Schizophrenic Diblock-Copolymer-Functionalized Nanoparticles as Temperature-Responsive Pickering Emulsifiers

Temperature-responsive salt-resistant poly(sulfobetaine methacrylate)-based emulsifiers for heavy oils

The emulsions prepared with most currently reported emulsifiers are stable only at room temperature and are susceptible to demulsification at higher temperatures. This thermal instability prevents their use in high-temperature and high-salt environments encountered oilfield extraction. To address this issue, in this study, two temperature-responsive emulsifiers, PSBMA and CS-PSBMA, were synthesized. Both emulsifiers exhibited the ability to form stable emulsions within the temperature range of 60-80 °C and undergo demulsification at 20-40 °C. A comprehensive investigation was conducted to assess the impact of emulsifier concentration, water-to-oil ratio, and salt ion concentration on the stability of emulsions formed by these two emulsifiers. The results demonstrated their remarkable emulsification capabilities across diverse oil phases. Notably, the novel emulsifier CS-PSBMA, synthesized through the grafting chitosan (CS) onto PSBMA, not only exhibits superior emulsion stability and UCST temperature responsiveness but also significantly enhanced the salt resistance of the emulsion. Remarkably, the emulsion maintained its stability even in the presence of monovalent salt ions at concentrations up to 2 mol/L (equivalent to a mineralization level of 1.33 × 105 mg/L in water) and divalent salt ions at concentrations up to 3 mol/L (equivalent to a mineralization level of 2.7 × 105 mg/L in water). The emulsions stabilized by both emulsifiers are resilient to harsh reservoir conditions and effectively emulsify heavy oils, enabling high-temperature emulsification and low-temperature demulsification. These attributes indicate their promising potential for industrial applications, particularly in the field of enhanced oil recovery.

The Effect of Block Ratio and Structure on the Thermosensitivity of Double and Triple Betaine Block Copolymers

AB-type and BAB-type betaine block copolymers composed of a carboxybetaine methacrylate and a sulfobetaine methacrylate, PGLBT-b-PSPE and PSPE-b-PGLBT-b-PSPE, respectively, were synthesized by one-pot RAFT polymerization. By optimizing the concentration of the monomer, initiator, and chain transfer agent, block extension with precise ratio control was enabled and a full conversion (~99%) of betaine monomers was achieved at each step. Two sets (total degree of polymerization: ~300 and ~600) of diblock copolymers having four different PGLBT:PSPE ratios were prepared to compare the influence of block ratio and molecular weight on the temperature-responsive behavior in aqueous solution. A turbidimetry and dynamic light scattering study revealed a shift to higher temperatures of the cloud point and micelle formation by increasing the ratio of PSPE, which exhibit upper critical solution temperature (UCST) behavior. PSPE-dominant diblocks created spherical micelles stabilized by PGLBT motifs, and the transition behavior diminished by decreasing the PSPE ratio. No particular change was found in the diblocks that had an identical AB ratio. This trend reappeared in the other set whose entire molecular weight approximately doubled, and each transition point was not recognizably impacted by the total molecular weight. For triblocks, the PSPE double ends provided a higher probability of interchain attractions and resulted in a more turbid solution at higher temperatures, compared to the diblocks which had similar block ratios and molecular weights. The intermediates assumed as network-like soft aggregates eventually rearranged to monodisperse flowerlike micelles. It is expected that the method for obtaining well-defined betaine block copolymers, as well as the relationship of the block ratio and the chain conformation to the temperature-responsive behavior, will be helpful for designing betaine-based polymeric applications.

pH/magnetic dual responsive Pickering emulsion stabilized by Fe3O4@SiO2@chitosan nanoparticles

In recent years, Pickering emulsifiers have been widely used in various production fields due to their excellent structural stability, biocompatibility and environmental friendliness. For some applications, it is required that the emulsifier can quickly respond to environmental stimuli and control the transition between stable and unstable emulsions. In this paper, we report a novel composite Pickering emulsifier with Fe3O4 as the core and magnetic response recognition body, silica as the intermediate protective layer, and chitosan (CS) of different molecular weights to endow solid particles with surface activity and pH-responsive properties. This emulsifier can stabilize the emulsion in the emulsion system with deionized water as the aqueous phase and liquid paraffin as the oil phase and can control the demulsification of the formed emulsion under the dual pH/magnetic stimulation. The experimental results show that Fe3O4@SiO2@CS has good paramagnetism and pH responsiveness. The particle size of the composite emulsifier nanoparticles is between 90 nm and 120 nm, and the best stabilizing effect of the emulsion is achieved when the dosage is 0.5 wt%. In the pH range of 3-11, the emulsifier can rapidly demulsify a stable paraffin oil-water emulsion system under the action of a magnetic field of strength 0.4 T. The pH response of the emulsifier is as follows: when pH ≤ 2, the system can form a stable emulsion, which is composed of fully protonated chitosan as a free chain segment and Fe3O4@SiO2. Emulsion stabilization was achieved with monolithic Fe3O4@SiO2@CS as an emulsifier at pH > 2, and demulsification was achieved at pH ≈ pKb (CS) at 298 K. The research in this paper can provide a feasible idea and synthesis method for the preparation of organic-inorganic composite structure emulsifier.

Pickering Emulsion Stabilized by β-Cyclodextrin and Cinnamaldehyde/β-Cyclodextrin Composite

A Pickering emulsion was prepared using β-cyclodextrin (β-CD) and a cinnamaldehyde (CA)/β-CD composite as emulsifiers and corn oil, camellia oil, lard oil, and fish oil as oil phases. It was confirmed that Pickering emulsions prepared with β-CD and CA/β-CD had good storage stability. The rheological experiments showed that all emulsions had G' values higher than G″, thus confirming their gel properties. The results of temperature scanning rheology experiments revealed that the Pickering emulsion prepared with β-CD and CA/β-CD composites had high stability, in the range of 20-65 °C. The chewing properties of Pickering emulsions prepared by β-CD and corn oil, camellia oil, lard, and herring oil were 8.02 ± 0.24 N, 7.94 ± 0.16 N, 36.41 ± 1.25 N, and 5.17 ± 0.13 N, respectively. The chewing properties of Pickering emulsions made with the CA/β-CD composite and corn oil, camellia oil, lard, and herring oil were 2.51 ± 0.05 N, 2.56 ± 0.05 N, 22.67 ± 1.70 N, 3.83 ± 0.29 N, respectively. The texture properties confirmed that the CA/β-CD-composite-stabilized-emulsion had superior palatability. After 28 days at 50 °C, malondialdehyde (MDA) was detected in the emulsion. Compared with the β-CD and CA + β-CD emulsion, the CA/β-CD composite emulsion had the lowest content of MDA (182.23 ± 8.93 nmol/kg). The in vitro digestion results showed that the free fatty acid (FFA) release rates of the CA/β-CD composite emulsion (87.49 ± 3.40%) were higher than those of the β-CD emulsion (74.32 ± 2.11%). This strategy provides ideas for expanding the application range of emulsifier particles and developing food-grade Pickering emulsions with antioxidant capacity.

Recent Progress toward Physical Stimuli-Responsive Emulsions

Emulsion as a fine dispersion of immiscible liquids has involved widespread applications in industry, pharmaceuticals, agriculture and personal care. Stimuli-responsive emulsions capable of on-demand demulsification or changing their properties are required in many cases such as controllable release cargo, oil recovery, emulsifiers recycle and product separation, great progress has been achieved in these areas. Among these various triggers, much effort has been made to develop physical stimuli, due to the noninvasive and environmentally friendly characteristics. Physical stimuli-responsive emulsions provide a plenty of valuable practical applications in the fields of sustainable industry, biomedical reaction, drug delivery. Here, we summarize the recent development in the field of emulsions in response to physical stimuli consisting of temperature, light, magnetic field, electrical field, etc. The preparation methods and mechanisms of physical stimuli-responsive emulsions and their applications of catalysis reaction, drug delivery, and oil recovery are highlighted in this review. The future directions and outstanding problems of the physical stimuli-responsive emulsions are also discussed. This article is protected by copyright. All rights reserved.

Pickering foams and parameters influencing their characteristics

Pickering foams are available in many applications and have been continually gaining interest in the last two decades. Pickering foams are multifaceted, and their characteristics are highly dependent on many factors, such as particle size, charge, hydrophobicity and concentration as well as the charge and concentration of surfactants and salts available in the system. A literature review of these individual studies at first might seem confusing and somewhat contradictory, particularly in multi-component systems with particles and surfactants with different charges in the presence of salts. This paper provides a comprehensive overview of particle-stabilized foams, also known as Pickering foams and froths. Underlying mechanisms of foam stabilization by particles with different morphology, surface chemistry, size and type are reviewed and clarified. This paper also outlines the role of salts and different factors such as pH, temperature and gas type on Pickering foams. Further, we highlight recent developments in Pickering foams in different applications such as food, mining, oil and gas, and wastewater treatment industries, where Pickering foams are abundant. We conclude this overview by presenting important research avenues based on the gaps identified here. The focus of this review is limited to Pickering foams of surfactants with added salts and does not include studies on polymers, proteins, or other macromolecules.

Pickering Emulsions Stabilized by Diblock Copolymer Worms Prepared via Reversible Addition-Fragmentation Chain Transfer Aqueous Dispersion Polymerization: How Does the Stimulus Sensitivity Affect the Rate of Demulsification?

Responsive Pickering emulsions exhibit promising application in industry owing to the integration of the high storage stability with on-demand demulsification. In this study, stimuli-responsive Pickering emulsions stabilized by poly[oligo(ethylene glycol) methyl ether methacrylate]₁₅-b-poly(diacetone acrylamide)₁₂₀ (E₁₅D₁₂₀) worms were indicated, in which E₁₅D₁₂₀ worms were prepared via reversible addition-fragmentation chain transfer-based aqueous dispersion polymerization using thermo-sensitive POEGMA₁₅ as both the stabilizer block and macro-chain transfer agent. The factors influencing the morphologies of copolymers during polymerization-induced self assembly have been investigated. A series of different morphological polymer nanoparticles including spheres, worms, and vesicles could be produced through rational synthesis. E₁₅D₁₂₀ worms demonstrated excellent emulsifying performances and could be used as emulsifiers to form n-dodecane-in-water Pickering emulsions at a low content. The formed n-dodecane-in-water Pickering emulsions revealed a slow demulsification at pH 10 or 70 °C or pH 10/70 °C combinations, and several hours were needed for the demulsification of Pickering emulsions. However, n-dodecane-in-water Pickering emulsions displayed a rapid demulsification (∼10 min) at an elevated temperature, such as 90 °C. The different demulsification rates were attributed to different sensitivities of E₁₅D₁₂₀ worms to external stimuli. Pickering emulsions integrating a rapid responsive demulsification with a slow one would be well satisfactory on different occasions.

Salt-Dependent Phase Transition Behavior of Doubly Thermoresponsive Poly(sulfobetaine)-Based Diblock Copolymer Thin Films

The water vapor-induced swelling, as well as subsequent phase-transition kinetics, of thin films of a diblock copolymer (DBC) loaded with different amounts of the salt NaBr, is investigated in situ. In dilute aqueous solution, the DBC features an orthogonally thermoresponsive behavior. It consists of a zwitterionic poly(sulfobetaine) block, namely, poly(4-(N-(3'-methacrylamidopropyl)-N,N-dimethylammonio) butane-1-sulfonate) (PSBP), showing an upper critical solution temperature, and a nonionic block, namely, poly(N-isopropylmethacrylamide) (PNIPMAM), exhibiting a lower critical solution temperature. The swelling kinetics in D₂O vapor at 15 °C and the phase transition kinetics upon heating the swollen film to 60 °C and cooling back to 15 °C are followed with simultaneous time-of-flight neutron reflectometry and spectral reflectance measurements. These are complemented by Fourier transform infrared spectroscopy. The collapse temperature of PNIPMAM and the swelling temperature of PSBP are found at lower temperatures than in aqueous solution, which is attributed to the high polymer concentration in the thin-film geometry. Upon inclusion of sub-stoichiometric amounts (relative to the monomer units) of NaBr in the films, the water incorporation is significantly increased. This increase is mainly attributed to a salting-in effect on the zwitterionic PSBP block. Whereas the addition of NaBr notably shifts the swelling temperature of PSBP to lower temperatures, the collapse temperature of PNIPMAM remains unaffected by the presence of salt in the films.

One-pot synthesis and aqueous solution properties of pH-responsive schizophrenic diblock copolymer nanoparticles prepared via RAFT aqueous dispersion polymerization

Well-defined doubly pH-responsive schizophrenic diblock copolymer nanoparticles with tunable isoelectric points are prepared via RAFT aqueous dispersion polymerization using an efficient one-pot protocol.

Unique Oil-in-Brine Pickering Emulsion Using Responsive Antipolyelectrolyte Functionalized Latex: A Versatile Emulsion Stabilizer

A simple and straightforward approach to synthesize oil-in-water (O/W) emulsions under high salinity and temperature using zwitterion-functionalized latexes are presented in this work. First, well-defined functionalized latexes were synthesized by emulsifier-free emulsion copolymerization in the presence of precursor sulfobetaine comonomer using brine as a continuous phase. The surface-functionalized latex particles were then characterized by DLS, SEM, TEM, XPS, and TGA. The functionalized latex exhibited antipolyelectrolyte behavior in high salinity brine and at high temperatures. The effects of salinity, temperature, and pH on the long-term stability of the particles were investigated. Further, to evaluate the potential in high salinity brine and high temperature, the saltphilic functionalized latexes were utilized to stabilize the oil/brine (O/W) interface without any other additives. The latex enabled the formation of a stable Pickering emulsion system with low solid content (<0.02% w/w) in the presence of 50% v/v n-decane. The functionalized latexes were self-assembled at the O/W interface as a spherical colloidosome in high salinity brine through hydrophobic interactions and irreversible adsorption. The supraparticles were imaged with SEM, providing an insight that the exterior of the emulsion droplets is stabilized by the saltphilic latex particles, forming a protective layer at the oil-water interface through electrostatic repulsion. The antipolyelectrolyte latex can be utilized as a novel emulsion stabilizer, which can provide a versatile alternative for applications in a complex environment such as high salinity, temperature, and low or high pH.

Multistimuli-Responsive Pickering Emulsion Stabilized by Se-Containing Surfactant-Modified Chitosan

Particle-stabilized emulsions that can respond to external stimuli have attracted significant concerns due to their intelligent-controlled stability, whereas particle-stabilized Pickering emulsions responding to multistimuli but based on biomass have been rarely reported. Here, a multistimuli-responsive Pickering emulsion was developed using the modified chitosan as stabilizer. Due to electrostatic attraction, Se-containing anionic surfactant, sodium 11-(butylselenyl)undecylsulfate (C₄SeC₁₁S), can bind with CS at an acidic pH and form CS-C₄SeC₁₁S complexes which can further self-associate to form micrometer-sized particles with the character of partially hydrophobicity. Therefore, at pH < pK_a, an oil-in-water Pickering emulsion can be formed using CS-C₄SeC₁₁S particles as stabilizers and can spontaneously respond to redox, ion, and pH. First, with the addition of oxidation, the hydrophilicity of C₄SeC₁₁S was enhanced, and thus, hydrophobic association of CS-C₄SeC₁₁S decreased, leading to the disruption of CS-C₄SeC₁₁S particles. Hence, the emulsion destabilized. The demulsification process is closely related with the dosage of oxidant and the oxidation time. Second, introduction of a competitive ion (e.g., CTAB) could break the binding between C₄SeC₁₁S and CS, leading to the disruption of particle emulsifier. Thereby, demulsification occurred. Third, with sequentially increasing/decreasing pH, the emulsion can be switched from stable to unstable and then to stable again accordingly. Such a unique pH-responsive behavior has never been discovered in other pH-responsive Pickering emulsions. All of the stimuli-responsive behaviors were reversible. Upon alternately adding oxidant/reductant, CTAB/C₄SeC₁₁S, or base/acid, the current emulsion can be reversibly switched off (destabilization) and on (stabilization). Such a Pickering emulsion may be a good candidate as a vehicle of functional ingredient.

Redox and pH Dual-Responsive Emulsion Using Ferrocenecarboxylic Acid and N,N-Dimethyldodecylamine

The derivatives of ferrocene with redox properties are widely used. Some studies have used complex synthesis processes to obtain surfactants with redox properties. In order to simplify the synthesis process, FA-DMDA-Ox, a surfactant with redox and pH dual responses, was prepared by simple electrostatic interaction between ferrocenecarboxylic acid (FA) and N,N-dimethyldodecylamine (DMDA). A stable oil-in-water emulsion was prepared by using FA-DMDA-Ox at 25 °C. When sodium sulfite was added to the emulsion, the emulsion was demulsified. This was due to the oxidized ferrocene group that was reduced from the charged hydrophilic state to the uncharged hydrophobic state, which destroyed the original surface activity. In addition, when added HCl or NaOH to the emulsion changed pH, demulsification was caused by the dissociation of FA-DMDA-Ox.

“Smart” self-assembled structures: toward intelligent dual responsive drug delivery systems

In the current review, we summarized the polymer and peptide-based schizophrenic copolymers which could form micellar and vesicular (polymersome) systems providing novel structures with beneficial applications.

Triple-Responsive Pickering Emulsion Stabilized by Core Cross-linked Supramolecular Polymer Particles

It is significant to explore multiresponsive Pickering emulsions because of their flexibility in terms of demulsification in comparison with the single stimuli-responsive systems. In this study, we described a triple-responsive oil-in-water Pickering emulsion that was stabilized by amphiphilic core cross-linked supramolecular polymer particles (CCSPs). For this purpose, β-cyclodextrin-terminated poly(N-isopropylacrylamide) (PNIPAM-β-CD) and azobenzene-capped poly(4-vinylpyridine) (P4VP-azo) were separately synthesized by reversible addition-fragmentation chain transfer polymerization. By virtue of the inclusion interaction between the β-CD host and the azobenzene guest in dimethyl sulfoxide, the amphiphilic supramolecular block copolymer, poly(4-vinylpyridine)-b-poly(N-isopropylacrylamide) (P4VP-b-PNIPAM), was formed. CCSPs were prepared through the combination of the self-assembly of P4VP-b-PNIPAM in the selective solvent, water, and the cross-linking of the P4VP core with 1,4-dibromobutane. Due to thermoresponsiveness of PNIPAM shells and the supramolecular linkages between the cross-linked hydrophobic P4VP core and hydrophilic PNIPAM shells, the as-prepared CCSPs exhibited temperature-, light-, and amantadine hydrochloride guest-triggered morphological transitions. Such triple-responsive morphological transitions gifted CCSPs stabilized oil-in-water Pickering emulsion with flexible demulsification in response to various factors, such as thermo, light, and amantadine hydrochloride or their combinations. Such triple-responsive oil-in-water Pickering emulsion also provided an ideal platform for heterogeneous reactions conducted at the oil-water interface. A large interfacial area and responsive demulsification allowed the reaction to be performed with an efficient and sustainable pattern.

Switch It Inside-Out: "Schizophrenic" Behavior of All Thermoresponsive UCST-LCST Diblock Copolymers

This feature article reviews our recent advancements on the synthesis, phase behavior, and micellar structures of diblock copolymers consisting of oppositely thermoresponsive blocks in aqueous environments. These copolymers combine a nonionic block, which shows lower critical solution temperature (LCST) behavior, with a zwitterionic block that exhibits an upper critical solution temperature (UCST). The transition temperature of the latter class of polymers is strongly controlled by its molar mass and by the salt concentration, in contrast to the rather invariant transition of nonionic polymers with type II LCST behavior such as poly(N-isopropylacrylamide) or poly(N-isopropyl methacrylamide). This allows for implementing the sequence of the UCST and LCST transitions of the polymers at will by adjusting either molecular or, alternatively, physical parameters. Depending on the location of the transition temperatures of both blocks, different switching scenarios are realized from micelles to inverse micelles, namely via the molecularly dissolved state, the aggregated state, or directly. In addition to studies of (semi)dilute aqueous solutions, highly concentrated systems have also been explored, namely water-swollen thin films. Concerning applications, we discuss the possible use of the diblock copolymers as "smart" nanocarriers.

All-In-One "Schizophrenic" Self-Assembly of Orthogonally Tuned Thermoresponsive Diblock Copolymers

Smart, fully orthogonal switching was realized in a highly biocompatible diblock copolymer system with variable trigger-induced aqueous self-assembly. The polymers are composed of nonionic and zwitterionic blocks featuring lower and upper critical solution temperatures (LCSTs and UCSTs). In the system investigated, diblock copolymers from poly( N-isopropyl methacrylamide) (PNIPMAM) and a poly(sulfobetaine methacrylamide), systematic variation of the molar mass of the latter block allowed for shifting the UCST of the latter above the LCST of the PNIPMAM block in a salt-free condition. Thus, successive thermal switching results in "schizophrenic" micellization, in which the roles of the hydrophobic core block and the hydrophilic shell block are interchanged depending on the temperature. Furthermore, by virtue of the strong electrolyte-sensitivity of the zwitterionic polysulfobetaine block, we succeeded to shift its UCST below the LCST of the PNIPMAM block by adding small amounts of an electrolyte, thus inverting the pathway of switching. This superimposed orthogonal switching by electrolyte addition enabled us to control the switching scenarios between the two types of micelles (i) via an insoluble state, if the LCST-type cloud point is below the UCST-type cloud point, which is the case at low salt concentrations or (ii) via a molecularly dissolved state, if the LCST-type cloud point is above the UCST-type cloud point, which is the case at high salt concentrations. Systematic variation of the block lengths allowed for verifying the anticipated behavior and identifying the molecular architecture needed. The versatile and tunable self-assembly offers manifold opportunities, for example, for smart emulsifiers or for sophisticated carrier systems.

Dual CO2/temperature-responsive diblock copolymers confer controlled reversible emulsion behavior

Dual-stimuli responsive diblock copolymers possessing unique temperature-sensitive and CO₂/N₂-switching ability were successfully developed to promote efficient manipulation of reversible emulsification processes.

Soluble-Insoluble-Soluble Transitions of Thermoresponsive Cryptand-Containing Graft Copolymers

Cryptand-containing alternative copolymers were first made from copolymerization of styrenic derivatives and maleic anhydride and then chemically modified in this work by grafting methoxy poly(ethylene glycol) (MPEG) onto the maleic functional groups. These graft copolymers show interesting multistep soluble-insoluble-soluble (S-I-S) transitions in acidic aqueous media at a cloud point (T cp) and a subsequent mixing temperature (T mix). Turbidity measurements and dynamic light scattering studies indicate that such complex transitions may be attributed to the entropic contribution associated with the dehydration and aggregation of the MPEG groups and then the enthalpic contribution associated with the hydrogen bonding between ethylene glycol and carboxylic acid groups. More importantly, the phase transition temperatures and insoluble temperature ranges are very sensitive to changes in subtle hydrophobic-hydrophilic balance of the copolymers, such as the variation of pH, the cryptand size, and the length of the MPEG graft. The understanding of the S-I-S transition in relation to the structure of the copolymers and the external conditions may be useful in the design of smart materials and sensors.

A pH and salt dually responsive emulsion in the presence of amphiphilic macromolecules

A pH and salt dually responsive emulsion has been designed on the basis of a novel amphiphilic macromolecule. It was found that the water separation of an oil-in-water emulsion reached up to ∼60% after standing for 10 min at low pH. 2-(Diethylamino)ethyl methacrylate (DEA) residues were found to induce the macromolecules to protonate and to be hydrophilic at pH values between 2 and 6, resulting in dewetting from oil droplet surfaces in water. Besides, the macromolecules form aggregates with different structures at the water/oil interface, depending on the pH value or salt concentration of the emulsion system, enabling the system to be demulsified in response to the pH or salt stimulus. The experimental results also showed that with the addition of aluminium chloride at 100 mg L^-1, the water separation was about 70% after 20 min. A possible mechanism with respect to demulsifying was proposed on the basis of an "ion bridge" among sodium acrylate (SA) residues, inducing the macromolecules to "cross-link" and become insoluble, and leading to oil/water separation. Furthermore, at a fixed pH of 5, addition of salt to the aqueous dispersion increased the degree of oil-water interfacial activity and batch emulsions were significantly unstable to coalesce at a low salinity of 25-50 mg L^-1. This finding presents a new manipulation on emulsion stability and potential applications in the fields of oil recovery, wastewater treatment, sludge removal, and so on.