ANALYSIS OF LAMELLAR STRUCTURE IN SEMICRYSTALLINE POLYMERS BY STUDYING THE ABSORPTION OF WATER AND ETHYLENE-GLYCOL IN NYLONS USING SMALL-ANGLE NEUTRON-SCATTERING
Ns. Murthy et al., ANALYSIS OF LAMELLAR STRUCTURE IN SEMICRYSTALLINE POLYMERS BY STUDYING THE ABSORPTION OF WATER AND ETHYLENE-GLYCOL IN NYLONS USING SMALL-ANGLE NEUTRON-SCATTERING, Macromolecules, 31(1), 1998, pp. 142-152
Preferential diffusion of deuterated solvents into the amorphous regio
ns of a semicrystalline polymer enhances the contrast between the crys
talline and amorphous regions measurable by small-angle neutron scatte
ring. This scattering in nylons from the diffusion of D2O and deuterat
ed ethylene glycol (d-EG) is analyzed by identifying the distinct cont
ribution to scattering From the two amorphous regions, one in the inte
rlamellar spaces and the other outside the lamellar stacks. The centra
l diffuse scattering (I-d) is the non-Bragg, liquidlike, or independen
t scattering, and is attributed to the solvents (D2O/d-EG) in the amor
phous domains outside the lamellar stacks. The lamellar scattering (I-
l) is the interference peak from the lamellae in the stacks and is use
d to evaluate the distance between the lamellae, the thickness of the
interlamellar spaces, and the coherence length of the lamellar stacks.
The invariant calculations show that 70%-80% of the lamellar stack is
crystalline. About one-third of the amorphous material in a highly cr
ystalline nylon is in the interlamellar space, and two-thirds is outsi
de the lamellar stacks. The thickness of the interlamellar amorphous r
egions into which solvent molecules diffuse varies from 10 to 60 Angst
rom depending on the thermal history and is a major contributor to the
observed increase in lamellae spacing. Structural changes in nylon 6
immersed in water are accelerated at 125 degrees C, and this temperatu
re could be the hydrated-equivalent of the Brill transition observed a
t 160 degrees C in dry nylon 6. Water or EG diffuses into the fold sur
faces of nylon lamellae at elevated temperatures, and subsequent struc
tural changes are accompanied by hydrolysis of the nylon chains. EG be
ing a stronger solvent reduces the lamellar thickness at elevated temp
eratures.