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.

A Study on the Dual Thermo- and pH-Responsive Behaviors of Well-Defined Star-like Block Copolymers Synthesize by Combining of RAFT Polymerization and Thiol-Ene Click Reaction

A series of stimuli-responsive star-like block copolymers are synthesized via the combination of reversible addition, fragmentation chain transfer (RAFT) polymerization, and photo-initiated thiol-ene (PITE) click reaction. The controllable block ratio and block sequence, narrow distribution of molecular weight, and customized arm numbers of the star-shaped copolymers reveal the feasibility and benefits of combination of RAFT polymerization and PITE click reaction for synthesis of well-defined star-like (co)polymers. A clear insight into the relationship among the arm number, block sequence, and block ratio of the star-like block copolymers and their stimuli-responsive aggregation behavior was achieved via dynamic light scattering and UV-vis spectroscopy study. Notably, the star-like poly(acrylic acid)-b-poly(2-(dimethylamino) ethyl methacrylate) (star-PAA-b-PDMAEMA) shows higher lower critical solution temperature (LCST) compared to star-PDMAEMA-b-PAA with the same arm number and block ratio due to the inner charged PAA segments at pH > IEP. In addition, for star-like PAA-b-PDMAEMA, higher PAA content enhances the hydrophilicity of the polymer in basic solution and leads to the LCST increase, except for star-PAA1-b-PDMAEMA4 at pH = 9.0 (≈IEP). For star-PDMAEMA-b-PAA, the PAA content shows minimal effect on their LCSTs, except for the polymer in solution with pH = 9.5, which is far from their IEP. The star-like block copolymers with well-defined structure and tunable composition, especially the facile-controlled block sequence, bring us a challenging opportunity to control the stimuli-responsive properties of star-like block copolymers.

CO2-Responsive Water-Soluble Conjugated Polymers for In Vitro and In Vivo Biological Imaging

Water-soluble conjugated polymers (WCPs) composed of a hydrophobic polythiophene main chain with hydrophilic tertiary amine side-chains can directly self-assemble into sphere-like nano-objects in an aqueous solution due to phase separation between the hydrophilic and hydrophobic segments of the polymeric structure. Due to the presence of gas-responsive tertiary amine moieties in the spherical structure, the resulting polymers rapidly and reversibly tune their structural features, surface charge, and fluorescence performance in response to alternating carbon dioxide (CO₂) and nitrogen (N₂) bubbling, which leads to significantly enhanced fluorescence and surface charge switching properties and a stable cycle of on and off switching response. In vitro studies confirmed that the CO₂-treated polymers exhibited extremely low cytotoxicity and enhanced cellular uptake ability in normal and tumor cells, and thus possess significantly improved fluorescence stability, distribution, and endocytic uptake efficiency within cellular organisms compared to the pristine polymer. More importantly, in vivo assays demonstrated that the CO₂-treated polymers displayed excellent biocompatibility and high fluorescence enhancement in living zebrafish, whereas the fluorescence intensity and stability of zebrafish incubated with the pristine polymer decreased linearly over time. Thus, these CO₂ and N₂-responsive WCPs could potentially be applied as multifunctional fluorescent probes for in vivo biological imaging.

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.

Two-Way CO2-Responsive Polymer Particles with Controllable Amphiphilic Properties

Multiple stimuli-responsive amphiphilic block copolymers of poly(methacrylic acid) (PMAA) and poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) were used as emulsifiers to prepare two-way CO2 stimuli-responsive poly(methyl methacrylate) (PMMA) latex particles via aqueous emulsion polymerization. The polymerization at pH 2 and 50 °C produced mainly PDMAEMA-surfaced PMMA latex particles, whereas the polymerization at pH 12 and 50 °C produced mainly PMAA-surfaced particles. Both types of latex particles appeared to precipitate at higher pH values from the emulsifier of a longer PDMAEMA block length. The direction from precipitation to dispersion for PDMAEMA-surfaced particles or from dispersion to precipitation for PMAA-surfaced particles in response to CO2 bubbling of the pH 12 dispersion of particles depended on the PDMAEMA block length. Together, this study reveals that-by tuning the PDMAEMA block length in PMAA-b-PDMAEMA used as an emulsifier and polymerization at pH 2 or 12-PMMA latex particles can exhibit two-way CO2 responsiveness between dispersion and precipitation. Thus, due to their simple preparation and unique dual pH and CO2 responsiveness, these newly developed PMAA-b-PDMAEMA emulsifiers provide a highly efficient approach for the development of smart PMMA latex nanoparticles with desirable multifunctional properties.

Multistimuli-Responsive Emulsifiers Based on Two-Way Amphiphilic Diblock Polymers

Diblock copolymers of poly(tert-butyl methacrylate) (PtBuMA) and poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) of four different block lengths were prepared by sequential two-step reversible addition-fragmentation chain transfer radical polymerization, followed by hydrolysis of the PtBuMA blocks to obtain poly(methacrylic acid)-b-PDMAEMA (PMAA-b-PDMAEMA). The effect of the PDMAEMA block length on the multistimuli-responsive amphiphilic features of both types of diblock copolymers was investigated as CO2-switchable emulsifiers for emulsification/demulsification of n-octane (an oil) in water in response to CO2/N2 bubbling. The amphiphilicity of PtBuMA-b-PDMAEMA was switched on, and the amphiphilicity of PMAA-b-PDMAEMA was switched off by CO2 bubbling at pH 12 and 25 °C to achieve emulsification/demulsification. A longer PDMAEMA block length in PMAA-b-PDMAEMA conferred more sensitive CO2-responsive amphiphilicity but reduced the extent of recovery of emulsification ability on N2 bubbling. This newly developed diblock copolymer system could potentially serve as a "multifunctional surfactant" for CO2-switchable emulsification/demulsification of oil-in-water and water-in-oil mixtures.