Florian Trummer

Abstract

Gelled lyotropic liquid crystals (G-LLCs) and gelled micellar solutions (G-MS) are promising soft materials for biomedical applications, combining mechanical stability with functional nanostructures capable of encapsulation and delivery. In such systems, the interactions between the gel network and the self-assembled surfactant structures significantly influence their properties. We investigated the simultaneous self-assembly of the biosurfactant di-rhamnolipid (Rha2C10C10) and the low molecular weight gelator 12-hydroxyoctadecanoic acid (12-HOA). We showed the dual role of 12-HOA as both gelator and co-surfactant at two different pH-values. Rheological measurements confirmed successful gelation, with enhanced elastic properties observed in both isotropic and liquid crystalline phases. SAXS and FFEM analyses reveal the coexistence of the gel network and the respective surfactant structure (LLCs or micelles). Furthermore, pH-dependent variations in fibre morphology suggest interactions between protonated rhamnolipid molecules and growing gel fibres, leading to structural defects and altered chirality. These findings highlight the complex interplay between surfactant self-assembly and gelation, providing design principles for tunable hybrid soft materials.

Abstract

Binders play a key role in fabricating efficient gas diffusion electrodes (GDEs), where catalyst layers are sprayed onto hydrophobic gas diffusion layers (GDLs). In a previous work, we investigated the use of a dry-pressed single-layer GDE composed of Polytetrafluoroethylene (PTFE) and SnO2 supported on carbon black for CO2 reduction to formic acid (FA) with high Faradaic efficiencies (FEs) of 80%–90% at current densities of 200 mA cm−2. However, dry-pressed single-layer electrodes suffer from progressive electrowetting and flooding during the reduction. To address these limitations, we transferred this approach to catalyst-coated hydrophobic GDLs, which require suitable binders/ionomers. We examined Nafion, Sustainion, PTFE, and an imidazolium-based polymeric ionic liquid (PIL), specifically poly(1-vinyl-3-dodecylimidazolium bromide) (PIL1-d), which was anticipated to provide enhanced performance. The results demonstrated that incorporation of the PIL significantly improved electrode performance for electrochemical CO2 reduction (eCO2RR). This improvement was most pronounced for unsupported SnO2 and for larger SnO2 nanoparticles (>100 nm). Dynamic light scattering measurements indicated that the PIL already stabilized the SnO2 dispersion in the catalyst ink during spray coating through interactions with the oxide nanoparticles. An ionomer loading of 5 wt.% PIL in the catalyst layer was optimal, yielding a maximum FE of 92% FA at 200 mA cm−2.

Abstract

Sustainable biosurfactants, such as rhamnolipids (RL), have been attracting increasing attention because of their enhanced biocompatibility and high biodegradability compared to conventional synthetic surfactants. To enable large-scale application of rhamnolipids, such as cleaning or washing, we studied symmetric, biocompatible microemulsions of the type H2O (KCl brine)–isopropyl myristate (IPM)–di-RL (Rha2C10C10)–alkane-1,2-diol. We present a systematic study on the influence of major formulation parameters, namely temperature, salinity, pH, and co-surfactant chain length, on the phase behavior and nanostructure. At pH = 8.0 ≫ pKa, Rha2C10C10 behaves similarly to double-tail anionic surfactants, including AOT, and does not form oil-continuous microemulsions at low salinities. At higher salinities, a classical fish phase diagram with a three-phase body was observed, implying that the addition of octane-1,2-diol causes an inversion of the amphiphilic film curvature from being curved around IPM to around brine. Lowering the pH to pH = 6.0 ∼ pKa leads to the partial protonation of the di-RL and a more hydrophobic behavior. Longer chain alkanediols substantially improve the solubilization efficiency of the amphiphile mixture. Small-angle neutron scattering (SANS) measurements showed an interaction peak at low q with values of the amphiphilicity factor fa around −0.7, confirming the presence of well-structured microemulsions. Data analysis at high q with a modified Porod law revealed surprisingly low values of blurriness t, in view of the di-RL’s large headgroup, and a geometrical factor a significantly larger than predicted by models of the bicontinuous structure. Both observations might be linked to a scattering contribution of the bulky sugar head groups. Finally, at high pH and low salinity, an additional high-q scattering feature is observed, which could be related to the packing of the rhamnose moieties or to the local segregation of di-RLs and alkane-1,2-diols in the amphiphilic film.

Abstract

The growing demand for sustainable surfactants has led to increased interest in biosurfactants such as rhamnolipids. We studied the self-assembly of the biosurfactant di-rhamnolipid (Image 1) in Image 2 starting at the cmc up to the Lyotropic Liquid Crystal (LLC) regime. Measuring the phase behaviour at two different pH values, 6.0 () and 8.0 (), one sees how the charge of the surfactant influences the properties. At a , Image 3 behaves similar to nonionic alkyl polyglucoside surfactants, and forms micelles over a large concentration range and a lamellar phase at high concentrations. In contrast, at a the surfactant's carboxyl group is deprotonated, leading to ionic behaviour and the formation of globular micelles at low concentrations and a hexagonal phase at higher concentrations. The transition between the micellar and the phase occurs over a narrow concentration range, suggesting a sharp structural reorganisation. Our findings highlight the strong influence of the pH on the self-assembly of di-rhamnolipid over a broad concentration range.

Abstract

The competition between the bimolecular nucleophilic substitution (SN2) and base-induced elimination (E2) reaction and their intrinsic reactivity is of key interest in organic chemistry. To investigate the effect of suppressing the E2 pathway on SN2 reactivity, we compared the reactions F− + CH3CH2I and F− + CF3CH2I. Differential cross-sections have been measured in a crossed-beam setup combined with velocity map imaging, giving insight into the underlying mechanisms of the individual pathways. Additionally, we employed a selected-ion flow tube to obtain reaction rates and high-level ab initio computations to characterize the different reaction pathways and product channels. The fluorination of the β-carbon not only suppresses the E2-reaction but opens up additional channels involving the abstraction of fluorine. The overall SN2 reactivity is reduced compared to the non-fluorinated iodoethane. This reduction is presumably due to the competition with the highly reactive channels forming FHF− and CF2CI−.

Abstract

In contrast to their more common counterparts in aqueous solutions, inverse ISAsomes (internally self-assembled somes/particles) are formulated as kinetically stabilised dispersions of hydrophilic, lyotropic liquid-crystalline (LC) phases in non-polar oils. This contribution reports on their formation in bio-compatible oils. We found that it is possible to create inverse hexosomes, inverse micellar cubosomes (Fd3m) and an inverse emulsified microemulsion (EME) in excess squalane with a polyethylene glycol alkyl ether as the primary surfactant forming the LC phase and to stabilise them with hydrophobised silica nanoparticles. Furthermore, an emulsified L1-phase and inverse hexosomes were formed in excess triolein with the triblock-copolymer Pluronic® P94 as the primary surfactant. Stabilisation was achieved with a molecular stabiliser of type polyethylene glycol (PEG)-dipolyhydroxystearate. For the inverse hexosomes in triolein, the possibility of a formulation without any additional stabiliser was explored. It was found that a sufficiently strong stabilisation effect was created by the primary surfactant alone. Finally, triolein was replaced with olive oil which also led to the successful formation of inverse hexosomes. As far as we know, there exists no previous contribution about inverse ISAsomes in complex oils such as triolein or plant oils, and the existence of stabiliser-free (i.e., self-stabilising) inverse hexosomes has also not been reported until now.