846
D. P. GRAHAM AND A . F. BEA3ING
T H E C O S T R I B U T I O S OF SOLT’ATIOS TO T H E STABILITY OF A S T H R X Q U I S O S E T-AT DYE SUSPESSIONS
E VALL-ATION
ASD
CORRELATION WITH D. P. GRAHAM
AKD
THE
PHEXOMESOX OF MIGRATIOK~
A . F. B E X N I K G
Jackson Laboratory, E . I . d u Pont de A’emours and Company, Wilmington, Delaware Received September 8, 1948
Aqueous suspensions of anthraquinone vat dyes2 are essentially hydrophobic in that they are not flocculated and redispersed reversibly. However, although many approach the properties of unsolvated suspensions, others show much greater stability to flocculation by electrolytes. This occasional high stability may limit the value of a color for specific dyeing methods. I n certain processes for the application of anthraquinone vat dyes, the fabric is first passed through an aqueous suspension of unreduced but finely dispersed dyestuff and then through rolls t o remove excess water. If the process is interrupted a t this point, and the fabric stored wet in rolls or dried, the residual water tends t o move through the fabric under the influence of gravity or capillary action. ’ Some dyestuffs tend t o be carried with the flow of water, resulting in nonuniform deposition of the color. This phenomenon, referred t o in the trade and in this paper as “migration,” causes uneven or two-sided effects in the finished dyeing. This subject is discussed in more detail by Killheffer (2). Particles of dyestuff which adhere t o the fibers do not migrate, and therefore suspensions which are stable alone but which flocculate readily upon cotton are preferred. It is, therefore, desirable to relate the stability of an anthraquinone vat dyestuff suspension to its migration tendency, in terms of the principal factor or factors determining that stability. It was noted early in this study that the electrokinetic (or zeta) potentials of anthraquinone vat dyestuff suspensions (50-85 mv.) were consistently higher than that of cotton (reported variously a t 30 to 42 mv.). As will be made clear later in this paper, the electrical energy resisting flocculation of two particles is approximated by a function including the product of their zeta potentials. Therefore, when a vat dyestuff suspension is sensitized in the presence of cotton, for example by the addition of an electrolyte, it will tend to “precipitate” upon the fibers before flocculation. 1 Contribution S o . 74 from the Jackson Laboratory, E . I. du Pont de Kemours and Company, Wilmington, Delan-are. Presented in part a t the Symposium on the Stability of Colloidal Dispersions which was held under the auspices of the Division of Colloid Chemistry a t the 110th Aleeting of t h e American Chemical Society, Chicago, Illinois, September, 1946. 2 Anthraquinone v a t dyes are colored mono-, di-, tri-, or polynuclear polycyclic ketonic compounds which may be reduced with alkaline hydrosulfite t o a soluble leuco form, substantive t o cotton, and which when deposited upon cotton in the leuco form are retained by the fiber through and after oxidation.
SThBILITT OF VAT D Y E SUGPESSIOSS
847
The phenomenon of migration 11-as found to be associated with a stability to precipitation by electrolytes, much greater than that of non-migrating colors. Solvation n-as suggested as the cause by the fact that the most serious offenders are compounds capable of multiple hydrogen bonding. The stability of these dyestuff suspensions relative to that of purely hydrophobic sols was therefore studied to afford a measure of the contribution of solvation to their stability. Hydrophobic suspensions have been examined by numeroils u-orliers who have derived expressions for the criteria of stability based on the energy balance within the system. Consideration has been given to: electrical repulsion energy determined by surface charge, ional concentration, character of the medium, and geometry of the system; kinetic energy as a function of the product of the absolute temperature and the Boltzmann constant; and van der Waals attraction energy. Particle size is of minor importance in the consideration of finely dispersed suspensions. The energy contours of Levine and Duhe (4) agree xvith the generally accepted theory of decreased stability with increased particle size in the coagulation zone. However, within the narron- range of borderline stability or incipient flocculation, these same contours indicate that variation of particle diameter from 0.02 p to 0.2 p has very little effect upon the energy balance. T-ern.ey ( 3 ) has evaluated the potential energy of interaction of two charged particles as the resultant of an electrical repulsion energy and a van der Waals attraction energy. On this basis, stability requires a i2et repulsion energy of a t least a fen- times k T (the product of the Boltzmann constant and the absolute temperature). His general expression for repulsion energy is quite formidable but is somen-hat simplified when limited to symmetrical electrolytes. T’ern-ey has plotted (5, figure 3 ) surface potential us. electrolyte concentration at the point of incipient flocculation for 1-1, 2-2, and 3-3 electrolytes, using two different valuer of the still somey-hat uncertain van der Waals “constant.” His n-ork thus provides a relationship by means of which the concentration of an electrolyte required to bring an unsolvated suspension to the state of incipient flocculation may be estimated if the surface potential at this point is known. The purposes of this investigation, however, ~ o u l dbe served better by an expression using the readily measured electrokinetic or zeta potential instead of the surface potential, and in a form more adaptable to unsymmetrical electrolytes. Since highly solvated suspensions are very much more stable than true hydrophobes, a simple rough approximation would suffice. Eilers and Korff (1) have reported that although the electrokinetic potential 3f a hydrophobic sol at incipient flocculation may vary n-idely n-ith the flocculatng electrolyte, the empirical ratio [? K is, for a given sol, approximately constant. [n this expression { represents the electrolhetic potential and l / the ~ effective hickness of the ionic double layer. K is the Debye-Hucliel constant defined )y the expression : =
p
w 1000Dk T
848
in which
D. P. GR.IH.131 d S D A . F. B E S S I S G
I’
= = =
D E T
= = =
E
charge of the electron A%vogadronumber “ional concentration” or the sum of the products of the molar concentrations of the ions present and the squares of their respective valences; r = ZC,Z~ dielectric constant Boltzmann constant absolute temperature
I n Tmter, at 23”C., the expression may be simplified to K = 2.32 X lo7 (v‘F). The ratio 1 2 / ~having , the dimensions of energy, is considered proportional to the repulsion energy or the work required to bring t v o particles together. I t is apparently assumed that the van der Waals forces, oning to their short range, act principally t o stabilize flocculation once contact is established. Consideration of T’ern-ey’s generalization leads to the conclusion that the ratio { * / K at the point of incipient flocculation, if constant for a single hydrophobic sol, should be roughly constant for all suspensions of this class. Further scrutiny of the data quoted by Eilers and Korff (from the literature) reveals that those of Powis for the coagulation of cylinder oil emulsions and arsenic sulfide suspensions, and of Briggs for the coagulation of gold sols, \Then expressed in the same units, give values of j-* h as constant from one set of data to another as for a single set, roughly 7 . 5 X \$-hen{ is expressed in millivolts and 1,’~ in centimeters. For the suspensions under consideration (in water at 25’C.), the empirical expression
3” = 7.5 x
10-4
K
may be simplified to
l2 = 1.74 x 104(v‘F) relating the electrokinetic potential directly to the ional concentration at the point of incipient flocculation. This relationship is plotted in figure l . 3 Sinw in the presence of only 1-1 electrolytes the difference between j- and surface potential i- comparatively small (a. indicated by the small change of { with cmcentration), this relationship may be compared directly with that of Verney. On this basis, our entire curve (figure I ) lies n-ell within J-erwey’a limits, as determined by the uncertainty in the van der Waals constant ( 5 , figure 5). The correlation is somen hat less exact for 2-2 and 3-3 electrolytes. .+plication of the relationship
p
=
1.-( 4
x
lo4 (43
nith its neglect of variation in particle size, to the evaluation of dyestuff suspensions was justified as follows: The vat dye pastes used in this work showed 3 The significance of the term “zeta potential” as used hereinafter is limited by the empirical nature of the Eilers and Korff ratio t o the simple textbook definition in terms of mobility. It is used only t o provide continuity with earlier work.
STABILITY OF VAT DYE SUSPESSIOSS
849
wide particle-size distributions, frequently including aggregates as large a’i 10-20 p . However, a large part of the color (and a very much larger fraction of the number of particles present) usually comprised units smaller than 0.2 p in diameter. The result of a collision of two particles of ividely different sizes is determined principally by the kinetics of the smaller particle. Consequently, for purposes of this study, the larger units ivere ignored and the pastes considered to be characterized by the large number of particles in the size range 0.02-0.2 1.1 in diameter, within which variation in particle size does not materially affect the stability.
FIG.1. The relationship between { and flocculation.
rofor
a hydrophobic suspension of incipient
The general expression relating electrokinetic potential to ional concentration the point of incipient flocculation of a hydrophobic suspension makes it possible to evaluate the contribution of solvation t o the stability of any suspension neeting the stipulated requirements (small particles suspended in water a t G’C.). The function selected for this purpose was the ratio of the ional con,entration of an electrolyte experimentally found to effect incipient flocculation )f a suspension, to that calculated (from [? = 1.74 X lo4 (2/‘;))t o produce the ame effect upon an unsolvated suspension at the same [-potential. This value, tereinafter referred to as the “solvation ratio” or S , affords a measure of all ontributions to the stability of a suspension in addition to that of electrical epulsion, grouped under the classification of solvation. This would incliide, I addition t o hydration, the contribution of dispersing agents, probably closely dated to that of hydration as will be brought out later (nith the conderation f lyotropy).
2t
850
D. P. GRAHbJI AKD A. F. R C S S I S G EXPEKIMENT.\L
METHODS
’
The dyestuffs used in this study were either esperimental or commercial pastes containing 10-20 per cent of color solids, 0.1-2.0 per cent of a surface-active agent (a condensation product of naphthalene-p-sulfonic acid with formaldehyde], and sniall quantities of electrolyte. Their structural formulas are listed in tahle 1. I n other parts of this paper, the individual dyestuffs will be cited b y the number accomponying the formula in table 1. The pastes n-ere diluted for use to 0.3 per cent solids with carbon dioxide-free water (conductivity 10W to mhos) and adjusted by the addition of diliite hydrochloric acid to pH 7 . .It this point. the wspensions contained total “background” electrolytes equivalent t o 0.001-0.003 S sodium chloride, as determined by conductivity measurements. Electrolyte was then added to the concentration producing incipient flocculation. Several rims a t different electrolyte concentrations were required t o establish this point, as described in a subsequent paragraph. The electrokinetic potential 11as determined in a simple C-tube apparatus, with platinum electrodes in large, baffled electrode chambers. The unit was immersed in a water bath a t 25OC. The clear solution above the suspension in the L--tube contained the same ions and was carefully adjusted t o the same conductivity arid pH as the suspension. The potential gradient used was 0.35 t o 0.70 per centimeter and the movement of the boundary n-as followed with the aid of a cathetometer. Mobilities were talien from the average of ascending and descending houndaries, JI hich usually differed by less than 10 per cent. The electrokinetic potential \I :is calculated by use of the expression: 17.
{ = -4 H T I d g
x
10’)
ND in n-hich {
= 7 = = H = D =
electrokinetic potential in millivolts viscosity of the medium velocity of boundary in centimeters per second potential gradient in volts per centimeter dielectric constant of mediiini
The values of { thus obtained I\-cre ~ s ~ i a l reproducible ly within 10 per cent and frequently within 5 per cent. Care 1va5 taken t o insure completion of the run within 2 to 2; hr. of the dilution of the suspension. The electrolyte concentration selected as representative of incipient flocculation n-as the highest value a t I\ hich consistent {-potential readings were obtainable without evidence of flocculation in the U-tube within 2: hr. from the dilution of the paste. Flocculation \vas made apparent by an increase in the velocity of the falling boundary, a decrease in the length of the colored segment, and sometimes by visible aggregation of color. Electrolyte concentrations reproducible within 10 to 30 per cent were determined by this method. The best data were usually obtained with 1-1 electrolytes, probably owing t o the compsratively slow rate of change of electrokinetic potential with concentration. The values thus
TABLE 1 Chemical structures of eat dyestugs used
-
NO.
1.
STRUCTURE
NAME
0
?yranthrone
0 2.
Dichloroisodibenzanthrone
,.
1,5-Dibenzoylaminoanthraquinone
0
0 3,3’-Dichloroindanthrone
0 II
Ii 0
851
852
D. P. GRAHAM A S D A . F. BESSING
TABLE 1-Continued NO
-
NAME
5.
Diethyldipyra. zolanthronyl
6.
STRUCTURE
I
1
A benzanthrone scridine deriv ative .4mixture in which X = H, OH, OCH,, or 1 a n aromatic radical; see C.S. patent ’ 2,212,029, Ex. 1
1
Ii 0
7.
8.
1 , 1 ’ , 4 , 1 ” .5 1”’ , 8,1””-Pentan. thrimidecarbazole
Dibenzanthrone
,
TSBLE 1-Cont inued so.
I
NAME
i I
9.
4,4’-Dibenzoyl- I amino-1 , 1‘-di- I anthrimide- I carbazole
STRCCTURE
0
i ~
10. Anthraquinone1,2-naphthacridone
0 11. 1-(1,O-Anthra-
isothiazole-2csrbony1)amino-5-benzoylaminoanthrnquinone
0 5-Benzoylamino-1, 1’-dianthrimidecarbazole
0
854
D. P. GR.iHhlI .\SD
.‘.,
F. RESSISG
TABLE 1-Concl uded so.
STRUCTURE
SASIE
1 3 , Bis (1-ant hraquinonylnmino)pyrnnthrone; see T. S.patent 1!975,288, Es.1
0
2
l
0 1-i i ’ , h ’ - t l ) - i ” , s ” 1 (\-) -Dilbenze-’
’
cridono)-1,l’5,l”-trinnthrimidecnrbJzole; see P. S patent 1,969, 210, EY.4
A 1-H
0
0
I!
obtained Ivere close to but more clear-cut than those indicated b y gravity sedimentation tests, which were used only a.; a first approximation. The limitq of error cited abow are rppresentative of ideal conditions. Suspensions prepared from pastes ivith n high concentration of dispersing agent or a preponderance of large particles (n-ith diameters exceeding 1 p ) gave ambiguous results, as might have been expected, and \yere omitted from this paper. Others of very wide particle-size distribution gave indistinct precipitation points, making it difficult to establish the electrolyte concentration representative of incipient flocculation u-ithin 100 per cent. However, errors of 20 per cent in ( or 100 per cent in electrolyte concentration involve errors in the solvation ratio corresponding only t o a factor of two. This error is small in comparison with the 100-fold variation in the solvation ratio. In the more favorable cases, particularly with 1-1 electrolytes, the S-values were consistent n-ithin 10 to 30 per cent. On-ing to the tendency for hydrolysis of some salts with the liberation of acid, the effect of p H was eraluated by the use of hydrochloric acid as the added electrolyte. The effect (exemplified by colors 4 and 14 in figure 2) was within
855
STABILITY O F VAT DI-E STSPESSIOSS
the experimental error for acidities resulting from hydrolysis of the salts used (pH > 4.5) and was therefore not considered further. Keglect of this factor was also justified by the fact that closely comparable solvation ratios n-ere obtained with aluminum chloride (pH 4.5-6.5) and lanthanum nitrate (pH 6.5-7.0). Determination of the electrolyte concentration and zeta potential at the point of incipient flocculation provided the data necessary for evaluating the
8
5 4 3 2 1 PH FIG.2. The effect of acidity upoii zeta potential, exemplified by colors 4 and 14 W
'
7
6
TABLE 3 The solvation ratios o j color 14 wilh carious electrolytes
Ionnl concentration of background electrolyte (rl) = 0.0075; electrokinetic potentinl Kith (I.']) alone, T O = 63 mv. llOL.\R C O S -
O F ADDED LLECTRO-
IOSAL COXCESTRATIOS O F .\DDCD ELECTRO-
LxTE
LYTE
1 CESTRATlOX E L E C T R O L T T C ADDED
IOs,L COsCEsTRA-
~IION, I I
ELECTROKISETIC = , POTEZTIAL
(rj) (r2),
c
P
HVDROPROEE VALKE O F i 9 x - t ~tnsCEXTRhTIOS (FROU FiGL-RE 1')
SOLVATION RAT;O
s=
(E)
TO
.I1
YaC1.. . . . . . . . . . . . . . . . . . -,IC1... . ................. : ~. .1. . . . . . . . . . . . . . . . . . . dgcl?.. . . . . . . . . . . . . . . . . 11C1, . . . . . . . . . . . . . . . . . . .
.............
,3(S03!3.,
0.35 0.40 0.25 0.005 0.000G 0.0001
'
1
0.s0 0.50 0.030 0 007% 0.0012
I
0.81 0.51 0.035 0.015 0.0057
37 33 24 37 33
0.0040 0.0061 0.0040 0.0011 0.0061 0.0040
130 130 130 34 '7
2
olvation ratio. The total ional concentration, I'p, x-as calculated from the oncentrations of the electrolytes present (rz = ZC,Z?). From tlie zeta. poential, the corresponding value of rofor an unsolvated suspension a t incipient occulation a t the same potential TT-asdetermined by rcference t o the plot of gure 1. The solvation ratio was then calculated as S = rz/rO. The method by n-hich the experimental data are combined in the cnlculatlon f the solvation ratio is exemplified in detail by color 1-1in table 2 . The results btnined n-ith a number of dyestuffs are summarized in table 3. These dnta
856 TABLE 3 T h e solz'ation of anthraquinone oat dyestuffs i n the presence of various electrolytes COLOR E L X B E R (TABLE 1)
1,
I
UOLAR COSCESTRATIOrL' O F ELECTROLYTE ADDED
I
ELECTROKIhTTfC POTESTIAL
SOLVATION RATIO
P
S
m:
. . . . . . . . . .I
0.05
45
S
0.12 0.0035 0.00033 0 .mol7
52 35 36 32
10
0.10 0.0015
48 23
12
0.10 0 .002 0 .00033 0.00017
47 28 43 32
13 7 1 2
0.2 0.00023 0 . 000BO
53 31 35
16 5 3
6 ..............
0.05 0.0010 0.00017 0.0000;
41 32 36 35
11 4 2 1
7..............
0.05 0.0015 0 .00027 0.00010
39 26 36 34
14 10 2 2
s. . . . . . . . . . . . . .
0.20 0,006 0.0004
42 27 36
41 21 2
9. . . . . . . . . . . . . .
0.17 0.003.5 0.00023 0.00017
41 27 29 31
37
10..............
0.25 0.0020 0.00033 0.00013
46 25 40 31
3G 13 1 2
............
0.20 0.005 0.00017 0.00008
40 27 33 30
48
i
. , . .. . . . . . . . .
I
1
. . . .. . . . . . . . . .
..........
. . . . . . . . . .,
11..
6 2 3
fi
14 3 2
17 1 1
STABILITY OF VA4T DYE SUSPESSIOSS
TABLE 3-Concluded
ADDED
I
ADDED
i
m..
12 . . . . . . . . . . . . . . .1 I
Sac1 1IgCl2 AlClS La(S03'I1
0.20 0.005 0.00060 0.00033
50 29 30 32
sac1 LiCl
0.20 0.10 0.15 0.005 0.00033 0.00020
37 31 31 24 36 37 33
La(SOz)1
0.25 0.10 0.25 0.005 O.OO06 0.0001
SnCl
0.03
S I
I I
49 16 2 4
I
..
13
IiI MgCl. AlCl I
La(SOr)r
I
I
I I
68 70 100 38 3 2
I
14
.
,
. .. .,.., .
1
sac1 LiCl
ri I 11gc1, AlClJ
4.\
37 33 24 3; 33
33 ~-
j
I
I
I
I
I
130 130 130 31 2 2 12
'how not only the wide variation in degree of solvation of different dyestuffs )ut also the effect of lyotropy. For a given dyestuff, the solvation ratio is oughly constant 11-ith 1-1 electrolytes (e.g., alliali halides) hut drops rapidly v-ith hifts down the lyotropic series, approaching unity (or complete inhibit ion of olvation) with salts of poly\-alent metals. ;1 more detailed consickration of he data suggests that the ions of the electrolyte may function in three m y * : 1 ) On the basis of the ional concentration, they fix the thickness of the douhle tyer (except as this factor may lie influenced by solvation). ( 2 ) Specific ions lay be adsorbed on the particles and determine the zeta potential. ( 3 ) Certain dsorbed ions limit the degree of soll-ation t o a degree dependent upon their posion in the lyotropic series. The alkali halides have very little effect on solvation and, in proportion t o ieir concentration, verj- little on the potential except as they control the thickess of the double layer. - i s v-e pass down the lyotropic series through mag&um to aluminum and lanthanum, the effects on potential and degree of Ilvation increase rapidly. These trivalent cations, owing to their lon-er ional mcentrations, have in some cases even less effect on the thickness of the doubk yer than the "background" electrolyte, bringing the suspensions to the point ' incipient flocculation through their reduction of zeta potential and solvation. This clearly defined lyotropic effect strongly supports the hypothesis that Idration is the principal factor determining the solvation ratio and that the lect of the small quantities of dispersing agents present is closely related to
858
D. P. GR.1H.111 AND A . F. B E X S I S G
that of hydration. It is also indicated that, owing t o their small effects upon soh-ation and potential, onIy 1-1 electrolytes should he used t o measure the degree of solvation of a suspension. I n order t o relate the foregoing stability-solvation results t o the migration tendencies of the variouq dyestuffs studied, strips of IT hite cloth n-ere passed through 0.3 per cent aqueous suspensions of the individual dyestuffs. The excess water was removed by n-ringing and the fabric subjected to an air stream TI hich favored drying on one aide. The resulting migration or tn-o-sidedness \vas evaluated in terms of reflectance, as measured by a Beckman or Hardy spectrophotometer n it11 a magnesium oxide itandard. It Ivas determined exT.1BLE 4 The rclntionship
bttictoi
solintion
nrid t h e ji1igration o j anthraquinone eat
intio
dpstiij'? COLOR S L X B E R
s i x i a, ~ , 1
PER CFST ~ILIGR.,Tlr,s
S o L I l T I O + R.\TIO
CGLOR SC-\IBI R
__
-~
1. . . . . . . . . . 2.. . . . . . . . . . . . 3. . . . . . . . . . 4. . . . . . . . . . .
4
s
-
a. . . . . . . . . . . 6. . . . . . . . . . i. . . . . . . . . . . .
X
10 1% 13 16 11 1-1 41
-
s.
. . . . . . . .
I
I
F !I
$1
20 ~_~
~
~~
..
9 . . 1 0 . . .
', ;,
'I
11.. .. 12 . . . . . 13 ..
14 14.1. ~~
~
...~.~
-___-
37 36
20 22 28 33 41 55 10
48
49 68 130 12 ~~
perimentally that the anmint of color deposited on the cloth vas closely proportional t o the change in the function
in which X i m s the rt~Aec.tn1ic.emeasurrtl at n s:pec.ifitd ivave length, preferably t h a t of mnsimuni orption. This relationship is similar to that developed by Kubellia and l\lunl; (3) hut lncBs the rigor of the ori,qinal, in that the reflectance measured svas relati\-(. rat hcr than uh.olute and the film t1iicknw;c;i m s finite. The function C' \\-as clctermind for cncGii side of Ihr pigmented cloth and a h for the white cloth frec of tiyeltiiff. The per cent migation was defined as the per cent of tlie color originally on the weak side of tlie fahric Ivliich p a w d t o the other side in drying aiitl x i s calciilated as follmvs: Per cent migration
=
C(strong side) - _ Cin-e:tk side) ____~____ 4- C'(i\-eak side) - ZC(\vhite cloth)
C'(strong side)
The per cent migration and solvent ratios (Tvith sodium chloride) for tlie dyestuffs stmildiedare listed in table 4 and the relationship is shon-n graphically in figure 3. I s the solvation ratio (5')becomes greater, the severit'y of the observed migration also increases, indicatiiig that the latter is quite closely associated \\-it11solvation of the suspension.
STABILITY O F Y.iT
DYE SUSPESSIOSs
839
Dyestuffs containing but fen- hydrogen-bonding groups in their molecules usually show very little solvation or tendency for migration. Other colors containing many hydrogen-bonding groups may or may not shon- a high degree of solvation (and consequent severe migration), depending on some other variahle. A case in point is that of color 14*1, which is chemically qimilar to color 14 hut was prepared in very pure form. It shows very little solvation, whereas the less pure color 14 mts the n-orst offender.
8
-
3000 -
I
I
1
l -
I
hA
I
1
FIG.3. The relationship betn-een solvation ratio and per cent migration SChfMdRY
The conclusions derived from this study may be summarized as follon-s: 1. The tendency of certain anthraquinone vat dyestuffs t o “migrate” is asociated with an unusually high stability of their aqueous suspensions to floccuLtion hy electrolytes. 2. Solvation is indicated to be a principal source of this “escess” stability. 3. The criteria for incipient flocculation of an unsolmtecl aqueous smpenqion re roughly defined by the empirical relationship : {?
=
1.74 X 10‘
(d?)
4. The clegree of solration of a given suspension has been evaluated in terms f the ratio of the experimentally determined concentration of sodium chloride :quired for incipient flocculation to that calculated to produce the same effect pon a hypothetical unsolvated suspension a t the same potential. 5. The solvation ratio for a dyestuff suspension is commensurate n-ith the :verity of its observed migration. (Exceptions are found among dyestuff astes containing a large preponderance of particles n-ith diameters esceeding micron or high concentrations of dispersing agents.) REF ERE S C E S ) EILERSASD KORFF:Trans. Faraday Soc. 36, 229 (1940). ) KILLHEFFER: Technical Bulletin 20,257 (1940) ; published by the Technical Laboratory,
860
H. E . ROBISOS A S D S. XV. MARTIS
Dyestuffs Division, Organic Chemicals Department, E. I. du Pont de Semours and Company, Wilmington, Delavare. (3) KUBELKA AND J I r x : Z. tech. Physik 12,593 (1931). (4) LEVISEA N D DUBE:J. P h p . Chem. 46, 239 (19-12). (5) VERVEY:Phillips Research Reports 1, 33 (1945).
BEAKER-TYPE CESTRIFUG-41, SEIII1\IEST;ITIOS SOLID-IJQUID DISPERSIOSS. I1
O F SGBSIEI-E
EXPERIUESTAL’ IT. E. ROBISOY
AsD
S. W. JIARTIS~
Institute of Gas Technology, Chicago, Illinois Received September 1 1 , 1948 I. IZTIZODUCTION
In a previous paper ( 7 ) the literature on tieaker-type centrifugal sedimentation of subsieve solid-liquid dispersions n-as thoroughly reviewed and a mathematical basis \vas evolved for calculating the dispersions from beaker-type centrifugal sedimentation data obtained by the ‘ ~ a r i a b l etime-constant height” method. Final results for this colloidal ten1 are compared with thetivariable height-constant time“ method of Brou-n (2). Both procedures for beaker-type centrifugal sedimentation are checked with an electron-microscopic. particle-size distribution analysis of the titanium dioxide pigment select X I for this experimental investigation. Beaker-type centrifugd sedimentation theory postdates the iiw of sect or ~ 1 1 s . Because of convenience, ull puliliwtions on tmtke!.-type cent rifilgiltion have been confined to the use of cylindricd cells. It \vas considered nwth\vhile t o evaluate the effect of cell shape on final results. Consequently, the “variahle timeconstant height” as developed by the miters and the “variaiile height’-constant time” method of Bron-n were suhjected to a comparison in both beaker-type sector and cylindrical cells. Heference is made t o Rohison (6) for detailed descriptions of experimental techniques and a complete record of all data accnmulated. This paper represents a condensation of an extensive esperimental study, ivhich \vas initiated with the ohject of placing in particular the ‘.rariahle time-constant height” method of beaker-type centrifugation on a sound theoretical and quantitative esperimental basis. 1 This communication is based on the dissertation submitted by H. E. Robison t o the Graduate School of Illinois Institute of Technology in partial fulfillment of the requirements for the degree of Doct,oq of Philosophy, June. 19-16. 2 Present address: AhmiourResearch Found:ttion, Chicago: Illinois. Present address: Portland Gas & Coke Co., Portland, Oregon.
