There has been recognized that there exist three basic relaxation modes in the molecular dynamics of liquid crystalline side chain polymers (SCLCP) – the α-, β- and δ-relaxation process, and the ...molecular mechanism of the δ-relaxation has been in controversy, i.e. whether it is a “flip-flop” transition or a continuous rotation. The current study provides the experimental evidence of the multiple steps relaxation by time-resolved emission spectroscopy, taking the intrinsic fluorescence from the model mesogen group of 4-cyanobiphenyl. The temperature dependence of the spectra and its dynamics provides new information on the microscopic picture of the δ-relaxation.
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•The δ-relaxation of liquid crystalline polymer has been considered to be of “flipflop” nature.•Time-resolved fluorescence emission spectroscopy discovers evidence of continuous motion.•The single step δ-relaxaion is mainly influenced by the local ordered structure.
Surface anchoring plays a fundamental role in controlling the molecular alignment of a bulk liquid crystal (LC). It has been previously shown that the pretilt angle of a nematic liquid crystal (NLC) ...can be controlled by changing the grafting density of a liquid crystalline polymer, poly(6-(4-methoxy-azobenzene-4′-oxy) hexyl methacrylate) (PMMAZO). In this study, the thickness of the swollen PMMAZO brush was measured by employing the surface forces apparatus (SFA). NLC 4-cyano-4′-pentylbiphenyl (5CB) and toluene were used as the solvents. It was shown that both 5CB and toluene were good solvents for PMMAZO. The repulsive force in 5CB appeared at D0 = 98.2 ± 4.6 nm for high grafting density (HD) surfaces, and at 32.1 ± 4.5 nm for the low grafting density (LD) surfaces. These results indicated that the PMMAZO molecules extended nearly perpendicular to the HD surfaces, while they laid on the substrate for the LD surfaces. The interaction between 5CB and the mesogenic group of PMMAZO was stronger than that for toluene. These results could support the expected surface anchoring mechanism of 5CB by the PMMAZO brush.
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•Swelling of a side-chain liquid crystalline polymer brush was observed by using SFA.•Configuration of swollen brush was controlled by changing the grafting density.•Results of force measurement showed the stacking between 5CB and mesogenic group.•Surface anchoring was examined by FECO.
A series of side‐chain liquid crystalline polymers P4VP(CN‐DBE)x, where x is the molar ratio of cyanostilbene (CN‐DBE) to poly(4‐vinylpyridine) (P4VP) repeating unit, was synthesized based on the ...intermolecular hydrogen bonding between P4VP and CN‐DBE. Their luminescent property, liquid crystalline structure and photo‐thermo‐electric property were elucidated using photoluminescence spectra, X‐ray diffraction, thermal imaging and thermoelectric experiments. With the increase of x, the supramolecular system can be changed from lamellar structure to hexagonal columnar structure. Moreover, the P4VP(CN‐DBE)x polymer with columnar structure exhibits more efficient photothermal effect. The temperature of P4VP(CN‐DBE)0.6 can rise to 130 °C within 10 s under the irradiation of ultraviolet lamp. In addition, the supramolecular system possesses unique photo‐thermo‐electric conversion ability, and 25 mA current can be detected in the circuit coupled with the thermoelectric module. This work broadens the potential applications of hydrogen‐bonded polymer, and provides a simple and facile strategy to prepare liquid crystalline polymers with photo‐thermo‐electric property.
With the increase of x, the liquid crystalline polymers P4VP(CN‐DBE)x changed from lamellar structure to columnar structure. The polymer with columnar structure exhibits more efficient photo‐thermo‐electric effect, with 25 mA current under UV irradiation.
Terahertz (THz) microstrip patch antenna arrays have been designed on liquid crystalline polymer substrate at 0.835-, 0.635-, and 0.1-THz frequencies in such a way that they could be fabricated with ...the simple laboratory-based printed circuit board etching process. The antenna array at 0.835- and 0.635-THz frequencies may be deployed for various applications in medicine including cancer detection through THz spectroscopy techniques and vital sign detection through Doppler radar and/or on-body techniques. A prototype antenna array at 0.1-THz frequency has been fabricated and tested to verify the proposed designing approach. The measured and the simulation results of the tested 0.1-THz array are in good agreement.
A humidity-responsive bilayer actuator has been developed that consists of an oriented polyamide-6 substrate and a liquid-crystalline polymer coating. The oriented substrate acts as an alignment ...layer for the liquid crystal. The liquid-crystalline polymer consists of a supramolecular network having hydrogen-bonded entities that, after activation with an alkaline solution, exhibit deformation in response to a change in humidity. The bending behavior of the bilayer actuator was analyzed, showing a large response to a change in the humidity.
With the excessive consumption of natural resources and the miniaturization trends of advanced electronic products and equipment, there is an urgent need to improve the energy density and efficiency ...of polymeric dielectrics. In this paper, we explore the effect of rod–coil block copolymer polystyrene-b-polybis(4-cyanophenyl) 2-vinylterephthalate (denoted as PS-b-PBCN) on the dielectric behavior and energy storage properties of PS-based blend films. The dipolar glass rigid polymer PBCN can have a columnar nematic phase, a high glass-transition temperature of 156 °C, a high relative permittivity (εr) of 14, and a low band gap of ≈3.44 eV; however, it has poor film-forming properties. Linear dielectric PS possesses low cost, and good film-forming and insulation properties, with a low εr value of 2.5. Two types of PS-b-PBCN block copolymers (PS158-b-PBCN78 and PS158-b-PBCN16), including a coil PS block and an electronically polarized rod PBCN block, are fabricated via reversible addition–fragmentation chain transfer polymerization polymerization. The PBCN/PS- and PS-b-PBCN/PS-blended films are synthesized by solution casting. The experimental results indicate that the εr and breakdown strength of the blend films improve with an increasing mass content of homopolymer PBCN or block copolymer PS-b-PBCN. A maximum εr value of 5.8 at 1 kHz is obtained in the 30 wt % PS158-b-PBCN78/PS blend film owing to the good compatibility and high loading of the polar polymer PBCN. Moreover, a low dielectric loss of 0.018 is found. A discharged energy density of 2.16 J/cm3 with a high efficiency of 90% at 295 MV/m is achieved because PBCN can immobilize free electrons and restrict the long-distance migration of charges. This work provides an idea for the fabrication of all-organic PS-based dielectrics with a high energy storage performance by introducing rod–coil block copolymers.
Organic phototransistors, with their electrically adjustable photo-sensing characteristics and mechanical flexibility, are promising components of multifunctional optoelectronics. For practical ...applications of the optoelectronics, it is essential to develop organic phototransistors with high photo-sensing performances and wavelength selectivity. Although, several studies have been conducted on improving the photo-sensing performances of organic phototransistors through the molecular engineering of organic materials, achieving improved light absorption and stable electrical performance remains a challenge. Here, we propose a new organic phototransistor structure that improves photo-sensing performances and wavelength selectivity by introducing helical photonic crystal (HPC) insulators. To realize the HPC film acting as a reliable insulator and an effective blue-wavelength reflector, a numerical analysis is performed. In the developed device, the blue light transmitting the semiconductor medium is effectively reflected by the HPC insulator, thereby improving the absorption of blue light in the channel region. Our device exhibits higher photo-sensing performances than the reference device without HPC film in terms of photosensitivity, photoresponsivity, and blue-wavelength selectivity. This novel concept of improving the wavelength selectivity of organic phototransistors will become an effective part of the development of practical photodetectors related to next-generation light and image sensors.
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•A novel method to improve photo-sensing performances of organic phototransistors is proposed.•A helical photonic crystal insulator is systematically designed by the liquid crystalline polymer.•The developed helical photonic crystal film acts as a reliable insulator and blue-wavelength reflector.•The helical photonic crystal based organic phototransistor shows improved photo-sensing performances under blue light.
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