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SMMA blends by PAL method
NIM B Beam Interactions with Materials & Atoms
Nuclear Instruments and Methods in Physics Research B 245 (2006) 491–494 www.elsevier.com/locate/nimb
Dynamics study of free volume properties of SMA/SMMA blends by PAL method Z.Y. Jiang
a,b
, X.Q. Jiang c, Y.J. Huang a, J. Lin a, S.M. Li a, S.Z. Li a, Y.F. Hsia
a,*
a
c
Department of Physics, Nanjing University, 22 Hankou Road, Nanjing 210093, China b Department of Physics, Yili Normal Institute, Yining 835000, China Department of Polymer Science and Engineering, College of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China Received 18 January 2005; received in revised form 15 October 2005 Available online 27 December 2005
Abstract Miscibility of poly(styrene-co-maleic anhydride) (containing 7 wt% maleic anhydride)/poly(styrene-co-methyl methacrylate) (containing 40 wt% styrene) blends were previously studied. It was obtained that SMA70 (containing 70 wt% of SMA in SMA/SMMA blends) is miscible in molecular level but SMA20 is not. In this paper, the two blends selected were used to investigate the temperature dependence of free volume parameters. It showed there are different deviations of free volume parameters in SMA20 and SMA70, and it was interesting that temperature dependence of ortho-positronium lifetime s3 of the SMA20 mixture exhibits two breaks in the range temperature from 90 C to 120 C, which revealed that the mixture has two glass transition ranges. Also, ortho-positronium lifetime s3 of the SMA20 mixture is nearly constant in the temperature range from 130 C to 160 C. These indicated that SMA20 blend is phase-separated in room temperature and become miscible above 130 C, which may be due to steric hindrance effect of phenyl rings of SMMA and SMA. From the deviation of o-Ps lifetimes of SMA70, the single glass transition temperature of SMA70 blend was shown. Combining the previous study, it was further concluded that PAL method seems to be a powerful method to detect in situ phase behavior of immiscible polymer blends and glass transition of miscible polymer blends. 2005 Elsevier B.V. All rights reserved. PACS: 78.70.B; 36.10.D; 64.75 Keywords: Polymer blends; Positron annihilation; Phase separation; Free volume properties; Miscibility; Glass transition
1. Introduction In the past few decades, polymer blends have been an open subject of intensive investigation in both industrial and academic domain. Miscibility and phase separation behavior of polymer blends that depends largely on the specific interactions between polymers have received significant attention in the polymer application. Miscibility of polymer blend has been judged by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA),
*
Corresponding author. Tel./fax: +86 25 8359 4234. E-mail addresses: [email protected] (Z.Y. Jiang), [email protected] (Y.F. Hsia). 0168-583X/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.11.003
dielectric measurements and nuclear magnetic resonance (NMR) and so on. Positron annihilation lifetime (PAL) spectroscopy is sensitive to small change in free volume in polymer and polymer blends resulting from temperature changes and composition changes [1–8]. The pick-off lifetime s3 of ortho-positronium (o-Ps) is correlated to the free volume hole sizes in polymer and polymer blends, and the corresponding intensity which is proportional to the number of annihilations, may be used to estimate relative number of free volume hole. Many studies about polymer blends by PAL method were done to investigate correlation between miscibility and free volume properties [9–11], some other studies were done to reveal the temperature dependence of free volume parameters in polymer or polymer
Z.Y. Jiang et al. / Nucl. Instr. and Meth. in Phys. Res. B 245 (2006) 491–494
blends [12,13]. Recently, it has been attempted to use PAL method to explore kinetics of phase separation in the miscible blends [14]. It proved that PAL method is a powerful tool to study glass transition and phase behavior of polymer blends. In this paper, the different composition SMA/SMMA blends selected were studied. It is well known that there exists miscible window in SMA/SMMA blend pairs due to specific interaction between polymers. In the previous study [15], miscibility of the different compositional SMA/SMMA blends was studied. It was concluded that a difference of SMA (containing 7 wt% MA) component in SMA/SMMA blends marked a transition from miscible to immiscible SMA/SMMA blends. The boundary encompassed a very small compositional region, estimated from 40 to 60 wt% SMA in SMA/SMMA blends, where partial miscibility was clearly evident. The present study was undertaken by PAL method to investigate temperature dependence of phase behavior in the immiscible SMA20 and the miscible SMA70, which was explained by studying the different deviations of free volume parameters versus temperature between SMA20 and SMA70. 2. Experimental 2.1. Material, sample preparation and characterization The random copolymer of styrene-co-maleic anhydride (SMA), containing 7 wt% maleic anhydride, and polydisperse copolymer of styrene-co-methylmethacrylate (SMMA), containing 40% styrene, were purchased from Aldrich. The molecular characteristics of SMA and SMMA used in this study were described in the former study [15]. Tetrahydrofuran (THF) was used without furthering purification. Blends of SMA/SMMA comprised of the required weight fraction of both SMMA and SMA containing variable MA content were codissolved in THF solvent in concentration of 5 g/100 ml at room temperature, and the mixtures were stirred by magnetic force stirrer for 8 h for complete mixing at a appropriate rotating speed and cast onto a Teflon plate. The sample films were dried at room temperature for 3 days and then in a vacuum oven at 25 C (±0.2 C) for 4 days and at 60 C (±0.2 C) for 2 days to remove the residual solvent slowly. Faster evaporation results in bubbles bringing. The samples with 0.30 mm thickness were stacked tightly together to 1.2 mm for the PALS measurements. All the samples used were annealed at 130 C for 20 min before PALS measurements.
activity of approximate 7.0 · 105 Bq was deposited between two 3 lm thick Ti foils. The source was placed between two identical pieces sample with 1 mm thickness. After a sample was kept at each temperature for 1 h, then the spectroscopy begin to work. A positron lifetime spectrum was collected after 12 000 s. The spectra were analyzed with POSITRONFIT software into three mean lifetimes and intensities without source correction or any constrains. The variations of the fit (v2) were smaller than 1.15. The longest-lived component s3 of lifetimes was attributed to o-Ps annihilation, its yield is given as I3, that is the relative intensity of the longest-lived component. 3. Results and discussion 3.1. Temperature dependence of free volume parameters in SMA20 Blend Temperature dependence of free volume parameters of SMA20 blend was studied using PAL method. It is interesting that the variation of o-Ps lifetime s3 versus temperature in SMA20 blend which is shown in Fig. 1 is quite different from that in other polymer blends selected in the former study [4,16,17]. The inflection point temperature at 50 C is identified as b-transition related to segment motions of the phenyl ring molecules. Variation of o-Ps lifetime s3 with temperature in temperature range between two glass transition temperatures of pure SMMA and pure SMA is not linear relationship but complicated. It can be obviously observed that there exists two inflexions in the temperature range and SMA copolymer and SMMA copolymer in the SMA20 almost respectively lonely experience their own glass transition ranges. It seems to be due to the presence of specific repulsive force of molecules [15] between SMA and SMMA in the SMA20 blend. This result further proved that the SMA20 blend is immiscible [15] at the room temperature. After 110 C, the value of s3 increase,
3.2
3.0
o-Ps lifetimes (ns)
492
2.8
2.6
Tβ 2.4
2.2. Positron annihilation lifetime (PAL) spectroscopy
2.2
Positron lifetime measurements were conducted with conventional fast–fast coincident positron lifetime spectrometer with a time resolution of about 290 ps at 30– 190 C at a vacuum chamber. The source 22Na with an
2.0 20
40
60
80
100
120
140
160
180
200
Temperature (°C) Fig. 1. Temperature dependence of o-Ps lifetime s3 in SMA20 blend.
Z.Y. Jiang et al. / Nucl. Instr. and Meth. in Phys. Res. B 245 (2006) 491–494
3.2. Temperature dependence of free volume parameters in SMA70 blend Temperature dependence of the o-Ps lifetime s3 in SMA 70 blend is shown in Fig. 3. It is clearly observed that the o-Ps lifetime increases with increasing temperature, which demonstrates an increase of the free volume hole size with temperature. The temperature range of about 50 C may be response to the so-called b-transition of the blends, which is believed to result from intramolecular relaxation associated with the phenyl groups [18]. The temperature at about 100 C is defined as glass transition temperature Tg of the SMA70, in which a sudden increase in thermal expansion coefficient of the free volume cavities. It is certain that the SMA70 has only one glass transition temperature, so it is further proved that SMA70 is miscible in molecular level. The corresponding variation of the o-Ps intensity I3 is presented in Fig. 4. It is observed that linear change of I3 3.0
2.8
o-Ps lifetime τ3 (ns)
that is due to normal thermal expansion of polymer blends. The o-Ps lifetime begins decrease after 120 C, and then almost keep invariable in error range of s3 in the temperature region from 130 C to 160 C. The phenomena can be due to steric hindrance effect of phenyl rings of SMMA and that of SMA confining the increasing of free volume hole, and interdiffusion between SMA and SMMA inducing intermolecular rearrangement. Those are the reasons for the collapse of the holes of free volume in SMA20 blend. It suggests that SMA20 blend could become miscible blend above 120 C. The o-Ps lifetime steplikes at 170 C due to both main segment motions of SMA and SMMA are superior to impact compression of copolymer–copolymer interaction between SMA and SMMA. So variation of o-Ps lifetime (relative to free volume hole radius) with temperature can provide the direct information of phase behavior change in the immiscible blend. The variation of o-Ps intensity I3 in SMA20 blend versus temperature is shown in Fig. 2. It is also observed there is b-transition at 50 C which is related to segment motions of the phenyl ring molecules. At the temperature range of from 50 C to 100 C, the variation of o-Ps intensity with temperature represents linear relationship, which means phase behaviors of SMA20 blend do no change in the temperature range. From Fig. 2, it is difficult to determine glass transition of SMA20 blend, which can be due to specific structure of SMA and SMMA causing the complication of o-Ps intensities in the vicinity of Tg. From 130 C to 160 C, variation of o-Ps intensity I3 with temperature is nearly constant, which may be also due to steric hindrance effect of phenyl groups of SMMA and SMA, that is the reason for limitation of the numbers of free volume hole in SMA20 blend. At 170 C, pronounced rise of o-Ps intensity I3 signifies the main chain motions of SMMA and SMA are superior to the steric hindrance effect of phenyl groups.
493
2.6
Tg 2.4
Tβ
2.2
2.0
20
40
60
80
100
120
140
160
180
200
Temperature (°C)
Fig. 3. o-Ps lifetimes in SMA70 blend versus temperature. Tb 31
27
30
26
o-Ps intensity I3 (%)
o-Ps intensities I3 (%)
29 28 27 26 25
Tβ
24 23
25 24 23 22 21
22
20 20
40
60
80
100
120
140
160
180
200
Temperature (°C)
Fig. 2. Temperature dependence of o-Ps intensity I3 in SMA20 blend.
20
40
60
80
100
120
140
160
180
200
Temperature (°C) Fig. 4. o-Ps intensities I3 in SMA70 blend versus temperature.
494
Z.Y. Jiang et al. / Nucl. Instr. and Meth. in Phys. Res. B 245 (2006) 491–494
with temperature in the SMA70 blend below 90 C, and fluctuation change of I3 above 90 C, which can be due to structure relaxation of SMMA and SMA. To make its problem clear, further study is needed. The specific feature of the variations of free volume parameters in the mixture of SMA (containing 7% MA) and SMMA (containing 40%) is exciting our more attention to studying systemically temperature dependence of phase behavior of the different composition blends by the other methods such as nuclear magnetic resonance (NMR) method and atomic force microscopy (AFM) method, and further exploration about dynamic mechanism of phase behavior in polymer blends is needed as well. 4. Conclusion The positron annihilation lifetime measurements as a function of temperature were made in the miscible SMA70 blend and the immiscible SMA20 blend. From this study, it was seen that the change of free volume parameters in SMA20 blend as a function of temperature is completely different from those in SMA70 blend. It was interesting that the negative deviation of s3 of SMA20 is very large relative to expansion of the normal free volume hole. We thought that steric hindrance effect of phenyl rings of SMMA and SMA on free volume expansion may be dominant over main chain motion of polymer blends in the temperature region above 130 C, resulting in invariation of free volume hole values of SMA20 blend. It showed that the immiscible SMA20 blend converts to miscible blend above 130 C. However, the miscible SMA70 blend presented the normal variation of free volume parameters as a function of temperature, from which single
glass transition of SMA70 has been determined. From the study, it concluded that PAL method is a useful tool to study in situ temperature dependence of phase behavior of immiscible polymer blends and glass transition temperature of miscible blends. References [1] J.C. Machado, G. Goulart Silva, L.S. Soares, J. Polym. Sci. Part B: Polym. Phys. 38 (2000) 1045. [2] S.Y. Kwak, S.H. Kim, T. Suzuki, Polymer 45 (2004) 8153. [3] T.-T. Hsieh, C. Tiu, G.P. Simon, Polymer 41 (2000) 1045. [4] H.L. Li, Y. Ujihira, A. Nanasawa, Y.C. Jean, Polymer 40 (1999) 349. [5] Y. Li, R. Zhang, H. Chen, J. Zhang, R. Suzuki, T. Ohdaira, M.M. Feldstein, Y.C. Jean, Biomacromolecules 4 (2003) 1856. [6] S.J. Tao, J. Chem. Phys. 56 (1972) 5499. [7] Y.C. Jean, in: A. Dupapsquier, A.P. Mills Jr. (Eds.), Positron Spectroscopy of Solids, IOS Press, Amsterdam, 1995, p. 563. [8] P.E. Mallon, in: Y.C. Jean, P.E. Mallon, D.M. Schraderm (Eds.), Principles and Applications of Positron and Positronium Chemistry, World Scientific Publisher, 2003, p. 253. [9] J. Liu, Y.C. Jean, Macromolecules 28 (1995) 5774. [10] Y.H. Hu, C.Z. Qi, W.M. Liu, B.Y. Wang, H.T. Zheng, X.D. Sun, X.M. Zheng, J. Appl. Polym. Sci. 90 (2003) 1507. [11] T.T. Hsieh, C. Tiu, P. George, Polymer 42 (2001) 8007. [12] C. Wa¨stlund, M. Schmidt, S. Schantz, F.H.J. Maurer, Polym. Eng. Sci. 38 (1998) 1286. [13] C.L. Wang, Y. Kobayashi, W. Zheng, C. Zhang, Polymer 42 (2001) 2359. [14] K. Gunther-Schade, D.W. Schubert, F. Faupel, Macromolecules 35 (2002) 9074. [15] Z.Y. Jiang, X.Q. Jiang, Y.X. Yang, Y.J. Huang, H.B. Huang, Y.F. Hsia, Nucl. Instr. and Meth. B 229 (2005) 309. [16] D. Lin, S.J. Wang, J. Phys.: Condens. Matter 4 (1992) 3331. [17] C.Q. He, T. Suzuki, V.P. Shantarovich, K. Kondo, Y. Ito, Chem. Phys. 286 (2003) 3939. [18] Z.L. Peng, B.G. Olson, J.D. McGervey, A.M. Jamieson, Polymer 40 (1999) 3033.
Nuclear Instruments and Methods in Physics Research B 245 (2006) 491–494 www.elsevier.com/locate/nimb
Dynamics study of free volume properties of SMA/SMMA blends by PAL method Z.Y. Jiang
a,b
, X.Q. Jiang c, Y.J. Huang a, J. Lin a, S.M. Li a, S.Z. Li a, Y.F. Hsia
a,*
a
c
Department of Physics, Nanjing University, 22 Hankou Road, Nanjing 210093, China b Department of Physics, Yili Normal Institute, Yining 835000, China Department of Polymer Science and Engineering, College of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China Received 18 January 2005; received in revised form 15 October 2005 Available online 27 December 2005
Abstract Miscibility of poly(styrene-co-maleic anhydride) (containing 7 wt% maleic anhydride)/poly(styrene-co-methyl methacrylate) (containing 40 wt% styrene) blends were previously studied. It was obtained that SMA70 (containing 70 wt% of SMA in SMA/SMMA blends) is miscible in molecular level but SMA20 is not. In this paper, the two blends selected were used to investigate the temperature dependence of free volume parameters. It showed there are different deviations of free volume parameters in SMA20 and SMA70, and it was interesting that temperature dependence of ortho-positronium lifetime s3 of the SMA20 mixture exhibits two breaks in the range temperature from 90 C to 120 C, which revealed that the mixture has two glass transition ranges. Also, ortho-positronium lifetime s3 of the SMA20 mixture is nearly constant in the temperature range from 130 C to 160 C. These indicated that SMA20 blend is phase-separated in room temperature and become miscible above 130 C, which may be due to steric hindrance effect of phenyl rings of SMMA and SMA. From the deviation of o-Ps lifetimes of SMA70, the single glass transition temperature of SMA70 blend was shown. Combining the previous study, it was further concluded that PAL method seems to be a powerful method to detect in situ phase behavior of immiscible polymer blends and glass transition of miscible polymer blends. 2005 Elsevier B.V. All rights reserved. PACS: 78.70.B; 36.10.D; 64.75 Keywords: Polymer blends; Positron annihilation; Phase separation; Free volume properties; Miscibility; Glass transition
1. Introduction In the past few decades, polymer blends have been an open subject of intensive investigation in both industrial and academic domain. Miscibility and phase separation behavior of polymer blends that depends largely on the specific interactions between polymers have received significant attention in the polymer application. Miscibility of polymer blend has been judged by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA),
*
Corresponding author. Tel./fax: +86 25 8359 4234. E-mail addresses: [email protected] (Z.Y. Jiang), [email protected] (Y.F. Hsia). 0168-583X/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.11.003
dielectric measurements and nuclear magnetic resonance (NMR) and so on. Positron annihilation lifetime (PAL) spectroscopy is sensitive to small change in free volume in polymer and polymer blends resulting from temperature changes and composition changes [1–8]. The pick-off lifetime s3 of ortho-positronium (o-Ps) is correlated to the free volume hole sizes in polymer and polymer blends, and the corresponding intensity which is proportional to the number of annihilations, may be used to estimate relative number of free volume hole. Many studies about polymer blends by PAL method were done to investigate correlation between miscibility and free volume properties [9–11], some other studies were done to reveal the temperature dependence of free volume parameters in polymer or polymer
Z.Y. Jiang et al. / Nucl. Instr. and Meth. in Phys. Res. B 245 (2006) 491–494
blends [12,13]. Recently, it has been attempted to use PAL method to explore kinetics of phase separation in the miscible blends [14]. It proved that PAL method is a powerful tool to study glass transition and phase behavior of polymer blends. In this paper, the different composition SMA/SMMA blends selected were studied. It is well known that there exists miscible window in SMA/SMMA blend pairs due to specific interaction between polymers. In the previous study [15], miscibility of the different compositional SMA/SMMA blends was studied. It was concluded that a difference of SMA (containing 7 wt% MA) component in SMA/SMMA blends marked a transition from miscible to immiscible SMA/SMMA blends. The boundary encompassed a very small compositional region, estimated from 40 to 60 wt% SMA in SMA/SMMA blends, where partial miscibility was clearly evident. The present study was undertaken by PAL method to investigate temperature dependence of phase behavior in the immiscible SMA20 and the miscible SMA70, which was explained by studying the different deviations of free volume parameters versus temperature between SMA20 and SMA70. 2. Experimental 2.1. Material, sample preparation and characterization The random copolymer of styrene-co-maleic anhydride (SMA), containing 7 wt% maleic anhydride, and polydisperse copolymer of styrene-co-methylmethacrylate (SMMA), containing 40% styrene, were purchased from Aldrich. The molecular characteristics of SMA and SMMA used in this study were described in the former study [15]. Tetrahydrofuran (THF) was used without furthering purification. Blends of SMA/SMMA comprised of the required weight fraction of both SMMA and SMA containing variable MA content were codissolved in THF solvent in concentration of 5 g/100 ml at room temperature, and the mixtures were stirred by magnetic force stirrer for 8 h for complete mixing at a appropriate rotating speed and cast onto a Teflon plate. The sample films were dried at room temperature for 3 days and then in a vacuum oven at 25 C (±0.2 C) for 4 days and at 60 C (±0.2 C) for 2 days to remove the residual solvent slowly. Faster evaporation results in bubbles bringing. The samples with 0.30 mm thickness were stacked tightly together to 1.2 mm for the PALS measurements. All the samples used were annealed at 130 C for 20 min before PALS measurements.
activity of approximate 7.0 · 105 Bq was deposited between two 3 lm thick Ti foils. The source was placed between two identical pieces sample with 1 mm thickness. After a sample was kept at each temperature for 1 h, then the spectroscopy begin to work. A positron lifetime spectrum was collected after 12 000 s. The spectra were analyzed with POSITRONFIT software into three mean lifetimes and intensities without source correction or any constrains. The variations of the fit (v2) were smaller than 1.15. The longest-lived component s3 of lifetimes was attributed to o-Ps annihilation, its yield is given as I3, that is the relative intensity of the longest-lived component. 3. Results and discussion 3.1. Temperature dependence of free volume parameters in SMA20 Blend Temperature dependence of free volume parameters of SMA20 blend was studied using PAL method. It is interesting that the variation of o-Ps lifetime s3 versus temperature in SMA20 blend which is shown in Fig. 1 is quite different from that in other polymer blends selected in the former study [4,16,17]. The inflection point temperature at 50 C is identified as b-transition related to segment motions of the phenyl ring molecules. Variation of o-Ps lifetime s3 with temperature in temperature range between two glass transition temperatures of pure SMMA and pure SMA is not linear relationship but complicated. It can be obviously observed that there exists two inflexions in the temperature range and SMA copolymer and SMMA copolymer in the SMA20 almost respectively lonely experience their own glass transition ranges. It seems to be due to the presence of specific repulsive force of molecules [15] between SMA and SMMA in the SMA20 blend. This result further proved that the SMA20 blend is immiscible [15] at the room temperature. After 110 C, the value of s3 increase,
3.2
3.0
o-Ps lifetimes (ns)
492
2.8
2.6
Tβ 2.4
2.2. Positron annihilation lifetime (PAL) spectroscopy
2.2
Positron lifetime measurements were conducted with conventional fast–fast coincident positron lifetime spectrometer with a time resolution of about 290 ps at 30– 190 C at a vacuum chamber. The source 22Na with an
2.0 20
40
60
80
100
120
140
160
180
200
Temperature (°C) Fig. 1. Temperature dependence of o-Ps lifetime s3 in SMA20 blend.
Z.Y. Jiang et al. / Nucl. Instr. and Meth. in Phys. Res. B 245 (2006) 491–494
3.2. Temperature dependence of free volume parameters in SMA70 blend Temperature dependence of the o-Ps lifetime s3 in SMA 70 blend is shown in Fig. 3. It is clearly observed that the o-Ps lifetime increases with increasing temperature, which demonstrates an increase of the free volume hole size with temperature. The temperature range of about 50 C may be response to the so-called b-transition of the blends, which is believed to result from intramolecular relaxation associated with the phenyl groups [18]. The temperature at about 100 C is defined as glass transition temperature Tg of the SMA70, in which a sudden increase in thermal expansion coefficient of the free volume cavities. It is certain that the SMA70 has only one glass transition temperature, so it is further proved that SMA70 is miscible in molecular level. The corresponding variation of the o-Ps intensity I3 is presented in Fig. 4. It is observed that linear change of I3 3.0
2.8
o-Ps lifetime τ3 (ns)
that is due to normal thermal expansion of polymer blends. The o-Ps lifetime begins decrease after 120 C, and then almost keep invariable in error range of s3 in the temperature region from 130 C to 160 C. The phenomena can be due to steric hindrance effect of phenyl rings of SMMA and that of SMA confining the increasing of free volume hole, and interdiffusion between SMA and SMMA inducing intermolecular rearrangement. Those are the reasons for the collapse of the holes of free volume in SMA20 blend. It suggests that SMA20 blend could become miscible blend above 120 C. The o-Ps lifetime steplikes at 170 C due to both main segment motions of SMA and SMMA are superior to impact compression of copolymer–copolymer interaction between SMA and SMMA. So variation of o-Ps lifetime (relative to free volume hole radius) with temperature can provide the direct information of phase behavior change in the immiscible blend. The variation of o-Ps intensity I3 in SMA20 blend versus temperature is shown in Fig. 2. It is also observed there is b-transition at 50 C which is related to segment motions of the phenyl ring molecules. At the temperature range of from 50 C to 100 C, the variation of o-Ps intensity with temperature represents linear relationship, which means phase behaviors of SMA20 blend do no change in the temperature range. From Fig. 2, it is difficult to determine glass transition of SMA20 blend, which can be due to specific structure of SMA and SMMA causing the complication of o-Ps intensities in the vicinity of Tg. From 130 C to 160 C, variation of o-Ps intensity I3 with temperature is nearly constant, which may be also due to steric hindrance effect of phenyl groups of SMMA and SMA, that is the reason for limitation of the numbers of free volume hole in SMA20 blend. At 170 C, pronounced rise of o-Ps intensity I3 signifies the main chain motions of SMMA and SMA are superior to the steric hindrance effect of phenyl groups.
493
2.6
Tg 2.4
Tβ
2.2
2.0
20
40
60
80
100
120
140
160
180
200
Temperature (°C)
Fig. 3. o-Ps lifetimes in SMA70 blend versus temperature. Tb 31
27
30
26
o-Ps intensity I3 (%)
o-Ps intensities I3 (%)
29 28 27 26 25
Tβ
24 23
25 24 23 22 21
22
20 20
40
60
80
100
120
140
160
180
200
Temperature (°C)
Fig. 2. Temperature dependence of o-Ps intensity I3 in SMA20 blend.
20
40
60
80
100
120
140
160
180
200
Temperature (°C) Fig. 4. o-Ps intensities I3 in SMA70 blend versus temperature.
494
Z.Y. Jiang et al. / Nucl. Instr. and Meth. in Phys. Res. B 245 (2006) 491–494
with temperature in the SMA70 blend below 90 C, and fluctuation change of I3 above 90 C, which can be due to structure relaxation of SMMA and SMA. To make its problem clear, further study is needed. The specific feature of the variations of free volume parameters in the mixture of SMA (containing 7% MA) and SMMA (containing 40%) is exciting our more attention to studying systemically temperature dependence of phase behavior of the different composition blends by the other methods such as nuclear magnetic resonance (NMR) method and atomic force microscopy (AFM) method, and further exploration about dynamic mechanism of phase behavior in polymer blends is needed as well. 4. Conclusion The positron annihilation lifetime measurements as a function of temperature were made in the miscible SMA70 blend and the immiscible SMA20 blend. From this study, it was seen that the change of free volume parameters in SMA20 blend as a function of temperature is completely different from those in SMA70 blend. It was interesting that the negative deviation of s3 of SMA20 is very large relative to expansion of the normal free volume hole. We thought that steric hindrance effect of phenyl rings of SMMA and SMA on free volume expansion may be dominant over main chain motion of polymer blends in the temperature region above 130 C, resulting in invariation of free volume hole values of SMA20 blend. It showed that the immiscible SMA20 blend converts to miscible blend above 130 C. However, the miscible SMA70 blend presented the normal variation of free volume parameters as a function of temperature, from which single
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