The interaction of polymer dispersed liquid crystal sensors with ultrasound

Abstract

Polymer dispersed liquid crystals (PDLCs) have been shown to be sensitive to ultrasound through the acousto-optic effect. The acousto-optic response of PDLCs was studied over a broad frequency range (0.3–10 MHz). We demonstrate that the displacements required to produce acousto-optic clearing of PDLC films can be as low as a few nanometers, which is at least 103 times smaller than the PDLC droplet size, is 105 times smaller than the PDLC layer thickness, and of the order of the molecular size of the liquid crystal constituents. This suggests that the acousto-optic effect in PDLCs is due to the microscopic effects of the LC reorientation under torques or flows rather than the LC reorientation through macroscopic droplet deformation. The displacement required for clearing is related to the frequency of operation via an exponential decay. We attribute the observed frequency response to a freezing out of the rotational motion around the short axis of the liquid crystal. The reported frequency dependence and displacements required indicate that the effects and materials described here could be used for ultrasound visualization in a non-destructive testing context.

Recent Advances in The Polymer Dispersed Liquid Crystal Composite and Its Applications

“…PDLCs were also shown to be sensitive to ultrasound through the acousto-optic effect. In the United Kingdom, Edwards et al [ 144 ] of the University of Warwick, Coventry, prepared a PDLC sensor (E7: NOA68= 75:25) and studied the acousto-optic response of PDLCs coupled with an ultrasound transducer over a broad frequency range (0.3–10 MHz). The displacements required to produce acousto-optic clearing of PDLC films were between around 2 and 50 nm.…”

Polymer-Dispersed Liquid Crystal Films on Flexible Substrates with Excellent Bending Resistance and Spacing Stability

“…It consists of micrometer-sized liquid crystal droplets embedded into a polymer network matrix, which can be graphically described as a “Swiss cheese” structure. − Without an electric field, the LC molecules are randomly oriented, which leads to a refractive index mismatch between the LC droplets and the polymer network, so that the film exhibits an opaque state of light scattering. Once a sufficient electric field is applied, the PDLC films will become transparent since the LC molecules tend to align parallel to the electric field direction. − The electrically switchable property of PDLC films is an important application foundation for many optoelectronic devices, such as smart windows, − displays, − holographic gratings, − sensors, − optical switches, , and light-responsive actuator films …”

Organic Solvent Sensors Using Polymer-Dispersed Liquid Crystal Films with a Pillar Pattern

“…The combination of polymers and liquid crystals (LCs) can be classified into different configurations via the properties of the polymers, including LC cells with photoconductive polymer films [ 1 , 2 ], LC cells with polymer structures [ 3 , 4 ], polymer-stabilized LCs (PSLCs) [ 5 , 6 , 7 ], polymer-dispersed LCs (PDLCs) [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ], and LC elastomers [ 19 ]. PDLC films that comprise LC droplets dispersed in polymers are formed due to the light-induced phase separation in the precursors of the PDLCs.…”

“…The transmittances of the PDLC films can be modulated by external voltages, and polarizers are not required at the transmittance modulation. Therefore, PDLC films have potential in developing electro-optic devices such as displays [ 8 , 9 , 10 , 11 , 12 ], lenses [ 13 , 14 ], sensors [ 15 , 16 ], gratings [ 17 , 18 ], lasers [ 20 , 21 , 22 ], and light modulators [ 23 , 24 , 25 ].…”