Modifications of FLC Physical Properties through Doping with Fe2O3 Nanoparticles (Part I)

Abstract

The aim of this paper is to show, by systematic studies, the influence of γ-Fe2O3 nanoparticles on the physical parameters of the liquid crystalline matrix, exhibiting a ferroelectric phase in a wide temperature range. The detailed research was carried out by using diffraction (PXRD), microscopic (OM, SEM, FCPM, POM), thermal (DSC), optical (TLI), electric and spectroscopic (FTIR) methods. We show that even the smallest concentration of γ-Fe2O3 nanoparticles largely modifies the parameters of the ferroelectric SmC* phase, such as spontaneous polarization, switching time, tilt angle, rotational viscosity, dispersion anchoring energy coefficient and helix pitch. The admixture also causes a significant reduction in the temperature of phase transitions, broadening the SmA* phase at the expense of the SmC* phase and strong streaking of the texture. We present and explain the non-monotonic modification of these parameters with an increase in the nanoparticle concentration. The influence of oleic acid admixture on these parameters is also widely discussed. We have shown that certain parameters of organic-metal nanocomposites can be controlled by the appropriate amount of metal admixture.

Modifications of EHPDB Physical Properties through Doping with Fe2O3 Nanoparticles (Part II)

“…Figure S1 presents the absorption spectra registered for several chosen temperatures during heating of Composite 1, and for better clarity, the temperature dependence of the first derivative of the absorbance for selected wavelengths. After heating above 70 • C (see Figure 2b and Figure S1), for wavelengths of 225 nm, 240 nm, and 290 nm, the absorbance slightly decreased, which was related to the phase transition of crystal to liquid crystalline state, and was in good agreement with the DSC results [39]. Upon further heating, the absorbance increased for wavelengths of 225 nm and 240 nm exponentially up to about 95 • C, above which the absorbance stabilized up to at least 120 • C (Figure 2b).…”

“…The nanoparticles in the organic matrix most likely acted as a scattering agent in the UV region. As is seen in Figure S3, the temperatures at which the absorbance changed corresponded to the phase transition temperatures obtained by the DSC method [39]. Both the undoped sample (Composite 1) and doped samples (Composites 2-5) showed no absorption of incident light in the 500-850 nm range (the absorbance was below 5%; however, this spectral range had a low signal-to-noise ratio, regardless of temperature), which means that Composites 1-5 were transparent in this range.…”

“…Wu et al showed that the T B for γ-Fe 2 O 3 short nanotubes very strongly depended on the DC magnetic field used to register the ZFC/FC curves (T B decreased from 275 K to 40 K when the applied magnetic field changed from 500 Oe to 5000 Oe) [81]. Summarizing the above, apart from the modification of the phase transition temperatures and the degradation of mesophases [39], this was another reason not to use any surfactant in the preparation of composites. Since all samples consisted of the same γ-Fe2O3 nanoparticles (confirmed by XRD measurements [39]), all experimental data were scaled to the average value of magnetic properties from three independent measurements for pure γ-Fe2O3 nanoparticles.…”

“…Summarizing the above, apart from the modification of the phase transition temperatures and the degradation of mesophases [39], this was another reason not to use any surfactant in the preparation of composites. Since all samples consisted of the same γ-Fe2O3 nanoparticles (confirmed by XRD measurements [39]), all experimental data were scaled to the average value of magnetic properties from three independent measurements for pure γ-Fe2O3 nanoparticles. This approach allowed the determination of the estimated weight concentration of γ-Fe2O3 nano particles used for the preparation of mixtures with EHPDB and/or oleic acid, as well as a direct comparison of the magnetic properties.…”

“…Properties of six nanocomposites denoted as Composites 1-6 (Composite 1 (0.0 wt %), Composite 2 (0.3 wt %), Composite 3 (0.5 wt %), Composite 4 (0.7 wt %), Composite 5 (0.9 wt %) and Composite 6 (0.3 wt % + oleic acid)), as well as pure nanoparticles of γ-Fe 2 O 3 (Sample 1) and nanoparticles decorated with oleic acid (Sample 2), were studied. A detailed description of the sample preparation can be found in our recent paper [39], while phase sequence during cooling of the prepared composites was as follows (phase transition temperatures in parentheses are in Celsius): A question mark in parentheses means that the transition temperature could not be determined (or was subject to a very large error), while P denotes the blue phase.…”