Gel Thin Films Research Articles

TiO2 sol–gel thin films: effect of acidic and basic pH on physical characteristics

TiO2 sol–gel thin films: effect of acidic and basic pH on physical characteristics

Confined Gel-Electromembrane Extraction of Oligonucleotides.

Gel-electromembrane extraction (G-EME) is an increasingly popular green variant of electromembrane extraction (EME). However, the electroendosmosis (EEO) flow associated with G-EME greatly limits the development of this technology. To address this challenge, the current study proposed the concept of confined G-EME (CG-EME), and a three-dimensional-printed modular device was elaborately designed to realize this concept. The device blocked the EEO flow by limiting the volume of the sample compartment. Moreover, the mesh structure at the bottom of the extraction module helps to prepare thin and stable gel films, which enhance the electromigration driving force and shorten the migration path. In addition, polar oligonucleotides, a nucleic acid analyte, were extracted for the first time to prove the concept of CG-EME. After optimization, 62% of the oligonucleotides were extracted at 50 V voltage for 15 min using a 3 mm thick agarose (3%) gel film. Finally, the application capability of CG-EME was further demonstrated by recovering DNA primers and isolating disease biomarkers (miRNA-181b) from real samples. In combination with CG-EME and quantitative polymerase chain reaction (qPCR) analysis, the upregulation of miRNA-181b expression in the peripheral blood of patients with schizophrenia was observed. In conclusion, this study proposes CG-EME to diminish EEO and push EME into the clinical field to isolate nucleic acid biomarkers, which will greatly expand the application scenarios of this emerging technology.

Imaging a solvent‐swollen polymer gel network by open liquid transmission electron microscopy

AbstractVisualizing the network of a solvent‐swollen polymer gel remains problematic. To address this challenge, open transmission electron microscopy (TEM) was applied to thin gel films permeated by a nonvolatile ionic liquid. The targeted physical gels were prepared by cooling concentrated solutions of poly(ethylene glycol) in 1‐ethyl‐3‐methyl imidazolium ethyl sulfate [EMIM][EtSO4]. During the cooling, gelation occurred by a frustrated crystallization of the dissolved polymer, leading to a percolated, solvent‐permeated semicrystalline network in which nanoscale polymer crystals acted as crosslinks. Crystalline features ranging from ~5 to ~200 nm were observed, with the visible network strands dominantly consisting of long curvilinear crystallites of ~15–20 nm diameter. Nascent spherulites irregularly decorated the network, creating a complex structural hierarchy that complicated analyses. Lacking diffraction contrast, TEM did not visualize the many disordered, fully solvated PEG chains present in the voids between crystals. Recognizing that a network's three dimensionality is ambiguous when assessed through two‐dimensional microscopy projections, a small gel region was studied by TEM tomography, revealing a nearly isotropic three‐dimensional arrangement of the curvilinear crystallites, which displayed remarkably uniform cylindrical cross sections.

The AA7075–CS1018 Galvanic Couple under Evaporating Droplets

The galvanic corrosion behavior of the AA7075–CS1018 couple was examined in dynamic electrolytes using the ZRA technique. A modified electrochemical setup was developed to support the use of thin-film gel and liquid electrolytes on metallic surfaces. This allowed the collection of chemical information, left behind by the liquid electrolyte during evaporation, through a thin-film gel. The analysis of the gel electrolyte film confirmed the acidification on AA7075 and the alkalinization on CS1018 but also offered novel insights on their dependence on the galvanic current. The galvanic current was proportional to the initial NaCl concentration in the range of 0.01 to 0.06 M. However, due to continuous evaporation, the NaCl concentration increased, limiting oxygen diffusion and decreasing the galvanic current, especially for electrolytes exceeding 0.06 M. The galvanic current was determined by considering the dynamic evolution (caused by the evaporation of the electrolyte film) of both the thickness of the electrolyte and its concentration.

Ce-doped MgO films on AZ31 alloy substrate for biomedical applications: preparation, characterization and testing

Magnesium ions, MgO nanoparticles and thin films, magnesium alloys and cerium compounds are materials intensively studied due to their corrosion protection, antibacterial and pharmacological properties. In this work, we have designed, prepared and investigated, novel thin films of MgO doped with cerium, deposited on Mg alloy (AZ31) for temporary implants, in order to enhance their life time. More precisely, we report on microstructure and corrosion behavior of MgO pure and doped with 0.1 at % Ce films, fabricated by sol–gel route coupled with spin-coating technique, on AZ31 alloy substrate. A modified sol–gel method that start from magnesium acetylacetonate, cerium nitrate and 2–methoxyethanol (as a stabilizer for the sol) was been used successfully for cerium doped MgO sol precursor preparation. The structure and morphology of the surface of the coatings, before and after immersion for 7–30 d in Hank’s solution at 37 °C, were characterized by x-ray diffraction (XRD), scanning electron microscopy, high-resolution transmission electron microscope, x-ray photoelectron spectroscopy and Fourier infrared transmittance spectrum (FT–IR). A comparison between the corrosion protection of undoped MgO and MgO doped with 0.1 at % Ce coatings on the AZ31 alloy substrate is performed by electrochemical tests and immersion tests using open circuit potential and electrochemical impedance spectroscopy in Hank’s solution, at 37 °C. The electrochemical results showed that the protection of the AZ31 alloy substrate against corrosion was better with the doped with 0.1 at % Ce MgO film deposited than with pure MgO coting. The investigations of the films after immersion in Hank’s solution, at 37 °C, for 7, 21 and 30 d indicated that the grown layer on the film is bone like apatite that suggests a good bioactivity of 0.1 at % Ce–doped MgO coating. Our work demonstrates that the performance corrosion protection of the biodegradable magnesium alloys used for orthopedic applications, in simulated physiological environments (Hank and Ringer) can be enhanced through coating with Ce3+ doped MgO sol–gel thin film.

Aggregate-state-dependent photochromism and circularly polarized luminescence of a chiral biquinoline amphiphile.

The photophysical and chiroptical properties of a chiral biquinoline amphiphile were found to be closely related to its aggregate states. Photochromism through photo-induced radical and circularly polarized luminescence were realized in its gel state and thin film state, respectively.

Statically Very Hydrophilic but Dynamically Hydrophobic Surfaces Showing Surprising Water Sliding Performance

AbstractIt is generally believed that water droplets on (super)hydrophilic surfaces is spread and strongly pin to the surface. The surface chemistry that achieves the paradoxical surface properties of being statically very hydrophilic, but exhibiting outstanding water sliding properties, has not yet established. Here, a facile approach to prepare such unusual surfaces based on a combination of a sol–gel process using an organosilane containing polyethylene glycol units and tetraethoxysilane, and subsequent alkali‐treatment is reported. The resulting sol–gel thin films are smooth, transparent, hydrophilic (static contact angle (CA) (θS) of ≈37°) and show a liquid‐like nature with both low CA hysteresis (≈4°) and sliding angle (α) for 10 µL water droplets (≈10°). Surprisingly, after alkali‐treatment for sufficient time, the surface becomes very hydrophilic (θS of ≈14°) while improving its dynamic wetting behaviors (CA hysteresis of ≈3° and α for 10 µL water droplet of ≈4°), such that even a mere 0.5 µL water drop can slide down smoothly without pinning and/or tailing.

Ag nanoparticles effects on physical properties of ZnO and AZO sol–gel thin films

Ag nanoparticles effects on physical properties of ZnO and AZO sol–gel thin films

Two-Dimensional Mapping of Arsenic Concentration and Speciation with Diffusive Equilibrium in Thin-Film Gels.

We present a new approach combining diffusive equilibrium in thin-film gels and spectrophotometric methods to determine the spatial distribution of arsenite, arsenate, and phosphate at submillimeter resolution. The method relies on the simultaneous deployment of three gel probes. Each retrieved gel is exposed to malachite green reagent gels differing in acidity and oxidant addition, leading to green coloration dependent on analyte speciation and concentration. Hyperspectral images of the gels enable mapping the three analytes in the 2.5-20 μM range. This method was applied in a contaminated brook in the Harz mountains, Germany, together with established mapping of dissolved iron. The use of two-dimensional (2D) gel probes was compared to traditional porewater extraction. The gels revealed banded porewater patterns on a mm-scale, which were undetectable using traditional methods. Small-scale correlation analyses of arsenic and iron microstructures in the gels suggested active iron-driven local redox cycling of arsenic. Overall, the results indicate continuous net release of arsenic from contaminant particles and deepen our understanding of arsenate transformation under anaerobic conditions. This study is the first fine-scale 2D characterization of arsenic speciation in porewater and represents a crucial step toward understanding the transfer and redox cycling of arsenic in contaminated sediment/soil ecosystems.

Copaiba Oil-Based Emulsion as a Natural Chemotherapeutic Agent for the Treatment of Bovine Mastitis: In Vivo Studies

Copaiba oil-resin (COR) extracted from Copaifera reticulata Ducke has been used as a natural chemotherapeutic agent for a wide range of therapeutic applications. This study presents an emulgel design with a high concentration of COR, designed to prevent and treat mastitis. The COR was stabilized in a gel matrix constituted by carbopol C934P and Pluronic® F127 (ECO formulation) ratios. The permeation study of ECO was accessed by Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS). The results reveal a high capacity of ECO to permeate deep skin layers. Dairy cows with a history of mastitis were used as in vivo models and exposed to ECO treatment. Monitoring of the teat's inflammatory response showed that ECO effectively prevents mastitis. Furthermore, the ECO formulation was able to form a thin film gel on the application side, preventing fly proliferation and significantly reducing the pathogen load. This study reveals a drug that can used as an alternative application for mastitis in human or veterinary clinics.

Influence of elapsed time on adsorption equilibrium of water vapor to silica gel film

For adsorption chillers or desiccant systems, thin film adsorbents coated on heat exchanger surfaces contribute to enhance adsorption/desorption rate of vapor, due to low thermal resistance leading to quick exothermic/endothermic heat exchange with external cooling/hot fluid. They enable to downsize adsorbent heat exchanger in systems. In the present study, a silica gel thin film synthesized on aluminum plate was proposed as a novel adsorbent. Pore structure of this new adsorbent changed during 15 months after synthesis: pore diameter enlarging and specific surface area decreasing. Upon this, the influence of time elapsed after synthesis on equilibrium adsorption of water vapor was examined under various adsorbing conditions until 22 months after synthesis. The equilibrium showed S-shape curve characteristics with respect to relative humidity, and decreased monotonously with elapsed time in wide relative humidity range, which was attributed to the pore structure change. Decreasing of equilibrium was not seen after 15 months from synthesis, that is, stabilization was attained. The equilibrium reduction in low relative humidity range was analyzed with the BET equation. Moreover, relative humidity of capillary condensation occurring was compared to the Kelvin equation. Finally, the equilibrium was formulated which reproduced well the measurements over the entire relative humidity range.

Chiroptical 3D Actuators for Smart Sensors

AbstractExamples of anisotropic movement paired with helical geometry abound in the animal and plant kingdoms are used for a variety of reasons, such as diverse social signaling directed at conspecifics or camouflage to avoid predation. Inspired by these natural phenomena, a smart sensor is developed with a chiroptical 3D actuator that can fold, bend, and twist in response to external stimuli, reflecting light of specific wavelengths, and possessing circular polarization properties. Chirophotonic crystal actuators are constructed with an asymmetric Janus structure and are fabricated by self‐assembly, screen printing, and in situ photopolymerization. The optically active layer consists of cholesteric liquid crystal polymer, and the mechanically active layer is composed of a polymeric gel thin film. The programmed in‐planar and out‐of‐planar asymmetric Janus structures control the directionality of various shapes morphing from 2D to 3D. Finite element simulations allow to predict the shape changes associated with these chirophotonic crystal actuators: flower blooming, tendril climbing, eagle hunting, ant lifting, and inchworm moving motions. By utilizing the chirophotonic crystal actuator, a reusable and portable methanol‐laced water identifier is developed.

Versatile Micro and Nano Patterning Technique for TiO2 and TiN‐Based Sol–Gel Thin Films

AbstractThis paper describes a tailored and versatile technology route to achieve micro and nanopatterning of both TiO2 and TiN thin films using a direct photo patternable sol–gel approach combined with a rapid thermal annealing and nitridation process. The approach consists in multi‐scale structuring TiO2 using laser direct writing or mask/colloidal lithography on a wide range of substrates including materials and of diverse geometry. These patterned TiO2 layers can subsequently be converted into a micro‐structured metallic TiN layer using a direct rapid thermal nitridation process that results in metallic thin films (TiN). This work demonstrates the versatility of this complete chain of soft chemistry based new process for patterning TiO2 and TiN thin films thereby avoiding expensive processes such as etching and lift‐off, while preserving their diffractive properties and high thermal stability, that is, up to 1000 °C under vacuum. The process is compatible with different kinds of substrates of different shapes and sizes. These results pave the way for developing a cost‐effective and time‐saving approach to different cutting‐edge applications such as metasurfaces, sensors, and applications in the luxury and decoration sector.

Flexible Sustained Ionogels with Ionic Hyperbranched Polymers for Enhanced Ion-Conduction and Energy Storage.

Flexible and mechanically robust gel-like electrolytes offer enhanced energy storage capabilities, versatility, and safety in batteries and supercapacitors. However, the trade-off between ion conduction and mechanical robustness remains a challenge for these materials. Here, we suggest that the introduction of ionic hyperbranched polymers in structured sustained ionogels will lead to both enhanced ion conduction and mechanical performance because of the hyperbranched polymers' ionically conductive groups and the complementary interfacial interactions with ionic liquids. More specifically, we investigate the effect of hyperbranched polymers with carboxylate terminal groups and imidazolium counterions with various ionic group densities on the properties of ionogels composed of coassembled cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs) as sustainable open pore frame for ionic liquid immersion. The addition of hyperbranched polymers leads to the formation of highly interconnected openly porous, lightweight, and shape-persistent materials by harnessing hydrogen bonding between the polymers and the CNFs/CNCs "frame". Notably, these materials possess a 2-fold improvement in ionic conductivity combined with many-fold increase in Young's modulus, tensile strength, and toughness, making them comparable to common reinforced nanocomposite materials. Furthermore, the corresponding thin-film gel supercapacitors possess enhanced electrochemical cycling stability upon repeated bending with an 85% capacitance retention after 10 000 cycles, promising new insight in the development of simultaneously conductive and flexible gel electrolytes with sustained performance.

Mechanical and Lubrication Properties of Double Network Ion Gels Obtained by a One-Step Process.

Human joints support us to reduce the impact on our body and move them smoothly. As they are composed of gel-like structures, gel materials with soft and resilient properties are expected, as lubricants, to provide high efficiency and a long lifetime for mechanical parts. While double network gels including ionic liquids as swelling agents possess high mechanical strength and stable low friction under high temperature or vacuum, their fabrication process is complex and time-consuming. In this study, we applied one-pot synthesis to a double network ion gel (DNIG) to obtain a thin gel film by a simple coating method and examined its thermal, mechanical and tribological properties. The DNIG was obtained by one-pot synthesis (DNIG-1) combining polycondensation of tetraethoxysilane and radical polymerization of methyl methacrylate to form silica and poly(methyl methacrylate) as a 1st and 2nd network, respectively. Such obtained DNIG-1 was characterized and compared with DNIG obtained by a conventional two-step process (DNIG-2). Thermogravimetric analysis and the compressive stress–strain test showed high thermal stability and mechanical strength of DNIG-1. As friction at the glass/DNIG-1 interface showed high friction compared with that at glass/DNIG-2, various counterface materials were applied to examine their effect on the friction of DNIG-1. As SUS304/DNIG-1 showed much lower friction compared with glass/DNIG-1, the difference in the friction was presumably due to the different adsorption forces and compatibility between the materials.

Synthesis of TiO2 Thin Films Nanoparticles with Different Layers using Simple Sol-Gel Method

In this study, titanium dioxide (TiO2 (are synthesized by sol– gel simple method. Thin films of sol, gel, and sol- gel on relatively flat glass substrates are applied with Spin coating technique with multilayers. The optical and morphological properties (studied using AFM) of TiO2 layers show good properties, with particles diameters less than 4 nm for all prepared samples and have maximum length 62 nm for TiO2 gel thin films of three layers. The results show low roughness values for all films especially for 4 layers sol (8.37nm), which improve the application in dye sensitive solar cell (DSSc) .

Full Factorial Design Analysis and Characterization of Polyethylene, Starch and Aloe Vera Gel Thin Film Formulation

The polyethylene-thermoplastic (PE/TPS) based film was introduced many years ago, but the compatibility of PE/TPS still an issue because synthetic compatibilizer has a safety drawback. In this work, aloe vera (AV) was introduced as a compatibilizer to enhance stress and characteristics of PE/TPS film. This paper determines the optimum PE/TPS/AV film formulation using full factorial design (FFD) analysis. Melt blending and hot-press techniques were used to prepare the film. Four selected PE/TPS/AV samples were chosen to discuss mechanical properties, functional groups, thermal degradation, and thermal properties changes. Based on FFD, PE was the most significant material that caused substantial changes in the film's mechanical properties. Concurrently, the interaction between PE/TPS and TPS/AV significantly influenced the value of the secant modulus. The addition of AV into TPS improved the stress and reduced the strain. New peaks are present in TPS/AV that share the same functional group with PE. Thus, improving the stress of the film. The presence of AV caused peaks 2916 cm^-1and 2849 cm^-1 of TPS to strengthen at once; the thermal degradation increases tremendously from 282 °C to 354.70 °C. The melting temperature showed a reduction when TPS/AV was added into PE, but the crystallization temperature did not significantly change. However, significant changes occurred for crystallization enthalpy when TPS/AV was incorporated in PE at once, affecting the degree of crystallinity. In conclusion, AV was suggested to act as a compatibilizer/crosslinker or plasticizer to improve PE film packaging properties.

Optimization of the production process of BZT–BCT sol–gel thin films obtained from a highly stable and green precursor solution

ABSTRACT Barium Zirconate Titanate–Barium Calcium Titanate (BZT–BCT) is an environmentally friendly piezoelectric-ferroelectric ceramic that is a promising alternative to lead zirconate titanate (PZT), whose toxicity is well known. Producing thin films by sol–gel deposition with properties comparable to their bulk counterparts is quite a difficult task, because of the substrate constraints which typically generate residual stresses during the production process, leading to the onset of cracks. Moreover, typically employed solutions contain toxic and harmful substances or are unstable over time. Recently, we produced a highly stable BZT–BCT precursor solution based on nontoxic and non-carcinogenic solvents. In this work, we optimized the BZT–BCT sol–gel deposition process by varying the spin coating velocity, which influences the thickness of each deposited layer, and the pyrolysis temperature, which impacts on the formation of cracks. Moreover, we explored the possibility to add a third heat treatment step to the deposition process with the aim of releasing the residual stresses, further improving the film properties. As a result, 250 nm thick films were obtained with optimized morphology and limited presence of cracks, thus enhancing the ferroelectric properties (Pr = 33.26 μC cm−2, Ec = 220.6 kV cm−1, ε = 1817).

Relationship between the Omniphobic Properties and the Swelling Degree of SLIPS Coatings Based on Polymer Gel Thin Films

Relationship between the Omniphobic Properties and the Swelling Degree of SLIPS Coatings Based on Polymer Gel Thin Films

Reducing the сontact angle hysteresis of thin polymer films by oil impregnation in supercritical carbon dioxide

In the present work, a novel one-stage approach to the creation of omniphobic surface using supercritical carbon dioxide as a solvent is proposed. Poly(perfluorohexyl ethyl methacrylate - hydroxypropyl methacrylate) copolymer cross-linked with hexamethylene diisocyanate is used as a polymer matrix, and polyoxaperfluorobutyl bromide (oil) is used as a lubricant. Oil content in the obtained films is measured by thermogravimetry and compared with the classical Flory-Rehner theory. It is shown that the addition of fluorinated oil to the synthesis process results in a significant decrease of apparent contact angle hysteresis and sliding angles of the obtained gel thin films. The proposed technique may be of interest for SLIPS application on surfaces with a complex structure like fabrics.