Pattern electric field-induced

Cholesteric LCs can act as hosts for dyes to produce coloured displays (see section 5.2.2.1 below) " their temperature dependent colour change has found applications in thermochromic inks, °" and as pigments and copy safe colours their selective reflecting capabilities have been applied in colours and filters for reflective displays and projection systems, " reflective polarisers and their electrical field induced switching in displays and smart reflectors, in colour patterning for full-colour recording. ... 

N. E. Voicu, S. Harkema, and U. Steiner, Electric-field-induced pattern morphologies in thin liquid films. Adv. Funct. Mat. 16, 926 (2006). 

Abstract A systematic overview of various electric-field induced pattern forming instabilities in nematic liquid crystals is given. Particular emphasis is laid on the characterization of the threshold voltage and the critical wavenumber of the resulting patterns. The standard hydrodynamic description of nematics predicts the occurrence of striped patterns (rolls) in five different wavenumber ranges, which depend on the anisotropies of the dielectric permittivity and of the electrical conductivity as well as on the initial director orientation (planar or homeotropic). Experiments have revealed two additional pattern types which are not captured by the standard model of electroconvection and which still need a theoretical explanation. 

With the AFM tip as the cathode, nanowires of polycarbazole were also patterned by electric-field-induced cross-Unking and polymerization of carbazole units on an Au/mica or Si substrate (anode) spin-coated with insulating poly(vinylcarbazole) film [23,24]. Figure 10.9 shows a schematic of the experimental setup and Figure 10.10 shows an AFM image of the patterned CP nanostractures [24]. Similarly, electrochemical oxidation and cross-linking of carbazole and thiophene due to the flow of electrons from the conductive AFM tip to the polymer (polystyrene functionalized with carbazole and thiophene groups) precursor film on an Si substrate produced CP nanofeatures in the precursor polymer film [25]. 

Verma, R., Sharma, A., Kargupta, K., Bhaumik, J. Electric field induced instability and pattern formation in thin liquid films. Langmuir 21, 3710-3721 (2005)... 

As depicted in Chap. 3, the ability to pattern functional polymers at different length scales is important for a range of applications and developments including the fabrication of micro plastic electronics, the production of optical components and bio-medicinal related research. EHD patterning can also be exploited for the fabrication of hierarchical functional patterns using electric field induced... 

N. Eber, L.O. Palomares, P. Salamon, A. Krekhov and A. Buka, Temporal evolution and morphological transitions of electric field induced patterns at low frequency driving, (unpublished). 

N. Arun, A. Sharma, P. S. G. Pattader, I. Banerjee, H. M. Dixit, and K. S. Narayan, Electric-field-induced patterns in soft viscoelastic films from long waves of viscous liquids to short waves of elastic solids, Phys. Rev. Lett., 102, 254502 [2009]. 

Pattern Formation by Electric-Field-Induced Dewetting... 

A typical experimental set-up for electric field-induced pattern formation comprises sandwiching aliquid polymer film between two electrodes. The film is coated onto one of the electrodes, maintaining an air gap with the second electrode, as shown in Figure 11.14 [241-264]. Avoltage is applied between the two electrodes, resultingin an electric field across the sandwiched film (Figure 11.14a). Uponapplication of the field, the capillary fluctuations at the liquid-air interface amplify in the direction of the field. 

Electric Field-Induced Patterning of Polymer Bilayers... 

At present, at least three types of steady-state dielectrically driven pattern are known for nematics. The electric-field-induced periodic bend distortion in the form of parallel stripes has been observed in a homeotropi-cally oriented layer of 5-CB ( a= 13) in the presence of a stabilizing magnetic field [75, 76]. The stripes with a wavevector q were parallel to the electric field E and stationary at low fields. It was shown that a stable periodic pattern of the director minimizes the free energy of the cell when the ela.stic moduli and A 33 are similar to each other. In these experiments the Frederiks transition is of first order, the nonde-formed and deformed areas coexist at a given voltage, and the front between them may propagate along the direction y perpendicular to both fields [77]. 

The last problem of this series concerns femtosecond laser ablation from gold nanoparticles [87]. In this process, solid material transforms into a volatile phase initiated by rapid deposition of energy. This ablation is nonthermal in nature. Material ejection is induced by the enhancement of the electric field close to the curved nanoparticle surface. This ablation is achievable for laser excitation powers far below the onset of general catastrophic material deterioration, such as plasma formation or laser-induced explosive boiling. Anisotropy in the ablation pattern was observed. It coincides with a reduction of the surface barrier from water vaporization and particle melting. This effect limits any high-power manipulation of nanostructured surfaces such as surface-enhanced Raman measurements or plasmonics with femtosecond pulses. 

Regions in a liquid crystal having a specific cellular periodic flow-pattern in the form of long rolls induced by the application of an electric field perpendicular to a nematic layer with an initial planar alignment of the director. 

Protonation of the amino group usually induces a shielding of all carbon atoms, explained in terms of electric field effects [84] and CH bond polarizations [338], and follows the pattern observed on protonation of carboxylate anions (Section 4.7.4). 

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