0.67 and additional S gives rise t o a second liquid hlicroscopic examination of the adsorption-desor tion phase of almost pure S. The limits of miscibility of phenomena was carried out with a Bausch and t o m b microscope; photomicrographs (100 X and 450 X ) these two liquids were not investigated and so are polarizing of the various samples were taken with an Exa single lem represented as dotted lines. reflex camera with adapter. Acknowledgments.-Much of the experimental Results work was performed by Mr. William E. Robbinfi. Spectral Reflectance.-Mereuric iodide mixed Dr. J. W. Johnson showed us that silica-glass with alumina was found to show a gradual increase would stand up to these conditions. in absorbance a t 290 mp, a t the same time the absorption peak a t 576 mp decreases steadily and THE COLOR OF MERCURIC IODIDE ON finally becomes unobservable. When adsorbed on sodium fluoride the color of the mercuric iodide ALUMINA remains unchanged, the discrete absorption maxima BY HARRY GOYA,JOHKL. T.WAUGH,AND HARRY ZEITLIN a t 293 and 573 mp increasing only slightly with time, without any shift in the wave length being detectDepartment of Chemistry, University of Hawaiz, Honolulu, Hawaii able. Exposure of the mercuric iodide-alumina Received December WW, 1061 mixtures to the moist atmosphere was observed to The red, tetragonal modification of mercuric result in desorption of the iodide. This process iodide undergoes an enantiotropic transformation also was followed by reflectance measurements and to a yellow, orthorhombic form when heated above the observed spectra indicated that the changes its transition temperature of 127'. When initially occurring were essentially the reverse of the adprecipitated from solution or when formed from sorption process. the vapor phase, the yellow modification reverts Microscopic Studies.-Red mercuric iodide is spontaneously to the red, normally stable form. soluble in acetone to form a colorless ~olut~ion. Recently, a red to yellow transition has been ob- Crystallization from this solution, and the subseserved to take place, apparently similar to the quent transformation of the red to the yellow moditransformation which takes place on heating above fications on heating and the reverse conversion the transition temperature, when mercuric iodide from the yellow to the red forms on cooling were is adsorbed on alumina a t normal atmospheric carefully observed a t various magnifications. Simitemperatures.l However, in the adsorbed state lar observations were made of the yellow material under anhydrous conditions, the yellow species on desorption from alumina and its subsequent remains as such indefinitely. I n a preliminary reversion to the red variety. This latter effect communication, this phenomenon was attributed could be accomplished either mechanically, by to a polymorphic conversion, rather than to any suitable prodding with a needle, or by moistening change in particle size or to ionization by polariza- the yellow material adsorbed on alumina; in either t i ~ n . ~It, now ~ has been established, by means of case, the yellow material is initially detached from X-ray powder, diffraction studies, reflectance anal- the alumina as yellow crystals, which then transysis, and microscopic examination that the yellow form to the red variety, in a manner very similar to material, which is stable when adsorbed on alumina the initial precipitation of mercuric iodide from a t atmospheric temperatures, is the same species solution as the. yellow form. The homogeneous which results on heating mercuric iodide above nature and the stability of the yellow iodide when 127'. adsorbed on alumina is quite remarkable. X-Ray Diffraction Data.-Powder photographs Experimental Reagents.-Woelm alumina, grade 1 activity, ground t o of the red, tetragonal mercuric iodide showed narless than 200 mesh; C.P. grade sodium fluoride, less than row, well-defined diffraction maxima, while those 140 mesh; reagent grade mercuric iodide, less than 200 mesh; of alumina and of mercuric iodide adsorbed on all mesh sizes refer to U.S. standard screens. The alumina and sodium fluoride were dried for 48 hr. a t 115" prior t o alumina displayed broader, more diffuse maxima. use and desiccated until required. Samples containing 8% The relative intensities and the observed interby weight of mercuric iodide adsorbed on alumina were planar spacing values as obtained from the powder used. photographs are shown in Table I. The spacings Apparatus and Procedure. The powdered samples were packed into lithium borate glass capillaries of 0.5 mm. di- for the mercuric iodide-alumina mixture are those ameter and 0.01 mm. wall thickness and mounted in a 114.59 observed after subtracting the spacings which mm. diameter Straumanis-VCiilson camera, to record their correspond to those due to alumina. The interX-ray powder diffraction patterns, using Cu Ka: radiation. planar spacings corresponding to the strongest arcs The diffuse reflection spectra of the solid mixtures were measured with st Beckman DK-2 automatic recording spec- on the red mercuric iodide photographs are not trophotometer, equipped with a reflectance attachment; observed for the yellow mixture and those corabsorbance as a function of wave length was examined. responding to the medium and weak arcs are disConcentrations used were 200 mg. of adsorbate mixed with similar. It was not possible to obtain a powder 10 g. of adsorbent. The samples were mixed, mechanically agitated for 6 to 9 min., and poured into 6-ml. cylindrical, photograph of the pure, yellow form of mercuric quartz cells of 1-cm. light path, which were fitted with iodide. However, from the unit cell dimensions of ground glass stoppers. The reflection spectra were measured the yellow form reported in the l i t e r a t ~ r e ,inter~,~ a t varying intervals of up t o 45 days, after initial mixing. planar spacings were calculated for a small field of indices hlcl with the results shown in the last column (1) H. Goya and H. Zeitlin. Nature, 18, 1941 (1959). ( 2 ) E. U'eitz and F. Schmidt, BET.Deut. Chem. Ces., l B , 2099 of the table. [
1939). 13) G . Kortunr, J. T'iipel and W. Braun. Angew. Chem., 21, 651
(1936).
(4)
W. S. Gorsky, Ph&k Z . Sowjetmion, 6 , 367 (1934).
( 5 ) €1. .J. \'errreel and J. M. Bijvoet, 2. K r i s t . , 7 7 , 122 (1931).
dobad
(Aa) intensityo (1.) md 7.14 s 7.31 13.93 \v 4.70 6.46 9.92 4.38 6.63 4.43 W 8.25 3.12 1%. .vwd 4.45 3.87 md 3.82 7.05 2.88 3.33 m 3.74 6.02 2.69 w S 3.54 3.51 4.09 m S 2.47 3.44 d 3.41 3.53 2.33 m m 2.85 2.96 2.86 md 2.27 m 1.96 2.73 md w m 2.15 1.71 2.50 d 2.08 W vw 2.17 1.61 vvw vsd 6 2.01 2.09 d 1.44 vvw w 1.93 2.03 vuTd 0.998 vw m 1.87 1.92 md 0.811 VW 1.56 w wd 0.796 1.85 1.48 m 1.75 0.772 W vsd W 1.41 1.64 d 1.37 vv 1.54 wd 1.14 w 1.53 n-d 1.01 JV 1.49 m d 0.997 1.46 W 0.890 vwd 1.43 0.871 d VW 1.40 ni 0.865 vw 1.36 w 0.812 md 1.34 w 0.798 d 1.31 m 0.771 W 1.26 S 1.25 1.23 w 1.21 VW 1.19 w 1.15 w 1.09 w 1.08 W 1.04 VJV 1.03 vvw 0.977 w 0.963 w 0.942 w 0.922 w 0.891 w a v j very; 5, strollg; m, medium; W, wgak; d, diffuse. I,Orthorhombic unit cell with a~ = 4.674 A . ; bo = 13.76 A.; eo = 7.32 A.
Discussion On the basis of the evidence reported above, the very marked color transformation from red to yellow, when mercuric iodide is adsorbed on the active adsorbent alumina but not on sodium fluoride, ol-)viouslyis not due sinlply to a change in size. T ~ $distiIlct ,~ alld stable phases are i l l v o h d before and after adsorptio11. The bility of tlhe yellow form on alumina is quite remarkable; no trace of decompositioii could be obfor served on heating to 1300 in vacuum Several hours, whereas the yellow modification of mercuric iodide itself decomposes subststiitially under these circumstances. The spectral refleetance measurements as well as the optical and X-ray diffraction data all point to a polymorphic
as Iong as moisture is excluded, under the influence of the polarizing action of the crystal field of the alumina. The work described was supported in part by grants from the Petroleum Research Fund and the Research Corporation of Kew York (to H.Z.). WETTIXG PROPERTIES O F ACRYLIC AND METHACRYLIC POLYXERS CONTAINISG FLUORINATED SIDE CHAINS BY MARIANNE K. BERNETT AND W. A. ZISMAN U. 8.Naval Research Laboratory, Washington, D. C. Received January 6, 106R
Recent studies1s2have shown that several new types of solid polymers have lower surface energies These materials than polytetrafluoroethylene. are copolymers of tetrafluoroethylene and hexafluoropropylene (HFP) in various molar proportions and a HFP homopolymer. Depending upon the molar proportions of the polymer constituents, the critical surface tension of wetting (rc)of the respective copolymer decreases as perfluoromethyl groups in each surface replace perfluoromethylene groups and reaches its lowest value of 16.2 dynes/ CM. for poly-HFP, which in this series presents the highest proportion of perfluoromethyl groups in the surface. The present investigation reports on the mettability of two partially fluorinated polymers. In each polymer the molecular portion determining the surface energy is a linear seven or eight carbon perfluoro chain linked to the polymer backbone by a different group. If such perfluoro chains could orient vertically in close packing at the surface, they should present the lowest surface energy as yet reported for a bulk solid, comparable to the surface energy of monolayers of perfluoroalkanoic acids3 and 17-perfluo~roalkylheptadecanoicacids. Experimental The two polymers studied were pure experimental compounds generously donated for this investigation by the Commercial Chemicals Department of the Minnesota Mining and Manufacturing Company. Each was in the form of a 20% solution in xylene hexafluoride. The formulas of the respective homopolymers are CTF,,CH~OOC-C(CH,)= CHz (polymer A) and CiFi7SOnN(C3H7)-CH&H:OOC-CH= CH2 (polymer 8 ) . The films were cast by pouring measured quantities on smooth 13yrex and stainless steel surfaces, with later slow and controlled evaporating of the solvent a t room temperature in a dust-free environment and a final exposure for 24 hr. in a vacuum oveii a t 50”. The resulting smooth and specular films, which were from 6 to 9 mils thick, adhered well to t h e underlying surface. They were firm and transparent aiid could be removed in small fragments only by chipping from the substrate. Liquids for the wetting studies and the procedure for their purification have
w.
(1) h i K. Bernett and A. Zisman, J Phya. Chem., 64, 1292 (1960). (2) M.K. Bernett and W. A. Zisman, zbzd 66, 2268 (1961). (3) E. F Hare, E. G. Shafrin, and W A. Zisman, % b i d , 68, 236 I
(1g54) (4)
E. G. Shafrin and
w. A . Zisman, ibzd ,615,740 (1962).
