Page 49 - ILL Annual Report 2019

108
108
106 6 10
104 4 10
2
102
100
100
10−2
10−2
x5 107 0.0%D2O
x5 107 0.0%D2O
x5 106 25.0%D2O
x5 106 25.0%D2O
x5 5104780.60%D2OO x55 1480.6%D2O 2
Contrast variation SANS experiment of PA-b-PSS block copolymer micelles. Solid lines indicate a fit to the model of a spherical, block copolymer micelle.
10
x105
10x102 80.605%.8D%2DO2O
48.6%D O 2
x5 10
0.0%D2O
108
106 65.8%D2O
x5 106 25.0%D2O 65.8%D2O
-4
65.8%D2O
65.8%D2O
65.8%D2O 100.0%D2O
5 48.6%D2O x1042 80.0%D2O
x105 x5 10
10
2
100.0%D2O
100 −2−2
100.05%D2O x10
x102
80.0%D2O
100.0%D O 2
−1
1010 10 1 10
0
q (nm )
-2
-2
−2 −1 0
10 −2 10−1
10 101110
010
q ((nnmm) )
100.0%D120O0.0%D2O
-4
-4
-2
SANS instrument D11 at the ILL allows us to perform SANS experiments at very small momentum transfers with a high flux. This is crucial for the present study as the micelles are relatively large and the contrast variation technique results in a decrease of the scattering intensity, compared with classical experiments in full-contrast conditions.
In this study we also show that micelle formation is
triggered by alternately adding Ca2+ cations and EDTA to
and dissolve (ΔT < 0) micelles (figure 3b). This feature 105 arises from the entropically driven binding of Ca2+ to the PA
block [4]. The binding is accompanied by the release of
two sodium counter-ions and several water molecules from
the hydrated shell, which is favourable in terms of entropy. 107 The temperature increase therefore results in the stronger 107 6 7
a polymer solution. EDTA has a very high tendency to bind
2+ 66
to Ca cations and therefore reverses the micellization 10 1076 process (figure 3a). More strikingly, small temperature 10
5 changes can also be employed to reversibly form (ΔT > 0) 105 1065
binding of Ca2+ to the PA block.
10 6 The micelle formation is entirely reversible and opens up 10
a new route for the uptake and release of cargo. New
3+ 3+ 105 1055
single chains single chains
contrast agents produced by using Gd or Eu and new 10 strategies for ion separation are just a few of the possible
applications of this block copolymer system.
single chains single chains
0.0%D2O
0.0%D O 2
48.6%D2O
48.6%D2O
Figure 2
Figure 3
Molecular weight after alternating additions of Ca2+ and EDTA (a) and temperatures cycles between 25 and 65 °C (b) indicating the reversibility of the micelle formation.
a)
107 107 7 10
micelles micellemsicelles
micelles
b)
single chains micelles
65 10 106
10
single chains
11007 10
single chains single chains
micelles micelles
micelles
SCIENTIFIC HIGHLIGHTS
46-47
25 C
2560C C
2+ 2+ Ca Ca
6025C C
2560C C
Ca CaCa 2+
2560C C
Ca
6025C C
2+ CEaDTA
2560C C
EDTA Ca2 +
6025C C 25 C
2+ CEaDTA
25C 25C
Ca2 +
60C 60C
2+ CEaDTA EDTA EDTA
25C 25C
2+ E2D+TA 2+
60C 60C
6025C25CC 25C
EDCTEaADETDATA
60C 60C
Ca2+ 2C+a2+ EDTA
25C 25C
EDTA EDTA
60C 60C
Ca2 + Ca2 +
25C 25C
EDTA EDTA
Mw (gmol 1)
Mw (gmol 1)
1 1 MMw(g(gmMmwol(g)m) ol )
1 11 Mw M(gMmw(ogl(gm)mooll ))
ww
EDTA
d /d
d / d d / d ( c ( mc m 1 1 ) ) (cm 1)
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