Ferromagnetic Ordering Theory of Colloidal Suspension of Magnetic Particles in Liquid Crystal

A molecular-statistical theory of colloidal suspension of spherical ferromagnetic particles in a nematic liquid crystal matrix is considered. A tensor expression of the suspension Hamiltonian is proposed, which contains contributions that make it possible to describe the ferromagnetic state of the studied system. Within the mean-field approximation, a system of equations is obtained that describes various orientational states of the suspension. Phase diagrams of the suspension are plotted. It is shown that depending on temperature and intensity of particles interaction with the liquid crystal matrix, the suspension can be in an ordered state with different magnetic properties, namely, in the ferromagnetic and superparamagnetic nematic phases, in addition to the isotropic phase.

Super Stability of Ag Nanoparticle in Crystalline Lamellar (Lc) Liquid Crystal Matrix at Different pH Environment

The symmetry concept in this paper is related to the natural self-assembly of noble metal nanoparticles in the long range periodic structure of liquid crystal (LC). The current study deliberates the effect of pH on the stability of nanoparticles (NPs) in the lamellar phase of a lyotropic LC environment. The LC was prepared by the mass ratio 0.33:0.22:0.45 for (HDTABr):1-pentanol:water. The LC containing silver nanoparticles (AgNPs) was prepared by replacing the water with Ag solution. The AgNPs were produced by the in situ preparation method in LC. The solution of AgNPs-LC was varied at different pH. The absorption intensities were determined by using ultra-violet spectroscopy (UV-vis). The surface potential and hydrodynamic particle size were determined by using Zeta-potential (measurements). The surface enhanced Raman spectroscopy (SERS) was carried out to enhance the Raman signals of 4-aminobenzenethiol (4-ABT) deposited onto AgNPs as substrate. It is found that all characterizations exhibited super stability for AgNPs dispersed in LC at pH = 3 to 12 with the optimum stability at pH = 5–6. The remarkable stability of NPs is an important indicator of the various applications in nanotechnology and nanoscience fields.

SYNTHESIS AND OPTICAL PROPERTIES OF NANOCOMPOSITES BASED ON LIQUID CRYSTAL WITH BIMETALLIC Au + Ag NANOPARTICLES OF ALLOY TYPE.

In this work, we have carried out a research which aimed to obtain complex nanoparticles of noble metals Au + Ag in the form of bimetallic alloys. Bimetallic nanoparticles were synthesized directly in a liquid-crystalline cadmium caprylate melt in an argon atmosphere in the temperature range of mesophase existence by the simultaneous chemical reduction of cations of gold (Au3+) and silver (Ag+) from their compounds, tetrachloroaurate acid (H[AuCl4]×3Н2О) and silver nitrate AgNO3, respectively. The effect of synthesis duration (3 and 5 hours) on the spectral behavior of binary nanoparticles have been studied. It has been shown that when the synthesis duration is 3 h, mainly homogeneous bimetallic alloys are obtained, and when it is 5 h, both homogeneous and gradient alloys can be obtained. The absorption spectra of homogeneous alloys are characterized by the presence of one surface plasmon resonance (SPR) peak, which occupies an intermediate position relative to the SPR peaks for monometallic nanoparticles, i.e. between 425 and 560 nm. When forming heterogeneous alloys, which are formed in the molar ratio range where the amount of silver ions predominates, the absorption spectra exhibit two SPR peaks which relate to nanoparticles with different metallic silver content. The formation of metallic nanoparticles containing different metals may be due both to the different mobility of noble metals ions in the liquid crystal matrix and to the different rate of rearrangement of metals in the new formed heteronanoparticle. It has been found by electron spectroscopy and transmission electron microscopy that the nanoparticles in this matrix have mostly a spherical shape with a mean diameter of 15 nm. The possibility of the fine control of the position of SPR peak of bimetallic nanoparticles in a liquid crystal matrix over a wide optical range of 422–580 nm is shown.