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.

We address the structure of homogeneous mixtures of equal volumes of water and oil rendered miscible by the addition of amphiphilic molecules. Specifically, we study the pathway from regular ternary solutions to structured microemulsions with increasing amphiphilic chain length, i.e., increasing i and j for alkyl polyglycol ether surfactants (CiEj) from C3E0 (i.e., propanol) to C5E2, using contrast variation small angle neutron scattering (SANS). The bulk-contrast SANS pattern of the symmetric system water-cyclohexane-(2-propanol/1-propanol) with nearly horizontal tie-lines matches Ornstein-Zernike behavior with characteristic q-2 decay, implying critical composition fluctuations occurring predominantly in the water-oil ratio. Weak scattering signals were detected in film-contrast SANS possibly due to the existence of the nearby tricritical point (TCP). After passing the TCP, the increasing amphiphilic strength leads to the gradual build-up of well-defined amphiphilic interfaces stabilizing water- and oil-rich domains of colloidal dimensions, as evidenced by the well-known q-4 behavior observed in bulk-contrast SANS pattern at large q. The amphiphilicity factor fa ranging from +1.15 to -0.60 reveals the crossing of the disorder line, the Lifshitz line, and the wetting to non-wetting transition. Precursors of structuring in those mixtures with compositions, where the lamellar phase appears for even longer-chain amphiphiles, are also borne out by the experiments.

Sustainability has become essential in addressing the substitution of depleting fossil‐based resources with bio‐renewable alternatives, including products active at interfaces, such as surfactants. Enhancing their efficiency reduces both ecological and economic impact. Here, we present amphiphilic poly(ethylene glycol)‐ b ‐poly(terpenyl glycidyl ether) diblock copolymers synthesized via anionic ring‐opening polymerization from two terpenyl glycidyl ethers (TGE) based on the naturally occurring terpenoid farnesol, farnesyl glycidyl ether (FarGE), and its hydrogenated derivative hexahydrofarnesyl glycidyl ether (HHFarGE). Using poly(ethylene glycol) monomethyl ether (mPEG 114 ) as a macroinitiator resulted in controlled molecular weights (5600 – 8400 g·mol −1 ) with low dispersities Đ (1.04–1.07). Fluorescence spectroscopy and light scattering revealed low critical micelle concentrations with a systematic decrease with increasing TGE block size due to the hydrophobic effect. The addition of small amounts of mPEG 114 ‐ b ‐PTGE m to microemulsions leads to a significant increase of the solubilization efficiency not limited to conventional H 2 O/NaCl – n ‐decane – tetraethylene glycol monodecyl ether microemulsions, but also in sustainable H 2 O – isopropyl myristate – n ‐octyl β‐D‐glucopyranoside – farnesol formulations, serving as model systems for cosmetic applications. Using SANS, we observed that adsorption of the copolymer at the amphiphilic film leads to an increased structural order of bicontinuous microemulsions due to a higher film bending rigidity.

Poly(dihydrocarvide) (PDHC) is synthesized through ring-opening polymerization (ROP) of terpene-based 7-membered lactone dihydrocarvide (DHC) using an amino-alkoxy-bis(phenolate) yttrium amido catalyst and isopropanol (iPrOH) as a chain transfer agent while retaining the pendant-group double bond in the monomer unit. Polymerization under conditions found to be favorable (60 degrees C, 1 eq. iPrOH) yielding PDHC with tunable molecular weights and low to moderate polydispersities (D = 1.2-1.5). Crystalline fractions are introduced into amorphous PDHC by producing block copolymers with 16-membered omega-pentadecalactone (PDL) or 4-membered racemic beta-butyrolactone (BBL) via sequential addition following the coordination strength hierarchy (PDL < DHC < BBL). This resulted in semi-crystalline renewable block copolymers P(PDL-b-DHC) and P(DHC-b-PHB) that were further analyzed by PXRD and SAXS measurements. Additionally, PDHC is functionalized via thiol-ene reaction with 2-mercaptoethanol, introducing hydroxyl functionality and opening up a multitude of functionalization possibilities. As one example, atom transfer radical polymerization (ATRP) initiators are attached, and SARA and ARGET ATRP techniques are employed to graft poly(ethyl acrylate) (PEA) as model compound, forming PDHC-g-PEA brush polymers. The TPMA(2)(NMe)-based ARGET ATRP system demonstrates superior control over molecular weight and polydispersity compared to SARA ATRP, though both methods yield well-defined polymer brushes with molecular weight growth correlating with the initial amount of ethyl acrylate. This approach demonstrates the potential of PDHC for constructing diverse polymer architectures from different types of lactones or vinyl monomers by combining ROP and ATRP.

In our recent work, we investigated the influence of pressure on the temperature-dependent phase behavior of symmetric, application-relevant microemulsions containing propane, stabilized by an extended surfactant mixture. By means of high-pressure small-angle neutron scattering, the present study provides further insights by unraveling the impact of pressure and propane on the nanostructure of these microemulsions near their optimum point. Despite the obvious presence of multiple scattering, all recorded scattering curves show the typical characteristics of symmetric bicontinuous microemulsions. Analysis of the scattering data using the Teubner-Strey model and Porod's law for diffuse interfaces provided the periodicity dTS, the correlation length ξTS, and the specific interface S/V, as well as the amphiphilicity factor fa and the effective bending rigidity κeff of the amphiphilic film. The overall structural order of pure propane microemulsions was found to be markedly lower compared to the n-decane microemulsions. While the structure of n-decane-rich microemulsions only shows a weak pressure dependence, propane-rich formulations exhibit a significant increase of ξTS with pressure due to an increasing surfactant monolayer rigidity, caused by enhanced interactions of the compressible propane with the surfactant tails. Microemulsions containing mixtures of the two hydrocarbons behave accordingly, demonstrating that the presence of the short-chain alkane gradually amplifies the sensitivity of the amphiphilic film to pressure changes. Interestingly, the geometric prefactor a of bicontinuous structure models increases from slightly above 7 for n-decane microemulsions to a > 8 for propane formulations, owing to the increasing disorder.

The immobilization of molecular catalysts in confined geometries of mesoporous support materials has been shown to selectively control catalytic performances. An additional in-crease in yield and selectivity of the catalytic reaction is expected by the combination of the spatial confinement of the pores with an ionic liquid thin film at the pore surface. Small angle X-ray scattering (SAXS) can provide an important contribution to the structural characterization of such materials. Here we investigate the structure of unfilled and EMIM-PF6-filled porous SFB-15 produced via true liquid crystal templating using SAXS. In particular, the focus of this work was set on mesoporous silica materials with cylindrical mesopores ordered in a two-dimensional hexagonal lattice and pore radii of rpore = 3.7 nm. Taking into account the scattering contributions from the silica grain surfaces, as well as meso- and micropores, the combination of appropriate form and structure factor models allowed to determine essential structural parameters, such as the lattice parameter, the pore radius as well as the thickness and correlation length of a microporous corona. Finally, the growth of the EMIM-PF6 liquid film induced by the loading of the porous materials with EMIM-PF6 could be monitored by systematic SAXS measurements. By knowing the relationship between filling degree, i.e. EMIM-PF6 pore volume fraction φ_IL and film thickness, it is now possible to set the optimal EMIM-PF6 film thickness required for SILP catalysis.

Hypothesis : Amphiphilic diblock copolymers are known to increase the surfactant's efficiency to stabilize microemulsion, leading to higher structural order and monolayer rigidity. We thus seek to evaluate whether the addition of such polymers alters the shear behavior of bicontinuous microemulsions, in particular, their shear transformation towards lamellar structures. Experiments : We examine the initial structure and shear response of bicontinuous D 2 O/ n -octane/C 10 E 4 /PEP 5 - b - PEO 5 microemulsions by coupling microfluidics with small -angle neutron scattering (SANS), attaining wall shear rates in excess of 10 5 s -1 . The azimuthal analysis of the obtained 2D scattering patterns allows us to follow their structural transformation by means of the degree of anisotropy. Findings : The amphiphilic diblock copolymer promotes the shear -induced transformation of bicontinuous microemulsions, resulting in up to similar to 30 % higher degrees of anisotropy than for corresponding polymer -free microemulsions. The increased shear response observed with increasing polymer content is rationalized by combining the influence of domain size and viscosity with the stability limits of the bicontinuous microemulsion in the isothermal phase diagram. As a result, a consistent description of the degree of anisotropy is obtained, enabling the prediction of the shear -induced bicontinuous-to-lamellar transformation.

Formic acid is a potential liquid hydrogen carrier (LHC) for storage and transport of hydrogen, which requires the rapid and efficient recovery of hydrogen from formic acid (through catalysis). Various homogeneous complexes fulfill all of the desired criteria for a formic acid dehydrogenation catalyst. Immobilization of such complexes on solid supports is a common strategy for their application industrially in flow reactors. However, the properties of the support can change the reactivity of the catalyst, often reducing the catalytic activity in ways that are difficult to predict. Here we examine the effect of supports on the dehydrogenation of formic acid using H2Ru(PPh3)(2)(PPh2)(2)N-C3H6-Si(OEt)(3) (1) through a combination of kinetic measurements, molecular dynamics (MD) simulations, and small-angle neutron scattering (SANS). Immobilization of 1 on all supports decreases the rate of formic acid conversion in the order SiO2 > Al2O3 > ZnO > SBA-TMS > SBA-15. Combination of MD simulations and SANS shows that high affinity of formic acid for the surfaces and in particular when confined in the pores results in a high local FA concentration, which inhibits the catalytic rate. Collapse of the Ru complex onto the surface/pore wall may also contribute to this overall inhibition.

Summary Surfactant flooding is an attractive EOR technique making use of the formation of a thermodynamically stable microemulsion and the concomitant decrease of the oil/water interfacial tension. However, surfactant formulation design in the lab is typically done at ambient pressure with so-called dead oil. Understanding and predicting the impact of pressure and volatile gases on application-relevant microemulsions enables a formulation adjustment to achieve high oil production under field conditions. We have gained novel insights into how pressure affects the surfactant membrane in the presence of short-chain alkanes in synthetic live oil formulations, which in turn influences interfacial tensions and hence recovery potential. Nanoscopically, this behavior can be related to the competing effects of headgroup hydration and oil penetration, manifested in a pressure-dependent interplay of water-surfactant head, oil-surfactant alkyl chain, and oil-oil interactions, which favor curvature of the amphiphilic film towards either oil in o/w- or water in w/o-microemulsions. Interestingly, the sign of the HLD pressure coefficient (3 changes more drastically in the presence of methane compared to propane, owing to the higher compressibility of methane. Moreover, our investigations allow a prediction of the properties of these EOR-relevant microemulsions by applying the HLD concept, offering the potential for an optimized production.

The effect of non-saturated corner and edge sites of Pd particles on the long-term selectivity of cis-3-hexen-1-ol in the hydrogenation of 3-hexyn-1-ol was studied in this work. Non-supported Pd agglomerates were synthesized through the microemulsion synthesis route and used at nalkynol/APd ratios between 0.08 and 21 mol/m2 for the catalytic conversion of 3-hexyn-1-ol for 20 h. The selectivity of the cis-hexenol product increased by reducing the quantity of Pd catalytic sites (increasing the nalkynol/APd ratio) without introducing any modifier or doping agent to poison the nonselective sites. Then, Pd aggregates with fused primary particles and, thus, fewer corner and edge sites were produced through thermal sintering of the agglomerates at 473–723 K. By comparing the catalytic performance of the agglomerates and aggregates, it was observed that at a rather similar kinetic behavior (99.99% conversion and 85–89% selectivity to cis-hexenol), the sintered aggregates could stay selective despite a catalytic surface area about seven times larger. This emphasizes the role of low-coordinated edge and corner sites on the final selectivity of the cis product and demonstrates that thermal sintering allows the number of non-selective sites to be reduced without any need for toxic or organic doping agents or modifiers.

The influence of pressure on microemulsion properties is generally weak given the components' low compressibility. However, pressure can become decisive if short-chain alkanes are present, e.g., in enhanced oil recovery, where the impact of live oils contributes to formulation design optimization. Supporting the transfer from laboratory to oil field, we investigated the pressure-dependent phase behavior of application-relevant brine/butyldiglycol & horbar;n-decane/propane & horbar;alkyl alkoxy sulfate/alkyl sulfonate microemulsions. Equal amounts of water/oil were solubilized into a one-phase microemulsion using only a few wt % of surfactant. In n-decane-rich microemulsions, pressure leads to an inversion from water-in-oil to oil-in-water microemulsions, resulting from stronger surfactant headgroup hydration, whereas in propane-rich microemulsions, curvature changes from o/w to w/o, caused by better interactions between the compressible propane and the surfactant tails at elevated pressures. These effects lead to an inversion of the sign of the hydrophilic-lipophilic deviation pressure coefficient beta and compensate each other with roughly 80 mol % of propane in the oil mixture, where the microemulsion is pressure-independent, i.e., beta = 0 at 25 degrees C.

Hypothesis: Shear flow applied to bicontinuous microemulsions is expected to induce a transition to lamellae via the suppression of surfactant monolayer fluctuations. Compared to the topologically analogous L3 (sponge) phase, composed of surfactant bilayers, this transition is likely to occur at much higher shear rates.Experiments: We examine the flow response of a model bicontinuous microemulsion, D2O/n-octane/C10E4 by coupling microfluidics with small-angle neutron scattering (SANS), attaining wall shear rates in excess of 105 s-1. The reduction of probed sample volumes down to-10 nL allows the spatial mapping of the structural and orientation changes within the microchannel, as a function of the flow field components. Findings: With increasing flow rate, we observe a gradual increase in scattering anisotropy, accompanied by a decrease of the microemulsion domain size along the main flow orientation. A consistent description of the degree of anisotropy was obtained when considering the velocity gradient along the scattering plane perpendicular to the flow. We discuss the flow dependence of the effective bending rigidity, rationalizing a strong influence of shear on thermal membrane fluctuations. Assuming a similar shear dependence for the saddle splay modulus, the bicontinuous-to-lamellar transition can be attributed to the gradual disappearance of inter-lamellar passages.(c) 2022 The Author(s). Published by Elsevier Inc.

In the context of a more sustainable economy, bio-surfactants become increasingly important, due to their independence of petrol-based chemistry, their usually mild synthesis conditions, and in certain cases their pharmacological activity. We have recently discussed self-assembly studies in binary systems of bio-surfactants of microbial origin, or saponins extracted from plants (Hellweg et al., Frontiers in Soft Matter, 2023, 2). In the present review, we focus on the formation of microemulsions based on these molecules. We review the formation and structure of microemulsion systems formed by oil, water, and biosurfactants, with a particular focus on Quillaja saponins and rhamnolipids.

Motivated by increasing attention to biobased and potentiallysustainablepolymers from renewable sources, this work describes the synthesisand anionic ring-opening polymerization (AROP) of the terpenoid-derivedfarnesyl glycidyl ether (FarGE) as a hydrophobic epoxide buildingblock for the synthesis of biobased, amphiphilic polyethers that representnovel, nonionic surfactants. In combination with ethylene oxide (EO),the synthetic strategies employed provide access to both amphiphilicdiblock (mPEG(114)-b-PFarGE( m )) and statistical copolymers (PEG( n )-co-PFarGE( m )),featuring facile tunability of their amphiphilic and surfactant properties.The versatile application of FarGE for different polyether architecturesis demonstrated by the well-controlled molecular weights in the rangeof 5040-11170 g mol(-1) and narrow molecularweight distributions (D = 1.04-1.11),both for block and statistical architectures. Owing to the unexpected,nearly ideally random microstructure of the statistical EO/FarGE copolyethers,determined by in situ kinetics (r (EO) =1.18 and r (FarGE) = 0.85), the branchedalkenyl side chain impedes the crystallization of polyethylene glycol(PEG) with increasing FarGE incorporation, allowing for fine-tuningof polymer properties. Observing a low glass transition temperature(T (g)) of around -70 & DEG;C forthe PFarGE homopolymer, the thermal analysis also unveils farnesylside-chain control of the T (g) even at lowFarGE content (7.6 mol %). Detailed investigations of aqueous polymersolutions reveal self-assembly of the amphiphilic copolymers intomicelles and aggregates, characterized by very low critical micelleconcentrations (CMC, 10-53 mg L-1), as wellas larger clusters (R (H,micelle) = 17-35nm and R (H,cluster) = 59-107 nm).The results demonstrate the enormous potential of terpenes and terpenoidsfor partially biobased surfactant alternatives.

Recent studies of self-assembly in binary systems of bio-surfactants, either of microbial origin or saponins extracted from plants, are reviewed. Saponins in water reported in the first section include aescin, glycyrrhizin, and quillaja saponins, while rhamnolipids are discussed in the second section on microbial surfactants. Studies of surface activities are a natural starting point of the characterization of surfactants, but here we focus mainly on physico-chemical and structural properties of self-assembled bulk structures in solution, often characterized by scattering techniques. When quantitative modelling is performed, self-assembly parameters like aggregation numbers, head group areas, and resulting shapes can be followed as a function of physical-chemical parameters like concentration, composition, temperature, or pH. Morphologies include micelles and their structural evolution with addition of other bio- or synthetic surfactants, co-surfactants, proteins or phospholipids.

Coupling microfluidics and small-angle neutron scattering (SANS), we investigate the influence of shear flow on a model bicontinuous microemulsion of D2O/n-octane/C10E4, examining the role of membrane volume fraction in the transformation towards a lamellar structure. We employ a contraction-expansion geometry with flow velocities in excess of 10 m s(-1) and spatially map the microfluidic field using a small SANS beam, illuminating down to 10 nL sample volumes. The shear-induced, progressive, bicontinuous-to-lamellar transition is found to be promoted by additional extensional flow (>10(3) s(-1)), while fast relaxation kinetics (<2 ms) return the scattering pattern to isotropic shortly after the constriction. Further, increasing the domain size of the bicontinuous structure (determined by the membrane volume fraction) appears to amplify its response to shear. Hence, the structural changes within the dilute bicontinuous microemulsions simply scale with the volume fraction of the membrane. By contrast, the stronger response of the microemulsion with the smallest domain size, located near the bicontinuous/lamellar coexistence, indicates an influence of an already more ordered structure with fewer passages. Our findings provide insight into the high shear behaviour of microemulsions of both academic and industrial relevance.

This paper completes previous studies on the phase behaviour and microstructure of the quaternary microemulsion water – cyclohexane – n-octyl-β-D-glucoside (β-C8G1) – geraniol. The properties of this system are almost insensitive to temperature, while they can be tuned easily by adding an alcohol as co-surfactant. The addition of the alcohol changes the composition of the interfacial film, which, in turn, is the tuning parameter for the quaternary system. Studies of the phase behaviour together with SANS and NMR measurements allow drawing a quantitative picture of how the domain size ξ, the curvature H, and the interfacial tension σab depend on the composition of the interfacial film. The SANS data of both oil-in-water and water-in-oil droplet microemulsions recorded near the emulsification failure boundary were evaluated with the Generalised Indirect Fourier Transformation (GIFT), revealing a growth towards cylindrical structures when approaching the respective critical end point. We will show that the general behaviour of ternary and quaternary systems is equal if the appropriate tuning parameters are chosen. In addition, we will show that it is possible to apply the scaling description derived for temperature-dependent ternary systems to composition-dependent quaternary systems: plotting the reduced domain size, the reduced curvature and the reduced interfacial tension against the proper reduced tuning parameter, i.e., either the reduced temperature or the reduced interfacial composition, leads to one master curve for all systems.