Macroscopic alignment

Macroscopic alignment of LC side chain polymers has been achieved using electric, magnetic and lear fields [27, 35, 142-146]. Generally, the degree of macroorder. 

Experimental values of the macroorder parameters S. , and (see Sect. 3.3), obtained for the various systems, are listed in Table 5. Drastic variations are observed. Apparently, a complete uniform alignment (S,., . = 1.0, Sy.. = 8., .. = —0.5) of the director axes is achieved for the LCP 2 and the monomeric analogue 5. The observed macroorder parameters are consistent with a positive diamagnetic (A 0) and a negative dielectric anisotropy (As 0). 

It has been shown that the magnetic field induced deformations the macroorder 

Interestingly, the macroorder of LC side chain polymers can be frozen in at the glass transition. No electric or magnetic field is required to maintain the director distribution 

Macroscopic alignment was attempted at T = 0.98 with the quartz plates of the electric field cell (50 kV/cm, 50 kHz) parallel to a magnetic field of 0.33 T. 

---

Consider a lamellar mesophase, being macroscopically aligned so that the symmetry axis, referred to as the director, has the same direction throughout the sample. If the transformation from the molecular coordinate system to the laboratory system is performed via the director coordinate system (D), Equation 2 reads... 

Comparison of experimental data with Equation 7 makes it possible to determine how the director is oriented with respect to the constraint (14) responsible for macroscopic alignment. 

The macroscopic alignment of polymer chains was also achieved by depositing soluble poly(p-phenylenes), such as 37 or poly(3-thiophenes) such as 26, from solution by the Langmuir-Blodgett technique. However, low polarisation ratios ( u/ x) were found for electroluminescence (3 1). 

The homopolymer showed an enantiotropic nematic mesophase, whereas the diblock copolymer generated microphase-separated lamellae, in which the SCLCP block possessed a nematic-isotropization transition similar to the homopolymer (Table 17). Upon heating, the nematic microphase decreased continuously in the nematic phase from 38.5 nm to 27 nm and showed a constant value of about 26 nm after the nematic-isotropization transition. Therefore, materials in which these block copolymers are macroscopically aligned are expected to show reversible contraction in one dimension, making this polymer system an interesting candidates for an artificial muscle or actuator. 

In contrast with our earlier findings for siloxane homopolymers, we found that polymer I could be aligned directly by application of a strong a.c. electric field to the polymer in its LC state. The kinetics of the alignment behaviour will be described in a future paper, but it should be said that we found that the rate of macroscopic alignment decreased rapidly as the sample temperature was... 

According to these relations, four relaxation modes occur which are appropriately weighted for samples having different degrees of macroscopic alignment. For a fully homeotropic sample = 1 and two modes labelled as fJ(cij) and Fjj(uj) contribute to the overall... 

A particularly interesting study that exemplifies the effect of nano-confinement is one where poly(phenylene vinylene) PPV, a luminescent polymer, was incorporated into the channels formed from these polymerized hexagonal phases [78]. These hexagonal PPV nanocomposites exhibited a significant enhancement in the photoluminescence quantum yields, from ca. 25 to 80%. The origin of this enhancement is ascribed to the prevention of the formation of poorly emissive inter-chain excitonic species as a result of the confinement of the PPV chains into well-defined and well-separated nanochannels. An important feature of these nanocomposites was that they could be readily processed into thin films and fibres and, more importantly, macroscopic alignment of the channels encapsulating the PPV chains led to polarized emission [79]. 

One of the guiding principles underlying much of the physics in conventional polymers is that many macroscopic macromolecular properties, not least the structure formation, can be satisfactorily understood even when the details of single molecules are ignored [11]. As is discussed later in this review, this idea still remains relevant for the intermolecular self-organization of hairy-rod PFs and for their macroscopic alignment. However, much of the behavior seen in PFs (and virtually all other electronic polymers as well) is an excep-... 

Achieving controlled macroscopic alignment of PF films is important for a wealth of reasons. Oriented samples exhibit anisotropic charge transport properties with enhanced mobilities and PF examples include F8BT [92],... 

The basic concept of utilizing anisotropic chemical shifts in macroscopically aligned membranes, pioneered by Opella and Cross, was initially developed using gramicidin A. The 15 amino acid peptide is readily synthesized with selective N or C-labels in the backbone, " or with N or F-labels in the side chains (as well as H for quadrupolar couplings). Numerous individual orientational constraints were thus used to determine the detailed p-helical structure of the membrane-bound ion channel, which was refined... 

Everett TA, Higgins DA (2009) Electrostatic self-assembly of ordered perylene-diimide/ polyelectrolyte nanofibers in fluidic devices from nematic domains to macroscopic alignment. Langmuir 25(22) 13045-13051... 

Cross-linked liquid crystalline polymers with the optical axis being macroscopically and uniformly aligned are called liquid single crystalline elastomers (LSCE). Without an external field cross-linking of linear liquid crystalline polymers result in macroscopically non-ordered polydomain samples with an isotropic director orientation. The networks behave like crystal powder with respect to their optical properties. Applying a uniaxial strain to the polydomain network causes a reorientation process and the director of liquid crystalline elastomers becomes macroscopically aligned by the mechanical deformation. The samples become optically transparent (Figure 9.7). This process, however, does not lead to a permanent orientation of the director. 

---