TiO2 nanotubes and mesoporous silica as containers in self-healing epoxy coatings

The potential of inorganic nanomaterials as reservoirs for healing agents is presented here. Mesoporous silica (SBA-15) and TiO2 nanotubes (TNTs) were synthesized. Both epoxy-encapsulated TiO2 nanotubes and amine-immobilized mesoporous silica were incorporated into epoxy and subsequently coated on a carbon steel substrate. The encapsulated TiO2 nanotubes was quantitatively estimated using a ‘dead pore ratio’ calculation. The morphology of the composite coating was studied in detail using transmission electron microscopic (TEM) analysis. The self-healing ability of the coating was monitored using electrochemical impedance spectroscopy (EIS); the coating recovered 57% of its anticorrosive property in 5 days. The self-healing of the scratch on the coating was monitored using Scanning Electron Microscopy (SEM). The results confirmed that the epoxy pre-polymer was slowly released into the crack. The released epoxy pre-polymer came into contact with the amine immobilized in mesoporous silica and cross-linked to heal the scratch.This paper was made possible by PDRA grant # PDRA1-1216-13014 from the Qatar National Research Fund (a member of Qatar Foundation)

Inorganic Porous Materials Based Epoxy Self-Healing Coatings

The long-term stability of protective coating for metal is critically important for structural applications [1, 2]. Self-healing ability extend the service life of protective coatings leading to a significant reduction in maintenance cost for oil and gas pipe lines and structural parts in civil and construction industry. Recently, the self-healing technology based on healing agent loaded containers has been receiving attention [3, 4]. The incorporation of self- healing agent loaded containers into polymer matrix can be carried out using existing blending techniques. Hence, this technology facilitate large-scale application of self-healing materials [5]. Different micro or nano containers has been used for the storage and release of self-healing agents upon specific corrosion triggering conditions (e.g. on pH change) or upon mechanical damage [6]. Polymer capsules, polymer nanofibers, hollow glass bubbles, hollow glass fibers etc. were used by the researchers to load the healing agent inside their cavity. The inorganic particles with nano cavity offers large surface area, high pore volume and good stability favorable for the storage of the healing agents. Moreover, the usage of inorganic nanomaterials as reservoirs for healing agent can eliminate the tedious encapsulation process. The present study aims to use inorganic nanotubes and mesoporous silica as containers for healing agents in epoxy coating. The ability of Halloysite nanotubes (HNT), titanium dioxide (TiO2) nanotube and mesoporous silica to load and release the healing agents are investigated and compared their performance. Among them, Halloysite nanotubes are naturally occurring clay mineral. Meanwhile, TiO2 nanotube and mesoporous silica are synthesised in laboratory and characterised using scanning electron microscopic (SEM), transmission electron microscopic (TEM) techniques and Brunauer-Emmett-Teller (BET) surface area analysis. The morphology of the nanotubes and mesoporous silica are shown in Fig. 1 (in supporting file). In this study, the epoxy pre-polymer and hardener are used as healing agents. Containers loaded with epoxy and hardener can provide a repair system with matching chemical entity with host epoxy coating. Both epoxy encapsulated nanotubes (either Halloysite or TiO2 nanotubes) and amine immobilized mesoporous silica are incorporated into epoxy, followed by the addition of diethylenetriamine curing agent. The mixture is coated on the metal with an average thickness of 300 ?m. The controlled epoxy coatings are also prepared without nanotube and mesoporous silica. Epoxy coating loaded with encapsulated Halloysite nanotubes and immobilized mesoporous silica is abbreviated as 'EP/HNT/SiO2' and the one loaded with encapsulated TiO2 nanotubes and immobilized mesoporous silica is abbreviated as 'EP/ TiO2/SiO2'. The self-healing ability of the scratched coatings is monitored by electrochemical impedance spectroscopy (EIS) in definite time intervals for 5 days. Both EIS bode plots and tafel polarization curves are analysed to observe the self-healing ability of the coatings. For the scratched controlled epoxy coating, after an immersion time of 24 hours, the impedance curve drop to its minimum value over the entire frequency range and on further immersion period the impedance curve remains its minimum value. However, in the case of self-healing coatings, the initially declined impedance value recovers in successive days. The recovery in low frequency impedance values (at 0.01 Hz), which is a direct reflection of the recovery of corrosion resistance of the coating are evaluated. While EP/TiO2/SiO2 coating recovered 57% of its anticorrosive property, the EP/HNT/SiO2 coating recovered only 0.026%. This results suggest that the nature of the nanotubes affect the amount and rate of healing agent released into the scratched area from the tube lumen which itself affect the self-healing ability of the coating. SEM is also used to observe the healed scratches on the coatings. After 96 hours of immersion in 3.5 wt% NaCl solution, the scratches in EP/TiO2/SiO2 self-healing coatings are found to be almost covered. The results confirm the effective self-healing ability of the EP/TiO2/SiO2 coating in which the released epoxy pre-polymer from nanotube lumen get contact with the amine hardener immobilized in mesoporous silica and cross-link to cover the scratch. Acknowledgment: This abstract was made possible by PDRA grant # PDRA1-1216-13014 from the Qatar national research fund (a member of Qatar foundation).qscienc

Flexible pressure sensor based on PVDF nanocomposites containing reduced graphene oxide-titania hybrid nanolayers

A novel flexible nanocomposite pressure sensor with a tensile strength of about 47 MPa is fabricated in this work. Nanolayers of titanium dioxide (titania nanolayers, TNL) synthesized by hydrothermal method are used to reinforce the polyvinylidene fluoride (PVDF) by simple solution mixing. A hybrid composite is prepared by incorporating the TNL (2.5 wt %) with reduced graphene oxide (rGO) (2.5 wt %) synthesized by improved graphene oxide synthesis to form a PVDF/rGO-TNL composite. A comparison between PVDF, PVDF/rGO (5 wt %), PVDF/TNL (5 wt %) and PVDF/rGO-TNL (total additives 5 wt %) samples are analyzed for their sensing, thermal and dielectric characteristics. The new shape of additives (with sharp morphology), good interaction and well distributed hybrid additives in the matrix increased the sensitivity by 333.46% at 5 kPa, 200.7% at 10.7 kPa and 246.7% at 17.6 kPa compared to the individual PVDF composite of TNL, confirming its possible application in fabricating low cost and light weight pressure sensing devices and electronic devices with reduced quantity of metal oxides. Increase in the β crystallinity percentage and removal of α phase for PVDF was detected for the hybrid composite and linked to the improvement in the mechanical properties. Tensile strength for the hybrid composite (46.91 MPa) was 115% higher than that of the neat polymer matrix. Improvement in the wettability and less roughness in the hybrid composites were observed, which can prevent fouling, a major disadvantage in many sensor applications.Scopu

Sugarcane Bagasse-Derived Activated Carbon- (AC-) Epoxy Vitrimer Biocomposite: Thermomechanical and Self-Healing Performance

Vitrimeric materials have emerged as fascinating and sustainable materials owing to their malleability, reprocessability, and recyclability. Sustainable vitrimeric materials can be prepared by reinforcing polymeric matrix with bioderived fillers. In the current work, a sustainable vitrimer is prepared by incorporating biomass-derived activated carbon (AC) filler into the epoxy matrix to achieve enhanced thermal and mechanical properties. Thus, prepared biocomposite vitrimers demonstrate a lower-temperature self-healing (70°C for 5 min) via disulfide exchanges, compared to the pristine epoxy vitrimers (80°C for 5 min). Significantly, the self-healing performances have been studied extensively with the flexural studies; and changes in material healing efficiency have been demonstrated based on the observed changes in modulus

Self-Repairing Composites for Corrosion Protection: A Review on Recent Strategies and Evaluation Methods

The use of self-healing coatings to protect metal substrates, such as aluminum alloys, stainless steel, carbon steel, and Mg alloys from corrosion is an important aspect for protecting metals and for the economy. During the past decade, extensive transformations on self-healing strategies were introduced in protective coatings, including the use of green components. Scientists used extracts of henna leaves, aloe vera, tobacco, etc. as corrosion inhibitors, and cellulose nanofibers, hallyosite nanotubes, etc. as healing agent containers. This review gives a concise description on the need for self-healing protective coatings for metal parts, the latest extrinsic self-healing strategies, and the techniques used to follow-up the self-healing process to control the corrosion of metal substrates. Common techniques, such as accelerated salt immersion test and electrochemical impedance spectroscopy (EIS), for evaluating the self-healing process in protective coatings are explained. We also show recent advancements procedures, such as scanning vibrating electrode technique (SVET) and scanning electrochemical microscopy (SECM), as successful techniques in evaluating the self-healing process in protective coatings

3D architectures of titania nanotubes and graphene with efficient nanosynergy for supercapacitors

One dimensional titanium dioxide nanotubes (titania nanotubes or TNT) are grown on the surface of two dimensional graphene sheets by hydrothermal method so that desirable out of plane properties are obtained in the final three dimensional composite structure. The graphene oxide (GO) was first synthesized from the graphite precursor following the improved graphene oxide synthesis method and the metal oxide nanotubes, through hydrothermal method. The morphology analysis of the hybrid nanostructure illustrates the growth of nanotubes of titania on and in between the reduced GO layers and the structural details are investigated by infrared spectroscopy, X-ray photoelectron spectroscopy and Brunauer, Emmett and Teller (BET) surface area measurements. The dielectric properties illustrate the significance of this particular graphene-titania composite in fabricating supercapacitors as it exhibited a dielectric constant of 6.4�?�106 which is about three times more than that of the TNT. The electrochemical experiments in terms of cyclic voltammetry, Nyquist plots and charge discharge measurements further substantiate the applicability of the rationally designed nanostructure in fabricating supercapacitors.This publication is made possible by NPRP grant 6-282-2-119 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors.Scopu

The role of clay modifier on cure characteristics and properties of epoxy/clay/carboxyl-terminated poly(butadiene-co-acrylonitrile) (CTBN) hybrid

Epoxy/clay/carboxyl-terminated poly(butadiene-co-acrylonitrile) (CTBN) hybrids were prepared with two different organically modified clays. Octadecyl amine and trimethyl stearyl ammonium-modified nanoclays (Nanomer I.30E and I.28E, respectively) were used. The dispersion of the nanoclay in binary epoxy/clay and epoxy/clay/CTBN hybrid nanocomposites was investigated using scanning electron microscopy and optical microscopy, and the observed morphological details were explained by the prediction of solubility parameter for each component in the nanocomposites. The effect of clay modifier on cure characteristics of binary epoxy/clay and epoxy/clay/CTBN hybrid nanocomposites was studied using rheological analysis. Glass transition temperatures (Tg) and thermal stability of binary and hybrid nanocomposites were also measured. The reduced cross-link density via epoxy homopolymerization, the plasticizing effect of clay modifier/dissolved liquid rubber and the interfacial adhesion between the polymer and the clay platelets were found to affect the Tg of epoxy/clay/CTBN hybrid. In epoxy/clay/CTBN hybrid, the thermal stability was mainly attributed to the presence of CTBN which hide the effect of clay modifiers.Scopu

Cellulose nanofibers to assist the release of healing agents in epoxy coatings

Epoxy monomer and amine curing agents were immobilized on cellulose nanofibers (CNF). Obtained epoxy immobilized CNF (EiCNF) and amine curing agent immobilized CNF (AiCNF) were characterized using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The mechanism and nature of interaction in EiCNF and AiCNF were elucidated. While chemical interaction was observed between amine curing agent and CNF, only physical interaction exists between epoxy monomer and CNF. Preliminary investigation of self-healing ability of epoxy coating incorporated in both EiCNF and AiCNF was carried out. The dual healing agents supported on CNF were effective in imparting self-healing ability to epoxy coatings. 1 2017 Elsevier B.V.This paper was made possible by PDRA grant # PDRA1-1216-13014 from the Qatar National Research Fund (a member of Qatar Foundation). The findings achieved herein are solely the responsibility of the authors.Scopu

Flexible Pressure Sensor Based on PVDF Nanocomposites Containing Reduced Graphene Oxide-Titania Hybrid Nanolayers

A novel flexible nanocomposite pressure sensor with a tensile strength of about 47 MPa is fabricated in this work. Nanolayers of titanium dioxide (titania nanolayers, TNL) synthesized by hydrothermal method are used to reinforce the polyvinylidene fluoride (PVDF) by simple solution mixing. A hybrid composite is prepared by incorporating the TNL (2.5 wt %) with reduced graphene oxide (rGO) (2.5 wt %) synthesized by improved graphene oxide synthesis to form a PVDF/rGO-TNL composite. A comparison between PVDF, PVDF/rGO (5 wt %), PVDF/TNL (5 wt %) and PVDF/rGO-TNL (total additives 5 wt %) samples are analyzed for their sensing, thermal and dielectric characteristics. The new shape of additives (with sharp morphology), good interaction and well distributed hybrid additives in the matrix increased the sensitivity by 333.46% at 5 kPa, 200.7% at 10.7 kPa and 246.7% at 17.6 kPa compared to the individual PVDF composite of TNL, confirming its possible application in fabricating low cost and light weight pressure sensing devices and electronic devices with reduced quantity of metal oxides. Increase in the β crystallinity percentage and removal of α phase for PVDF was detected for the hybrid composite and linked to the improvement in the mechanical properties. Tensile strength for the hybrid composite (46.91 MPa) was 115% higher than that of the neat polymer matrix. Improvement in the wettability and less roughness in the hybrid composites were observed, which can prevent fouling, a major disadvantage in many sensor applications