Harada, Kensuke

Sakai, Toru

English

Kyoto University Research Information Repository

RIGHT:URL:CITATION:AUTHOR(S):ISSUE DATE:TITLE:The Effect of Electric Field upon theStructure of Thin Films of SomeDipolar Long-chain MoleculesHarada, Kensuke; Sakai, ToruHarada, Kensuke ...[et al]. The Effect of Electric Field upon the Structure of Thin Films ofSome Dipolar Long-chain Molecules. Memoirs of the College of Science, University ofKyoto. Series A 1958, 28(4): 283-2921958-05http://hdl.handle.net/2433/257405Memoirs of the College of Science, University ef Kyoto, Series A,Vol. XXVIII, No. 4, Article 1, 1958.        THE EFFECT OF ELECTRIC FIELD UPON THE             STRUCTURE OF THIN FILMS OF SOME               DIPOLAR LONG-CHAIN MOLECULES                                     BY                    Kensuke HARADA and T6ru SAKAI                          (Received Nove2nber 29, 1957)                                 ABSTRACT        Tke effect of static electric field applied to thin films of stearic acid and ectadecyl    alcohol upon the structure of the films was investigated by the method of electron    diffraction. The electric field was applied when the films were formed by evaporation. of solution or by rnelting. In the case of stearic acid, some definite relation between    the orientation of the crystals in the film and the direction of the applied field was    found. While, in the case of ectadeÅëyl alcohol, the applied field affected the lattice    dimension of the crystals.1. Introductien    The investigation of crysÅíal structure of long-chain compouRd was initiated byA. Mtt}ier (1) in his X-ray diffraction analysis of a paraMn. Later, C. A. Murison (2),J.J. Trillat and H. Motz (3), C.H. MacGil!avry (4) and others examined, by themethod of e!ectroft diffraction, the molecular arrangement in thin films of some long-chain compounds formed on solid substrates. The structure of built-ttp films aRdpolymorphism of these substaRces were also investigated by L. H. Germer and K. H.Storks (5) and P. A. Thiessen and T. SchooR (8) respectively. Temperature depend-ence of the molecular structure of such films were observed by K. Tanaka (6). Y.Kakiuchi (7) and M. Ida <9) have examined the crystal arrangement in the specimenof some long-chain compounds prepared by cooliRg from molten state under the pre-sence of strong electric field. In Åíhe following, some resuits of observation on theeffect of electric field applied ttpon the molecular arrangement in the films of stearicacid and octadecyi alcohol.2. Experirnental method    As the specimen holder, we prepared a narrow paral!el slit of O.2-vO.3mm widthand 8mrn length with two metal p!ates, and covered it with thin film of Formbar.Static e!ectric field of about 9kV/cm was applied between these two metal plates.Various test specimens were prepared by dropping a drop of freshly prepared benzene284 K. HARADA and T. SAKAIsolution of the compound on the holder and then ietting it to evaporate, or by melt-ing asmall piece of the compound on the holder. The specimens thus prepared wereinvestigated by the Åíransmission rnethod of electron diffraction. The applied voltageto the electron-gun was about 40 kV.3. Resuks and discussion  Case of stearic aeid    (a) Thin films prepared by evaPoration of benaene solution    Piffraction patterns of thin films prepared from benzene solution in the absenceof aR electric field are shown in Plates l and 2, while those of fi!rns prepared underthe presence of an eiectric field are shown in P!ates 3, 4 and 5, as examp}es. Thinfilms prepared in Åíhe absence of an electric field have different structures accordingto some condltion of preparation. In most cases the film consists of two crystalgroups: one with their c-axes inc}ined to the surface of the film, while iR the otherthe said axes are nearly paralie! to the same surface.    It is known that there are various types of structure of the crystal. in the pre-sent case the crysta!s in the film seemed to be somewhat deformed from the known                                                                ooe2-type whose monoclinic unit cell has the dimensions of a=9.12A, b==4.94A andB=56011'. The observed lattice spacings for various thin films examined are tabulatedin Table 1 in the columns 1-v4. The vaiues in the sixth column are the spacings                                         o                                Table l. (A-unit)14.35 s4.17 s4.13 ss3.35m3.27m3.17m2.48 s2.38m2.33m2.16w2.05m1.59m1.44w1.28w24.56 s4.35 s4.12 ss2.49 s2.375w2.17w2.06m1.63w34.46 s4.35m4.12 ss3.75m3.22w2.48 s2.06rn44.30 s4.12 ss3.31m3.23m2.47 s2.38w2.34m2.16w' 2.04ml.61w54.15 s3.78 s2.47wE2-type4.57(112)4.36<111)4.17(201)4.12(110)3.79(200)3.33(O19)3.25(114)3.15(201)2.47(e20)2.38(Ol, 15)2.34(120)2.18(222)2.06(220)1.44(520)124(43e)      STRUCTURE OF THIN FILMS OF SOME DIPOLAR LONG-CHAIN MOLECULES 285calculated for e,-type. Some of these thin films show re}atively simple diffractionpatterns as shown in Plate 2. The observed spacings for such a film are shown inthe fifth column. This crystal is considered as the elementary type, i.e. the crysta!                             eohaving the unit cell of a=:4.94A, b--7.58A and3=:900 a3sumed by T. Schoon. In eachcase, the crystals in the thin film cannot be considered as to be composed of crystalsof a single type.    When thin films of stearic acld are prepared under the presence of an electricfield, the small crystals in the film have a general tendency of definite orientation inwhich the b-axis or the a-axis of the crystal is arranged perpendicularly to theapplied eiectric field. The values of the lattice spacings observed in the cases of                                         o                                Table 2. (A-unit)13.86 s4.16 s2.47rn2.05w1.61w23.87m3.67m4.16 s4,12 s2.96 rn2.48 s  34.35m4.07m3.87m3.70rn4.16 s4.12 s2.97m2.47m2.33w2.13w1.60wMtt11er             Germer3.69(020)4.12(110)2.96(220)2.48(200)2.11(220)1.61(310)3.88(200)4.18(110)2.48(020)2.09(220)l.62(130)Plates 3, 4 and 5 are shown in Table 2 in the columns 1, 2and 3 fespectively. Fromthe observed spacings, the crysta}s ln a film which has comparatively regular arrange-ment of crystals as shown in ?}ate 3 are considered to be similar to those found byGermer and Storks in a bui!t-up film of stearic acid, which was investigated by themin detail. The values in the fourth and the fifth columRs in Table 2 are respectively                                            ooethe calculated spacings for the values a==5.546A, b=7.38A, c==48.84A and B==63038',which were given to the unit cell of a single crystal of stearic acid by Mifiler as theresult of his X-ray examinatien, and those calcu!ated for the unit cell of the crystal                                                                              oin the buiit-up filrn, whose dimensions were given by Germer ac nd qvtorks as a=r8.27A,       oob==4.96A, c=49.0A and B=-in63038'. As can be seeR in Tab}e 2, a lattice plane havinga spacing 3.87A is found in all diffraction patterns examined and the plane is per-                                                           ependicular to the applied electric field. And a lattice p!ane 3.7A also appears perpen-                                                   eodicular!y to the fieid. Occasionally, lattice planes 4.e5A and 4.35A appeared.    From these observations it can be seen that the crystals in a thin film preparedin an eiectric fie!d have tendencies to lie in such a manner that their b-axes are286 K. HARADA and T. SAKAIperpendicular to the applied field when the crystals are of Muller type, while theira-axes are perpendicular to the field when the crystals are of Germer type. Frequently,these two types of crystals appeared in a film. In every case, the axes of the long-chain molecuies have a tendency to arrange themselves perpendicu!arly to the appliedfield.    (b) Thin films PrePared by melting    Plates 6 afid 7 show diffraction patterns of specimens prepared by heating a filmof stearic acid on the holder up to about 850C in air and by succesive cooling-down                    . to room temperature without an applied          Tab}e 3, (A-unit) ,. .                                electric                              specimens show rmgThese   f eld.      Plate6 Plate7 patterns as shown in Plate6 and rarely 7.86w singie crystai patterns as shown iR P!ate 7. 4•83ww The lattice spacings observed ilt Piates6 4.50m 4•58S (SPOt) and7are shown in Table 3. The spacingS 4.42s 4-42W (ring) obtained from piate6 coincide well With                           (spot)4.32s (diffuse)       4.38 s 4.12m 4.12w (ring) thOSe obtained from Piate 7. But, both of                     4.11s (spot) these spacings do not coin"cide with the 3.93w 3.95w (spot) spacings of crystals prepared by evaporation 3.84s 3•83S (spot) of benzene solution in the absence of applied                     3•81W (ring) field. These films consist of miXtUreS Of 3.77s (diffuse) 3.79w (ring)                                       two kinds of crystals with slight!y different 3.67s 3.65s (spot) 2.48w 2.s6s (spot) cross-sections. In the case of Plate 7, the                                    rm c-axes of both crystals are parailel to each                                               other and their (iOO) and (OIO)                                               planes are also parailel to each                                               other respectively. The cross-section                                        .<c of one kind of crystals is shown in                                        ;il Fig. 1. Ring pattern in Plate6                                        KF shows that the film has fibrous   83ol••e------- 7.34A-                   Fig. 1specimens prepared under an applied electricis considered that the crystals grown ttnderin fibrous structure. As can be seen in Fig.the pattern consists of spots on parallel lines     structures of two kinds of crystal     appeared in Plate7 and each of     them has its c-axis as fiber axis.         A pattern such as shown in     Plate 8 is always obtained for   field of about 9kV/cm. From this, itan electric fie}d always arrange themse}ves2, the schematic representation of Plate 8, with equal distances of two groups (K      STRUCTURE OF THIN FILMS OF SOME DIPOLAR LONG-CffAIN MOLECULES 287                                                                       '                                      Å~ S?3                                                       62-type                                               yz                               .                    X ;(2m XXx, rvx                                                   /X.v        ' i(201) '(111) (021) -v,                                                                       E  X B(10s03). A>(o16) x.o.                                                   o                                                K`ilSS )V•t                                                .                                     '(2-Ot) ;{Y<;-•'i                         .(iIl)                                              '                                                o                            I(2il) beg%> $N                                                            E: Electric field                               e $"                                 $N                        'S5Li                                    Fig. 2and L). Each spot on the intersection of these lines is split up into several spots inthe direction of appiied electric fie!d. In Fig. 2, the spacings corresponding to the!engths of OA and OB are 4.96A and 7.35A respectively. And the aRg}e betweenK-lines and L-lines is about 830. Therefore, the film contalns mostiy the crystals ofthe same dimensioRs as that shown in Fig. 1 and except them there are a few kindsof crystals with s}ightiy different dimensions as can be seeR from the splitting-up ofthe spots. The orientatlons of the microcrystals of these kinds are not parallel toeach other but dlstrlbuted in the angular range of about 100. But there could not befound any definite relation betweeR the orientation of the crystal around its c-axisand the direction of the applied electric fieid excepting that the splitting-up of eachspot always occurred in the direction of tke applied field.288 KHARADA and T. SAKAI  Case of oetadecyl aleohol    (a) Thin films PrePared by evaPoration of benzene solution    Observed spacings for various thin films prepared by evaporation of benzenesolution are shown in Tacble 4. Mean values of observed (100) and (OIO) spacingsfor six films prepared under no applied electric field are shown in the second row.In this case, the differences of the spacings from the mean values were very smali                                         e                                Table 4. (A-unit)Applied voltage    V/cmo(100) (OIO)7.44A-O.04 E 5.05-FO,02               9000               9000               6000               6eoofor six specimens. On theunder an applied eiectrictable and ali of theseprepared without an applied    When these filmsature of about 4eOC for                 ethe values of 7.26A andwhen the films preparedminutes, the corresponding    o5.03A respectively. Fromrhombic system with theoctadecyl alcohoi in suchthin filmsfieid.    (b) Thin films         melting    Piates 10 and 11 areof diffraction pattems ofprepared by meltingwith an applied electric fieldtively. Figs. 3and 4atic representations of theseIn each case, the film"r .217.26li- O.04Z367.44I4.934.95+O.045.025.04Number ofspeclmens63                 other hand, these lattice spacings of the films prepared              field took severai different va!ues as shown in the same          spacings are smaller than the corresponding ones of the fiims                fie q.          prepared under an applied field are heated in air at an temper-           several minutes, the spacings of (100) and (101) change from                 aoo           4.95A to 7.34A and 5.03A respectively. In the same rnanner,             ttnder no applied fieid are heated at about 500C for several                            oo o               spacings 7.44A and 5.03A turn into the values 7.34A and              these facts it can be considered that the crystai of ortho-                                   oo                dimensions a=7.34A and b=:5.03A is a stable form of             films. Plate 9 is an example of the diffraction patterns ofprepared under an electric                                             3.75 (200)                                             d'r-                                             391(200)           Prepared by                                    /-4.23(1 10j)                                                       x              examp!es                        g i-;            thin films                                                                2.56                                    X 1 ,(02Q.    without and                 respec-          are the schem- .                                             -.di               plat s.              contains Fig• 3STRUCTURE OFTHIN FILMS OF SOMEDIPOLARLONG-CHAiN MOLECULES289{                   5.06(020)w          /393(200)w  '- E-4.25(llO)w           s--4.44(200)S /4.o3(2eo)s/ll- 4. 16(1 10>w Nxx  K4.28(llO)s                              `                             2.43                            (o2e)s                                  ,NXN /1/x-Fig. 4-         oTable 5. (A-unit)severai crystal forms slightlydifferent from each other. Themean lattice spacings observedfor many specimens are tabulatedin Table 5. These spaeings aredifferent from those observed inthe case of films prepared byevaporation. Plate 12 is arefiec-tion pattern of a film and showsthat all molecular axes in thefilm are nearly perpendicular tothe surface of the substrate.    As can be seen from Table 5,Applied voltage    V/cmo50009000(IOO) (OIO)7.5 G-O.17.92+e.227.3 +O.047.48--Fe.e47.72--l-O.048.12A-O.047.3 ---O.047.9 +O.e48.2 -l-O.068.94"O.065.1 +O.04   1!7oo.ts,055. •l4.87N-O,02   ))5.064.87-l-O.02(110)4,22-l-O.06   1!4.16-i-O.03   lr   1)4.33-FO.024.05-FO.034.16--O.024.26•---O.034.26rf-O.03there are many kinds of crystal forms in the case of applied field and they havelarger spaclngs than those formed under no app!ied field. It seems from Fig. 4 thatthe orientations of the orthorhombic crystals are such that they are forrned a singlehigh temperature hexagonal crysta} through the transition point of the compound.Though we ceuld not find any definite relation between the orientation of the crystalsin the film and the direction of the applied electric fie}d as in the case of stearicacid, the variation of the lattice dimensions seems to be caused by the applied field,since the latter affects the interaction between polar molecules of the alcohol whenthe crystal is formed.    In conclusion, the writers wish to express their sincere thanks to Prof. K. Tanakafor his kind guidance throughout the present research.o92iiil                     K. }IARADA and T. SAI<AI                         REFERENCESA. MULLER, Proc. Roy. Soc., A 120 <1928), 437.C. A. MvRisoN, Phil. Mag., 17 (1934), 201.J. J. TmLLAT and H. MoTz, Trans. Faraclay Sec., 31 (l935), 1127; Z. Krist., 91 (1935), 248.C. K. MAcGiLLAvRy, Z. Krist., 98 (1938), 407.L. H. GERMER and K. H. SToRKs, Proc. Nat. AÅëad., 23 (1937), 39e ; J Chem. Phys., 6 (1938), 280.K. TANAi<A, Memoirs Coll. Sci., Kyoto Univ., 21 (1938), 2i; 22 (1939), 377; 23 (1941), 195.Y. KAi<iucm, Sci. Pap. I. P. C. R., 40 (i943), 189.P. A. THiEsEN and T. ScHooN, Z. Phys. Chem., B 3 (1937), 216.M. IDA, J. Phys. Soc. Japan, le (1955), 318.! STRUCTUOE OF THIN FILMS OF SOMEDIPOLARLONG-C[{AINMOLECULES291PIate 1 Plate 2sPlate 3 Plate 4%L•Plate 5 PIate 6292 K. HARADA andT'. SAKAIPlate 7 Plate 8kP12te 9 Plate 10Plate 11 Plate 12

The Effect of Electric Field upon the Structure of Thin Films of Some Dipolar Long-chain Molecules

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The Effect of Electric Field upon the Structure of Thin Films of Some Dipolar Long-chain Molecules

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