A new apparatus for simultaneous observation of optical microscopy and small-angle light scattering measurements of polymers under shear flow

7: Kume, K. Asakawa+, E. Moses”, K. Matsuzaka‘” and 7: Hashimoto* Division of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 606-01, Japan

+ Present address: Toshiba Corporation, Research and Development Center, 1, Komukai Toshiba-cho, Saiwai-ku, Kawasaki 210, Japan ++ Present address: Weizmann Institute of Science, Physics Department, Rehovot 76100, Israel +++ Present address: The Hashimoto Polymer Phasing Project, ERATO, Research Development Co. of Japan, 15 Morimoto-cho, Shimo-

gamo, Sakyoku, Kyoto 606, Japan

A new apparatus which makes it possible to measure flow small-angle light scattering (“flow-SALS”) and to observe the development of the supramolecular structure by an optical microscope (“shear microscopy”) has been developed in our laboratory. It simultaneously provides information on reciprocal space from SALS and on real space from optical micros- copy. Therefore, the development of the supramolecular structure in systems such as polymer solutions and polymer mixtures as well as liquid crystals and colloidal systems under shear can be investigated in depth. Shear-induced phase separation and shear-induced homogenization of some polymer solution systems were investigated using this apparatus.

1. Introduction

The mixing or demixing phenomena of polymers have been studied theoretically and experimentally since the 1970s. Recently, the effect of shear flow on them has attracted much attention [l-191. The essence of this subject is the topic of open non-equilibrium systems. Several methods, such as transmitted light intensity [2, 121, flow form dichroism [lo, 12, 131, small-angle light scattering [3-131, and small-angle neutron scattering [ 141, have been used to understand these phenomena. These methods are indirect methods, bearing the advantage of providing infor- mation that is a statistical average over the system as a whole, but it is difficult to get detailed features of the struc- tures. In contrast, optical microscopy is a direct method but it can investigate only a rather small part of the system. It does not always cover all of the system, i.e., it is not statis- tical. Thus the two approaches are complementary to each other. Therefore to understand the supramolecular struc- tures of polymeric solutions and polymer mixtures deve- loped under shear flow, we tried to combine the small-angle light scattering method with optical microscopy. A new flow small-angle light scattering apparatus with an optical microscope was constructed in our laboratory for this purpose. The structures of polymeric systems in liquid and solution can be simultaneoulsy investigated by flow small- angle light scattering (designated hereafter as “flow- SALS”) and by optical microscopy (designated hereafter as “shear microscopy”). The flow-SALS technique gives funda- mental information on the nature of supramolecular struc- tures developing under shear flow. It is, however, hard to sketch the image of the structures in the system by the flow- SALS when the structures are too complicated, because phase information of the structures is lost in the scattering image. Thus the scattering pattern does not have a one-to- one correspondence to the structure. In our case, the optical microscope measurement provides helpful information about the structure. Therefore we believe that this is an important and effective technique for studying the shear flow effects.

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Acta Polymer., 46,79-85 (1995) 0 VCH Verlagsgesellschaft mbH, D-69451 Weinheim, 1995

2. New rheo-optical apparatus of combined shear microscopy and flow-SALS

The new apparatus was constructed by modifying an existing rheometer (IR-200, Iwamoto Seisakusho, CO., LTD., Kyoto, Japan). Figure 1 shows a schematic diagram of the whole apparatus. Unlike the apparatus previously deve- loped [3]. this new apparatus does not have a transducer which measures the rheological properties of samples. Therefore there is open free space above the temperature enclosure. The apparatus previously developed has a big mirror to reflect the scattering light above the temperature enclosure, because the transducer disturbs the detection of the scattered light. The new apparatus does not have such a mirror.The scattering light can be directly detected without an upper mirror, and artifacts due to the mirror can thus be avoided.

This apparatus consists of four main parts, A to D, as shown in Fig. 1. Part A is made of several control units for

..............______..

D C B A Fig. 1. Schematic representation of the new flow small-angle laser light scattering apparatus and the shear microscopy apparatus. Part A: (a) several control units for the shear cell, (b) power units for the laser unit, (c) power units for the shear cell, (d) laser unit. Part B: (e) Macintosh IIci, (f) MO disk drive, (g) hard disk drive. Part C: (h) and (i) optical benches, a) CCD camera, (k) screen, (I) optical microscope, (m) temperature enclosure, (n) shear cell, (0) motor unit, (p) microscope bench. Part D: (9) VCR, (r) TV monitor, (s) video printer.

0323-7648/95/0102-0079$5.00 + .25/0 79

the shear cell (a), power units for the laser unit (b), for the motor (c) that drives the shear cell, and the laser unit (d). A He-Ne CW gas laser is used as an incident light source (do = 632.8 nm, 15 mW) for the scattering measurement. A halogen white lamp, on an optical bench (i), is used as a light source for microscope observation. Part B is composed of a personal computer, Macintosh IIci (e) with MO disk drive (f) and hard disk drive (g), in order to capture images from the CCD camera and to analyze digital images imme- diately. A frame grabber board is set up in the Macintosh IIci for capturing images. In digital image analyses we made extensive use of the image program,NIH Image, developed by Wayne Rasband at NIH [20]. Part C is the core of this apparatus: an optical bench (h) carries the CCD camera u) and screen (k) up and down, which detect two-dimensional scattering profiles. When necessary, an analyzer is placed in front of a screen (k) for depolarized light scattering experi- ments. The halogen white lamp unit, which we mentioned above, and a polarizer to polarize the incident light beam from the lamp are put on an optical bench (i) for shear microscopy. For flow-SALS, neutral density filters, pinholes and a half wavelength plate to rotate the polarization direc- tion of incident laser beam are put on the optical bench (i). The optical microscope (1) is supported by the microscope bench (p), and by rotating its arm we can easily remove the microscope when we take scattering profiles. We set thick rubber under the microscope bench (p) to avoid vibration from the motor unit. The temperature enclosure (m), shear cell (n) and motor unit (0 ) will be introduced in detail later. Part D is composed of the VCR (q), TV monitor (r) and video printer ( s ) to display or record scattering patterns or microscope images.

Figure 2 shows a schematic diagram of the shear cell and represents a flow chart of the video signal in optical micros- copy. We use a set of optically transparent cone and plate or parallel plates made of quartz as a shear cell. The cone is

placed on the incident beam side so as to avoid complex reflection of the scattering light at the oblique surface which could occur if the cone were placed on the scattered beam side. The cones and plates used have the same radius of 40 mm, but we used cones with different angles ranging from 1.0" to 2.6" in order to adjust for the varying transpar- ency of the samples. We use Nicon 10 x ,20 x , 40 x and 60 x long focus type objectives. The shear flow is imposed on the sample by applying steady-state rotations, oscillatory rota- tions, or "saw-tooth" rotations to the lower cone or plate, as was done before with the apparatus previously constructed [3]. In this new apparatus the rotation can be reversed. We can also impose transient step-wise shear flow on the sample. The definition of the coordinate system is also the same as that used previously [3]. The inset at the top left- hand corner of Fig. 2 shows a schematic diagram of Couette flow in the sample. Ox is parallel to the propagation direc- tion of the incident beam, and to the velocity gradient direc- tion, whilst Oz is parallel to the flow direction and Oy is the neutral axis.

To the optical microscope we connected a fast shutter (1110 000 s ) CCD video camera (Sony SSC-M370), which is connected in parallel to a video printer, a TV monitor, a SVHS VCR (Victor HR-S6600), and a Macintosh IIci with frame grabber board (RasterOps 24STV). For the observa- tion of samples under shear flow by optical microscope, a fast shutter CCD camera is needed because the samples quickly flow out of sight of the microscope. The video printer allows easy and quick recording. Focus and real- time observation are made using the TV monitor. The VCR carries out analog and continuous recording. The Macin- tosh computer is used for digital image capturing and processing, e.g., contrast enhancement, background subtraction and artifacts correction. For the digital image capturing, the largest size of captured images is 640 x 480 pixels, and their resolution is 8 bits. It takes a few seconds to

Fig. 2. Schematic diagram of the shear microscopy and a flow chart of the video signal. The temperature enclosure corresponds to (m) in Fig. 1. The inset at the top left-hand corner shows a schematic diagram of Couette flow in the sample.The Ox, 0, and 0, axes are parallel to the velocity gradient direction, the neutral axis and the flow direction, respectively.

Acta Polymer., 46.79-85 (1995) 80 Kume, Asakawa, Moses, Matsuzaka, Hashimoto

capture the largest size image and save it onto the hard disk. For the digital image processing, we carry out several filtering operations on captured images (see Sec. 3.1 below for details). Furthermore we can easily carry out image analyses, e.g., fast Fourier transform (FFT), using digital images.

The temperature enclosure is a double layer enclosure which can control the temperature of the samples in the range of 0 "C to 200 "C with an accuracy ofk0.3 "C. We need such an accuracy because we treat critical phenomena, which are very sensitive to temperature. Below room tempe- rature we use a cooling system which cools the air before entering the temperature enclosure. Small windows are opened on the upper and lower sides of the temperature enclosure to insert the optical microscope or to let incident and scattered beams pass. These windows define the appa- ratus coverage of the scattering-angular range from ca. 0 to 30" (in the medium).

For the quantitative measurements of light scattering we use the CCD camera and screen.The flow chart of the video signal after the CCD camera is the same as for shear micros- copy. Thus we can handle scattering profiles as digital data, i.e., contrast enhancement, background subtraction and correction for artifacts are possible as for shear microscopy. Moreover, photographic films can be used instead of the screen (k in Fig. 1) to detect the scattering profiles for quali- tative observation.

For both shear microscopy and flow-SALS measure- ments, experiments under various polarization conditions are possible. For shear microscopy, we use the polarizer which is set on top of the halogen white lamp and analyzer in the microscope. For light scattering, the laser beam is polarized, thus we do not need a polarizer. The half wave- length plate, which is on the optical bench (i in Fig. l), can rotate the orientation of the electric vectors of the incident laser beam. The analyzer is put between the screen and temperature enclosure. Therefore we can detect Hv,VH, HH, and Vv components of the scattering profiles and micros- cope images, with large H, V defining analyzer orientation and subscript H, V denoting polarizer orientation.

Since flow-SALS and shear microscopy are combined, we can very effectively use the information given by them. Calculating the 2D-FFT of microscope images [21] and comparing them with scattering profiles confirm whether the microscope images are a true representation or not. Furthermore, when we know the dominant wave numbers, q = (4n/A) sin(0/2) (1 and 0 being the wavelength and scat- tering angle in the medium, respectively), of the system, we

can eliminate other structures arising from unimportant wave numbers by performing filtering operations on the microscope images and obtain images of the dominant structures. We show some examples in the next section.

3. Application of flow-SALS and shear microscopy to poly- meric systems

3.1. Shear-induced phase separation in semidilute polymer solutions

Effects of shear flow on the phase transition and self- assembly of multicomponent mixtures have been attracting a great deal of attention from both theoretical and experi- mental viewpoints as an intriguing subject in statistical physics [ 1-19]. Shear-induced phase separation in semidi- lute polymer solutions is one of the striking results of combining hydrodynamics with the special elastic and viscous properties of polymers, and has been the focus of a concentrated effort in recent years [2, 6-10, 12-14]. More recently, it has attracted much theoretical interest in the nonequilibrium statistical physics of polymers [16-191. Using the flow-SALS apparatus previously constructed [3], we have found a strong anisotropy of the scattering pattern with respect to the flow direction and an anomaly at high shearrates. Here we demonstrate the merits of applying this appratus to studying the shear-induced structure formation. The details were described elsewhere [22].

In this study, polystyrene (PS) with weight average mole- cular weight M, of 5.48 x lo6 and heterogeneity index MW/ M,= 1.15 (M, is the number average molecular weight) was dissolved at a concentration of 6.0 wt.% in dioctylphthalate (DOP), a 0-solvent at 22 "C. This concentration is about 40 times higher than the overlap concentration [23] 6", and its cloud point is 13.8 O C . The experiment was done in the one-phase region at 27 "C.

Figure 3 shows two light scattering patterns recorded on photographic films in the quiescent state and the steady shear state.The shear rates of (a) and (b) were 0 s-l and 0.23 s-', respectively. The pattern (a) has almost no scattering intensity, the only signal resulting from the direct beam, so that the solution is in the one-phase region at zero shear. The pattern (b), which was taken in the plane of Oyz with the incident beam parallel to the velocity gradient direction (see Fig. 2), has a strong intensity along the flow, but no intensity perpendicular to the flow. This unique pattern has been designated as the "butterfly pattern" [6, 81. The

(a> o sec-' (b)0.23 see'

Fig. 3. SALS patterns of a PS/DOP solution (6.0 wt.%) show the features of the butterfly pattern at 27 OC: shear rate = O sC1 (a) and 0.23 s-l (b). The halo around the beam stop at 0 sC1 indicates the parasitic scattering.

*Flow direction

Acta Polymer., 46,79-85 (1995) Simultaneous optical microscopy and observation of small-angle light scattering 81

(b) Fig. 4. Sketches of concentration fluctuations in polymer solutions. The clusters (the dark regions containing more entanglements and are less subjected to deformation) are shown in the quiescent state or at i < it, (a) and at j > j ~ , (h),where ic is a critical shear rate above which shear-enhanced concentration fluctuations and scattering are observed.

butterfly pattern has also been observed in other polymer systems, e.g., stretched elastomeric block copolymer films, polymer gels, entangled polymer melts and silica colloids in a polymer matrix, and is attracting much attention [24-32]. It suggests that spatial heterogeneities of concentration fluctuations of polymer molecules, block copolymer micro- domains or colloidal particles are enhanced in the direction of shear flow, while the heterogeneities remain essentially unaltered from the homogeneous solution in quiescent state in the direction perpendicular to shear flow, leading to a proposal [8] of the model shown in Fig. 4. Figure 4a sche- matically shows that the dark regions are clusters in semidi- lute polymer solution in the quiescent state which have higher polymer concentration and hence more entangle- ment points and which are less deformed than less entan- gled regions having lower polymer concentration (the bright region). In the quiescent state these clusters, which are generated by thermal concentration fluctuations, are undetectable by scattering because the intracluster correla- tions compensate (screen) exactly the intercluster correla- tions, as proposed by Bastide et al. [27]. In the shear flow situation the clusters are less deformed than the interstitial medium, resulting in separation of the clusters parallel to the flow and higher interpenetration of the clusters perpen- dicular to it, as schematically shown in Fig. 4b. Thus the clusters are detectable along the flow but remain undetect- able normal to it. In other words, the concentration fluctua- tions are enhanced along the flow but remain unaffected or even suppressed normal to it, which explains the butterfly patterns.

The microscope visualization of the structures in the flow is presented in Fig. 5.The images of (a) and (b) are raw microscopic images at shear rate 0 s-l and 0.23 s-l, respecti- vely. Moreover, the images of (c) and (d) are contrast- enhanced images from those of (a) and (b), respectively. The picture of zero shear (c) has no distinctive feature, but

(a) o sec-’

(c) o sec-’

(b) 0.23 sec-’

(d) 0.23 sec-’

(e) 0.23 sec-’ (f) 0.23 sec-’ +Flow direction

Fig. 5. Microscopic images of the concentration fluctuations. (a, c) Quiescent state. (b, d, e, f) Shear rate 0.23 s-’ (> fc). (a, b) Raw images. (c, d) Contrast-enhanced from (a) and (b), respectively. (e) Image of dominant fluctuations extracted from (d). (f) Binary image thresholding (e).

the picture (d) under shear flow has some enhanced contrast variation and hence concentration fluctuations along the shear flow. The image (e) is filtered from the image (d) using a bandpass “Mexican hat” filter which effects both smoothing and edge detection. We select the size of the bandpass filter which correspond to the dominant structures using scattering information. Thus the image of (e) is that of the dominant structures at 0.23 s-’. Furthermore, the thresholded image of (e) is the binary image (0. The binary image enables the distribution of waves at different angles to be calculated [22].

Nevertheless, it is important to confirm whether or not the structure observed in Fig. 5d reflects the true structure occurring in sheared solution. For this purpose we calcu- lated the two-dimensional fast Fourier transform (2-D FFT) pattern from the structure in Figs. 5c and d and compare the FFT patterns with real scattering patterns. Figures 6a and b show 2-D FFT images corresponding to Figs. 5c and d, respectively. To reconstruct the light scat- tering representation of q-space (wave number or Fourier space) of Fig. 5, we use in Fig. 6 a logarithmic gray scale

82 Kume, Asakawa, Moses, Matsuzaka, Hashimoto Acta Polymer., 46.79-85 (1995)

3.2. Shear-induced homogenization in semidilute solutions of a polymer mixture

(a) o sec' (b)0.23 see' *Flow direction

Fig. 6. 2D-FFT patterns. (a, b) Calculated from the microscopic images in Figs. 5c and d, respectively. These images are basically similar to the patterns obtained by light scattering in Fig. 3.

representation with constant contrast enhancement. It is evident that the calculated 2-D FFT patterns are basically similar to the patterns obtained by light scattering, ascer- taining that the microscopic image in Fig. 5d is a true repre- sentation in real space of the butterfly-type scattering pattern.Thus the image in Fig. 5d is believed to be the direct visualization of the concentration fluctuations induced by shear flow, which is obtained for the first time for this system. This image directly confirms our conjecture shown in Fig. 4b from the light scattering pattern.

We have thus demonstrated that we can directly take images of concentration fluctuations of semidilute, high molecular weight polymer solutions under shear flow with shear microscopy, and shown that the origin of the butterfly pattern is the existence of hydrodynamic modes (or ripples) or Concentration fluctuations along the flow direction.

We studied effects of the shear on ternary system consisting of polystyrene (PS), polybutadiene (PB), and dioctylphthalate (DOP) using the flow-SALS apparatus previously constructed [4, 5, 111. Some models have been proposed for the structures occurring in the sheared solu- tions. These, however, have never been directly confirmed by real space analysis. Here we demonstrate the merits of using the apparatus for the solution with a near critical composition [4].

We used PS with M,=2.14 x lo5 and heterogeneityindex M,/M,, = 1.05, and PB with M, = 3.13 x 10' and M,lM,, = 1.90.These samples were mixed at a ratio of50/50 byweight (46154 by volume), and a solution containing the mixture by 3.3 wt.% in DOP was prepared. At this concentration, the ternary system satisfies c/c* 2, where c* is the overlap concentration [23], and its cloud point is 74 OC in the quiescent state. The experiment was done in the two-phase region at 66 OC ( A T = 8 K). More detailed results are described elsewhere [33].

Figure 7 shows a set of light scattering patterns obtained under different steady shear flows at shear rates between 0.0033 and 40 s-l recorded by the CCD camera. These patterns are the same as the patterns in our previous work (Fig. 1 in [ 5 ] ) , indicating that our experiment is reproduc- ible. As we showed for the model of self-assembled domain structure in our previous work (Fig. 14 in [5] reproduced here as Fig. 8), we can classify the shear rate into five regimes from I to V by the scattering pattern variation. The shear rates between 0.0033 and 40 s-l, which we treat here, correspond to regimes 11,111 and IV. These regimes are the two-phase regions below the critical shear rate j c (= 127 s-l)

Fig. 7. SALS patterns of a PS/PB/DOP system at different shear rates (s-') under steady shear flow. The ratio of PS to PB is 5050. The concentration of polymers is 3.3% by weight.The measuring temperture is 66 "C, which is 8 K lower than the cloud point. Regimes 11,111, and IVare the two-phase regions below the critical shear rate y , (= 127 s-I). Regime I1 is the low shear region,O< j , <0.0063 s-'.Regime I11 is 0.0063 < j~ < 0.25 s-'. Regime IV is the high shear region, 0.25 s-' < j , < 9,.

+ Flow direction Fig. 8. Schematic summary of the self-assembled domain structures deduced from the SALS results in previous experiments.This figure is the same as Fig. 14 in [5].The flow direction is vertical in the panels (a) to (e).The definition of regimes II,III,and IVare the same as for Fig. 7. Regime V is the one-phase region (homogenized state) above the critical shear rate j , , (= 127 s-l).

Acta Polymer., 46,7945 (1995) Simultaneous optical microscopy and observation of small-angle light scattering 83

Fig. 9. Microscopic images at different shear rates under steady shear flow. The sample and experimental'conditions used are the same as those in Fig. 7.

[I 11. Though not shown here, in the regime I (i.e., quiescent state or very low )), the solution separated into two macros- copic phases, a PB-rich DOP solution (on top) and a PS-rich DOP solution (below it). In regime I1 (the low shear region, 0 < j < 0.0063 s-'), the scattering patterns are circular, so it is expected that the domains are isotropic. In regime I11 (0.0063 < ) < 0.25 s-'), the scattering patterns are elongated in the direction normal to shear flow, hence domains are elongated in the direction of shear flow. In regime IV (the high shear region, but lower than iC), the elongated scat- tering patterns change into' sharp streaks perpendicular to the flow direction. This suggests that the elongated domains change into long percolated structures oriented along the flow direction. Furthermore, the lateral size of the elongated domains and the contrast between domains and matrix decrease with increasing ), and eventually shear- induced single phase formation occurs in regime V (y > ),). However, it was previously impossible to obtain direct images of these structures.

Figure 9 shows the variation of the structures of the same solution as what used for the flow-SALS (Fig. 7) under steady shear observed by the shear microscopy. The same solution was simultaneously observed by the flow-SALS and the shear microscopy. These pictures indicate that domains changed from spherical droplets into long elon- gated domains oriented along the flow direction. At the lowest shear rate, j , =0.0033 s-' (regime II), structures in the sample are spherical domains.At the shear rate between ) = 0.0063 and 0.1 s-l (regime 111), domains are elongated along the shear direction. At the shear rate above 0.25 s-' (regime IV), domains are elongated much more, and

change into string-like domains which extend along the flow direction. Since the sample composition is PS/PB 50150 wt.%, the sample structure is expected to be biconti- nuous or percolated at ) =0.0033 s-' (regime 11). However, note that the ratio of two phases in Fig. 9 is not 46/54 vol%, i.e., the ratio of polymer components which we dissolved into DOP solution. In this case the two coexisting phases are PS-rich phase (solution) and PB-rich phase (solution). We found that the ratio of PS-rich phase to PB-rich phase is ca. 40/60 vol.% after the solution completes phase separa- tion and gravity divides it into top (PB-rich) and bottom (PS-rich) solution phases, i.e. after it has been kept fora few weeks at the measuring temperature. This is because the PS/PB/DOP phase diagram is not symmetrical, in a way that makes the dispersed domains and matrix the PS-rich phase and PB-rich phase, respectivley, at lower shear rates. This expectation was proven by transmission optical micros- cope with the solution stained by Os04 [33]. In the high shear regime (regime IV), however, their ratio probably changes, because of a downward shift of coexistence curve with shear [ 1 I].

Figure 10 shows 2-D FFT patterns calculated from pictures of Fig. 9 which are consistent with the corre- sponding SALS pictures of Fig. 7. Therefore we could confirm again that the images captured really reflect the domain structures in the sample under shear flow. Thus the combined shear microscopy and flow-SALS technique leads us to propose a new model, as shown in Fig. 11. The schematic pictures (a), (b), (c), and (0 are same as those (a), (b), (c) and (e) in Fig. 8, respectively. However, the picture (d) in Fig. 8 should be replaced by the pictures (d) and (e) in

Fig. 10.2D-FFT patterns calculated from the microscopic images in Fig. 9.These patterns are basically similar to the patterns obtained by light scattering in Fig. 7.

84 Kume, Asakawa, Moses, Matsuzaka, Hashimoto Acta Polymer., 46,79-85 (1995)

Increasing ? b

Isotropic Elongated String-like Homogenized Domains Domains Domains

+ Flow direction Fig. 11. Summary of the self-assembled domain structures observed by shear microscopy under steady state shearflow.The flow direction is vertical in the panels (a) to (f).The new model adds the new features as shown in the panel (d) and (e) in Fig. 1 1 to the previous model obtained by the flow-SALS (Fig. 8).

Fig. 11. These latter pictures constitute new models in regime IV which the shear microscopy study indicates. In this regime, the string-like domains oriented along the shear flow can be macroscopically long while their diame- ters are less than 10 pm. The contrast between the two phases becomes weak and the diameter of the strings becomes small with further increasing shear rates, as shown in (d) and (e) in Fig. 11. Surprisingly the surface undula- tions of the strings is very much suppressed at higher shear rates in Regime IV. In summary, we could confirm and gene- ralize our model describing a solution of polymer mixtures under the shear flow.

In our experiment, we also found a limit for using shear microscopy. When the shear rate is higher than 100 s-', even using a shutter speed of 1/10 000 s , the pattern travels about 10 pm during the exposure time, and it is difficult to image the supramolecular structure of the sample by means of CCD, not only because the contrast between two phases becomes too weak to capture the images, but also because the spatial structures quickly run away out of the sight ofthe microscope at high shear rate. However, it is still possible to explore the development of the supramolecular structure in the polymer solutions at high shear rate using flow-SALS.

Acknowledgements

The authors are grateful to Iwamoto Seisakusho Co., LTD., Kyoto, Japan for their technical assistance in constructing the new flow-SALS apparatus. This work was supported in part by a Grant-in-aid for Scientific Research (05453 149) and by a Grant-in-aid for Encouragements of Young Scientists-A (00062753), both from the Ministry of Education, Science and Culture, Japan.

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Received June 27, 1994

Final version August 17, 1994

Acta Polymer., 46,79-85 (1995) Simultaneous optical microscopy and observation of small-angle light scattering 85