LAMELLAR DIBLOCK COPOLYMERS UNDER LARGE-AMPLITUDE OSCILLATORY SHEAR-FLOW - ORDER AND DYNAMICS

A survey is given on the effects of large amplitude oscillatory shear (LAOS) flow on the orientation behavior of lamellar polystyrene-block- polyisoprene (PS-b-PI) diblock copolymers with emphasis on the identif ication of key parameters that govern the observed behavior. For LAOS at temperatures close to the order-disorder transition temperature, T- ODT, three orientation regimes related to the dynamic shear viscosity of the polymers are observed: parallel orientation at high frequencies , perpendicular orientation at intermediate frequencies, and parallel orientation again at very low shear frequencies. In annealing experime nts it is found that the low frequency orientation behavior depends st rongly on the thermal history of the samples. In conceptually new ''du al frequency'' experiments the effect of the superposition of two defo rmation components with frequencies in two different orientation regim es is described. From further studies identifying strain as the contro l parameter in these nonequilibrium experiments an orientation diagram for the long time orientation behavior of lamellar PS-b-PI diblock co polymers is constructed as a function of strain and frequency. For int ermediate time scales in the experiments it is shown that the third or thogonal orientation component, the transverse orientation, can be obt ained as a transient state. For all orientation components possible or ientation mechanisms are discussed.