1826
ROGER8. PORTER
AND JULIAN
w.
H. wADE.--’CTre observe variations with particle size for samples where surface concentration of impurities is negligible; therefore, the variation for these hi6h area samples must be due to another cause. Of course, with low area samples, this does become a serious consideration. Our rutile studies do not necessarily contradict previous measurements since there is no fundamental reason why an amorphous layer should dissolve more rapidly than a crystalline layer.
F. Jomsoiv
Vol. 60
R. J. GOOD(General Dynamics).--I wish to call your attention to Conway Pierce’s recent papers on the effect of intergranular condensation on heat of adsorption.
w.
studies of a H. WADE.--There are several similar nature but none are applicable to gels in any sort of quantitative way.
ORIENTATION OF NEMATIC R!IESOPHASES* BYROGER S. PORTER AND JULIAN F. JOHNSON California Research Corporation, Richmond, California Received March lt,1961
Orientation studies have been performed on pure, one-component mesophase systems. Both the mesophase, ie., liquid crystal state, and the isotropic liquid range have been studied for the two compounds, p-azoxyanisole and anisaldazine. These two compounds exhibit a nematic type meso hase between defined temperature limits. New results on viscosity and orientation are reported, Previous magnetic an$ shear orientation results for the nematic phases of these compounds have been placed on an absolute scale, reinterpreted, and compared with new data. The rigid rod approximation for the nematic phase is discussed. Flow activation energies for various orientations are calculated. The size of nematic aggregates and the thickness of adsorbed layers are discussed. The general characteristics of the nernatic phase are compared with those for the other major types of mesophase.
Introduction This study of liquid crystals gives results which substantiate and extend an understanding of the flow properties and order of the nematic and isotropic states of p-asoxyanisole and anisaldaaine. Experimental
quire a meniscus observation, which can be diEcult with mesophases.8
Results Orientation Viscosities : p-Azoxyaniso1e.-In the stable solid of p-azoxyanisole, the molecules are oriented with their axes parallel. The aaoxy group of one molecule is adjacent to the ether group The compounds were obtained from Eastman Kodak Company and the Matheson Company, Inc. The com- of another. These dipoles lead to threadlike pounds were purified by dissolving them in either hot abso- molecular aggregates which are typical of the fluid lute alcohol or toluene, followed by filtration and recrystal- nematic phase.g The viscosity measured by both lization. Elemental analyses indicate excellent purity conventional capillary flow and by the concentric for the recrystallized compounds. This also is indicated by a comparison of transition temperatures for these com- cylinder viscometer corresponds to the lowest of pounds with values reported in the literature. Table I magnetic orientation viscosities. This indicates gives the nematic temperature ranges for the compounds that nematic aggregates readily attain maximum studied.1-4 orientation in the direction of f10w.1°-13 The consistent concentric cylinder results indicate that the TABLE I nematic phase orients not only in a plane parallel TRANSITION TEMPERATURES FOR COMPOUNDS STUDIED to the shearing surfaces but also aligns totally in Literature values, oc.ifa,4 This work, “C. the direction of flow. Data in Fig. 1 show that SolidNematicSolidNematicnematic aggregates are at maximum orientation Compound nematia isotropic nematic isot,ropic over a wide range of shear rates. Figure 1 also 118 135 118.5 135 p-Azoxyanisole indicates that shear rates to above a half million 169 182 Anisaldazine 169 182 reciprocal seconds do not orient individual moleCross-arm capillary viscometers were used to obtain low cules in the isotropic liquid. Viscosities for the shear viscosity measurements.6 Viscosity measurements, nematic state do increase, however, if shear rate is made in closely regulated oil baths, are accurate to =!=0.20/,. High shear viscosity measurements were made with a thin decreased below a homogeneous value of about film, double-thermostated concentric cylinder rotational 2000 sec.-l. This agrees with the general region v i s ~ o m e t e r . ~The . ~ accuracy of high shear viscosity and of fractional orientation and noli-Newtonian flow shear rate measurements is about f 2 % . Within these indicated by previous light transparency and low limits, pure, linear hydrocarbons with molecular weights to above 500 show entirely Kewtonian flow up to near IOe shear, capillary flow measurements. l 3 The energy conversion in the concentric cylinder se(:.-*.7 The concentric cylinder viscometer has the advantage of being a “working” viscometer and does not re- viscometer causes small temperature gradients within the test fluid. These gradients represent a * P a r t I of a series on Order and Flow of Liquid Crystah. force for orienting the nematic phase.14.15 This (1) G. H. Brown and W. G. Shaw, Chem. Rep., 67, 1049 (1957). (8) W. Ostwald and H. Malss, Kolloid-Z., 63, 192 (1933). (2) V. Frederiks and V. Zolina, Trane. Faraday Soc., 29, 919 (1933). (3) “International Critical Tables.” Vol. 1, 192G, p. 314. (4) D. Vorlander, “Chemische Kristallographie der Flussigkeiten,” Leipzig, 1924. (6) J. F. Johnson, R. L. LeTourneau, and R. Matteson, Anal. Chem., 24, 1505 (1952). ( 6 ) E. M. Barber, J. R. Muenger, and I“. J. Villforth, Jr., ibid., 27, 425 (1955). (7) R. S. Porter and J. F. Johnson, Wear, 4, 32 (1961).
(9) J. D. Bernal and D. Crowfoot, Trans. Faraday Soc., 29, 1032 (1933). (10) M. Miesowicz, Nature, 158, 27 (1946). (11) J. Falgueirettes, Compt. Rend., 241, 71 (1955). (12) G. Becherer and W . Kast, Ann. Physzk., 41, 355 (1942). ( 1 3 ) S. Peters and H. Peters, Z. Physik. Chem. (Frankfurt), 3 , 103 (1955). (14) G. W. Stewart, Phys. Rev., 69, 51 (1945).
ORIEYTATION OF XEMATIC MESOPHASES
Oct., 19621
thermal alignment is perpendicular and in opposition to orientation in the direction of fl0w.'~1'~ The observation of maximum orientation nematic viscosity in the rotational viscometer thus indicates that neither random nor directional thermal effects in the nematic phase compete successfully with shear orientation a t stresses above 500 dynes/cm.2 Miesowicz has shown the influence of an orienting magnetic field on the viscosity of p-azoxyanisole."J,L6 Limiting high and low viscosities were obtained as a function of temperature a t 3800 gauss for orientation parallel to the direction of flow and parallel to the velocity gradient. These values of Miesowicz have been replotted in Fig. 2. The previously described capillary and rotational viscometer measurements also are plotted; they agree within precision with the Miesowicz values for magnetic orientation in the direction of flow. Viscosities for unoriented nematic structures of pueoxyanisole have been measured by Becherer and Kast using the Helmholtz method.12 The Becherer and Kast values have been replotted and reinterpreted by least squares analyses as given in Fig. 2. It is of interest that neither oriented nor unoriented nematic viscosities form a continuous series with isotropic viscosities. For anisaldazine a continuous series of nematic and isotropic values has been ]proposed in terms of microwave dielectric loss.18 Because of the change of state at the nematic-isotropic transition, a continuous series for viscosities or dielectric properties would seem not to be required. The dielectric loss for the randomly oriented nematic state also has been related to the corresponding quantities in a perpendicular magnetic field and in a parallel field.'8 Applying the approximation that the nematic liquid crystalline state consists of rigid rods leads to a simple integer relationship between the dielectric loss for the various orientations. Such simple exlpressions have been only moderately successful.l 7 , I 8 An orientation relationship of the general dielectric type has been applied to viscosity data for the nematic state of p-azoxyanisole. The use of this form is rationalized by the fact that dielectric loss can be inversely proportional to relaxation times. Hence, by simple Debye theory, dielectric loss should be proportional to T/q, where T is absolute temperature and q is absolute viscosity.18 By these considerations, a strikingly simple and accurate re1,ationshiphas been developed for nematic Orientation viscosities. 4_ -- -3 + -1 770
71
72
Equation 1 describes within the precision of measurement the relation between viscosity for the random oriented nematic phase, qo, and the limiting low and high viscosities, vl and 772, for nematic orientation parallel to flow and parallel to the shear gradient, respectively. Equation 1 holds with (15) R. C. Davis and G. W. Stewart, Proc. I o w a Acad. Sei., 45, 189 (1938). (16) M. Miesowicz, Bull. Acad. Pol., A, 228 (1936). (17) E. F. Cart, J . Ctkelcenz. Phys., 26, 420 (1957). (18) E. F. Carr and R. D. Spenoe ibid., 23, 1481 (1964).
1827
------+35
v) w
Lo
: -: I-
530 U
r '
t u)
U 0
> Lo 25
le
12
8
4
28
24
20
32
BE
38
SHEAR RATE, SECONDS-' X
Fig. 1.-p-Azoxyanisole:
viscosity os. shear rate.
._._,
8.0
A MEISOWICZ'~ A ME150WlCZ10 o BECHERER AND K A S T I ~ T H I S WORK 0 R O T A T I O N A L VISCOMETRY V CAPILLARY VISCOMETRY v)
>-
t 3.5v) u 0
2 3.02.5
2.0
,
I
,
,
2.58
,
,
2.52
, , , 2.$8
,
I
!
I
l
l
I
1
2140
2.$4
YT.~ x io3 I
lie
120
124
Fig. 2.-Orientation
128
132
I
136
I
140
I
144
'
I
1
TEMPERATURE,'^ viscosities for p-azoxyanisole.
notable constancy over the entire nematic range for p-asoxyanisole. Flow Activation Energies.---The original presentations of random and magnetic orientation viscosities for p-azoxyanisole were in plots of linear viscosity vs. linear temperature.12J6 The log viscosity us. reciprocal of absolute temperature plot, used in Fig. 2, gives a generally more linear correlation. Apparent flow activation energies also may be calculated from slopes for the linear portions in Fig. 2. Flow activation energy is defined here as R(d In q/l/Tox), where R is the gas constant and rl is absolute viscosity. Flow activation energies calculated from least squares analyses are given in Table 11. Values for flow oriented nematic viscosities and for the isotropic state of p-azoxyanisole have been derived from more complete data.l3 Adsorption.--Adsorption represents a potential error in viscosity measurements. Viscosities meaSured in the concentric cylinder instrument generally were found to be independent of fluid thickness and to agree with limiting orientqtion yatues;
ROGERS. PORTER ASD JULIAX F. JOHKSOX
1828
-
CALIBRATED BOSE DATA 0
OBSERVER C20 TUBE 3 - 6 0 0 M M Hg2'
V
TUBE 4
0
NEUFELD
b
NEUFELD
A
I
v)
u
0 V v) > 1.5 uLE-
- 75
Vol. 66
CALIBRATION DATA CAPILLARY VISCOMETRY 0 THIS WORK
MM Hg 2 '
I II.
I S O T R O P I C STATE
2.0
v)
a
NEMATIC S T A T E
-
I
W
z s
1.0
1
1
2.28
I
I
I
2.26
,
I
I
I65
I
2.24
I
2.20
1
I
170
I
I
2.22
I75
180
I
I
2.18
I
I85
I
I
I
2.16
I
190
I
I
2.14
I
195
1
2.12
I
200
TEMPERATURE ,"C Fig. 3.--Mesophase transition viscosities for anisaldaxine.
TABLE I1 FLOW ACTIVATION ENERGIES FOR 'pL4ZOXYANISOLE Fluid state Nematic liquid crystals, 119-132O Isotropic Flow Gradient >135O Molecular orientation oriented oriented Unoriented Unoriented
Flow activation energy
2.7
13.0
3.5
5.7
compare Fig. 1 and 2. I n several nematic phase determinations, however, apparent viscosities were above precision limits. For example at 128", high apparent viscosities near 2.8 and 2.9 cp. were obtained with fluid thicknesses of 3.35 and 2.79 X 10-4 cm., respectively. This corresponds to an effective decrease in fluid thickness of about 0.6 p. This suggests an adsorbed film of p-azoxyanisole of 0.3-0.6 p, depending on whether the film is adsorbed on one or both of the steel cylinders. I n two cases, the probable adsorbed layer appeared to be slightly less thick, but not destroyed, at high shear. Apparent adsorption was observed at temperatures in the nematic range and LIP to 137". Previously reported dimensions for nematic aggregates are similar to thicknesses of adsorption layers measured here. From nematic viscosities in a rotating magnetic field, it appears that pazoxyanisole is associated in groups with diameters of the order of 0.7 p.1 By studying light diffusion, it has been concluded that nematic structures of 0.2-0.3 p in largest dimension are present.l The nematic aggregates decrease in size with in-
creasing temperature. From the effect of orientation of the aggregates on the mobility of foreign ions, aggregate size has been calculated to vary from 106-105molecules over the nematic range.lg Anisa1dazine.-Figure 3 compares new viscosity results with the earlier values for anisaldazine. The data of Bose have been put on an absolute kinematic scale by using new anisaldazine nematic and isotropic viscosities obtained in this study. 2 0 , 2 1 The calibrated Bose data, Observer C, are in excellent accord with the new results over the full temperature range. Bose's data, Observer B, also show agreement but with less definition.20 The earlier data are generally less accurate as temperature fluctuations of over 1" were reported during individual capillary flow measurements. Xeufeld's capillary flow data on anisaldazine also have been calibrated with new data obtained here.22 The lowest values for the nematic state, obtained in Poiseuille or laminar flow, likely correspond to maximum orientation in shear flow. This is because results with different viscometers give equivalent results. Bose was able to obtain flow measurements up to 5' below the nominal transition for his good quality anisaldazine. Similarly, (19) L. S. Ornstein and W. Kast, Trans. Faraday Soc., 29, 951 (1933). (20) E. Bose and F. Conrat, 2. Physzk., 9, 169 (1908). (21) E. Bose, zbzd., 10, 32 (1909). (22) F. Krugei, ibzd., 14, 651 (1913).
Oct., 196%
HYAMINE 1622-IODIXECOMPLEX SYSTEMS
in this study viscosity measurements were obtainable to several degrees below the observed solid transition of p-aeoxyanisole; see Fig. 2 and Table I. The higher nematic viscosities in Fig. 3 have been obtained by Bose and by n’eufeld from measurements a t higher shear induced by an overpressure on special capillary viscometers.21J2 The increase in nematic viscosity has been attributed to Reynolds type turbulence. 21 The Reynolds numbers for turbulence, however, may not be sufficiently large, although they cannot be calculated exactly. It is possible that other causes are responsible for the viscosity increase, such as need for capillary corrections or capillary residence times approaching relaxation times for the nematic microstructure. Kruger, who quotes Neufeld’s thesis data, says nematic anisaldaeine at high pressure shoots
1829
through the capillary viscometer like a rigid body.22 It is significant that such high shear anomalies were not observed here for nematic structures of pazoxyanisole; see Fig. 1. The results in Fig. 1 also indicate that oriented nematic structures are not broken up a t high shear. Such a speculation has been made to account for the higher nematic viscosities in Fig. 3 induced by higher pressures and shear rates in capillary viscometers.22 Tests comparable to those in Fig. 1 were not made on anisaldaeine, as its nematic state exists beyond the operational temperature limits of the concentric cylinder viscometer. Acknowledgment.-The authors express appreciation to Mr. A. R. Bruzzone for help in the experimental work.
CRITICAL PHENOMENON IN AQUEOUS s o L m m x s OF LONG CHAIN QUATERNARY AMMONIUM SALTS. IV. HYAMIKE 1622-IODINE COMPLEX SYSTEMS BYIRVING COHEN,PETER ECONOMOU, AND ANFIRLIBACKYJ Department of Chemistry, Polytechnic Institute of Brooklyn, Brooklyn 1, New York Received March 6 . 1968
The coacervating quaternary ammonium salt, Hyamine 1622, forms a complex with molecular iodine. The micellar molecular weights and the charge properties of the homogeneous phase of this cationic soap system, as a function of NaC1 concentration and IZconcentration, were determined from light scattering measurements. An over-all two-stage growth process is indicated in these systems. At low NaCl concentration, the micelle grows to a limiting isotropic structure. At higher NaCl concentrations, the micellar growth is an exponential function of the NaCl concentration. The Hyamine-12 complex systems ahow the typical micellar ionization suppression with increasing NaCl concentration encountered in a number of icoacervating cationic soap systems.8 The infusion of small quantities of 1 2 in an aqueous Hyamine 1622 solution produces changes in all of the characteristic properties of the system. Experimentally, detectable changes in the critical electrolyte concenixation (c.e.c,) necessary for two-solution phase formation may be observed for an Iz/Hyamine 1622 molecular ratio as low as 10-3. A number of simple empirical equations have been developed which show the functional relationships that exist among several characteristic properties of these solutions. S ecifically, the c.e.c. may be predicted for these systems from the rate of micellar growth in the initial growth process as a gnction of NaCl concentration, and independent1,y from the initial ionization properties of these aqueous polyelectrolyte systems.
Introduction The separation of aqueous soaps into two solution phases (coacervation) occurs for a number of cationic’ rand anionic2 soap species with the addition of simple electrolytes to their aqueous solutions. The homogeneous phase of several cationic soaps, which form coacervates, shows two pronounced eff ects prior to two-phase formation3: (a) a t low electrolyte concentrations, the degree of micellar ionization is critically suppressed and (b) the soap micelles grow to a size which is of the order of IO2- to 5 X 102-fold larger than the micelles in an electrolyte-free solution. An additional effect has been ~ b s e r v e d . ~Intermediate between zero electrolyte and the critical electrolyte concentration (o.e.c.), a narrow electrolyte transition range (e.t.r.) may be identified, for each coacervating system at a fixed temperature, in which light scattering, viscosity, and diffusion studies indicate an apparent transformation of the micellar species (1) I. Cohen, C. F. Hiskey, and G. Oster, J . CoZZoirt SOL, 9, 243 (1954). (2) A. C. Bungenberg de Jong, “H. R. Kruyt Colloid Soi.,” Vol. 11, Elsevier. Amsterdam, 1949, Chap. X. (2) I . Cohen and T. Vassiliadea, J . Phya. Chem., 66, 1781 (1961).
from an essentially isotropic to an anisotropic entity. The purpose of this study is a detailed examination of soap micellar growth as a function of electrolyte concentration in a typical cationic coacervating system. The system chosen for this study was the Hyamine 1622 (Hy)-NaC1-H20 system. Although structurally the Hy soap monomer is a rather complicated molecule, this system has the advantage that gross changes in the system may be observed for small electrolyte increments. A further advantage of this system rests in the fact that Hy forms a complex with molecular If. The infusion of small quantities of Iz into this micellar system produces changes in all of the characteristic properties (of the homogeneous phase) of the system. Specifically, in an over-all aqueous 1% Hy solution for a 12/Hy molecular ratio of 1.25 X 10-3 the critical NaCl concentration is lowered by 0.01 M as compared to the non-iodinated system. A comparable shift in the e.t.r. for the system is observed. In addition to the non-iodinated system, this investigation encompasses Hy-I, complex systems in which I2/Hy molecular ratios ( R ) range between 5 X and 5 X
