Dynamic Imine Bonds Research Articles

A Comprehensive Chemical Experiment: Preparation and Performance Analysis of Self-Healing Oxidized Sodium Alginate-Carboxymethyl Chitosan Hydrogels

Through cutting-edge scientific research, an innovative comprehensive chemical experiment has been developed for polymer or chemistry majors: A self-healing oxidized sodium alginate-carboxymethyl chitosan hydrogel (OSA-CMCS) with self-healing properties was synthesized based on dynamic imine bonds. In this study, sodium alginate was oxidized with sodium periodate as an oxidant, and a self-healing OSA-CMCS hydrogel was prepared by reaction with Schiff base of carboxymethyl chitosan. The experimental procedures include the operation of chemical experiments, analysis of instruments, spectral analysis, etc., covering the content of chemistry courses in a comprehensive manner, stimulating students’ interest in scientific research. It provides a solid foundation for undergraduate graduation projects, scientific research training projects, and the development of future scientific research.

Development of self-healing vanillin/PEI hydrogels for tissue engineering

Self-healing materials recover mechanical damages to expand the lifetime of the material provided. In this study, self-healing hydrogels have been successfully prepared using a novel and simple technique. Vanillin is a natural monomer, used as a bio-based cross-linker for UV-induced bonding and Schiff-base bonding. Methacrylate-functionalized vanillin (M-VAN) is covalently integrated with the polymer matrix. While M-VAN supports polymer matrix with its vinyl group, its aldehyde functionality helps the formation of dynamic covalent imine bonds via Schiff-base formation. The hydrogel showed excellent self-healing ability overnight under physiological conditions without external addition. In addition, the hydrogel surface was modified by collagen and its cell viability was investigated. The prepared scaffolds showed good cell viability of 124% and 163% compared to the control sample. The developed self-healing material reveals that it has possible uses for future biomedical applications and tissue engineering studies due to the self-healing mechanism taking place under ambient conditions.

Bio-based dynamically crosslinked networks/Fe3O4 nanoparticles composites with self-healing ability driven by multiple stimuli for non-contact welding

Polymers with repairability driven by multiple stimuli and its functional composite materials are desired for practical applications. However, to date, study on dynamically crosslinked networks with multi-stimuli response or multichannel self-healing ability derived from green, renewable precursors has been rarely reported. Herein, bio-based dynamically crosslinked network based on Schiff base (dynamic imine bonds) and multiple hydrogen bonds were fabricated from soybean oil and vanillin. The reprocessing and self-healing properties could be customized by varying the ratio of methacrylation of the obtained fatty amide (MASO) UV-curable prepolymer and methacrylate functionalized vanillin (MAV). The introduction of Schiff base and hydrogen bonds endowed reprocessability for the material. Moreover, the resulting bio-based dynamically crosslinked network exhibited outstanding self-healing performance stimulated by heat, organic solvent, infrared radiation, and microwave. The bio-based composites with Fe3O4 nanoparticles were also investigated to realize non-contact welding of fracture. This study provided a promising strategy for the development of biomass resources and bio-based dynamically crosslinked network composites with good repairability.

Multiway Softness Polyurethane Elastomeric Composite with Enhanced Thermal Conductivity and Application as Thermal Interface Materials

AbstractThe ever‐increasing computing power in modern electronics comes with significant heat waste that can't be ignored. For microchips to dissipate heat efficiently, thermal interface materials (TIMs) are the most critical components in semiconductor packaging. Soft elastomer composites are often used as TIMs due to their large‐strain reversible deformability with a small external force. For TIMs to cushion between the microchip and heat spreader, they must have high thermal conductivity and temperature‐tunable softness to reduce thermal resistance and relieve the warpage failure caused by thermal stress. However, thermal conductivity and softness are interrelated and restrict each other. To address this challenge, a radical strategy of introducing dynamic covalent bonds in the polyurethane/aluminum composite is used. The reversible and low energy of dynamic imine bonds along with the lengthening of the Khun segment in the crosslinking network imbues the material with temperature‐tunable softness function while maintaining high thermal conductivity. The resulting polyurethane elastomer (PUE) composite exhibits remarkable thermal conductivity (6.90 W m−1 K−1), low thermal resistance (0.13 K cm2 W−1), and excellent softness (elastic modulus 759.50 kPa, and stretchability 140.30%). This work provides a practical method to design thermally conductive and temperature‐tunable soft elastomer composites as TIMs in semiconductor packaging.

Ultra‐Histocompatible and Electrophysiological‐Adapted PEDOT‐Based Hydrogels Designed for Cardiac Repair

AbstractCurrently, although conducting polymers have exhibited potential electrophysiological modulation, designing bioinspired ultra‐histocompatible conducting polymers remains a long‐standing challenge. Moreover, the water dispersibility, conductivity, and biocompatibility of conducting polymers are incompatible, which restricts their application in tissue engineering. Herein, a multilevel template dispersion strategy is presented to produce poly(3,4‐ethylenedioxythiophene):(dextran sulfate/carboxymethyl chitosan) (PEDOT:(DSS/CMCS)) with biocompatibility superior to that of commercial poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) without sacrificing processability and conductivity. The PEDOT:(DSS/CMCS) and oxidized dextran solutions form an injectable PEDOT‐based hydrogel (PDCOH) mediated by dynamic covalent imine bonds under mild conditions. The PDCOH has a tissue‐matched modulus and conductivity to adapt to the mechanical environment of dynamic tissue and modulate fibrosis‐induced electrical decoupling. The PDCOH combined with adipose‐derived stem cells demonstrates superior cardiac repair effects over cell suspensions and nonconductive hydrogels, inhibiting ventricular remodeling, reducing fibrous scarring, promoting vascular regeneration, and restoring electrophysiological and pulsatile functions.

Electroactive injectable hydrogel based on oxidized sodium alginate and carboxymethyl chitosan for wound healing

Electroactive hydrogel is of great significance in restoring wound currents, promoting cell proliferation, and accelerating the wound healing process. However, the poor dispersity and underlying toxicity of electronic conductive fillers and high concentration of ionic conductors in traditional electroactive hydrogel limited its application in medical care. Herein, an electroactive oxidized sodium alginate/carboxymethyl chitosan/silver nanoparticles (OSA/CMCS/AgNPs) hydrogel was constructed with no additional conductive fillers or synthesized conductive polymers being added, in which the dynamic imine bonds were rapidly formed between aldehyde groups in OSA and amino groups in CMCS, and AgNPs were further in situ formed by UV irradiation. The electroactive hydrogel exhibited the injectable property, strong self-healing ability, excellent biocompatibility, and high antibacterial activities. Moreover, the electroactive hydrogel can significantly promote the proliferation of L929 cells under electrical stimulation. Furthermore, the electroactive hydrogel was proved to significantly accelerate the wound healing process in the full-thickness skin defect model, exhibiting anti-inflammation, promoting the fibroblasts proliferation, angiogenesis, and collagen deposition under electrical stimulation. In summary, the current work explored a novel strategy to construct the polysaccharides-based electroactive hydrogel with good biocompatibility and multi-functions, which is promising to be used in deep wound treatment.

A chitosan-based self-healing hydrogel for accelerating infected wound healing.

Wound infection causes irregular tissue closure, often with prolonged healing. Traditional therapies based on antibiotic delivery have resulted in reduced therapeutic efficiency and drug resistance. Such features make it highly desirable to develop an antibiotic-free material for wound infection in clinical applications. Herein, a self-healing antibacterial hydrogel was designed to realize the treatment of S. aureus-infected wounds. The design of the dynamic imine bond endows hydrogels with self-healing and adaptive properties, which could cover the irregular wound and improve the safety of administration. In addition, benefiting from quaternized chitosan, the designed hydrogels also present fascinating antimicrobial properties and favorable biocompatibility. The evaluation in a rat skin wound infection model indicates that the fascinating antimicrobial effect accelerates wound healing by the designed hydrogels. This facile design of an antibiotic-free material allows effective wound infection management, which may be promising in coping with other complex wound healings.

Dynamic Imine Bonding Facilitates Mannan Release from a Nanofibrous Peptide Hydrogel.

Recently, there has been increased interest in using mannan as an immunomodulatory bioconjugate. Despite notable immunological and functional differences between the reduced (R-Man) and oxidized (O-Man) forms of mannan, little is known about the impact of mannan oxidation state on its in vivo persistence or its potential controlled release from biomaterials that may improve immunotherapeutic or prophylactic efficacy. Here, we investigate the impact of oxidation state on the in vitro and in vivo release of mannan from a biocompatible and immunostimulatory multidomain peptide hydrogel, K2(SL)6K2 (abbreviated as K2), that has been previously used for the controlled release of protein and small molecule payloads. We observed that O-Man released more slowly from K2 hydrogels in vitro than R-Man. In vivo, the clearance of O-Man from K2 hydrogels was slower than O-Man alone. We attributed the slower release rate to the formation of dynamic imine bonds between reactive aldehyde groups on O-Man and the lysine residues on K2. This imine interaction was also observed to improve K2 + O-Man hydrogel strength and shear recovery without significantly influencing secondary structure or peptide nanofiber formation. There were no observed differences in the in vivo release rates of O-Man loaded in K2, R-Man loaded in K2, and R-Man alone. These data suggest that, after subcutaneous injection, R-Man naturally persists longer in vivo than O-Man and minimally interacts with the peptide hydrogel. These results highlight a potentially critical, but previously unreported, difference in the in vivo behavior of O-Man and R-Man and demonstrate that K2 can be used to normalize the release of O-Man to that of R-Man. Further, since K2 itself is an adjuvant, a combination of O-Man and K2 could be used to enhance the immunostimulatory effects of O-Man for applications such as infectious disease vaccines and cancer immunotherapy.

A Self-Healing Gel Polymer Electrolyte, Based on a Macromolecule Cross-Linked Chitosan for Flexible Supercapacitors

Gel polymer electrolytes with a satisfied ionic conductivity have attracted interest in flexible energy storage technologies, such as supercapacitors and rechargeable batteries. However, the poor mechanical strength inhibits its widespread application. One of the most significant ways to avoid the drawbacks of the gel polymer electrolytes without compromising their ion transportation capabilities is to create a self-healing structure with the cross-linking segment. Herein, a new kind of macromolecule chemical cross-linked network ionic gel polymer electrolyte (MCIGPE) with superior electrochemical characteristics, a high flexibility, and an excellent self-healing ability were designed, based on chitosan and dibenzaldehyde-terminated poly (ethylene glycol) (PEGDA) via dynamic imine bonds. The ionic conductivity of the MCIGPE-65 can achieve 2.75 × 10-2 S cm-1. A symmetric all-solid-state supercapacitor employing carbon cloth as current collectors, activated a carbon film as electrodes, and MCIGPE-65 as a gel polymer electrolyte exhibits a high specific capacitance of 51.1 F g-1 at 1 A g-1, and the energy density of 7.1 Wh kg-1 at a power density of 500.2 W kg-1. This research proves the enormous potential of incorporating, environmentally and economically, chitosan into gel polymer electrolytes for supercapacitors.

Developing Easy Processable, Recyclable, and Self-Healable Biobased Epoxy Resin through Dynamic Covalent Imine Bonds

Growing sustainability concerns have promoted the rapid development of reusable and environmentally friendly thermosetting materials. Herein, a recyclable biobased curing agent (vanillin-based imine curing agent) was produced from vanillin in a single-stage process. However, this curing agent was fully solid and difficult to process, requiring large amounts of solvent during processing. Since the viscosity of 4-methyl-1,3-cyclohexendiamine (HTDA) is low, it can be used as a cocuring agent at various amounts to make a viscous liquid curing agent for diglycidyl ether of bisphenol F. The curing behaviors and thermomechanical and mechanical properties of the cured thermosets were evaluated along with their self-healing ability. The results reveal that the viscosity and activation energy of curing are reduced as the weight ratio of HTDA increases, whereas the flexural strength (106–122 MPa), moduli (2365–2587 MPa), and Tg values (95–110 °C) increase gradually. Additionally, the heat-resistant temperature (Ts) values (166–162 °C) and char residue at 700 °C (26–10%) of the cured samples continuously decreased. Overall, 40% HDTA containing VH03 showed a suitable viscous form for processing and mechanical and thermal properties. Subsequently, the flexural strength retention and Tg were still 80% and 115 °C, respectively, and it also demonstrated absolute solvent resistance at room temperature. The excellent integrated properties clarified that VH03 is favorable for easy processability, recyclability, and sustainable improvement.

Design of Near-Infrared-Triggered Cellulose Nanocrystal-Based In Situ Intelligent Wound Dressings for Drug-Resistant Bacteria-Infected Wound Healing

Postoperative infected wound complications caused by residual tumor cells, bacterial biofilms, and drug-resistant bacteria have become the main challenge in postsurgical skin regeneration. Herein, a bionic cellulose nanocrystal (CNC)-based in situ intelligent wound dressing with near-infrared (NIR)-, temperature-, and pH-responsive functions was designed by using NIR-responsive CNC as the network skeleton, dynamic imine bonds between dialdehyde cellulose nanocrystals and doxorubicin, chitosan oligosaccharide as the pH-responsive switch, and temperature-sensitive poly(N-isopropyl acrylamide) as the temperature-responsive in situ formation switch. The as-prepared wound dressing with the intertwining three-dimensional (3D) network structure possessed high drug loadability of indocyanine green (30 mg/g) and doxorubicin (420 mg/g) simultaneously. The temperature-, NIR-, and pH-responsive switches endowed the wound dressing with controllable on-demand drug release behavior. In particular, the temperature switch endowed the dressing with a shape-adaptable ability on irregularly infected wounds. Interestingly, the wound dressing showed excellent antitumor activity for A375 tumor cells, antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) and bacterial biofilm removal ability. Therefore, the developed wound dressing can provide an ideal synergistic treatment strategy combined with chemotherapy and photodynamic and photothermal therapy for postoperative drug-resistant bacteria-infected wound healing.

Synthesis of epoxidized soybean oil-derived covalent adaptable networks through melt Schiff base condensation

Thermosets derived from epoxidized soybean oil (ESO) are restricted drastically because they have inferior mechanical properties, are not reprocessable, and are difficult to recycle due to their irreversible cross-linking structures. Herein, we report malleable and recyclable poly(epoxy imine) covalent adaptable networks (CANs) with tunable mechanical properties synthesized via a novel two-step procedure with ESO, vanillin (VAN), and diamines as raw materials. In the first step, ESO was reacted with VAN to generate aldehyde-terminated ESO (VESO). In the second step, poly(epoxy imine) CANs containing dynamic imine bonds were obtained by Schiff base condensation of VESO with diamines. The structure of poly(epoxy imine) CANs can be easily controlled by simply changing the structure of diamine, which in turn enables their mechanical properties to be regulated conveniently. Soft poly(epoxy imine) CAN with tensile strength (σ) and elongation at break (ε) 6.61 MPa and 54% was obtained by using flexible aliphatic diamine. Tough and strong poly(epoxy imine) CANs with σ and ε of higher than 25 MPa and 22% were achieved by using rigid aromatic diamines. All the poly(epoxy imine) CANs synthesized with different diamines showed various functionalities including reprocessability, recyclability, and weldability owning to the dynamic imine bonds. The tunable mechanical properties and excellent integrated functionalities make the biobased poly(epoxy imine) CANs more attractive than traditional ESO-derived thermosets. • A new approach was designed to synthesize epoxy covalent adaptable networks (ECANs). • The structure and property of the ECANs can be easily regulated by changing diamines. • The ECANs showed excellent reprocessability and weldability.

Self-healing, reprocessable, degradable, thermadapt shape memory multifunctional polymers based on dynamic imine bonds and their application in nondestructively recyclable carbon fiber composites

Traditional epoxy thermosets have been extensively used in many fields, including the field of carbon fiber composite materials, which is favored by a large number of researchers. But they usually cannot be recycled under mild conditions. To make matters worse, the material loses its usefulness once it is damaged. Self-healing and degradable thermosetting resins with dynamic covalent bonds offer a potential solution to this conflict. In this paper, a series of epoxy polymers named EPCN based on dynamic imine bonds were easily prepared by a one-pot method using inexpensive industrial materials terephthalaldehyde and common bisphenol A diglycidyl ether as raw materials, which were cured by D230. The results show that the materials exhibit certain self-healing, reprocessability and thermadapt shape memory properties due to the dynamic properties of the imine bonds. Moreover, EPCN epoxy polymers can be degraded due to the hydrolysis of dynamic imine bonds, and their degradation exhibit temperature and acidity dependence. More importantly, the recyclable carbon fiber reinforced polymer composites prepared with EPCN-4 as the resin matrix can be completely degraded under weak acid conditions, leading to the ready and non-destructive recycling of its carbon fiber composite. We envision this reprocessable and degradable carbon fiber-reinforced composite material with cheap raw materials, simple process, and suitable for mass production will make it a potential candidate for sustainable structural material applications.

Fabricating switchable Pickering emulsions by dynamic covalent copolymer amphiphiles

In this work, amphiphilic copolymers D-An based on the dynamic imine bonds were generated in-situ in the aqueous solutions by two water-soluble precursors, the random copolymer poly(N-(2-methacryloylxyethyl)-random-poly(4-(formaldehyde) phenyl methacrylate) (PNMP83-co-PBFMA4, Precursor D) and alkylamines (Precursor An, n represents the carbon number in the alkyl chain that is ranging from 4 to 10). Amphiphiles D-An formed micelles spontaneously in the aqueous solutions, which were studied by the surface tension and cryogen-transmission electron microscopy (cryo-TEM) measurements. Moreover, the CO2/N2 responsive micellization of D-An due to the reversible formation and breaking of the dynamic imine bond (-CH=N-) was confirmed by the nuclear magnetic resonance (NMR) measurements. Accordingly, the emulsification of dynamic covalent amphiphilic copolymers D-An was studied in detail. O/W Pickering emulsions with excellent stability were commonly generated by employing D-An as emulsifiers regardless of n and the nature of oil employed, which was significantly different from the weak emulsification of either precursor D or precursor An. The synergistic emulsification of D-An monomers and micelles was proved to be the major cause as evidenced by the confocal laser scanning microscopy (CLSM) method. Noticeably, the abundant alkylamines were also advantageous in stabilizing emulsions. Attributing to the stimuli-responses of amphiphiles D-An to CO2/N2, the stability of Pickering emulsions could be reversibly controlled by CO2/N2 as well.

An injectable and self-healing cellulose nanofiber-reinforced alginate hydrogel for bone repair

Biomedical materials are in high demand for transplantation in cases of diseased or damaged bone tissue. Hydrogels are potential candidates for bone defect repair; however, traditional hydrogels lack the necessary strength and multiple functions. Herein, we effectively synthesized a cellulose nanofiber (CNF)-reinforced oxidized alginate (OSA)/gelatin (Gel) semi-interpenetrating network hydrogel through a facile one-step approach without a cross-linker by using the synergistic effects of dynamic imine bonds and hydrogen bonds. The OSA/Gel/CNF sample showed a notable compressive modulus (up to 361.3 KPa). The gelation time (~150 s) ensured excellent injectability. Self-healing exhibited a high efficiency of up to 92 %, which would enable minimally invasive, dynamic adjustments and personalized therapies. Furthermore, the OSA/Gel/CNF hydrogel showed excellent biomineralization (Ca/P ratio ~ 1.69) and enhanced preosteoblast cell (MC3T3-E1) viability (over 96 %), proliferation, and osteogenic differentiation. Thus, this multifunctional hydrogel has promising potential for using in the bone tissue repairs.

Design of inherent fire retarding and degradable bio-based epoxy vitrimer with excellent self-healing and mechanical reprocessability

Epoxy resins possess poor flame retardancy and have difficulty in both recycling and reprocess ability which largely limit their application. Herein, two vanillin-based epoxy monomers, shorted as VAD-EP and VDP-EP, containing both imine bonds and inherently fire retarding phosphorus elements, were synthesized via in situ condensation reaction with DDM and addition reaction with DOPO, followed by the epoxidation by epichlorohydrin. Epoxy vitrimer materials were then cured by D230 diamine hardener by adjusting the proportion of VAD-EP and VDP-EP monomer. When the mass ratio of VAD-EP and VDP-EP was 8:2, A8P2-D230 reached the fire retarding UL-94 V0 rating and LOI value of 27.0% with only 0.66% of phosphorus content, this behavior was ascribed to condensed phase and free radical scavenging mechanisms. When the mass ratio was 7:3, the tensile strength and elastic modulus of the A7P3-D230 epoxy were 75.5 MPa and 2.5 GPa, respectively, i.e. 48.6% and 18.8% higher than A10P0-D230 sample. Meanwhile, the material showed high stress relaxation rate, due to the presence of dynamic imine bonds in the topological crosslinking network. As a consequence, the epoxy vitrimer exhibited excellent self-healing capability, reprocessability and degradation behaviors. The biobased epoxy vitrimer was then used to prepare the carbon fibers (CFs) reinforced epoxy composites, results showed that CFs can be completely recycled. Interestingly, the recycled CFs maintain unchanged chemical structure, mechanical properties and morphology as the original CFs.

Versatile levulinic acid-derived dynamic covalent thermosets enabled by in situ generated imine and multiple hydrogen bonds

Bio-based dynamic covalent thermosets have attracted extensive attention as they are expected to break conventional thermosets' reliance on fossil resources and address the recycling issue after disposal. However, there has always been a contradiction between using bio-based feedstocks and possessing high properties, as well as a conflict between high performance and rapid recycling (reprocessing and degradation). In this work, a simple approach was developed to prepare bio-based thermosets with high performance, rapid reprocessing, high flame retardancy, and antibacterial properties enabled by in-situ generated dynamic covalent imine (Schiff base) bonds and multiple hydrogen bonds. The levulinic acid epoxy (ELA) was successfully synthesized and cured with 2-(4-aminophenyl)-1H-benzimidazol-5-amine (BIA) containing benzimidazole structures. The high concentration of Schiff bases and multiple hydrogen bonds of ELA-BIA endowed it with high glass transition temperature and mechanical properties, as well as satisfactory catalyst-free malleability, rapid reprocessing and repairing. Furthermore, due to the combined effect of the in-situ Schiff base and benzimidazole structure, ELA-BIA exhibited excellent condensed phase char formation ability, resulting in intrinsic flame retardancy with a limiting oxygen index of 33.8 % and a UL-94 V-0 rating, both of which were significantly higher than 4, 4′-diaminodiphenyl methane (DDM) cured ELA or DDM cured bisphenol A epoxy. Moreover, the Schiff bases bonded in the networks provided 100 % of the intrinsic antibacterial rates. This work provides a feasible and simple strategy for the preparation of high-performance and versatile bio-based dynamic covalent thermosets.

Self-Healing Approach toward Catalytic Soft Robots

Soft robotics is a rapidly evolving research field that focuses on developing robots with bioinspired actuation/sensing mechanisms and highly flexible soft materials, some of which are similar to those found in living organisms. The hydrogel has the characteristics of excellent biocompatibility, softness, and elasticity, which makes it an ideal candidate material for the preparation of soft robots. Here we utilized a self-healing approach to develop a catalytically driven soft robot, which was constructed by dynamic imine bonds between modular hydrogels. One of the modules was a hydrogel formed by dynamic aldimine cross-linking of chitosan and glutaraldehyde, and the other module was a hydrogel embedded with catalase. The soft hydrogel robot moved because of catalytic reactions between the robot and environment [hydrogen peroxide (H2O2) fuel], giving rise to a fluidic release that supports propulsion, as inspired by the jet-propulsive mechanism in swimming dragonfly larvae. The speed of the soft robot can be mediated by adjusting the concentration of H2O2 and enable/disable movement based on the folding and unfolding of enzymes. In addition, the hydrogel formed by replacing glutaraldehyde with dialdehyde-functionalized PEG2000 had excellent elastic properties, and the soft robot based on PEG2000 had a higher movement speed than that based on glutaraldehyde under the same H2O2 concentration. Moreover, the addition of iron oxide nanoparticles can realize the magnetic guidance of the soft robot and the combination of different modules can realize different motion modes. The highly configurable self-healing catalytic soft robot holds great potential for a variety of interesting applications, including swimming robots, robot-assisted water treatment, and drug release.

Molecular Exchange of Dynamic Imine Bond for the Etching of Polymer Particles

The underlying trend of colloidal synthesis has focused on extending the structure and composition complexity of colloidal particles. Hollow and yolk-shell particles are successful examples that have potential applications in frontier fields. In this paper, a facile and controllable etching method based on the molecular exchange of the dynamic imine bond to generate cavities in polymer particles is developed. Starting from boronate ester polymer particles and inorganic@boronate core-shell particles with the imine bonds incorporated in the polymer networks, the etching method easily affords hollow and yolk-shell particles with tunable shell thicknesses. The molecular exchange dynamics analysis indicates that guest amine molecules cause the reconstruction of imine bonds and the leakage of molecular and oligomer fragments, resulting in the formation of the hollow structure. This molecular exchange-based etching method may be of interest in the construction of polymer architectures with increased composition and structure complexities.

Alkyl chain length influence of hydrotrope on the pH responsiveness of surfactant aggregates based on dynamic imine bond

• Ionic hydrotropes with different chain length based on imine bond is prepared. • The pH responsiveness of solution by mixing CTAB and hydrotrope is explored. • The mechanism of different pH responsiveness of mixture is analyzed. The combination of pH-responsive hydrotropes and cationic surfactants is a novel way to construct pH-responsive surfactant aggregates. Herein, in order to investigate the chain length influence of hydrotrope on surfactant aggregate, three hydrotropes were formed from p-hydroxybenzaldehyde (HB) and added amine (hexylamine (HA), octylamine (OA), dodecylamine (DA)) respectively based on dynamic imine bonds. Then the surfactant aggregates were constructed by adding cetyltrimethyl ammonium bromide (CTAB). The molar ratio of CTAB: HB: HA/OA/DA was fixed at 100:55:55. The formation of imine bonds was proved by means of 1 H NMR measurement. Rheological measurements, and cryo -TEM were used to explore the pH responsiveness of the surfactant aggregates. The results showed that as pH increased from 6.0 to 12.0, the CTAB/HB/HA system changed from a low viscosity fluid to a viscoelastic fluid, as the CTAB/HB/OA system transformed from aqueous liquid via a transparent gel solution to a turbid fluid. On the other hand, the CTAB/HB/DA system can achieve four state transitions, from a non-viscosity fluid, via a viscoelastic fluid, turbid fluid and finally to a viscoelastic fluid. With the change of pH, the CTAB/HB/HA system turned from spherical to wormlike micelles, while CTAB/HB/OA experienced changes from spherical micelles via wormlike micelles to vesicles. Finally, the CTAB/HB/DA system was the most complex one, which converted from spherical micelles, wormlike micelles via vesicle, into final wormlike micelles. In conclusion, the sensitivity of pH responsiveness among these three systems gradually improved by increasing the chain length of the hydrotrope formed by HB and amine. This can be attributed to the different growth rates of the packing parameter. This work demonstrated the feasibility of constructing pH responsive surfactant aggregates by introducing hydrotropes to cationic surfactants.