Master's thesis presentation Ebba Grönfors

Examiner: Per Rudquist
Supervisor: Per Rudquist
Opponent: Christian Rutgersson

Abstrakt: A nematic liquid crystal is an orientationally ordered liquid where molecules align
along a local director but with no polar order. The material RM734 is one of very
few discovered substances which can assume the ferroelectric nematic phase, a liquid
crystal phase first practically realized in 2017 where the director has not only an
orientation, but also a direction. This thesis qualitatively describes the alignment
of RM734 in the nematic and ferroelectric nematic phase on a surface treated with
oblique evaporation of SiO2. We find that the material aligns at an azimuthal angle
0° < φ < 90° from the evaporation plane in either of two symmetrical directions ap-
proximately in the substrate plane, potentially opening up for the design of devices
based on bistable alignment. The angle φ depends on both temperature and evap-
oration angle, and turns out to fixate under certain conditions. This adds a new
layer of complexity to the alignment, as time becomes an important factor. The
alignment on SiO2 surfaces was studied by means a cell where the opposite surface
is a circularly rubbed polymer to achieve circular boundary conditions. The align-
ment is revealed by the formation and behavior of domains, depending on the local
mutual alignment directions on the two surfaces. The domains created in the higher
symmetry nematic phase has a large impact on the alignment in the ferroelectric
nematic phase.