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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
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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
I. COHEN,P. ECONOMOU, AND A. LIBACKYJ
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In a previous study of the electrolyte specificity observed in aqueous Hy systems with a number of monovalent anions4 it was shown that the c.e.c. for each of the systems studied may be qualitatively correlated with the initial ionization properties of the system a t low electrolyte concentrations. The primary observable effects of relatively small infusions of I2 in aqueous Hy solutions are small changes in the initial ionization properties of the Hy micelles. A functional regularity is observed in the ionization changes with increasing I2 concentration. Hence, an examination of Hy-12 complex systems provides a method for developing quantitative relationships between the various properties of the homogeneous phase of these systems. Of special interest are quantitative relationships between the c.e.c. and characteristic properties of the homogeneous phase. Experimental Materials.-The investigation
following materials were used in this CH3
CHa
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dilutions with HzO and 12-free Hy solutions. All experimental solutions were equilibrated in a thermostat for at least 3 hr. prior to making any measurements on these solutions.
Results and Discussion Micellar Molecular Weights.-Figure 2 represents the micellar molecular weights of a series of aqueous Hy-I2 complex systems with 12/Hy molecular ratios ( R )ranging from 5 X 10-3 to 5 X in addition to the non-iodinated system. It is apparent from these curves that the micellar molecular weights are not a monotonic function of NaC1 concentration. In fact, a complicated micellar growth pattern is indicated with the addition of NaCl in small increments to the system. Initially there occurs a relatively small micellar growth with the first small additions of NaC1. The initial small growth is followed by a relatively sharp rise in micellar molecular weight over a narrow range of KaC1 concentration, to a near plateau. This transition resembles a disorderCHs
C H ~ - ~ - C H ~ ~ ~ - O - C H ~ - C H Z - O - C H ~ C H ~ - ~ - C -.HZ0 H ~ ~ C ~ _ .
CHJ I AH3 AH3 Hyamine 1622-diisobutylphenoxyethoxyeth~yldimethylbenzylammonium chloride monohydrate (1) Hyamine 1622 (Hy) is a commercial bactericide produced by Rohm and Haas. This material was purified in the following manner. A quantity of Hy was dissolved in boiling acetone. The concentrated solution was filtered while hot and left to cool slowly. A crystalline product precipitated. The crystals were filtered, washed with diethyl ether, then dried in a vacuum desiccator for 24 hr. ( 2 ) I?:was C.P. grade which was freshly sublimed before use in these experiments. (3) KaC1 was C.P. grade. Apparatus. Light Scattering.-Light scattering measurements were performed in a Brice-Phoenix photometer, using incident unpolarized monochromatic light of wave length 5460 A. In this spectral region, I?:absorption is minimal and does not interfere with light scattering measurements. The measurements were carried out in a cylindrical cell, with solutions which had been filtered through millipore filters of 0.45 p pore size. Refractive index increments (dnldc) were measured with a Zeiss dipping refractometer. For soap concentrations in excess of the critical micelle concentration (dnldc) is independent of electrolyte concentration, iodine concentration, micellar size, and micellar Ehape. The refractive index increment for Hy-12-NaC1H20 systems is 0.1913 ~ m . ~ / g . Hyamine-I?: Complex.-Molecular I?: forms a complex with Hy. Figure 1represents the optical absorption spectra for the titration of a C H C ~ S -solution I~ in which the IZconcentration is 2.53 X M, with a CHCl3-Hy solution. These curves show typical two-component spectra for the solvated I2 and the Hy-I?: complex. A binding constant for the Hy-IZ complex was calculated from these data. The mode of preparation of the Hy-IZ complex is the addition of solid freshly sublimed 1 2 to an aqueous Hy solution. The heterogeneous mixture is then shaken for a prolonged period of time (5-6 days) until all of the I?: goes into solution. In a 6% Hy solution a t room temperature, when the L/Hy molecular ratio is an excess of two immiscible products are formed, a heavy opaque viscous material, and a supernatant aqueous solution of the Hy-I2 complex. The heavy opaque material was not investigated beyond the extraction of IZwith CHCls from this material. 1 2 could not be extracted with CHC13 from the aqueous Hy-12 complex phase. The complex is soluble in both the HzO and CHC4 layers. A carefully prepared stock solution of 6% Hy was made up in which the L/Hy molecular ratio was 5 X Experimental solutions were prepared by appropriate __ (4) I. Cohen and T. Vaasiliades, J . Phys. Chem., 66, 1774 (1961).
order transition of higher order than one. Small infusions of I2in these systems make t,he transition sharper and shift the transition to lower NaCl concentrations. With further additions of NaCl beyond the plateau, a sharp djscontinuity is observed in the micellar molecular weights corresponding to a 20% growth of the micelle. The remaining micellar growth to the c.e.c. falls on a smoooth curve. In the latter NaCl interval, the micellar growth is an exponential function of the NaCl concentration (Fig. 3) and, for the noniodinated system a t 30°, may be represented by
M
= Mxe12.26(C-Cx)
(1) where 44 is the micellar molecular weight a t NaCl concentration, C; M x is the micellar molecular v-eight at IKaC1 concentration, C,, which was arbitrarily chosen as the first experimental point on the smooth curve which characterizes micellar growth a t higher NaC1 concentrations. This expression may be related to the 12/Hymolecular ratio (R) by The differential equation describing the growth process at, higher XaCl concentrations may be p11t in the form dM/M = 12.2.5e1'" dc (22) It previously was observed4 that! the micellar molecular weights at the onset of two-phase formation for a number of coacervating cationic soap systems varied over a considerable range of approximately loGto 5 x loG. This same variability in micellar molecular weights is observed in t h r Hy-I2 complex system. The vertical lines in Fig. 3 represent the critical micelle molecular weights for the non-iodinated and for iodinated systems. The derived critical micelle moleculwr weight for
HYAMINE 1622-IODINECOMPLEX SYSTEMS
Oct., 19612
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180I
A.
170.
\\
160. 150140.
I30
I
\
\ \
I20
I
**
110 100
90
f
80
70
60 50
Fig. 1.--Absorption spectra of CHCls-Hy-I2 solutions I2concn., M Hy concn., M IdHy (R) (1) 2.53 x 10-4 0 (2) 2 . 5 3 x 10-4 2.59 x 10-4 0.94 ( 3 )2.53 x 10-4 5.37 x 10-4 -47 (4)2.53 x 10-4 1.17 X 10+ .21 (5) 2.53 x 10-4 2.49 x 10-3 .10
the non-iodinated Ry-NaC1 system is 1.98 X lo8; for the iodinated system in which the (Ig/Hy) moleculax ratio is 5 X the derived critical micellar molecular weight is 1.10 X lo6. This is a further indication of the fact, previously noted,4 that micellar size is not the sole critical factor related t o coacervation in soap systems and coacervation can occur in the same cationic systems of different critical micellar sizes. Flory" has developed the theory for the limiting case of coacervation in uncharged rodlike macromolecular solute systems. The driving force for coacervation in anisotropic non-electrolyte systems is the geometry of the system. When the effective volume of a solute particle exceeds the total available volume per solute particle the systems separate into two phases, an ordered phase and a randomly oriented phase. In aqueous macro-ion systems, the geometry of the solute particles is complicated by double layer charge effects. Ostera reported that in salt-free, highly purified aqueous tobacco mosaic virus solutions (TMV), the co-volume of a rodlike TMV particle is approximately ten times the co-volume calculated for mon-interacting rods. The addition of NaCl to a TMV solution reduces the virus covolume iby virtue of shrinking the diffuse double layer of the charged TMV solute particle. Two macroscopic effects are observed with the addition of NaCl to a 'TMV solution. At low NaCl concentrations (leas than 0.05 M ) , the critical virus concentration necessary for two-phase formation is increased as compared to salt-free TMV solutions. At higher NaCl concentrations, the two-phase TMV sy,ystem is dispersed and the system becomes a homogeneous solution. In the latter region of NaCl coincentration, the virus co-volume is twice the co-volume calculated for non-interacting rods. I n the Hy-In systems, a further complication is observed with the addition of NaCl to the systems. I n the NaC1 concentration region, corresponding ( 5 ) P. J. l~lory,Proc. Rog. 8 0 0 . (London), A234, 73 (1958). (6) G. Oater, J . Qen. Phy8
