Hydration studies in polymer hydrogels

Polymer hydrogels have attracted much interest in recent years based on numerous applications mainly in biotechnology and medicine. For the knowledge‐based design and development of new materials for these and similar applications, it is essential to understand better the hydration properties of hydrogels and of polymers in general. With this term, we mean the particular organization of water in the hydrogel, which determines the properties of the water component, typically different than those of bulk water, and the impact of water on the properties of the polymer matrix itself. In this review, we focus on recent work with hydrogels based on poly(hydroxyethyl acrylate), mostly copolymers with a second hydrophobic polymer and silica nanocomposites. The combination of water sorption/diffusion, thermal and dielectric studies, by fully exploiting the capabilities of each individual technique, proves essential in providing significant information on particular aspects of hydration, such as water uptake, water organization, and diffusion coefficients; glass transition and plasticization; water and polymer dynamics; protonic conductivity, and in revealing interesting correlations between these particular aspects. In the outlook similarities and differences to other related systems, such as protein‐water and polymer solutions in non‐polar solvents, are stressed in the perspective of a broader study. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Deuterium isotope effect on charge-transfer fluorescence

Quantum yields and decay times of fluorescence of charge-transfer complexes of tetracyanoethylene (an electron acceptor) with protonated and deuterated aromatic hydrocarbon donors were measured. The deuterium isotope effect on radiationless transition (identified as the

internal conversion) was observed. This observation is taken as evidence of the dominant role of intramolecular within the donor and/or the acceptor molecule) vibrations in radiationless transitions from excited charge-transfer states of molecular complexes.     

Composite polymer hydrogels

Methods of preparing and properties of composite hydrogels based on various hydrophilic polymers and their mixtures with inorganic nanosized additives are considered. The effect of the type of physical or covalent bonding between components on the formation of composite hydrogels and their characteristics is discussed. The biphasic character of composite hydrogels determines as a rule their advantages as supersorbents, membrane materials, living-tissue substitutes, drug carriers, and soft-contact-lens materials.     

Conducting polymer hydrogels

Conducting polymer hydrogels are gels, which are swollen with water, and contain a conducting polymer along with a supporting polymer as constituents. Polyaniline, polypyrrole or poly(3,4-ethylenedioxythiophene) represent the conducting moiety, while water-soluble polymers the other part. Various ways of hydrogel preparation are reviewed. The properties, such as mixed electronic and ionic conductivity, redox activity, and responsivity, are conveniently combined with materials properties afforded by supporting polymers, such as elasticity, mechanical integrity, and biocompatibility. The derived materials, aerogels obtained after freeze-drying of hydrogels, or carbogels produced after carbonization of aerogels, are also considered. The applications are expected especially in biomedicine and energy-storage devices but many other uses proposed in the literature are listed and discussed.     

Growing polymer hydrogels

A new nontoxic spongy hydrogel material is synthesized via the precipitative polymerization of hydroxyethyl methacrylate, and implants for the ophthalmic reconstructive surgery are created on its basis. The obtained endoprostheses are well compatible with eye-socket tissues. The copolymerization of hydroxyethyl methacrylate with acrylamide yields a material that is able to increase its degree of swelling in aqueous solutions. As a result, implants that controllably change in size during use may be created.     

Nanocomposite polymer hydrogels

The technological need for new and better soft materials as well as the drive for new knowledge and fundamental understanding has led to significant advances in the field of nanocomposite gels. A variety of complex gel structures with unique chemical, physical, and biological properties have been engineered or discovered at the nanoscale. The possibility to form self-assembled and supramolecular morphologies makes organic polymers and inorganic nanoparticles desirable building blocks for the design of water based gels. In this review, we highlight the most recent (2004–2008) accomplishments and trends in the field of nanocomposite polymer hydrogels with a focus on creative approaches to generating structures, properties, and function within mostly biotechnological applications. We examine the impact of published work and conclude with an outline on future directions and challenges that come with the design and engineering of new nanocomposite gels.     

Photomechanical polymer hydrogels based on molecular photoswitches

As intelligent materials responsive to light, photomechanical hydrogels not only possess high-water content, excellent softness and biocompatibility, but also can accomplish various mechanical motions upon spatiotemporal stimulation of external light, which exhibit great potential in biomedical and underwater bionic fields. Molecular photoswitches have been used broadly in preparation of photomechanical hydrogels owing to their high photosensitivity and reversible molecular structure transformations induced by light. Herein, the current progress of photomechanical hydrogels based on typical molecular photoswitches such as spiropyran, azobenzene, and hexaarylbiimidazole (HABI) are introduced. Especially, as a promising building unit for photomechanical hydrogels, HABI has been highlighted due to the unique molecular structures and reversible photoswitching capability. HABI-derived polymer hydrogels demonstrate flexible mechanical behaviors upon localized light irradiation. The characteristics and challenges of photomechanical hydrogels based on molecular photoswitches are also prospected.     

Polychromatic femtosecond fluorescence studies of metal-polypyridine complexes in solution

Femtosecond-resolved broadband fluorescence studies are reported for[M(bpy)₃]²⁺ (M = Fe, Ru), RuN3 and RuN719 complexes in solution. We investigated the pump wavelength dependence of the fluorescence of aqueous [Fe(bpy)₃]²⁺ and the solvent and ligand dependence of the fluorescence of Ru-complexes excited at 400 nm. For all complexes, the ¹MLCT fluorescence appears at zero time delay with a mirror-like image with respect to the absorption. It decays in ?30-45 fs due to intersystem crossing to the ³MLCT states, but a longer lived component of ∼190 fs additionally shows up in RuN719 and RuN3. No solvent effects are detected. The very early dynamics are characterized by internal conversion (IC) and intramolecular vibrational redistribution (IVR) processes on a time scale which we estimate to ?10 fs using the ¹MLCT lifetime as an internal clock.     

Synthesis,spectral, fluorescence and thermal studies on ionic hafnocene thiopurine complexes

Ionic chelates of hafnocene, with 6-mercaptopurine (HL¹) (A) and 6-thioguanine (HL²) (B) of the type [( ⁵-C₅H₅)₂HfL¹]⁺X^– (C) and [( ⁵-C₅H₅)₂HfL²]⁺X^– (D) (X = CuCl₃, ZnCl₃, CdCl₃, HgCl₃, PhNHNHCS₂) have been prepared and characterized by conductivity measurements and by i.r., electronic, ¹H-n.m.r. and ¹³C-n.m.r. spectra. Fluorescence studies of the complexes containing Hg in the anionic moiety, and relevant photochemical parameters, have been elucidated. Thermodynamic parameters have been calculated using thermogravimetric (t.g.) and differential thermal analytical (d.t.a.) curves and their variations have been correlated with some structural parameters of the complexes. The ligands, as well as their hafnium(IV) complexes, exhibit appreciable antibacterial and antifungal activity against E. coli, S. typhi, P. aeruginosa, Z. mobilis bacterial strains and versus A. awamori, A. niger fungal strains, respectively.     

New hydrogels based on carbohydrate and on carbohydrate-synthetic polymer networks

Novel synthetic routes recently explored in our laboratories in order to obtain crosslinked polymeric samples, comprising either chitosan or gellan as polysaccharidic components, are outlined. The former networks, in which different crosslinking partners have been used (i.e. oxidized cyclodextrin and telechelic poly(vinylalcohol)), can bear fixed positive charges while the latter are anionic. Zwitterionic networks formed by the template polymerization of acrylic acid onto chitosan with concomitant crosslinking (bisacrylamide) have also been prepared. Procedures adopted are simple and, once optimized, may lead to biocompatible hydrogels, with easily tunable physical properties, of potential interest in the biomedical area.     

Synthesis,spectral, fluorescence,thermal and biological studies on ionic hafnocene pyrimidine complexes

Ionic chelates of hafnocene with uracil (HL¹) (A) and 5-fluorouracil (HL²) (B) of the type [(⁵- C₅H₅)₂HfL¹]⁺X^– (C) and [(⁵- C₅H₅)₂HfL²]⁺X^– (D) (X = CuCl₃, ZnCl₃, CdCl₃, HgCl₃, PhNHNHCS₂) have been prepared and characterised by conductivity measurements and by i.r., electronic, ¹H-n.m.r. and ¹³C-n.m.r. spectra. Fluorescence studies of the complexes containing Hg in the anionic moiety, and relevant photochemical parameters, have been elucidated. Thermodynamic parameters have been calculated using thermogravimetric (t.g.) and differential thermal analytical (d.t.a.) curves, and their variations have been correlated with some structural parameters of the complexes. The ligands, as well as their hafnium(IV) complexes, exhibit appreciable antibacterial and antifungal activity against E. coli, S. typhi, P. aeruginosa and Z. mobilis bacterial strains, and versus A. awamori and A. niger fungal strains, respectively.     

Strong and tough hydrogels crosslinked by multi-functional polymer colloids

Tough polymer hydrogels have great potential applications in soft actuators, artificial muscles, tissue engineering, and so forth. To improve the strength and toughness of hydrogels, numerous strategies have been developed to integrate efficient energy dissipation mechanisms into the hydrophilic networks. Among them, the use of macro-crosslinkers to replace conventional chemical ones has become promising to develop tough hydrogels. Polymer colloids—including nano-/microparticles, nano-/microgels, hydrophobic associates, and block copolymer assemblies—have been employed in literature as multi-functional macro-crosslinkers that link polymer chains through covalent bonds or noncovalent interactions. The dislocation, deformation, desociation, and rupture of polymer colloids upon loadings are the major mechanisms to dissipate energy. This article provides a comprehensive account of most recent progresses on tough hydrogels crosslinked by polymer colloids, and explores the toughening mechanisms. It aims to inspire novel designs of tough hydrogels with multi-functionalities. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1336–1350     

Polymer complexes. LXXII. Spectroscopic studies,thermodynamics, DNA binding and biological activity of polymer complexes

A novel series of copper polymer complexes ( 1 – 4 ) were synthesized and characterized using various spectroscopic techniques. Spectra of all polymer complexes a tetragonal distorted geometry for the Cu(II) ion. The electronic spectra, magnetic moments and electron spin resonance results indicate tetragonal distortion geometry for the Cu(II) polymer complexes. The effects of various solvents on absorption spectra of the ligand are discussed. A prediction of the interaction of the ligand against anti‐cancer receptors was carried out using AutoDock server. The affinity of the compounds to calf thymus DNA was determined through UV–visible DNA binding titration, and intrinsic binding constant (K_b) was found to be 4.16 × 10³, 3.10 × 10⁵, 3.18 × 10⁴ and 2.91 × 10⁵ for polymer complexes 1 – 4 , respectively. The antimicrobial activity of the polymer complexes against bacterial species (Bacillus cereus, Staphylococcus aureus, Escherichia coli, Klebsiella pneumonia, Enterococcus faecalis and Pseudomonas aeruginosa) and fungal species (Aspergillus niger, Fusarium oxysporum and Candida albicans) was investigated.     

Equilibrium studies on Schiff base complexes of copper(II) and nickel(II): Ligand substitution and formation of mixed ligand complexes

Summary Vis spectrophotometry has been used to study various ligand substitution equilibria (1) and (2) involving four-coordinate copper(II) and nickel(II) his chelate complexes in methanol, propan-2-ol and toluene. MA₂ + HB MAB+HA, K₁ (1) MAB + HB MB₂ + HA, K₂ (2) The Schiff base ligands, HA and HB, which are monobasic and bidentate, represent salicylaldimine type N,O-ligands ( HSA=NR) (1) or pyrrole-2-aldimine type N,N-ligands ( HPA=NR) (2) with different branching at the - or (3-carbon of the organic group R. For both types of ligand the relative thermodynamic stability of their copper and nickel complexes is governed mainly by the steric demands of R, which determine the degree of tetrahedral distortion. The order of stability as given by = K₁ K₂ is: t-Bu < neo-Pent < i-Pr < i-Bu < Et < n-Pr. The K₁/K₂ ratio is strongly solvent dependent in the sense that the mixed ligand species MAB is stabilised in toluene relative to methanol. Such a solvent effect is not observed for . The MAB complexes could not be isolated. The vis spectrum of the mixed ligand species Ni(SA=NiPr, SA=NEt) was calculated by computer fitting of the experimental data.     

Polymer complexes. LXXI. Spectroscopic studies,thermal properties,DNA binding and antimicrobial activity of polymer complexes

Polymer complexes of Co(II), Ni(II), Mn(II), Cr(III) and Cd(II) were prepared by the reaction of 3‐allyl‐5‐[(4‐nitrophenylazo)]‐2‐thioxothiazolidine‐4‐one (HL) with metal ions. The structure of polymer complexes was characterized by elemental analysis, IR, UV–Vis spectra, X‐ray diffraction analysis, magnetic susceptibility, conductivity measurements and thermal analysis. Reaction of HL with Co(II), Ni(II), Mn(II), Cr(III) and Cd(II) ions (acetate or chloride) give polymer complexes ( 1–5 ) with general stoichiometric [M(L)(O₂CCH₃)(H₂O)₂]_n (where L = anionic of HL and M = Co(II) (1) or Ni(II) (2) ), [Mn(HL)₂(OCOCH₃)₂]_n (3) , [Cr(L)₂(Cl)(H₂O)]_n (4) and [Cd(HL)(O₂CCH₃)₂]_n (5) . The value of HOMO–LUMO energy gap (ΔE) for forms (A‐C) of monomer (HL) is 2.529, 2.296 and 2.235 eV, respectively. According to ΔE value, compound has minimum ΔE is the more stable, so keto hydrazone form (C) is more stable than the other forms (azo keto form (A), azo enol form (B)). The interaction between HL, polymer complexes of Co(II), Ni(II), Mn(II), Cr(III) and Cd(II) with Calf thymus DNA showed hypochromism effect. The HL and its polymer complexes were tested against some bacterial and fungal species. The results showed that the Cr(III) polymer complex (4) has more antibacterial activity than HL and polymer complexes (1–3 and 5) against Bacillus subtilis, Staphylococcus aureus and Salmonella typhimurium.     

Effect of polymer entanglement on the toughening of double network hydrogels

The mechanical strength of double network (DN) gels consisting of highly cross-linked poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) as the first component and linear polyacrylamide (PAAm) as the second component has been investigated by varying the molecular weight of the second polymer PAAm, M(w). The experimental results reveal that, for toughening of the DN gels, (1) M(w) is one of the dominant parameters; (2) there is a critical value of M(w) = 10(6) for a remarkable enhancement; (3) the fracture energy of DN gels with a M(w) larger than 10(6) reaches a value as high as 10(3) J/m(2). By plotting the strength of DN gels (fracture stress sigma and fracture energy G) against a characteristic parameter of c[eta], where c is the average concentration of PAAm in the DN gels and [eta] is the intrinsic viscosity of PAAm, it is found that the dramatic increase in the mechanical strength of the DN gels occurs above the region where linear PAAm chains are entangled with each other. Thus, we conclude that the entanglement between the second component PAAm plays an important role of the toughening mechanism of DN gels. This result supports the heterogeneous model, which predicts the presence of "voids" of the first network PAMPS with a size much larger than the radius of the second polymer PAAm.     

Properties of conductive polymer hydrogels and their application in sensors

Conductive polymer hydrogels (CPHs), which combine the unique advantages of hydrogels and organic conductors, have received wide attention due to their adjustable mechanical properties, biocompatibility, self‐healing, hydrophilicity, and ease of preparation. With doping engineering and incorporation with other functional nanomaterials, CPHs have exhibited excellent physical/chemical properties. CPHs have been widely used in various electronic devices, especially in the field of sensors due to its sensitivity to external stimuli. This review summarizes recent progress in CPHs from the aspect of the CPHs' properties and their application in advanced sensor technology. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1606–1621     

Deuterium and nitrogen-14 nuclear quadrupole resonance spectra of cytosine-amino acid complexes

The ¹⁴N and ²H nuclear quadrupole resonance spectra of cytosine complexes of the acids N-formylglycine, N-benzoylglycine and N-phthaloylglutamic, and of the cytidine complex of salicylic acid have been obtained at 77 K on powdered samples, using the double resonance level crossing technique, DRLC. Both normal abundance and deuterium-enriched forms of the compounds were studied. Use of various assignment aids, discussed at length, make it possible to completely assign the electric field gradient parameters to all ¹⁴N and ²H sites in the compounds.     

Interferometric studies on polymer structure

A multiple-beam interferometric method is used to study the change of optical orientation function and molecular structure of nylon-6 fibres due to γ-irradiation under vacuum. It was found that γ-radiation causes alignment to the fibre chains in the direction of the fibre axis, this alignment gives an increase in the optical orientation function. A two-beam interferometric method is used to study the changes in optical orientation function on drawn polypropylene fibres. Empirical formulae are suggested to correlate these changes in the optical orientation function with the dose and with the draw ratio. This study aims to show that the multiple-beam and two-beam interferometric methods can be used to study the changes that take place in polymers and fibres by irradiation or drawing.