A new method for determining the surface tension of liquids has been derived. This involves the consideration of the advancing and receding contact angles of a liquid drop on a tilted solid surface. The theory has been tested by an improved optical projection technique for a variety of liquid/ solid systems and the results obtained are in agreement with the accepted values. It is shown that the advancing and receding contact angles are characteristic constants of liquid/solid system s and the calculated and measured values of the minimum receding angles are in agreement. The prevailing views of ‘hysteresis’ effects or ‘stationary’ contact angles which have arisen to account for the data available are incorrect and the discordant experimental results reported are due to inadequate technique. The difference between the adhesions corresponding to the advancing and receding angles is ascribed to the work done in removing an adsorbed unimolecular layer. The work done in gcal./mol. in forming this adsorbed layer is in reasonable agreement with that expected from studies in gas/solid systems and the forces involved are van der Waals’. Further, different solids that might be expected to show similar surface structures yield similar values for the work done. The variation in the value of the advancing angle in some liquid/solid systems and its constancy in others is reconciled with the polar character of the solid surface, i.e. it is suggested that short-range forces are involved. It has been found that monolayers of ferric stearate on glass are orientated with their hydrocarbon tails away from the interface in agreement with electron diffraction measurements. It is suggested that the methods may be useful for investigating the structure of monofilms and built-up layers of monofilms.

A STUDY has been made of the densities, the surface tensions and their temperature coefficients, the interfacial tensions against water, the spreading pressures, and the force-area and potential-area relations of monolayers on water of various types of linear polyorganosiloxanes. The McLeod constants and parachors have been calculated, and their application to the type analysis of the silicones is discussed. Relations have been found between the critical spreading pressure, the spreading coefficient, and the viscosity. A study of the force-area curves revealed that the polymethylsiloxanes and the related polymers containing a small proportion of phenyl substituents are able to coil reversibly into helices made up of about six monomers per turn. Conclusions relative to the molecular structures in thin films have been carried over to the three-dimensional liquid state.

Tbe relationship of contact angles to surface structure is outlined. The difference between the advancing and receding contact angles is discussed in terms of the modern theory of multimolecular adsorption; this theory indicates that the advancing angle will be unique, whilst the receding one will generally be less than the advancing angle and need not have a unique value.

Dependence of the wetting characteristics of a solid on the roughness of its surface is inherent in the fundamental theory of wetting action (R. N. Wenzel: Ind. Eng. Chem. 28, 988 (1936)). This is immediately apparent when analyses of wetting phenomena take into account the actual areas of the several inter-faces involved as well as their respective specific energy values. The same method of analysis has led to quantitative evaluationof the effects of surface heterogeneity and surface porosity (A. B. D. Cassie and S. Baxter: Trans. Faraday Soc. 40, 546 (1944)).

1. Methods of preparing surfaces of polytetrafluoroethylene (TFE) are described which permit obtaining reproducible and reliable measurements of contact angles with liquids. Polytetrafluoroethylene is found to be an ideal low energy surface for the study of the wetting relations of a solid with a wide variety of organic and inorganic liquids.

2. It is shown that all but the lowest-boiling liquids studied do not adsorb on TFE sufficiently from the vapor to produce a significant spreading pressure. Hence the π_E term in the expression for the work of adhesion (W_A) is negligible and W_A = γ_LV(1 + cos θ). The calculated values of W_A are found to be consistent and reasonable.

3. It is found that for each homologous series of liquids cos θ is a linear function of γ_LV. The constants of the resulting relations are given. From this W_A − W_c can be expressed as a function of γ_LV alone.

4. The observations show that there is a critical surface tension (17.5–20.5 dynes/cm.) below which liquids wet TFE.

5. It is concluded that the corrected Young-Dupré relation coupled with the spreading coefficient permits a rational description of the results. The Doss and Rao relation for the surface condensation leads to such high values for high-boiling liquids as to make it unlikely that the theory is correct.

The wettability of crystals, glasses, and even of water itself can be temporarily decreased by bringing ions of high polarizability into their surfaces. Base exchange experiments are described where the hydrogen ions present in the surface layers of bentonite (a clay mineral of high exchange capacity) and of a soda‐lime glass are replaced by different cations. This substitution seems to have no particular effect on the hydrophilic and rheological properties of the carriers as long as their surfaces are kept in contact with water. After drying, however, the surfaces which contain ions of high polarizability become hydrophobic, at least temporarily. A porous clay film will no longer absorb water instantaneously after having been treated with Ni²⁺, Mn²⁺, Hg²⁺, or similar ions with incomplete outer electron shells. Contact angles with water up to 70° could be observed for a short period for Hg²⁺ and Pb²⁺ clays.

Glass capillary tubes which have been treated with non‐noble gas‐type ions show a capillary rise which is much smaller than that observed with the tubes which have been treated with HCl and water only. This depression of the capillary rise, too, is temporary and can be observed only if the glass wall has been thoroughly dried previous to the experiment and if the capillary rise is measured in the upward direction.

An explanation is presented for these and allied phenomena on the basis of the polarization of ions in the strongly asymmetrical forcefields of interfaces. The experiments are correlated with the hysteresis of the contact angle and with observations concerning adhesion phenomena and catalytic activities of heavy metal ions at interfaces.

FUNDAMENTAL quantities associated with the wetting of solids are the free energies of the solid/vapor boundary ('Y SV) and the solid/liquid boundary ('Y SL). These have been obtained for the special case of a glassy solid fluorocarbon on which the con tact angles (8) have been measured for liquids of widely different surface tension ('Y LV). The excellent agreement between the observed angles and those calculated from the theoretical relation,

1. Data are presented on the equilibrium contact angles of a wide variety of liquids on specially prepared surfaces of halogenated derivatives of polyethylene. The free energy decrease of immersion (f_SL), the work of adhesion (W_A), and the spreading coefficients have been calculated for the liquids which do not spread. The free energy decrease on immersion of these solids in the saturated vapor of most of the liquids of this study is shown to be negligible.

2. For each solid surface the contact angle and spreading coefficient follow the relation to liquid surface tension reported previously for polytetrafluoroethylene, i.e., as the liquid surface tension increases, the contact angle increases and the spreading coefficient decreases.

3. Substitution of chlorine or hydrogen for fluorine in these polymers increases W_A, f_SL, and the spreading coefficient with respect to a given liquid, the increase depending on the proportion of nonfluorine substituent. Substitution of hydrogen for fluorine has a smaller effect in this respect than substitution of chlorine for fluorine.

4. It is shown that when f_SL for a given solid in a series of liquids is constant, the plots of W_A υs. surface tension and spreading coefficient υs. surface tension should be straight lines with positive and negative 45° slopes, respectively. The data presented for the fluorinated polymers and the liquid n-alkanes and di-n-alkyl ethers fall on such lines. The values of f_SL for the fluorinated polymers plot as a straight line against mole per cent fluorine substitution.

5. There appears to be a maximum value of W_A characteristic of the polymer, which is identical with the work of adhesion given by the liquid having a contact angle of 90° on the given solid.

6. It is shown experimentally that there are many exceptions to the “rule” that nonpolar liquids wet nonpolar solids.

7. From the data it is shown that recent attempts to measure the surface tension of solids by contact angle measurements alone involve unjustifiable assumptions.

1. Contact angle measurements have been made of a wide variety of liquids on clean, smooth surfaces of polyethylene, paraffin, and surfaces of single crystals of n-hexatriacontane (C₃₆). The calculated value of the final spreading coefficient (S_{LV^∘/SV^∘}) is given and from the data there can be calculated the values of the free energy of immersion (f_SL), and the work of adhesion (W_A). The free energy of immersion of the solid in the liquid vapor can be neglected in these calculations since it is believed to be quite small for surfaces of low adsorptivity and low free surface energy. It is shown that the methyl-rich surfaces of C₃₆ and paraffin are not wetted by a wide variety of organic liquids, including the n-alkanes, so that the rule that nonpolar solids are wetted by nonpolar liquids is again found to be erroneous.

2. Wettability is found to decrease in the order polyethylene, paraffin, C₃₆. This is attributed to the increase in the proportion of methyl to methylene groups in the surface. The C₃₆ surface, like all higher n-alkane crystals, is shown to be the least wettable of all hydrocarbon surfaces since its surface comprises only methyl groups arranged in the closest possible packing. It is shown that it should be possible to estimate the packing of adsorbed monolayers of straight-chain hydrocarbon derivatives by comparing the hydrophobic contact angle to the angle on C₃₆. Many of the variations of the hydrophobic contact angle on paraffin found in the literature are shown to be attributable to variations in the methylmethylene ratio in the surface.

3. In contrast to the fluorinated polymers, paraffin and C₃₆ are shown to have multiple curves of cos θ vs. γ. The multiplicity of these curves is attributed to differing dependencies of γ_SL on γ_LV^∘ due to variation in the constitution of the liquid. Increase in adhesion of hydrocarbon surfaces to liquids is found to be in the order: liquids containing oxygen or fluorine; aliphatic hydrocarbons, aromatic hydrocarbons.

4. It is shown that variation of the free energy of immersion of the n-alkane series of liquids on a given hydrocarbon surface is the resultant of two competing tendencies: i.e., increased adhesion due to increase in methylene to methyl ratio in the liquid, and decrease in adhesion due to increase in surface tension of the liquid. For the C₃₆ surface, the latter tendency predominates; for the paraffin surface, the former tendency predominates, f_SL is shown to be the upper bound of the solid surface tension for systems where γ_SL ⩾ 0.

5. It is shown that in general there is more than one value of the critical surface tension (below which liquids spread on a given surface) for hydrocarbon surfaces, depending on the value of γ_SL given by a liquid of given surface tension. The fluorinated polymers are shown to be a special case where the surfaces are independent of the nature of the liquid and therefore have essentially a single value of γ_C.

Wenzel’s modification of Young’s equation for contact angles, equation (1), may be derived from considerations of free surface energy, though not from the assumption that surface “tensions” may be represented by vectors. A theory is presented for the hysteresis of contact angles. The “driving force” toward the attainment of an equilibrium contact angle is found to be equal to the surface tension of the liquid times the deviation of the cosine of the contact angle from its equilibrium value. It is shown that this may be equated to the “contortional energy” Fc that the drop must have in order for its edge to surmount a ridge. The result is in the same form as the equation of Adam and Jessop: í-(-yi— 72)= 72 cos 6,, r± Fc, but with a new and physically meaningful interpretation of Fc.

The equilibrium contact angle (θ_E) has been measured for some sixty diverse liquids with respect to a smooth platinum surface coated with an adsorbed oriented monolayer of n-octadecylamine. Linear relations were found between cosine θ_E and the liquid surface tension (gg_LV^∘) for every homologous series. When homology was disregarded, the cos θ_E-υs.-γ_LV^∘ data for all the liquids collected on three straight lines, two of which were approximately parallel. Simple curvilinear relations obtained between the work of adhesion (W_A) and γ_LV^∘ and between the final spreading coefficient (S_{LV^∘/SV^∘}) and γ_LV^∘, the constituents of each set of three curves being the same as before. The grouping onto multiple lines corresponds to differences in the solid/liquid interfacial tension, γ_SL, and to the relative solvent power of the liquids for the adsorbed octadecylamine. The same correlation obtained for the critical surface tension (γ_C), which was shown to be specific both to the homologous series and to the solid surface.

Constant values of the free energy decrease on immersion (f_SL) were observed for the homologous series of n-alkanes and n-alkyl ethers, while the alkylbenzene series showed a linear decrease with increasing γ_LV^∘. From the small range and low experimental values of f_SL observed for many unrelated liquids, it is concluded that the free surface energy of the monolayer-coated solid is probably not much more than 28.5 erg/cm.².

The striking similarity observed for the wetting properties of the monolayer-coated surfaces compared with those reported previously for surfaces of single crystals of n-hexatriacontane and bulk paraffin (5) demonstrates that the wetting behavior of a surface is essentially controlled by the nature and packing of the outermost group of atoms in the molecules. Intercomparison of wetting data for the monolayer with reference data obtained for a surface of methyl groups in closest packing (i.e., n-hexatriacontane single crystals) is proposed as an approach for determining, from contact angle measurements, the packing of adsorbed films at the solid/air interface.

A study has been made of the wettability of adsorbed monolayers of branched-chain and cyclic molecules. It is shown that such monolayers are nonwetted by organic liquids with surface tensions higher than a critical value characteristic of the monolayer. Oleophobicity is therefore not restricted to monolayers whose surfaces comprise close-packed methyl groups, the latter merely representing an extreme case. It is shown, further, that adsorbed layers of nonpolar liquids behave, as regards wettability, like low-energy solids with the same atomic groups exposed in the surface. It is concluded that the free surface energy of adsorbed liquid or solid films depends only on the atomic groups in the surface and their packing.

Data are given for the free surface energy of a number of fluorocarbons. These data show that fluorocarbons as a class have lower surfaceenergies than all other compounds. Curves for the lowering of surface tension as a function of concentration are given for a series ofcompletely fluorinated acids. These surface active compounds cause a greater lowering of the surface tension of water than has ever been found before. Fluorocarbon surface active compounds are shown to lower the surface tension of organic substances very materially. Some measurements of interfacial tensions between fluorocarbons and water and between fluorocarbons and organic solvents are presented. An attempt is made to show some correlation between the above effects in the formation of emulsions and in the wetting of fluorocarbon surfaces.

(1) A study hasbeen made of the wettability of adsorbed monolayers of monohydroperfluoroundecanoic acid. The results obtained on this surface (comprising CF₂H groups) are compared with previous results on adsorbed monolayers of perfluorodecanoic acid (comprising CF₃ groups) and solid polytetrafluoroethylene (comprising CF₂ groups).(2) It is shown that for “normal” liquids [ie, those for which only van der Waals forces of adhesion are operative) the contact angles on CF₂H surfaces are larger than on CF₂ surfaces and nearly as large as on CF₃ surfaces.(3) Alcohols, acids and amines are found to give abnormally low contact angles on CF₂H and CF₃ surfaces, but only amines give low angles on polytetrafluoroethylene. This can be accounted for by the ability of these polar liquids to form hydrogen bonds with the fluorinecontaining surfaces. Esters, lacking a suitable hydrogen atom, are shown to bond only to the CF₂H surface (which can supply the necessary hydrogen atom); alcohols and acids bond to CF₂H and CF₃ surfaces; primary amines bond to all three fluorinated surfaces because of their ability to form “double” hydrogen bonds. These phenomena are believed to be new examples of the “unsymmetrical hydrogen bond” described by Pauling.

The wettability by organic liquids containing Cl, Br or I is less affected by the amide or ester groups as might be expected from the inability of halogenated liquids to form hydrogen bonds. Reasons are given for believing that hydrogen-bonding takes placein the wetting of nylon by water, glycerol, formamide and thiodiglycol and does not take place in the wetting of polyethylene terephthalate by these liquids. The postulated mechanism of wetting led to an experiment which showed that perfluorolauric acid could be adsorbed on nylon from n-decane solution rendering thenylon surface oleophobic.

Wettability of solid surfaces containing covalent chlorine increases greatly with the chlorine content. There is no indication of hydrogen-bonding at the solid/liquid interface for surfaces containing carbon, hydrogen and chlorine. A close packed monolayer of perchloro-2, 4-pentadienoic acid adsorbed on a polished metal is shown to behave with respect to wetting like an organic surface comprising Í00 atom per cent, of chlorine substitution. Increased wettability of fluorine-containing surfaces by hydrogen-bonding liquids is reported for a number of new, partially fluorinated plastic surfaces. The wettability of fluorinated surfaces varies with the type of spreading liquid. For non-polar liquids the wettability decreases with increasing fluorine substitution. For hydrogen-bonding liquids, the wettability increases in the order: polytetrafluoroethylene, polytrifluoroethylene, polyethylene, polvvinylidene fluoride and polyvinyl fluoride. The corresponding order for the haligenated liquids is polytetrufluoroet. hylene, polytrifluoroethylene, polyvinylidene fluoride, polyethylene and polyvinyl fluoride. Explanations are offered for the relation between wettability and the atom per cent, fluorine substitution in the surface based on the electronegativity of the fluorine atoms in the surface and the molecular structure of the spreading liquid.

If the surface of a polyethylene film is subjected to certain treatments, printing on the surface becomes possible, or, in other words, the bonding properties of the polyethylene film are improved. Two forms of treatment, involving the use of a Tesla coil discharge at atmospheric pressure and of a glow discharge at reduced pressure, have been developed. Through the use of a Beckman IR-3 spectrophotometer, it has been found that the treatments cause formation of unsaturated (CC) bonds and carbonyl (CO) groups in the polyethylene molecule. The improved bonding properties may be due to oxidation of the plastic surface.

There is, consequently, a great need for methods for the estimation of surface and interfacial energies — even if only approximate ones. It was as an approach to these problems that the following treatment was developed. Theory of Interfacial Energies — The Berthelot relation for the attractive constants between like molecules...

An analogy between the phenomena of miscibility and wetting is pointed out, and developed to predict critical wetting temperatures: and a relation between the contact angle and the respective latent heats of evaporation between two phases. The theory is compared with experimental results on oleophobic monolayers.

We wish to propose that the surface entropy of a liquid may be taken as a criterion of surface orientation. Orientation in the surface will lead to a lower entropy than that in the condition where the surface molecules are disordered. The question is, first, how much lower is the surface entropy of polar substances than that of non-polar substances? And second, can we set up a simple model which will account for the lower entropy of polar liquids, as resulting from surface orientation?

Ramsay and Shields4 reached the conclusion empirically that there was a “normal” value (2.1) for the Eötvös constant, which is directly related to the molar surface entropy.^6-7 From various theo-retical studies,^6-9 particularly that of Born and Courant, it might be expected that there should be a “normal” value for nearly spherical non-polar molecules. (The extension of this concept to non-spherical molecules cannot be made very simply, because the number of molecules “in the surface” per unit area depends on the degree of orientation as well as the ratio of length to thickness.⁷) The hypothesis of Ramsay and Shields, that the degree of association could be calculated from the ratio of the observed Eötvös constant to the “normal” value, 2.1, has of course long sincebeen discredited;⁷ but it persists in textbooks and the literature, probably because of the lack of a plausible alternative. We will show that surface orientation furnishes a much more reasonable explanation.

Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin

A method of treating plastic film to improve the adhesion of ink impressions imprinted thereon comprises subjecting the opposite surfaces of the plastic film simultaneously to the action of high voltage stress accompanied by corona discharge. As shown, a web 10 is unwound from a supply reel 12 and after passing over rollers 16, 18 passes between electrodes 24, 26 one of which is earthed and the other of which has a high voltage applied thereto by means of a high-voltage transformer 60. The web then passes over rollers 20, 22 on to a take-up roll 14. Alternatively the web may be fed directly to a printing machine. The ground electrode 24 is carried on posts 30 and is provided with notches, Fig. 3 (not shown), on each longitudinal edge so that a glass cord may be threaded therethrough and held in position, thus acting as a spacing member for the web. The high voltage electrode 26 is secured in a recess formed in the inner periphery of a frame 40 formed of insulating material and a solid dielectric 42 is disposed on the upper surface of the electrode. The electrode 26 is supported on posts 50, and a glass cord 46, for spacing purposes, is wound on pins .44 extending from the frame 40. In alternative arrangements the glass cords may be wound spirally around the electrodes, Fig. 4 (not shown), or a fabric may be disposed over each electrode, Fig. 5 (not shown), or both methods employed. The voltage on the high voltage electrode 26 is preferably between 10,000 and 20,000 v., and the electrode may be made of stainless steel.

This invention relates to the treatment of plastic material, and more particularly polyethylene, to improve the anchorage or adherence characteristics of the surface thereof. More particularly the invention is concerned with such a treatment or the control of such a treatment which does not destroy the heat scalability characteristic of the material or result in an unsatisfactory one.

This invention relates to a method of treating plastic materials in various structural forms to improve the anchorage characteristics of the surfaces thereof, more especially relating to the treatment of polyethylene, principally in sheet or film form, to improve the anchorage characteristics of its exposed surface whereby various coating materials such as printing ink may be more firmly secured thereto. In particular the invention is concerned with an improvement in the treating method fully disclosed and claimed in copending application Ser. No. 359,352 filed on June 3, 1953 and assigned to the same assignee as is this invention.

A method of treating the surface of an organic plastic material, to improve the receptivity and adhering of said surface to substances such as ink, coating materials, decorations, or laminations, comprises contacting said surface with a dielectric material different from said organic plastic material in the presence of a varying electric field. As shown, a plastic web P is passed between a drum 16, having a conducting surface or covered with a dielectric material the same as that of the web, and a series of drums 34 covered with a dielectric material other than that of the web, and in contact with at least the latter dielectric. The drums 34 are of steel with a copper-plated layer and an outer chromium layer, and may be slightly shorter than the web width to leave the edges of the web untreated. The upper drums are the treating drums, and increased receptivity to ink &c. is imparted to the upper surface of the web. Alternatively, the lower drum may be used as the treating drum by reversing the dielectrics. The dielectric on the treating drums may be of kraft paper, nylon, varnished or shellaced silk, linen or cabric, with underlayers of wax paper, and less than 20 mm. thick, and should exhibit higher dielectric losses than the web material. The web may be of polyethylene and may contain slip-agents, or may be of polytetrafluorethylene, polymonochlorotrifluoroethylene, or copolymerized vinyl chloride-vinyl acetate. The drums 34 are electrically connected through inductors, the drum 16 is grounded, and the drums 34 are connected to the + terminal of a D.C. supply 65, the negative terminal of which is grounded. A coil 63 is provided in the circuit. A triode 50 is provided, of which the cathode is grounded, the grid is grounded through a resistor 52, and the anode is connected through an R.F. choke 60 to the positive terminal of a D.C. supply, the negative terminal of which is grounded. Connected between the anode and grid through coupling and isolating condensers 54 is a coil 56, across which are connected the stators of a tuning condenser 58, the rotor of which is grounded. By means of the condenser 58, the frequency of the oscillator constituted by the triode and its associated circuits is adjusted to the resonant frequency of the electrode circuit, which is a function of the coil 63 and the inter-electrode capacitance. By means of the coils 56, 63 a high-frequency A.C. voltage is superimposed on the D.C. voltage. The A.C. voltage, owing to the inductors connecting the drums 34, will appear on successive drums 34 in phase-delayed relationship. The D.C. voltage may be 1000-3000 and the A.C. voltage 900-2000 at from 1 Kc. to 1 mc. In general, a higher voltage rate is required for a higher treatment rate, higher speed of web feed, and greater slip-agent content. The voltage required is reduced if the web is given a prior electrostatic charge by passing it over a burlap apron. Alternatively, an A.C. voltage of 800-1500 at 1-1000 kc/s. may be superimposed on the low-frequency A.C. voltage of 900-2000 at 25-500 cycles. For treating separate flat articles of organic plastic material, one of the electrodes may be an endless belt having a conducting core or surface. The non-treating surface may be spaced 1/8 -\ba1/4 inch from the web, in which case it is a conducting surface, the D.C. voltage applied is in the neighbourhood of gaseous discharge point in the electrode zone, and the A.C. voltage alternately establishes and extinguishes an electrical gaseous discharge between the electrodes. The drum 16 may be replaced by a number of small rollers, which may each be earthed, or alternatively may be connected by phase delay element, only one then being earthed.

The apparatus described provides a direct-reading instrument for the measurement of the spreading coefficient of a liquid on a solid surface. The determination is based on the measurement of the maximum height of a sessile drop of the liquid-solid system.

Wettability studies of aqueous solutionsof several series of pure, highly fluorinated, aliphatic acids and salts were carried out on two low-energy organic solids, polyethylene and Teflon. As anticipated, the fluorinated compounds were able to depress the surface tension of water below the critical surface tension (γ_c) of Teflon, and were therefore capable of completely wetting it. In contrast, conventional hydrocarbon wetting agents do not depress the surface tension of water to this extent. Whenever possible, wettability curves were obtained for each...

Previous studies have shown that small amounts of amphipathic (i.e., polar non-polar) molecules, in particular oleamide, cause a marked lowering of the coefficient of friction between thin films of polyethylene. In this paper the surface chemical properties of the aging film and the nascent film (i.e., during the flat film extrusion process) have been studied. The wettability (contact angle) and friction of the aging film at room temperature show that the friction is reduced only when sufficient additive is present to form a weakly held monomolecular layer. This monolayer is formed by almost complete exudation of the additive from the bulk. Contact angle measurements show that the molecules become oriented on the surface such that the polar groups are in contact with the polyethylene and the hydrocarbon chains project into the air. The stability of the monolayer to water condensation is much improved by flame treatment of the film immediately on extrusion. On preparing film by extrusion through a water-quenching bath it has been found that water adheres more easily to films containing oleamide. By suitable adjustments, the water bath was modified to form a “dynamic” Langmuir trough. Contact angle measurements on the emerging film and studies on the effect of sweeping the water surface around the emerging film show that the surface tension of the water is lowered by the amphipathic molecule being quantitatively stripped off the film as it emerges through the water/air interface. From surface pressure/area relationships, the surface concentrations of the spreading molecules are calculated. It is found that there is a surface concentration about one hundred times greater than would be expected from a uniform distribution of the additive throughout the polymer. This large surface excess is approximately proportional to the bulk concentration and implies a pronounced adsorption at the polymer melt/metal or polymer melt/air interface.

This invention relates principally to apparatus for treating plastic sheet materials, especially polyethylene sheets or film to improve the anchorage or adherence More particularly the invention is concerned with an apparatus which constitutes an improvement over that disclosed and claimed in copending application Serial No. 359,35l, filed June 3, 1953 and assigned to the same assignee as is this invention.

A theory is proposed by which the surface free energy of certain solids can be estimated from the contact angles ofliquids on them. The method is verified using contact angle and surface tension data from the literature, for benzene and a-methylnaphthalene on liquid and solid fractions of a fluorinated lubricating oil. The method is then applied to data on the contact angles of various liquids on Teflon and on an octadecylamine monolayer. The surface tensions of these solids are estimated to be, respectively, about 28 and 30 ergs/cm…

Earlier systematic studies of the angle of contact (9) exhibited by drops of liquid on plane, solid surfaces of low surface energy have revealed a regular linear variation in cos 9 with the surface tension (ylv) of a large variety of liquids; this led to the concept of the critical surface tension of spreading (yc) and its use in characterizing the wettability of organic solids and of high energy surfaces coated with adsorbed organic films. Effects of the nature and packing of the atoms or organic radicals in the organic surface in determining the wetting of the solid are summarized. Simple and useful correlations have been found between „and the constitution of low energy solid surfaces. It is concluded that usually atoms more than a few atom diameters below the surface have no influence on wetting. The “retraction method” of preparing monomolecular films from solutions on solids is shown to be a direct consequence of the above constitutive law of wetting. The same analysis can be applied to a pure liquid also, and it results in the explanation of the behavior of the autophobic liquids at room temperature and of the process of depositing a monolayer on a solid by retraction from the melt over a range of temperatures.

The maximum bubble pressure method for the determination of surface tension has been modified for use with thermally unstable, viscous, opaque polymers at high temperatures. A value of 35.1 dynes/cm. was obtained for nylon 66 at 285°C. The order of this value and those for other polymers has been compared with the values for simpler compounds. Further evidence for the persistence of association between polyamide molecules in the molten state is presented.