Molecular Dynamics Simulations on the Blends of Poly(vinyl pyrrolidone) and Poly(bisphenol-A-ether sulfone) S. S. Jawalkar, S. K. Nataraj, A. V. Raghu, T. M. Aminabhavi Molecular Modeling Division, Center of Excellence in Polymer Science, Karnatak University, Dharwad, India 580 003 Received 11 June 2007; accepted 1 January 2008 DOI 10.1002/app.28005 Published online 6 March 2008 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Molecular simulations are the most impor- tant tools to predict the properties of polymers and their blends. In this work, we have predicted the blend incom- patibility of poly(n-vinyl pyrrolidone) (PVP) and poly(bi- sphenol-A-ether sulfone) (PES). Atomistic simulations were performed to compute the Flory-Higgins interaction parameter over all the compositions ranging from 90 to 10% of the individual polymers, which confirmed that the blends are incompatible (Bhattacharya et al., J Membr Sci 2003, 227, 23). Kinetics of phase separation was examined via density profiles calculated using MesoDyn approach. For incompatible blends, the critical value of 0.32 com- puted from the Flory-Huggins theory agreed with the value of 0.29, suggesting the validity of our ap- proach. Ó 2008 Wiley Periodicals, Inc. J Appl Polym Sci 108: 3572–3576, 2008 Key words: molecular dynamics; cohesive energy density; Flory-Huggins theory; interaction parameter; blend com- patibility INTRODUCTION Poly(vinyl pyrolidone) (PVP) and poly(bisphenol-A- ether sulfone) (PES) are the most widely used poly- mers in drug delivery and separation science. 1,2 X-ray diffraction (XRD) and scanning electron mi- croscopy (SEM) indicated that these polymers are in- compatible. 1 Blend compatibility/incompatibility of polymers can be studied by innumerable experimen- tal techniques, 3,4 because readily miscible polymer blends are seldom obtained. However, it is impor- tant to determine the properties of the blends before their intended applications. Despite the progress made in experimental tools to study the blend com- patibility, theoretical studies are somewhat rare. 5–9 Atomistic simulations would provide reliable predic- tions on the blend properties of polymers provided accurate experimental parameters are used in the simulations. Self-consistent field theory (SCFT) has led to the investigation on the microphase separation of diblock and triblock copolymers. 10 In contrast, molecular dynamic (MD) simulations would permit the modeling of polymeric chains during the phase separation. On the other hand, mesoscopic 11,12 (MesoDyn) and dissipative particle dynamic (DPD) methods 13 treat the polymeric chains in a coarse- grained (mesoscopic) level by grouping the atoms together up to the persistence length of the polymer chains. This treatment can also be extended to length and time scales by several orders of magnitude com- pared to the atomistic simulations. MesoDyn deals with the dynamic mean field density functional theory in which dynamics of phase separation is described by the Langevin-type equations to investi- gate polymer diffusion. This study is a continuation of our earlier work 14–18 in predicting blend compatibility/incompatibility of polymers. In this study, atomistic and mesoscopic calculations have been performed on PVP and PES polymers to confirm their immiscibility through the calculations of Flory-Huggins 19 interaction parame- ter. The computed results are in agreement with the experimental observations 1 of immiscible behavior of these polymers in solid film forms investigated by XRD and SEM techniques along with theoretical pre- dictions based on the Flory-Huggins theory. Our present MD simulations also suggested that the blends of PVP and PES are immiscible in the entire range of their compositions. Even though the exact reason for this type of behavior is not fully explored, our predicted results and published experimental data agreed that the presence of aromatic rings and bulky CH 3 group in PES might restrict the free rota- tion around CC bond of its backbone, thereby hindering the chain mobility. On the other hand, Correspondence to: T. M. Aminabhavi (aminabhavi@ yahoo.com). Contract grant sponsor: University Grants Commission (UGC), New Delhi, India; contract grant number: F1-41/ 2001/CPP-II. Journal of Applied Polymer Science, Vol. 108, 3572–3576 (2008) V V C 2008 Wiley Periodicals, Inc.