POLICRYPS-based electrically switchable Bragg reflector

The formation and characterization of a switchable volume reflective element fabricated from a polymer liquid crystal (LC) polymer slice (POLICRYPS) structure by holographic photopolymerization at high temperature (65 °C) using a photosensitive/nematic liquid crystal prepolymer mixture is reported. The submicron Bragg structure formed consists of periodic continuous polymeric walls separated by periodic LC channels. The phase separated NLC self-aligns in a homeotropic alignment between the polymer walls as indicated by polarizing optical microscopy analysis (Maltese cross). The resulting periodic grating structure results in a Bragg reflection notch upon illumination with white light due to the periodic variation in refractive index. Electro-optical experiments realized through in-plane electrodes and temperature experiments confirm that the multilayer structure acts as a Bragg mirror whose reflection efficiency can be controlled by either a small (∼3V/μm) electric field or temperature

Control of the plasmonic resonance of a graphene coated plasmonic nanoparticle array combined with a nematic liquid crystal

We report on the fabrication and characterization of a switchable plasmonic device based on a conductive graphene oxide (cGO) coated plasmonic nanoparticle (NP) array, layered with nematic liquid crystal (NLC) as an active medium. A monolayer of NPs has been immobilized on a glass substrate through electrostatic interaction, and then grown in place using nanochemistry. This monolayer is then coated with a thin (less then 100nm) cGO film which acts simultaneously as both an electro-conductive and active medium. The combination of the conductive NP array with a separate top cover substrate having both cGO and a standard LC alignment layer is used for aligning a NLC film in a hybrid configuration. The system is analysed in terms of morphological and electro-optical properties. The spectral response of the sample characterized after each element is added (air, cGO, NLC) reveals a red-shift of the localized plasmonic resonance (LPR) frequency of approximately 62nm with respect to the NP array surrounded by air. The application of an external voltage (8Vpp) is suitable to modulate (blue shift) the LPR frequency by approximately 22nm

Light-addressable liquid crystal polymer dispersed liquid crystal

Scattering-free liquid crystal polymer-dispersed liquid crystal polymer (LCPDLC) films are fabricated by combining a room temperature polymerizable liquid crystal (LC) monomer with a mesogenic photosensitive LC. The morphological and photosensitive properties of the system are analysed with polarized optical microscopy and high resolution scanning and transmission electron microscopy. A two-phase morphology comprised of oriented fibril-like polymeric structures interwoven with nanoscale domains of phase separated LC exists. The nanoscale of the structures enables an absence of scattering which allows imaging through the LCPDLC sample without optical distortion. The use of a mesogenic monomer enables much smaller phase separated domains as compared to nonmesogenic systems. All-optical experiments show that the transmitted intensity, measured through parallel polarizers, can be modulated by the low power density radiation (31 mW/cm2) of a suitable wavelength (532 nm). The reversible and repeatable transmission change is due to the photoinduced trans-cis photoisomerization process. The birefringence variation (0.01) obtained by optically pumping the LCPDLC films allow their use as an alloptical phase modulato

Pattern forming instability induced by light in pure and dye-doped nematic liquid crystals

We study theoretically the instabilities induced by a linearly polarized ordinary light wave incident at a small oblique angle on a thin layer of homeotropically oriented nematic liquid crystal with special emphasis on the dye-doped case. The spatially periodic Hopf bifurcation that occurs as the secondary instability after the stationary Freedericksz transition is analyzed.Comment: 8 pages, 7 figures, LaTeX, accepted to Phys. Rev.

Transfer of momentum and torque from a light beam to a liquid

Refraction or absorption of light results in the force and torque, i.e., transfer of momentum and angular momentum from light to the medium. In transversely inhomogeneous beams, the force per unit volume f may have curlf not equal 0 leading to flow or to nonthermal and nongravitational convection in liquids. The force and the torque in scattering systems are as strong as in absorbing materials and may allow one to carry out experiments avoiding thermal effects. Nonlinear optical response of liquid crystals due to this convection is discussed

Complex dynamics and configurational entropy of spatial optical solitons in nonlocal media

Intense light propagating in a nonlinear medium can generate an ensemble of interacting filaments of light, or spatial solitons. Using nematic liquid crystals, we demonstrate that they undergo a collective behavior typical of complex systems, including the formation of clusters and sound-like vibrations, as well as the reduction of the configurational entropy, controlled by the degree of nonlocality of the medium.Comment: 14 pages, 4 figures. Optics Letters, to be publishe

Chromatic dispersion of liquid crystal infiltrated capillary tubes and photonic crystal fibers

We consider chromatic dispersion of capillary tubes and photonic crystal fibers infiltrated with liquid crystals. A perturbative scheme for inclusion of material dispersion of both liquid crystal and the surrounding waveguide material is derived. The method is used to calculate the chromatic dispersion at different temperatures.Comment: 18 pages, 8 figures. Manuscript layout changed Feb. 10th 200

POLICRYPS Composite Materials: Features and Applications

Physical chemistr

Tailoring symmetry groups using external alternate fields

Macroscopic systems with continuous symmetries subjected to oscillatory fields have phases and transitions that are qualitatively different from their equilibrium ones. Depending on the amplitude and frequency of the fields applied, Heisenberg ferromagnets can become XY or Ising-like -or, conversely, anisotropies can be compensated -thus changing the nature of the ordered phase and the topology of defects. The phenomena can be viewed as a dynamic form of "order by disorder".Comment: 4 pages, 2 figures finite dimension and selection mechanism clarifie

Thermoplasmonics with Gold Nanoparticles: A New Weapon in Modern Optics and Biomedicine

Thermoplasmonics deals with the generation and manipulation of nanoscale heating associated with noble metallic nanoparticles. To this end, gold nanoparticles (AuNPs) are unique nanomaterials with the intrinsic capability to generate a nanoscale confined light‐triggered thermal effect. This phenomenon is produced under the excitation of a suitable light of a wavelength that matches the localized surface plasmonic resonance frequency of AuNPs. Liquid crystals (LCs) and hydrogels are temperature‐sensitive materials that can detect the host AuNPs and their photo‐induced temperature variations. In this perspective, new insight into thermoplasmonics, by describing a series of methodologies for monitoring, detecting, and exploiting the photothermal properties of AuNPs, is offered. From conventional infrared thermography to highly sophisticated temperature‐sensitive materials such as LCs and hydrogels, a new scenario in thermoplasmonic‐based, next generation, photonic components is presented and discussed. Moreover, a new road in thermoplasmonic‐driven biomedical applications, by describing compelling and innovative health technologies such as on‐demand drug‐release and smart face masks with smart nano‐assisted destruction of pathogens, is proposed. The latter represents a new weapon in the fight against COVID‐19