电场敏感的智能性水凝胶*

电场敏感水凝胶是一类在电刺激下可以溶胀、收缩或弯曲的智能性水凝胶,其主要特点是可以将电能转化为机械能。本文对近年来已见报道的电场敏感水凝胶的研究进行了较为详细的综述。同时,对电场敏感水凝胶的响应机理、影响水凝胶响应性的因素以及其在能量转换装置、人工肌肉等方面的应用也作了相应的介绍。     

Modeling and simulation of chemo-electro-mechanical behavior of pH-electric-sensitive hydrogel

A chemo-electro-mechanical multi-field model, termed the multi-effect-coupling pH-electric-stimuli (MECpHe) model, has been developed to simulate the response behavior of smart hydrogels subject to pH and electric voltage coupled stimuli when the hydrogels are immersed in a pH buffer solution subject to an externally applied electric field. The MECpHe model developed considers multiphysics effects and formulates the fixed charge density with the coupled buffer solution pH and electric voltage effects, expressed by a set of nonlinear partial differential governing equations. The model can be used to predict the hydrogel displacement and the distributive profiles of the concentrations of diffusive ionic species and the electric potential and the fixed charge density in both the hydrogels and surrounding solution. After validation of the model by comparison of current numerical results with experiment data extracted from the literature, one-dimensional steady-state simulations were carried out for equilibrium of the smart hydrogels subject to pH and electric coupled stimuli. The effects of several important physical conditions, including the externally applied electric voltage, on the distributions of the concentrations of diffusive ionic species, the electric potential, the fixed charge density, and the displacement of the hydrogel strip were studied in detail. The effects of the ionic strength on the bending deformation of the hydrogels under the solution pH and electric voltage coupled stimuli are also discussed.     

聚乙烯醇硫酸钾水凝胶电机械化学行为研究

通过将交联聚乙烯醇硫酸酯化的方法制备了一种新型电刺激响应性聚乙烯醇硫酸钾(PVSK)智能水凝胶,并探讨了溶液离子强度和pH对PVSK水凝胶的溶胀吸水率、机械性能以及电机械化学行为的影响.结果表明,制备的PVSK水凝胶的平衡溶胀比随NaCl溶液离子强度的增大而减小,在pH2.39～10.83范围内基本不受溶液pH的影响;经不同离子强度和pH的NaCl溶液充分溶胀的PVSK水凝胶具有良好的机械性能,在非接触的直流电场作用下,该水凝胶向电场负极弯曲,凝胶的弯曲速度和弯曲偏转量随外加电场强度的增加而增大,随NaCl溶液离子强度的增大出现临界最大值,但不随溶液pH(2.08～10.53)的改变而改变;在循环电场作用下,PVSK水凝胶的电机械化学行为具有良好的可逆性.     

PVA/PAA水凝胶纤维的电刺激响应性能

以过硫酸胺为引发剂,在PVA水溶液中原位聚合丙烯酸单体,得到的PVA／PAA混合水溶液在凝固浴硫酸胺饱和水溶液中纺丝制备了物理缠结和氢固定网络形式的PVA／PAA水凝胶纤维。该纤维于NaCl溶液中在直流电场作用下具有电流－刺激敏感性,表现为溶胀、收缩、弯曲行为。纤维的弯曲速度和最大弯曲度随电场强度和凝胶网络中PAA含量的增加而增大,随电解质溶液离子强度的变化出现临界最大值。纤维向负极弯曲的过程中,在电场下自由离子和反庆子迁移引起的渗透压主导作用,弯曲过程主要是溶胀弯曲;向正极弯曲过程中,由于电化学反应和电场作用下产生的PH梯度导致凝胶网络构像变化主导作用,弯曲主要是收缩弯曲;弯曲由负极向正极转化过程中,两种机理对弯曲的影响相对平衡。     

Electroresponsive Behavior of Sodium Alginate-g-Poly (acrylic acid) Hydrogel Under DC Electric Field

A novel sodium alginate-graft-poly(acrylic acid) (SA-g-PAA) hydrogel was prepared by radical graft copolymerization with ammonium persulfate (APS) as initiator and N,N′-methylene-bis-(acrylamide) (MBAA) as crosslinker, and its swelling properties and electroresponsive behavior in aqueous NaCl solutions were studied. The results indicated that the water take-up ability of the hydrogel decreased with the increasing ionic strength of aqueous NaCl solution. The hydrogel swollen in a NaCl solution bent toward the cathode under non-contact dc electric fields, and its bending speed and equilibrium strain increased with the increasing of applied voltage. With the increasing of ionic strength of aqueous NaCl solution, the equilibrium strain of the hydrogel increased first and then decreased gradually. The maximum equilibrium strain occurs when the ionic strength of aqueous NaCl solution is 0.03. By changing the direction of the applied potential cyclically, the hydrogel exhibited good reversible bending behavior.     

Multiphysical modeling and meshless simulation of electric‐sensitive hydrogels

According to a multiphase mixture theory, we have mathematically developed a multiphysical model with chemoelectromechanical coupling considerations, termed the multieffect‐coupling electric‐stimulus (MECe) model, to simulate the responsive behavior of electric‐sensitive hydrogels immersed in a bath solution under an externally applied electric field. For solutions of the MECe model consisting of coupled nonlinear partial differential governing equations, a meshless Hermite–Cloud method with a hierarchical iteration technique has been used for a one‐dimensional steady‐state analysis of a hydrogel strip. The computed results are compared with the experimental data, and there is very good agreement. Simulations within the domains of both hydrogels and surrounding solutions also present distributions of the ionic concentrations and electric potential as well as the hydrogel displacement. The effects of various physical parameters on the response behavior of electric‐stimulus responsive hydrogels are discussed in detail. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1514–1531, 2004     

明胶水凝胶电刺激响应行为的研究

制备了戊二醛交联的明胶水凝胶 ,并研究了其吸水率、力学性能和电刺激响应行为 .结果表明 ,在NaCl溶液中 ,明胶水凝胶的平衡溶胀比随NaCl溶液的浓度增大而减小 ,经 0 0 1mol LNaCl溶液充分溶胀的明胶水凝胶膜其弹性模量为 4.2 9kPa ,抗张强度为 5 11kPa ,断裂伸长率为 110 %.在NaCl溶液中于非接触的直流电场作用下 ,明胶水凝胶向电场负极弯曲 ,凝胶的弯曲速度和弯曲偏转程度随外加电场的增大而增大 ,随NaCl溶液离子强度的增大出现临界最大值 .在周期性电场作用下 ,其弯曲响应行为具有良好的可逆性 .通过聚电解质凝胶弯曲理论初步解释了其弯曲机理 .     

Electroresponsive Behavior of Sulfonated Benzal Poly(vinyl alcohol) Hydrogel Under Direct-Current Electric Field

A novel sulfonated benzal poly(vinyl alcohol) (S-B-PVA) hydrogel was prepared by sulfonating benzal poly(vinyl alcohol) hydrogel with concentrated sulfuric acid, and its swelling properties, mechanical properties, and electroresponsive behavior in Na₂SO₄ solutions were studied. The results indicated that the water take-up ability of the hydrogel decreased with the increasing ionic strength of Na₂SO₄ solution. The Young's modulus, elongation at break and tensile strength of the hydrogel swollen in deionized water is 8.38 MPa, 22.2% and 3.14 MPa, respectively. The hydrogel swollen in Na₂SO₄ solution bent toward the cathode under non-contact dc electric fields, and its bending speed and equilibrium strain increased with the increasing of applied voltage. The electroresponsive behavior of the hydrogel was also affected by the electrolyte concentration of external Na₂SO₄ solution, and there is a critical ionic strength of 0.1 at which the maximum equilibrium strain of the hydrogel occurs. Under a cyclically varying electric field, the hydrogel exhibited a good reversible bending behavior.     

Multiphysics Modeling of Electrochemomechanically Smart Microgels Responsive to Coupled pH/Electric Stimuli

A multiphysics model is developed to simulate the responsive behavior of smart pH‐/electric‐sensitive hydrogels when immersed into pH buffer solution and subjected to an externally applied electric field, which is termed the MECpHe model. Comparison with experimental data shows the MECpHe model to be accurate and stable. The influence of the externally applied electric voltage is discussed with respect to the distribution of diffusive ionic species and the displacement of the hydrogel strip. The influences of initial charge density and ionic strength on the swelling ratio and the bending deformation of the microgel strip are studied.

     

Novel transmittance change of polyelectrolyte hydrogel in DC electric field

A novel transmittance change of poly(acrylamide‐co‐acrylic acid) hydrogel in a DC electric field was observed. Transmittance of a specimen increased when the electric field was on and decreased by removing the electric force. In certain cases, the sample was able to switch from white opaque to colorless transparent. The rate and extent of the transition depended on the applied electric potential, ambient temperature, and composition of the specimen. These observations are closely related to the dissociation of hydrogen bonding in the network induced by an external electric field. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2290–2295, 2003     

Meshless simulation of equilibrium swelling/deswelling of pH‐sensitive hydrogels

Hydrogels have been widely used in microelectromechanical systems (MEMS) and Bio‐MEMS devices. In this article, the equilibrium swelling/deswelling of the pH‐stimulus cylindrical hydrogel in the microchannel is studied and simulated by the meshless method. The multi‐field coupling model, called multi‐effect‐coupling pH‐stimulus (MECpH) model, is presented and used to describe the chemical field, electric field, and the mechanical field involved in the problem. The partial differential equations (PDEs) describing these three fields are either nonlinear or coupled together. This multi‐field coupling and high nonlinear characteristics produce difficulties for the conventional numerical methods (e.g., the finite element method or the finite difference method), so an alternative—meshless method is developed to discretize the PDEs, and the efficient iteration technique is adopted to solve the nonlinear problem. The computational results for the swelling/deswelling diameter of the hydrogel under the different pH values are firstly compared with experimental results, and they have a good agreement. The influences of other parameters on the mechanical properties of the hydrogel are also investigated in detail. It is shown that the multi‐field coupling model and the developed meshless method are efficient, stable, and accurate for simulation of the properties of the stimuli‐sensitive hydrogel. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 326–337, 2006     

Ultrastretchable and conductive core/sheath hydrogel fibers with multifunctionality

Conductive hydrogels with ionic compounds possess great potential for the development of soft smart devices. A dielectric scarfskin is typically required for these devices to prevent short circuiting, leading to devices with lower stretchability than the hydrogel. Henceforth, commonly used dielectric materials, such as PDMS and Ecoflex, cannot be largely stretched. Hydrogel devices with ultrastretchability are required to accommodate hostile application environments. Herein, we propose a hydrogel fiber coated with a dielectric layer that can be stretched to over 2000% of its initial length. The fiber remains conductive when stretched to ~1300%. In addition, the core/sheath hydrogel fiber can be endowed with a variety of functional properties, such as electroluminescence (EL), photoluminescence (PL), and magnetic‐responsiveness, demonstrating scalability of the resultant fiber. The present work can pave the way for numerous next‐generation soft devices, such as smart textiles and wearable electronics. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 272–280     

Electromechanical Response and Structure of Chitosan–Polyaniline Composite Systems

Swelling chitosan–polyaniline composite systems demonstrating a pronounced electromechanical response are obtained. The formation of a crosslinked structure in chitosan allows one to enhance elasticstrain properties of composites, but this is accompanied by a decrease in the bending angle under an electric field. Polyaniline as an electroactive component improves the composite system capability of deformation induced by an electric field. The factors contributing to the deformation value are investigated.     

Characteristics of charged networks under an electric stimulus

The electrokinetic phenomena of poly(2-acrylamido-2-methyl-1-propane sulfonic acid-co-n-butylmethacrylate) were examined to investigate physical changes of the gel under an applied electric current. When an electrical stimulus was applied to a piece of the gel, without being in contact with an electrode, reversible gel bending was observed. The bending degree was directly proportional to the intensity of the applied electric stimulus. This was explained by ‘depletion polarization’ of ionic species under the stimulus. The swelling of the gel surface facing the anode increased, due to the decreased ionic strength of the boundary layer upon electric stimulation, while gel shrinking occurred at the cathode. When the gel is in direct contact with electrodes, deswelling of the gel was observed at the anode side, while water seepage occurred at the cathode side. This observation was attributed to the electro-osmosis inside the gel, combined with local pH changes around the electrodes resulting from electrochemical reactions, particularly water electrolysis. © 1994 John Wiley & Sons, Inc.     

Bending of polyelectrolyte membrane platinum composites by electric stimuli: Part II. Response kinetics

In previous papers, it was reported that a solid polymer electrolyte membrane-platinum (SPM-Pt) composite bent in response to electric stimuli. In this paper, a model, in which electric fields can induce mechanical deformation in the SPM via electrokinetically induced pressure gradients, was applied to the kinetics of the bending response. In order to compare the theoretical model with the experimental result, simultaneous measurement was carried out with the displacement and the electrochemical properties for the composites prepared from membranes of different thickness in various kinds of salt solution. The curvature response was simulated by the empirical equations having one characteristic time. The characteristic time was linearly proportional to the square of the thickness of the membrane. The parameter which means curvature per unit charge was linearly proportional to the reciprocal of the square of the membrane thickness, and the water transference coefficient of the membrane of various ionic forms. The results support the theoretical model. In addition to the electrokinetic effect, the model includes the effect of the interfacial stress between the Pt electrode and the SPM. The bending behavior after the characteristic time can be explained successfully by the model including the interfacial effect.     

Polyrotaxane derivatives. II. Preparation and characterization of ionic polyrotaxanes and ionic slide‐ring gels

Four types of ionic polyrotaxane (PR) derivatives, that is, carboxymethylated, sulfoethylated, diethylaminoethylated, and trimethylammoniohydroxypropylated PRs, were successfully prepared starting from the same PR consisting of poly(ethylene glycol) as an axis and α‐cyclodextrins as ring molecules. The structures of the ionic PR derivatives were analyzed by ¹H and ¹³C nuclear magnetic resonance (NMR), attenuated‐total reflection Fourier transform‐infrared, and colloidal titration. Degrees of substitution of the ionic PRs were calculated from results of ¹H NMR and colloidal titrations; both sets of results satisfactorily agreed. Cross‐linking of sulfoethylated and quaternized PRs yielded ionic slide‐ring gels carrying sulfoethyl and quaternary ammonium groups on the mobile cross‐links, respectively. The former gel showed intriguing phenomena, including a large degree of swelling of up to 1147, drastic change in its swelling ratio by the presence of electrolyte and bending under a moderate applied electric field (7 V/cm). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Stretchable and transparent hydrogels as soft conductors for dielectric elastomer actuators

A soft ionic conductor can serve as an artificial nerve in an artificial muscle. A polyacrylamide hydrogel is synthesized containing a hygroscopic salt, lithium chloride. Two layers of the hydrogel are used as ionic conductors to sandwich a dielectric elastomer and fabricate a highly stretchable and transparent actuator. When the two layers of the hydrogels are subject to a voltage, the actuator reduces its thickness and expands. An areal strain of 134% is demonstrated. The voltage‐strain curves are calculated by using a model that accounts for the elastic constraint of the hydrogel and the inhomogeneous deformation of the actuator. For actuators fabricated with the hydrogel of various thicknesses and with the dielectric elastomer of various prestretches, excellent agreements are found between experimental data and theoretical predictions. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1055–1060     

Synthesis of poly(ethylene glycol)‐based hydrogels and their swelling/shrinking response to molecular recognition

To synthesize the novel molecular‐ and pH‐stimulus‐responsive hydrogel, we prepared poly(ethylene glycol)‐based hydrogel containing ionic groups. We evaluated the fundamental swelling/shrinking properties of the hydrogels synthesized by various conditions. Decreasing the molecular weight of a crosslinker provided the increasing of the equilibrium swelling ratio. Also, the equilibrium swelling ratio was changed by the introduction of functional ionic monomers and its compositions. Furthermore, the swelling/shrinking behaviors of the hydrogels were affected by the environmental condition of aqueous solution, in fact the hydrogels were considerably shrunk (to one‐fifth volume) using a di‐ionic solute in the aqueous solution through the ionic interactions between the hydrogel and the solutes. Additionally, the specific shrinking to diamine compounds was also observed in response to pH change. These results clearly show the swelling/shrinking responsibility of the hydrogels toward the molecular recognitions and its pH conditions. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3153–3158     

DNA hydrogels formed of bended DNA scaffolds and properties study

In recent years,DNA supramolecular hydrogels have attracted much attention due to their injectability,biocompatibility,responsiveness and self-healing properties.In this work,we designed a linear DNA brick containing one duplex with two cytosine (C)-rich sequence on both ends.This brick can first assemble to form duplex under pH 8 condition.After adjusting the pH to 5,the C-rich sequence tends to form intermolecular i-motif structure,which joins the linear DNA molecules together to form interlocked cyclic structures and yield the DNA hydrogel.By adjusting the length and bending curvature of the duplex part of the molecule,one can change the basic unit of the hydrogel structure to tune the properties of the DNA hydrogel.     

The Research of Biomedical Intelligent Polymer Materials

The properties of biomedical intelligent polymer materials can be changed obviously when there is a little physical or chemical change caused by external condition. They are in the forms of solids, solutions and the polymers on the surface of carrier, and include water solution of hydrophilic polymers, cross-linking hydrophilic polymers(i.e. hydrogels) and the polymers on the surface of carrier. The environmental stimulating factors are temperature, pH value, composition of solution, ionic intention, light intention, electric field, stress field and magnetic field etc.. The properties of intelligent polymer are those of phase, photics, mechanics, electric field, surface energy,reaction ratio, penetrating ratio and recognition etc..Stimulation-response of intelligent water-soluble polymerWater-soluble intelligent polymer can be separated out from solution under special external condition. It can be used as the switch of temperature or pH indicator. When water-soluble intelligent polymer is mixed with soluble-enzyme matter or cell suspension, the polymer can bring phase separation and react with soluble-enzyme matter or cell membrane through accepting some external stimulation. Other water-soluble intelligent polymer is that can make the main chemical group of some natural biomolecular recognition sequence section to arrange on skeleton of polymer at random. It is the same ratio as natural biomolecules.Stimulation-response of intelligent polymer of carrier surface Intelligent polymer can be fixed on the surface of solid polymer carrier through chemical grafting or physical adsorption. When the external conditions are changed, the thickness, humidity and electric field of the surface layer will be changed. Intelligent polymer can be preparated the permanence switch by precipitating into the hole of porous surface, and it can control on-off state of the hole. When protein or cell interacts with intelligent polymer surface to be placed in to open or close, they can be selectively absorbed on hydrophobic surface.Stimulation-response of intelligent polymer hydrogelIntelligent polymer hydrogel's construction, physical property, and chemical property can change with the changing of external environmental conditions. When environmental stimulation signal, for example, solution composition, pH value, ionic intention, temperature, light intention, electric field,magnetic field and substance etc. changes, the intelligent polymer will occur to break of volume.This is the intelligence of polymer hydrogel.The intelligence of these polymers will be widely applied in biomedical fields.