Interfacial Tension in Binary Polymer Blends and the Effects of Copolymers as Emulsifying Agents - Polymer Thermodynamics - page 217

Fig. 14 Comparison of experimental interfacial tension for PS/PBDH 4080 at 171 C with the
square gradient theory where the square gradient coefficient is given by ( 84a )( solid line ) and
( 84b )( dotted line ). The dashed line is a linear fit to the data. Adjustable parameters were not
allowed in this comparison [ 20 ]

polymer species. Actually, Broseta estimated that the compositions of the two
coexisting phases are given by:
f A ¼

f B

ð wr B Þ

1 1 exp (85a)

f A ¼ f B 1 exp ð wr A Þ (85b)

The interfacial tension for high but finite molecular weights was, then, calculated to
be given as:

2

p 1

wr A þ

1
wr B

g ¼ g 1 1 þ ... (86)

12

where g 1 is the interfacial tension for infinite molecular weights as calculated by
Helfand Tagami, ( 40 ). As discussed by Broseta, this equation should be the
asymptotic behavior of the theory of Anastasiadis and coworkers [ 20 ]; however,
that regime was apparently not explored in the numerical calculations of Anasta-
siadis [ 20 ]. Moreover, the interfacial width was estimated as:

1
wr A þ

1
wr B

a I ¼ a I 1 1 þ ln 2 þ ... (87)