Influence of molecular design on the morphology of nanoparticles formed from 1-alkyl-6-alkoxy-quinolinium cations and 4-sulfonatocalix[n]arenes

In order to reveal the influence of the guest molecular structure, the interactions between 4-sulfonatocalix[n]arene (SCXn) cavitands (n = 4 or 6) and two series of quinolinium derivatives were studied in neutral aqueous solutions at 298 K. For this, the long alkyl chain of the quinoliniums was attached either to the heterocyclic nitrogen (CmC1OQ+ m = 10, 12, or 14) or to the oxygen located in position 6 of the aromatic system (C1CmOQ+ m = 8, 10, or 12). All the quinolinium derivatives self-assembled with SCXn into nanoparticles (NP), whose size, zeta potential and composition were determined over a large molar mixing ratio range. Isothermal titration calorimetry showed that host-guest binding assisted the formation of negatively charged NPs in exothermic processes. The enthalpy gain in these associations significantly increased with the lengthening of the 1-alkyl group but was insensitive to the size of the SCXn macrocycle. The morphology of NPs was studied by cryo-TEM method. CmC1OQ+ organization with SCXn led to spherical NPs without regular inner structure. In contrast, C1CmOQ+-SCXn nanoaggregates usually had various shapes and the original morphologies exhibited lamellar domains with ~3 nm layer thickness. The different orientation of CmC1OQ+ and C1CmOQ+ in the cavitand was proposed to rationalize the morphological alterations

Effect of Macrocycle Size on the Self-Assembly of Methylimidazolium Surfactant with Sulfonatocalix[n]arenes

The effect of macrocycle size on the association of supramolecular amphiphiles composed of 4-sulfonatocalix[n]arene and 1-methyl-3-tetradecylimidazolium (C14mim+) was studied in aqueous solutions at pH 7. When the cavitand contained four sulfonatophenol units (SCX4), spherical nanoparticle (NP) formation was observed. In contrast, both supramolecular micelle (SM) and NP formation could be attained in the presence of NaCl when the larger, more flexible 4-sulfonatocalix[8]arene (SCX8) served as host compound. The SCX8-promoted self-assembly into SM was enthalpically more favorable than NP production but the molar heat capacity changes in the two processes barely differed. Addition of 50 mM NaCl significantly increased the enthalpy of C14mim+−SCX8 NP formation making thereby the self-organization into SM more favorable. The transformation of SM into NP at high temperature was due to the substantial entropic contribution to the driving force of NP formation. The critical micelle concentration and the local polarity in the headgroup domain were considerably lower for SM compared to those of C14mim+Br conventional micelle

Effect of Headgroup Variation on the Self-Assembly of Cationic Surfactants with Sulfonatocalix[6]arene

The effect of headgroup variation on the association of supramolecular amphiphiles composed of 4-sulfonatocalix[6]arene (SCX6) and cationic surfactant possessing tetradecyl substituent was studied in aqueous solutions at pH 7. When the surfactant contained hydrophilic trimethylammonium, pyridinium, or 1-methylimidazolium headgroup, highly reversible temperature-responsive nanoparticle-supramolecular micelle transformation could be attained at appropriately chosen component mixing ratios and NaCl concentrations. In these cases, the substantial negative molar heat capacity change (ΔCp) rendered nanoparticle formation strongly endothermic at low temperature, whereas the assembly to supramolecular micelle was always accompanied by enthalpy gain. The ΔCp values became less negative when the charge density and the hydrophilic character of the surfactant headgroup diminished. The association of the more hydrophobic 6-methoxyquinolinium and quinolinium surfactants with SCX6 did not lead to supramolecular micelle formation because the self-assembly into nanoparticles was highly exothermic

Toward an Understanding of the Microstructure and Interfacial Properties of PIMs/ZIF-8 Mixed Matrix Membranes

A study integrating advanced experimental and modeling tools was undertaken to characterize the microstructural and interfacial properties of mixed matrix membranes (MMMs) composed of the zeolitic imidazolate framework ZIF-8 nanoparticles (NPs) and two polymers of intrinsic microporosity (PIM-1 and PIM-EA-TB). Analysis probed both the initial ZIF-8/PIM-1 colloidal suspensions and the final hybrid membranes. By combination of dynamic light scattering (DLS) and transmission electron microscopy (TEM) analytical and imaging techniques with small-angle X-ray scattering (SAXS), the colloidal suspensions were shown to consist mainly of two distinct kinds of particles, namely, polymer aggregates of about 200 nm in diameter and densely packed ZIF-8-NP aggregates of a few 100 nm in diameter with a 3 nm thick polymer top-layer. Such aggregates are likely to impart the granular texture of ZIF-8/PIMs MMMs as shown by SEM-XEDS analysis. At the molecular scale, modeling studies showed that the surface coverage of ZIF-8 NPs by both polymers appears not to be optimal with the presence of microvoids at the interfaces that indicates only a moderate compatibility between the polymer and ZIF-8. This study shows that the microstructure of MMMs results from a complex interplay between the ZIF-8/PIM compatibility, solvent, surface chemistry of the ZIF-8 NPs, and the physicochemical properties of the polymers such as molecular structure and rigidity

Reversible Nanoparticle–Micelle Transformation of Ionic Liquid–Sulfonatocalix[6]arene Aggregates

The effect of temperature and NaCl concentration variations on the self-assembly of 1-methyl-3- tetradecylimidazolium (C14mim+) and 4-sulfonatocalix[6]- arene (SCX6) was studied by dynamic light scattering and isothermal calorimetric methods at pH 7. Inclusion complex formation promoted the self-assembly to spherical nanoparticles (NP), which transformed to supramolecular micelles (SM) in the presence of NaCl. Highly reversible, temperature-responsive behavior was observed, and the conditions of the NP−SM transition could be tuned by the alteration of C14mim+:SCX6 mixing ratio and NaCl concentration. The association to SM was always exothermic with enthalpy independent of the amount of NaCl. In contrast, NPs were produced in endothermic process at low temperature, and the enthalpy change became less favorable upon increase in NaCl concentration. The NP formation was accompanied by negative molar heat capacity change, which further diminished when NaCl concentration was raised

Glassy states in adsorbing surfactant-microgel soft nanocomposites

International audienceMixtures of polymer-colloid hybrids such as star polymers and microgels with nonadsorbing 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

Templated-PISA: Driving Polymerization-Induced Self-Assembly towards the Fibre Morphology

International audienceDispersions of block-copolymer fibres in water have many potential applications and can be obtained by polymerization-induced self-assembly (PISA), but only in very restricted experimental conditions. In order to enlarge this experimental window, we introduced a supramolecular moiety, a hydrogen-bonded bis-urea sticker, in the macromolecular reversible addition-fragmentation chain transfer agent to drive the morphology of the nano-objects produced by RAFT-mediated PISA towards the fibre morphology. This novel concept is tested in the synthesis of a series of poly(N,N-dimethylacrylamide)-b-poly(2-methoxyethyl acrylate) (PDMAc-b-PMEA) diblock copolymers prepared by dispersion polymerization in water. The results prove that the introduction of the templating bis-urea stickers into PISA greatly promotes the formation of fibres in a large experimental window