PHYS01200704032 Debes Ray - Homi Bhabha National Institute

Absorbance
Chapter 5: Correlating Block Copolymer Self-Assembly to the Gold Nanoparticle Synthesis
systems. Figure 5.7 shows transmission electron micrographs of gold nanoparticles for the
block copolymers corresponding to the samples of their maximum yields. It is observed that
the size of the nanoparticles depends on the block copolymer. The block copolymer F88
mostly consists of block copolymer cross-linked small gold nanoparticles while the size of
the nanoparticles for P85 is ~ 15 nm. The P105 block copolymer having highest tendency of
self-assembly forms the nanoparticles with largest sizes (~ 30 nm). These studies thus show
that the self-assembly of block copolymers controls the yield and formation rate as well as
the structure of the gold nanoparticles.
5.3.3. Temperature-Induced Synthesis
Micelle formation, in aqueous solutions of amphiphilic block copolymers, is critically
dependent upon temperature [96,98,146]. This is a result of the successive dehydration of PO
and EO chains upon the increase in temperature. At low temperatures, both types of blocks
within block copolymer molecules are hydrated and therefore they are soluble in water. When
the temperature increases, the PO block dehydrates and becomes insoluble, resulting in the
formation of micelles. The temperature at which micelles are formed is referred to as the
CMT and for most of the block copolymers it has value in the range of 25 to 40 o C.
0.5
0.4
0.3
1 wt% F88 + 0.004 wt% HAuCl4.3H2O
30 o C
50 o C
75 o C
0.2
0.1
0.0
400 500 600 700 800 900 1000
Wavelength (nm)
122