Phase Behavior of Lipid–Based Lyotropic Liquid Crystals in Presence of Colloidal Nanoparticles

Abstract

We have investigated the microstructure and phase behavior of monoglyceride-based lyotropic liquid crystals in the presence of hydrophilic silica colloidal particles of size comparable to or slightly exceeding the repeat units of the different liquid crystalline phases. Using small angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC), we compare the structural properties of the neat mesophases with those of the systems containing silica colloidal particles. It is found that the colloidal particles always macrophase separate in inverse bicontinuous cubic phases of gyroid (Ia3d) and double diamond (Pn3m) symmetries. SAXS data for the inverse columnar hexagonal phase (H(II)) and lamellar phase (L(α)) suggest that a low volume fraction of the nanoparticles can be accommodated within the mesophases, but that at concentrations above a given threshold, the particles do macrophase separate also in these systems. The behavior is interpreted in terms of the enthalpic and entropic interactions of the nanoparticles with the lamellar and hexagonal phases, and we propose that, in the low concentration limit, the nanoparticles are acting as point defects within the mesophases and, upon further increase in concentration, initiate nucleation of nanoparticles clusters, leading to a macroscopic phase separation.

Inorganic nanoparticles modify the phase behavior and viscoelastic properties of non-lamellar lipid mesophases

“…The SAXS profile of dry SPIONs (Figure 2c, red curve) is characterized by an intense peak (centered at 0.07 Å -1 ), which is slightly shifted at higher scattering vectors with respect to the extra-peak in the corresponding mixed mesophase. We attribute the peaks observed for the dry films as arising from interparticle correlations, thereby ascribing the extra-peaks in the hybrid samples to a partial clusterization of NPs along the grain boundaries of the polycrystalline mesophases, as previously shown for similar systems in other studies [13,43,44]. The difference in the correlation length of SPIONs and AuNPs in the dry film might be both related to the core differences or to the slightly different hydrophobic coating of NPs, which might lead to a different arrangement of the alkyl chains between the neighboring NPs.…”

“…The most explored amphiphilic scaffolds are lipid vesicles, but more recently some studies have addressed the insertion of inorganic NPs [12,13] into non-lamellar lipid assemblies formed through self-assembly of polymorphic lipids. While some applicative examples have been reported, a fundamental understanding of the impact of NPs on lipid phase behavior, necessary to design these materials for a specific biomedical application is, to date, very limited.…”

Size and Phase Control of Cubic Lyotropic Liquid Crystal Nanoparticles

“…35 36 and have recently demonstrated this experimentally from a curved lipid bilayer. 37 They found that the transition from SUVs to the cubic phase has an intermediate tetrahedral packed bilayer vesicle stage before forming the larger cubosomes.…”

Hydrophobic nanoparticles promote lamellar to inverted hexagonal transition in phospholipid mesophases

“…Venugopal et al 47 studied the phase behaviour of monolinolein, which has a single chain rather than the two of DOPE, with added hydrophilic silica NPs of 5 nm diameter. They found that an increasing concentration of NPs decreased the lattice parameter of the cubic phase and that at higher concentrations the NPs exhibited an independent structure factor peak in the SAXS patterns, which indicated that the NPs were macrophase separated rather than incorporated into the structure and that they dehydrated the lipid mesophase by removal of water from lipid head groups to stabilise the NP aggregates.…”