COMMUNICATIONS TO THE EDITOR
2034 quite misleading, since they include a cratic term which is of little significance in describing the events taking place during the formation of a micelle. On the other hand, use of eq 3 provides entropy values which more closely resemble unitary functions, since it excludes the entropy of mixing. This procedure would appear to offer more advantage, at least until such time as precise calorimetric data become available. Finally, it should be pointed out that the compatibility of the mass action and phase separation approaches is not in dispute. As previous work showedJ2 the data for the N-alkyl betaines support the view, widely held, that the longer the alkyl chain of the amphiphile, the better the agreement between the two models. DIVISIONO F PHARMACEUTICS SCHOOL OF PHARMACY OF CONNECTICUT, UNIVERSITY STORRS,CONNECTICUT 06268
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RICHARDE. LINDSTROM JAMES SWARBRICK 10-
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Molecular Mobility in Simple .Glasses Sir: I n a recent paper, one of us’ proposed a picture of viscous flow and the glass transition that suggested that secondary relaxations in the glassy state could arise solely from intermolecular processes, thus leading to the prediction that such molecular relaxations could be a universal feature of the glassy state. Argon2 made a similar conjecture on the basis of a ~ description of viscous flow due to O r ~ w a n ,whose ideas were also used as the basis of the picture referred to earlier.’ To test this hypothesis we have studied, by dielectric relaxation measurements, molecular mobility in glasses formed from molecules lacking obvious internal degrees of freedom capable of giving relaxations due to intramolecular processes. We studied the fused-salt glasses Ca(N03)2.4H20 and a 45 mol % Ca(N03)2-KN03 mixture; simple molecular glasses of 10-15 mol % ’ solutions of several mono- and di-halogen substituted benzenes and naphthalenes in the nonpolar solvent decalin; 50-60 mol % mixtures of pyridine with several halogensubstituted benzenes and naphthalenes and several pure aromatic hydrocarbons and aliphatic alcohols. We used a General Radio 1615A capacitance bridge and a parallel plate guarded electrode assembly as the dielectric cell. Measurements were made in the frequency range 50 HZ to 200 kHz and a t several temperatures near and below the respective glass transition temperature, T,. We may summarize our results by stating that almost all of these glasses show a secondary relaxation below T,. Figure 1 shows the dielectric loss factor (tan 6) a t 1 kHz plotted on a logarithmic scale against temThe Journal of Physical Chemistry
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Figure 1. Dielectric loss factor of (1) 63.2 mol % pyridine in 1-chloronaphthalene (scale has been shifted to the right by 100’); (2) 16.5 mol % chlorobenzene in decalin; (3) 45 mol % Ca(NO3)2-KNO8 mixture; (4)o-terphenyl; and ( 5 ) Ca(N03)2. 4Hz0 (scale has been shifted downwards by two logarithmic cycles) a t 1 kHz as a function of temperature. Arrows indicate the literature values for T , when known.
perature for five of the systems studied. The Ca(N03)2-KWOa glass is atypical in that the secondary relaxation does not appear near T , (60”) but instead tan 6 shows a rise below 200”K, indicative of a maximum below the boiling point of liquid nitrogen. The behavior of most other systems we studied is more like that of the other four shown in the figure in that: (1) A secondary transition (peak in tan 6) appears some 30-50” below T , at a measuring frequency of lo3 Hz, (2) The “activation energy” of the main transition is much greater than that of the secondary peak, so that the two relaxations must either cross in a temperature-frequency diagram or else merge into a single loss region above T , a t higher frequencies. (3) Neither relaxation is described by a single relaxation (1) M. Goldstein, J . Chem. Phys., 51, 3728 (1969). (2) A. S.Argon, J . A p p l . Phys., 39, 4080 (1968). (3) E. Orowan, “Creep in Metallic and Non-Metallic Materials,” “Proceedings of the First National Congress of Applied Mechanics,” American Society of Mechanical Engineers, New York, N. Y., 1952, p p 453-472.
COMMUNICATIONS TO THE EDITOR time. (4) The relaxation time spectra are markedly temperature dependent, broadening as temperature is lowered. The similarity to behavior in many polymer glasses is striking. One alternative explanation that could be given to some of our results is that phase separation occurs in glasses formed from mixtures of simple molecules and that the appearance of secondary relaxation peaks (below Tg)is an artifact due to this. But the near universality of this behavior both in a wide variety of mixtures, and in pure substances as well, leads us to exclude this possibility. Most molecular explanations for the presence of molecular mobility (indicated by secondary relaxation regions below Tg)have been in terms of internal molecular motions involving hindered rotation around chemical b o n d ~ . ~ In J this view these relaxations are extrinsic to the glassy state and arise from intramolecular modes of motion that remain active even when the molecule as a whole is frozen in the glassy matrix. On the basis of our studies, we suggest that relaxations in the glassy state need to be reexamined from the point of view of intermolecular rather than intramolecular degrees of freedom. We are continuing these studies on additional simple glass forming systems and will report this work in detail and discuss implications of this picture on dielectric relaxation in liquids later.
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Figure 1. Postirradiation polymerization of hydrated barium methacrylate at 35". Dose 0.86 Mrad at -78"; in vacuo: A, 0.6 days; 0, 27.6 days; in air: 0, 34 days.
hydrate.2b Our studies have shown it to be a monohydrate and this observation is in agreement with the recent report of Bowden and O'DonnelL2" These workers, however, have studied the dehydration process in air, for comparison with polymerization studies, believing the polymerization to be unaffected by the presence of oxygen. Results obtained in our laboratory indicate that this conclusion is valid only for the monohydrate and anhydrate. At all intermediate states of hydration, the polymerization is observed to be extremely sensitive to the presence of oxygen. In Acknowledgment. We are grateful to the OwenFigure 1 the yields of polymer on postirradiation polyIllinois Foundation and to the Department of Defense merization in vacuo at 35" for 0.6 and 27.6 days are (Grant No. N00014-69-A-0411) for the support of shown as a function of water content. (The loss of this research. water from the crystal hydrates, under the experimental conditions used, is negligible even at the longest (4! N. G.McCrum, B. E. Read, and G . Williams, "Anelastic and Dielectric Effects in Polymeric Solids," John Wiley and Sons, New polymerization times.3 Therefore, the quoted level York, N. Y., 1967. of hydration is the correct one at any time.) A maxi(5) A. E . Woodward and J. A. Sauer in "Physics and Chemistry of mum in the polymerization rate is observed at the the Organic Solid State," Vol. 11, Interscience Publishers, New York, N. Y., 1965, p 638. 0.25 hydrate. In the presence of air, however, while BELFERGRADUATE SCHOOL OF SCIENCE GYANP. JOHARI the rates a t the zero and monohydrate compositions YESHIVA UNJVERSITY MARTINGOLDSTEIN are unchanged, those at all other compositions show NEW YORK,NEWYORK 10033 an inversion relative to the vacuum polymerizations. We have therefore examined the dehydration process RECEIVED NOVEMBER 20, 1969 in vacuo at 47". The results show that dehydration proceeds with no loss in crystallinity. Infrared spectra and X-ray powder diffraction measurements were Dehydration and Polymerization of Barium identical with those reported by Bowden and O'Donnell. In addition, density measurements of monoMethacrylate Monohydrate1 hydrate, anhydrate and intermediate compositions show that there is no collapse of the lattice upon Xir: The thermal degradation of barium methacrylate removal of the water of crystallization. A minor exmonohydrate has recently been reported by Bowden (3%) along the C axis was observed. pansion and O'Donnell.2a An understanding of this process can play an important role in defining the mechanisms of (1) Paper presented in part a t the 15th Canadian High Polymer the solid-state polymerizations of acrylate and methForum, Kingston, Ontario, Sept 3-5, 1969. acrylate salts. We report here some additional ob(2) (a) M .J. Bowden and J. H. O'Donnell, J . Phys. Chem., 73, 2871 (1969); (b) J. B. Lando and H. Morawetz, J . Poly. Sci., C, 4, 789 servations on the dehydration phenomenon. (1964). The salt of barium methacrylate has been previ(3) F. M. Costaschuk, D. F. R. Gilson, and L. E. St. Pierre, to be ously reported by Lando and Morawetz to be a dipublished. Volume 74, Number 9
April SO, 1970
