Micellar Network Research Articles

Effect of Micellar Morphology on the Temperature-Induced Structural Evolution of ABC Polypeptoid Triblock Terpolymers into Two-Compartment Hydrogel Network.

We investigated the temperature-dependent structural evolution of thermoreversible triblock terpolypeptoid hydrogels, namely poly(N-allyl glycine)-b-poly(N-methyl glycine)-b-poly(N-decyl glycine) (AMD), using small-angle neutron scattering (SANS) with contrast matching in conjunction with X-ray scattering and cryogenic transmission electron microscopy (cryo-TEM) techniques. At room temperature, A100M101D10 triblock terpolypeptoids self-assemble into core-corona-type spherical micelles in aqueous solution. Upon heating above the critical gelation temperature (T gel), SANS analysis revealed the formation of a two-compartment hydrogel network comprising distinct micellar cores composed of dehydrated A blocks and hydrophobic D blocks. At T ≳ T gel, the temperature-dependent dehydration of A block further leads to the gradual rearrangement of both A and D domains, forming well-ordered micellar network at higher temperatures. For AMD polymers with either longer D block or shorter A block, such as A101M111D21 and A43M92D9, elongated nonspherical micelles with a crystalline D core were observed at T < T gel. Although these enlarged crystalline micelles still undergo a sharp sol-to-gel transition upon heating, the higher aggregation number of chains results in the immediate association of the micelles into ordered aggregates at the initial stage, followed by a disruption of the spatial ordering as the temperature further increases. On the other hand, fiber-like structures were also observed for AMD with longer A block, such as A153M127D10, due to the crystallization of A domains. This also influences the assembly pathway of the two-compartment network. Our findings emphasize the critical impact of initial micellar morphology on the structural evolution of AMD hydrogels during the sol-to-gel transition, providing valuable insights for the rational design of thermoresponsive hydrogels with tunable network structures at the nanometer scale.

Saturated Micellar Networks: Phase Separation and Nanoemulsification Capacity

Different oils can be homogeneously dispersed in the network junctions of the separated bicontinuous micellar phases. Upon dilution, these dispersions spontaneously form nanoemulsions. The possibility of a micellar sponge phase formation in the case of mixtures with three anionic and two zwitterionic surfactants in the presence of divalent and monovalent salts is studied. The best results are obtained using sodium lauryl ether sulfate with 1 ethylene oxide group (SLES-1EO) and both cocamidopropyl betaine (CAPB) or N,N-dimethyldodecylamine N-oxide (DDAO) in the presence of an appropriate small amount of MgCl2 and CaCl2. Bicontinuous micellar phases can be produced also in high-salinity NaCl solutions. The bulk properties of these phases are independent of the concentration of the initial solutions from which they are separated, and their Newtonian viscosities are in the range from 0.3 Pa·s to 0.8 Pa·s. Both 8 wt% CAPB- and DDAO-containing sponge phases engulf up to 10 wt% limonene and spontaneously form nanoemulsion upon dilution with droplet sizes of 110–120 nm. Vitamin E can be homogeneously dispersed only in CAPB-containing saturated micellar network, and upon dilution, these dispersions spontaneously form nanoemulsions with smaller droplet sizes of 66 nm for both 8 diastereomers and 2 diastereomers mixtures of vitamin E.

Self-Healing of Pluronic® F127 Hydrogels in the Presence of Various Polysaccharides.

Thermoresponsive Pluronic® F127 (PL) gels in water were investigated through rheological tests in different shear conditions. The gel strength was tuned with the addition of 1% polysaccharide solution. In the presence of xanthan gum (XG), the viscoelastic behavior of PL-based hydrogels was improved in aqueous environment, but the rheological behavior was less changed with the addition of XG in PBS solutions, whereas in the presence of 0.1 M NaCl, the viscoelastic parameters decreased. PL micellar networks exhibited a self-healing ability, recovering their initial structure after applying cycles of high strain. The rheological characteristics of the PL hydrogel changed with the addition of 1% polysaccharides (xanthan gum, alginate, κ-carrageenan, gellan, or chitosan). PL/polysaccharide systems form temperature-responsive hydrogels with shear thinning behavior, yield stress, and self-healing ability, being considered a versatile platform for injectable biomaterials or bioinks. Thus, in the presence of xanthan gum in aqueous medium, the gel strength was improved after applying a high strain (the values of elastic modulus increased). The other investigated natural polymers induced specific self-healing behaviors. Good performances were observed with the addition of gellan gum, alginate, and κ-carrageenan, but for high values of strain, the ability to recover the initial structure decreased. A modest self-healing behavior was observed in the presence of chitosan and xanthan gum dissolved in NaCl solution.

Topical Cream Carrying Drug-Loaded Nanogels for Melanoma Treatment.

In this study, nanogel creams carrying paclitaxel (PTX) and temozolomide (TMZ) were prepared for thetopical treatment of melanoma. PTX and TMZ were first loaded in poly-(D,L-lactide-co-glycolide)-block-poly(ethylene glycol)-block-poly-(D,L-lactide-co-glycolide) (PLAG-b-PEG-b-PLGA)thermosensitive nanogels, which made a transition from a free-flowing sol (formation of micellar network) at 25°C with the z-average particle size of c.a. 96nm to a gel (aggregation of micelles) at 33°C with the z-average particle size of c.a. 427nm. An anhydrous absorption ointment base, aquaphor, was then added to drug-loaded nanogels to form nanogel creams carrying PTX and TMZ. Nanogel creams permitted controlled release of the payloads and improved the penetration of the payloads through the rodent skin compared to drug(s)-loaded nanogels. PTX and TMZ in a combination were synergistically effective in inhibiting SK-MEL28, A375, and B16-F10 melanoma cancer cells in vitro. Topically applied nanogel creams carrying TMZ/PTX (4mg/1.5mg/dose) showed a trend of tumor volume inhibition on B16-F10-bearing xenograft mice in vivo.

On the startup behavior of wormlike micellar networks: The effect of different salts bound to the same surfactant molecule

We report on shear startup data for two wormlike micellar solutions, differing only in concentration and type of two binding aromatic sodium salts. The surfactant molecule is cetylpiridinium chloride at a fixed concentration (100 mM). Sodium salicylate (NaSal) and diclofenac sodium (Diclo) are used as binding salts at concentrations 68 mM NaSal and 52 mM Diclo such that both systems are fully entangled and their linear viscoelastic response is essentially identical. Both systems show the linear response typical of a wormlike micellar solution, with terminal behavior at low frequencies, a well-defined moduli crossover, and a plateau modulus. In the nonlinear regime, however, the behavior of the two systems is totally different, suggesting that the molecular structure difference of the salts and their binding activity to the surfactant molecule are both crucial to determine the fast flow behavior. The NaSal solution shows a very complex rheological response, with strain hardening and very sharp stress peaks, whereas the solution containing Diclo behaves much like ordinary linear polymers, exhibiting pronounced overshoots as well as moderate undershoots in the transient shear viscosity, before approaching the steady state. This polymerlike behavior has also been proved by successfully comparing data with predictions of a constitutive equation recently adopted for both entangled polymers and linear wormlike micelles. As far as NaSal is concerned, a phenomenological model based on rubber network theory is developed, which describes the flow singularities. A physical interpretation of the different behavior in the nonlinear regime is also suggested.

A Generalized Mechano-statistical Transient Network Model for Unravelling the Network Topology and Elasticity of Hydrophobically Associating Multiblock Copolymers in Aqueous Solutions

In this contribution, we unravel the transient network topology and elasticity of micellar networks formed by hydrophobically associating multiblock copolymers in aqueous solutions. Unlike studies on conventional triblock copolymers bearing hydrophobic blocks as end groups, our research focuses on alternating poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) multiblock copolymers having multiple hydrophobic PPO blocks along the chain. We adopt a combinatorics approach to extend and generalize the mechano-statistical transient network model developed by Annable et al. for telechelic triblock copolymers [ Journal of Rheology, 1993, 37, 695] to multiblock copolymers. The model allows one to predict the concentration dependent elasticity of networks formed by multiblock copolymers with known molecular characteristics by using knowledge of the micellar network microstructure. The spatial distribution of the hydrophobic nodes is inferred from Small-Angle X-ray Scattering (SAXS) by converting the structure factor to the radial distribution function. The number of closely neighboring micellar cores between which an elastic bridge can be formed (nm) is calculated by spherical integration of the radial distribution function up to a distance of the radius of gyration of an intermediate soluble PEO block. Using the evolution of nm with concentration as an input for the model, the predictions show good agreement with experimental elasticity data, as inferred from the plateau modulus in linear shear rheology. The network evolves from loop-dominated, poorly elastic with cross-linking nodes with low functionality at low concentrations to bridge-dominated, highly elastic with higher node functionalities at more elevated concentrations. It is anticipated that our generalized mechano-statistical transient network model can also be used for equally spaced, multisticker associating polymers forming networks by multifunctional interactions other than micellar aggregation.

Semi-conductive micellar networks of all-conjugated diblock and triblock copolymer blends.

The crystallization-driven self-assembly of the blends of the all-conjugated block copolymers of poly(3-hexylthiophene) (P3HT) and poly(3-ethylhexylthiophene) (P3EHT) results in the cross-linking of the one-dimensional nanowires of P3HT-b-P3EHT, which is achieved by intercalating P3HT-b-P3EHT-b-P3HT into the nanowire cores. The micellar networks constitute flexible and porous materials that conduct electricity upon doping.

Rheology and microstructure of thermoresponsive composite gels of hematite pseudocubes and Pluronic F127.

Stimuli-responsive materials or smart materials are designed materials whose properties can be changed significantly by applying external stimuli, such as stress, electric or magnetic fields, light, temperature, and pH. We report the linear and nonlinear rheological properties of thermoresponsive composite gels based on submicron-sized hematite pseudocube-shaped particles and a triblock copolymer Pluronic F127 (PF127). These novel composites form hard gels at an elevated temperature of 37°C. For certain concentrations (<20 w/v. %) of hematite pseudocubes in 17.5 w/v. % of PF127, the gel strength is enhanced and the brittleness of the gels decreases. Higher concentrations (>20 w/v. %) of hematite pseudocubes in PF127 result in weaker and fragile gels. We develop an extensive rheological fingerprint using linear and nonlinear rheological studies. Adsorption of PF127 copolymer molecules on the hematite cube surfaces would further assist the formation of particle clusters along with magnetic interactions to be held effectively in the PF127 micellar network at elevated temperatures. The microscopic structure of these composite gels is visualized through a confocal microscope. Our experiments show that addition of hematite cubes up to 20 w/v. % does not change the rapid thermal gelation of PF127 solutions; hence, the hematite-PF127 composite, which transforms into a hard gel near human body temperature of 37°C, could be suitable for use in smart drug delivery systems.

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.

Rheology of saturated micellar networks: Wormlike micellar solutions vs. bicontinuous micellar phases

The subject of this work is to investigate the rheological behavior of mixed micellar solutions (sodium laurylethersulfate and cocamidopropyl betaine) in the presence of Mg2+ divalent counterions. With the rise of salt concentration, the viscosity of micellar solutions increases to a high maximum followed by a steep decrease because of the initial growth and entanglement of wormlike micelles and a subsequent transition to branched micelles forming of a saturated micellar network. The proposed systematic rheological measurements show considerable variations in the rheological responses of the solutions when increasing the salt concentration. Rheological behavior and data are used to distinguish the micellar phases and to study the relation to micellar structures. The wormlike micellar solutions have a typical shear thinning behavior with a well-defined zero-shear viscosity, η0, described by the Cates reptation-reaction model or the augmented Maxwell model. Our data show that the power law dependence of η0 on the surfactant concentration is stronger than that reported in the literature and it is influenced of the added electrolytes. The branched micellar structures are characterized by the lower viscosities and larger elasticities, which follow the Maxwell model up to the intermediate values of the frequency of oscillations, however peculiar deviations from the Cole-Cole plot at large frequencies are detected. The isolated bicontinuous micellar phases are Newtonian fluids with viscosity 0.4–0.7 Pa.s independent on the salt concentration up to high shear rates. The threshold salt concentration ensuring the onset of the bicontinuous micellar phase is described by a simple empirical rule. These phases are characterized by large elasticities and not negligible yield stresses. The property of the bicontinuous micellar phases to form spontaneously oil-in-water nanoemulsions could find applications in drug delivery, extraction and separation processes, pharmaceutics production, etc.

Micellar entanglement and its relation to the elastic behavior of wormlike micelle fluids

HypothesisThe elastic contribution to the fluid dynamics of wormlike micellar solutions makes these fluids unique due to the distinctive self-assembled micellar network formed by tubular micelles. Measured mesoscopic scales of the micellar network related to the degree of entanglement can give guidelines for understanding the origin of elastic forces and their effect on rheological response. ExperimentsDifferent experiments were made as flow curves, rotating the internal or external cylinder in a Couette geometry, small and large oscillatory shear tests, and linear shear banding observations, all of them to determine how elastic forces modify the rheological behavior in systems made of different ratios of hexadecyltrimethylammonium bromide (CTAB)/sodium salicylate (NaSal) and different ratios of CTAB/NaNO3. Diffusive wave spectroscopy micro-rheology was also performed to measure the mean square displacements of microspheres embedded in the micellar fluids to obtain their high-frequency viscoelastic spectra. With this information, the entanglement index κ, the ratio of the total contour of the micelles to the entanglement length, was estimated and correlated with the rheological behavior. FindingsThe entanglement index is a valuable piece of information to understand the origin of the contribution of the elastic forces from a molecular point of view on the fluid dynamics of wormlike micelle solutions.

Spanning BODIPY fluorescence with self-assembled micellar clusters

BODIPY dyes possess favorable optical properties for a variety of applications including in vivo and in vitro diagnostics. However, their utilization might be limited by their water insolubility and incompatibility with chemical modifications, resulting in low aggregation stability. Here, we outline the route for addressing this issue. We have demonstrated two approaches, based on dye entrapment in micellar coordination clusters (MCCs); this provides a general solution for water solubility as well as aggregation stability of the seven BODIPY derivatives. These derivatives have various bulky aromatic substituents in the 2,3,5,6- and meso-positions and can rotate relative to a dipyrrin core, which also provides molecular rotor properties. The molecular structural features and the presence of aromatic groups allows BODIPY dyes to be used as "supporting molecules", thus promoting micelle-micelle interaction and micellar network stabilization. In the second approach, self-micellization, following BODIPY use, leads to MCC formation without the use of any mediators, including chelators and/or metal ions. In both approaches, BODIPY exhibits an excellent optical response, at a concentration beyond its solubilization limit in aqueous media and without undesired crystallization. The suggested approaches represent systems used to encapsulate BODIPY in a capsule-based surfactant environment, enabling one to track the aggregation of BODIPY; these approaches represent an alternative system to study and apply BODIPY’s molecular rotor properties. The stabilized compounds, i.e., the BODIPY-loaded MCCs, provide a unique feature of permeability to hydrophilic ligand-switching proteins such as BSA; they exhibit a bright “turn-on” fluorescence signal within the clusters via macromolecular complexation, thus expanding the possibilities of water-soluble BODIPY-loaded MCCs utilization for functional indicators.

Morphological Diversity from the Solution Self-Assembly of Block Copolymer Blends Containing High Molecular-Weight Hydrophobic Blocks.

Self-assembled structures of high molecular-weight block copolymers (BCPs) can prematurely settle to local energy minima without reaching a time-averaged equilibrium, resulting in the emergence of intriguing morphologies, such as 3D micellar networks. This nonergodic behavior is evident in binary blends of BCPs with different molecular weights. This study reports the solution self-assembly of the blends of two branched-linear BCPs with similar block chemistries but different molecular weights of the hydrophobic blocks. A progressive transition of morphologies from hexosomes and cubosomes to 3D micellar networks, short cylinders, and spherical micelles is demonstrated, which is driven by the increase in the composition of low-molecular-weight BCP in the blend. The labeling of the micellar networks using Au nanoparticles confirms that lower molecular-weight BCP concentrates at the surface of micellar networks.

Activation energy, spatial confinement, and mean first passage and escape times of a tracer in a wormlike micellar fluid: an effective potential approach

Wormlike micelles are long semiflexible cylindrical polymer structures formed by amphiphiles. In solution, these linear micelles percolate in multiconected entangled networks, where cross-links can break and recombine dynamically. Technological applications of wormlike micellar fluids include tunable encapsulation/delivery of molecules or colloids in biomedicine, oil industry, and/or cleaning processes. In this work, we propose that the experimental activation energy, the spatial confinement, and the mean first passage and escape times of a spherical tracer immersed in wormlike micellar network, in which caging effects are observed, can be estimated from economic Brownian dynamics simulations of a single particle interacting with an effective one-dimensional cosine-like potential of amplitude U 0 and periodicity L. The proposed one-fitting parameter method has been used to characterize the long-time dynamics of wormlike micellar solutions formed by the self-assembly of a mixture of zwitterionic and anionic surfactants at several temperatures and different concentrations of surfactant and brine. The amplitude U 0 has displayed a good agreement regarding the corresponding experimental activation energy at different temperatures. The periodicity L has shown to be an upper bound of the mesh size ξ and of the same order of magnitude regarding the entanglement length l e, obtained from rheology and microrheology experiments. The escape time of the tracer in the effective potential τ escape and the time t*, at which a change of curvature in the mean square displacement occurs, are upper and lower limits, respectively, of the experimental relaxation time. Our method is simple and fast, and we foresee that it should be applicable to model the long-time behaviour of tracers in other polymer systems, in which caging effects are present.

The rise and fall of branching: A slowing down mechanism in relaxing wormlike micellar networks.

A mean-field kinetic model suggests that the relaxation dynamics of wormlike micellar networks is a long and complex process due to the problem of reducing the number of free end-caps (or dangling ends) while also reaching an equilibrium level of branching after an earlier overgrowth. The model is validated against mesoscopic molecular dynamics simulations and is based on kinetic equations accounting for scission and synthesis processes of blobs of surfactants. A long relaxation time scale is reached with both thermal quenches and small perturbations of the system. The scaling of this relaxation time is exponential with the free energy of an end cap and with the branching free energy. We argue that the subtle end-recombination dynamics might yield effects that are difficult to detect in rheology experiments, with possible underestimates of the typical time scales of viscoelastic fluids.

Measuring mesoscopic scales in complex fluids embedded with giant cylindrical micelles with diffusing wave spectroscopy micro-rheology

This review paper presents a procedure for measuring the mesoscopic scales in micellar solutions embedded with giant cylindrical micelles using the mean square displacement determined with a quasi-elastic multiple light scattering method (diffusing wave spectroscopy) and theory. The mesoscopic scales of interest are the micelles’ total contour length, persistence and entanglement lengths, and the mesh size of the entangled micellar network. All of them depend on the physicochemical parameters of the solutions and determine the rheological behavior. We present an assessment of the whole procedure, the scattering experiments performance, the recovery of optical parameters, which includes dealing with the light absorption and its treatment, and how to develop the micro-rheology for obtaining the mesoscopic scales in these complex fluids.

Shear-induced nanostructural changes in micelles formed by sugar-based surfactants with varied anomeric configuration

HypothesisThe self-assembly of long tail sugar-based surfactants into worm-like micelles has recently been demonstrated, and the rheological properties of such systems have been shown to be tuneable through subtle modifications of the molecular characteristics of the surfactant monomer. In particular, the anomeric configuration of the hexadecylmaltoside headgroup was shown to induce profound changes in the nanostructure and rheology of the system. The origin of such changes is hypothesised to arise from differences in the structure and relaxation of the micellar networks in the semi-dilute regime. ExperimentsHere we explore the molecular background to the flow properties of the two anomers of hexadecylmaltoside (α- and β-C16G2) by directly connecting their rheological behaviour to the micelle morphology. For this purpose, 1–3 plane rheo-small-angle neutron scattering measurements, using a Couette cell geometry, probed the structural changes in the micellar phase under shear. The effect of surfactant anomeric configuration, surfactant concentration, temperature and mixing ratio of the two anomers were investigated. The static micelle structure in the semi-dilute regime was determined using the polymer reference interaction site model. FindingsThe segmental alignment of the micellar phase was studied under several flow conditions, showing that the shear-thinning behaviour relates to the re-arrangement of β-C16G2 worm-like micelles, whilst shorter α-C16G2 micelles are considerably less affected by the flow. The results are rationalised in terms of micelle alignment and disruption of the entangled network, providing a detailed mechanism by which sugar-based surfactants control the rheology of the fluid. To further enable future studies, we provide the complete code for modelling micelle structure in the semi-dilute regime using the polymer reference interaction site model.

Mucoadhesive and Rheological Studies on the Co-Hydrogel Systems of Poly(Ethylene Glycol) Copolymers with Fluoroalkyl and Poly(Acrylic Acid)

A self-assembled co-hydrogel system with sol-gel two-phase coexistence and mucoadhesive properties was developed based on the combined properties of fluoroalkyl double-ended poly(ethylene glycol) (Rf-PEG-Rf) and poly(acrylic acid) (PAA), respectively. We have synthesized an Rf-PEG-g-PAA (where g denotes grafted) copolymer and integrated it into the Rf-PEG-Rf physically cross-linked micellar network to form a co-hydrogel system. Tensile strengths between the co-hydrogel surfaces and two different sets of mucosal surfaces were acquired. One mucosal surface was made of porcine stomach mucin Type II, while the other one is a pig small intestine. The experimental results show that the largest maximum detachment stresses (MDSs) were obtained when the Rf-PEG-g-PAA’s weight percent in the dehydrated polymer mixture is ~15%. Tensile experiments also found that MDSs are greater in acidic conditions (pH = 4–5) (123.3 g/cm2 for the artificial mucus, and 43.0 g/cm2 for pig small intestine) and basic conditions (pH = 10.6) (126.9 g/cm2, and 44.6 g.cm2, respectively) than in neutral pH (45.4 g/cm2, and 30.7 g.cm2, respectively). Results of the rheological analyses using shear strain amplitude sweep and frequency sweep reveal that the Rf-PEG-g-PAA was physically integrated into the Rf-PEG-Rf micellar network, and the co-hydrogels remain physically cross-linked in three-dimensional micellar networks with long-term physical dispersion stability. Therefore, the co-hydrogel system is promising for drug delivery applications on mucosal surfaces.

Abstract P-3: The Structure of Self-Assembled Surfactant Micellar Networks by in situ Cryo-Electron Tomography

Background: Surfactant molecules can form various self-assembled structures in aqueous solutions, including spherical and cylindrical micelles, lamellae, vesicles, etc. Elongated cylindrical (wormlike) micelles can entangle and form a dense network. The study of the un-perturbed native structure of wormlike micelles in such networks presents a great challenge, since the micelles are formed due to weak non-covalent interactions and may easily break when external conditions are changed. In this work in situ cryo-electron tomography (cryo-ET) was applied to reveal the relaxed structure of such entangled systems. Methods: To prepare samples for the cryo-ET study 1 µl of the aqueous surfactant-containing solution was applied to the glow discharged grid, blotted with filter paper for 10 sec, drained for 60 sec to allow for the relaxation of the system and plunge-frozen with Vitrobot Mark IV. The vitrified sample was transferred to Versa 3D cryo-focused ion beam / scanning electron microscope (cryo-FIB/SEM) to prepare thin (100-150 nm) sections of the sample. Cryo-ET study was conducted using Titan Krios. IMOD and Avizo software packages were used for data processing. Results: In this work, wormlike micelles formed by a mixture of an anionic and a cationic surfactant were investigated at the excess of the anionic surfactant. Cryo-ET study of the obtained lamellae demonstrated the formation of two different phases, consisting of straight rods oriented along the grid substrate (phase 1) and isotropic network formed by wormlike micelles (phase 2) above it. The topology of the second phase corresponded to the branched saturated network or entangled network depending on cation/anion ratio of the sample. However, the analysis of the thin samples obtained without cryo-FIB demonstrated only the presence of the metastable phase (phase 1), which could lead to false conclusions regarding the morphology of the micelles. Conclusion: Here we discuss the influence of different sample preparation approaches on the sample structure and demonstrate that the native un-perturbed conformation of charged cylindrical surfactant micelles in the dense network is that of a slightly bent rod or a wormlike chain with high persistence length.

Rheology, Sticky Chain, and Sticker Dynamics of Supramolecular Elastomers Based on Cluster-Forming Telechelic Linear and Star Polymers

We elucidate the properties of unentangled telechelic poly(isobutylene) (PIB) chains in bulk forming dynamic micellar networks mediated by endgroups capable of hydrogen-bonding and π–π interactions. The effects of the molecular architecture and type of endgroup on the properties of networks are studied by a combination of small-angle X-ray scattering (SAXS), rheology, low-resolution NMR, and dielectric spectroscopy (DS). It is found that star-shaped molecules form more time-stable networks with larger and somewhat more distantly arranged aggregates compared to their linear counterparts. Using stickers providing less hydrogen bonds speeds up terminal flow significantly, yet surprisingly, the nanoscale morphology, apparent activation energies, and the timescale of endgroup fluctuations probed by DS are very similar across the two sample series. The correlation of results from the three dynamic methods (rheology, NMR, and DS) thus fortifies previous findings for linear chains: (i) even for star molecules, terminal stress relaxation is governed by single-chain relaxation rather than the reorganization of whole micelles, and (ii) the cluster-related relaxation time accessed by DS has no trivial relation to the actual sticky bond lifetime, the determination of which is concluded to be an open problem.