Magneto-optical study of the orientation confinement of particles in ferrolyotropic systems

Abstract

Ferrosmectics and ferrohexagonals are magnetic liquid crystals which consist of a lamellar and a hexagonal phase in which magnetic nanoparticles are incorporated. The magnetic field variation and the relaxation of the linear optical birefringence of ferrosmectics and ferrohexagonals and its time relaxation are measured in different geometries and compared with that of a ferrofluid sample. We interpret our data by the existence of a mean orientation of the magnetic particles in the lyotropic structure, which appears to be non-random in zero field. We conclude that the magnetic moments of the particles are preferentially aligned in the plane of the ferrosmectic layers and along the axis of the ferrohexagonal cylinders, respectively. To account for this preferred alignment, we propose that some of the particles in the ferrosmectic are adsorbed on the surfactant layers with their moment aligned in the lamellar plane, while the orientation of the moments in the ferrohexagonal is restricted to a cone around the cylinder axis.PACS. 75.50.Mm Magnetic liquids -78.20.Ls Magnetooptical effects -61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

Twofold Light and Magnetic Responsive Behavior in Nanoparticle–Lyotropic Liquid Crystal Systems

“…20,21 Nonetheless, this remains a highly challenging task due to the restriction in the choice of nanoparticle size, 22 which should typically remain smaller than lamellar periodicity, and the pronounced tendency of the nanoparticles to aggregate. 20,22,23 We have however recently shown that by cooling through the disorder-order transition a mesophase loaded with magnetic nanoparticles can lead to a significant orientational order without restrictions on the size of nanoparticles used. 24 Light responsive systems are also particularly appealing due to their noninvasive character and the ease of handling.…”

“…When mixed with water, lipid based surfactant self-assemble into different liquid crystalline symmetries such as the lamellar phase (Lα), inverted hexagonal phase (H II ), bicontinuous cubic phases ( Ia 3 d and Pn 3 m ) and find diverse applications in food, cosmetics, and pharmaceuticals for controlled release and delivery systems. ,, Ferromagnetic nanoparticles, on the other hand, are also getting significant interest in a number of applications including in vitro and in vivo targeted drug delivery, magnetic resonance imaging (MRI) contrast agents, cell signaling, thermal imaging, and in hyperthermic treatment of tumors, where researchers make use of inductive heating of magnetic nanoparticle for therapeutic purposes . Although neat lyotropic liquid crystals can in principle be oriented in presence of high magnetic field, , doping them with magnetic nanoparticles can greatly enhance the level of macroscopic alignment in low magnetic field. , Nonetheless, this remains a highly challenging task due to the restriction in the choice of nanoparticle size, which should typically remain smaller than lamellar periodicity, and the pronounced tendency of the nanoparticles to aggregate. ,, We have however recently shown that by cooling through the disorder-order transition a mesophase loaded with magnetic nanoparticles can lead to a significant orientational order without restrictions on the size of nanoparticles used …”

Macroscopic Alignment of Lyotropic Liquid Crystals Using Magnetic Nanoparticles

“…The authors concluded that the magnetic layers tend to orient parallel to the applied field. The compatibility of magnetic nanoparticles in lamellar phase15 and their magneto‐optical properties are also extensively studied 19. Recently, it has been reported that in a dilute lamellar phase, magnetic nanorods can be oriented using an applied magnetic field, and at high magnetic field, the bilayers can also “follow” the nanorods and tend to align perpendicular to the field 20, 21.…”

Effect of magnetic nanoparticles on the nematic-smectic-A phase transition

“…The mixture of nematic and smectic liquid crystals and magnetic nanoparticles is known as a ferronematic and ferrosmectic. A number of experimental studies [12][13][14][15][16][17][18][19][20] are devoted to study of ferrosmectic phase in both in thermotropic and lyotropic liquid crystals. The most essential feature of the ferrosmectics is that their structure aligns parallel to an external magnetic field.…”