Observation of steady shear-induced nematic ordering of selenium chain moieties in arsenic selenide liquids

Structural anisotropy induced by steady shear and its mechanistic relation with shear thinning are investigated in As_xSe_100-x glasses (5 ≤ x ≤ 30) quenched from parent liquids subjected to shear rates ranging between 0 and 10⁴ s⁻1 using polarized Raman spectroscopy and two-dimensional X-ray diffraction. When taken together, the results demonstrate significant shear-induced partial alignment of −Se−Se−Se− chain moieties in the flow direction of the extruded fibers. This alignment is reminiscent of nematic liquid crystals where orientational order exists without positional order. The degree of this structural alignment in quenched glasses appears to be practically independent of the shear rate, although the parent liquids undergo shear thinning at the highest shear rates. It is conjectured that any causal relationship between structural alignment and shear thinning in the liquid may be masked in the glassy state by the postextrusion structural relaxation of the parent liquid.