Ind. Eng. Chem. Prod. R8S. Dev. 1960, 19, 622-624
622
U = superficial air velocity, ft/s
is given for completion of drying of 97.3 and 99.2%. All variations are from the previously stated base case. It is seen that this agreement is generally good for these cases. Acknowledgment The author is indebted to L. C. Cha, L. R. Darbee, and C. A. Gray of FMC Corporation for their comments and suggestions.
a = thermal diffusivity, ft2/h e
= porosity
[ = reduced radial position in the dehydrated shell, r / R w
tB= reduced radius of the hydrated core, rB/Rw 0 = time, h OD = drying time, h I.( = viscosity, lb/ft s p = density, lb/ft3 r = pore tortuosity
Nomenclature c = water concentration, mol/ft3 c = heat capacity, Btu/lb O F = diameter of particle, f t 2l = diffusion coefficient, ft2/h g = number of moles of water in the hydrate molecule AH = heat of dehydration, Btu/lb-mol of hydrate H 2 0 h = heat transfer coefficient, Btu/ft2 O F h k = thermal conductivity, Btu/ft h O F kG = mass transfer coefficient, lb-mol of H20/h ft2 atm L e = Lewis number M = molecular weight Nu = Nusselt number NuEX= external Nusselt number, h D / k A N U I N= internal Nusselt number, hRw/kDH P B M = log mean partial pressures of stagnant species, atm p = partial pressure of water vapor, atm Pt = total pressure, atm Pr = Prandtl number Q = heat rate, Btu/h r = radial position in monohydrate shell, f t R = gas constant R , = outside radius of particle, f t Re = Reynolds number Sc = Schmidt number S h I N= Sherwood number, kJITR,/a)IN T = temperature, O F or OR
Subscripts A = air DH = dehydrated EX = external (fluid) conditions f = fluid H = hydrate IN = internal (particle) conditions s = surface of the hydrate spherical core w = exterior dehydrated material surface
d
Superscript * = denotes variable is assigned a constant value
Literature Cited Froessiing, N. Oerlend Bekt W p h y s . 1938, 52, 170. Kunii, D.; Levenspiel, 0. “Fluidization Engineering”, Wiiey: New York, 1969. Levenspiel. 0. “Chemical Reactlon Engineering”, 2nd ed.; Wlley: New York, 1972. Rank, W. E.;Marshall, W. R., Jr. Chem. Eng. hog. 1952. 48(4), 173. Ruether, J. A. Can. J. Chem. Eng. 1979, 57, 242. Satterfleld, C. N.; Sherwood, T. K. “The Role of Diffusion in Catalysis”, AddC son-Wesley: Reading, Mass., 1963. Shen, J.; Smith, J. M. Id. Eng. Chem. Fundam. 1965, 4 , 293. Taylor, T. L.; Taylor, G. G. Ind. Eng. Chem. 1935, 27, 672. Treybal, R. E. “MassTransfer Operations”, 2nd ed.; McGrawHiii: New York, 1968.
Receiued for review November 26, 1979 Accepted June 16,1980
Surface Properties of Plasma Polymers from Diethylaminotrimethylsilane and Hexamethyldisilazane Toshlhlro Hlrotsu Research Institute for Po&mers and Textiles, Tsukuba, Ibaraki 305, Japan
Plasma polymers of some silyl amines were produced and investigated on their surface properties. The polymers formed from diethylaminotrimethylsilane and hexamethyldisilazane were found to be as hydrophobic as those of tetramethylsihne. The hydrophobicity can be attributed to the loss of nitrogen (which will form the more hydrophilic functional groups in other nitrogen monomers) in the course of polymerization. Orientational behavior of some liquid crystals was investigated on these polymer layers and it was found that the layers gave orientation of the biphenyl-type liquid crystal with good heat resistance.
Ltd. The polymer is hydrophobic, but hydrophilicity is sometimes preferable. Some attempts have been made for effecting this property on the surface by graft polymerization of the monomelg with hydrophilic functional groups under irradiation of y-rays (Ratner et al., 1978), and ultraviolet light (Tazuke and Kimura, 1978). One of the unique methods is the plasma surface modification by ammonia and nitrogen (Hoollahan et al., 1969). Nitrogen functional groups such as amines which are more hydrophilic can be incorporated onto the surfaces by exposure to plasmas.
Introduction Silyl compounds are the easily polymerizable monomers in glow discharges to give highly cross-linked products. The reactivity is attributed mainly to the Si-Si couplings. The products whose hydrophobicity is one of the interesting characteristics have been investigated for practical purposes, i.e., for medical use, anti-fogging, soil repellant, and so on. Nowadays, the silyl polymers or the silicon rubbers are popular and valuable in many fields. One of the best known plastics is Silastic available from Dow Corning Co. 0196-4321/80/ 1219-0622$01 .OO/O
0
1980 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 4, 1980 623 150 1
Table I
monomer (MW) DATMS (145) HMDSZ (161) "MS (88)
flow rate, crn3(STP)/min
dep rate, mg/(cm2 x min) ~
11.5 11.2 10.0
~~
1.75 x 10-3 1.80 x 10-3 1.10 x 10-3
I t has been well known that silicon and nitrogen give quite opposite effects on the surface properties with regard to wettability, when they participate in plasma polymerization. From this point of view, the surface properties of plasma polymers formed from silyl amines which contain both silicon and nitrogen should be interesting. In this study, the surface properties of plasma polymers of diethylaminotrimethylsilane and hexamethyldisilazane were investigated as to their wettability, and their thin coating layers were examined for the orientational properties of some liquid crystals.
Experimental Section Materials. The silyl compounds used in this study were the following: diethylaminotrimethylsilane(DATMS) and hexamethyldisilazane (HMDSZ) obtained from Tokyo Chemical industry Co. Ltd., and tetramethylsilane (TMS) from Merck Co., Ltd. Although there are some other silyl amines available, the two are suitable for plasma reactions because of their vapor pressure. Other silyl amines with higher molecular weights are less easily evaporated and do not sustain a glow (dischargefor polymerization. The monomers were used as supplied but were fully degassed before polymerization. The liquid crystals used were the mixture types of biphenyls and cyclohexyl esters, respectively, obtained from Nissei Electronics Co. Ltd. Procedure of Plasma Polymerization. Plasma polymerization was carried out using glow discharges generated by a radiofrequency of 13.56 MHz employing an inductive coupling method. The reaction apparatus used in this study is simila,r in design to the one previously reported (Yasuda and Hirotsu, 1978), although the exact polymerization conditions such as the flow rates vs. pressure relations and the efficiency of the power input are slightly different. In this study, the pla3ma polymerization conditions were torr and a power of 50 selected as a pressure of 60 X W. These operating parameters produced tight polymeric films which do not crack or powder. Deposition rates which are often shown to represent growth rates of the po1,ymerswere obtained on aluminum foil (2.0 cm X 2.5 cm) by weighing the amount of products per minute. Typical results are shown in Table I. Deposition rates were also obtained on glass slides which were used for contact angle measurements. The rates are nearly equal. Results and Discussion Contact Angle of Water. Wettability is one of the practical and valuable properties representing the surface characteristics of materials. In order to evaluate the properties of the resulting polymers, contact angles of water were obtained with a shadowgraph from Nikon Co. Ltd., Tokyo. The water was distilled and purified before measurements. As mentioned previously, the polymeric films were formed on glass slides, and the approximate thickness was given by changing the duration of polymerization while taking the deposition rates into account. In order to see the effect of film thickness on the wettability characteristics, the thickness dependence of the contact angle was investigated. As shown in Figure 1, the contact angle increased sharply with increasing film
thickness from that of the original glass slide (about 2 5 O ) and reached a limiting value of approximate1 50 A thickness. Therefore, it can be stated that 50 is the effective thickness in developing hydrophobicity. In addition, it is also interesting to note that the thickness dependence and the limiting contact angles of the silyl amine plasma polymers are quite similar to that of TMS. Plasma polymers prepared from nitrogen-containing hydrocarbons usually exhibit a higher degree of hydrophilicity, for example for the polymers of vinyl pyridine and allyl amine, which were often used for reverse osmosis membranes (Yasuda and Lamaze, 1973; Perric et al., 1977). In these cases, nitrogen functional groups with hydrophilic properties which are formed by rearrangements in the polymeric films seem to play important roles in the characteristics. However, in the silyl amines, the effects are much less pronounced and the properties are similar to those of TMS. The hydrophobic character can be attributed to the lack of nitrogen-functional groups such as amines and amides which give hydrophilicity. These groups are considered to be hardly formed in the course of polymerization because of the liability to fragmentation of nitrogen in plasma. In contrast to this, silicon remains in large amounts in such forms as Si< and Si-Si bondings, which principally affect the hydrophobicity of these polymers. The surface phenomena are explained spectroscopically on ATR-IR and ESCA data. For example, the bands of N-H stretching and vending vibrations respectively at around 3400 and 1500 cm-l in the HMDSZ monomer have almost disappeared in the IR spectra of the polymers, and the elemental analyses performed by the peak intensities of ESCA suggested that the decrease of the elements is on the order of N, C, and Si, i.e., silicon remains most in these elements (Hirotsu, 1979). Alignment of Liquid Crystals. One of the advantages of glow discharge polymerization is that the products are very thin, pin-hole free, and often transparent films. Because of these properties, they may be useful for electrooptical devices. Liquid crystal orientation induced by the plasma polymeric surfaces has been investigated, and some good results have been obtained in silyl and fluoro plasma polymers (Dubois et al., 1976; Spoke1 and Gibson, 1977). Low surface energy or hydrophobicity of the coating layers seems to be preferable for these orientations. In these silyl amine plasma polymers, the orientating properties of liquid crystals were also examined. The polymer layers were formed about 500 A in thickness on the thin indium-tin oxide coating layers on glass plates. Orientating of liquid crystals was investigated between the two layers spaced 8 pm apart. In the two types of liquid crystals, the biphenyl type gave good results of the perpendicular orientation on both DATMS and HMDSZ
1
Ind. Eng. Chem. Prod. Res. Dev. 1980, 79, 624-628
624
Table 11. The Orientational Behavior of the Biphenyl-Qpe Liquid Crystal on the Plasma Polymer Layers Prepared from DATMS and HMDSZ in the Temperature Range between 400 and 500 "C plasma polymer from DATMS HMDSZ
temperature, C
400 +a
+
-
450
490
+ +
+
-b
-
-
a Represents perpendicular orientation. random orientation.
500
Represents
latter, are fairly good for heat resistance. Both plasma polymers were observed to decrease slightly in weight in the thermogravimetric analyses in the temperature range investigated for liquid crystal orientation. For example, in the DATMS plasma polymers, the decrease in weight starts at about 420 "C and the relative amount of decrease is 3.3% at 490 "C and 4.1% at 500 "C. Therefore, the breakdown of the orientation is likely to be due to a kind of crack of the polymer layers caused by the partial degradation and the stress at that temperature.
Literature Cited polymers, but the cyclohexyl ester type did not reveal the orientation and remained random on both polymers. Because the heat resistant properties are important for electrooptical devices, the orientation behavior was investigated in the range of about 400 to 500 "C, and the heat resistance was examined. Typical results of the orientation of the biphenyl-type liquid crystal are shown in Table 11. Although the orientation on the HMDSZ plasma polymers was broken at 490 "C, it was still good for the coating layers from DATMS plasma polymers at that temperature. These results suggest that the polymers, especially the
Dubols, J. C.; Gazard, M.; a n n , A. J . Appl. fhys. 1978, 47, 1270. Hlrotsu, T. J . Appl. folym. Sci. 1979, 24, 1957. Hollahan, J. R.; Stafford, P. B.; Falb, R. D.; Payne, S. T. J . Appl. folym. Scl. 1989, 73,807. Perrlc, D.; Bell, A. T.; Shen, M. J . Appl. folym. Scl. 1977, 27, 2661. Ratner, B. D.; Weathersby, P. K.; Hoffman, A. S.; Keliy, M. A,; Scharpen, L. H. J . Appl. Po&m. Sci. 1978, 22, 643. Sprokel, G. J.; Gibson, R. M. J . Electrochem. SOC.1977, 724, 557. Tazuke, S.; Kimura, H. Makroml. Chem. 1969, 779, 2603. Yasuda, H.; Hlrotsu, T. J . folym. Scl., folym. Chem. Ed. 1978, 76, 229. Yasuda, H.; Lamaze, C. E. J . Appi. folym. Sci. 1973, 77, 201.
Received for review January 21, 1980 Accepted July 21, 1980
Physical Stability Testing of Ion-Exchange Resins. 1. A New Test Method M. Skrlba' and W. M. Alvlno Westinghouse Research and Development Center, Pittsburgh, Pennsylvania 75235
R. Kunln Yardley, Pennsylvania 79067
In operating a continuous countercurrent ion-exchange system, unacceptably high resin breakage was encountered. A method was developed that can test resins under simulated process conditions for mechanical and osmotic shock resistance either separately or in combination. This method has been shown to be able to predict plant behavior and to differentiate between good and bad resins.
Introduction Traditionally, development of bead type ion-exchange resins has been along the lines of enhancement of the chemical performance properties of the resins. Some of these developments have included increased exchange capacity, higher selectivity coefficients, increased kinetics of loading and stripping, and greater resistance to fouling. On the other hand, although the physical stability of resins has received some attention (see Kunin, 1972; Golden and Irving, 1972; Ball and Ray, 1976), its measurement to predict resin attrition has not been of paramount importance because ion-exchange systems were generally confined to low flow, fixed bed operations in which the resin beads are treated relatively gently from a physical standpoint. That this condition exists is apparent from the multitude of chemical tests available and the paucity of physical 0196-4321/80/ 1219-0624$01.OO/O
tests which have been published. Contrast the list of tests shown in Table I. It is quite apparent that the chemical nature of the resins has been of primary concern and it is right that it should be since resins are functional chemical systems. Westinghouse had embarked on a program that was aimed at the recovery of low grade mineral values from acid leach liquors containing a low concentration of this mineral. The economics of this operation dictated the use of a deep bed high flow rate system. This requirement led to the selection of a continuous countercurrent contactor as the choice for the plant process. The initial resin fill, recommended by the contractor supplier, was a strong base anionic gel type resin commonly used successfully in other mineral recovery operations in this industry. In the first attempt at system startup, the resin deteriorated badly at operating conditions far below design 0 1980 American Chemical Society
