Strengthened graphene oxide/diazoresin multilayer composites from layer-by-layer assembly and cross-linking

The layer-by-layer assembly of graphene oxide and diazoresin is carried out via the electrostatic and hydrogen bond interactions on planar substrates and colloidal templates. The successful planar and spherical growth of multilayer could be investigated by UV-vis spectrophotometry and scanning electron microscopy, respectively. Subsequent UV irradiation or heating would convert the ionic bonds and hydrogen bonds to covalent bands, which significantly improves the stability of the multilayer composite against solvent etching. For the cross-linked core-shell composites, the template cores could be removed by dissolution and hollow microspheres are obtained.     

Phosphorus based epoxy terminated structural adhesive 2. Curing, adhesive strength and thermal stability

The curing behavior of phosphorus based epoxy terminated polymers was studied using diaminodiphenyl ether, diaminodiphenyl sulfone, benzophenone tetracarboxylic dianhydride and the commercial hardener of Ciba-Geigy's two-pack araldite, as curing agent. The adhesive strength of these adhesives was measured by various ASTM methods like lap-shear, peel, and cohesive tests on metal-metal, wood-wood and wood-metal interfaces. All these results were compared with the synthesized epoxy resins prepared from bisphenol-A and epichlorohydrin having the epoxy equivalent value of 0.519. The thermal stability of both the virgin resin and its cured form was also studied by thermogravimetric analysis.     

Multiscale and multicomponent layer by layer assembly of optical thin films triggered by electrochemical coupling reactions of N-alkylcarbazoles

The integration of multiscale and multicomponent of molecules and nanoparticles into thin films for applications requires the abilities of controlled their processing and assembly,which has been an great challenge because of the difficulty in manipulating the various materials such as small molecules,complexes,polymers,and inorganic nanomaterials through synergetic combinations of chemical or physical fabrications.Eletropolymerization is of great significance to fabricate polymeric film materials straight on the conductive substrates with tunable morphologies and thicknesses.However,unlimited electrochemical reactions(polymerization)have been usually leading to disadvantageous in ill-defined structure and highly doped state.Thanks to finding of exceptional electrochemical reaction(oligomerization)of N-alkylcarbazole,electrochemical layer by layer assembly has emerged as a promising strategy for a wide library of applications.The capability of this strategy can manipulate various molecules and nanoparticles into the scale and component controllable thin films.Unlike other electropolymerizable precursors such as aniline and thiophene,the resulting di-N-alkylcarbazole is transparent in the visible light region and thus does not impair the intrinsic properties of the components in the film.This account highlights of the typical findings in investigating both single-and multi-components thin films as a forum for discussing new opportunities in exploiting novel designs and applications of optical thin films.     

Waterborne epoxy adhesive derived from epoxidized soybean oil and dextrin: Synthesis and characterization

In the present study, waterborne epoxy (WBE) was prepared and the parameters involved in the synthesis of WBE have been optimized based on physicochemical analysis. A dextrin-based curing agent (DCA) was synthesized from dextrin and trimellitic anhydride at variable molar ratios, reaction temperature, reaction duration, and solvent. Furthermore, the optimized composition of DCA and WBE system was used as adhesive in wood bonding. A comparative analysis of DCA-cured-bonded system was studied with phenol-formaldehyde (PF)-bonded adhesive system. From all the analyses, the performance characteristic WBE–DCA adhesive system was found comparable with that of PF-bonded system.     

Cold water fish gelatin films: Effects of cross-linking on thermal, mechanical, barrier, and biodegradation properties

Gelatin was extracted from Alaska pollock (Theragra chalcogramma) and Alaska pink salmon (Oncorhynchus gorbuscha) skins and cast into films. The fish gelatin films’ tensile, thermal, water vapor permeability, oxygen permeability, and biodegradation properties were compared to those of bovine and porcine gelatin films. In addition, fish gelatin films were cross-linked with glutaraldehyde. Pollock and salmon gelatin films had comparable tensile properties, but had lower tensile strength and percent elongation than mammalian gelatin films. The lower strength and elongation might have been due to lower structural gelatin levels present in fish gelatin films. The addition of cross-linkers had little effect on tensile properties and melting temperatures of fish gelatin films. Pollock gelatin films had the lowest water vapor and oxygen permeability values, whereas mammalian gelatin films had the highest permeability values. Cross-linking resulted in lower water vapor permeability for salmon gelatin films and higher oxygen permeability for pollock gelatin films. However, all fish gelatin films had better water vapor and oxygen barrier properties than mammalian gelatin films. Also, fish gelatin films degraded faster than mammalian gelatin films.     

Nacre-inspired green artificial bionanocomposite films from the layerby-layer assembly of montmorillonite and chitosan

The simple LBL technique was introduced to fabricate green nacre-like chatosan/montmorillonite(CHI/MMT) films. The results of SEM and XRD analysis demonstrate that the produced CHI/MMT composites films stacked densely together to bring out well-defined nacre-like brick-mortar structure. The nanoindentation technique is used to characterize the mechanical properties of the layered nanocomposite films, which show enhanced mechanical modulus(up to ～6.64 GPa) compared with the pure chitosan.     

Electrochemistry and Electrocatalysis of Myoglobin Loaded into Multilayer Films Assembled with Phytic Acid and Chitosan

Natural polymer polysaccharides chitosan (CS) was successfully assembled with phytic acid (PA) into {PA/CS}_n layer-by-layer films. Myoglobin (Mb) could be gradually “absorbed” or loaded into {PA/CS}_n films when the films were immersed into Mb solutions, forming {PA/CS}_n-Mb films. The {PA/CS}_n-Mb films demonstrated well-defined and quasi-reversible cyclic voltammetry (CV) responses for Mb Fe^III/Fe^II redox couple and were used to catalyze electrochemical reduction of oxygen and hydrogen peroxide. The interaction between Mb and {PA/CS}_n films was explored and discussed, which suggested that the electrostatic attraction might play a major role in loading Mb into the films. This new kind of film incorporated with redox proteins could be used to fabricate the new type of biosensors or bioreactors without using mediators.     

Rheological, mechanical and transport properties of blown films of high density polyethylene nanocomposites

In this work, high density polyethylene (HDPE) was mixed in a twin screw extruder with organophilic treated clay, Cloisite 20A, and a compatibility agent, a HDPE grafted with maleic anhydride (PEMA). The screw profile was changed from a less dispersive (Profile 1) to a high dispersive configuration (Profile 2). A masterbatch procedure was used to obtain a final organoclay concentration of 5 wt.%. Both profiles allowed the intercalation of the HDPE into the clay, increasing the clay’s gallery distance to 3.7 nm. However, the samples produced with Profile 2 (Nano 2 samples) were more elastic and had a more stable structure than the samples produced with Profile 1. Therefore, two kind of blown films of Nano 2 samples were made: FN1 and FN2. The last one was blown at a higher screw velocity than the FN1. Both films had an increase of 95% in the elastic modulus and a reduction of 60% and 45% in O₂ and water vapor permeability rates, respectively, compared to the film of pure HDPE. However, the FN2 structure was more unstable than the FN1 structure. It was concluded that both screw profiles gave the same level of HDPE intercalation in the clay; however, the more dispersive profile produced more time-stable and elastic structures. The increase in the elongation rate during the film blowing process produced also more time-stable morphologies; however, this higher orientation created matrix/filler interfacial defects.     

Copper selenide film electrodes prepared by combined electrochemical/chemical bath depositions with high photo-electrochemical conversion efficiency and stability

Copper selenide (of the type Cu_2-xSe) film electrodes, prepared by combined electrochemical (ECD) followed by chemical bath deposition (CBD), may yield high photo-electrochemical (PEC) conversion efficiency (∼14.6%) with no further treatment. The new ECD/CBD-copper selenide film electrodes show enhanced PEC characteristics and exhibit high stability under PEC conditions, compared to the ECD or the CBD films deposited separately. The electrodes combine the advantages of both ECD-copper selenide electrodes (in terms of good adherence to FTO surface and high surface uniformity) and CBD-copper selenide electrodes (suitable film thickness). Effect of annealing temperature, on the ECD/CBD film electrode composition and efficiency, is discussed.     

Studies on synthesis,characterization and adhesive strength evaluation of KFA substituted resole adhesives

Preliminary investigations revealed the presence of appreciable amount of gum rich in lignin and tannin in kendu fruit (Diospyros Cordifolia Roxb). The kendu fruit adhesive (KFA) was used to substitute phenol in resole formulations to achieve cost effectiveness. Substituted resole formulations with 50 and 100% KFA were prepared in alkaline medium through stepwise addition process. Unsubstituted and KFA substituted resole adhesives were then characterized by FT‐IR, thermogravimetric analysis, differential scanning calorimetry and X‐ray diffraction analysis. The adhesive strength of the above mentioned formulations were evaluated by comparing the results of mechanical tests as per the ASTM specifications using UTM‐LR‐100K LLOYD Instruments, UK. Analytical characterizations revealed the substitutions of phenol by KFA in the substituted resole formulations. The results of adhesive strength test revealed that the 50% KFA substituted PF resin exhibits better adhesive strength than the virgin phenol‐formaldehyde and 100% KFA‐formaldehyde resole formulation. Copyright © 2001 John Wiley & Sons, Ltd.     

Influence of the type of foam films and the type of surfactant on foam stability

The behaviour and the life time ( _p) of different types of foam films (thin liquid films, for which DLVO-theory is valid; common black films, Newton black films) have been studied as a function of external pressure (P), applied in the Plateau-Gibbs-borders of the foam. The foam stability and the course of thep/P-dependence are determined mainly by the type of the foam films. A criterion for estimation of foam stability is proposed on the base of the obtained experimental results.     

Layer-by-layer films of hemoglobin or myoglobin assembled with zeolite particles: electrochemistry and electrocatalysis

Positively charged hemoglobin (Hb) or myoglobin (Mb) at pH 5.0 in solutions and negatively charged zeolite particles in dispersions were alternately adsorbed onto solid surfaces forming [zeolite/protein](n) layer-by-layer films, which was confirmed by quartz crystal microbalance (QCM) and cyclic voltammetry (CV). The protein films assembled on pyrolytic graphite (PG) electrodes exhibited a pair of well-defined, nearly reversible CV peaks at about -0.35 V vs. SCE at pH 7.0, characteristic of the heme Fe(III)/Fe(II) redox couples. Hydrogen peroxide (H(2)O(2)) and nitrite (NO(2)(-)) in solution were catalytically reduced at [zeolite/protein](7) film modified electrodes, and could be quantitatively determined by CV and amperometry. The shape and position of infrared amide I and II bands of Hb or Mb in [zeolite/protein](7) films suggest that the proteins retain their near-native structure in the films. The penetration experiments of Fe(CN)(6)(3-) as the electroactive probe into these films and scanning electron microscopy (SEM) results indicate that the films possess a great amount of pores or channels. The porous structure of ]zeolite/protein](n) films is beneficial to counterion transport, which is crucial for protein electrochemistry in films controlled by the charge-hopping mechanism, and is also helpful for the diffusion of catalysis substrates into the films. The proteins with negatively charged net surface charges at pH 9.0 were also successfully assembled with like-charged zeolite particles into layer-by-layer films, although the adsorption amount was less than that assembled at pH 5.0. The possible reasons for this were discussed, and the driving forces were explored.     

Organosoluble and transparent polyimides derived from alicyclic dianhydride and aromatic diamines

Organosoluble polyimides were synthesized with the alicyclic dianhydride 1,8‐dimethylbicyclo[2,2,2]oct‐7‐ene‐2,3,5,6‐tetracarboxylic dianhydride and aromatic diamines. The polyimides possessed good solubility both in strong dipolar solvents and in common solvents; the thermal decomposition temperature of the polyimides exceeded 420 °C. Strong and flexible films of the polyimides, with the cutoff of ultraviolet–visible absorption lower than 310–320 nm, exhibited good features as the alignment layers for nematic liquid crystals with pretilt angles of 1.5–2.9°. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 110–119, 2002     

Phosphonium‐based polyelectrolyte networks with high thermal stability,high alkaline stability,and high surface areas

Phosphonium‐containing polyelectrolyte networks (PENs) ( P1 – P4 ) were prepared by cyclotrimerization of bis(4‐acetylphenyl)diphenylphosphonium bromide ( M1 ) and 1,4‐diacetylbenzene ( M2 ) with p‐toluene sulfonic acid in various M1:M2 ratios (1,0, 1:1, 1:2, and 1:4). The relative abundance of the PAr₄⁺ units in each PEN was demonstrated to influence thermal stability, alkaline stability, water uptake, surface area, and CO₂ uptake in predictable ways. Impressively, PENs with NTf₂^? counterions (Tf = CF₃SO₃) did not exhibit 5% mass loss until heating above 400 °C. Alkaline stability, tested by challenging a PEN with 6 M NaOH(aq) at 65 °C for 120 h, increased with increasing PAr₄⁺ content, which reflected the enhanced reactivity of the HO^? anion in more hydrophobic materials (i.e., PENs with lower M1:M2 ratios). The specific surface areas estimated by Brunauer‐Emmett‐Teller (BET) analysis for these PENs were above 60 m²/g under N₂ and nearly 90 m²/g under CO₂. Notably, P3 (in which 33% of monomers comprise a phosphonium moiety) exhibited a CO₂ uptake affinity of one CO₂ molecule adsorbed for every phosphonium site. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 598–604     

Analysis of the mechanical and degradation performances of optimised agricultural biodegradable films

The introduction and the expanding use of biodegradable materials represent a really promising alternative for enhancing sustainable and environmentally friendly agricultural activities in mulching and low-tunnel cultivation. The main challenges for the development of agricultural films biodegradable in the soil concern primarily the effects of ageing and degradation during the useful lifetime, which may cause premature losses in their mechanical performance. A set of Mater-Bi based biodegradable films was developed and tested, following the selective optimisation of some processing parameters of the film manufacturing along with the optimisation of the structural low-tunnel system design. The behaviour experienced during the experiments suggests that the so optimised biodegradable films perform in a way comparable to the corresponding LDPE films, within the period of their useful lifetime. Experimental investigation indicates that water and high temperatures do not affect the mechanical behaviour of the biodegradable films significantly, as it is experienced during the first period of their exposure to real field conditions. A high dose of UV radiation has detrimental effects, however, on the elongation at break of both mulching and low-tunnel films. These films are shown to be readily degraded within 4-6 months under irrigated agricultural soil conditions, indicating a high biodegradability rate.     

Thermal and structural stability of composite systems based on polyaniline deposited on porous polyethylene films

Conducting composite systems containing polyaniline layers produced on the surface and inside the pores of polyethylene support have been prepared. Microporous polyethylene films were obtained by melt extrusion with subsequent annealing, uniaxial extension, and thermal fixation. Polyaniline layers were formed by in-situ polymerization of aniline onto polyethylene porous support placed into the aqueous reaction mixture. Structural and chemical transformations upon heating of these systems in air in free state and in vacuum under load have been investigated by thermo-mechanical tests, IR spectrometry, and electron microscopy. Changes in mechanical properties of composites after heating have been analyzed. Composite systems have been found to demonstrate a considerably lower shrinkage upon heating than microporous polyethylene substrates. It has been discovered that the composites preserve mechanical integrity on heating up to temperatures much higher than the polyethylene melting point. It is concluded that thermo-mechanical behaviour of the composites is determined by the space-continuous phase of polyaniline on the surface and in the bulk of polyethylene support.     

Biocompatible hydrogels based on chitosan,cellulose/starch,PVA and PEDOT:PSS with high flexibility and high mechanical strength

Fabricating mechanically strong hydrogels that can withstand the conditions in internal tissues is a challenging task. We have designed hydrogels based on multicomponent systems by combining chitosan, starch/cellulose, PVA, and PEDOT:PSS via one-pot synthesis. The starch-based hydrogels were homogeneous, while the cellulose-based hydrogels showed the presence of cellulose micro- and nanofibers. The cellulose-based hydrogels demonstrated a swelling ratio between 121 and 156%, while the starch-based hydrogels showed higher values, from 234 to 280%. Tensile tests indicated that the presence of starch in the hydrogels provided high flexibility (strain at break?>?300%), while combination with cellulose led to the formation of stiffer hydrogels (elastic moduli 3.9–6.6 MPa). The ultimate tensile strength for both types of hydrogels was similar (2.8–3.9 MPa). The adhesion and growth of human osteoblast-like SAOS-2 cells was higher on hydrogels with cellulose than on hydrogels with starch, and was higher on hydrogels with PEDOT:PSS than on hydrogels without this polymer. The metabolic activity of cells cultivated for 3 days in the hydrogel infusions indicated that no acutely toxic compounds were released. This is promising for further possible applications of these hydrogels in tissue engineering or in wound dressings.

Graphical abstract

     

Large continuous, transparent and oriented self-supporting films of layered double hydroxides with tunable chemical composition

Highly ordered transparent self-supporting films of layered double hydroxides (LDHs) with a size of the order of cm2 have been obtained by a simple method; the chemical composition of both the layers and interlayers can be readily tuned, as demonstrated by the preparation of [ZnAl-NO3] LDH, [NiAl-NO3] LDH and [Tb(EDTA)]- intercalated-ZnAl LDH films.     

Biocompatible agar/xanthan gum composite films: Thermal,mechanical, UV,and water barrier properties

Binary composite films were prepared from agar (A) and xanthan gum (X) with different weight percentages. The composite films were transparent, lightweight, eco‐friendly, and biodegradable. The structure and morphology of the prepared agar and AX composite films were confirmed by Fourier transform infrared spectroscopy (FT‐IR), X‐ray powder diffraction (XRD), and scanning electron microscopy (SEM) technique. The glass transition temperature (T_g) and melting temperature (T_m) of the AX composite films was slightly improved, when compared with the neat agar. Thermogravimetric analysis (TGA) analysis showed a considerable increment in the char yield and an improved thermal stability. The tensile strength was in the range of 25 to 40 MPa, and elongation at break was in the range of 28.9 to 39.4%. Though, the water vapor permeability (WVP) value reduced in the composite films the difference was not significant. From the mechanical studies, we can deduce that agar and xanthan gum are compatible and miscible with one another leading to prospects of their composite films being considered for different biomedical and packaging applications.     

Soluble and transparent polyimides with high Tg from a new diamine containing tert‐butyl and fluorene units

A novel diamine monomer 1 , 4,4'‐(9H‐fluorene‐9,9‐diyl)‐bis(2‐tert‐butylaniline), was synthesized from 9‐fluorenone and 2‐tert‐butylaniline by the condensation reaction. Then it was polymerized with several commercial aromatic dianhydrides, respectively, to produce polyimides (PIs) by the one‐pot method. The number‐averaged molecular weights of the resulting PIs are in the range of (4.54–8.82) × 10⁴ with polydispersity indices from 2.51 to 4.33 by gel permeation chromatography measurement. They are soluble in many organic solvents and can form transparent and tough films by solution‐casting. The cut‐off wavelengths of UV–vis absorption for the PI films are below 360 nm, which are much lower than that of Kapton film. The light transparency of them is above 90% in the visible light range from 400 to 760 nm. They also display relatively low dielectric constants (from 2.79 to 3.00), low water absorption rates (<1%), and high tensile strength (> 50 MPa). Their excellent solubility and transparency can be attributed to the incorporation of tert‐butyl groups and fluorene units into the rigid backbones of PIs. Simultaneously, they still maintain the high thermal stability (the 5% weight loss temperature in the range from 526 to 539 °C in nitrogen) and the high glass transition temperatures (T_g > 340 °C). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 976–984