Sunscreens have primarily been developed in the form of oil-in-water (O/W) or water-in-oil (W/O) emulsions to protect against ultraviolet (UV) radiation, which can cause sunburn and increase the risk of skin cancer. However, the oils used in these formulations have raised concerns due to their environmental impact and potential toxicity. In particular, concerns about the cytotoxicity and ecological effects of lipophilic UV filters have been increasingly highlighted. To address these issues, this study introduces, for the first time, an innovative sunscreen system that completely excludes oil. The proposed system is based on an aqueous biphasic water-in-water (W/W) emulsion, which eliminates oil-related issues while offering an eco-friendly and biocompatible solution. This system can incorporate water-soluble UV filters and inorganic particles, functioning as an effective sunscreen. Compared to colloidal aqueous suspension formulations, it shows excellent UV protection performance and high uniformity in application over the entire surface. In particular, W/W emulsions with 15 w/v% TiO2achieved an in vitro SPF of about 40, surpassing the value of about 30 observed for a commercial SPF 50 product. While suspensions became increasingly non-uniform as the TiO2concentration increased, reaching a standard deviation of 0.148 at 15 w/v%, the emulsions maintained a much lower deviation of 0.041, demonstrating superior film uniformity even at high particle loadings. This innovative approach significantly expands formulation options for sunscreen development and opens new avenues for aqueous-template-based sunscreen technologies.

Gradient porous polymers are engineered to vary the pore size, porosity, and interconnectivity in a single direction, enabling controlled mass transport and mechanical properties. This unique design makes them ideal candidates for applications in tissue engineering scaffolds, advanced filtration systems, and absorbent materials for environmental remediation. While various methods have been developed to create porous polymers with gradients in pore size and porosity, techniques for generating openness gradients remain largely unexplored. In this study, we present a novel approach for producing porous materials with a gradient openness through the photopolymerization of emulsion templates. By modulating the light intensity across the height of the emulsion templates during the photopolymerization process, we induce a gradual change in openness within polymerized high internal phase emulsions (polyHIPEs). This effect arises from the interplay between interfacial and bulk polymerization, influenced by the partitioning behavior of photoinitiators in the continuous phase, light intensity, and distance from the light source. Stronger light sources enhance the openness and produce more pronounced openness gradients. The progressive attenuation of light within the emulsion templates is primarily governed by UV transparency, which is controlled by incorporating different radical monomers, such as acrylic acid and acrylamide. This single-step process allows for the fabrication of porous polymers with precisely tuned mass transfer properties through controlled interconnectivity gradients.

Aqueous two-phase systems (ATPS), formed from immiscible polymer-polymer or polymer-salt solutions in water, have gained attention for their biocompatibility and eco-friendly properties, making them suitable for applications in biomedical engineering and green chemistry. To enhance their effectiveness, maximizing the internal interfacial area is critical, leading to recent advancements in emulsion-based ATPS. However, stabilizing the water-water interface with colloidal particles remains a significant challenge. This study investigates colloidal particle behavior at the water-water interface, analyzing their aggregation, growth into larger structures, and detachment from the interface over time at varying concentrations. By quantifying key interaction forces, including depletion, capillary, van der Waals, and electric double-layer forces, we identify dominant forces at each stage. Using image processing to assess aggregate sizes before detachment, we develop a novel method for measuring interfacial tension. This versatile approach accommodates diverse particle sizes and densities, offering insights into the mechanisms governing particle behavior at water-water interfaces.

Phenylbenzimidazole sulfonic acid (PBSA) is a representative water-soluble UV filter, yet its practical use is hampered by poor spreading and film formation in aqueous formulations, leading to limited UV-blocking efficiency. To address this, we examined the effect of hydrophilic polymers—poly(vinyl alcohol) (PVA), gelatin, polyethylene glycol (PEG), and dextran (DEX)—on PBSA performance. UV–Vis spectroscopy and fluorescence imaging showed that PVA and gelatin facilitated continuous film coverage and enhanced UV absorbance, whereas PEG and DEX produced discontinuous coatings with little improvement. Rheological analyses revealed that PVA–PBSA maintained network stability via hydrogen bonding, while gelatin–PBSA formed weaker gels and PEG/DEX–PBSA exhibited negligible effects. Interfacial adsorption measurements further confirmed synergistic film formation only for PVA and gelatin. Overall, our findings demonstrate that effective UV protection with water-soluble PBSA requires the combined presence of suitable bulk rheology and strong interfacial activity, establishing oil-free, water-based polymer–PBSA formulations as a sustainable route for next-generation sunscreens.

We present an interfacial assembly strategy for constructing asymmetric multilayered colloidal films through lateral compression of laterally segregated particle microdomains at the air–water interface. These microdomains—composed of polystyrene (PS) and silica (SiO2) particles—serve as lateral templates that direct vertical rearrangement during monolayer collapse. Utilizing hydrophilic PS and SiO2 particles with distinct interfacial adsorption affinities, we demonstrate that depletion interactions and compression-induced instabilities induce domain-selective subduction, a process in which one type of particle domain is driven beneath another. Specifically, more hydrophilic silica domains preferentially collapse and subduct beneath less hydrophilic PS domains, resulting in pronounced vertical asymmetry concentrated at the domain boundaries. Langmuir isotherm analysis and SEM imaging reveal that both the lateral extent of domain segregation and the vertical thickness of the resulting multilayers can be tuned by varying the compression distance and depletant concentration. Lower depletant concentrations reduce depletion pressure, facilitating enhanced particle desorption and enabling the formation of broader and more asymmetric multilayer structures. Importantly, this assembly framework remains effective even when the relative wettability of the particle types is reversed. By introducing sulfonic acid functional groups onto PS, we transform it into a highly hydrophilic species. Adjusting subphase pH to suppress SO3H dissociation allows both particle types to adsorb at the interface. Under acidic conditions, the PS–SO3H particles collapse first and subduct beneath silica domains, producing inverted stratification. This inversion confirms that the subduction-driven assembly is not limited to specific wettability pairings, but instead governed by dynamic interfacial energetics and domain interactions.

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.

Water-in-oil high internal phase Pickering emulsions (W/O HIPPEs) are known for their polyhedral droplet structures and viscoelastic properties, attributed to their high dispersed phase volume fraction. These emulsions are particularly useful for encapsulating water-soluble compounds while minimizing the use of the oil phase, making them highly desirable for applications in industries such as pharmaceuticals, cosmetics, and food. While most studies have focused on stabilizing oil-in-water (O/W) HIPPEs using amorphous TiO2 particles, this study, for the first time, investigates the stabilization of W/O HIPPEs using TiO2 particles modified with hydrophobic stearic acid to enhance stability. Additionally, we explore the critical role of particle shape—comparing spindle-shaped and amorphous particles—on the interfacial stability and mechanical properties of W/O HIPPEs. Through detailed analysis of droplet size, particle behavior at the interface, and the rheological properties of the emulsions, we demonstrate the versatility of these TiO2 particles in stabilizing HIPPEs with tunable internal structures. This research provides a foundation for the customizable design of HIPPE formulations, paving the way for targeted applications across a wide range of industries.

Stratified films offer high performance and multifunctionality, yet achieving fully stratified films remains a challenge. The layer-by-layer method, involving the sequential deposition of each layer, has been commonly utilized for stratified film fabrication. However, this approach is time-consuming, labor-intensive, and prone to leaving defects within the film. Alternatively, the self-stratification process exploiting a drying binary colloidal mixture is intensively developed recently, but it relies on strict operating conditions, typically yielding a heterogeneous interlayer. In this study, an active interfacial stratification process for creating completely stratified nanoparticle (NP) films is introduced. The technique leverages NPs with varying interfacial activity at the air-water interface. With the help of depletion pressure, the lateral compression of NP mixtures at the interface induces individual desorption of less interfacial active NPs into the subphase, while more interfacial active NPs remain at the interface. This simple compression leads to nearly perfect stratified NP films with controllability, universality, and scalability. Combined with a solvent annealing process, the active stratification process enables the fabrication of stratified films comprising a polymeric layer atop a NP layer. This work provides insightful implications for designing drug encapsulation and controlled release, as well as manufacturing transparent and flexible electrodes. Colloidal mixtures are stratified at the air-water interface depending on their interfacial activity, forming asymmetric multilayers. With the help of depletion pressure, lateral compression induces individual desorption of less interfacial active nanoparticles (NPs) into the subphase, while more interfacial active NPs remain at the interface. This active stratification process leads to nearly perfect stratified NP films with controllability, universality, and scalability. image

To achieve the successful separation of emulsions containing fine dispersed droplets and low volume fractions, a membrane with pore sizes comparable to or smaller than the droplet size is typically required. Although this approach is effective, its utilization is limited to the separation of emulsions with relatively large droplets. To overcome this limitation, a secondary membrane can be formed on the primary membrane to reduce pore size, but this can also be time-consuming and costly. Therefore, a facile and effective method is still required to be developed for separating emulsions with fine droplets. We introduce a pre-wetted mesh membrane with a pore size significantly larger than droplets, easily fabricated by wetting a hydrophilic stainless-steel mesh with water. Applying this membrane to emulsion separation via gravity-driven flow confirms a high efficiency greater than 98%, even with droplets approximately 10 times smaller than the pore size.

Polyhexamethylene guanidine (PHMG) is a guanidine-based chemical that has long been used as an antimicrobial agent. However, recently raised concerns regarding the pulmonary toxicity of PHMG in humans and aquatic organisms have led to research in this area. Along with PHMG, there are concerns about the safety of non-guanidine 5-chloro-2-methylisothiazol-3(2H)-one/2-methylisothiazol-3(2H)-one (CMIT/MIT) in human lungs; however, the safety of such chemicals can be affected by many factors, and it is difficult to rationalize their toxicity. In this study, we investigated the adsorption characteristics of CMIT/ MIT on a model pulmonary surfactant (lung surfactant, LS) using a Langmuir trough attached to a fluorescence microscope. Analysis of the π-A isotherms and lipid raft morphology revealed that CMIT/MIT exhibited minimal adsorption onto the LS monolayer deposited at the air/water interface. Meanwhile, PHMG showed clear signs of adsorption to LS, as manifested by the acceleration of the L o phase growth with increasing surface pressure. Consequently, in the presence of CMIT/MIT, the interfacial properties of the model LS monolayer exhibited significantly fewer changes than PHMG.

High internal phase emulsions stabilized with colloidal particles (Pickering HIPEs) have recently been studied intensively because of their great stability achieved by the irreversible adsorption of particles onto the oil-water interface and their usage as a template for synthesizing porous polymeric materials, called PolyHIPEs. In most cases, Pickering HIPEs with microscale droplets ranging from tens of micrometers to hundreds of micrometers have been successfully achieved, but the stabilization of Pickering HIPEs with millimeter-sized droplets is rarely reported. In this study, we report for the first time that, by using shape-anisotropic silica particle aggregates as a stabilizer, successful stabilization of Pickering HIPEs with millimeter-sized droplets can be achieved, and the size of droplets can be simply controlled. Additionally, we demonstrate that stable PolyHIPEs with large pores can be readily converted to PolyHIPEs with millimeter-scale pores, which have advantages in absorbent materials and biomedical engineering applications.

PolyHIPE, a polymerized high internal phase emulsion, is considered a promising platform for producing porous polymers. In particular, photo-polymerized HIPE has recently been utilized in the 3D printing of porous materials and other applications due to its rapid curing. However, unlike polyHIPEs prepared by thermal polymerization, a systemic study for the structural control of photo-polymerized HIPE has not yet been reported. To achieve this, here, we examine the influence of various parameters, such as partition behavior of the photo-initiator, the intensity of light, and type of emulsifier, on the structure of photo-polymerized oil-in-water HIPE. As a result, we, for the first time, report the guidelines to effectively regulate morphology of photo-polymerized HIPEs, including void interconnectivity and shape.

Pickering emulsion, which is stabilized by colloidal particles, has shown great promise in various fields due to its great stability and processibility. Depending on the type, size, number of colloidal particles, volume fraction of the dispersed phase, and emulsification method, various Pickering emulsions with different internal structures can easily be produced. Furthermore, according to the internal structure, the considerably different rheological properties can be achieved, from Newtonian viscous-like response to Hookean solid-like response. This strongly suggests that the rheological properties of Pickering emulsions can be tuned, especially for specific applications. In this paper, we summarize the progress in the measurement and understanding of the rheological properties of Pickering emulsions. We also categorize them into three different sections, depending on the volume fraction of the dispersed phase. Furthermore, we introduce the applications of Pickering emulsions that have recently become popular due to their distinctive rheological properties.

In this study, the effect of NaOH on the synthesis of mesoporous silica (MS) by using municipal solid-waste incinerator (MSWI) ash slag was investigated. Moreover, the prepared MS was used as a support to evaluate its potential for the recovery of gold ions (Au(III)) from aqueous solution. The extraction process for the MSWI ash slag activated through mechanical grinding entailed alkali treatment, using varying concentrations of NaOH. The content of Si extracted from MSWI ash slag increased with the increasing grinding time and NaOH concentration. As the NaOH concentration increased, the pore structure (e.g., Brunauer–Emmett–Teller (BET) surface area and pore volume) of the synthesized MS improved. In addition, the amount of adsorbed Au(III) increased with increasing sulfur content immobilized on the support, and the sulfur content was in turn governed by the silanol content of the MS support. The adsorbent prepared by using the MS-3M support exhibited the highest Au(III) adsorption capacity (110.3 mg/g), and its adsorption–desorption efficiency was not significantly affected even after five adsorption–desorption cycles.

A high internal phase emulsion (HIPE), which has a volume fraction of dispersed phase of over 74%, shows a solid-like property because of concentrated polyhedral droplets. Although many studies have proposed theoretical and empirical models to explain the rheological properties of HIPEs, most of them are only limited to the emulsions stabilized by surfactants. In the case of high internal phase Pickering emulsions (HIPPEs), much greater values of elastic modulus have been reported, compared to those of surfactant-stabilized HIPEs, but so far, there have been no clear explanations for this. In this study, we investigate how colloidal particles attribute to the significantly high elasticity of HIPPEs, specifically considering two different contributions, namely, interfacial rheological properties and bulk rheological properties. Our results reveal that the flocculated structures of colloidal particles that possess a significant elasticity can be interconnected between dispersed droplets. Furthermore, this elastic structure is a crucial factor in the high elasticity of HIPPEs, which is also supported by a simple theoretical model.

ABSTRACTA superabsorbent polymer (SAP) possesses an ability to absorb an aqueous solution up to several hundred times its own weight. To utilize a SAP effectively, a high absorption rate is also essential in addition to a high absorption capability. Herein, using a template based on a high internal phase Pickering emulsion (HIPPE) stabilized by aluminum oxide (Al2O3) nanoparticles, we synthesize a SAP with a high absorption rate by forming macropores. In particular, by adjusting three different parameters, the concentration of the crosslinker, the internal volume fraction of the emulsion, and the particle concentration, we successfully formed a HIPPE‐templated SAP with a high absorption rate for a saline solution, which was 51.6 g g−1 of the absorbency within 10 s. We confirm that the swelling kinetics is mainly determined by the interconnectivity between the internal macro‐pores. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48133.

We report a systematic rheological analysis of perfluorosulfonic acid (PFSA) ionomer monolayers at the air/water interface. Equipped with a custom-designed double wall knife-edge interfacial rheometer, we measure both the linear and nonlinear viscoelasticity of various PFSA ionomer monolayers. Based on rheological measurements along with other static measurements, we find that the rheological properties of the PFSA ionomer monolayers mainly originate from the electrostatic interaction of negatively charged groups (SO3-) rather than direct interactions between backbones, as is typical of other polymeric monolayers. Although the rheological properties mainly come from the SO3- groups, equivalent weight (EW) and length of the side chain affect the rheological properties as well: (1) surface activity increases with EW, thereby a larger EW tends to have stiffer interfaces; (2) PFSA ionomer with longer side chains also has larger shear moduli at the same surface pressure (Pi), presumably because the longer side chain has larger configurational entropy, thus leading to better closed packing. Moreover, it is found from Pi dependent measurements that both the elastic and viscous moduli exhibit unusually weak dependence on Pi compared with typical polymeric and surfactant monolayers. The weak Pi dependence can be explained in terms of charged colloids with long-range repulsive interactions, as they are susceptible to shear stress but resistive to compressional stress. This rheology of ionomers and their underlying morphology at the interface are expected to provide useful information for various membrane applications where ultrathin membranes can be helpful, such as ion exchange membranes and fuel cell/flow battery membranes.

Various collapse mechanisms of colloidal particle layers (e.g., wrinkling, flipping, folding, etc.) at a fluid–fluid interface have been reported, but formation of particle multilayers with large areas has not been observed yet. With the help of depletion pressure that provides a resistance to out-of-plane deformations of a colloidal particle monolayer, we report a new collapse mechanism of the particle monolayer at an air–water interface, which forms large-area particle multilayers with more than two layers. Furthermore, by adjusting the strength of the depletion pressure or the compression distance at the state of collapse, we also observe that the number of layers of particle multilayers varies significantly, and these results agree well with classical theories for thin elastic films floating atop water.

With the increasing interest and demand for epidermal electronics, a strong interface between a sensor and a biological surface is essential, yet achieving such interface is still a challenge. Here, a calcium (Ca)-modified biocompatible silk fibroin as a strong adhesive for epidermal electronics is proposed and the physical principles behind its interfacial and adhesive properties are reported. A strong adhesive characteristic (>800 N m −1 ) is observed because of the increase in both viscoelastic property and mechanical interlocking through the incorporation of Ca ions. Furthermore, additional key characteristics of the Ca-modified silk: reusability, stretchability, biocompatibility, and conductivity, are reported. These characteristics enable a wide range of applications as demonstrated in four epidermal electronic systems: capacitive touch sensor, resistive strain sensor, hydrogel-based drug delivery, and electrocardiogram monitoring sensor. As a reusable, biocompatible, conductive, and strong adhesive with water-degradability, the Ca-modified silk adhesive is a promising candidate for the next-generation adhesive for epidermal biomedical sensors.

Despite the enormous potential of cellulose nanofibrils (CNFs) as a reinforcing filler in various fields, the use of them has been limited by high-energy mechanical treatments that require a lot of energy and time consumption. To reduce the demands of energy and time required for mechanical treatments, microalgae, in particular, Nannochloropsis oceanica, which has small size, rapid growth rate, and high productivity was used as a CNFs source. This study obtains the CNFs by lipid/protein extraction, purification, and TEMPO-mediated oxidation processes under gentle mixing without high-energy mechanical treatments. Furthermore, to evaluate the applicability of microalgal CNFs as a reinforcing filler, this study estimated the mechanical strength of the fibrils by the sonication-induced scission method. To achieve a precise estimation, an effective method to distinguish straight fibrils from buckled fibrils was also developed, and subsequently, only straight fibrils were used to calculate the mechanical strength in the sonication-induced scission method. Consequently, the tensile strength of the N. oceanica CNFs is around 3-4GPa on average which is comparable with the mechanical strength of general reinforcing fillers and even higher than that of wood CNFs. Thus, this study has shown that the newly proposed simplified method using N. oceanica is very successful in producing CNFs with great mechanical strength which could be used in various reinforcement fields.