xxiii πανελληνιο ÏƒÏ Î½ÎµÎ´ÏÎ¹Î¿ Ï†Ï ÏƒÎ¹ÎºÎ·Ï‚ στερεας καταστασης & επιστημης ...

In contrast to this system, a similar soft copolymer micelle PS – PB with polybutadiene core (56% PB) and
polystyrene corona (44% PS) in DBP solvent exhibits the same behaviour in the size dependence with the temperature but the
viscoelastic properties are different. The size can be tuned from 45 nm up to 100 nm as the temperature goes from 20 to
90 o C. The solvent is dibutyl-phthalate which is theta for polystyrene at 22 o C and for polybutadiene at 90 o C. In particular, an
initial viscosity increase with temperature was attributed to the swelling of the core and thus, to an increase of inter-particles
interactions. For concentrations above the overlapping limit, we observed a solid-to-liquid transition followed by a liquid-tosolid
transition by further increasing the temperature. Then, for still higher concentrations, the system vitrified (see Figure 3).
For such a system, both the mass concentration and the temperature increase yielded a larger effective volume fraction and
thus induced a kinetic arrest. On the other hand, as observed for the PS-PI block copolymer micelles, master-curves of the
relative zero-shear viscosity versus the effective volume fraction could not be obtained, pointing again to the quantitative
different effect of mass concentration and temperature on the system’s response (see Figure 4).
G' ( ) , G" ( ) (Pa)
10 3
10 2
10 1
10 0
10 -1
Concentrations
8 % wt
24 % wt
η 0
/η s
PMMA in Decalin (640 nm)
Star 32/80
Star 64/07
10 3 Star 128/07
Star 128/80
linear polymer
Eintein's equation
2.1 % wt
10 2 4.2 % wt
8.05 % wt
12.1 % wt
14.19 % wt
15.31 % wt
10 1
T 1
T 2
T 3
10 -2
10 4 ϖ (rad/s)
10 -2 10 -1 10 0 10 1 10 2
10 0
10 -1 10 0
φ eff
=c/c*
Figure 3: Dynamic frequency sweep tests at 2 different
concentrations (8% and 24% wt) at 20 o C for PS-PB. All
strains are in the linear regime.
Figure 4: Relative viscosity with the effective volume
fraction for spheres, stars, linear polymers and star-like
micelles. Our experimental data from PS-PB are with red
color. T 1 , T 2 , and T 3 are the temperatures 20 o , 30 o and
50 o C respectively.
[1] B. Loppinet et al. , Macromol. Chem Phys. , 2005 , 206 , 163
[2] M.J. Solomon , S.J. Muller , Journal of Polymer Science: Part B: Polymer Physics , Vol. 34 , 181 , 1996
[3] X. Jin , T.P. Lodge , Rheol. Acta , 36:229 ,1997
150