Binary Blend Compatibility of PVA and PMMA
J. Phys. Chem. B, Vol. 109, No. 32, 2005 15619 blend miscibility patterns for the lesser and higher time intervals. It may be noted that phase separation proceeds via diffusion of the components through the interfaces. Thus, it appears that hydrodynamics is important, especially in the later stages of phase separation, creating more flexible barriers for further diffusion.40 The results of this study are in agreement with our experimental observations.4 Conclusions
Figure 15. Mesophase order parameter of PVA as a function of volume fraction of PMMA for 5 µs (4) and 200 µs simulation time (2) for a 50:50 blend of PVA/PMMA and for 5 µs (O) and 200 µs (b) simulation time for an 80:20 PVA/PMMA blend.
where ηi is dimensionless density (volume fraction) for species i. Order parameters with large values indicate a strong phase segregation, which is observed for the 50:50 blend. Conversely, very small values of Pi indicate the 80:20 blend. As displayed in Figure 15, it can be seen that for the 50:50 blend, the order parameter is >0.1, indicating the immiscible nature of the blend, whereas for the 80:20 blend, the order parameter is 60 wt % of PVA. This was confirmed by differential scanning calorimetry; furthermore, blends exhibited an anomalous thermodynamic behavior. The concentration dependence of χ calculated from MD calculations exhibits trends similar to those of the concentration dependence of the melting temperature and χ values calculated from simulation procedure matched with experimental results. It is demonstrated that NVT-based MD simulations are useful in understanding molecular level interactions between the chosen PVA and PMMA polymers and to understand the forces responsible for investigating the miscibility of PVA/PMMA blends. Because the size of the blend system is large, MD simulations consumed a bit longer computer time, but results are encouraging. The χ values of the blends that are
Figure 16. Density profile slices for a 50:50 blend of PVA/PMMA for different simulation times: (a) 5 µs; (b) 200 µs. Green represents pristine PVA; red, pristine PMMA; and gray, the shaded pockets, which correspond to the interface between them.
Figure 17. Density profile slices for an 80:20 blend of PVA/PMMA for the simulation times of (a) 5 µs and (b) 200 µs. Color notations are the same as mentioned in Figure 16.
15620 J. Phys. Chem. B, Vol. 109, No. 32, 2005 below 0.133 (i.e., below the χcritical value) indicated miscibility of PVA/PMMA blends, indicating atomistic simulation is in agreement with the mesoscopic simulation. Furthermore, an order parameter value of 60 wt %. Mesoscopic density slices (regions) confirm phase separation between PVA and PMMA, further supporting the atomistic simulation calculations. From the free energy density calculations, it is observed that the system approaches stability with time. Similar computations on other polymeric systems are currently in progress and will be published in the future. Acknowledgment. We acknowledge financial support from University Grants Commission (UGC), New Delhi, India, for major funding (F1-41/2001/CPP-II) to establish the Center of Excellence in Polymer Science at Karnatak University, Dharwad. We are also thankful to Mr. Anand Gupta of Apsara Innovations, Bangalore, India, for providing us a trial MesoDyn program used in this research. We also thank Dr. B. V. K. Naidu for his help in the project. This paper is Center of Excellence in Polymer Science communication #65. References and Notes (1) Munk, P.; Aminabhavi, T. M. Introduction to Macromolecular Science; Wiley-VCH: New York, 2002. (2) Seymour, R. B.; Carraher, C. E., Jr., Polymer Chemistry: An Introduction; Dekker: New York, 1988. (3) Carraher, C. E., Giant Molecules: Essential Materials for EVeryday LiVing and Problem SolVing, 2nd ed.; Wiley-Interscience: New York, 2003. (4) Adoor, S. G.; Manjeshwar, L. M.; Krishana Rao, K. S. V.; Naidu, B. V. K.; Aminabhavi, T. M. J. Appl. Polym. Sci. 2005, in press. (5) Krause, S. Polymer-Polymer Compatibility in Polymer Blends; Paul, D. R., Newman, S., Eds.; Academic Press: New York, 1978; Vol. 1. (6) Naidu, B. V. K.; Sairam, M.; Raju, K. V. S. N.; Aminabhavi, T. M. Carbohydr. Polym. 2005, 61, 52. (7) Papke, N.; Karger-Kocsis. Polymer 2001, 42, 1109. (8) George, J.; Joseph, R.; Thomas, S.; Varughese, K. T. J. Appl. Polym. Sci. 1995, 57, 449. (9) Naidu, B. V. K.; Mallikarjuna, N. N.; Aminabhavi, T. M. J. Appl. Polym. Sci. 2004, 94, 2548.
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