Anti-polyelectrolyte Effect Research Articles

A Total Internal Reflection Microscopy (TIRM)-Based Approach for Direct Characterization of Polymer Brush Conformational Change in Aqueous Solution.

This study presents a novel approach utilizing total internal reflection microscopy (TIRM) to effectively characterize the swelling and collapse of polymer brushes in aqueous solutions. Zwitterionic poly(carboxybetaine methacrylate) (PCBMA) and nonionic poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA) brushes are chosen as model systems. By investigation of an intriguing theory-experiment discrepancy observed during the measurement of near-wall hindered diffusion, valuable insights into the compressibility of polymer brushes are obtained, revealing their conformational information in aqueous solution. The results demonstrate that zwitterionic PCBMA brushes exhibit minimal antipolyelectrolyte effects in 0.1-10 mM NaCl solution but undergo significant swelling with increasing pH. On the other hand, nonionic POEGMA brushes exhibit similar responses to ionic strength as weak polyelectrolyte brushes. These unexpected findings enhance our understanding of polymer brushes beyond classical theories. The TIRM-based approach proves to be effective for characterizing polymer brushes and other soft nanomaterials.

Polyzwitterionic hydrogel using waste biomass as solar absorbent for efficient evaporation in high salinity brine

Solar-driven interfacial vapor generation (SVG) is a promising strategy for brine purification. However, the effective combination of functional evaporator backbones and solar absorbers for SVG enhancement remains challenging in high-salinity brines (≥10 wt%). Herein, a biomass-based polyzwitterionic hydrogel (PZH) was developed to improve the SVG performances in 10 wt% brine. Zwitterions with specific anti-polyelectrolyte effects served as backbones for accelerating H2O transportation, with fewer salt deposits and macropore channels. The biomass of straw prepared at a pyrolysis temperature at 600 ℃ was the most effective solar absorber. The synthesis of So600-PZH-8mm yielded the optimal solar evaporator with a low evaporation enthalpy of 877.79 J·g−1, a remarkable solar-to-vapor energy efficiency of 87.1 %, and a high evaporation rate of 3.57 kg·m−2·h−1 under 1 sun irradiation and a relative humidity of 30 %. Multi-cycle evaporation tests further verified the high quality of the steam water, high salt resistance, reliability, and durability of So600-PZH-8mm in practical applications. Furthermore, density functional theory calculations of the binding energies of charged groups and ions verified the anti-polyelectrolyte effect and swelling behavior of the PZHs. Overall, this study demonstrated the effectiveness of waste biomass as solar absorber for high-efficiency solar adsorption and water activation, which opens a new perspective to inspire the up-conversion of waste biomass in more valuable and meaningful ways.

Anti-Biofouling Polyzwitterion-Poly(amidoxime) Composite Hydrogel for Highly Enhanced Uranium Extraction from Seawater.

Amidoxime-functionalized hydrogels are one of most promising adsorbents for high-efficiency uranium (U) extraction from seawater, but bioadhesion on their surface seriously decreases their adsorption efficiency and largely shortens their service life. Herein, a semi-interpenetrating zwitterion-poly(amidoxime) (ZW-PAO) hydrogel was explored through introducing a PAO polymer into a poly [3-(dimethyl 4-vinylbenzyl amino) propyl sulfonate] (PDVBAP) polyzwitterionic (PZW) network via ultraviolet (UV) polymerization. Owing to the anti-polyelectrolyte effect of the PZW network, this ZW-PAO hydrogel can provide excellent super-hydrophilicity in seawater for high-efficiency U-adsorption from seawater. Furthermore, the ZW-PAO hydrogel had outstanding anti-biofouling performance for both highly enhanced U-adsorption and a relatively long working life in natural seawater. As a result, during only 25 days in seawater (without filtering bacteria), the U-uptake amount of this ZW-PAO hydrogel can reach 9.38 mg/g and its average rate can reach 0.375 mg/(g∙day), which is excellent among reported adsorbents. This work has explored a promising hydrogel for high-efficiency U-recovery from natural seawater and will inspire new strategy for U-adsorbing materials.

Incorporation of polyzwitterions in superabsorbent network membranes for enhanced saltwater absorption and retention

BackgroundSuperabsorbent polymers (SAPs) have a remarkable ability to absorb significant quantities of water. However, their absorption capacity is significantly reduced when exposed to saline solutions, such as urine, due to the polyelectrolyte effect and charge screening. MethodsIn this study, we demonstrate a zwitterionic superabsorbent polymer (ZSAP) with excellent salt-water absorption and retention capacities. ZSAP was synthesized by grafting a copolymer of p(sulfobetaine methacrylate-co-2-hydroxyethyl methacrylate) (p(SBMA-co-HEMA)) onto an acrylic acid (AA)-based hydrogel via free-radical polymerization. The introduction of zwitterionic SBMA significantly enhances the hydrophilicity of the polymer, particularly in a saline solution due to the anti-polyelectrolyte effect, thereby accelerating the rate of salt absorption. Additionally, the hydroxyl groups from HEMA facilitate the formation of covalent bonds with the AA network membrane through esterification, effectively mitigating polymer leaching. The hydration/dehydration behaviors of linear polymers were measured using the dynamic vapor sorption (DVS) method. Moreover, the salt-water absorption capacity, centrifuge retention capacity (CRC), and absorbency under load (AUL) of ZSAP with various SBMA moieties and copolymer dosages were comprehensively evaluated in a 0.9 wt% sodium chloride solution. Additionally, the water retention under different temperatures and polymer leaching of ZSAP were investigated. Significant FindingsThe copolymer p(SBMA-co-HEMA) not only demonstrates a high salt-water absorption rate at 90% RH in a 0.9 wt% NaCl solution but also exhibits superior water retention at 0% RH compared to the AA polymer. Moreover, the ZSAP exhibits superior salt-water absorption capacity and AUL in a 0.9 wt% NaCl solution compared to conventional AA-based SAP. Additionally, the introduction of the hydroxyl moiety from the p(SBMA-co-HEMA) copolymer reduces free polymer leaching from ZSAP. This work presents an approach for the development of new SAP with high salt-water absorption and retention.

Anionic Hofmeister Effect Regulated Conductivity in Polyelectrolyte Hydrogels for High-Performance Supercapacitor.

The Hofmeister effect not only affects the stability and solubility of protein colloids but also has specific effects on the polymer molecules. Here, the impact of the Hofmeister effect on the electrochemical properties of polyelectrolyte hydrogels at room temperature and subzero temperature studied for the first time. Polyelectrolyte hydrogels exhibit an anti-polyelectrolyte effect in low concentrations of ammonium salt, while they exhibit an obvious Hofmeister effect in high concentrations of ammonium salt. Kosmotropic ions demonstrate strong interaction with water molecules or polymer chains, resulting in the reduction of conductivity of polyelectrolyte hydrogels. However, chaotropic ions exhibit weak interactions with water molecules or molecular chains, leading to an increase in conductivity. The Hofmeister effect has a more significant effect on the polyzwitterion electrolyte. The conductivity of polyzwitterion hydrogel soaked in chaotropic ion is up to 6.2 mS cm-1 at -40°C. The supercapacitor assembled by polyzwitterion electrolytes maintains a capacitance retention rate of 85% and ≈100% coulomb efficiency after 15 000 cycles at -40°C. This study elucidates the influence of the Hofmeister effect on conductivity in polyelectrolytes and expands the regulatory approach for improving the performance of energy storage devices.

Dipole Theory of Polyzwitterion Microgels and Gels.

The behavior of polyzwitterions, constituted by dipole-like zwitterionic monomers, is significantly different from that of uniformly charged polyelectrolytes. The origin of this difference lies in the intrinsic capacity of polyzwitterions to self-associate intramolecularly and associate with interpenetrating chains driven by dominant dipolar interactions. Earlier attempts to treat polyzwitterions implicitly assume that the dipoles of zwitterion monomers are randomly oriented. At ambient temperatures, the dipolar zwitterion monomers can readily align with each other generating quadrupoles and other multipoles and thus generating heterogeneous structures even in homogeneous solutions. Towards an attempt to understand the role of such dipolar associations, we present a mean field theory of solutions of polyzwitterions. Generally, we delineate a high-temperature regime where the zwitterion dipoles are randomly oriented from a low-temperature regime where quadrupole formation is significantly prevalent. We present closed-form formulas for: (1) Coil-globule transition in the low-temperature regime, the anti-polyelectrolyte effect of chain expansion upon addition of low molar mass salt, and chain relaxation times in dilute solutions. (2) Spontaneous formation of a mesomorphic state at the borderline between the high-temperature and low-temperature regimes and its characteristics. A universal law is presented for the radius of gyration of the microgel, as a proportionality to one-sixth power of the polymer concentration. (3) Swelling equilibrium of chemically cross-linked polyzwitterion gels in both the high temperature and low-temperature regimes. Addressing the hierarchical internal dynamics of polyzwitterion gels, we present a general stretched exponential law for the time-correlation function of gel displacement vector, that can be measured in dynamic light scattering experiments. The present theory is of direct experimental relevance and additional theoretical developments to all polyzwitterion systems, and generally to biological macromolecular systems such as intrinsically disordered proteins.

Moisture self-regulating ionic skins with ultra-long ambient stability for self-healing energy and sensing systems

Dehydration has been a key limiting factor for the operation of conductive hydrogels in practical application. Here, we report self-healable ionic skins that can self-regulate their internal moisture level by capturing extenral moistures via hygroscopic ion-coordinated polymer backbones through antipolyelectrolyte effect. Results show the ionic skin can maintain its mechanical and electrical functions over 16 months in the ambient environment with high stretchability (fracture stretch ∼2216 %) and conductivity (23.5 mS/cm). The moisture self-regulating capability is further demonstrated by repeated exposures to harsh environments such as 200°C heating, freezing, and vacuum drying with recovered conductivity and stretchability. Their reversible ionic and hydrogen bonds also enable self-healing feature as a sample with the fully cut-through damage can restore its conductivity after 24 h at 40 % relative humidity. Utilizing the ionic skin as a building block, self-healing flexible piezoelecret sensors have been constructed to monitor physiological signals. Together with a facile transfer-printing process, a self-powered sensing system with a self-healable supercapacitor and humidity sensor has been successfully demonstrated. These results illustrate broad-ranging possibilities for the ionic skins in applications such as energy storage, wearable sensors, and human-machine interfaces.

Three-dimensional zwitterionic hydrogel-based evaporators with simultaneous ultrahigh evaporation rates and anti-fouling performance

Zwitterionic hydrogels (ZHs) are commonly adopted as evaporators to address the issues of low evaporation rate and poor salt resistance in solar-driven interfacial desalination due to their unique anti-polyelectrolyte (AP) effect. However, the inherent limitations of ZHs, including low water transfer rates compared to their evaporation rates and poor mechanical properties, have restricted their applications to two-dimensional (2D) evaporator configurations. Herein, we proposed a unique design of three-dimensional (3D) composite solar evaporators based on ZHs and polyvinyl alcohol (PVA) sponge to improve the water transfer capacity and mechanical properties of ZHs, and thus achieve ultrahigh evaporation rates and excellent anti-fouling performance. The porous structure and super hydrophilicity of PVA sponge endowed the prepared 5-cm-high ZH-based solar evaporators (ZHSE) with water transfer rates significantly faster than those without PVA sponge. In addition, the elastic PVA sponge component enhanced the mechanical properties of ZHSE, allowing it to easily fabricate 3D structures to obtain higher evaporation rates. Moreover, PVA sponge barely weakened the AP effect of poly(sulfobetaine methacrylate) (PSBMA) hydrogels in the ZHSE. Consequently, the evaporation rate of ZHSE reached 4.66 kg m-2 h-1 at 3.5 wt%, one of the highest among previous reports, attributed to the contributions from the 3D structural design of the evaporator and AP effect of ZHs. Meanwhile, ZHSE showed outstanding anti-fouling properties and excellent shape stability, working in 20 wt% brine ten hours a day for ten consecutive days without noticeable salt deposition and volume shrinkage. This work provides a new route to design high-performance hydrogel-based evaporators with high water transfer rates.

Construction of a Soft Antifouling PAA/PSBMA Hydrogel Coating with High Toughness and Low Swelling through the Dynamic Coordination Bonding Provided by Al(OH)3 Nanoparticles.

Marine biofouling, resulting from the adhesion of marine organisms to ship surfaces, has long been a significant issue in the maritime industry. In this paper, we focused on utilizing soft and hydrophilic hydrogels as a potential approach for antifouling (AF) coatings. Acrylic acid (AA) with a polyelectrolyte effect and N-(3-sulfopropyl)-N-(methacryloxyethyl)-N,N-dimethylammonium betaine (SBMA) with an antipolyelectrolyte effect were selected as monomers. By adjusting the monomer ratio, we were able to create hydrogel coatings that exhibited low swelling ratio in both fresh water and seawater. The Al(OH)3 nanoparticle, as a physical cross-linker, provided better mechanical properties (higher tensile strength and larger elongation at break) than the chemical cross-linker through the dynamic coordination bonds and plentiful hydrogen bonds. Additionally, we incorporated trehalose into the hydrogel, enabling the repair of the hydrogel network through covalent-like hydrogen bonding. The zwitterion compound SBMA endowed the hydrogel with excellent AF performance. It was found that the highest SBMA content did not lead to the best antibacterial performance, as bacterial adhesion quantity was also influenced by the charge of the hydrogel. The hydrogel with appropriate SBMA content being close to electrical neutrality exhibits the strongest zwitterionic property of PSBMA chains, resulting in the best antibacterial adhesion performance. Furthermore, the pronounced hydrophilicity of SBMA enhanced the lubrication of the hydrogel surface, thereby reducing the friction resistance when applied to the hull surface during ship navigation.

Anti‐Polyelectrolyte Effect of Zwitterionic Hydrogel Electrolytes Enabling High‐Voltage Zinc‐Ion Hybrid Capacitors

AbstractTo date, the exploration of zwitterionic application is confined to the function of electrolyte's additives to improve the properties of the electrolytes. However, reports on the unique properties of zwitterions, namely the anti‐polyelectrolyte effect (APE), as the regulators of the electrochemical stability windows (ESWs) of the zwitterionic electrolytes are scarce. Herein, a zwitterionic electrolyte system is designed and study the relationship between the APE and the ESWs of the zwitterionic electrolytes. The hydrogen/oxygen evolution in the zwitterionic electrolytes is significantly inhibited under the action of the APE. On this basis, the ESWs of zwitterionic electrolytes can be expanded, ultimately achieving an effective improvement in the energy density of zinc‐ion hybrid capacitors (ZHCs). The sulfonic‐based zwitterionic hydrogel electrolytes prepared based on this strategy achieve a wide ESW of 2.58 V and high ionic conductivity of 29.3 mS cm−1. Meanwhile, the corresponding ZHCs possess a high working voltage of 2.1 V (1.6 V for the traditional ZHCs), a high capacity of 188.9 mAh g−1 and a high energy density of 110 Wh kg−1. The way utilizing the APE of zwitterions to expand the ESWs opens up a new avenue to improve the energy density of energy storage devices.

Poly(amidoxime)/polyzwitterionic semi-interpenetrating network hydrogel with robust salt-shrinkage resistance for enhanced uranium extraction from seawater

Effective uranium extraction from seawater can contribute greatly for meeting the needs of low carbon energy. Extensive studies have been conducted on polyamidoxime-based (PAO-based) adsorbents for their exceptional uranium adsorption capabilities. However, the salt-shrinkage effect severely hinders the extraction of uranium from seawater using traditional PAO-based adsorbents. This study synthesizes a novel semi-interpenetrating polymer network hydrogel, designated as PAO/PMPC-SH, using a free-radical polymerization approach utilizing PAO and zwitterionic poly (2-methacryloyloxyethyl phosphorylcholine) (PMPC). The incorporation of the PMPC component endows the adsorbent with exceptional resistance to salt shrinkage owing to the antipolyelectrolyte effect. This characteristic facilitates the diffusion of uranyl ions within PAO/PMPC-SH, even in a high-salt environment with a salt concentration as high as 25 wt%, thereby exposing the uranium binding sites in the adsorbent. Moreover, PAO/PMPC-SH exhibits exceptional antibacterial activity. After 28 days of test in natural seawater, PAO/PMPC-SH demonstrates a high uranium extraction capacity of 6.26 mg g−1, representing only a 9.14 % decrease compared with the capacity of adsorbing in marine microorganism-removed natural seawater. Overall, the notable performance of PAO/PMPC-SH in uranium extraction highlights its potential as a highly effective adsorbent for uranium extraction from seawater.

A high-temperature resistant and high-density polymeric saturated brine-based drilling fluid

Three high-temperature resistant polymeric additives for water-based drilling fluids are designed and developed: weakly cross-linked zwitterionic polymer fluid loss reducer (WCZ), flexible polymer microsphere nano-plugging agent (FPM) and comb-structure polymeric lubricant (CSP). A high-temperature resistant and high-density polymeric saturated brine-based drilling fluid was developed for deep drilling. The WCZ has a good anti-polyelectrolyte effect and exhibits the API fluid loss less than 8 mL after aging in saturated salt environment at 200 °C. The FPM can reduce the fluid loss by improving the quality of the mud cake and has a good plugging effect on nano-scale pores/fractures. The CSP, with a weight average molecular weight of 4804, has multiple polar adsorption sites and exhibits excellent lubricating performance under high temperature and high salt conditions. The developed drilling fluid system with a density of 2.0 g/cm3 has good rheological properties. It shows a fluid loss less than 15 mL at 200 °C and high pressure, a sedimentation factor (SF) smaller than 0.52 after standing at high temperature for 5 d, and a rolling recovery of hydratable drill cuttings similar to oil-based drilling fluid. Besides, it has good plugging and lubricating performance.

Amphoteric nano‐ and microgels with acrylamide backbone for potential application in oil recovery

AbstractAmphoteric nano‐ and microgels based on acrylamide (AAm), 3‐acrylamidopropyltrimethylammonium chloride (APTAC) and 2‐acrylamido‐2‐propanesulfonate sodium salt (AMPS) were prepared via inverse emulsion polymerization in the presence of crosslinking agent—N,N′‐methylenebisacrylamide (MBAA). Several polyampholyte nano‐ and microgel samples AAm‐APTAC‐AMPS with compositions (70:15:15, 80:10:10, and 90:5:5 mol%) were obtained and they were abbreviated as AAm70‐APTAC15‐AMPS15, AAm80‐APTAC10‐AMPS10 AAm90‐APTAC5‐AMPS5 (where the lower indexes indicate the molar concentration of monomers). The nano‐ and microgels were characterized by Fourier‐transform infrared spectroscopy, dynamic light scattering (DLS), transmission electron microscope (TEM), thermogravimetric analysis and interfacial tension measurements. The most attention was paid to the AAm80‐APTAC10‐AMPS10 microgel because its linear analog showed the best swelling capacity and the viscosifying effect for potential application in oil recovery. The influence of monomer concentration, surfactants, volume ratio of the water/organic phases, and the hydrophilic–lyophilic balance (HLB) on the average hydrodynamic size of the AAm80‐APTAC10‐AMPS10 nano‐ and microgels was studied. The size distribution of nano‐ and microgels derived from DLS data and TEM images was compared as a function of monomer concentration at constant surfactant concentration (6 wt%), HLB = 5.5 and mixture of water:oil = 60:40 vol%. Swelling of microgel particles in saline water due to the antipolyelectrolyte effect was observed. The applicability of amphoteric microgels AAm80‐APTAC10‐AMPS10 for oil recovery was tested on cores simulating the conditions of a model oil reservoir. The obtained results indicated that after the injection of around three pore volumes of the 2500 ppm microgel suspension into the sandstone core the permeability to brine decreased from 1.5 to 0.78 mD. For the first half of core sample the residual resistance factor was higher than the resistance factor, whereas for the second part of core sample these parameters were almost equal. Additional experiments with longer cores are needed to evaluate in‐depth propagation of microgels and permeability reduction in porous media.

Unveiling the Layered Structure of Sulfobetaine Polymer Brushes through Bimodal Atomic Force Microscopy

Many zwitterionic polymer brushes exhibit highly stimuli-responsive properties stemming from the strong dipole and electrostatic interaction of their building blocks. Here, we showed how a combination of two atomic force microscopy (AFM) modes can reveal the layered structure of poly(sulfobetaine methacrylate) brushes synthesized by surface-initiated atom-transfer radical polymerization. Due to polydispersity and anti-polyelectrolyte effect, a diffused layer emerges on top of a condensed layer of the brush as a function of salt concentration. The amplitude-modulation mode of the AFM, owing to the tip’s dynamic motion, can only probe the more stable condensed layer near the substrate, whereas the force-spectroscopic mode with its high sensitivity can accurately detect the diffused layer and hence determine the total brush thickness. Infrared spectroscopy and quartz crystal microbalance monitoring revealed the strong ion-screening effect and higher brush hydration propensity of multivalent ions. Different cation valencies also showed subtle effects on the dimensionality of the layered structure. Our results highlight the usefulness of AFM in revealing various contextual phenomena that arise from the unique properties of zwitterionic polymers.

Anti-polyelectrolyte and polyelectrolyte effects on conformations of polyzwitterionic chains in dilute aqueous solutions.

Polyzwitterions (PZs) are considered as model synthetic analogs of intrinsically disordered proteins. Based on this analogy, PZs in dilute aqueous solutions are expected to attain either globular (i.e. molten, compact) or random coil conformations. Addition of salt is expected to open these conformations. To the best of our knowledge, these hypotheses about conformations of PZs have never been verified. In this study, we test these hypotheses by studying effects of added salt [potassium bromide (KBr)] on gyration and hydrodynamic radii of poly(sulfobetaine methacrylate) in dilute aqueous solutions using dynamic light scattering and small-angle X-ray scattering, respectively. Effects of zwitteration are revealed by direct comparisons of the PZs with the polymers of the same backbone but containing (1) no explicit charges on side groups such as poly(2-dimethylaminoethyl methacrylate)s and (2) explicit cationic side groups with tertiary amino bromide pendants. Zeta-potential measurements, transmission electron microscopy, and ab initio molecular dynamics simulations reveal that the PZs acquire net positive charge in near salt-free conditions due to protonation but retain coiled conformations. Added KBr leads to nonmonotonic changes exhibiting an increase followed by a decrease in radius of gyration (and hydrodynamic radius), which are called antipolyelectrolyte and polyelectrolyte effects, respectively. Charge regulation and screening of charge-charge interactions are discussed in relation to the antipolyelectrolyte and polyelectrolyte effects, respectively, which highlight the importance of salt in affecting net charge and conformations of PZs.

Salt-Added Solutions of Markov Polyampholytes: Diagram of States, Antipolyelectrolyte Effect, and Self-Coacervate Dynamics

Field-theoretic and scaling approaches are combined to predict conformational behaviors of single-chain globally neutral polyampholytes (PAs) in the presence of salt, the viscosity of their dilute solutions, and the rheology of condensed self-coacervate phases. To reveal the role of the monomer sequence, we consider PAs with Markov statistics of positive and negative charges. The diagram of globular regimes of single-chain PAs in Θ solvent is constructed with the coordinates of the charge blockiness and salt concentrations. For highly flexible chains, it contains six scaling regimes corresponding to low/high salt concentrations and (i) almost alternating, (ii) random correlated, and (iii) highly blocky sequences of ionic monomers. At increasing salt concentration, PAs of any sequence swell until reaching an ideal-coil size. The amplitude of the salt-induced globule-to-coil transition increases with increasing charge blockiness. So does the change in the viscosity of dilute PA solutions, indicating the sequence specificity in the antipolyelectrolyte effect. The similarity between the internal structure of the globules and macroscopic self-coacervate phases enables prediction of the viscosity of the latter. The respective scaling dependencies for self-coacervates of short unentangled and long entangled PAs are provided. Self-coacervate viscosity is the highest for the most blocky PAs and, for any sequence, decreases with the addition of salt. Our findings serve as important guidelines for understanding the dynamics of intracellular condensates, which form from polyampholytic disordered proteins/regions and exhibit the salt-induced viscosity drop described herein.

Phase‐Separated Polyzwitterionic Hydrogels with Tunable Sponge‐Like Structures for Stable Solar Steam Generation (Adv. Funct. Mater. 18/2023)

Phase-Separated Polyzwitterionic Hydrogels In article number 2214045, Lianbin Zhang and co-workers construct a polyzwitterionic hydrogel evaporator with tunable sponge-like structures by a phase separation strategy for stable solar steam generation. Owing to the anti-polyelectrolyte effects and the highly interconnected pore structure, the evaporator enables adequate seawater uptake and transport to ensure a fast and stable water evaporation process.

Titanium surface-grafted zwitterionic polymers with an anti-polyelectrolyte effect enhances osteogenesis

Zwitterionic polymers have attracted considerable attention because of their anti-adsorption and unique anti-polyelectrolyte effects and was widely used in surface modification. In this study, zwitterionic copolymers (poly (sulfobetaine methacrylate-co-butyl acrylate) (pSB) coating on the surface of a hydroxylated titanium sheet using surface-initiated atom transfer radical polymerization (SI-ATRP) was successfully constructed. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and Water contact angle (WCA) analysis proved the successful preparation of the coating. The swelling effect caused by the anti-polyelectrolyte effect was reflected in the simulation experiment in vitro, and this coating can promote the proliferation and osteogenesis of MC3T3-E1. Therefore, this study provides a new strategy for designing multifunctional biomaterials for implant surface modifications.

Ion-Specific Antipolyelectrolyte Effect on the Swelling Behavior of Polyzwitterionic Layers

In this study, we systematically investigate the interactions between mobile ions generated from added salts and immobile charges within a sulfobetaine-based polyzwitterionic film in the presence of five salts (KCl, KBr, KSCN, LiCl, and CsCl). The sulfobetaine groups contain quaternary alkylammonium and sulfonate groups, giving the positive and negative charges. The swelling of the zwitterionic film in the presence of different salts is compared with the swelling behavior of a polycationic or polyanionic film containing the same charged groups. For such a comparative study, we design cross-linked terpolymer films with similar thicknesses, cross-link densities, and charge fractions, but with varying charged moieties. While the addition of salt in general leads to a collapse of both cationic and anionic films, the presence of specific types of mobile anions (Cl-, Br-, and SCN-) considerably influences the swelling behavior of polycationic films. We attribute this observation to a different degree of ion-pair formations between the different types of anionic counterions and the immobile cationic quaternary alkylammonium groups in the films where highly polarizable counterions such as SCN- lead to a high degree of ion pairing and less polarizable counterions, such as Cl-, cause a low degree of ion pairing. Conversely, we do not observe any substantial effect of varying the type of cationic counterions (K+, Li+, and Cs+), which we assign to the lack of ion pairing between the weakly polarizable cations and the immobile anionic sulfonate groups in the films. In addition, we observe that the zwitterionic films swell with increasing ionic strength and the degree of swelling is anion dependent, which is in agreement with previous reports on the "antipolyelectrolyte effect". Herein, we explain this ion-specific swelling behavior with the different cation and anion abilities to form ion pairs with quaternary alkylammonium and sulfonate in the sulfobetaine groups.

Structures, properties, and applications of zwitterionic polymers

Zwitterionic polymers have attracted research attention in recent years owing to their unique molecular structures. In the same repeat unit, positive and negative charges are simultaneously located on a pair of cationic and anionic groups; therefore, zwitterionic polymers have a large dipole moment and numerous charged groups. Although the molecular chain of the zwitterionic polymer can be maintained in an electrically neutral state overall, the coexistence of the oppositely charged groups confers extremely high polarity and excellent hydrophilicity to the polymer. At the same time, the electricality of the polymer can be further regulated by the environmental pH and salt ions, which greatly broadens the scope of applications in different fields. This review introduces various structures of zwitterionic polymers and analyzes the reasons why zwitterionic polymers exhibit pH responsiveness, anti-polyelectrolyte effects, and superior electrical conductivity. The application fields are also summarized by generalizing the research status of zwitterionic polymers, including applications in antifouling coatings, drug delivery, wastewater treatment, and sensors, etc.