The PSD/PB blend exhibited upper critical solution .... 0.03 mass fraction of PSD-PB diblock additive de- ..... best at the shallowest quench depth, AT = 1.1 °C.
Journal of Polymer Research Vol. 3, No. 3, 139-150, July 1996
139
Phase Separation Kinetics and Morphology in a Polymer Blend with Diblock Copolymer Additive Lipiin Sung*, Diana B. Hesst, Catheryn L. Jackson, and Charles C. Han Polymers Division, National Institute of Standards and Technology Gaithersburg, Maryland 20899
Abstract: The phase diagram for a low molecular weight blend of deuterated polystyrene (PSD) and polybutadiene (PB) was determined by temperature jump light scattering (TJLS) measurements and phase contrast optical microscopy (PCOM). The PSD/PB blend exhibited upper critical solution temperature behavior, and the critical temperatures measured by these two techniques were consistent. Upon addition of 0 to 0.12 mass fraction of a comparable molecular weight PSDPB symmetric diblock copolymer, a linear decrease in the phase transition temperature was observed with increasing diblock copolymer content. At a constant, shallow quench depth, the kinetics of phase separation via spinodal decomposition as measured by TJLS were greatly retarded by the presence of the copolymer. Additionally, the time dependence of the concentration fluctuation growth did not seem to follow a universal functional form anywhere in the accessible q range when the diblock was present. The results of morphology study of the blends in the late stage of phase separation by PCOM also indicated that the phase separated domain sizes did not grow to the same size for a given annealing time as diblock content increased. Keywords: Polymer blends, Copolymer, Light scattering, Microscopy, Phase separation.
Introduction Multicomponent polymeric materials or blends have been extensively studied and used in industry to extend and enhance the properties of homopolymers [1-5]. The incompatibility of many polymer blends often limits their use, but their properties may be modified with block copolymer additives [1, 6-9]. The use of copolymers in blends as compatiblizing agents is well-established in many applications, although the precise mechanism by which they function is not completely understood. In order to gain a better understanding of this mechanism, more fundamental investigations of the phase behavior and morphology of multicomponent polymer blends are required. The ultimate goal of these studies is to control the final morphology, improve mechanical properties, and achieve greater economic success for commercial products using blends. Blends generally fall into two classes: "mechanically mixed" and "thermodynamically mixed" systems. The "mechanically mixed" blends are twophase systems for which the thermodynamic phase
boundary is not accessible. Most high molecular weight blends fall into this class [10-14]. In these systems, mixing can often result in a finer dispersion and reduction of the phase domain size to the 0.1-10 p.m range. These dispersions can have improved physical properties, such as toughness or impact strength. The "thermodynamically mixed" blends have an experimentally accessible phase boundary which is above the glass transition temperature, Tg, of the blend components, but below the degradation temperature of either homopolymer. In the laboratory, low molecular weight "model" blends [6-9] or films cast from solubilized blends [15-17] are often studied. The "thermodynamically mixed" blends or solutions are either of the upper critical solution temperature (UCST) [6-9, 15-17] or lower critical solution temperature (LCST) [18, 19] type. In both "mechanically mixed" and "thermodynamically mixed" blends of the UCST variety, the addition of diblock copolymer has been shown to compatibilize the blend by reducing the size of the dispersion [11-13, 20, 2i] or lowering the phase
¢Current Address: Departmentof ChemicalEngineering, University of California, Berkeley, CA.
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boundary [6-9]. Most microscopy studies [11-13, 20, 21] have demonstrated that the effect of copolymer on incompatible ("mechanically mixed") blends during the mechanical mixing is to reduce the phase sizes. The dispersed phases break up into smaller, more uniform particles, and the adhesion between the two-separated phases is enhanced. These effects are hypothesized to result from a reduction in interfacial tension between the two immicible polymers. In the case of the "thermodynamically mixed" blend, there are fewer reports on the microscopy results. Park and Roe [9] observed that the rate of late-stage coarsening of dispersed polystyrene-rich particles in a polystyrene/polybutadiene (PS/PB) mixture was appreciably reduced by the addition of block copolymer, which was also consistent with light scattering results by Roe and Kuo [8] obtained on similar blend systems. This retardation effect became more pronounced as the concentration and the molecular weight of copolymer were increased. A few theories [22-24] treat blends as macroscopically demixed systems, with the copolymer located preferentially at the interface. The copolymer is said to modify the interfacial tension between the two phases, reducing the phase-separated domain size and enhancing the adhesion between the two homopolymer phases. Noolandi and Hong [23] suggested that the reduction of interfacial tension is approximately linear with the concentration of copolymer, and at a fixed concentration, with the molecular weight of copolymer. This assumption is consistent with Park and Roe's results [9] for the late-stage coarsening of the phase-separated domains for various molecular weight diblock copolymers. Recent measurements by Anastasiadis et al. [25] have also shown a 40% reduction in interracial tension with the addition of 3.5% PS-PB diblock copolymer (number average molecular weight [26] Mn = 18,600 g/mol) into an immiscible blend of PS (M n = 2,200 g/mol) and PB (M~ = 7,800 g/mol). Using the theory of Noolandi and Hong [23], an apparent critical micelle concentration (CMC) was estimated to be 1.6 g of copolymer per 100 g of polystyrene for this system. For concentrations below the CMC, a linear decrease in interracial tension was observed with the increase of copolymer concentration. This result was consistent with that of Gaillard et al. [27] on a PS (Mn = 762,000 g/mol)/PB (Mn = 120,000 g/mol) system with a higher PS-PB diblock copolymer molecular weight (M~ = 225,000 g/mol), though a stronger interfacial reduction was observed in this case. Few measurements of the phase separation kinetics of a ternary blend containing a diblock copolymer and two homopolymers have been reported [8, 28-30]. At constant final quench temperature,
Tf, Roe and Kuo [8] found a small suppression in the growth rate of scattered intensity after adding a small amount (1% by weight) of. PS-PB diblock copolymer (Mn = 25,000 g/mol) to off-critical mixtures of a low molecular weight PS/PB (Mn -- 1900/ 2650 g/mol) polymer blend• They also reported a downward shift of 2 °C in the cloud point temperature due to the 1% copolymer additive. However, the effect of quench depth on the kinetics was not addressed in their paper. For a near-critical mixture in a PB (Mn = 165,000 g/mol) / poly(styrene-ranbutadiene) (SBR, Mn = 100,000 g/mol) / poly-((styrene-ran-butadiene)-block-butadiene)(SBR-b-PB, Mn = 211,000 g/mol) blend, Hashimoto and Izumitani [28] reported that the growth rate of the scattering intensity (i.e., concentration fluctuation) was slower for shallower than deeper quenches in each case. This implies that the growth rate was diffusion-controlled, a common phenomenon for any binary mixture. They also found that the growth rate decreased significantly with an increasing amount of block copolymer up to 6%. This decrease in diffusivity of the blend may have been due to the fact that block copolymer had a molecular weight much higher than those of PB and SBR. After taking into account the change in diffusivity as a function of quench temperature, Hashimoto and Izumitani observed that the coarsening rate for the blend containing 6% copolymer was a factor of 2.4 slower than that of a PB/ SBR binary blend. This suppression of the coarsening rate of the most probable domain size, which is related to the time dependence of the spinodal peak position, is consistent with the results obtained from a computer simulation by Kawakatsu and his coworkers [31] for an immiscible binary mixture containing surfactants. In a preliminary study [30], we reported that the kinetics of phase separation on a similar low molecular weight PSD/PB blend with 0.03 mass fraction of PSD-PB diblock additive depends strongly on the quench depth. For quenches beyond a certain depth (AT = Tc-Tf > 10 °C~, the influence of glass transition temperature, Tg, became significant. This slowing down in the coarsening is probably due to the reduced mobility in the PSD rich phase. In contrast, Lin et al. [29] reported an acceleration in the growth rate of the concentration fluctuations due to the addition of 20 % by weight of low molecular weight polymethylbutyleneb-polyethylbutylene (PM-PE, Mn = 46,000 g/mol) into a polyolefin blend (UCST type) of polymethylbutylene (PM, M. = 173,000 g/mol) and polyethylbutylene (PE, Mn = 221,000 g/mol). The experiments were all conducted at the same final quench temperature (room temperature), and the quench depth was relatively deep into the spinodal
J. Polym. Res., Vol. 3, No. 3, 139-150, July 1996
region for blends both with and without diblock copolymer added. The addition of block copolymer is expected to slow down the kinetics relative to the homopolymer blend due to the lower phase transition temperature and resulting shallower quench depth if the transport properties are not changed. This result of Lin et al. [29] suggested the importance of the viscosity and consequently the change of mass transport coefficient due to the addition of diblock copolymer. In their experiment, the diblock copolymer molecular weight was much lower than that of the blend, therefore the kinetics was accelerated. From these studies [8, 28-30], it can be seen that many variables affect the kinetics of phase separation of a polymer blend, including quench depth, proximity to the critical point and glass transition temperature, and overall viscosity of the blend as dictated by the molecular weight of each component. To gain a better understanding of the effect of diblock copolymer on the kinetics of phase separation, a systematic study, using equivalent quench depths for each blend and a closer matching of the molecular weights of each component, will be reported. A low molecular weight blend of deuterated polystyrene (PSD, weight average molecular weight, Mw = 1,000 g/mol) and polybutadiene (PB, Mw = 5,300 g/mol) was used in this study for its accessible phase boundary far above the Tg of the blend components. Thermodynamic and kinetic measurements of the phase separation process have been conducted over a wide range of polymer concentrations and quench temperatures using temperature jump light scattering (TJLS) and phase contrast optical microscopy (PCOM). It is found that this PSD/PB blend exhibits an UCST type critical behavior with a critical temperature of 51 °C at the critical composition of 0.75 mass fraction of PSD [30]. A symmetric diblock copolymer of comparable molecular weight, PSD-PB, (M~ = 5,300 - 5,300 g/mol) is then added to the blend at various concentrations. Since the molecular weights of diblock copolymer and homopolymer are similar, and the amount of copolymer additive is small, the viscosity of the blend is not likely to change significantly with the addition of the diblock. This simplifies.the interpretation of the kinetics. Moreover, the concentration of copolymer additive presented in this work is far below the CMC, which is estimated to be about 15 % by weight from the theory of Noolandi and Hong [23] and the interfacial experimental data of Anastasiadis et al. [25]. This estimated CMC is also consistent with small angle neutron scattering measurements [32]. The phase boundaries of the blends with various amounts of diblock copolymer are carefully determined by two independent techniques: TJLS and
141
PCOM. The critical temperatures, Te, obtained from these two techniques are consistent. For the kinetics study by TJLS, we compare the effect of different'amounts of diblock copolymer on the kinetics, especially the time dependence of the concentration fluctuation growth in the intermediate to late stages of the phase separation, at constant, shallow quench depths (AT = 1.6 °C) near the critical composition. The morphology of the blend in the late stage of the phase separation is also studies by PCOM. r
Experimental 1. Materials PSD of Mw = 1,000 g/mol and Mw/M n = 1.13 and diblock copolymer of PSD-PB, with PSD precursor M n = 5,100 g/mol and total Mw = 10,600 g/mol were synthesized and characterized by Professor J. W. Mays of the University of Alabama, Birmingham. PB of Mw = 5,300 g/mol and Mw/Mn = 1.07 was obtained from Goodyear Tire and Rubber Co. [33]. Before being mixed, the PSD, PB and PSD-PB diblock copolymer were dissolved in dichloromethane separately and filtered through a 0.45 mm Gelman Acrodisc filter (type CR PTFE) [33]. The purified polymers were cast directly into vials and dried in a vacuum oven at 50 °C for several days to constant weight. Polymer mixtures of various compositions were then dissolved in dichloromethane with 0.03% Goodyear Wingstay type #29 liquid antioxidant [33] and again cast into vials. After most of the solvent had evaporated, the samples were annealed under vacuum at ~ 80 °C (in the one-phase region) for several days before being pressed into film specimens. A Perkin-Elmer DSC7 instrument [33] was used to measure the glass transition temperature of the pure polymers and mixtures.
2. Temperature jump light scattering (TJLS) The time-resolved, temperature jump light scattering (TJLS) method was employed to determine the phase boundaries (coexistence and spinodal curves) [34] and to study the phase separation kinetics of the PSD/PB/PSD-PB ternary blends at various compositions. The specimens were prepared by melt pressing between two quartz plates with a teflon spacer of 200 gm to maintain a constant film thickness. All samples were annealed for a minimum of one hour at 80 °C before any measurements were taken. The TJLS apparatus is equipped with a silicon photodiode array detector with 1024 pixel elements (EG&G PARC Model 1453A) and an optical multichannel analyzer (OMA 3, Princeton Applied Research) [33] for data acquisition, as described pre-
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viously [35]. A 7 mW vertically polarized He-No laser with wavelength X = 632.8 nm is the incident light source, and various optical neutral density filters are used to attenuate the laser intensity. With a special design of collimating lenses in this instrument, scattering intensity over a range of 60 degrees can be observed simultaneously, and the time-evolution of scattered intensity in a range of 0.002 < q < 0.02 nm-t can be obtained by adjusting the detection angle. Two sets of heating blocks were used for the temperature jump experiments: one was used to preheat the sample to a temperature above the binodal temperature in the miscible region, while the other was controlled at the desired experimental temperature within 0.02 °C. The sensitivity for each pixel element of silicon detector was corrected with fluorescence radiation from Nile Blue dye (5 x 10-6 g/mL) dissolved in gelatin in a flat cell of 100 mm in thickness. 3. Phrase contrast optical microscopy (PCOM) A transmission optical microscope, equipped with phase contrast optics (Ernst Leitz, type Z)IAI2UX-Pol) [33], was used to determine the phase transition temperature and morphology of the blends. Lorlg-working-distance objectives were used to accommodate a Mettler hot-stage apparatus. The highest magnification objective available was nominally ~,t~lfffliti'ng the resolution of the optical measurements to ~ 2.5 ~tm. The pre-melted blends were pressed at a temperature above the phase boundary between a microscope slide and cover slip with a spacer to ensure a uniform thickness of 40 ~m. The films were then re-heated in the hot-stage at 130 °C to homogenize for a minimum of 30 minutes. In the determination of the phase boundary, the samples were slowly cooled at 10 °C intervals for ~ 30 minutes each, as indicated by path B of Figure 1. This method approximates a cooling rate of 0.5 °C/rain. Near the phase boundary, the intervals were shortened to 2-5 °C to more accurately pinpoint'the transition temperature.
Results and Discussions 1. Binary blend of PSD and PB A series of temperature jump (from a singlephase to a two-phase region) and reverse quench (from a two-phase to a single-phase region) light scattering experiments were used to determine the spinodal and coexistence curves as schematically shown in Figure 1. The sample was placed at the "final" experimental temperature, Tf, below the coexistence curve, after being preheated at an initial temperature, Ti, for at least one hour, as indicated
B A
~1 Ti i one-phase region
T,
III
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I~ " ~ / ~'~" ~
spinodal curve
[..,
• ::::::
two-phase region
::::::::1
:1 Composition
Figure 1. Schematic diagram of quench sequences for the TJLS experiment as indicated along path A (solid circles and solid line), and the slow cooling sequences for PCOM experiment along Path B (solid squares and dashed line).
by path A of Figure 1. The quench depth, AT, is defined as: AT = Tsp - Tt
(I)
where Tsp is the spinodal temperature. Note that near the critical composition Tsp is very close to coexistence temperature, To. The kinetics of phase separation in TJLS experiments can be determined by monitoring the change in the scattering intensity, I(q), as a function of the scattering wavevector, q, with time. The scattering wavevector, q, is defined as
q = (4nn/L) sin (0/2),
(2)
where 0 is the scattering angle, ~, is the wavelength of the incident light, and n is the refractive index of the sample. For a typical binary mixture, a peak in the scattered intensity is often observed, and this peak shifts to lower angles and increases in intensity as the sample phase separates in the unstable region (spinodal region). Typical data are shown in Figure 2 for a blend composition of PSD/PB (mass fraction of PSD, tOPSD= 0.75) at two different quench depths. The deeper quench AT = 1.8 °C is represented by dashed lines, and the shallower quench AT = 1.0 °C is represented by the solid lines. The q value of the peak position is defined as qm, and the corresponding intensity is designated as I(qm). Since the scattered intensity at a given q value is related to the amplitude of the concentration fluctuation of the corresponding size, q-l, a mean-field spinodal tempera-
J. Polym. Res., Vol. 3, No..3, 139-150, July 1996
0.8
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({OpsD= 0.75) at two different quench depths. The deeper quench, AT = 1.8 °C, is represented by dashed lines, and the shallower quench, AT = 1.0 °C, is represented by the solid lines at different times as indicated by different symbols: (0) 10 s, (x) 70 s, (.) 130 s and (A) 150 s.
ture can be determined at a fixed composition by measuring the growth rate of concentration fluctuations at various quench depths [34]. Similarly, a coexistence curve can be determined from a series of reverse quench experiments (from a two-phase to a one-phase region) by measuring the decay rate of the concentration fluctuations at various compositions. The phase transition temperature of the blend can also be determined by PCOM using a slow cooling method [36, 37]. The onset of phase separation is illustrated for a PSD/PB blend of 0.5 mass fraction of PSD in Figure 3- The single-phase blend at 90 °C is homogeneous, as shown by the featureless image in Figure 3a. The initial phase separation occurs at 40 °C and is manifested by the formation of dark regions, as shown in Figure 3b. The dark regions are PSD-rich domains in a PB-rich matrix, the contrast is a result of the difference in the refractive indices of PSD and PB (1.59 vs. 1.51) [38]. Upon further cooling, the morphology becomes more distinct, as shown in Figure 3c at a temperature of 30 °C. In addition to indicating the incipient phase separation and thus the phase boundary, PCOM was employed to study the blend morphology in the late stages of phase separation. The coarsening proceeded very slowly at room temperature for the higher PSD content blends, where the matrix is comprised of the PSD-rich phase and the Tg is closer to room temperature. Figure 4 a-c shows the morphology of three PSD/PB binary blends with the mass fraction of PSD at COpsD= 0.5, 0.7 and 0.9, respectively. These images were taken following a very slow cooling process of the blend through the phase boundary, from 130 °C to room temperature, as de-
Figure 3. Phase cohtrast optical micrographs "(PCOM3~of a PSD/ PB blend of ¢OpsD=0.5 using a step-wise cooling method along path B of the Figure 1. (3a) 90 oC, one-phase region showsno texture; (3b) 40 °C, 20 minutes shows incipient phase separation below Tc; and (3c) 30 °C , 20 minutes shows further structure
growth bf'tiS-rich domains. "'"
I
I'"'
ll~
,
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scribed by path B in Figure 1. These samples did not change significantly after sitting at room temperature overnight, but we did observe further coars-
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J. Polym. Res., Vol. 3, No. 3, 139-150, July 1996
and that at fops D ---- 0.9 the size of the phase-separated domains was barely large enough to resolve the morphology (< 2.5 gm) by PCOM. The phase diagram for the binary blend of PSD and PB without added diblock c o p o l y m e r obtained by TJLS and P C O M is shown in Figure 5. The c o e x i s t e n c e c u r v e is shown by the open circles (TJLS) and closed circles (PCOM), and the spinodal is indicated by the open triangles (TJLS). The critical t e m p e r a t u r e and c r i t i c a l c o m p o s i t i o n were 50.8+0.4 °C [39] and COpsD = 0.75 [30]. These values are consistent with previous results on a similar system with which small angle neutron scattering (SANS) was used [40]. The glass transition temperature, Tg, of the PSD-rich phase was well below room temperature, as shown by solid squares in Figure 5, and about 20 to 30 °C below the phase boundary. The values of Tc (for ¢Opso < 0.8) obtained by P C O M are slightly lower than those obtained by TJLS, but in general the agreement between the two methods is reasonable. There are two possible reasons why a lower phase boundary was obtained from PCOM: a difference in the detection limit of the two techniques, and a difference in the method of changing the temperature to approach the phase boundary (Figure 1). In our experimental set-up, the resolution of the optical microscope is limited to 2.5 mm, larger than the largest size scale detectable by light scattering (q ~ 0.003 nm -1, d = 2.0 gm), so it is not surprising that the P C O M experiment measures a slightly lower temperature for the phase boundary. The rate of phase separation of the binary P S D / PB blend at various quench depths and compositions was studied by TJLS. W e note that the gen-
60
•----Tc (TJLS) (PCOM)
5O 4o 30
T s (PSD-rich phase) IO
Figure 4. Micrographs by PCOM, using a very slowing cooling process from one phase (130 *C) to room temperature, of binary blends with COpsD = 0.5(4a), 0.7(4b), and 0.9(4c) taken after being at room temperature overnight.
ening on a time scale of weeks. It is noticeable that the average domain size of the phase-separated structures decreased with increasing mass fraction of PSD,
0
0.2 0.4 0.6 0.8 COpsD (Mass Fraction of PSD)
1.0
Figure 5. Equilibrium phase diagram of PSD (Mw = 1000 g/mol) and PB (Mw = 5300 g/tool) blend including coexistence and spinodal curves determined by TJLS. The transition temperature obtained from PCOM using a very slow cooling process is also indicated by solid circles. Ts obtained from DSC is also shown by solid squares.
J. Polym. Res., Vol. 3, No.. 3, 139-150, July 1996
eral shape of the scattering profiles, as shown in Figure 2, is broader than that expected from the Cahn-Hillard-Cook (CHC) [41, 42] prediction for a temperature jump from the one-phase to the twophase region. This broadening was also observed by Jinnai et al. [43] and may be a result of incipient phase separation as the experimental temperature passes through the unstable region during quenching of the blend. This is consistent with a broadening of the intensity profile for both lower PSD compositions and deeper temperature jumps at a fixed composition. For example, at the same initial quench temperature, the growth rate of peak intensity is quite different for the PSD/PB binary blend of C0pso = 0.75 at two different quench depths as shown previously in Figure 2. The data for a deeper quench (AT = 1.8 °C) are connected by dashed lines, and the data for a shallower quench (AT = 1.0 °C) are connected by solid lines. The data displayed are for equivalent times after quenching (t = 10 s = 0; t = 70s=x;t= 1 3 0 s = • a n d t = 1 5 0 s = A). The rate of phase separation is much slower for the shallow quench as evidenced by the scattering intensity at equivalent times being much less than that for the deeper quench. The spinodal decomposition theory of binary blends predicts a power-law time dependence of I(qm) and qra in the intermediate and late stages of growth as shown below I(qm) ~ t~ and qm ~ t-~.
(3)
The value of exponent 13 should change from 1 in the intermediate stage, to 3 in the coarsening or late-stage and exhibit a nearly exponential growth with t in the initial stage, while the value of et should change from 1/3 in the intermediate stage, to 1 in the coarsening or late-stage [44] and exhibit a constant value (to) in the initial stage. The ratio of these two exponents is predicted to be [3/tx -- 3 in the intermediate and late stages of the spinodal decomposition. Experiments have shown these predictions to hold true for most polymeric blends [34, 44, 45]. To better understand the time-dependence of the scattering behavior, peak intensity, I(qm), and position, qm, are plotted as a function of time on a double logarithmic scale in Figure 6 for three different quench depths for the binary PSD/PB blend with COasD = 0.75. As shown in Figure 6, the limiting power law exponents at late times in the accessible q-range (0.006 to 0.02 nm-~) for the time dependence of I(qm) and qm are close to 3 and - 1 , agreeing with the theoretical predictions for binary blends. In addition, the kinetics are slowest for the shallowest quench depth, AT = 1.1 °C. The agreement with theoretical predictions is
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F i g u r e 6. T J L S d a t a ( a ) P e a k i n t e n s i t y , I(qm) v e r s u s t i m e a n d ( b ) p e a k p o s i t i o n , qm v e r s u s t i m e f o r a b i n a r y P S D / P B b l e n d w i t h tOpsD = 0 . 7 5 at t h r e e d i f f e r e n t q u e n c h d e p t h s a s i n d i c a t e d b y d i f f e r e n t s y m b o l s : A T = 3 . 7 ° C ( . ) , A T = 2 . 7 ° C (11) a n d A T = 1.1 °C ( A )
best at the shallowest quench depth, AT = 1.1 °C. At deeper quench depths, the change in slope from 1 to 3 which depicts early- to late-stage behavior is smeared out due to the peak broadening described above. In addition to slower kinetics due to the proximity to critical temperature, seen in Figures 2 and 6, we observe an additional slowing down due to the influence of the glass transition for higher PSD content blends. For example, at a fixed quench depth of 3.7 °C, the kinetics of the phase separation were about, one hundred times slower for blends of fopsD = 0.85 than for blends of flopso = 0.75, as shown in Figure 7. The influence of the glass transition temperature, especially at high PSD content when the matrix becomes the PS-rich phase, is observed with or without the diblock copolymer added [30]. 2. Blends with diblock copolymer additives From TJLS measurements, we have learned that the phase boundary shifts to a lower "temperature and the critical point shifts to lower PSD content upon the addition of 0 to 0.086 mass fraction of a PSD-PB symmetric diblock copolymer [32, 46]. To understand the relationship between the phase transition temperature, Te, of the blend and the mass fraction diblock copolymer concentration, O~blk, T c as a function of f.l)blk is plotted in Figure 8. A linear
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J. Polym. Res., Vol. 3, No. 3, 139-150, July 1996
10 4
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peak position, qm versus time at same quench depth (AT = 3.7 °C) for a binary PSD/PB blend of three different compositions ¢0pSD= 0.7, 0.75 and 0.85 as indicated in the legend.
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.
u s i n g lattice cluster e x p a n s i o n theory. Again, since the c o p o l y m e r c o n c e n t r a t i o n used in this study is b e l o w the C M C , no micelle f o r m a t i o n was e x p e c t e d at any e x p e r i m e n t a l t e m p e r a t u r e s . T h e t r a n s i t i o n t e m p e r a t u r e s of b l e n d s with d i f f e r e n t a m o u n t s o f diblock c o p o l y m e r can also be d e t e r m i n e d by P C O M , as s h o w n by solid d i a m o n d s in F i g u r e 8. As previously d e s c r i b e d for Figure 5, h o w e v e r , the values o f Tc o b t a i n e d f r o m P C O M are s o m e w h a t l o w e r than those from T J L S b e c a u s e of d i f f e r e n c e s in resolution and c o n s e q u e n t delays in the d e t e c t i o n of p h a s e s e p a r a t e d d o m a i n s by P C O M . S i n c e the p h a s e b o u n d a r y shifts to l o w e r temperatures with the addition o f the d i b l o c k copolymer, and the q u e n c h depths, p r o x i m i t y to Tc and Tg c a n also a f f e c t the k i n e t i c s , a c o n s t a n t , s h a l l o w q u e n c h d e p t h was used to i n v e s t i g a t e the effect o f d i b l o c k c o p o l y m e r additives on the k i n e t i c s of p h a s e s e p a r a t i o n for e a c h blend. F i g u r e 9 shows I(qm) n o r m a l i z e d by I(qm, t = 0) (Figure 9a) and qm (Figure 9b) as a f u n c t i o n of time on a d o u b l e logarithmic scale for the near critical b l e n d with 0~PSD = 0.7 ( P S D / P B : 7 0 / 3 0 ) with various a m o u n t s o f d i b l o c k c o p o l y m e r . All data p r e s e n t e d here were taken at the s a m e q u e n c h depth, AT = 1.6 °C. T h e g r o w t h rate o f the s c a t t e r e d p e a k i n t e n s i t y greatly d e c r e a s e d as m o r e d i b l o c k c o p o l y m e r was added, as s h o w n in
•
Fixed Ratio of PSD/PB (70130)
50
I
(a)
-.- T
