INVESTIGADORES
GOYANES Silvia Nair
artículos
Título:
PALS study of epoxy matrices: self-assembly of block copolymers and its capability for nanostructuring thermosetting systems
Autor/es:
J A RAMOS; E. SERRANO; A. TERCJAK; W. SALGUEIRO; S. GOYANES; I. MONDRAGON
Revista:
physica status solidi (c)
Editorial:
wiley
Referencias:
Año: 2007 vol. 4 p. 3690 - 3699
ISSN:
1610-1642
Resumen:
The free volume in epoxy systems based on diglycidyl ether of bisphenol-A (DGEBA) fully cured with
aminic hardeners having different chemical structures has been studied by means of positron annihilation
lifetimes spectroscopy. The results are compared with those obtained from the analysis of the macroscopic
specific volume changes by using pressure-volume-temperature (PVT) experimental technique. An excellent
correlation between the volumes measured at macro and nanoscales was found for the epoxy systems
fully cured with aminic hardeners. On the other hand, a systematic study on the dependence of the volumes
at nano-scale in epoxy systems cured with two selected aminic hardeners at different pre-cure temperatures
revealed that the pre-cure temperature, as well as, the structure of the hardeners governs the packing
of the molecular chains of the epoxy network and its influence in the volume and number density of
the nanoholes. In the second part of this work, a systematic study of the effect of several epoxidation degrees
of butadiene block in a commercial polystyrene-polybutadiene star block copolymer (SB) has been
carried out to control nano-ordering in thermosetting epoxy systems. For this purpose, blends of DGEBA
cured with 4,4´-methylenebis(3-chloro-2,6-diethylaniline) (MCDEA) containing 30 wt % neat SB and several
epoxidized SB star block copolymers have been synthesized. At low epoxidation degrees, interactions
with the epoxy matrix are not sufficiently favorable and macroscopic phase separation takes place,
leading to a phase-inverted morphology where the block copolymer may become the matrix. For high epoxidation
degrees, however, nanostructured thermosetting systems, being the epoxy-rich phase the matrix
of the blends, have been obtained. It has been proved that, in blends containing SepB61 and SepB76
star block copolymers, the copolymer self-assembles into a well-defined hexagonally ordered structure,
where cylinders are formed by PS arranged in an epoxy matrix containing both epoxidized and nonepoxidized
butadiene units. SAXS experiments show that there are not strong differences in the long spacing
between the different systems because the repeated distance between PS cylinders for all the blends
is around 41-42 nm.