I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
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Vol. 21, No. 2
Supermolecular State of Polymerized Substances in Relation to Thin Films and Interfaces‘ S . E. Sheppard, A. H. Nietz, and R. L. Keenan EASTYAN KODAKCOMPANY, ROCHESTER, N. Y.
HE divergence of views on the “molecular constitution”
coordination values. With multiatomic complexes the of a large number of very important biocolloids and, values may be very large, corresponding to the high potentialassociated therewith, of synthetic resins and other ity of electrostriction (internal deformation) of such a comlaboratory products is well known. It is the raison d’etre of plex. Marinesco4 has shown that with certain dyestuffs the this symposium, so that no attempt will be made to discuss adsorption of solvent (solvation) can amount to 20 to 30 it fully. The term “supermolecular state” is used, therefore, molecules in a monomolecular layer of oriented dipoles. It simply to indicate this unknown. Such terms as “multi- is the deformable (polar) part of the oriented solvate molecule molecular,” “high molecular,” %on-molecular,” etc., might which acts as a dipole-. g., OH in water-while the nonhave been used but these seemed rather more question-beg- polar parts form a perisphere stabilizing the interface. For the micellar sols of the solvated colloids, one of the ging. “Supermolecular” was therefore adopted, without mtention of much more than a useful label. writers has suggested5 that the micelle results from a balance By taking as typical examples of the substances in question, of solvation (involving dispersion) and self-attraction of the rubber, cellulose, and proatom-groups of the colloid, tein, it becomes possible to in fine, a balance of the The two esisting theories regarding the molecular contrast the existing points p o 1a r -n o n- po la r valence , constitution of certain biocolloids and related subof view m o r e definitely. forces for which the writers ’ stances-the association theory of Hess and Pringsheim These substances can be rephave given evidence in the and the macromolecular theory of Staudinger-are resented by the empirical w o r k o n cellulose esters. formulas, rubber (CaH&, contrasted by means of a study of three typical subFurther evidence from the stances-rubber, cellulose, and protein. cellulose (CsHlOO~),,protein viscosity and plasticity of (NHCHRCO), (very simthese micellar solutions will plied, a n h y d r o pol y pe p be presented in a later paper. tide), where n indicates an unknown magnitude as well as Measurement of Energy of Adhesion of Non-Solvents to an U&own quality or kind of aggregation of the residues in Solid Gels the brackets. The problem of the energy of adhesion of non-solvents to The contrasted views as to the constitution of such subsolid gels has required preliminary work on the measurement stances were well brought out in a valuable series of addresses on the “Structure Theories of High Molecular Colloids, No- of work of adhesion of liquids to organic solids of known conably Carbohydrates and Proteins” presented before the 89th stitution, with a view to obtaining both technical improveconvention of the Deutsche Naturforscher und Aerzte at ment of method, and data on the behavior of the simpler atom-groups.6 Dusseldorf, September, 1926, and published in extenso This has now been followed by attack on the energy of adIt must suffice here to point out that the contrast is between hesion of liquids to some of these high-molecular substances. the association theory of Hess and Pringsheim, which supposes that the unit groups of cellulose and the like are mono- The methods developed and a more detailed account of the meric or dimeric glucose anhydride residues held together in experiments are given in a separate communication.7 It cellulose by association through secondary valencies, and the must suffice to say here that evidence has been obtained that macromolecular theory of Staudinger, which considers the the adhesion of a non-solvent-in this case non-polar, nonfundamental groups to be chains of such residues, of length solvent, benzene-could bring about a reversible orientation and molecular weight greater as the degree of polymerization of part of the gel atom-groups opposite to that produced by the adhesion of another polar non-solvent, water. is higher. The properties of the solutions a t higher concentrations It has appeared to the writers that some light on this complex question may be thrown, on the one hand, by a study of the are no less complex than those of concentrated solutions of properties of the solutions of these substances where such are admitted low-molecular substances. formed; on the other, by measurements of the energy of adhe- Determination of Ultimate Film Thickness of Solid Gel sion of non-solvent liquids to the substances in the solid state. It is obviously inviting to consider whether dilute solutions might not give more information on the solute entities. The Properties of Solutions diffusion method of Herzog and the ultra-centrifuge of SvedI n a paper by Sheppard, Carver, and Houck3 evidence was berg promise much in this direction-viz., as to average parpresented on the viscosity of cellulose acetate solutions which ticle size. The present writers have considered it possible supported a “solvation” theory of the viscous effects with that another datum might be obtainable-viz., the ultimate mixed solvents. By “soIvation” is meant an oriented mono- film thickness of the solid gel left by evaporation from such molecular layer, which in true solutions of atom ions may be solutions on an immiscible liquid. The liquid most generally no more extensive than one or two molecules or may reach suitable is mercury.
T
1 Presented as part of the Polymerization Symposium before the Division of Rubber Chemistry at the 76th Meeting of the American Chemical Society, Swampscott, Mass., September 10 to 14, 1928. Communication No. 361 from the Kodak Research Laboratories. 4 * B e y . , 69, 2973 (1926). * Colloid Symposium Monograph, Vol. V, p. 243 (1927).
4 6
J . chim. phys., !24, 593 (1927). Sheppard, Nature, 107, 73 (1921). Nietz, J . Phys. Chem., 32, 255 (1928).
7 Nietz, paper presented before the Division of Physical and Inorganic Chemistry at the 76th Meeting of the American Chemical Society, Swampscott, Mass., September 10 to 14, 1928.
INDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1929
The method consisted in allowing drops of solutions of the substances of varying concentration to spread on a mercury surface cleaned by the sweeping procedure, the amount of substance being insufficient to cover the liquid surface completely. The film area.was developed with talc powder and measured by a planimeter. On plotting the thickness of the film, calculated by assuming the density of the massive material, against concentration, a point is reached where this thickness value becomes independent of the concentration (or dilution). The method and its control by measurements of the length of the molecules of fatty acids and other known molecules are described separately by Keenan.8 Some of the results will be summarized here and their application to the polymerization problem discussed. Table I
SUBSTANCS Rubber Cellulose nitrate
SOLUTION Ether (petrol) Acetone
COMPARATIVE FILM VISCOSITY THICKNESS
A
3025,O 776.0 13.5 2.1 0.2
1960.0
1.5 2.50 3.60 4.23
4.50
5.00
Cellulose triacetate
Chloroform
Cellulose diacetate
Acetone
4.1
Gelatin
Water
7.0
Monomolecular F i l m s of Polymers
9.85
3.8 4.2
127
teristic of the fatty acids is not present? A tentative suggestion on these points will be made. Whether the association theory or the macromolecular theory of Staudinger is accepted it is evident that insolubility is related to increasing degree of mutual orientation of the elementary units. The viscosity phenomena, while agreeing with the polar-non-polar theory of solvent action, point definitely to some form of chain structure of the elementary units, and with chainsof varying length, according to the degree of polymerization. Since the chains are repetitions of certain unit atom-groups, it is relatively easy to see, and in most cases clearly indicated, that there will be a state of potential alternating polarity along the chain. This condition will become more and more definitely actual as parallel orientation of like chains occurs-for example, by double bonds passing to semi-polar bonds. Where this parallel orientation-which is only equivalent to a smectic phase formation (Friedel)-occurs, the capacity for alternating polarity can level up the chains so that the sub-elements can form a space lattice. A single sheet form of the type -A-V-A-V-V-A-V-A-
with a packing in the sheet corresponding to the proportions of longer and shorter chains, is the simplest form of condensation from the completely dispersed state. The dimensions of the films measured are concordant with this view. For rubber the film thickness would be approximately that of the methyl group in Staudinger’s isoprene chain formula
On comparing these values with those obtained for the CHI CHs CHs thickness of monomolecular films of the fatty acids and kin-CHz. CH: C. CH,. CH1. CH: C. CHz. CH: C. CHodred compounds by Langmuir, Adams, and others, one is a t which is nearly 1.5 A. The recent conclusion of Hauserloand once struck with the thinness of these giant molecules. It Mark that this chain must be able to twist a t the linkage may be suggested that since these are average values using CH2-C-C does not necessarily invalidate the existence of the the density of the compact solid, perhaps we have only extended chains in the limit film, or in the dilute solutions. networks full of pores-and much thicker between the pores. We may suppose that the twisting moment is only fully deThe writers hope to determine the pore space later, but veloped when the chains are completely oriented in the latwould point out that the limit thickness and its reproduci- tice a t the minimum distances apart. bility can hardly represent a casual network. I n the case of cellulose nitrate6 there appears to be a relaI n confirmation of this it may be observed that the proced- tion between the viscosity or average length of chain of gluure gives a value for protein in good agreement with that cose anhydride residues and the thinness of the limit film, found for protein films on water by Gorter and G~-endel.~This may be explained by assuming that the shorter the These results lead to certain interesting conclusions. First chains the greater the tendency to vertical piling and overit appears that the rubber and the cellulose esters must be lap. This becomes still more marked in certain proteins, and separating from the solution with one dimension, a t least, of is further associated with the growing complexity of the the solute units considerably less than any dimension of the chain elements] and development of electric moments of higher elementary cell of the structure deduced from x-ray examina- order. tion for the solids. The limit thickness increases on passing Conclusion from rubber through the carbohydrate derivatives to the protein-that is, with increasing complexity of atom groups + The behavior of high-molecular substances in thin films and a t interfaces is in agreement with Staudinger’s concep (C, H)+(C, H, O)+(C, H, 0, N) If these limit films are of elementary thickness-i. e., com- tion of extended chains of atoms held by homopolar primary parable with the monomolecular films of simpler crystalloid valences. The remaining interactions-i. e., orientations and substance-the molecular dimension in question can be only condensations of these chains-are effected by development of alternating polarity along the chains and consequent the thickness of a chain or sheet of atoms. This conclusion is in agreement with the results of x-ray mutual induction. The binding forces in this case (between analysis of these materials if the material is supposed to be the chains) may vary from Van der Waal’s forces to electrodispersed by the solvent a t high dilutions beyond the elemen- static constraints. Under the influence of dissolvents the tary cells. Since in most of these configurations the binding macromolecular state may be brought to incipient dissociain the groups forming the cell has to be attributed to second- tion-a state comparable with that postulated by the associaary valences, the conclusion is not unreasonable. The ques- tionists. tion then arises-what is the configuration of the elementary l o Sixth Colloid Symposium, Toronto, 1928. substances in these polymers which permits such films to be formed? I n particular, how does the formation take place Believing that there is no need for the exploitation of new seams without piling or overlap, if the “end-on” orientation charac6
To be published shortly, Trans. Faraday SOC.,11, 477 (1926).
of potash, the German Government has prolonged until December 31, 1931, the provisions of the law prohibiting shaft-sinking in potash mines.
