Two-dimensional light scattering and digital imaging studies of the st
ructural evolution in a graft copolymer-homopolymer blend under quasi-
static elongation are reported. The graft copolymer consists of a poly
disperse elastomeric poly(ethyl acrylate) (PEA) backbone onto which mo
nodisperse thermoplastic polystyrene (PS) chains are grafted. The homo
polymer poly(ethyl acrylate) is produced in situ since grafts are not
incorporated into every chain. The 'quasi-equilibrium'' structure of t
he graft copolymer blend cast from a good solvent exhibits isotropic s
cattering (i.e., appearance of a spinodal ring) with an inverse charac
teristic length q(m) almost-equal-to 4 mum-1. When the blend is subjec
t to a quasi-static elongation ratio lambda (=final length/initial len
gth), three regimes are observed: (i) A transition regime at very low
elongation ratios where the system behaves reversibly. (ii) A hyperela
stic regime where the spinodal ring deforms in an anisotropic manner,
i.e., ellipsoid-shaped scattering elongated in the direction perpendic
ular to the applied strain. The intensity I(parallel-to) (q(z)) parall
el to the elongation increases in an exponential manner due to coopera
tive alignment of the hard PS-rich phase, and its peak position shifts
in an affine manner to smaller values (i.e., q(zm) approximately lamb
da-1). Moreover, the scattered light perpendicular to the elongation,
I(perpendicular-to) (q(y)), decreases in intensity as its peak positio
n q(ym) diverges to infinity. (iii) A plastic regime where I(parallel-
to)(q(z)) remains nearly constant as its position q(zm) converges to a
finite value at q(zm) almost-equal-to 0.9 mum-1. In the three regimes
, the structure factor parallel to the elongation, S(parallel-to)(q(z)
), remains self-similar. The underlying mechanism of the deformation w
ill be discussed within the framework of concentration fluctuations in
''soft'' elastic two-component solids.