Two Distinct Types of Orientation Process Observed in Uniaxially Elongated Smectic LC Melt

Abstract

We examine the tensile deformation of the smectic melt of a main-chain liquid crystalline polymer. A film molded in isotropic melt is heated to a smectic temperature of 60 °C and then stretched at selected strain rates. In the initial stage of strain below 100% (defined as {(l − l 0)/l 0} × 100%), smectic layers align parallel to the stretching direction; i.e., polymer chains orient perpendicularly (so-called “perpendicular orientation”). This perpendicular orientation in the low-strain region is invariably observed at any strain rate. Upon succeeding elongation, however, two distinct types of orientation process are observed depending on the strain rate. On elongation at strain rates as low as 5%/min, the perpendicular orientation is improved until the sample breaks at 400% strain (process A). At a high strain rate of 100%/min, in contrast, the perpendicular orientation initially observed is eventually altered to the “parallel orientation” with polymer chains lying parallel to the tensile axis (process B). In this case, the well-known necking takes place, and the sample breaks at an extremely large strain more than 3000%. These two distinct elongation processes are also dependent on temperature; processes A and B are observed in higher and lower temperature regions, respectively. On the basis of these data, the molecular orientation mechanisms in smectic field are discussed by coupling together the nature of smectic liquid crystal and dynamics of polymer chains.

Microphase‐Separated Morphology and Liquid Crystal Orientation in Block Copolymers Comprising a Main‐Chain Liquid Crystalline Central Segment Connected to Side‐Chain Liquid Crystalline Segments at Both Ends

“…The intensity profile of the typical WAXD pattern measured for B5M10‐42 is shown in Figure . The three reflections at q = 2.04, 3.98, and 6.10 nm −1 ( d ‐spacing: 3.08, 1.58, and 1.03 nm, respectively) and the other two reflections at q = 3.81 and 7.77 nm −1 ( d ‐spacing: 1.65 and 0.809 nm, respectively) are ascribed to the Sm structures of M10 and B5, respectively; the M10 and B5 homopolymers display Sm layer spacings of 3.15 and 1.63 nm …”

Polydomain–Monodomain Orientational Process in Smectic‐C Main‐Chain Liquid‐Crystalline Elastomers

“…This SmC A distribution of layers has the layer normal perpendicular to the applied mechanical field and looks like the slow motion deformation process already observed during the deformation of main-chain liquid-crystalline polymers. [40] The first steps during the orientational process are actually identified by the strong increase of the order parameter from S ¼ 0.00 at l ¼ 1.0 to S ¼ 0.46 at l ¼ 1.5 (Figure 3b), where S reflects the product of the orientational and director order parameter.…”

Thermotropic Liquid Crystals of Main‐Chain Polyesters having a Mesogenic 4,4′‐Biphenyldicarboxylate Unit, 14

“…Here, the molecules lie perpendicular to its axis. This unusual orientation is considered to result from the preferential alignment of chain folded lamellae [11][12][13][14][15][16] under a flow of drawing or shearing. In this work, we performed dynamic mechanical measurements on fibrous BB-5(3-Me) polyester specimens with these two distinct orientations.…”