Influence of weak anchoring on flow instabilities in nematic liquid crystals

We analyse the homogeneous instabilities in a nematic liquid crystal subjec ted to plane steady Couette or Poiseuille flow in the case when the directo r is prealigned perpendicular to the flow plane taking into account weak an choring at the confining surfaces. The critical shear rate decreases for de creasing anchoring strength and goes to zero in the limit of torque-free bo undary conditions. For Poiseuille flow two types of instability arise depen ding on the values of the azimuthal (W-a) and polar (W-p) surface anchoring strengths. The critical line in (W-a, W-p) space which separates the two i nstabilities regimes is obtained.