arXiv subjects

Martin F. Haase

Publications and source records attributed to Martin F. Haase.

7 recordsLinked to original sources

arXiv2026

Lipid Hydrocarbon Tail Structure Governs Interfacial Anchoring and Stripe Morphology in Cholesteric Liquid Crystals

Liquid crystal-based biosensors exploit the sensitivity of interfacial anchoring to molecular adsorption. Cholesteric liquid crystals are especially useful because their helical structure supports multiple optically distinct textures that evolve with anchoring strength. Here, we compare saturated 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) and unsaturated 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) monolayers to determine how lipid acyl chain structure governs interfacial organization and director alignment. Mapping stripe spacing across lipid concentration, mixing ratio, cholesteric pitch, and confinement shows that the transition from fingerprint textures toward homeotropic alignment depends on both lipid structure and collective interfacial organization. DLPC produces comparatively regular textures and more readily promotes helix unwinding at high coverage, consistent with more spatially uniform collective anchoring. DOPC-containing interfaces show greater morphological heterogeneity, consistent with strong local anchoring from longer tails together with less uniform organization arising from cis-unsaturation. FRAP measurements provide complementary information on fluorescent-probe mobility, which becomes strongly restricted at high lipid concentration for both systems. Variations in pitch and film thickness further modulate the response, producing coexisting regular, distorted, and lipid-enriched textures. Together, these results show that lipid acyl chain structure regulates cholesteric anchoring through its effects on local interactions, collective interfacial organization, and mobility, providing design principles for responsive liquid-crystal interfaces.

cond-mat.soft↗

arXiv2026

Substrate-Directed Wetting Layers in Bicontinuous Particle-Stabilised Emulsions

Bicontinuous interfacially jammed emulsion gels (bijels) facilitate efficient mass transport across multiple length scales due to their interwoven structure of particle-stabilised liquid channels. This unique morphology imparts considerable potential for applications in separation and catalysis, particularly when fabricated \textit{via} solvent-transfer-induced phase separation (STrIPS). STrIPS enables the continuous, large-scale production of nanostructured bijel films on solid substrates, yet the influence of the substrate properties on the formation dynamics and final morphology remains insufficiently understood. In this study, this relationship is elucidated by preparing STrIPS bijel films on silane-functionalised glass substrates with selectively controlled wettability and analysing the resulting structure with confocal microscopy. The results showed the presence of notable wetting layers at the bijel-substrate interface, whose thicknesses could be tuned through the nanoparticle weight fraction. In line with numerical simulations, increasing the substrate hydrophobicity drove a transition from a laminar, water-rich surface layer to a patch-like, progressively oil-rich structure. These findings provide crucial insight into the structure-directing role of substrates in supported bijel films, which aids their application as functional materials.

cond-mat.soft↗

arXiv2026

Phase-Field Models for Particle-Stabilised Emulsions

Particle-stabilised emulsions are a cornerstone of soft matter science due to their broad application and fundamental relevance. Computer simulations provide key insights into the formation and behaviour of these emulsions, yet current methods are limited by the spatiotemporal scales accessible for study. The principal issue is that particles are resolved individually. In this work, an alternative strategy is introduced based on phase-field theory, for which we establish the framework. By evolving continuous fields, large-scale dynamics can be simulated in a computationally efficient manner. Our approach is then applied to model the complex formation of a bicontinuous interfacially jammed emulsion gel (bijel) via solvent-transfer induced phase separation (STrIPS). By resolving the coupled dynamics of liquid phase separation and nanoparticle adsorption, the model allows for the characterisation of the influence of nanoparticles on the morphology. Higher concentrations of nanoparticles are found to reduce the average domain size of STrIPS bijels, in line with previous experimental evidence. The presented phase-field model thus represents a promising approach for the morphological investigation of complex particle-stabilised emulsions.

cond-mat.soft↗

arXiv2025

Insights into Formation of Bicontinuous Emulsion Gels via in-situ (Ultra-)Small Angle X-ray Scattering

Nanostructured materials formed via kinetically controlled self-assembly processes gather more interest nowadays. Bicontinuous emulsion gels stabilized by colloidal particles, called bijels, are attractive materials in soft-matter as they combine bulk properties of two immiscible liquids into an interwoven network structure. The limited understanding of the complex formation phenomena of bijels restricts the control over the synthesis, and so its applicability. In this work, in-situ (ultra-) small-angle X-ray scattering is applied to gain insight into the phase separation and self-assembly kinetics of bijels formed via solvent transfer induced phase separation. An X-ray compatible microfluidic setup allows accessing the process kinetics with a millisecond resolution. The formation of such bijels is shown to occur via three consecutive steps related to fluid mechanics, nanoparticle self-assembly and liquid-liquid phase separation. This time-resolved monitor technique offers valuable insights into the structural evolution of kinetically controlled materials and enhances our understanding of the formation of bicontinuous emulsion gels.

cond-mat.soft↗

arXiv2023

Scalable fabrication of bijel films via continuous flow slit-coating

Nanocomposite membranes are an emerging filtration material in the production of clean water. Recently, the fabrication of porous nanocomposite membranes via solvent transfer induced phase separation (STrIPS) was introduced. During STrIPS, the phase separation of two immiscible liquids is arrested by the attachment of nanoparticles at the liquid-liquid interface, generating a porous particle-stabilized membrane template. STrIPS nanocomposite membranes, however, have so far only been produced as hollow fibers. To overcome this, we designed a roll-to-roll (R2R)-process for the continuous fabrication of flat-sheet nanocomposite membranes via STrIPS. We produce the STrIPS membrane by printing the membrane precursor on a carrier substrate. This allows for the continuous collection of STrIPS membranes with control over the membrane dimensions. Contact angle measurements elucidate the wetting dynamics of the STrIPS membrane on the substrate. Furthermore, we demonstrate control over the membrane pore structure by varying the precusor liquid composition and by changing the particle modification and loading in the membrane. With this, the R2R-approach may stimulate further advancements in the fabrication of flat-sheet nanocomposite membranes via STrIPS.

cond-mat.soft↗

arXiv2018

Shaping nanoparticle fingerprints at the interface of cholesteric droplets

The ordering of nanoparticles into predetermined configurations is of importance to the design of advanced technologies. In this work, we moderate the surface anchoring against the bulk elasticity of liquid crystals to dynamically shape nanoparticle assemblies at a fluid interface. By tuning the degree of nanoparticle hydrophobicity with surfactants that alter the molecular anchoring of liquid crystals, we pattern nanoparticles at the interface of cholesteric liquid crystal emulsions. Adjusting the particle hydrophobicity more finely further modifies the rigidity of assemblies. We establish that patterns are tunable by varying both surfactant and chiral dopant concentrations. Since particle assembly occurs at the interface with the desired structures exposed to the surrounding phase, we demonstrate that particles can be readily crosslinked and manipulated, forming structures that retain their shape under external perturbations. This study establishes the templating of nanomaterials into reconfigurable arrangements. Interfacial assembly is tempered by elastic patterns that arise from the geometric frustration of confined cholesterics. This work serves as a basis for creating materials with chemical heterogeneity and with linear, periodic structures, essential for optical and energy applications.

cond-mat.soft↗

arXiv2017

A change in stripes for cholesteric shells via anchoring in moderation

Chirality, ubiquitous in complex biological systems, can be controlled and quantified in synthetic materials such as cholesteric liquid crystal (CLC) systems. In this work, we study spherical shells of CLC under weak anchoring conditions. We induce anchoring transitions at the inner and outer boundaries using two independent methods: by changing the surfactant concentration or by raising the temperature close to the clearing point. The shell confinement leads to new states and associated surface structures: a state where large stripes on the shell can be filled with smaller, perpendicular sub-stripes, and a focal conic domain (FCD) state, where thin stripes wrap into at least two, topologically required, double spirals. Focusing on the latter state, we use a Landau-de Gennes model of the CLC to simulate its detailed configurations as a function of anchoring strength. By abruptly changing the topological constraints on the shell, we are able to study the interconversion between director defects and pitch defects, a phenomenon usually restricted by the complexity of the cholesteric phase. This work extends the knowledge of cholesteric patterns, structures that not only have potential for use as intricate, self-assembly blueprints but are pervasive in biological systems.

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