Higher Salt Hydrophobicity Lengthens Ionic Wormlike Micelles and Stabilizes Them upon Heating.

Tuning the rheological properties of surfactant solutions by charge screening is a convenient formulation tool in cosmetic, household, oil recovery, drag-reduction, and thickening applications. Surfactants self-assemble in water, and upon charge screening and core shielding, they grow into long wormlike micelles (WLMs). These are valuable model systems for soft matter physics, and the most explored formulation is hexadecyl-trimethylammonium bromide (CTAB) and sodium salicylate (NaSal). Replacing NaSal with aromatic salts of altered hydrophobicity results in different penetration of the additive in the CTAB micellar core. This altered penetration depth will determine the anisotropic micellar growth that tailors the viscoelastic response. Sodium 4-methylsalicylate (mNaSal) is a higher hydrophobicity alternative to NaSal, requiring less additive to induce strong changes in the viscoelastic properties. Herein, we provide a comparative study of the mNaSal/CTAB system with the reference NaSal/CTAB over a range of temperatures and salt concentrations. The findings from the well-known NaSal/CTAB pair are transferred to the mNaSal/CTAB system, revealing the origins of the WLM solution's viscoelastic properties by discerning contributions from charge screening and micellar core shielding upon small differences in hydrophobicity.

Ion-Induced Formation of Nanocrystalline Cellulose Colloidal Glasses Containing Nematic Domains.

Controlling the assembly of colloids in dispersion is a fundamental approach toward the production of functional materials. Nanocrystalline cellulose (NCC) is a charged nanoparticle whose colloidal interactions can be modulated from repulsive to attractive by increasing ionic strength. Here, we combine polarized optical microscopy, rheology, and small-angle scattering techniques to investigate (i) the concentration-driven transition from isotropic dispersion to cholesteric liquid crystals and (ii) salt-induced NCC phase transitions. In particular, we report on the formation of NCC attractive glasses containing nematic domains. At increasing NCC concentration, a structure peak was observed in small-angle X-ray scattering (SAXS) patterns. The evolution of the structure peak demonstrates the decrease in NCC interparticle distance, favoring orientational order during the isotropic-cholesteric phase transition. Small amounts of salt reduce the cholesteric volume fraction and pitch by a decrease in excluded volume. Beyond a critical salt concentration, NCC forms attractive glasses due to particle caging and reduced motility. This results in a sharp increase in viscosity and formation of viscoelastic glasses. The presence of nematic domains is suggested by the appearance of interference colors and the Cox-Merz rule failure and was confirmed by an anisotropic SAXS scattering pattern at q ranges associated with the presence of nematic domains. Thus, salt addition allows the formation of NCC attractive glasses with mechanical properties similar to those of gels while remaining optically active owed to entrapped nematic domains.

Tailoring rice flour structure by rubbery milling for improved gluten-free baked goods.

Ever-growing demand for gluten-free products calls for the development of novel food processing techniques to widen the range of existing baked goods. Extensive research has been targeted towards recipe optimization, widely neglecting the tailoring potential of process-induced structuring of gluten-free raw materials. Herein, we address this shortcoming by demonstrating the potential of rubbery milling for the generation of structure and techno-functionality in breads obtained from a variety of rice flour types. Moisture and temperature induced state transitions during milling were exploited to tailor the physicochemical properties of the flour. Moisture addition during conditioning of the different rice varieties and milling in the rubbery state considerably decreased starch damage due to more gentle disintegration. The degree of starch damage dictated the water absorption capacity of the rice flour types. Flour types with reduced starch damage upon milling offered lower dough densities, yielding bread loafs with a higher volume and better appearance. The choice of rice variety enables fine-tuning of the final product quality by influencing the dough viscoelasticity, which defines the final loaf volume. Whole grain rice flour dramatically increased the loaf volume, whilst simultaneously offering nutritional benefits. Combining the proposed functionalised flour types with current and future advances in product recipes paves the way towards optimised gluten-free goods.

Development of Smart Optical Gels with Highly Magnetically Responsive Bicelles.

Hydrogels delivering on-demand tailorable optical properties are formidable smart materials with promising perspectives in numerous fields, including the development of modern sensors and switches, the essential quality criterion being a defined and readily measured response to environmental changes. Lanthanide ion (Ln3+)-chelating bicelles are interesting building blocks for such materials because of their magnetic responsive nature. Imbedding these phospholipid-based nanodiscs in a magnetically aligned state in gelatin permits an orientation-dependent retardation of polarized light. The resulting tailorable anisotropy gives the gel a well-defined optical signature observed as a birefringence signal. These phenomena were only reported for a single bicelle-gelatin pair and required high magnetic field strengths of 8 T. Herein, we demonstrate the versatility and enhance the viability of this technology with a new generation of aminocholesterol (Chol-NH2)-doped bicelles imbedded in two different types of gelatin. The highly magnetically responsive nature of the bicelles allowed to gel the anisotropy at commercially viable magnetic field strengths between 1 and 3 T. Thermoreversible gels with a unique optical signature were generated by exposing the system to various temperature conditions and external magnetic field strengths. The resulting optical properties were a signature of the gel's environmental history, effectively acting as a sensor. Solutions containing the bicelles simultaneously aligning parallel and perpendicular to the magnetic field directions were obtained by mixing samples chelating Tm3+ and Dy3+. These systems were successfully gelled, providing a material with two distinct temperature-dependent optical characteristics. The high degree of tunability in the magnetic response of the bicelles enables encryption of the gel's optical properties. The proposed gels are viable candidates for temperature tracking of sensitive goods and provide numerous perspectives for future development of tomorrow's smart materials and technologies.

Fabrication Procedures and Birefringence Measurements for Designing Magnetically Responsive Lanthanide Ion Chelating Phospholipid Assemblies.

Bicelles are tunable disk-like polymolecular assemblies formed from a large variety of lipid mixtures. Applications range from membrane protein structural studies by nuclear magnetic resonance (NMR) to nanotechnological developments including the formation of optically active and magnetically switchable gels. Such technologies require high control of the assembly size, magnetic response and thermal resistance. Mixtures of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and its lanthanide ion (Ln3+) chelating phospholipid conjugate, 1,2-dimyristoyl-sn-glycero-3-phospho-ethanolamine-diethylene triaminepentaacetate (DMPE-DTPA), assemble into highly magnetically responsive assemblies such as DMPC/DMPE-DTPA/Ln3+ (molar ratio 4:1:1) bicelles. Introduction of cholesterol (Chol-OH) and steroid derivatives in the bilayer results in another set of assemblies offering unique physico-chemical properties. For a given lipid composition, the magnetic alignability is proportional to the bicelle size. The complexation of Ln3+ results in unprecedented magnetic responses in terms of both magnitude and alignment direction. The thermo-reversible collapse of the disk-like structures into vesicles upon heating allows tailoring of the assemblies' dimensions by extrusion through membrane filters with defined pore sizes. The magnetically alignable bicelles are regenerated by cooling to 5 °C, resulting in assembly dimensions defined by the vesicle precursors. Herein, this fabrication procedure is explained and the magnetic alignability of the assemblies is quantified by birefringence measurements under a 5.5 T magnetic field. The birefringence signal, originating from the phospholipid bilayer, further enables monitoring of polymolecular changes occurring in the bilayer. This simple technique is complementary to NMR experiments that are commonly employed to characterize bicelles.

Ion-Induced Hydrogel Formation and Nematic Ordering of Nanocrystalline Cellulose Suspensions.

Nanocrystalline cellulose (NCC) is a promising material for formation of hydrogels and nematic liquid crystals. While salt addition is known to facilitate hydrogel formation, it remains unclear whether this originates from cationic bridging or charge screening effects. Herein, we demonstrate the effect of mono- and divalent salts on NCC gelation and nematic ordering. A strong correlation of NCC suspension zeta-potential and rheological behavior was found. Lower concentrations of divalent cations were needed to decrease NCC zeta-potential and form hydrogels. The same zeta-potentials and gel strengths were achieved at higher concentrations of monovalent salts. Salt-induced NCC aggregation is thus caused by intermolecular attractive forces rather than cationic bridging. Against excluded volume argumentation, salt addition was found to promote NCC nematic phase formation. Increased nematic ordering was observed in a transition regime of moderate salt addition before complete aggregation occurs. This regime is governed by an equilibrium of repulsive and attractive forces. Small angle neutron scattering suggests lateral orientation of NCC. Hence, NCC gelation and nematic ordering can be modulated via its zeta-potential by targeted salt addition.

Understanding the Enhanced Magnetic Response of Aminocholesterol Doped Lanthanide-Ion-Chelating Phospholipid Bicelles.

Cholesterol (Chol-OH) and its conjugates are powerful molecules for engineering the physicochemical and magnetic properties of phospholipid bilayers in bicelles. Introduction of aminocholesterol (3ß-amino-5-cholestene, Chol-NH2) in bicelles composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and the thulium-ion-chelating phospholipid 1,2-dimyristoyl-sn-glycero-3-phospho-ethanolamine-diethylene triaminepentaacetate (DMPE-DTPA/Tm3+) results in unprecedented high magnetic alignments by selectively tuning the magnetic susceptibility Δχ of the bilayer. However, little is known on the underlying mechanisms behind the magnetic response and, more generally, on the physicochemical forces governing a Chol-NH2 doped DMPC bilayer. We tackled this shortcoming with a multiscale bottom-up comparative investigation of Chol-OH and Chol-NH2 mixed with DMPC. First, simplified monolayer models on a Langmuir trough were employed to compare the two steroid molecules at various contents in DMPC. In a second step, a molecular dynamics (MD) simulation allowed for a more representative model of the bicelle bilayer while monitoring the amphiphiles and their interactions on the molecular level. In a final step, we moved away from the models and investigated the effect of temperature on the structure and magnetic alignment of Chol-NH2 doped bicelles by SANS. The DMPC/steroid monolayer studies showed that Chol-OH induces a larger condensation effect than Chol-NH2 at steroid contents of 16 and 20 mol %. However, this tendency was inversed at steroid contents of 10, 30, and 40 mol %. Although the MD simulation with 16 mol % steroid revealed that both compounds induce a liquid-ordered state in DMPC, the bilayer containing Chol-NH2 was much less ordered than the analogous system containing Chol-OH. Chol-NH2 underwent significantly more hydrogen bonding interactions with neighboring DMPC lipids than Chol-OH. It seems that, by altering the dynamics of the hydrophilic environment of the bicelle, Chol-NH2 changes the crystal field and angle of the phospholipid-lanthanide DMPE-DTPA/Tm3+ complex. These parameters largely determine the magnetic susceptibility Δχ of the complex, explaining the SANS results, which show significant differences in magnetic alignment of the steroid doped bicelles. Highly magnetically alignable DMPC/Chol-NH2/DMPE-DTPA/Tm3+ (molar ratio 16:4:5:5) bicelles were achieved up to temperatures of 35 °C before a thermoreversible rearrangement into nonalignable vesicles occurred. The results confirm the potential of Chol-NH2 doped bicelles to act as building blocks for the development of the magnetically responsive soft materials of tomorrow.

Ionic micelles and aromatic additives: a closer look at the molecular packing parameter.

Wormlike micellar aggregates formed from the mixture of ionic surfactants with aromatic additives result in solutions with impressive viscoelastic properties. These properties are of high interest for numerous industrial applications and are often used as model systems for soft matter physics. However, robust and simple models for tailoring the viscoelastic response of the solution based on the molecular structure of the employed additive are required to fully exploit the potential of these systems. We address this shortcoming with a modified packing parameter based model, considering the additive-surfactant pair. The role of charge neutralization on anisotropic micellar growth was investigated with derivatives of sodium salicylate. The impact of the additives on the morphology of the micellar aggregates is explained from the molecular level to the macroscopic viscoelasticity. Changes in the micelle's volume, headgroup area and additive structure are explored to redefine the packing parameter. Uncharged additives penetrated deeper into the hydrophobic region of the micelle, whilst charged additives remained trapped in the polar region, as revealed by a combination of 1H-NMR, SAXS and rheological measurements. A deeper penetration of the additives densified the hydrophobic core of the micelle and induced anisotropic growth by increasing the effective volume of the additive-surfactant pair. This phenomenon largely influenced the viscosity of the solutions. Partially penetrating additives reduced the electrostatic repulsions between surfactant headgroups and neighboring micelles. The resulting increased network density governed the elasticity of the solutions. Considering a packing parameter composed of the additive-surfactant pair proved to be a facile means of engineering the viscoelastic response of surfactant solutions. The self-assembly of the wormlike micellar aggregates could be tailored to desired morphologies resulting in a specific and predictable rheological response.

Molecular engineering of lanthanide ion chelating phospholipids generating assemblies with a switched magnetic susceptibility.

Lanthanide ion (Ln3+) chelating amphiphiles are powerful molecules for tailoring the magnetic response of polymolecular assemblies. Mixtures of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dimyristoyl-sn-glycero-3-phospho-ethanolamine-diethylene triaminepentaacetate (DMPE-DTPA) complexed to Ln3+ deliver highly magnetically responsive bicelles. Their magnetic properties are readily tuned by changing the bicellar size or the magnetic susceptibility Δχ of the bilayer lipids. The former technique is intrinsically bound to the region of the phase diagram guarantying the formation of bicelles. Methods aiming towards manipulating the Δχ of the bilayer are comparatively more robust, flexible and lacking. Herein, we synthesized a new Ln3+ chelating phospholipid using glutamic acid as a backbone: DMPE-Glu-DTPA. The chelate polyhedron was specifically engineered to alter the Δχ, whilst remaining geometrically similar to DMPE-DTPA. Planar asymmetric assemblies hundreds of nanometers in size were achieved presenting unprecedented magnetic alignments. The DMPE-Glu-DTPA/Ln3+ complex switched the Δχ, achieving perpendicular alignment of assemblies containing Dy3+ and parallel alignment of those containing Tm3+. Moreover, samples with chelated Yb3+ were more alignable than the Tm3+ chelating counterparts. Such a possibility has never been demonstrated for planar Ln3+ chelating polymolecular assemblies. The physico-chemical properties of these novel assemblies were further studied by monitoring the alignment behavior at different temperatures and by including 16 mol% of cholesterol (Chol-OH) in the phospholipid bilayer. The DMPE-Glu-DTPA/Ln3+ complex and the resulting assemblies are promising candidates for applications in numerous fields including pharmaceutical technologies, structural characterization of membrane biomolecules by NMR spectroscopy, as contrasting agents for magnetic resonance imaging, and for the development of smart optical gels.

Methods for Generating Highly Magnetically Responsive Lanthanide-Chelating Phospholipid Polymolecular Assemblies.

Mixtures of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and its lanthanide ion (Ln3+) chelating phospholipid conjugate, 1,2-dimyristoyl-sn-glycero-3-phospho-ethanolamine-diethylene triaminepentaacetate (DMPE-DTPA), assemble into highly magnetically responsive polymolecular assemblies such as DMPC/DMPE-DTPA/Ln3+ (molar ratio 4:1:1) bicelles. Their geometry and magnetic alignability is enhanced by introducing cholesterol into the bilayer in DMPC/Cholesterol/DMPE-DTPA/Ln3+ (molar ratio 16:4:5:5). However, the reported fabrication procedures remain tedious and limit the generation of highly magnetically alignable species. Herein, a simplified procedure where freeze thawing cycles and extrusion are replaced by gentle heating and cooling cycles for the hydration of the dry lipid film was developed. Heating above the phase transition temperature Tm of the lipids composing the bilayer before cooling back below the Tm was essential to guarantee successful formation of the polymolecular assemblies composed of DMPC/DMPE-DTPA/Ln3+ (molar ratio 4:1:1). Planar polymolecular assemblies in the size range of hundreds of nanometers are achieved and deliver unprecedented gains in magnetic response. The proposed heating and cooling procedure further allowed to regenerate the highly magnetically alignable DMPC/Cholesterol/DMPE-DTPA/Ln3+ (molar ratio 16:4:5:5) species after storage for one month frozen at -18 °C. The simplicity and viability of the proposed fabrication procedure offers a new set of highly magnetically responsive lanthanide ion chelating phospholipid polymolecular assemblies as building blocks for the smart soft materials of tomorrow.

Mastering the magnetic susceptibility of magnetically responsive bicelles with 3ß-amino-5-cholestene and complexed lanthanide ions.

The magnetic susceptibility of lanthanide-chelating bicelles was selectively enhanced by introducing 3ß-amino-5-cholestene (aminocholesterol, Chol-NH2) in the bilayer. Unprecedented magnetic alignment of the bicelles was achieved without altering their size. An aminocholesterol conjugate (Chol-C2OC2-NH2), in combination with different lanthanide ions, offers the possibility of fine-tuning the bicelle's magnetic susceptibility.

Tailoring Bicelle Morphology and Thermal Stability with Lanthanide-Chelating Cholesterol Conjugates.

Bicelles composed of DMPC and phospholipids capable of chelating lanthanide ions, such as 1,2-dimyristoyl-sn-glycero-3-phospho-ethanolamine-diethylene triaminepentaacetate (DMPE-DTPA), are highly tunable magnetically responsive soft materials. Further doping of these systems with cholesterol-DTPA conjugates complexed to a lanthanide ion considerably enhances the bicelle's size and magnetic alignability. The high value of these cholesterol conjugates for bicelle design remains largely unexplored. Herein, we examine how molecular structural alterations within the cholesterol-DTPA conjugates lead to contrasting self-assembled polymolecular aggregate structures when incorporated into DMPC/DMPE-DTPA/Tm(3+) bilayers. The nature of the linker connecting the DTPA-chelating moiety to the sterol backbone is examined by synthesizing conjugates of various linker lengths and polarities. The incorporation of these compounds within the bilayer results in polymolecular aggregate geometries of higher curvature. The increasing degrees of freedom for conformational changes conveyed to the chelator headgroup with increasing linker atomic length reduce the cholesterol-DTPA conjugate's critical packing parameter. Consequently, an inverse correlation between the number of carbon atoms in the linker and the bicelle radius is established. The introduction of polarity into the carbon chain of the linker did not cause major changes in the polymolecular aggregate architecture. Under specific conditions, the additives permit the formation of remarkably temperature-resistant bicelles. The versatility of design offered by these amphiphiles gives rise to new and viable tools for the growing field of magnetically responsive soft materials.

Continuous Paranematic Ordering of Rigid and Semiflexible Amyloid-Fe3O4 Hybrid Fibrils in an External Magnetic Field.

External magnetic field is a powerful approach to induce orientational order in originally disordered suspensions of magneto-responsive anisotropic particles. By small angle neutron scattering and optical birefringence measurement technology, we investigated the effect of magnetic field on the spatial ordering of hybrid amyloid fibrils with different aspect ratios (length-to-diameter) and flexibilities decorated by spherical Fe3O4 nanoparticles. A continuous paranematic ordering from an initially isotropic suspension was observed upon increasing magnetic field strength, with spatial orientation increasing with colloidal volume fraction. At constant dimensionless concentration, stiff hybrid fibrils with varying aspect ratios and volume fractions, fall on the same master curve, with equivalent degrees of ordering at identical magnetic fields. However, the semiflexible hybrid fibrils with contour length close to persistence length exhibit a lower degree of alignment. This is consistent with Khokhlov-Semenov theoretical predictions. These findings sharpen the experimental toolbox to design colloidal systems with controllable degree of orientational ordering.