Impact of ferroelectric and superparaelectric nanoparticles on phase transitions and dynamics in nematic liquid crystals

Abstract

Broadband dielectric spectroscopy (BDS) of pure 5OCB and nanocolloids consisting of 5OCB and paraelectric or ferroelectric BaTiO3 nanoparticles (NPs) was performed on varying pressure or temperature. We found strong impact of NPs on static and dynamic phase behavior. In particular, strongest effects on pretransitional behavior were observed for a relatively low concentration of NPs which we attribute to the NPs-induced disorder. Paramagnetic or ferromagnetic character of NPs did not significantly influence measurements. However, several features measured using temperature or pressure path in nanocolloids where significantly different, contrary to the observed behaviour in pure LC compounds. Dynamical properties were tested using the FDSE (fractional Debye-Stokes-Einstein) relation, yielding the fractional coefficient S = 0.71 and S = 0.3 for the temperature and pressure path, respectively.

Polyvinylidene difluoride-based composite: glassy dynamics and pretransitional behaviour

“…Dielectric loss curves for the selected temperature, for BST/PVDF composite. Lines show the validity of Jonscher's relations given by equation(15).…”

“…For describing the previtreous behaviour of dynamic properties the SA equation (6) cannot be directly applied due to the unknown general form of the apparent activation energy and ersatz relations are used. The basic one is the Vogel-Fulcher Tamman (VFT) equation (15) [2,17,18]. There are other basic modelequations (MYEGA, AM, etc.)…”

“…To calculate experimental values of I DO (T ) the protocol for the non-biased determining of the apparent activation energy without the knowledge of τ 0 pre-factor in prior, was developed. It bases on the numerical solution, for the given set of τ (T ) data, of the differential equation resulted from the general SA equation (15) [21][22][23]:…”

“…For n = 1 one obtains the VFT equation (15) with the singular temperature T N = T 0 . Knowing values of T N and n from the analysis presented in Figure 5b -PVDF: τ 0 = 1.66 · 10 −12 s, D T = 6.6 and T N = 195 K, n = 0.92 for T > T g -BST/PVDF: τ 0 = 15 · 10 −9 s, D T = 7 and T N = 106 K, n = 1.32 for T < T g It is notable that that for the VFT equation the coefficient n = 1, i.e.…”

“…Consequently, focused studies beyond dominant paths can have a milestone meaning for approaching the ultimate insight into this a e-mail: szymon.starzonek@wp.pl puzzling topic. A possible milestone direction can offer studies in 'innovative' glass forming systems, such as composite materials benefiting from the combination of a polymeric glass matrix and solid nano-or microparticle [5][6][7][8][9][10][11][12][13][14][15][16]. This can lead to qualitatively new glassy metamaterial features, results for the added value combination of constituents' properties [14][15][16].…”