Non-Gaussian elasticity of swollen poly(N-isopropylacrylamide) gels at high charge densities

Modulus of elasticity of highly charged N-isopropylacrylamide (NIPA) based hydrogels (PNIPA) are measured at various swelling degrees in water. The sodium salt of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) was used as the ionic comonomer of NIPA in the hydrogel preparation. The mole fraction of AMPS in the comonomer feed was varied between 0 and 1, while the crosslinker ratio was fixed at 1/85. The elasticity data show that the equilibrium swollen PNIPA hydrogels are in the non-Gaussian regime. Equations were derived based on the inverse Langevin function for the swelling ratio and the modulus of highly charged PNIPA hydrogels and checked by experiments. Results of calculations show good agreement to the swelling and elasticity data of highly swollen PNIPA gels.     

Temperature‐induced aggregation of the copolymers of N‐isopropylacrylamide and sodium 2‐acrylamido‐2‐methyl‐1‐propanesulphonate in aqueous solutions

A series of random copolymers of N‐isopropylacrylamide (NIPAM) and sodium 2‐acrylamido‐2‐methyl‐1‐propanesulphonate (AMPS) was synthesized by free‐radical copolymerization. The content of AMPS in the copolymers ranged from 1.1 to 9.6 mol %. The lower critical‐solution temperature (LCST) of copolymers in water increased strongly with an increasing content of AMPS. The influence of polymer concentration on the LCST of the copolymers was studied. For the copolymers with a higher AMPS content, the LCST decreased faster with an increasing concentration than for copolymers with a low content of AMPS. For a copolymer containing 1.1 mol % of AMPS the LCST dropped by about 3 °C when the concentration increased from 1 to 10 g/L, whereas for a copolymer containing 9.6 mol % of AMPS the LCST dropped by about 10 °C in the concentration range from 2 to 10 g/L. It was observed that the ionic strength of the aqueous polymer solution very strongly influences the LCST. This effect was most visible for the copolymer with the highest content of AMPS (9.6 mol %) for which an increase in the ionic strength from 0.2 to 2.0 resulted in a decrease in the LCST by about 27 °C (from 55 to 28 °C), whereas for the copolymer containing 1.1 mol % of AMPS the LCST decreased only by about 6 °C (from 37 to 31 °C) when the ionic strength increased from 0.005 to 0.3. The reactivity ratios for the AMPS and NIPAM monomer pairs were determined using different methods. The values of r_AMPS and r_NIPAM obtained were 11.0–11.6 and 2.1–2.4, respectively. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2784–2792, 2001     

Poly(methacrylamide‐co‐2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid) hydrogels: Investigation of pH‐ and temperature‐dependent swelling characteristics and their characterization

Novel poly(methacrylamide‐co‐2‐acrylamido‐2‐methyl‐ 1‐propanesulfonic acid) (poly(MAAm‐co‐AMPS)) hydrogels were synthesized by free radical polymerization of methacrylamide (MAAm) and 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS) in deionized water at 60 °C by using ammonium peroxydisulfate (APS), N,N′‐methylenebisacrylamide (MBAAm) and N,N,N′,N′‐tetramethylethylenediamine (TEMED) as initiator, crosslinker, and activator, respectively. To investigate the effects of feed content on the pH‐ and temperature‐dependent swelling behavior of poly(MAAm‐co‐AMPS), molar ratio of MAAm to AMPS in feed was varied from 90/10 to 10/90. Structural characterization of gels was performed by Fourier transform infrared (FTIR) spectroscopy using attenuated total reflectance (ATR) technique. Thermal and morphological characterizations of gels were performed by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM), respectively. Although an apparent pH‐sensitivity was not observed for the poly(MAAm‐co‐AMPS) gels during the swelling in different buffer solutions, their temperature‐sensitivity became more evident with the increase in AMPS content of copolymer. Thermal stability of poly(MAAm‐co‐AMPS) gels increased with MAAm content. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

New solvent for polyrotaxane. II. Dissolution behavior of polyrotaxane in ionic liquids and preparation of ionic liquid‐containing slide‐ring gels

The dissolution behavior of polyrotaxanes, consisting of α‐cyclodextrin and poly(ethylene glycol), with different molecular weights (2000 and 35,000) was investigated. Halogen‐containing ionic liquids, such as chlorides or bromides, were found to be good solvents for polyrotaxanes, regardless of their cations. Dissolution required a high temperature (above 90 °C), while intensive heating over 105 °C seemed to cause decomposition of the polyrotaxane. The discovery of new solvents for polyrotaxane was applied in the preparation of ionic liquid‐containing slide‐ring gels (SR gels), that is supramolecular networks of polyrotaxane swollen with ionic liquids, using a devised “non‐drying” technique accompanied by solvent exchange. Significant swelling of the SR gels with the ionic liquids was confirmed by dynamic mechanical measurements. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1985–1994, 2006     

Copolymerization of ethylene and 1-butene using a Cr—silica catalyst in a slurry reactor

A novel slurry reactor was used to investigate the copolymerization behavior of ethylene and 1-butene in the presence of 1 wt % Cr on Davison silica (Phillips-type) catalyst over the temperature range of 0–50°C, space velocity of about 0.0051 [m³ (STP)]/(g of catalyst) h, and a fixed ethylene to 1-butene feed mole ratio of 95 : 5. The effect of varying the ethylene to 1-butene feed ratios, 100 : 0, 96.5 : 3.5, 95 : 5, 93 : 7, 90 : 10, 80 : 20, and 0 : 100 mol/mol at 50°C was also studied. The addition of 1-butene to ethylene typically increased both copolymerization rates and yields relative to ethylene homopolymerization with the same catalyst, reaching a maximum yield for an ethylene: 1-butene feed ratio of 95 : 5 at 50°C. The incorporation of 1-butene within the copolymer in all cases was less than 5 mol %. The average activation energy for the apparent reaction rate constant, k_a, based on total comonomer mole fraction in the slurry liquid for the ethylene to 1-butene feed mole ratio of 95 : 5 in the temperature range of 50–30°C measured 54.2 kJ/mol. The behavior for temperatures between 30 to 0°C differed with an activation energy of 98.2 kJ/mol; thus, some diffusion limitation likely influences the copolymerization rates at temperatures above 30°C. A kinetics analysis of the experimental data at 50°C for different ethylene to 1-butene feed ratios gave the values of the reactivity ratios, r₁ = 27.3 ± 3.6 and r₂ ≅ 0, for ethylene and 1-butene, respectively. © 1996 John Wiley & Sons, Inc.     

Temperature and pH sensitive ionic hydrogels based on new crosslinkers

New crosslinkers were synthesized from reaction of melamine with acryloyl and methacryloyl chloride in the presence of 1‐methyl‐2‐pyrrolidone as a solvent and triethyl amine as acid acceptor. The chemical structures of the prepared crosslinkers were elucidated from FT‐IR, ¹H‐NMR and ¹³C‐NMR analyses. Linear 2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid and methacrylic acid (AMPS/MAA) copolymers were prepared and their viscometric properties in aqueous solution were investigated. Different weight percentages of the prepared crosslinkers were used as crosslinking agent (AMPS/MAA) to prepare ionic copolymers using ammonium persulfate as initiator. The percentage of crosslinkers was varied from 0.5 to 4 wt%. The swelling behaviors of crosslinked AMPS/MAA gels in deionized water were measured at different pH and temperatures. All AMPS/MAA copolymers exhibit faster deswelling rate at 50°C except for the copolymer containing 0.9 (mol ratio) AMPS. Copyright © 2005 John Wiley & Sons, Ltd.     

Water-soluble polymers. 71. pH responsive behavior of terpolymers of sodium acrylate,acrylamide, and the zwitterionic monomer 4-(2-acrylamido-2-methylpropanedimethylammonio)butanoate

Terpolymers of sodium acrylate (NaA), acrylamide (AM), and the zwitterionic monomer 4-(2-acrylamido-2-methylpropanedimethylammonio) butanoate (AMPDAB) were prepared by the free radical polymerization in 0.5M NaBr aqueous solution using potassium persulfate as the initiator. The feed ratio of AMPDAB : NaA : AM was varied from 5 : 5 : 90 to 40 : 40 : 20 mol %, with the total monomer concentration held constant at 0.45M. Terpolymer compositions were determined by ¹³C NMR. Molecular weights varied from 3.0 × 10⁵ to 9.7 × 10⁶ g/mol. All terpolymers were soluble in deionized water and salt solutions at all pH values. The dilute and semidilute solution behavior of the terpolymers was studied as a function of composition, pH, and added electrolytes. Polyelectrolyte behavior was observed for all terpolymers at pH 8.5, as evidenced by high viscosity values at low polymer concentrations and viscosity decrease in the presence of added electrolytes. The reduced viscosity as a function of decreasing pH exhibits a minimum as the terpolymer undergoes a polyanion/polyzwitterion/polycation transition. Comparison of the solution behavior of the terpolymers to terpolymers of 3-(2-acrylamido-2-methylpropane dimethylammonio)-1-propane sulfonate (AMPDAPS), AM, and NaA (AADAPS series) as well as copolymers of AMPDAB and AM (AMPDAB series) have been made. © 1997 John Wiley & Sons, Inc.     

Ionic IPNs as novel candidates for highly conductive solid polymer electrolytes

Five ionic imidazolium based monomers, namely 1‐vinyl‐3‐ethylimidazolium bis(trifluoromethylsulfonyl)imide (ILM1), 1‐vinyl‐3‐(diethoxyphosphinyl)‐propylimidazolium bis(trifluoromethylsulfonyl)imide (ILM2), 1‐[2‐(2‐methyl‐acryloyloxy)‐propyl]‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (ILM3), 1‐[2‐(2‐methyl‐acryloyloxy)‐undecyl]‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (ILM4), 1‐vinyl‐3‐ethylimidazolium dicyanamide (ILM5) were prepared and used for the synthesis of linear polymeric ionic liquids (PILs), crosslinked networks with polyethyleneglycol dimethacrylate (PEGDM) and interpenetrating polymer networks (IPNs) based on polybutadiene (PB). The ionic conductivities of IPNs prepared using an in situ strategy were found to depend on the ILM nature, T_g and the ratio of the other components. Novel ionic IPNs are characterized by increased flexibility, small swelling ability in ionic liquids (ILs) along with high conductivity and preservation of mechanical stability even in a swollen state. The maximum conductivity for a pure IPN was equal to 3.6 × 10^?5 S/cm at 20 °C while for IPN swollen in [1‐Me‐3‐Etim] (CN)₂N σ reached 8.5 × 10^?3 S/cm at 20 °C or 1.4 × 10^?2 S/cm at 50 °C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4245–4266, 2009     

ATRP synthesis and association properties of thermoresponsive anionic block copolymers

Thermosensitive anionic block copolymers of sodium 2‐acrylamido‐2‐methylpropanesulfonate (AMPS) and N‐isopropylacrylamide (NIPAAM) with different block lengths were prepared by atom transfer radical polymerization (ATRP). Controlled polymerization was achieved by using ethyl 2‐chloropropionate (ECP) as initiator and CuCl/CuCl₂/tris(2‐dimethylaminoethyl)amine (Me₆TREN) catalytic system in DMF:water 50:50 (v/v) mixtures at 20 °C. Blocks lengths ranging from 36 to 98 repeating units were obtained. The association properties in aqueous solutions at different NaCl ionic strengths were studied as a function of temperature and polymer concentration by dynamic light scattering, fluorescence spectroscopy, and energy‐filtered transmission electron microscopy. The block copolymers with a higher pNIPAAM/pAMPS ratio formed spherical core‐shell type micelles independently of the ionic strength. The block copolymers with lower pNIPAAM/pAMPS ratio formed core‐shell type micelles at high ionic strength. Larger particles were observed at low ionic strength, which could be due to the formation of vesicles or compound micelles/micellar clusters. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4830–4842, 2008     

Swelling behavior of strong polyelectrolyte poly(N-t-butylacrylamide-co-acrylamide) hydrogels

Temperature-sensitive ionic hydrogels based on N-t-butylacrylamide (TBA), acrylamide (AAm), 2-acrylamido-2-methylpropane sulfonic acid sodium salt (AMPS) and N,N^′-methylenebis(acrylamide) (BAAm) monomers were prepared. The molar ratio of TBA to the monomers AAm and AMPS was fixed at 60/40, while the AMPS content of the hydrogels was varied. The elastic modulus of the hydrogels was in the range of 347-447 Pa, much lower than the modulus of PAAm or poly(N-isopropylacrylamide) hydrogels due to the reduced crosslinking efficiency of BAAm in TBA/AAm copolymerization. The hydrogels exhibited swelling-deswelling transition in water depending on the temperature. Increasing ionic group (AMPS) content resulted in shifting of the transition temperature interval in which the deswelling takes place. The higher the ionic group content, the broader the temperature interval at the phase transition. Ionic hydrogels exhibited first-order reentrant conformational transitions in ethanol-water and in dimethylsulfoxide (DMSO)-water mixtures. The higher the ionic group content of the hydrogels the narrower the ethanol (or DMSO) range in which the reentrant phenomena occur. By taking into account the difference of the solvent mixture composition inside and outside the gel, the equilibrium swelling theory provided a satisfactory agreement to the experimental swelling data of the hydrogels immersed in the solvent mixtures.     

Synthesis of thermosensitive hydrogels from acryloyloxyethyl trialkyl phosphonium chloride–N‐isopropylacrylamide–N,N′‐methylenebisacrylamide terpolymers and their temperature dependence of water absorption

Thermosensitive polymer hydrogels were prepared by the copolymerization of three kinds of acryloyloxyethyl trialkyl phosphonium chlorides (AETRs) with alkyl chains of different lengths, with N‐isopropyl acrylamide (NIPAAm) and N,N′‐methylenebisacrylamide (MBAAm). The water content of the AETR–NIPAAm–MBAAm terpolymers obtained at molar ratios of the crosslinking agent greater than 2 decreased with increasing temperature and decreased sharply around 35 °C. However, the water contents of the AETR–NIPAAm–MBAAm (X/100/1) terpolymers obtained at a molar ratio of 1 of the crosslinking agent increased once with increasing temperature and then decreased from 3 to around 40 °C. The water contents of the AETR–NIPAAm–MBAAm (3/100/1 or 2) terpolymers decreased with the increasing length of alkyl chains in phosphonium groups in the terpolymers. The water contents of the AETR–NIPAAm–MBAAm terpolymers increased by the addition of a small amount of urea and then decreased with increasing urea concentration. However, the water contents decreased abruptly with the addition of NaCl. The AETR–NIPAAm–MBAAm terpolymers exhibited high adsorption for sodium dodecylbenzene sulfonate but no adsorption for sodium benzene sulfonate. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1505–1514, 2001     

Synthesis and characterization of high molecular weight poly(1,2-propylene carbonate-<Emphasis Type="Italic">co</Emphasis>-1,2-cyclohexylene carbonate) using zinc complex catalyst

Using supported multi-component zinc dicarboxylate catalyst,poly（1,2-propylene carbonate-co-1,2-cyclohexylene carbonate）（PPCHC） was successfully synthesized from carbon dioxide（CO₂） with propylene oxide（PO） and cyclohexene oxide（CHO）.The conversion of epoxides dramatically increased up to 89.7%（yield:384.2 g of polymer per g of Zn） with increasing reaction temperature from 60℃to 80℃.The optimized reaction temperature is 80℃.The chemical structure,the molecular weight,as well as thermal and mechanical properties of the resulting terpolymers were investigated extensively. When CHO feed content（mol%） is lower than 10%,the PPCHC terpolymers have number average molecular weight（M_n） ranging from 102×10³ to 202×10³ and molecular weight distribution（MWD） values ranging from 2.8 to 3.5.In contrast to poly（propylene carbonate）（PPC）,the introduction of small amount of CHO leads to increase in the glass transition temperature from 38.0℃to 42.6℃.Similarly,the mechanical strength of the synthesized terpolymer is greatly enhanced due to the incorporation of CHO.These improvements in mechanical and thermal properties are of importance for the practical application of PPC.     

Viscosity behavior of polyelectrolyte copolymers containing sulfonate groups in mixed organic solvents

Copolymerization of 2-acrylamido-2-methylpropane sulfonic acid (AMPS, monomer 1) with 2-hydropropyl methacrylate (HPM, monomer 2) was conducted in ethylene glycol/water (1 : 1 in weight) at 70°C. The reactivity ratios estimated from the copolymer composition at low conversion are r₁ = 2.31 ± 0.25 and r₂ = 11.70 ± 1.05. The azeotropic composition was found at the monomer mole ratio AMPS/HPM equal to 8/2. Viscosity of these copolymers was measured in dimethyl sulfoxide (DMSO) and DMSO/tetrahydrofuran (THF) mixed solvent at 25 ± 0.05°C. Polyelectrolyte behavior was observed for all the copolymers, even in the mixed solvent containing 65 wt % of THF. The reduced viscosity at constant polymer concentration decreased with increasing THF content in the mixed solvent. The copolymers having AMPS repeat units more than 42 mol % precipitated in the mixed solvent when the THF was beyond 68 wt %. The viscosity reduction and precipitation in the copolymer solutions with increasing THF can be attributed to the dipole–dipole attraction between ion-pairs formed in less-polar medium. This is helpful in understanding the volume phase transition in highly charged hydrogels caused by mixing solvents. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1433–1438, 1997     

Polymerization of coordinated monomers. XIV. Systematic deviations from alternating regulation in copolymerization of methyl methacrylate with styrene in the presence of metal halides

Methyl methacrylate (MMA) and styrene (St) copolymerize in the presence of zinc chloride at 3°C under photoirradiation. The contents of methyl methacrylate in the copolymers obtained at a [ZnCl₂]/[MMA] molar ratio of 0.4 are systematically larger than 53 mole %, which is the limiting value at a small feed ratio of methyl methacrylate. The resulting copolymers are confirmed as the sole products and not the mixtures by thin layer chromatography. The effect of dilution of the monomer feed mixture with toluene on copolymer composition suggests that it depends chiefly on the feed concentration of styrene and hardly at all on monomer feed ratios. Copolymerizations are also conducted in the presence of stannic chloride at ?17°C under photoirradiation and in the presence of ethylaluminium sesquichloride at 0°C with spontaneous initiation. The contents of methyl methacrylate in both copolymers obtained at feed ratios lower than 60 mole % almost correspond to the 1:1 alternating copolymer and increase systematically with higher feed ratios. The systematic deviations of copolymer composition obtained in the presence of metal halides are reasonably interpreted by the participation of the binary molecular complex composed of metal halide and methyl methacrylate in the polymerization of the ternary molecular complex composed of metal halide, methyl methacrylate, and styrene.     

Anomalous solubility of polyacrylamide prepared by dispersion (precipitation) polymerization in aqueous tert‐butyl alcohol

Polyacrylamide prepared by dispersion (precipitation) polymerization in an aqueous t‐butyl alcohol (TBA) medium is only partially soluble when the TBA concentrations in the polymerization media are in the range 82 vol % < TBA < 95 vol %. Independent experiments with a soluble (linear) sample of polyacrylamide show that the polymer swells sufficiently in the aforementioned media to lower the glass‐transition temperature of the polymer below the polymerization temperature (50 °C). The anomalous solubility has been attributed to the crosslinking of polymer chains that occurs during the solid‐phase polymerization of acrylamide in the swollen polymer particles. It is postulated that some of the radical centers shift from the chain end to the chain backbone during solid‐phase polymerization by chain transfer to neighboring polymer molecules, and when pairs of such radicals come into close vicinity, crosslinking occurs. However, dispersion (precipitation) polymerization in other media such as aqueous methanol and aqueous acetone yields polymers that are soluble. This result has been attributed to the fact that the polymer radical undergoes a chain‐transfer reaction with these solvents at a much faster rate than with TBA, which overcomes the effect of the polymer‐transfer reaction. Even the addition of as little as 5% methanol to a TBA–water mixture (TBA:water = 85:10) gives rise to a soluble polymer. The chain‐transfer constants for acetone, methanol, and TBA have been determined to be 9.0 × 10^?6, 6.9 × 10^?6, and 1.48 × 10^?6, respectively, at 50 °C. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3434–3442, 2001     

Thermal behavior of the composite xerogels of zirconium oxyhydroxide and silicic acid

Gels were prepared via sol?Cgel method by addition of zirconium oxychloride solution into sodium metasilicate (SZ) and sodium metasilicate solution into zirconium oxychloride (ZS) at varying final pH. Si/Zr molar ratio equaled 1/1. Synthesized gels were dried with calcium chloride until they reached a constant mass. SEM and nitrogen adsorption analysis have shown that SZ gels have surface area 175?C200?m^2?g^?1, consist of 20?C30?nm grains. ZS samples have surface area about 1?m^2?g^?1, consist of grains smaller than 10?nm. Thermal and X-ray phase analysis have shown that transition of amorphous ZrO₂ to crystalline form shifts from 430 to 850?C870?°C for SZ gels. Unlike zirconia gels phase transitions that proceed in order: ??amorphous (430?°C)??tetragonal (800?°C)??monoclinic (1,000?°C) phases??, the monoclinic phase in ZS gels appears immediately after transition from amorphous to crystalline state; the tetragonal phase in SZ samples is stable until 1,000?°C.     

Spectrofluorimetric Study of the Complexes Between Calcein and Lanthanide(III) Ions

ABSTRACT

The equilibrium of calcein, an H6L type fluorescent ligand, with lanthanide(III) ions, Ln(III), was studied spectrofluorimetrically in aqueous solution at constant ionic strength =0.1 (KC1), pH 8.0 and 25.0±0.1°C. Application of the mole ratio and continuous variation methods reveals the formation of 1:1 complexes. The conditional stability constants (β') were calculated from the analysis of the observed fluorescence vs. [Ln(III)]/[calcein] mole ratio data by using an iterative non-linear least-squares computer program. The values obtained for β' are in the range 5.24×10⁶-5.77×10⁷ The thermodynamic stability constant (β) were estimated by calculating the sidereaction coefficients (α) fro lanthanides and calcein. The β values obtained were from 3.2×10¹² to 3.6×10¹³     

Synthesis of networked polymers with lithium counter cations from a difunctional epoxide containing poly(ethylene glycol) and an epoxide monomer carrying a lithium sulfonate salt moiety

Poly(ethylene glycol)‐based networked polymers that had lithium sulfonate salt structures on the network were prepared by heating a mixture of poly(ethylene glycol) diglycidyl ether (PEGGE), poly(ethylene glycol) bis(3‐aminopropyl) terminated (PEGBA), and an ionic epoxy monomer, lithium 3‐glycidyloxypropanesulfonate (LiGPS). Flexible self‐standing networked polymer films showed high thermal stability, low crystallinity, low glass transition temperature, and good mechanical strength. The materials were ion conductive at room temperature even under a dry condition, although the ionic conductivity was rather low (10^?6 to 10^?5 S/m). The ionic conductivity increased with the increase in temperature to above 1 × 10^?4 S/m at 90 °C. The film samples became swollen by immersing in propylene carbonate (PC) or PC solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The samples swollen in PC showed higher ionic conductivity (ca.1 × 10^?3 S/m at room temperature), and the samples swollen in LiTFSI/PC showed much higher ionic conductivity (nearly 1 S/m at room temperature). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3113–3118, 2010     

Temperature-dependent relaxation study of tertiary butyl alcohol–water mixtures using TDR technique

Using time-domain reflectometry (TDR) technique, we have measured the complex permittivity of tertiary butyl alcohol (TBA)–water mixtures in the frequency range of 10 MHz–30GHz, at temperatures 15°C, 20°C and 25°C. The complex permittivity of TBA–water mixture shows Debye-type behaviour. The dielectric parameters such as dielectric constant and relaxation time were obtained from the complex permittivity spectra. The Kirkwood correlation factor and Bruggeman factor have also been determined to investigate inter- and intramolecular interaction among associating liquids.     

Superfast Responsive Ionic Hydrogels: Effect of the Monomer Concentration

A series of strong polyelectrolyte gels were prepared in aqueous solution, using the sodium salt of 2‐acrylamido‐2‐methylpropane sulfonic acid (AMPS) as the monomer and N,N'‐methylene(bis)acrylamide (BAAm) as a crosslinker. The gels were both prepared below (?22°C) and above (25°C) the bulk freezing temperature of the water, producing cryogels and hydrogels, respectively. The crosslinker (BAAm) content was set at 17 mol%, while the initial monomer concentration C_o was varied over a wide range. It was found that, at ?22°C, a macroscopic network starts to form at an initial monomer concentration of as low as 0.1 w/v%. In contrast to the conventional hydrogels formed at 25°C, the cryogels have a discontinuous morphology consisting of polyhedral pores of sizes 10⁰–10² μm. The cryogels exhibit superfast swelling properties, as well as reversible swelling–deswelling cycles in water and acetone. An increase in the initial monomer concentration from 2.5 to 10% further increases the response rate of the cryogels due to the simultaneous increase of the porosity of the networks.