Organic Inorganic Hybrid Coatings Research Articles

Silica- and germania-based dual-ligand sol-gel organic-inorganic hybrid sorbents combining superhydrophobicity and π-π interaction. The role of inorganic substrate in sol-gel capillary microextraction

Principles of sol-gel chemistry were utilized to create silica- and germania-based dual-ligand surface-bonded sol-gel coatings providing enhanced performance in capillary microextraction (CME) through a combination of ligand superhydrophobicity and π-π interaction. These organic-inorganic hybrid coatings were prepared using sol-gel precursors with bonded perfluorododecyl (PF-C12) and phenethyl (PhE) ligands. Here, the ability of the PF-C12 ligand to provide enhanced hydrophobic interaction was advantageously combined with π-π interaction capability of the PhE moiety to attain the desired sorbent performance in CME. The effect of the inorganic sorbent component on microextraction performance of was explored by comparing microextraction characteristics of silica- and germania-based sol-gel sorbents. The germania–based dual-ligand sol-gel sorbent demonstrated superior CME performance compared to its silica-based counterpart. Thermogravimetric analysis (TGA) of the created silica- and germania-based dual-ligand sol-gel sorbents suggested higher carbon loading on the germania-based sorbent. This might be indicative of more effective condensation of the organic ligand-bearing sol-gel-active chemical species to the germania-based sol-gel network (than to its silica-based counterpart) evolving in the sol solution. The type and concentration of the organic ligands were varied in the sol-gel sorbents to fine-tune extraction selectivity toward different classes of analytes. Specific extraction (SE) values were used for an objective comparison of the prepared sol-gel CME sorbents. The sorbents with higher content of PF-C12 showed remarkable affinity for aliphatic hydrocarbons. Compared to their single-ligand sol-gel counterparts, the dual-ligand sol-gel coatings demonstrated significantly superior CME performance in the extraction of alkylbenzenes, providing up to ∼65.0% higher SE values. The prepared sol-gel CME coatings provided low ng L−1 limit of detections (LOD) (4.2–26.3 ng L−1) for environmentally important analytes including polycyclic aromatic hydrocarbons, ketones and aliphatic hydrocarbons. In CME-GC experiments (n = 5), the capillary-to-capillary RSD value was ∼2.1%; such a low RSD value is indicative of excellent reproducibility of the sol-gel method used for the preparation of these CME coatings. The dual-ligand sol-gel coating provided stable performance in capillary microextraction of analytes from saline samples.

Investigation of Coating Performance of UV-Curable Hybrid Polymers Containing 1H,1H,2H,2H-Perfluorooctyltriethoxysilane Coated on Aluminum Substrates

This study describes preparation and characterization of fluorine-containing organic-inorganic hybrid coatings. The organic part consists of bisphenol-A glycerolate (1 glycerol/phenol) diacrylate resin and 1,6-hexanediol diacrylate reactive diluent. The inorganically rich part comprises trimethoxysilane-terminated urethane, 1H,1H,2H,2H-perfluorooctyltriethoxysilane, 3-(trimethoxysilyl) propyl methacrylate and sol–gel precursors that are products of hydrolysis and condensation reactions. Bisphenol-A glycerolate (1 glycerol/phenol) diacrylate resin was added to the inorganic part in predetermined amounts. The resultant mixture was utilized in the preparation of free films as well as coatings on aluminum substrates. Thermal and mechanical tests such as DSC, thermo-gravimetric analysis (TGA), and tensile and shore D hardness tests were performed on free films. Water contact angle, gloss, Taber abrasion test, cross-cut and tubular impact tests were conducted on the coated samples. SEM examination and EDS analysis was performed on the fractured surfaces of free films. The hybrid coatings on the aluminum sheets gave rise to properties such as moderately glossed surface; low wear rate and hydrophobicity. Tensile strength of free films increased with up to 10% inorganic content in the hybrid structure and this increase was approximately three times that of the control sample. As expected; the % strain value decreased by 17.3 with the increase in inorganic content and elastic modulus values increased by a factor of approximately 6. Resistance to ketone-based solvents was proven and an increase in hardness was observed as the ratio of the inorganic part increased. Samples which contain 10% sol–gel content were observed to provide optimal properties.

Improvement of the Surface Properties of Polystyrene Sheets via UV Curable Organic-Inorganic Hybrid Coatings

Improvement of the Surface Properties of Polystyrene Sheets via UV Curable Organic-Inorganic Hybrid Coatings

Durable and Hydrophobic Organic-Inorganic Hybrid Coatings via Fluoride Rearrangement of Phenyl T12 Silsesquioxane and Siloxanes.

There have been many successful efforts to enhance the water shedding properties of hydrophobic and superhydrophobic coatings, but durability is often a secondary concern. Here, we describe durable and hydrophobic coatings prepared via fluoride catalyzed rearrangement reaction of dodecaphenylsilsesquioxane [PhSiO1.5]12 (DDPS) with octamethylcyclotetrasiloxane (D4). Hydrophobic properties and wear resistance are maximized by incorporating both low surface energy moieties and cross-linkable moieties into the siloxane network. Water contact angles as high as 150 ± 4° were achieved even after 150 wear cycles with SiC sandpaper (2000 grit, 2 kPa). These hybrid organic-inorganic copolymers also have high thermal stabilities after curing at 250 °C (Td5% ≥ 340 °C in air) due to the siloxane network with a maximum Td5% of >460 °C measured for the system with the highest silsesquioxane content. The coating systems presented here offer a unique combination of hydrophobicity and mechanical/thermal stability and could greatly expand the utility of water repellent coatings.

Improving photostability and efficiency of polymeric luminescent solar concentrators by PMMA/MgO nanohybrid coatings

ABSTRACTMgO nanocrystals were synthesized and doped with different concentrations in poly(methylmethacrylate) (PMMA) to prepare hybrid organic-inorganic coatings based on polymer nanohybrid thin films. The nanoparticles were found to be spherical with 62 nm diameter as determined by X-ray diffraction (XRD) and atomic force microscope (AFM). The coatings were characterized by spectroscopic tools such as optical absorption, transmission and fluorescence spectroscopy. The prepared nanohybrid films were spin-coated on cost-effective luminescent PMMA substrates doped with highly efficient luminescent dyes luminescent solar concentrators (LSCs). The outdoor photostability tests demonstrated enhanced protection against UVA radiation for coated LSCs compared to bare LSC substrates. The current–voltage characteristics of commercially produced LSC prototypes showed that the poor UV response of monocrystalline silicon solar cell can be improved by for LSCs coated by PMMA/MgO nanohybrid films which act as luminescent down shifting layer (LDSL).

PEG‐based organic–inorganic hybrid coatings prepared by the sol–gel dip‐coating process for biomedical applications

In the present work, the application of functional coatings on metallic implants was proposed to delay implant failure by improving tissue tolerance and implant osseointegration. Three bioactive and biocompatible organic–inorganic hybrid nanocomposites, consisting of polyethylene glycol (PEG) embedded in a SiO2, ZrO2, and TiO2 matrix, respectively, were synthesized via the sol–gel method. Materials in the sol phase were used to dip‐coat titanium grade 4 substrates for use as dental and orthopedic implant models. To investigate the influence of the glass matrix and the polymer amount on the coating structure, and thus on their biological properties, several hybrids were obtained by adding different weight percentages of PEG to each glass matrix. Attenuated total reflectance Fourier transform infrared spectroscopy confirmed the presence of the polymer in the nanocomposites and scanning electron microscopy showed that an increase in the PEG content allows crack‐free coatings to be obtained. Moreover, the bioactivity and biocompatibility of both the uncoated and coated titanium implants were investigated and compared by an in vitro test. The results revealed that coated substrates have more enhanced biological performance than the uncoated ones. The bioactivity is not significantly affected by either the inorganic matrix or the PEG amount, whereas the presence of polymer makes the films more biocompatible. POLYM. ENG. SCI., 57:478–484, 2017. © 2017 Society of Plastics Engineers

Modification of Ti6Al4V implant surfaces by biocompatible TiO2/PCL hybrid layers prepared via sol-gel dip coating: Structural characterization, mechanical and corrosion behavior

Surface modification of metallic implants is a promising strategy to improve tissue tolerance, osseointegration and corrosion resistance of them. In the present work, bioactive and biocompatible organic-inorganic hybrid coatings were prepared using a sol-gel dip coating route. They consist of an inorganic TiO2 matrix in which different percentages of poly(ε-caprolactone) (PCL), a biodegradable and biocompatible polymer, were incorporated. The coatings were used to modify the surface of Ti6Al4V substrates in order to improve their wear and corrosion resistance. The chemical structure of the coatings was analyzed by attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy. Coating microstructure, mechanical properties and ability to inhibit the corrosion of the substrates were evaluated as a function of the PCL amount.Scanning electron microscopy (SEM) showed that the polymer allows to obtain crack-free coatings, but when high percentages were added uncoated areas appear. Nano-indentation tests revealed that, as expected, surface hardness and elastic modulus decrease as the percentage of polymeric matrix increases, but scratch testing demonstrated that the coatings are effective in preventing scratching of the underlying metallic substrate, at least for PCL contents up to 20wt%.The electrochemical tests (polarization curves acquired in order to evaluate the corrosion resistance) allowed to asses that the coatings have a significant effect in term of corrosion potential (Ecorr) but they do not significantly affect the passivation process that titanium undergoes in contact with the test solution used (modified Dulbecco's phosphate-buffered saline or DPBS).

Investigation of vacuum deposited hybrid coatings of protic organic UV absorbers embedded in a silica matrix used for the UV protection of Polycarbonate glazing

A study of vacuum-deposited organic–inorganic hybrid coatings for UV protection of polycarbonate is presented. UV-absorbing compounds, which are commonly used for polycarbonate, were embedded in a silica matrix by thermal co-evaporation under high vacuum. In addition to the optical properties of the coatings, the influence of the silica network on the organic UV absorber and the stability of the intramolecular hydrogen bond (IMHB) are discussed. A model is presented to show the interaction between the organic compound and the silica matrix. It could be shown with UV irradiation experiments that the hydroxyphenyltriazine compound exhibits higher UV stability in the hybrid coating than the hydroxybenzotriazoles.

Corrosion behaviour of hybrid sol-gel coated steel embedded in carbonated Portland and fly ash mortars contaminated with chlorides

The protection of metals from their surrounding environment is usually achieved by deposition of protective coatings on the metal surface to establish a physical barrier against aggressive ions. The corrosion behaviour of hybrid organic–inorganic coatings for carbon steel embedded in carbonated ordinary Portland cement (OPC) and alkali activated fly ash (AAFA) mortars was studied, after different periods of immersion in a 3 wt.% sodium chloride solution using electrochemical techniques. Hybrid organic–inorganic films employed as protective coatings have been prepared via sol–gel using several silicon compounds: 3-methacryloxy-propyltrimethoxysilane or methyltriethoxysilane (MTES) and tetraethyl orthosilicate (TEOS) or tetramethyl orthosilicate (TMOS) precursors using a molar ratio of 1 and deposited on carbon steel substrates by dip-coating. The corrosion potential (Ecorr) values were higher and the current density (icorr) values were lower for AAFA mortars, indicating that the coatings were more efficient against rebar corrosion in this system than in OPC mortars. On the other hand, the hybrids synthesised with TEOS/MTES and TMOS/MTES for carbon steel embedded in carbonated AAFA mortars showed the lowest icorr values. This enhanced protection could be due to a structure denser and more compact and greater adhesion to the metallic surface.

Nonhydrolytic sol-gel approach to facile creation of surface-bonded zirconia organic-inorganic hybrid coatings for sample preparation. Ι. Capillary microextraction of catecholamine neurotransmitters

Nonhydrolytic sol-gel (NHSG) route was used for the creation of novel zirconia-polypropylene oxide (ZrO2-PPO) sol-gel hybrid sorbents in the form of surface coatings for the extraction and preconcentration of catecholamine neurotransmitters and molecules structurally related to their deaminated metabolites. In comparison to other sorbents made of inorganic transition metal oxides, the presented hybrid organic-inorganic sorbents facilitated reversible sorption properties that allowed for efficient desorption of the extracted analytes by LC–MS compatible mobile phases. The presented sol-gel hybrid sorbents effectively overcame the major drawbacks of traditional silica- or polymer-based sorbents by providing superior pH stability (pH range: 0–14), and a variety of intermolecular interactions. Nonaqueous sol-gel treatment of PPO with ZrCl4 was employed for the derivatization of the terminal hydroxyl groups on PPO, providing zirconium trichloride-containing end groups characterized by enhanced sol-gel reactivity. NHSG ZrO2-PPO sorbent provided excellent microextraction performance for catecholamines, low detection limits (5.6–9.6pM), high run-to-run reproducibility (RSD 0.6–5.1%), high desorption efficiency (95.0–99.5%) and high enrichment factors (∼1480–2650) for dopamine and epinephrine, respectively, extracted from synthetic urine samples. The presented sol-gel sorbents provided effective alternative to conventional extraction media providing unique physicochemical characteristics and excellent extraction capability.

EFFECT OF INHIBITOR AGENTS ADDITION ON CORROSION RESISTANCE PERFORMANCE OF TITANIA SOL–GEL COATINGS APPLIED ON 304 STAINLESS STEEL

Hybrid organic–inorganic coatings are deposited on 304 stainless steel substrates by the sol–gel technique to improve the corrosion resistance. A titania-based nanostructured hybrid sol–gel coating is impregnated with three different microencapsulated healing agents (inhibitors) including cerium, Benzotriazole (BTA), and 8-Hydroxyquinoline (8H). Field-emission scanning electron microscopy (FE-SEM) and electrochemical impedance spectroscopy (EIS) are performed to investigate the barrier performance properties. The optimum conditions to achieve corrosion protective coatings for 304 stainless steel were determined. The Nyquist plots demonstrate that the activation time of the coating containing 8H as an organic healing agent shows improved behavior when compared to other coatings including cerium and BTA. Cerium as an inorganic healing agent is second and BTA is third and minimum. An increase in the impedance parameters such as resistance and capacitance as a function of immersion time is achieved in a 3.5[Formula: see text]wt.% NaCl solution by using healing agents such as BTA. Actually, over the course of immersion, the barrier performance behavior of the coatings changes and reduction of the impedance observed from the coatings containing Ce and 8H discloses deterioration of the protection system after immersion for 96[Formula: see text]h of immersion in the 3.5% NaCl solution. However, after 96[Formula: see text]h of immersion time, the concentration of chloride ions is high and causes increase in defects, micro cracks, hole on the surface of hybrid titania nanostructured coating containing Ce and 8H by destruction of coating, and also hybrid titania nanostructured coating containing BTA; BTA is released from coating to improve the resistance of passive film, which is created on the surface.

Sol-Gel TiO2 and ZrO2-Nanocomposite Thin Films for Enhancing in Vitro Biocompatibility and Bio-Corrosion Resistance of Ti6Al4V Orthopaedic Implants

The aim of this work has been to study the effect of TiO2 and ZrO2-silane sol-gel coatings on the corrosion resistance and biocompatibility of Ti6Al4V biomedical alloys. The sol used for coating was an aqueous solution containing 3-methacryloxypropyltrimethoxysilane (MAPTMS), tetramethoxysilane (TMOS) and titanium tetrabutoxide (TBT) or zirconium tetrabutoxide (ZBT). A system without tetrabutoxides was used as reference. The effect of the addition of different amounts of TiO2 or ZrO2 precursors on the thermal stability of the prepared organic-inorganic hybrids was investigated by using thermal analysis (TG/DTG). Structural characterization of the coatings was carried out using Attenuated Total Reflectance Fourier Transformer Infrared Spectroscopy (ATR-FTIR). Contact angle measurements were used to study the hydrophilicity of the coatings. The thickness of the resulting sol-gel coatings was measured by using a profilometer. Scanning Electron Microscopy coupled with Energy Dispersive X-ray (SEM/EDX) were applied to study the surface morphology and composition of the MAPTMS/TMOS/TiO2 and MAPTMS/TMOS/ZrO2 coatings. Global and Local electrochemical Impedance Spectroscopies (EIS and LEIS) and potentiodynamic polarization measurements during immersion in Dulbecco’s Phosphate Buffered Saline with MgCl2 and CaCl2 (PBS) were carried out to evaluate the barrier properties on the coatings. In vitro bioactivity was assessed by soaking the nanocomposite coatings at 36.5ºC up to 14 days in the Kokubo’s simulated body fluid (SBF; pH 7.4). After applying the soaking tests the samples were removed from the SBF, rinsed with ddH2O and dried at room temperature and submitted to analysis by XRD, SEM and EDX. In parallel studies the biocompatibility of these sol-gel coatings has been evaluated. In this way protein adsorption was studied using fibrinogen as a representative protein. Adsorbed protein was determined by applying the Bradford method and ATR-FTIR after immersion the sol-gel thin films in fibrinogen. In summary SEM observations of these coatings showed the formation of a uniform, homogeneous, crack free and highly adherent protective film on the substrates. The electrochemical techniques indicated that the incorporation of TiO2 and ZrO2 nanoparticles in the MAPTMS-TMOS matrix improved the corrosion protection properties of the organic-inorganic hybrid coatings. SEM/EDX analyses showed bone-like precipitates after 14 days of immersion in SBF. XRD detected trace amounts of Ca and P in these precipitates but it was not possible to determine conclusively their nature. The in vitro biocompatibility studies confirmed that these sol-gel thin films can be good candidates to develop coatings for Ti6Al4V orthopaedic implants. Acknowledges: This work was supported by the Ministry of Economy and Competitiveness of Spain (Projects MAT2012-38541-C02-02, MAT2012-30854 and MAT2015-65445-C2-1-R).

Corrosion protection of aluminum alloy substrate with nano-silica reinforced organic–inorganic hybrid coatings

Organic–inorganic hybrid (OIH) thin films derived from the sol–gel process have emerged as sustainable metal pretreatment alternatives to toxic heavy metal-based systems. In recent years, such OIH systems based on Si, Zr, and Ti have been successfully developed and commercialized for pretreatment of aluminum alloys, galvanized steel, cold-rolled steel, and many other metals and alloys, for improving adhesion and corrosion resistance performance. A variety of approaches are being used to further enhance performance of such OIH systems to match or surpass that obtained from chromate-based systems. In the present study, a novel bis-silane compound has been synthesized and used as a primary sol–gel precursor for OIH coatings. In order to further improve their mechanical and corrosion resistance performance, colloidal nanoparticles have been incorporated. The microstructure of the deposited films as a function of their composition and formation of Si–O–Si structural network has been studied by Confocal Raman spectroscopic technique. The chemical structure of the OIH films has been characterized by FTIR analysis. Electrochemical impedance spectroscopy, DC polarization measurements, and accelerated neutral salt-fog test (ASTM B117) have been used to evaluate corrosion resistance performance of coatings on industrial aluminum alloy AA 3003 H14. Nano-indentation tests of these OIH films have been performed to study the effect of colloidal nanoparticles on coating micro/nano structure and their mechanical properties. The study reveals that colloidal nanoparticles improve the corrosion resistance of OIH coatings by formation of a protective barrier to diffusion of corrosive species to the metal surface. The optimum content of colloidal nanoparticles that can provide best corrosion protection has been determined. Electrochemical study provides useful insight into the significance of interaction between the sol–gel hybrid and silica particles in the corrosion protection mechanism.

Increased bending rigidity of wool fabric imparted by hybrid organic-inorganic sol–gel coatings

Hybrid organic–inorganic coatings prepared by the sol–gel method can impart desirable properties to textiles, but may adversely affect properties such as bending rigidity. This study investigated the causes of increased bending rigidity. Woven wool fabric was pad coated with formulations of methyltriethoxysilane (MTES) and Hercosett polyamide resin, examined by scanning electron microscopy, and the bending rigidities were determined. MTES coatings of up to 3.0% solids on mass of wool did not impart unacceptable bending rigidity. The coatings were not uniform on the fiber surfaces, and the increases in fabric bending rigidity could be partially attributed to inter-fiber bonding. In addition, the coatings “pinned” the edges of the cuticle scales, making individual fibers harder to bend. These effects are only weakly dependent on the Young's moduli of the coating materials.

Water-Based Organic–Inorganic Hybrid Coating for a High-Performance Separator

With the development of electric vehicles, the traditional polyolefin separators can not meet the increasing requirements of lithium ion batteries with high power density, high energy density, and high safety performance. Herein, a novel water-based binder is synthesized by grafting carboxyl groups onto cellulose diacetate. When the polyethylene (PE) separator is coated by this binder and SiO2 nanoparticles, the thermal shrinkage of the modified separator is observed to be almost 0% after exposure at 200 °C for 30 min. The puncture strength significantly increase from 5.10 MPa (PE separator) to 7.64 MPa. More importantly, the capacity retention of the cells assembled with modified separators after 100 cycles at 0.5 C increase from 73.3% (cells assembled with PE separator) to 81.6%, owing to the excellent electrolyte uptake and the good compatibility with lithium electrode. Besides, the modified separator shows excellent surface stability after 100 cycles. Considering the above excellent properties, this c...

Sol-gel hybrid coatings containing silica and a perfluoropolyether derivative with high resistance and anti-fouling properties in liquid media

Abstract Organic inorganic hybrid coatings were prepared using a commercial triethoxysilane α,ω substituted perfluoropolyether as organic phase in combination with tetraethyl orthosilicate (TEOS) as inorganic phase. The coatings were prepared by sol-gel synthesis of a silica coating in co-presence with the commercial polymer, and deposited on stainless steel substrates by dip-coating procedure. The interactions between the organic and the inorganic components were studied by means of X-ray photoelectron spectroscopy. The synergistic effect of the two opposite phases permitted to obtain hydrophobic coatings (contact angle CA of ∼140°) with high resistance against thermal or mechanical stresses induced in liquid media. The hybrid coatings thus obtained to possess suitable properties for application as anti-fouling coatings in liquid environments. Specific tests performed in particulate fouling conditions confirmed the ability of the hybrid coatings to mitigate CaSO 4 deposits formation, maintaining unaltered the CA value after exposition for 43 days to a flux of a CaSO 4 solution at a flowrate of 0.15 m/s.

Enhancing the thermo‐oxidative stability of PLA through the use of hybrid organic–inorganic coatings

ABSTRACTPLA samples have been coated with organic–inorganic hybrid films containing SiO2 as inorganic phase and two different types of organic phase PEO or PCL. Sol–gel solutions, spin coating deposition, and mild thermal treatments have been used to form thin protective coatings. Coated and uncoated PLA samples have been submitted to accelerated thermo‐oxidative stresses at 120 °C in air up to about 400 h. The extent of the damage induced by this treatment has been evaluated by different techniques. Coated samples of both compositions are able to increase the resistance to thermo‐oxidation of PLA as proved by the smaller reduction of molecular weight. This effect is probably deriving from the reduced oxygen permeability, as well as from the constrained outward diffusion and recombination of the cyclic oligomers produced by intramolecular transesterification reactions of polyester chains. Data so far collected underline also a long‐term stability and adherence of the hybrid coatings during the entire aging process and hint at the possibility of using PLA in more demanding applications than that of packaging (i.e., electric industry, automotive field, or housewares). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43897.

Corrosion behaviour of coated steel rebars in carbonated and chloride-contaminated alkali-activated fly ash mortar

The corrosion behaviour of hybrid organic-inorganic coatings applied on carbon steel embedded in carbonated ordinary Portland cement (OPC) and alkali-activated fly ash (AAFA) mortars and immersed in a 3 wt.% NaCl solution was evaluated using electrochemical methods. The sol-gel coatings were prepared by condensation and polymerization of TEOS/MPTS, TEOS/MTES, TMOS/MPTS and TMOS/MTES mixtures with a molar ratio of 1.0 and deposited by dip-coating on the carbon steel substrates. The coated steels embedded in AAFA mortar presented higher corrosion potential and lower corrosion current density values than those embedded in OPC mortar, indicating that the coatings were more efficient in preventing corrosion of the rebars in this environment. Hybrid coatings synthesized with TEOS/MTES and TMOS/MTES mixtures showed the longest permanence of steel in the passive state when covering rebars embedded in carbonated AAFA mortar. This enhancement of protection may be due to the denser and more compact structure of sol-gel coatings and their greater adhesion to the metallic surface. The study also considered uncoated steel specimens embedded in OPC and AAFA mortars for comparative purposes.

Coatings to prevent frost

The ability of hydrophobic, organic–inorganic hybrid coatings to decelerate frost propagation was investigated. Compared to a bare aluminum surface, the coatings do not significantly reduce the freezing probability of supercooled water drops. On both surfaces, the probability for ice nucleation at temperatures just below 0°C, for example at −4°C, is low. Freezing of a single drop on aluminum leads, however, to instant freezing of the complete surface. On hydrophobic coatings, such a freezing drop is isolated; the frozen area grows slowly. At −4°C surface temperature in a +12°C/90% relative humidity environment, on surfaces providing a water contact angle hysteresis of about 10° and receding water contact angles higher than 90°, a rate for the growth of the average radius of the frozen area of about 2 µm/s was observed. Submitting the surface to an airflow of 1 m/s led to faster frost spreading in flow direction. Although the airflow compromised the anti-ice properties to some extent, the application of the hydrophobic coating in a heat recovery ventilation experiment extended the time interval between defrosting cycles by a factor of 2.3.

Hybrid Organic/Inorganic Coatings Through Dual-Cure Processes: State of the Art and Perspectives

This paper reviews the current state of the art related to the synthesis and characterization of hybrid organic-inorganic (O/I) coatings obtained through the exploitation of dual-cure processes, which involve a photo-induced polymerization followed by a thermal treatment: this latter allows the occurrence of sol-gel reactions of suitable alkoxy precursors already embedded in the UV-curable system. After a brief introduction on hybrid organic-inorganic coatings, the first part of the review is focused on the design and feasibility issues provided by the dual-cure method, emphasizing the possibility of tuning the structure of the final hybrid network on the basis of the composition of the starting liquid mixture. Then, some recent examples of hybrid organic-inorganic networks are thoroughly described, showing their potential advances and the application fields to which they can be addressed.