Rheological, optical, and thermal characterization of temperature-induced transitions in liquid crystal ferrosuspensions

Abstract

Liquid crystal ferrosuspensions (LCFs) were obtained by inclusion of magnetic microparticles in a nematic liquid crystal (NLC) at mass fractions of up to 20%. The phase transition of the NLC promotes the formation of a space filling particle network and an enhancement of the mechanical properties. Polarized optical microscopy (POM) and differential scanning calorimetry were used to study microparticle network formation. POM images show that an anisotropic particle structure formed when an external magnetic field was applied, whereas a quasihomogeneous cellular network is obtained in the absence of the field. A jump in the viscoelastic moduli at the isotropic-nematic transition temperature of the NLC was observed for all particle concentrations and applied magnetic fields. Experimental results also showed that the rheological response of the LCFs increased with magnetic field and tend to saturate at high fields. A linear relation between the particle mass fraction and the saturation value of the storage modulus was found.

Hierarchical Microstructures Formed by Bidisperse Colloidal Suspensions within Colloid-in-Liquid Crystal Gels

“…This nucleation and growth mechanism is similar to that reported in earlier studies of monodisperse colloids in LCs. 12,14,17 In contrast, in the MP-rich regions of the composite material, the phase transition of the 5CB does not cause significant changes to the MP network (Figure 6d). This arises because the nucleation and growth of the nematic phase occurs within the 5CB-rich domains formed during the second phase transition at 40 °C.…”

“…In brief, MMPs were washed three times in DI water and recovered by centrifugation for 5 min at 9000 rpm. 5,17 At each step, following removal of the supernatant, the colloids were resuspended in DI water using sonication. The colloids were then dried in a vacuum oven at 50 °C for at least 1 week.…”

“…11−13 The above-described LCtemplated synthesis of colloidal networks has been observed for a wide variety of colloids, including poly(methyl methacrylate) (PMMA), 12 gold, 14 polymerized divinylbenzene, 15 CdSe/ZnS quantum dots, 16 and composite magnetic microspheres. 17 Recently, an alternative pathway leading to the synthesis of CLCGs was reported by Bukusoglu et al 5 In contrast to prior studies, when using polystyrene microparticles (MPs), phase separation of the MPs (into a network) was observed to occur within the isotropic phase of the mesogens (i.e., prior to cooling to the isotropic-to-nematic phase boundary). During the initial stage of this phase separation process, the characteristic sizes (L) of the domains were observed to be invariant with increasing time, consistent with the predictions of Cahn−Hilliard theory for the linear regime of spinodal decomposition (SD).…”

Polypeptide-Coated Silica Particles Dispersed in Lyotropic Liquid Crystals of the Same Polypeptide

“…Particles were able to reorient accordingly with the different directions of the applied magnetic field. 70 After the magnetic field was removed, the system evolved to an equilibrium state in which distorted ChLC droplets started to develop and pushed the MGT particles to their surfaces. The agglomerated polypeptide particles appear in Figure 10C as thick rings around "clear" droplets.…”

“…The orientation of the magnetic field was changed to test whether the particles were “locked” in the chain-like texture (see Figure S3.15). Particles were able to reorient accordingly with the different directions of the applied magnetic field . After the magnetic field was removed, the system evolved to an equilibrium state in which distorted ChLC droplets started to develop and pushed the MGT particles to their surfaces.…”