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.     

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.     

Ultrafine hydrogel fibers with dual temperature‐ and pH‐responsive swelling behaviors

Ultrafine hydrogel fibers that were responsive to both temperature and pH signals were prepared through the electrospinning of poly(N‐isopropylacrylamide) (PNIPAAm) and poly(acrylic acid) mixtures in dimethylformamide. Both the diameters (700 nm to 1.2 μm) and packing of the fibers could be controlled through changes in the polymer compositions and PNIPAAm molecular weights. These fibers were rendered water‐insoluble by the addition of either Na₂HPO₄ or poly(vinyl alcohol) (PVA) to the solution, followed by the heat curing of the fibers. The fibers crosslinked with Na₂HPO₄ swelled to 30–120 times in water; this was significantly higher than the swelling of those crosslinked with PVA. The PVA‐crosslinked hydrogel fibers, however, exhibited faster swelling kinetics; that is, they reached equilibrium swelling in less than 5 min at 25 °C. They were also more stable after 1 week of water exposure; that is, they lost less mass and retained their fibrous form better. All the hydrogel fibers showed a drastic increase in the swelling between pH 4 and 5. The PVA‐crosslinked hydrogel fibers exhibited distinct temperature‐responsive phase‐transition behavior of PNIPAAm, whereas the Na₂HPO₄‐crosslinked hydrogel fibers showed altered two‐stage phase transitions that reflected side‐chain modification of PNIPAAm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6331–6339, 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 .     

A Self‐Healing Integrated All‐in‐One Zinc‐Ion Battery

The self‐healing of zinc‐ion batteries (ZIBs) will not only significantly improve the durability and extend the lifetime of devices, but also decrease electronic waste and economic cost. A poly(vinyl alcohol)/zinc trifluoromethanesulfonate (PVA/Zn(CF₃SO₃)₂) hydrogel electrolyte was fabricated by a facile freeze/thaw strategy. PVA/Zn(CF₃SO₃)₂ hydrogels possess excellent ionic conductivity and stable electrochemical performance. Such hydrogel electrolytes can autonomously self‐heal by hydrogen bonding without any external stimulus. All‐in‐one integrated ZIBs can be assembled by incorporating the cathode, separator, and anode into hydrogel matrix since the fabrication of PVA/Zn(CF₃SO₃)₂ hydrogel is a process of converting the liquid to quasi‐solid state. The ZIBs show an outstanding self‐healing and can recover electrochemical performance completely even after several cutting/healing cycles.     

Anti-Hofmeister series properties found for a polymer having a π electron system and acidic protons

Anti-Hofmeister series properties have been found for a polymer (PVA-T) having a π electron system and acidic protons, which were prepared by introducing trimellitic anhydride to poly(vinyl alcohol) (PVA). Aqueous dispersion of PVA-T became clear in the presence of 1 M Na₂SO₄, a typical kosmotrope, due to dissolution of the solid polymer sample, while the turbidity in the presence of 1 M KSCN, a typical chaotrope, hardly changed. Being consistent to the salt effects, PVA-T hydrogel, which was prepared by chemical cross-linking, showed marked swelling in sulfate solutions, whereas the swelling degree was only marginal in thiocyanates.     

Poly(styrene sulfonic acid)–poly(vinylidene fluoride) interpolymer ion-exchange membranes. II. Ultrafiltration properties

Highly porous interpolymer ion-exchange membranes of poly(styrene sulfonic acid) and poly(vinylidene fluoride) have been investigated under pressure filtration with KCI, Na₂SO₄, erythrosin, and bovine serum albumin as solutes in the feed solution. The rejection of the ionic solutes is governed by a Donnan exclusion of electrolyte from the membrane phase. A model for the transport behavior is proposed that includes both diffusive and convective salt transport. The calculated rejections agree adequately with the observed data.     

高选择性透过二氧化硫气体分离膜的研究 （Ⅳ）不同烃基乙烯基亚砜接枝聚乙烯醇膜的透过性能

研究了不同烃基乙烯基亚砜接技聚乙烯醇（ＰＶＡ－ＲＶＳＯ，Ｒ＝Ｍｅ，Ｅｔ，ｔ－Ｂｕ，Ｐｈ）膜对纯ＳＯ２、Ｎ２的透过性能以及ＳＯ２／Ｎ２混合气体的分离性能，结果表明上述膜对ＳＯ２具有高的选择性，对不同烃基乙烯基亚砜接枝膜进行了比较。     

大孔PAMPS/PVA半互穿网络型水凝胶的制备及其性能研究

以PEG6000为成孔剂, 合成了大孔聚(2-丙烯酰胺-2-甲基丙磺酸)/聚乙烯醇半互穿网络型(s-IPN)水凝胶. 红外分析表明, PVA与PAMPS之间形成了较强的氢键, 使得PVA分子上的C—O伸缩振动吸收峰移向了低波数处. X射线衍射分析发现, 当PVA用量较高时, 由于部分的PVA结晶, 使得凝胶的半互穿网络结构不均匀. 电镜分析结果表明, 没有使用成孔剂的凝胶表面成褶皱形, 不存在任何孔洞结构; 而以PEG6000为成孔剂的凝胶表面存在相互贯穿的大孔结构. 研究了该水凝胶的溶胀性能, 结果表明, 该水凝胶的平衡溶胀度在116至320之间; 而成孔剂PEG6000的加入能较大幅度提高凝胶的溶胀速率, 凝胶在240 min之内就能达到溶胀平衡. 对凝胶抗压缩性能的研究表明, 当PVA用量为9.1% (w)时, 凝胶的抗压缩强度最大, 可达12.0 MPa; 而成孔剂的加入会在一定程度削弱凝胶的抗压缩强度. 该凝胶具有较好的电场敏感性, 研究发现, 将吸去离子水达到溶胀平衡的凝胶放入施加有电场的0.2 mol•L－1 NaCl溶液中时, 凝胶迅速偏向阳极. 而PVA和成孔剂PGE6000的用量均对凝胶的偏转速度以及最大偏转角存在较大的影响.     

Swelling behavior of a blend hydrogel made of poly(allylguanidino-co-allylamine) and poly(vinyl alcohol)

A hydrogel was prepared by mixing poly(allylguanidino-co-allylamine) hydrochloride (PAG) with poly(vinyl alcohol) (PVA) and repeatedly freezing and thawing the blend. The swelling behavior of the hydrogel was investigated as a function of the pH and ionic strength of the medium. In a salt-free aqueous medium, a size of the hydrogel was reduced below pH 3 and above pH 10, but the size was little affected in the pH range 3 ≈ 10. In a medium of constant ionic strength (μ = 0.1), the hydrogel's pH response was different: it was significantly reduced in size above pH 9, but the size was affected only moderately below pH 9. When the ionic strength of medium was varied at a fixed pH, the size change of the hydrogel was gradual. All these phenomena could be understood by observing that PAG displayed multiple protonation states due to pH and that the electrostatic interactions among the charges on the polymer backbone are shielded by the added electrolyte as the ionic strength of the medium is raised.     

The dynamical response of a hydrogel fiber to electrochemical stimulation

The preparation of a smart hydrogel fiber based on chitosan/poly(ethylene glycol) is presented. The dynamics of this hydrogel fiber in response to electric stimulation is reported. The effects of a number of factors have been systematically studied, including the fiber diameter, concentration of the crosslinking agent, electric potential imposed across the fiber, pH, and ionic strength of the bath solution. Fiber deformation is expressed in terms of the curvature at the midlength of the fiber for various times. The number of bending to a given extent within a given time period is used to describe the rate of cyclic deformation. Our experimental results show a stable reversibility of bending behavior under the applied electric field. The bending curvature is proportional to the intensity of the applied electric potential. Although adequate mechanical properties are maintained, the rate of deformation can be improved via the adjustment of a number of the aforementioned extrinsic factors. These observations are interpreted in terms of fiber stiffness, fixed charge density, and swelling pressure, which depend on the hydrogel equilibrium states in different pH and ionic environments along with the electrochemical reactions under the electric field. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 236–246, 2001     

Modification and characterization of semi-crystalline poly(vinyl alcohol) with interpenetrating poly(acrylic acid) by UV radiation method for alkaline solid polymer electrolytes membrane

Semi-crystalline poly(vinyl alcohol) was modified by UV radiation with acrylic acid monomer to get interpenetrating poly(acrylic acid) modified poly(vinyl alcohol), PVAAA, membrane. The stability of various PVAAA membranes in water, 2 M CH₃OH, 2 M H₂SO₄, and 40 wt% KOH aqueous media were evaluated. It was found that the stability of PVAAA membrane is stable in 40 wt% KOH solution. The PVAAA membranes were characterized by differential scanning calorimetry, X-ray diffraction, and thermogravimetry analysis. These results show that (1) the crystallinity in PVAAA decreased with increasing the content of poly(acrylic acid) in the PVAAA membranes. (2) The melting point of the PVAAA membrane is reduced with increasing the content of poly(acrylic acid) in the membrane. (3) Three stages of thermal degradation were found for pure PVA. Compared to pure PVA, the temperature of thermal degradation increased for the PVAAA membrane. The various PVAAA membranes were immersed in KOH solution to form polymer electrolyte membranes, PVAAA-KOH, and their performances for alkaline solid polymer electrolyte were conducted. At room temperature, the ionic conductivity increased from 0.044 to 0.312 S/cm. The result was due to the formation of interpenetrating polymer chain of poly(acrylic acid) in the PVAAA membrane and resulting in the increase of charge carriers in the PVA polymer matrix. Compared to the data reported for different membranes by other studies, our PVAAA membrane are highly ionic conducting alkaline solid polymer electrolytes membranes.     

Stretchable alkaline quasi-solid-state electrolytes created by super-tough,fatigue-resistant and alkali-resistant multi-bond network hydrogels

Hydrogel-based quasi-solid-state electrolytes (Q-SSEs) swollen with electrolyte solutions are important components in stretchable supercapacitors and other wearable devices. This work fabricates a super-tough, fatigue-resistant, and alkali-resistant multi-bond network (MBN) hydrogel aiming to be an alkaline Q-SSE. To synthesize the hydrogel, a 2-ureido-4[1H]-pyrimidone (UPy) motif is introduced into a poly(acrylic acid) polymer chain. The obtained MBN hydrogels with 75 wt% water content exhibit tensile strength as high as 2.47 MPa, which is enabled by the large energy dissipation ability originated from the dissociation of UPy dimers due to their high bond association energy. Owing to the high dimerization constant of UPy motifs, the dissociated UPy motifs are able to partially re-associate soon after being released from external forces, resulting in excellent fatigue-resistance. More importantly, the MBN hydrogels exhibit excellent alkali-resistance ability. The UPyGel-10 swollen with 1 mol/L KOH display a tensile strength as high as ～1.0 MPa with elongation at break of ～550%. At the same time, they show ionic conductivity of ～17 mS/cm, which do not decline even when the hydrogels are stretched to 500% strain. The excellent mechanical property and ionic conductivity of the present hydrogels demonstrate potential application as a stretchable alkaline Q-SSE.     

Compression elastic modulus of neutral and protonated poly(N-vinylimidazole) hydrogels

The compression modulus of poly(N-vinylimidazole) (PVI) hydrogels synthesized by cross-linking polymerization in aqueous solution, was measured at room temperature in several related systems: i) just after polymerization, ii) swollen at equilibrium in deionized water, iii) swollen in HCl (aq) (pH=2.5), iv) swollen in HCl (pH=2.5) and 1 M NaCl (aq) solution and v) swollen in H₂SO₄ (pH=2.5) (aq) solution. Samples of the first and second groups are neutral whereas hydrogels of the other three groups are ionic because of protonation of basic imidazole groups. The experimental results were fitted with the Erman-Monnerie theory, applied to compression measurements for the first time, to determine the phantom modulus, [f_ph*], and the parameter κ_G which measures the constraining role of entanglements on the fluctuations of chains between knots.     

Synthesis and burst strength of water‐swollen immunoisolatory tubules

A series of amphiphilic hydrogel tubules have been prepared by copolymerizing/crosslinking hydrophilic poly(dimethylacrylamide) segments with hydrophobic di‐, tri‐, and octamethacrylate‐telechelic polyisobutylene crosslinkers, and their elastic modulus and burst strength in the water‐swollen state were investigated. Because the burst characteristics of hydrogels have not yet been quantitatively investigated, equipment was designed and built to generate fundamental insight into the burst properties of thin‐walled (200–250 μm) narrow lumen (2–3 mm i.d.) water‐swollen tubules. The theory developed to describe quantitatively the inflation behavior of thin‐walled rubber tubules was adapted to treat our experimental observations. Changes in the burst strength, elastic modulus, and expansion during the inflation of hydrogel tubules were interpreted in terms of the molecular weight of the hydrophilic segments between crosslinking sites (M_{c,hydrophilic}), which in turn was calculated according to the rubber elasticity theory. According to these investigations, the burst strength of our water‐swollen amphiphilic tubules is in the 0.2–0.5 MPa range, which is sufficient for implantation and immunoisolatory applications. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2075–2084, 2002     

Synthesis, characterization and swelling properties of a chemically cross-linked poly(vinyl alcohol) hydrogel

A poly(vinyl alcohol) hydrogel was prepared by coupling poly(vinyl alcohol) with epichlorohydrin as the cross-linking agent. The structure of the hydrogel was characterized by FTIR and GPC techniques. Various amounts of water were added into the dry gel to swell it, and the quantity of water in various states in the partially swollen hydrogel was determined by DSC technique. The analytical results indicate that the water introduced into the dry gel first combines with the hydrophilic groups of the network chains through hydrogen bond forming non-freezable water. The weight ratio of the non-freezable water to dry gel in the hydrogels is about 0.20. After the non-freezable water is saturated, the additional water penetrates the network space and exists simultaneously both in the freezable and free water states until reaching equilibrium swelling. Translated from Acta Polymeric Sinica, 2006, (5): 671–675 (in Chinese)     

Polyelectrolyte membranes prepared by dynamic self-assembly of poly (4-styrenesulfonic acid-co-maleic acid) sodium salt (PSSMA) for nanofiltration (I)

In recent years, the layer-by-layer (LBL) self-assembly of polyelectrolyte has attracted much attention for the preparation of nanofiltration (NF) membranes. However, most researchers focused on the homopolymers, few studied on the copolymers for the preparation of NF membranes. In the present work, a series of nanofiltration membranes were prepared by dynamic self-assembly of a copolymer polyelectrolyte containing both weakly and strongly ionized groups, poly (4-styrenesulfonic acid-co-maleic acid) sodium salt (PSSMA), with poly (allylamine hydrochloride) (PAH) and poly (styrenesulfonic acid sodium salt) (PSS) on the modified polyacrylonitrile (PAN) ultra-filtration membranes. The effects of substrate, deposition pH, SS/MA ratio in PSSMA, concentration of the PSSMA and bilayer number on the properties of the NF membranes were investigated. The results indicated that the performances of the NF membranes prepared by dynamic self-assembly process were superior to those prepared by the static self-assembly process. The membranes terminated with PSSMA were negatively charged. Due to the changes of charge density and conformation of PSSMA in different pH conditions, the [PAH/PSS]₁PAH/PSSMA membrane prepared at pH 2.5 showed higher Na₂SO₄ rejection and larger flux than those of the membrane prepared at pH 5.7. The NF membrane [PAH/PSS]₁PAH/PSSMA composed of only two bilayers exhibited 91.4% Na₂SO₄ rejection and allowed solution flux of 28.6 L/m² h at 0.2 MPa. The solution flux increased to 106.6 L/m² h at 0.8 MPa, meanwhile, no obvious decrease in Na₂SO₄ rejection was observed.     

Calculation of the osmotic and activity coefficients of seawater at 25°C

The equation of Reilly, Wood, and Robinson was used to predict the osmotic coefficient of seawater and of its concentrates at molal ionic strengths of 0.5 to 6.0 at 25°C. The results agree closely with experimental data at ionic strengths below 5. The average difference in osmotic coefficients over the entire concentration range is 0.0014. The only serious discrepancy is at an ionic strength of 6, where a difference of 0.0068 is found. The accuracy of the predictions of osmotic coefficients prompted the calculation of the activity coefficients of NaCl, Na₂SO₄, MgCl₂, MgSO₄, KCl, and K₂SO₄ in the mixture. The calculated activity coefficients of NaCl and Na₂SO₄ agree within experimental error with previous measurements. This agreement demonstrates the prediction of activity and osmotic coefficients for complex mixtures.     

Preparation and characterization of poly(vinyl alcohol)/organo-modified cloisite Na+ with chiral L-leucine amino acid/TiO2 nanocomposites

Poly(vinyl alcohol)/organo-clay/TiO₂ nanocamposites films were prepared with 10 wt % of organo-nanoclay and various amount of TiO₂ nanoparticles. Cloisite Na⁺ has been modified via cation exchange reaction using ammonium salt of natural L-leucine amino acid as a cationic surfactant. After that poly(vinyl alcohol)/organo-nanoclay/TiO₂ nanocomposites were synthesized by dispersion of TiO₂ on the surfaces of organo-nanoclay in poly(vinyl alcohol) matrix by using ultrasonic energy. Three nanocomposites with different loading of TiO₂ were prepared and characterized by X-ray diffraction, fourier transform infrared spectroscopy, field emission type scanning electron microscope, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis and ultraviolet-visible transmission spectra. The results showed that the organo-nanoclay and TiO₂ were dispersed homogeneously in poly(vinyl alcohol) matrix and also showed improvement in their thermal properties compared with the pure poly(vinyl alcohol).     

Poly(vinyl methyl ether) hydrogel formed by high energy irradiation

Poly(vinyl methyl ether) shows a lower critical solution temperature behavior in water. The dimension of the polymer molecules depends on the temperature. A thermo‐sensitive hydrogel was synthesized by irradiation of an aqueous solution of poly(vinyl methyl ether) with electron beam and γ‐rays. At high polymer concentration a bulk gel was formed. The structure of the gel in the dry, swollen and shrunken state was investigated by field emission scanning electron microscopy (FESEM). It could be shown, that the gel synthesized by electron beam has a sponge‐like structure consisting of cavities (≈1 μm) separated from each other by a polymer layer full of holes (≈10 nm). The macroscopic gel is characterized by several techniques, e.g. determination of the M_c‐value by NMR‐relaxation measurements.