Fabrication of Macroporous Polymers via Water-in-Water Emulsion-Templating Technique

Processable and controllable all-aqueous gels based on high internal phase water-in-water emulsions

Aqueous two-phase systems (ATPSs) have primarily been developed in the form of emulsions to enhance their utilization in green and biocompatible applications. However, numerous challenges have arisen in forming stable and processable water-in-water (W/W) emulsion systems, as well as in fine-tuning the interconnectivity of their internal structure, which can significantly impact their performance. To effectively address these challenges, we elucidate, for the first time, the root cause of the poor stability of W/W emulsions. Leveraging this insight, we successfully stabilize W/W high internal phase emulsions (W/W HIPEs) characterized by an extremely thin continuous phase. This stabilization enables the fine-tuning of interconnectivity between dispersed droplets through photopolymerization of thin continuous phases, resulting in the fabrication of stable and processable all-aqueous gels. This W/W HIPE-based gel fabrication holds promise as a universal technology for a wide range of applications. It facilitates in situ polymerization of the continuous phase of W/W HIPEs, where target molecules are stored in the dispersed phase. Moreover, this method allows easy adjustment of the external release rate or internal transfer rate of target molecules by adjusting the interconnectivity of the internal structures.

Production of water-water emulsion gels by yerba mate extract

Yerba mate extract is a powerful antioxidant compound, but it can also be used as a gel network-forming agent. In this context, this study aimed to investigate the induction of gelation by yerba mate extract in protein-polysaccharide mixtures. W/W emulsions produced with sodium caseinate (SC) and gellan gum were characterized in terms of their physicochemical composition and rheological properties. The mechanical properties of the gels produced from the W/W emulsions in the presence of yerba mate extract were evaluated by uniaxial compression, oscillatory rheology and scanning electron microscopy. Different concentrations of SC-gellan promote distinct protein and carbohydrate compositions of the separated phase, with gellan concentration varying between 0.69 and 1.26 % w/w in the top phase. The top phase of these emulsions was used for gel formation by adding varying concentrations of yerba mate extract. The highest firmness (22.41 kPa) was identified with 2 % (w/w) extract and the highest gellan concentration, while gels with extreme extract concentrations (0.5 % and 8 % w/w) and the lowest gellan concentration presented lower hardness (0.6 and 0.92 kPa). Water-holding capacity was related to the quantity and size of the pores formed by the gel network in the different compositions, showing that the protein structures within the pores alter the firmness of the gels formed predominantly of polysaccharides. Our results indicate that W/W emulsions should be more intensively explored for the formation of structures that have different potential applications.

Mechanism of Interconnected Pore Formation in High Internal Phase Emulsion-Templated Polymer

High internal phase emulsion-templated polymer, named polyHIPE, has received widespread attention due to its great potential applications in many fields, such as separation, adsorption, heterogeneous catalysis, and sound absorption. The broad applicability is largely dependent on its adjustable opening structure. However, the question of why polyHIPE has an interconnected pore network structure is still to be discussed. Herein, different types (w/o, o/w, and o/o) of HIPEs are prepared and subsequently detected with laser scanning confocal microscopy (LSCM), and the polyHIPEs obtained by curing the HIPEs are characterized by SEM. The observations suggest that the interconnected pore formation is primarily due to the presence of the surfactant-rich phase in the film between the neighboring droplets in HIPE. The interconnected pores are generated by removal of the surfactant-rich domains in the postcuring procedure, and their sizes would be enlarged if the solubility of the surfactant in the continuous phase decreases in the curing stage.

Deep-Eutectic-Solvent-in-Water Pickering Emulsions Stabilized by Starch Nanoparticles

Deep eutectic solvents (DESs) have received extensive attention in green chemistry because of their ease of preparation, cost-effectiveness, and low toxicity. Pickering emulsions offer advantages such as long-term stability, low toxicity, and environmental friendliness. The oil phase in some Pickering emulsions is composed of solvents, and DESs can serve as a more effective alternative to these solvents. The combination of DESs and Pickering emulsions can improve the applications of green chemistry by reducing the use of harmful chemicals and enhancing sustainability. In this study, a Pickering emulsion consisting of a DES (menthol:octanoic acid = 1:1) in water was prepared and stabilized using starch nanoparticles (SNPs). The emulsion was thoroughly characterized using various techniques, including optical microscopy, transmission microscopy, laser particle size analysis, and rheological measurements. The results demonstrated that the DES-in-water Pickering emulsion stabilized by the SNPs had excellent stability and retained its structural integrity for more than 200 days at room temperature (20 °C). This prolonged stability has significant implications for many applications, particularly in the field of storage and transportation. This Pickering emulsion based on DESs and SNPs is sustainable and stable, and it has great potential to improve green chemistry practices in various fields.

Aminopoly(carboxylic acid)-Functionalized PolyHIPE Beads toward Eliminating Trace Heavy Metal Ions from Water

Many advanced materials are designed for the removal of heavy metal ions from water. However, materials for eliminating trace heavy metal ions from wastewater to meet drinking water standards remain a major challenge. Herein, epoxy group-functionalized open-cellular beads are synthesized by UV polymerization of a water-in-oil-in-water system. The epoxy groups are further transformed into diethylenetriaminepentaacetic acid (DTPA) with hexamethylene diamine as a bridging agent. The resulting material (DTPA@polyHIPE beads) can eliminate trace Cu(II), Cr(III), Pb(II), Fe(III), or Cd(II) from water. When 0.15 g of DTPA@polyHIPE beads are used to adsorb metal ions of 20 mg in 100 mL of water, the residue concentrations of Cu(II), Cr(III), Pb(II), Fe(III), and Cd(II) are reduced to 0.08, 0.06, 0.02, 0.09, and 0.07 mg/L, respectively. The adsorption efficiencies of the beads for these ions are all higher than 99.55%. The adsorbent is durable and exhibits good recyclability by retaining an adsorption capacity of ≥91% after 5 cycles. The negative values of ΔG in the adsorption process indicate that the adsorption is feasible and spontaneous. The chemical adsorption follows the Freundlich adsorption model, indicating a multilayer heterogeneous adsorption. The DTPA@polyHIPE beads have a great potential application in dealing with trace heavy metal ion polluted water.

Recent Advances in Flexible CNC-Based Chiral Nematic Film Materials

Cellulose nanocrystal (CNC) is a renewable resource derived from lignocellulosic materials, known for its optical permeability, biocompatibility, and unique self-assembly properties. Recent years have seen great progresses in cellulose nanocrystal-based chiral photonic materials. However, due to its inherent brittleness, cellulose nanocrystal shows limitations in the fields of flexible materials, optical sensors and food freshness testing. In order to solve the above limitations, attempts have been made to improve the flexibility of cellulose nanocrystal materials without destroying their structural color. Despite these progresses, a systematic review on them is lacking. This review aims to fill this gap by providing an overview of the main strategies and the latest research findings on the flexibilization of cellulose nanocrystal-based chiral nematic film materials (FCNM). Specifically, typical substances and methods used for their preparation are summarized. Moreover, different kinds of cellulose nanocrystal-based composites are compared in terms of flexibility. Finally, potential applications and future challenges of flexible cellulose nanocrystal-based chiral nematic materials are discussed, inspiring further research in this field.