Formation of liquid crystalline phases in aqueous suspensions of platelet-like tripalmitin nanoparticles

Abstract

Generation of frustrated liquid crystal phases by mixing an achiral nematic-smectic-C mesogen with an antiferroelectric chiral smectic liquid crystal J. Chem. Phys. 122, 144906 (2005) Suspensions of platelet-like shaped tripalmitin nanocrystals stabilized by the pure lecithin DLPC and the lecithin blend S100, respectively, have been studied by small-angle x-ray scattering (SAXS) and optical observation of their birefringence at different tripalmitin (PPP) concentrations ϕ PPP . It could be demonstrated that the platelets of these potential drug delivery systems start to form a liquid crystalline phase already at pharmaceutically relevant concentrations ϕ PPP of less than 10 wt. %. The details of this liquid crystalline phase are described here for the first time. As in a previous study [A. Illing et al., Pharm. Res. 21, 592 (2004)] some platelets are found to self-assemble into lamellar stacks above a critical tripalmitin concentration ϕ st P P P of 4 wt. %. In this study another critical concentration ϕ lc P P P ≈ 7 wt. % for DLPC and ϕ lc P P P ≈ 9 wt. % for S100 stabilized dispersions, respectively, has been observed. ϕ lc P P P describes the transition from a phase of randomly oriented stacked lamellae and remaining non-assembled individual platelets to a phase in which the stacks and nonassembled platelets exhibit an overall preferred orientation. A careful analysis of the experimental data indicates that for concentrations above ϕ lc P P P the stacked lamellae start to coalesce to rather small liquid crystalline domains of nematically ordered stacks. These liquid crystalline domains can be individually very differently oriented but possess an overall preferred orientation over macroscopic length scales which becomes successively more expressed when further increasing ϕ PPP . The lower critical concentration for the formation of liquid crystalline domains of the DLPC-stabilized suspension compared to ϕ lc P P P of the S100-stabilized suspension can be explained by a larger aspect ratio of the corresponding tripalmitin platelets. A geometrical model based on the excluded volumes of individual platelets and stacked lamellae has been developed and successfully applied to reproduce the critical volume fractions for both, the onset of stack formation and the appearance of the liquid crystalline phase.

Liquid Crystalline Phase Formation in Suspensions of Solid Trimyristin Nanoparticles

“…This is significantly lower than the aspect ratio ⟨D⟩/⟨h⟩ V = 13.0 that can be calculated in a similar way for S100-stabilized PPP platelets from a previous study (d PCS = 84.2 nm, d isl = 7.0 Å and d osl = 3.5 Å, ⟨i⟩ V = 2.79·d 001 , d 001 = 4.02 nm). 25 The lower critical concentrations of 4% PPP for the stack formation in PPP suspensions 22,25 is in good agreement with the observation that the propensity of triglyceride platelets to self-assemble in stacks rises with the length of the fatty acids of the triglyceride in the sequence trilaurin (C 12 ) < trimyristin (C 14 ) < tripalmitin (C 16 ) < tristearin (C 18 ). 21 Triglycerides with longer fatty acids produce platelets with higher aspect ratios that promote the formation of stacks and increase the viscosity of the suspensions.…”

Real‐Time Investigation of Intercalation and Structure Evolution in Printed Polymer:Fullerene Bulk Heterojunction Thin Films

“…For this purpose the apparently dried samples at the end of an in situ drying experiment were removed from the sample cell and dried in vacuum to reduce the solvent content in the samples as far as possible before performing the 2D‐GIXD measurement. The ex situ measurements were conducted inside the fully evacuated beam path of the highly customized Versatile Advanced X‐ray Scattering instrumenT ERlangen (VAXSTER) at the chair for Crystallography and Structural Physics (Universität Erlangen‐Nürnberg, Germany) …”

“…Respecting that the distance between the blade and the beam blocking frame of the applicator is 15 mm, the first time frame of the recorded X‐ray data with full scattering intensity corresponds to a time of 15 mm/15 mm s −1 = 1 s after film formation. The ex situ measurements were recorded with VAXSTER instrument using its former 30 W Cu Kα ( λ = 1.5418 Å) Microfocus X‐ray source GeniX with a FOX 2D parallel beam mirror optics (Xenocs, Sassenage, France) . The beam was shaped by two automated double slit systems (aperture sizes 0.7 × 0.7 and 0.4 × 0.4 mm 2 ) with a distance of about 1.2 m. The second slit system consists of four “scatterless” silicon single crystal blades.…”

A novel experimental approach for nanostructure analysis: simultaneous small-angle X-ray and neutron scattering

“…The first sample is an aqueous suspension of platelet-shaped tripalmitin nanocrystals (TP NCs). Corresponding systems of TP NCs have been intensively studied by our group (Schmiele et al, 2015;Schmiele, Gehrer et al, 2014) as potential drug delivery systems. The second sample is an aqueous dispersion of commercial silica particles (Ludox TM50, 50 wt%) purchased from Sigma-Aldrich; the average diameter of the SiO 2 NPs is about 26 AE 2 nm (see fitting results in Fig.…”

“…However, X-rays interact prevalently with the electron shell of the atoms, while neutrons interact with their nuclei, and thus the two radiations offer two different contrasts (X-ray and neutron scattering cross section). The SAS method has been used with great success in investigating the structure of soft condensed matter such as emulsions (Schmiele et al, 2016), micelles (Schmutzler, Schindler, Goetz et al, 2018; Schmutzler, Schindler, Schmiele et al, 2018), liquid crystalline structures (Gehrer et al, 2014;Schmiele, Gehrer et al, 2014;Schö nhals et al, 2010) and organic nanoparticle (NP) dispersions (Schuldes et al, 2019;Schmiele, Schindler et al, 2014;Unruh, 2007). For advanced functional materials applications (e.g.…”