Self-assembly, condensation, and order in aqueous lyotropic chromonic liquid crystals crowded with additives

Abstract

Dense multicomponent systems with macromolecules and small solutes attract a broad research interest as they mimic the molecularly crowded cellular interiors. The additives can condense and align the macromolecules, but they do not change the degree of covalent polymerization. We chose a lyotropic chromonic liquid crystal with reversibly and non-covalently assembled aggregates as a much softer system, reminiscent of ''living polymers'', to demonstrate that small neutral and charged additives cause condensation of aggregates with ensuing orientational and positional ordering and nontrivial morphologies of phase separation, such as tactoids and toroids of the nematic and hexagonal columnar phase coexisting with the isotropic melt. Scanning transmission X-ray microscopy (STXM) with near edge X-ray absorption fine structure (NEXAFS) analysis as well as fluorescent microscopy demonstrates segregation of the components. The observations suggest that self-assembly of chromonic aggregates in the presence of additives is controlled by both entropy effects and by specific molecular interactions and provide a new route to the regulated reversible assembly of soft materials formed by low-molecular weight components.

Straining soft colloids in aqueous nematic liquid crystals

“…Here, we note that a prior study has documented that the addition of high concentrations [> 6% (wt/wt)] of surfactants to isotropic phases of DSCG [5.5% (wt/wt) DSCG solutions at room temperature] generated nematic domains (31). Additional reports describe that similarly high concentrations of nonamphiphilic molecules, such as poly(vinyl alcohol) (32), PEG (33), and spermine (33), condense DSCG solutions and lead to the formation of nematic and columnar phases. Condensation of DSCG into higherorder phases by concentrated surfactant and polymer solutions is likely the result of depletion effects, whereas electrostatic interactions also may contribute in the case of spermine (33).…”

“…Additional reports describe that similarly high concentrations of nonamphiphilic molecules, such as poly(vinyl alcohol) (32), PEG (33), and spermine (33), condense DSCG solutions and lead to the formation of nematic and columnar phases. Condensation of DSCG into higherorder phases by concentrated surfactant and polymer solutions is likely the result of depletion effects, whereas electrostatic interactions also may contribute in the case of spermine (33). In contrast, our experiments use low lipid concentrations [∼0.04% (wt/wt)], and we emphasize that the DSCG phase behavior is not substantially perturbed by the presence of the low concentrations.…”

Chiral symmetry breaking by spatial confinement in tactoidal droplets of lyotropic chromonic liquid crystals

“…In the crowded solutions of DSCG, PEG facilitates phase separation into I and N phases, accumulating predominantly in the I phase and inserting an osmotic pressure on the N domains (23). As the concentration of PEG increases, the aggregates in the condensed N phase are packed more closely and their length increases; the extreme outcome is the PEGinduced formation of the columnar hexagonal phase (23). The closer packing and elongation of aggregates lead to (i) the increase of Θ and (ii) decrease of K 22 ∕K 11 , as discussed below.…”

“…In LCLCs, it serves a similar condensing role, causing phase separation of the homogeneous I or N phase into a biphasic I þ N region (23). PEG tends to remain in the I phase, exerting an osmotic pressure on the orientationally ordered condensed regions, promoting elongation of aggregates and their closer packing (23). Addition of PEG at concentration c PEG ¼ 0.005 mol∕kg to the DSCG solution with c DSCG ¼ 0.34 mol∕kg expands the temperature range of the biphasic region to 17°C < T < 37°C.…”

“…DSCG molecules in water reversibly assemble forming polydisperse elongated aggregates. Their length is influenced by temperature, volume fraction, and presence of condensing agents such as PEG (23). A pure DSCG solution with c DSCG ¼ 0.34 mol∕kg is isotropic at elevated temperatures T > 35°C, as the aggregates are too short to form an orientationally ordered phase.…”