Attila Kardos

Arrested interfaces formed through confined polyelectrolyte–surfactant association offer a promising route for designing emulsion systems with tailored properties. However, the impact of organic solvents on the formation, organization, and functionality of polyelectrolyte-surfactant assemblies at oil/water interfaces remains unexplored. In this study, we examine the structure and functionality of arrested interfacial assemblies of the oil-soluble surfactant hexadecylamine and the water-soluble polyelectrolyte sodium polystyrene sulfonate. To elucidate the role of the organic phase, undecanol/water and toluene/water systems were systematically compared. Structural evolution and organization of the interfacial assemblies were examined using interfacial tension measurements, infrared spectroscopy, small- and wide-angle X-ray scattering (SAXS/WAXS), freeze-fracture transmission electron microscopy, and differential scanning calorimetry (DSC).Undecanol molecules act as a cosurfactant at the undecanol/water interface, promoting the formation of multilamellar polyanion/mixed surfactant films with long-range order. Time-resolved SAXS reveals the gradual development of ordered structures, and temperature-dependent SAXS, WAXS, and DSC demonstrate a thermotropic transition from a gel-like lamellar phase to a fluid lamellar phase. In contrast, the toluene/water interface produces disordered polyelectrolyte-surfactant assemblies with finite curvature that lack lamellar ordering and detectable thermotropic transitions.These structural differences directly govern emulsion behavior. Multilamellar films formed at the undecanol/water interface stabilize oil-in-water emulsions and enable nonspherical droplet morphologies to persist. Conversely, assemblies formed at the toluene/water interface induce composition-dependent phase inversion and stabilize spherical droplets. These findings demonstrate that organic solvents play a decisive role in determining the structure of arrested interfaces and their macroscopic functionality, offering new insights into the design of structured liquid systems.

Aqueous two-phase systems (ATPSs) based on two incompatible polymers have recently garnered considerable attention due to the promising characteristics of all-aqueous emulsions for a range of applications. Recent investigations have indicated strong potential for interfacial assemblies of oppositely charged components in the stabilization of these emulsions. The formation of these confined assemblies is likely to depend on the size of the ATPS-constituting polymers; however, the role of this parameter remains to be elucidated. The primary objective of this study was to examine the effect of polyethylene oxide (PEO) molecular weight on the aging processes of PEO/dextran emulsions that are stabilized by the interfacial association of oppositely charged silica particles and polycations. It has been demonstrated that the stability of emulsions containing one high-molecular-weight dextran is significantly enhanced by increasing the size of the PEO molecules. Furthermore, a compression-induced bijel formation was observed in the ATPS with the largest molecular weight PEO sample. The observations were explained by the impact of the rheology of the aqueous phases on the aggregation, adsorption, and network formation capabilities of polycation/silica assemblies. These findings may facilitate the design of stable all-aqueous emulsions with optimal molecular weights for the ATPS-forming polymers.

Microgel particles can play a key role, e.g., in drug delivery systems, tissue engineering, advanced (bio)sensors or (bio)catalysis. Amine-functionalized microgels are particularly interesting in many applications since they can provide pH responsiveness, chemical functionalities for, e.g., bioconjugation, unique binding characteristics for pollutants and interactions with cell surfaces. Since the incorporation of amine functionalities in controlled amounts with predefined architectures is still a challenge, here, we present a novel method for the synthesis of responsive core–shell nanogels (d_h < 100 nm) with a poly(N-isopropylacrylamide) (pNIPAm) core and a polyamine shell. To achieve this goal, a surface-functionalized pNIPAm nanogel was first prepared in a semi-batch precipitation polymerization reaction. Surface functionalization was achieved by adding acrylic acid to the reaction mixture in the final stage of the precipitation polymerization. Under these conditions, the carboxyl functionalities were confined to the outer shell of the nanogel particles, preserving the core’s temperature-responsive behavior and providing reactive functionalities on the nanogel surface. The polyamine shell was prepared by the chemical coupling of polyethyleneimine to the nanogel’s carboxyl functionalities using a water-soluble carbodiimide (EDC) to facilitate the coupling reaction. The efficiency of the coupling was assessed by varying the EDC concentration and reaction temperature. The molecular weight of PEI was also varied in a wide range (M_w = 0.6 to 750 kDa), and we found that it had a profound effect on how many polyamine repeat units could be immobilized in the nanogel shell. The swelling and the electrophoretic mobility of the prepared core–shell nanogels were also studied as a function of pH and temperature, demonstrating the successful formation of the polyamine shell on the nanogel core and its effect on the nanogel characteristics. This study provides a general framework for the controlled synthesis of core–shell nanogels with tunable surface properties, which can be applied in many potential applications.

The interfacial structure and morphology of films spread from hyperbranched polyethylene imine/sodium dodecyl sulfate (PEI/SDS) aggregates at the air/water interface have been resolved for the first time with respect to polyelectrolyte charged density. A recently developed method to form efficient films from the dissociation of aggregates using a minimal quantity of materials is exploited as a step forward in enhancing understanding of the film properties with a view to their future use in technological applications. Interfacial techniques that resolve different time and length scales, namely, ellipsometry, Brewster angle microscopy, and neutron reflectometry, are used. Extended structures of both components are formed under a monolayer of the surfactant with bound polyelectrolytes upon film compression on subphases adjusted to pH 4 or 10, corresponding to high and low charge density of the polyelectrolyte, respectively. A rigid film is related to compact conformation of the PEI in the interfacial structure at pH 4, while it is observed that aggregates remain embedded in mobile films at pH 10. The ability to compact surfactants in the monolayer to the same extent as its maximum coverage in the absence of polyelectrolyte is distinct from the behavior observed for spread films involving linear polyelectrolytes, and intriguingly evidence points to the formation of extended structures over the full range of surface pressures. We conclude that the molecular architecture and charge density can be important parameters in controlling the structures and properties of spread polyelectrolyte/surfactant films, which holds relevance to a range of applications, such as those where PEI is used, including CO₂ capture, electronic devices, and gene transfection.

Responsive cationic microgels are a promising building block in several diagnostic and therapeutic applications, like transfection and RNA or enzyme packaging. Although the direct synthesis of cationic poly(N-isopropylacrylamide) (PNIPAm) microgel particles has a long history, these procedures typically resulted in low yield, low incorporation of the cationic comonomer, increased polydispersity, and pure size control. In this study, we investigated the possibility of the post-polymerization modification of P(NIPAm-co-acrylic acid) microgels to prepare primary amine functionalized microgels. To achieve this goal, we used 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide hydrochloride (EDC) mediated coupling of a diamine to the carboxyl groups. We found that by controlling the EDC excess in the reaction mixture, the amine functionalization of the carboxyl functionalized microgel could be varied and as much as 6–7 mol% amine content could be incorporated into the microgels. Importantly, the reaction was conducted at room temperature in an aqueous medium and it was found to be time efficient, making it a practical and convenient approach for synthesizing primary amine functionalized PNIPAm microgel particles.

In this work, host–guest supramolecular hydrogels were prepared from poly(N-isopropylacrylamide) (pNIPAm) microgels utilizing electrostatic and host/guest self-assembly. First, pNIPAm microgels bearing a poly(acrylic acid) (pAAc) shell were coated with positively charged β-cyclodextrin polymers. Addition of adamantane-substituted dextrans (Dex-Ada) allowed us to establish interparticle connections through β-cyclodextrin-adamantane (βCD-Ada) inclusion complex formation, and thus to prepare hierarchical hydrogels. Under the conditions of hydrogel formation, close contact between the microgels was ensured. To the best of our knowledge, this is the first example of doubly crosslinked microgels prepared by noncovalent crosslinking via host–guest interactions. The prepared macrogels were studied with rheology, and fast mechanical response to temperature variation was found. Furthermore, the hydrogels exhibit fully reversible temperature-induced gel–sol transition at the physiological temperature range (37–41 °C), due to the synergetic effect between shrinking of the microgels and dissociation of βCD-Ada crosslinks at higher temperatures. This opens up attractive prospects of their potential use in biomedical applications.