Supramolecular Packing Drives Morphological Transitions of Charged Surfactant Micelles

How tailor-made copolymers can control the structure and properties of hybrid nanomaterials: the case of polyionic complexes

Hybrid polyionic complexes (HPICs) are colloidal structures with a charged core rich in metal ions and a neutral hydrophilic corona. Their properties, whether as reservoirs or catalysts, depend on the accessibility and environment of the metal ions. This study demonstrates that modifying the coordination sphere of these ions can tune the properties of HPICs by altering the composition of the complexing block or varying formulation conditions. Hence, double hydrophilic block copolymers were synthesized using RAFT polymerization, with polyethylene glycol as the neutral block and different ratios of acrylic acid (AA) and vinylphosphonic acid (VPA) as the functional block and further complexed with Fe(III) ions. The resulting iron-based HPICs with higher VPA content were more stable at low pH due to stronger VPA-iron interactions, but their catalytic efficiency in the photo-Fenton process decreased at higher pH. In nanoparticle synthesis, polymers with higher VPA content produced smaller, less-defined Prussian blue nanoparticles, while a 50/50 AA/VPA ratio resulted in uniform nanoparticles and optimal reactivity. Multivariate analysis revealed that not only composition but also local structural organization impacts HPIC properties, influenced by changes in the complexing block structure (e.g., statistical, block) or formulation conditions.

Hydrogel Films with Impact Resistance by Sacrificial Micelle-Assisted-Alignment

Various strategies are developed to engineer aligned hierarchical architectures in polymer hydrogels for enhanced mechanical performance. However, chain alignment remains impeded by the presence of hydrogen bonds between adjacent chains. Herein, a facile sacrificial micelle-assisted-alignment strategy is proposed, leading to well-aligned, strong and tough pure chitosan hydrogels. The sacrificial sodium dodecyl sulfate micelles electrostatically interact with the protonated chitosan chains, enabling chain sliding and alignment under uniaxial forces. Subsequently, sacrificial micelles can be easily removed via NaOH treatment, causing the reforming of H-bond in the chain networks. The strength of the pure chitosan hydrogels increases 140-fold, reaching 58.9 ± 3.4 MPa; the modulus increases 595-fold, reaching 226.4 ± 42.8 MPa. After drying-rehydration, the strength and modulus further rise to 70.3 ± 2.4 and 403.5 ± 76.3 MPa, marking a significant advancement in high-strength pure chitosan hydrogel films. Furthermore, the designed multiscale architectures involving enhanced crystallinity, well-aligned fibers, strong interfaces, robust multilayer Bouligand assembly contribute to the exact replica of lobster underbelly with impact resistance up to 6.8 ± 1.0 kJ m-1. This work presents a promising strategy for strong, tough, stiff and impact-resistant polymer hydrogels via well-aligned hierarchical design.

Recent advances in synchrotron scattering methods for probing the structure and dynamics of colloids

Recent progress in synchrotron based X-ray scattering methods applied to colloid science is reviewed. An important figure of merit of these techniques is that they enable in situ investigations of colloidal systems under the desired thermophysical and rheological conditions. An ensemble averaged simultaneous structural and dynamical information can be derived albeit in reciprocal space. Significant improvements in X-ray source brilliance and advances in detector technology have overcome some of the limitations in the past. Notably coherent X-ray scattering techniques have become more competitive and they provide complementary information to laboratory based real space methods. For a system with sufficient scattering contrast, size ranges from nm to several μm and time scales down to μs are now amenable to X-ray scattering investigations. A wide variety of sample environments can be combined with scattering experiments further enriching the science that could be pursued by means of advanced X-ray scattering instruments. Some of these recent progresses are illustrated via representative examples. To derive quantitative information from the scattering data, rigorous data analysis or modeling is required. Development of powerful computational tools including the use of artificial intelligence have become the emerging trend.

Foam film stratification, viscosity, and small-angle X-ray scattering of micellar SDS solutions over an extended concentration range (1< c/CMC < 75)

Ultrathin foam films (thickness, h < 100 nm) containing micelles undergo drainage via stratification manifested as coexisting thick-thin flat regions, nanoscopic non-flat topography, and the stepwise decrease in film thickness that yields a characteristic step-size. Most studies characterize the variation in step size and stratification kinetics in micellar foam films in a limited concentration range, c/CMC < 12.5 (c < 100 mM). Likewise, most scattering studies characterize micelle dimensions, intermicellar distance, and volume fraction in bulk aqueous SDS solutions in this limited concentration range. In this contribution, we show drainage via stratification can be observed for concentrations up to c/CMC < 75 (c < 600 mM). Understanding the stratification behavior of freely draining micellar films with sodium dodecyl sulfate (SDS) concentration varying in the range 10 mM ≤ cSDS ≤ 600 mM is essential for molecular engineering, consumer product formulations, and controlling foaming in industrial processes. Here, we visualize and analyze nanoscopic thickness variations and transitions in stratifying foam films using Interferometry Digital Imaging Optical Microscopy (IDIOM) protocols. We compare step size obtained from foam stratification to micelle dimension, micelle volume fraction, and intermicellar distance obtained from small angle X-ray scattering studies. Even though the volume fraction increases and approaches 25% at c = 600 mM, the solution viscosity only increases by a factor of four compared to the solvent, consistent with the findings from both stratification and scattering studies. These comparisons allow us to explore the effect of micelle size, morphology, and intermicellar interactions on supramolecular oscillatory structural disjoining pressure, which influences the stratification behavior of draining foam films containing micelles under confinement.

Modeling Micellar Growth and Branching in Mixtures of Zwitterionic with Ionic Surfactants

Zwitterionic surfactants are widely applied as drag-reducing or thickening agents because their aggregation patterns may drastically change in response to variations of the system composition or external stimuli, which provides controllable viscoelasticity. For predicting aggregation behavior of surfactant mixtures, classical molecular thermodynamic models have been widely used. Particularly, the results of modeling have been reported for zwitterionic/ionic surfactant mixtures. However, for solutions containing a zwitterionic surfactant, no molecular thermodynamic model has been proposed for a micellar branch. In this work we extend the classical molecular thermodynamic aggregation model to describe aggregation in the aqueous mixtures that contain a zwitterionic and an ionic surfactant. We derive analytical expressions (1) for the contribution of dipoles to the electrostatic term of the standard free energy of aggregation into micellar branches and (2) for the dipolar contribution to the persistence length of wormlike micelles. The dependence of micellar branching on the surfactant concentration is taken into account by including the population of micellar branches in the material balance equations. This model is applied to predict aggregation equilibrium in aqueous salt solutions of betaine (oleoylamidopropyl-N,N-dimethylbetaine) mixed with sodium dodecyl sulfate (SDS) and the longer tail sodium n-alkyl sulfates. We discuss the predicted properties of the aggregates and micellar networks and compare our predictions with available experimental data.

A pH-Driven Small-Molecule Nanotransformer Hijacks Lysosomes and Overcomes Autophagy-Induced Resistance in Cancer

Smart conversion of supramolecular structures in vivo is an attractive strategy in cancer nanomedicine, which is usually achieved via specific peptide sequences. Here we developed a lysosomal targeting small-molecule conjugate, PBC, which self-assembles into nanoparticles at physiological pH and smartly converts to nanofibrils in lysosomes of tumor cells. Such a transformation mechanically leads to lysosomal dysfunction, autophagy inhibition, and unusual cytoplasmic vacuolation, thus granting PBC a unique anticancer activity as a monotherapy. Importantly, the photo-activated PBC elicits significant phototoxicity to lysosomes and shows enormous advantages in overcoming autophagy-caused treatment resistance frequently occurring in conventional phototherapy. This improved phototherapy achieves a complete cure of oral cancer xenografts upon limited administration. Our work provides a new paradigm for the construction of nonpeptide nanotransformers with biomedical activities.

Dilution-induced gel-sol-gel-sol transitions by competitive supramolecular pathways in water

Fascinating properties are displayed by synthetic multicomponent supramolecular systems that comprise a manifold of competitive interactions, thereby mimicking natural processes. We present the integration of two reentrant phase transitions based on an unexpected dilution-induced assembly process using supramolecular polymers and surfactants. The co-assembly of the water-soluble benzene-1,3,5-tricarboxamide (BTA-EG 4 ) and a surfactant at a specific ratio yielded small-sized aggregates. These interactions were modeled using the competition between self-sorting and co-assembly of both components. The small-sized aggregates were transformed into supramolecular polymer networks by a twofold dilution in water without changing their ratio. Kinetic experiments show the in situ growth of micrometer-long fibers in the dilution process. We were able to create systems that undergo fully reversible hydrogel-solution-hydrogel-solution transitions upon dilution by introducing another orthogonal interaction.

Glassy states in adsorbing surfactant-microgel soft nanocomposites

Mixtures of polymer-colloid hybrids such as star polymers and microgels with non-adsorbing polymeric additives have received a lot of attention. In these materials, the interplay between entropic forces and softness is responsible for a wealth of phenomena. By contrast, binary mixtures where one component can adsorb onto the other one have been far less studied. Yet real formulations in applications often contain low molecular weight additives that can adsorb onto soft colloids. Here we study the microstructure and rheology of soft nanocomposites made of surfactants and microgels using linear and nonlinear rheology, SAXS experiments, and cryo-TEM techniques. The results are used to build a dynamical state diagram encompassing various liquid, glassy, jammed, metastable, and reentrant liquid states, which results from a subtle interplay between enthalpic, entropic, and kinetic effects. We rationalize the rheological properties of the nanocomposites in each domain of the state diagram, thus providing exquisite solutions for designing new rheology modifiers at will.

A Bubble-Assisted Approach for Patterning Nanoscale Molecular Aggregates

We demonstrate a new approach to pattern functional organic molecules with a template of foams, and achieve a resolution of sub 100 nm. The bubble-assisted assembly (BAA) process is consisted of two periods, including bubble evolution and molecular assembly, which are dominated by the Laplace pressure and molecular interactions, respectively. Using TPPS (meso-tetra(4-sulfonatophenyl) porphyrin), we systematically investigate the patterns and assembly behaviour in the bubble system with a series of characterizations, which show good uniformity in nanoscale resolution. Theoretical simulations reveal that TPPS's J-aggregates contribute to the ordered construction of molecular patterns. Finally, we propose an empirical rule for molecular patterning approach, that the surfactant and functional molecules should have the same type of charge in a two-component system. This approach exhibits promising feasibility to assemble molecular patterns at nanoscale resolution for micro/nano functional devices.

Supramolecular Depolymerization in the Mixture of Two Poor Solvents: Mechanistic Insights and Modulation of Supramolecular Polymerization of Ionic π-Systems

Solvents are fundamentally essential for the synthesis and processing of soft materials. Supramolecular polymers (SPs), an emerging class of soft materials, are usually stable in single and mixtures of poor solvents. In contrast to these preconceived notions, here we report the depolymerization of SPs in the mixture of two poor solvents. This surprising behavior was observed for well-known cationic perylene diimides (cPDIs) in the mixtures of water and amphiphilic organic solvents such as isopropanol (IPA). cPDIs form stable SPs in water and IPA but readily depolymerize into monomers in 50-70 vol% IPA containing water. This is due to the selective solvation of the π-surface of cPDIs by alkyl chains of IPA and ionic side chains by water, as evidenced by molecular dynamic simulations. Moreover, by systematically changing the ratio between water and amphiphilic organic solvent, we could achieve an unprecedented supramolecular polymerization both by increasing and decreasing the solvent polarity.