TY - JOUR
T1 - Investigation of the phase diagram and critical fluctuations of the system polyvenylmethylether and d-polystyrene with neutron small angle scattering
AU - Schwahn, D.
AU - Mortensen, K.
AU - Springer, T.
AU - Yee-Madeira, H.
AU - Thomas, R.
PY - 1987
Y1 - 1987
N2 - The system PVME/d-PS has been investigated by neutron small angle scattering. By extrapolating the critical scattering, the spinodal was determined and used to calculate the Flory-Huggins parameter χ (φ,T) in the frame of mean field theory. Separating the Gibbs potential of mixing ΔG in a Flory-Huggins term χ (φ,T) and a configurational term for the entropy ΔS, it turns out that χ is independent of the molecular weight, and of the weight distribution, i.e., it is a local or "segmental" quantity. The critical scattering was carefully investigated at the critical concentration. At temperatures Tc - T> 2.4 K(Tc = 141.9 °C), a mean field behavior of the susceptibility S(Q = 0) was clearly observed, with a critical exponent γ= 1. However, in a region of Tc -2.4 K<T<Tc, a crossover occurs to a critical exponent γ≃ 1.26; it resembles the Ising behavior which is well established for normal liquid mixtures. The function S(Q) also describes the characteristic segmental length σ. Both σ and the range parameter of χ, r0, are independent of molecular weight and weight distribution within experimental errors. The binodal, i.e., the line between the homogeneous and the two-phase region was identified by a change of critical scattering caused by the precipitated domains. The spinodal approaches the binodal near Tc in a characteristic way as predicted for polydisperse systems.
AB - The system PVME/d-PS has been investigated by neutron small angle scattering. By extrapolating the critical scattering, the spinodal was determined and used to calculate the Flory-Huggins parameter χ (φ,T) in the frame of mean field theory. Separating the Gibbs potential of mixing ΔG in a Flory-Huggins term χ (φ,T) and a configurational term for the entropy ΔS, it turns out that χ is independent of the molecular weight, and of the weight distribution, i.e., it is a local or "segmental" quantity. The critical scattering was carefully investigated at the critical concentration. At temperatures Tc - T> 2.4 K(Tc = 141.9 °C), a mean field behavior of the susceptibility S(Q = 0) was clearly observed, with a critical exponent γ= 1. However, in a region of Tc -2.4 K<T<Tc, a crossover occurs to a critical exponent γ≃ 1.26; it resembles the Ising behavior which is well established for normal liquid mixtures. The function S(Q) also describes the characteristic segmental length σ. Both σ and the range parameter of χ, r0, are independent of molecular weight and weight distribution within experimental errors. The binodal, i.e., the line between the homogeneous and the two-phase region was identified by a change of critical scattering caused by the precipitated domains. The spinodal approaches the binodal near Tc in a characteristic way as predicted for polydisperse systems.
UR - http://www.scopus.com/inward/record.url?scp=0001009769&partnerID=8YFLogxK
U2 - 10.1063/1.453482
DO - 10.1063/1.453482
M3 - Artículo
SN - 0021-9606
VL - 87
SP - 6078
EP - 6087
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
IS - 10
ER -