TY - JOUR
T1 - Isotropic and anisotropic composition fluctuations close to the order-to-disorder transition in an asymmetric diblock copolymer melt subjected to reciprocating shear fields
AU - Almdal, K.
AU - Mortensen, K.
AU - Koppi, K.A.
AU - Tirrell, M.
AU - Bates, F.S.
PY - 1996
Y1 - 1996
N2 - An asymmetric poly(ethylene-propylene)-poly(ethylethylene) (PEP-PEE) di-block copolymer was examined near the order-to-disorder transition temperature, TODT, by small-angle neutron scattering as a function of shear rate, γ̇. Heating in the absence of shear disorders the material from a hexagonal structure at TODT = 155 ± 1°C. Application of a reciprocating simple shear field markedly influences the phase behaviour near the ODT. Application of shear while heating increases TODT consistent with the theoretical prediction, TODT ∼ γ̇2. During fast cooling studies we observe an additional characteristic temperature, TS, at which the material spontaneously orders, which we interpret as a stability (i.e., spinodal) limit. This result also agrees with the theoretical prediction, τS ∼ γ̇-1/3. Upon cessation of shear at temperatures close to but above the quiescent TODT a transient phase is observed before the system macroscopically disorders. The transient structure has a symmetry compatible with spheres arranged on a body centered cubic (BCC) space lattice, or undulating cylinders of the minority component (PEE). Anisotropic (i.e. lattice pinned) fluctuations can also be observed close to, but below, TODT upon heating the hexagonal structure under shear free conditions.
AB - An asymmetric poly(ethylene-propylene)-poly(ethylethylene) (PEP-PEE) di-block copolymer was examined near the order-to-disorder transition temperature, TODT, by small-angle neutron scattering as a function of shear rate, γ̇. Heating in the absence of shear disorders the material from a hexagonal structure at TODT = 155 ± 1°C. Application of a reciprocating simple shear field markedly influences the phase behaviour near the ODT. Application of shear while heating increases TODT consistent with the theoretical prediction, TODT ∼ γ̇2. During fast cooling studies we observe an additional characteristic temperature, TS, at which the material spontaneously orders, which we interpret as a stability (i.e., spinodal) limit. This result also agrees with the theoretical prediction, τS ∼ γ̇-1/3. Upon cessation of shear at temperatures close to but above the quiescent TODT a transient phase is observed before the system macroscopically disorders. The transient structure has a symmetry compatible with spheres arranged on a body centered cubic (BCC) space lattice, or undulating cylinders of the minority component (PEE). Anisotropic (i.e. lattice pinned) fluctuations can also be observed close to, but below, TODT upon heating the hexagonal structure under shear free conditions.
KW - Materialer med særlige fysiske og kemiske egenskaber; Nye funktionelle materialer
U2 - 10.1051/jp2:1996202
DO - 10.1051/jp2:1996202
M3 - Journal article
SN - 1155-4312
VL - 6
SP - 617
EP - 637
JO - Journal de Physique II
JF - Journal de Physique II
ER -