Polymer modifies the critical region of the coexisting liquid phases

P. Venkatesu1

1University of Delhi, Delhi, India

Keywords: polymer, coexisting liquid phases, critical parameters
property: refractive index
material: polymer

The behavior of a flexible linear or branched chain polymer (polyethylene oxide, PEO, molecular weight, Mw = 9x105, as an impurity) in the critical binary mixture of isobutyric acid (I)+ water (W) was studied by the refractive index (n) measurements using a very accurate and sensitive refractometer. We observed that the polymer was significantly affected in the critical region of IW and these various concentrations of PEO show an important behavior on the critical exponents (β), the critical temperatures (Tc) and critical composition, which are depicting the shape of the coexistence curve. The phase-transition region of coexisting phases of IW shifts down with the addition of PEO and Tc decreases linearly with increasing PEO concentrations. This may indicates that, the polymer chain entangle with each phases, thereby the polymer monomers strongly interact with neighbor solvent particles and also intrachain interaction between the polymer segments. At such conditions, the collapse of polymer chain is possible in the vicinity of the critical point. At temperatures T close enough to Tc, the critical exponent β was found to decrease from 0.382 to 0.360 when the PEO concentration changes from 0.395 to 1.605 mg/cc. It appears that the shape of the PEO in IW coexistence curves is similar from that of pure IW.

Corresponding author: e-mail: venkatesup@hotmail.com; pvenkatesu@chemistry.du.ac.in; Tel: +91-11-27666646-142; Fax: +91-11-2766 6605

  1. P. Venkatesu, J. Phys. Chem B 110, 17339 (2006)

  2. P. Venkatesu, J. Chemical Physics 123, 024902 (2005)

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