1 VI11
NPlO
NP30
A
A
B B A A B B
B
c
B
c
C C C
e
control
t
cloud point, "C NPlO
NP30
65 58 88 98 98 105 106 115 118
110 109 111 113 113 114 117 121 119
in Table V, where the cloud points are measured in order to know the extent of interaction; the higher cloud point indicates that the dye interacts more strongly with surfactant. The importance of cloud point has already been precisely discussed and established by the authors, as described above. From Table V, it is to be noted that the dyeing rate is more rapid as the dyes interact more weakly with the surfactant. Finally, on the basis of the results obtained from the interaction studies, we will explain the several modes of dye adsorption to fiber, which are usually observed in practical dyeings. Figure 14 shows the typical exhaustion curves of acid dye for wool or nylon. When a hydrophobic surfactant is adopted for a hydrophobic dye so that strong interaction may take place accompanying the formation of stable complexes in the dye bath, as shown in curve 2, the dye is not completely exhausted to fiber even a t high temperature of the final dyeing stages, and consequently the larger amount of the dye remains in the dye bath. Even with a hydrophilic surfactant. an exhaustion curve similar to curve 2 is obtained when the concentrations are higher; in this case also, a considerable amount of complexes is formed because of the higher surfactant concent,rations, even though the interaction force might not be so strong as that between a hydrophobic surfactant and dye. When a hydrophilic surfactant which interacts weakly with acid dye is used in the low concentrations, as shown in curve 3, the rate of dye exhaustion is close to that observed in curve 1 (control). On the other hand, sometimes a characteristic mode of dye exhaustion is found in the initial dyeing stages with a special couple of surfactant and dye, as shown in curve 4. Such a curve is observed when the formed complexes are less soluble in water and readily adhere to a fiber; in curve 4, the apparent rate of dyeing
Time (min) Ternp('c )
-+
--+
Figure 14. Typical dyeing curves of acid dye for wool or nylon, with and without auxiliary product.
rapidly increases in the initial and exceeds that in control. This is due to the adherence of complex onto fiber and such a dyeing cannot be regarded as real dyeing. However, the complex on the fiber would be dissociated into each component, surfactant and dye, during the dyeing with a rise in temperature of the dye bath. The dye dissociated is partially dissolved into the dye bath and adsorbed again onto the fiber. Thus the final amount of dye adsorbed onto the fiber, as shown in curve 4, does not exceed that in control. The problem is the migration of dye, which is very important to obtain a good level. The migration of dye depends upon the amount of dye in the dye bath. It has been established that generally in dyeing, there is an optimum amount of dye in order to obtain the best migration (Lemin, 1949).
Literature Cited Craven, B. R.. Datyner, A,, J . SOC. Dyers Colour., 77, 304 (1961). Craven, B. R., Datyner, A., J . SOC. Dyers Colour., 79, 515 (1963). Craven, B. R., Datyner, A., J . SOC.Dyers Colour., 83, 41 (1967). Jones, M. N., J . Colloid Interface Sci., 23, 36 (1967). Leerush, J., Hinton, E. H., Jr., Text. Chern. Color.. 11, 41 (1979). Lernin, Rattee, J. SOC.Dyers Colour., 65, 217 (1949). colour., 74, 221 (1958). Luck, W., J. SOC. Luck, w., AngeW. Chern., 72, 57 (1960a). Luck, W., Meliiand Textilber., 41, 315 (1960b). Maclay, W. N.. J . Colloid Sci., 11, 272 (1956). Nernoto, Y., Kogyo Kagaku Zasshi. 61, 316 (1958). Nemoto, Y., Kogyo Kagaku Zasshi, 62, 542 (1959). Nemoto, Y., "Proceedings of the IVth InternationalCongress on Surface Active Substances, Brussels (1964)", Vol. 111, p 537, Gordon and Breach, New York, 1967. Nernoto, Y., Funahashi, H., J . Colloid Interface Sci., 62. 95 (1977). Nernoto, Y., Funahashi, H., J . Colloid Interface Sci., in press (1980a). Nemoto, Y., Funahashi, H., J . Colloid Inferface Sci., in press (1980b). Nemoto, Y., Imai, T., Kogyo Kagaku Zasshi, 62, 1286 (1959).
Receiued for reuiew July 6, 1979 Accepted January 28, 1980 This work was presented at the ACS/CSJ Chemical Congress held in Honolulu, Hawaii, April 1979. Cellulose, Paper, and Textile Division.
