J . Phys. Chem. 1989, 93, 5305-5310 IV together with experimental values of translational diffusion coefficients and rotational relaxation time constants. Since the details of the hydrated structures of these -macromolecules in solution are not known, the simulated data cannot be used for an absolute test of our procedure. Nevertheless, a relative test is possible by a comparison of data for rotational and translational diffusion. As shown in Table IV, the experimental data for both modes of diffusion can be represented by one bead model each for a-chymotrypsin and for tRNAPhewhen we use our new procedure. Hydrodynamic simulations according to the other procedures may be used for a satisfactory fit of one mode of diffusion by a given bead model but not of both modes. We should add that the algorithm introduced for our new correction procedure does not lead to any noticeable increase in the computing time.
5305
In summary, we may conclude that the results of hydrodynamic simulations are improved by corrections with surface-accessible volumes, because rotational friction coefficients can be predicted at a higher accuracy and also are more consistent with translational coefficients. More experimental data for translational and rotational properties of macromolecules, referred to the same buffer conditions, would be useful as a further control of the new correction procedure. Acknowledgment. All calculations were performed at the facilities of the Gesellschaft fur wissenschaftliche Datenverarbeitung mbH, Gottingen. Models were drawn by the SHAKAL program written by E. Kellar. Registry No. Chymotrypsin, 9004-07-3.
Study on Polymerization Mechanism of Pentacosadiynoic Acid Langmuir-Blodgett Films Using High Energy Beam Irradiations Kazufumi Ogawa Semiconductor Research Center, Matsushita Electric Industrial Company, Ltd., 3- 15, Yagumo-Nakamachi, Moriguchi, Osaka, 570 Japan (Received: October 3, 1988)
Studies have been carried out on X-ray or KrF excimer laser light induced polymerization of pentacosadiynoic acid (PDA) Langmuir-Blodgett (LB) films in relation to the molecular density of the films. The polymerization sensitivity of PDA LB film was affected by the arrangement or molecular density in PDA LB film. On the low-density film (A type), the polymerization occurred by irradiation with either X-ray or excimer laser light, but on the high-density film (B type), the polymerization occurred only when the irradiation was carried out with X-ray. Decomposition of polymerized films was observed by excessive irradiation by X-ray or excimer laser light on A-type film but not on B-type films. It was revealed by the spectroscopic analysis that the polydiacetylene-type polymer was obtained on the A-type films by the X-ray or the excimer laser light irradiation and that the polymerized A-type film was decomposed at the polydiacetylene bond when the irradiation continued further. It was also shown that the polyacetylene-type polymer was obtained only when the B-type film was irradiated with X-ray.
Introduction When diacetylene derivatives are irradiated by UV light in the solid phase, they react to give polymers having conjugated double and triple bonds.'-4 Since the polymer main chain consists of a planar chain with alternating conjugated double and triple bonds that exhibit a number of interesting features with regard to optical and electronic properties such as a nonlinear optical effect or an electric conduction property, these polymers are studied widely as optical or electrofunctional m a t e r i a I ~ . ~ - ~ I t was reported that, with diacetylene derivatives that have a hydrophilic group and a hydrophobic group in a molecule, ultrathin films can be prepared by the Langmuir-Blodgett (LB) neth hod.^^^^ A characteristic of the LB method is that it is possible to prepare thin films having a desired molecular arrangement by building up monolayers under a properly selected surface pressure. Thus, in recent years, the LB method is thought to be one of the im(I) (2) (3) (4)
Wegner, G . Z . Naturforsch. 1969, B24, 824. Wegner, G . Makromol. Chem. 1972, 154, 35. Baughman, R. H . J. Appl. Phys. 1972, 43, 4362. Wegner, G.; Schermann, W. Colloid Polym. Sci. 1974, 252, 655. (5) Wilson, E. G . J. Phys. C 1975, 8, 727. (6) Bloor, D.; Ando, D. J.; Preston, F. H.; Stevens, G.C. Chem. Phys. Left. 1974, 24, 407. (7) Bloor, D.; Chance, R. R . Polydiacetylenes; Nijhoff: Boston, MA, 1985. (8) Mehring, H.; Roth, S. Elecfronic Properties of Polymers and Relafed Compounds; Springer-Verlag? Berlin, Heidelberg, 1985. (9) Blodgett, K. B. J . Am. Chem. SOC.1935, 57, 1007. (10) Blcdgett, K. B.; Langmuir, I . Phys. Reu. 1937, 51, 964.
portant means for construction of a molecular device'] having some functions at the molecular level. Many studies have been carried out on the polymerization process of LB films of diacetylene derivatives,l2-I4 and recently, it was reported that the photoreactivity of diacetylene derivatives is affected strongly by the arrangement of the diacetylene group. The photoreactivity of diacetylene derivatives whose substituents were replaced with other groups that affect the molecular arrangement in the LB films has also been studied.15*16 One of the interests in conducting these studies is to find the use of the LB layers that change their color by the action of heat, pressure, or light for application in optical recording media.]' The present study has been carried out to solve these problems and to obtain information that will be helpful for future studies to prepare functional polymer LB films from pentacosadiynoic acid (PDA: CH3(CH2)11C=CC=C(CH2)8COOH) LB films. ( I I ) Mcalear, J. H.; Wehrung, J. M. Digest of Technical Papers; 1981, Symposium on VLSI Technology; IEEE, Electron Devices Society, Piscataway, NJ, 1981; p 82. (12) Bubeck, G.; Tieke, B.; Wegner, G. Ber. Bunsen-Ges. Phys. Chem. 1982, 86, 495. (13) Bubeck, C.; Tieke, B.; Wegner, G. Mol. Crysr. Li9. Crysf.1983, 96, 109. (14) Tieke, B.; Lieser, G.; Weiss, K. Thin Solid Films 1983, 99, 95. (15) Wegner, G. J . Polymn. Sci., Part B 1971, 9, 133. (16) Nakanishi, H.; Matsuda, H.; Kato, K.; Thocharis, C.; Jones, W. Polym. Prepr. Jpn. 1984, 33, 2491. (17) Sandaman, D. J.; Tripathy, S. K.; Elman, B. S.; Samuelson, L. A. Synth. Met. 1986, 15, 229.
0022-365418912093-5305$01.50/0 0 1989 American Chemical Society
5306
The Journal of Physical Chemistry, Vol. 93, No. 13, 1989
PDA was selected as the film substance in this study because the photopolymerization process of PDA LB films by deep-UV irradiation has been studied extensively. I n an attempt to elucidate the reactivity of LB films as a function of molecular density or arrangement in the film, the reactivity of PDA LB films obtained from different buildup processes was investigated in detail by UV and Raman spectroscopy techniques that have been proven to be suitable in obtaining spectra for conjugated triple bond^^*.'^ of extremely thin organic layers in a number of polymerization2G25and phasetransitions s t ~ d i e s * ~of, ~diacetylene ' derivatives LB films. The two typical LB films of PDA were used: one, the lowdensity type (A type), and the other, the high-density type (B type). These were prepared under different subphase conditions and surface pressures. Some data in our study of w-tricosynoic acid (o-TCA: C H r C(CH,),COOH) LB films28,29are further discussed for reference pur poses. Experimental Section
Materials. PDA of reagent grade and chloroform of UV spectral grade were obtained from Wako Pure Chemical Industries, Ltd., and used without purification. Calcium chloride was also supplied by the same manufacturer and used after Soxhlet extraction to remove any surface-active contaminations. The water was purified by ultrafiltration of deionized water to satisfy the ultrapurified grade requirements in the semiconductor device process (conductivity, 16 M Q c m or higher; number of particles exceeding 0.5-pm diameter, smaller than 30 particles/cm3; concentration of total carbon, lower than 100 ppb). Apparatus and Circumstances. A Langmuir trough (JoyceLoebl Trough IV) was used for the buildup of PDA LB films. The preparations of the LB films were carried out in a class 100 clean room under yellow light cut below 500 nm. The temperature of the clean room was controlled at 23.0 i 1 "C, and the humidity was 40 f 5%. Procedures. 1 . Preparation of Films. PDA samples (ca. 0.1 mg) were spread on aqueous subphases containing CaC'12of two different concentrations: one containing 3.0 X IO4 mol/L at pH 5.6, for preparation of low-density PDA LB film (A type), and the other containing 1.3 X mol/L at pH 6.3, for high-density PDA LB film (B type) at 6.0 OC. The pH of the subphase was adjusted by using NaOH or HCI. Four types of solid substrates on which the LB films were built up were used depending on the type of measurement of the LB films: (i) a quartz plate, (ii) a silicon wafer whose surface was etched by H F to remove S O 2 , (iii) a silicon wafer on which S O 2 was grown by heating the wafer at 1100 OC in oxygen, and (iv) a silicon wafer on which AI was deposited by evaporation. The substrate was moved across the monolayer on the aqueous subphase at a constant velocity of 3 cm/min downward and 1 cm/min upward for PDA LB films. During the buildup of the LB films, the surface pressure was kept constant at pressures denoted as A or B on the surface pressure-area curves shown in
(18) Chen. Y . J.; Carter, G. M.; Tripathy, S. K. SolidStare Commun. 1985, 54, 19.
(19) Baughman, R. H.; Witt, J. D.; Yee, K . C. J. Chem. Phys. 1974.60, 4755. (20) Tieke, B.; Graf, H. J.; Wegner, G.; Naegele, B.; Ringsdorf, H.; Banerjie, A.; Day, D.; Lando, J . B. Colloid Polym. Sci. 1977, 255, 521. (21) Wegner, G . Pure Appl. Chem. 1977, 49, 443. (22) Tieke, B.; Lieser, G.; Wegner, G . J. Polym. Sci., Polym. Chem. Ed. 1979, 17, 1631. (23) Bubeck, C.; Tieke, B.; Wegner, G. Mol. Crysr. Liq. Crysr. 1983, 96, 109.
(24) Hupfer, B.; Ringsdorf, H.; Schupp, H . Makromol. Chem. 1981, 182, 247. (25) Tieke, B.; Lieser, G . J. Colloid Interface Sci. 1982, 88, 471. (26) Lieser, G.; Tieke, B.; Wegner, G. Thin Solid Films 1980, 68, 77. (27) Day, D. D.; Lando, J . B. Macromolecules 1980, 13, 1478. (28) Ogawa, K . Jpn. J. Appl. f h y s . 1988, 27, 855. (29) Ogawa, K.; Tamura, H.; Hatada, M.; Ishihara, T. Langmuir 1988, 4, 1229.
Ogawa
m,
Area
(
85 molecule )
Figure 1. Surface pressure-area curves for building up the different density PDA LB films and w-TCA LB films: (a) A-type film, (b) B-type film, (c) w-TCA film.
Figure I . In Figure 1, a similar plot obtained for w-TCA LB films from the previous report29 is also included for reference purposes. The PDA LB film, thus built up by the above procedure, was 25 or 50 layers, in which the first 12 layers were built up by 2-type deposition and then the deposition changed to that of Y type for both PDA LB films. The transfer ratios depended a little on the type of depositions, but the ratio was almost 1 for all buildup processes. 2. Irradiation by X-ray and Excimer Laser Light. Irradiations of LB films of both types (A and B types) were carried out with a KrF excimer laser light (248.4-nm) exposure apparatus, which was developed in our laboratory for semiconductor device production and an X-ray stepper (SX-5; Nippon Kougaku K.K.; an electron beam excitation type with Si target). For X-ray irradiation, a helium stream was introduced into the chamber during irradiation to keep oxygen away from the chamber. The dose rate of excimer laser light irradiation was 8 mJ/ cm*-pulse,and that of X-ray irradiation was 0.23 mW/cm2 at the beam current of 430 mA (acceleration voltage, 18 keV; wavelength, 7.13 ..&). In both cases, the temperature of the LB films did not exceed 30 OC during irradiation. 3. Solubility Test. The solubility test to confirm whether the polymerization occurred by the irradiation was carried out by dipping the film in ethanol for 1 min at 20 OC after exposure. The normalized residual thickness, which was measured by ellipsometry, after being dipped in ethanol is plotted as a function of exposure dose with the X-ray or excimer laser light irradiation. This plot will be referred to as the y-property curve of the film. 4 . Analysis of LB Films by UV and Visible and Raman Spectroscopies. UV and visible spectra and Raman spectra for PDA LB films were measured directly on those LB films to elucidate the polymerization reaction of PDA LB film. The U V and visible spectra were obtained on a multichannel spectrophotometer (MCPD-1 10A; Otsuka Electronics Co., Ltd.), which was operated with the acquisition time of 100-120 ms. The illuminance on the LB film during measurement was 0.05 mW/cm*, which was low enough that no photoreaction of the film during the measurement occurred. The visible absorption spectra of the polymerized films of both types were measured to study the difference in structure of the polymerized films prepared by the X-ray or excimer laser light irradiations. The visible spectra were obtained for the PDA LB films (25 layers on a quartz substrate) irradiated with X-ray and excimer laser light at the dose of 50 mL, which gives a normalized residual thickness of about 0.8 in the y-property curve (Figure 3a,b). The UV absorption spectra of PDA LB films (25 layers on a quartz substrate) in the wavelength region near 248.4 nm, which is the wavelength of KrF excimer laser light, were measured at about 23 OC at different exposure doses of excimer laser light. The Raman spectra of PDA LB films (25 layers on a Si substrate) before and after irradiation with X-ray were measured on a laser Raman spectrophotometer (NR- 1000; Japan Spectroscopic
The Journal of Physical Chemistry, Vol. 93, No. 13, 1989 5307
Pentacosadiynoic Acid Langmuir-Blodgett Films
I
05 1
I 450
500 Wavelength
600
700
2
0
(nm)
6
4 Irradiation
10
8
Dose ( pulse)
\
A type
Y) Y)
0
I 450
500
600
2
700
Ob’ Wavelength
(nm )
Figure 2. Visible absorption spectra of polymerized PDA LB films: (a) with X-ray irradiation, (b) with excimer laser light irradiation.
Co., Ltd.) which was composed of a double monochrometer (CT- 1000D; Japan Spectroscopic), photomultimeter (R-943; Hamamatsu Photonics Co., Ltd.), and 100-mW Ar laser (5145 A). The diameter of the incident light spot on the sample was about 40 pm. Assignments of the scattering bands were made in reference to the reports by Y. J. Chen et a1.I8 and R. H. Baughman et aI.l9
Results and Discussions Surface Pressure-Area Curve of the Monolayer. Different surface pressure-area curves of PDA monomolecular films were obtained depending on the concentration of Ca2+in the aqueous subphase. Two typical surface pressure-area curves of PDA monomolecular films used for the buildup of the PDA LB films are shown in Figure 1. Curve b obtained on a subphase containing mol/Ca2+ was more the condensed type than that in 1.3 X curve a obtained on a subphase containing 3.0 X lo4 mol/L Ca2+. The reason for this may be that more calcium bridges that tightly combine carboxyl groups of PDA are formed at a higher concentration of Ca2+ and a higher pH. Assuming that the molecular arrangement in PDA LB films maintains its state after the monomolecular films are built up, the molecular density in the PDA LB films built up at point A (A type) should be lower than that built up at point B (B type). That is, the molecules in the A-type film will be arranged somewhat in a tilted state as shown by I in Figure 8a where the molecules occupy 26,A2/molecule, while those in the B-type film will be in a more densely packed arrangement (VI in Figure 8c; molecular area, 20 A2/moIecuIe). Visible Absorption Spectra of Polymerized PDA LB Films of A and B Types. Two different absorption spectra were obtained for PDA LB films of A and B types after they were exposed to X-ray; as shown in Figure 2a, the spectrum observed for polymerized A-type film shows a peak maximum at 640 nm with a weak and broad shoulder at ca. 580 nm, while that observed for B-type film shows a peak maximum at 575 nm with shoulders at 530 and 630 nm. Since it is reported that the spectrum of a “blue”-form polymer has peaks at ca. 640 (s) and 590 nm (w) and that of a “red” form has peaks at ca. 530 (s) and 500 nm ( w ) ? ~the former spectrum is assigned to a blue-form polymer and the latter
5
3 ’
10
c
’
’
50 100 Irradiation
8 type
-
500 1000
5000
Dose ( mJ/cm2)
Figure 3. y-Property of two types of PDA and w-TCA LB films: (a)
excimer laser light irradiation, (b) X-ray irradiation.
spectrum is assigned to a red-form polymer with a small amount of blue-form polymer. The spectrum of the blue-form polymer was observed (peaks at 645 and 595 nm) when PDA LB films of A type were irradiated with excimer laser light, but very weak absorption due to blue-form polymer (peaks at 625 nm; peaks blue shifted a little from that observed on A-type LB film) was observed when the PDA films of B type were irradiated with excimer laser light as shown in Figure 2b. The peak in the 625-nm region that appeared in the B-type film contains a considerable amount of A-type film, which produces blue-form polymer of low molecular weight. Solubility Tests of the PDA LB Films. y-Properties of two types of LB films of PDA and w-TCA LB films (50 layers) are shown in Figure 3, parts a and b, respectively. In Figure 3b, a similar plot obtained for w-TCA LB films from the previous report2*is also included for reference purposes. With excimer laser light irradiation, it is clear that the A-type PDA LB films became insoluble from 8 mJ/cm2 (one pulse) to 56 mJ/cm2 (seven pulses) and soluble above 64 mJ/cm2 (eight pulses), but no films were found after the same procedure on B-type film and w-TCA film, even if sufficient irradiation was carried out, as shown in Figure 3a. That is, on the A-type PDA LB films, photoreaction further continues after polymerization. These results indicate that although polymerization does not occur on w-TCA or B-type PDA LB film at all, polymerization proceeded on A-type PDA LB film by excimer laser light irradiation, but the photodecompositions further proceeded on the polymerized film. On the other hand, with X-ray irradiation, the A-type PDA LB films were found to polymerize with 7-400 mJ/cm2 dose, but above the 100 mJ/cm2 dose, they decomposed. For B-type PDA LB film and w-TCA film, the polymerizations only occurred at about a 50 mJ/cm2 dose and the decomposition did not occur at all, even if sufficient irradiation was made, as shown in Figure 3b. The induction period was observed only for B-type film and not for A-type film as shown in Figure 3b. The reason for this is perhaps that the low molecular weight polymer that is soluble in ethanol was produced during the low-dose region below 30
5308
The Journal of Physical Chemistry, Vol. 93, No. 13, 1989
Ogawa (mJ)
type
( A
0 42
,
230
.
,
240
,
,
,
,
250 Wavelength
260 (
.
,
I
.
270
----
250
50
260
I360
I70
Dose
-----
Wavelength
05
nm )
.........
240
400
.
280
( B type)
2%
40
270
00
i
(
pulse
I
Figure 5. UV absorption intensity of A-type and B-type films at 240 nm
as a function of excimer laser light irradiation dose. (0)
280
(mn)
Figure 4. Change of UV spectra of two types of PDA LB films with excimer laser light irradiation: (a) A-type film, (b) B-type fim.
mJ/cm2. The dose giving the half-values of the highest normalized residual thickness of B-type PDA film (45 mJ/cm2) is quite larger than that of A-type PDA film (ca. 8 mJ/cm2) but is close to that of w-TCA film (60 mJ/cm2), which gives a polyacetylenic type polymer as B-type PDA film (discussed in a later section). Furthermore, the y-plot of w-TCA shows retardation in the small-dose region and is similar in shape to that of the B-type film rather than that of the A-type film. These facts together may support the above explanation and suggest that the polymerization mechanism of B-type film is different from that of A-type film. UVSpectra Change of PDA LB Films by Excimer Laser Light Irradiation. The changes of UV absorption spectra of PDA LB films of A and B types with increasing excimer laser light irradiation dose are shown in Figure 4 parts a and b, respectively. In Figure 4a, b, the absorptions at 240 and 254 nm are asigned to weak conjugated triple bonds in the PDA molecule, judged from the action spectra obtained by B. Tieke et aLZ2 The absorption intensities of the two absorption peaks of PDA films of the two types at 240 and 254 nm decreased more quickly between 0 and 5 pulses (40 mJ/cm2) but slowly between 50 pulses (400 mJ/cm2) and 170 pulses (1 360 mJ/cm2) as shown in Figure 4a, b. The relative absorption intensity at 240 nm normalized to that of unirradiated LB films is further plotted as a function of the irradiation dose in Figure 5 for A- and B-type PDA LB films. The curves for both types decreased up to the dose of 40 mJ (five pulses) and then decreased gradually as the dose increased, but the rate of the initial decrease was higher for A-type LB films than for B-type films, as shown in Figure 5. The initial decrease of B-type film may be due to the reaction of the A-type region in the B-type film as discussed in a former section (Figure 2b, and if this assumption is valid, the B-type film can be regarded as inactive to radiation at the low-dose region. Change of Raman Spectra of PDA LB Films by X-ray Irradiation. The change of Raman spectra of A-type LB films during irradiation is shown in Figure 6a. The intensities of the scattering bands due to conjugated triple-bond stretching vibrations (-C=
2500
25x
I500 Wave Number
loo0
500
(an-')
C 700
2500
I
I
2000
1500
Wave Number
I 1000 (
500
cm-' )
Figure 6. Change of Rainan spectra of two types of PDA LB films with X-ray irradiation: (a) A-type film, (b) B-type film.
C-CW-: conjugated v(C=C) = 2100 cm-') decreased with increasing dose, -CH2- scissoring vibrations (6(CH2) = 1485 cm-") shifted to higher wavenumber, and the progression bands due to -CH2- wagging and twist vibrations (w(CH,), y(CH2) = 1100 cm-I) became weaker as the dose increased. But the latter was still recognized at 700 mJ/cm2 irradiation. These results indicate that the cross-linking between the hydrocarbon chain of the LB layers occurred at unsaturated bonds by the irradiation and disturbed the mobility of the wagging vibration of the molecular
-
The Journal of Physical Chemistry, Vol. 93, No. 13, 1989 5309
Pentacosadiynoic Acid Langmuir-Blodgett Films
(a )
0
500 Dose
newconj/conj
(C.C)
(C.C)O
loo0
mJ/cm2 1
(
(-
4-
O---
I
A type
B+yw
IC)
0
500
Dose
loo0
(mJ/cm2)
Figure 7. Ranian scattering intensity of A-type and B-type LB films as a function of X-ray irradiation dose: (a) conjugated C=C at 2100 cm-I and =CH of w-TCA (replotted from IR data at 3300 C ~ - I ) ; (b) ~ ~ new conjugated C=C and new conjugated C=C produced, by the irradiation
at 1450 and 725 cm-I, respectively; (c) ratio of new conjugated C=C/ new conjugated C=C. ~ h a i n s . l * *The ~ ~ new scattering peaks that may be assigned as a stretching vibration of a new conjugated triple bond (triple bond in -C=C-C=C-: new conjugated ~ ( C E C ) = 725 cm-') and a new conjugated double bond (double bond in -C=C-C=Cor -C=C-C=C-: new conjugated u(C=C) = 1450 cm-I) appeared by irradiation and increased with increasing dose. The change of spectra of the B-type. LB films is shown in Figure 6b. A similar spectral change was observed for B-type LB films, but the degree of decrease or increase of the peak intensities was smaller than that observed for A-type LB films. The decrease of relative intensities of conjugated C s C bands is plotted as a function of dose in Figure 7a for the LB films of A and B types, comparatively. A similar plot obtained for w-TCA is also included in the LB films taken from the previous
figure for reference purposes. The conjugated CEC bonds in A-type LB films decreased more quickly than those in B-type LB films but reached a constant value of 0.5, while the conjugated C=C bonds in the B-type LB films continued to decrease gradually. The relative intensities of the new conjugated C=C and the new conjugated C=C (normalized to conjugated CEC band intensity before irradiation) are plotted as a function of dose in Figure 7b for the LB films of both types. It is evident from Figure 7b that the scattering intensities of new conjugated C=C and new conjugated C=C of A-type film increased more rapidly than those of B-type film with increasing dose until about 140 mJ/cm2. It is also recognized that the change of intensities of new conjugated C=C and new conjugated C W stretching vibration of the B type are on straight lines. The scattering intensity ratio of new conjugated C=C/new conjugated C=C of both films is further plotted as a function of X-ray irradiation dose, as shown in Figure 7c. It is recognized that the ratio of B-type films did not change but that of A-type film changed largely with increasing X-ray irradiation dose. That is, on A-type LB film, as shown in Figure 7a,c, the new conjugated C=C group was decreased gradually above 100 mJ/cm2, indicating that the decomposition proceeded at the new triple bonds of the polymerized A-type film. This idea is further supported with the result that the scattering intensity ratio of new conjugated C=C/new conjugated C=C was reversed above the 200 mJ/cm2 dose, as shown in Figure 7c. On the other hand, on the B-type LB film, the polymerization reaction continued up to 700 mJ/cm2. Polymerization Model at Diynoic Group of PDA LB Films. The polymerization mechanisms of the two type of films are different from each other and perhaps due to the arrangement of unsaturated groups in the PDA LB films, which may more strongly relate to surface pressure when the films were built up. The visible spectra and solubility test of irradiated PDA LB films show that polymers of both films are different from each other. From the solubility test, it was considered that A-type film was polymerized with dose range below about 50 mJ/cm2 and then decomposed with increasing X-ray or excimer laser light dose and that the decomposition of polymerized A-type film proceeded at the new conjugated triple bonds produced by the polymerization. This idea was supported with the results of Raman spectroscopy. It is clear with the solubility test, UV spectra, and Raman spectra that A-type film is more sensitive to X-ray or excimer laser light that B-type LB film and polymerized more quickly than B-type LB film but decomposed with increasing dose. On the other hand, for B-type films, the polymerization reaction proceeded with only X-ray irradiation and the decomposition reaction never occurred with increasing dose. The polymerization mechanism of B-type film may be similar to that of w-TCA, because the decrease of IR absorption intensity of the stretching band due to ECH was similar to that of Raman scattering intensity due to conjugated C=C, when the molecular densities of w-TCA and B-type PDA LB films were nearly equal each other, as shown in Figure 1. Accordingly, the suggested reaction schemes are as shown in Figure 8. The molecular configuration of A-type film may be the one shown by I in Figure 8a, in which the PDA molecular chain makes a sharp bend at C- 13 of the carbon chain. This molecular configuration may be reasonable from the experimental results that the film could not be built up as an LB film at 26 A2/molecule on the surface pressure-area curve (Figure lb), when the molecular configuration was more loosely packed within a wide molecular area. This configuration seems to be favorable for successive 1,4-addition (II), and this polymer is decomposed probably at new conjugated C z C bonds directly (from I1 to IV) with excessive excimer laser light or X-ray exposure as shown in Figure 8b. Other paths of decomposition through polyacetylene bonds (from I1 to IV or V through 111) may be excluded since the B-type polymer did not decompose by excessive irradiation as will be mentioned below. All these considerations may indicate that the polydiacetylene polymerization occurs in A-type films
5310 The Journal of Physical Chemistry. Vol. 93, No. 13, I989
I -
!I\\s, F,
-
0 0 - 0 0
F, - 0E,0-
0 0
Ogawa
//q J\ h E, 0 0-0 0-00-0 0-
-
Figure 8. Suggested reaction process for two types of PDA LB films under high-energy beam irradiations: (a,b) low-density film; (c,d) high-density
film.
with proper irradiation conditions,22 as shown in Figure 8a. On the other hand, in the B-type films, the vertically oriented diynoic groups may be straight and stacked parallel with each other in the most condensed region, as shown by VI in Figure 8c, d, and therefore, 1 , I - and 4,4-addition rather than successive 1,4-addition would occur favorably, resulting in a polydiacetylene bond that will be decomposed by further irradiation, as mentioned in Figure 8b. But, the fact that no decomposition of the polymerized B-type film occurred indicates that the polymerization by I , 1- and 4,4-addition (Figure 8c) does not occur. Therefore, in B-type films, either polymerization or ring dimerization including 1 , I -, 2,2-, 3,3-, 4,4-, 2,3-, or 3,2-additions is also probable from V I to V l l l , IX, X, or XI and their mixtures, as shown in Figure 8d. That is, this reaction process means that the polyacetylene polymerization occurs in B-type films with high energy beam irradiation such as an X-ray. The reason why polymerization of B-type film did not occur by excimer laser light but did by X-ray irradiation is that the formation of the polyacetylene bond by 1,2- or 3,4-addition requires irradiation by light below about 225 11111,~~ which is shorter than the wavelength of the KrF excimer laser light (248 nm) used in this study Conclusions The PDA LB films of two different molecular densities were polymerized to form different polymer LB films by X-ray irra-
diation. The polymerization sensitivity of PDA LB film was affected by the arrangement or density of PDA molecules in the film. Decomposition of polymerized low-density type (A-type) films by X-ray or excimer laser light further proceeded by excessive irradiation of X-ray or excimer laser light, but that of polymerized high-density type (B-type) films by X-ray did not occur. It was confirmed by the spectroscopic analysis that the polydiacetylene-type polymerization occurs only on A-type films by either excimer laser light or X-ray irradiation, but the polyacetylene-type polymerization occurs on B-type films only by X-ray irradiations and not by excimer laser light. Acknowledgment. I acknowledge the assistances of H. Izawa of Nippon Kougaku K.K. for X-ray exposure and Kumi Aono, nee Ueda, and H. Tamura of the Semiconductor Basic Research Laboratory, Matsushita Electric Industrial Co., Ltd., for preparation of the LB films. I also thank T. Ishihara of the Semiconductor Basic Research Laboratory, Dr. H. Mizuno of Matsushita Electric Industrial Co., Ltd., Dr. M. Hatada of Osaka Laboratory for Radiation Chemistry, Japan Atomic Energy Research Institute, Prof. T. Takenaka of the Institute for Chemical Research, Kyoto University, and Prof. T. Koda of the Faculty of Engineering, University of Tokyo, for their helpful comments. Registry No. PDA, 66990-32-7; PDA (homopolymer),66990-33-8.
