Nonporous Substrate Research Articles

Comparison of Derivatization Methods for Groomed Latent Print Residues Analysis via Gas Chromatography

The practice of latent print analysis is comprised of a visual examination and the comparison of the fingerprint pattern from a questioned print to an exemplar(s). When a questioned print is either smudged or contains little pattern detail, the print comparison would be considered an inconclusive determination. However, in these scenarios, the latent print residues (LPRs) could provide associative information to supplement the current ACE-V (Analysis, Comparison, Examination-Verification) process. Advancements using analytical techniques allow for the analysis of LPR chemistry; however, derivatization is generally required to increase the abundance of components not traditionally observed in gas chromatography. This study aimed to determine whether two derivatization reagents, boron trifluoride in methanol (BF3-MeOH) and N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA), provide a better recovery of LPR components from a porous or non-porous substrate. Five volunteers deposited groomed latent print samples onto two substrates: a microfiber filter (porous) and a microscope slide (non-porous). The residues were derivatized or evaporated prior to the gas chromatography-mass spectrometry (GC-MS) analysis. The percent recoveries were higher, >83%, in the DCM extracted samples for both substrates compared to those samples prepared in hexanes. DCM/MSTFA derivatization provided the recovery of fatty acids that ranged from 20 to 30% for both substrates and a recovery of squalene at a rate of 2.37% for the filter sample and 4.2% for the slide sample. These rates were higher than the recovery rates obtained for the hexanes/BF3-MeOH-derivatized samples, with a range of 1–8% for the fatty acids recovery rates and 0.6–0.85% for squalene from both substrates. Overall, the MSTFA derivatization reagent produced higher recoveries for LPR on porous and non-porous substrates while providing a LPR chromatographic profile similar to that of a non-derivatized sample. The use of DCM as a solvent provided a wider range of LPR components recovered than hexanes and, thus, should be used as the extraction solvent when derivatizing samples, regardless of the substrate.

Superspreading Surfactant on Hydrophobic Porous Substrates

The wetting behavior of droplets of aqueous surfactant solutions over hydrophobic thin PVDF porous membrane and non-porous hydrophobic PVDF film is investigated for small (~10 μL) droplets of aqueous trisiloxane surfactant solutions: superspreader S 240. The time dependencies of contact angle, droplet radius, wetted area and volume were monitored as well as penetration into the porous substrate. It is shown that the fast spreading of droplets of trisiloxane solutions takes place both in the case of porous and non-porous substrates at a concentration above some critical concentration. It was found that the trisiloxane droplets penetrate into the hydrophobic porous substrates and disappear much faster than on a corresponding hydrophobic non-porous substrate, which was not observed before. This phenomenon is referred to as “superpenetration”.

Effect of ethylene vinyl acetate on cement mortar – A review

Mortar is a mixture of sand, a binder and water. It is used as a paste, which hardens and fuses the masonry components used in the construction, such as stones, bricks or concrete. Polymers have been incorporated in Portland cement as property enhancers for a while. Since then, polymers have been used to improve the water retention, permeability, adhesive strength, workability and deformability of mortars and concretes. Cement concrete structures’ bearing capacity and durability are adversely affected by the brittleness of the cement material, which makes it simple to break under the influence of an external force. Various mechanical and physical properties of cement-based materials can be improved by using polymers, which have good elastic deformation capabilities, acid and alkali corrosion resistance, flexibility and compatibility with cement materials. Ethylene and vinyl acetate are copolymerized to form EVA or ethylene vinyl acetate. Excellent flex-crack and puncture resistance, a wide range of polar and nonporous substrate adhesion, and good hot-tack performance are just a few of the appealing qualities of EVA. The majority of research has demonstrated a beneficial effect of EVA on mortar performance. Foam rubber or Expanded rubber are the other popular names of EVA. EVA copolymers are adhesives that are utilised in packaging, bookbinding, and textile, for bonding plastic films, coated paper, and metal surfaces. The effectiveness of the EVA-modified mortar is examined in this paper. According to studies, the EVA-modified mortar's interface performance significantly increased as EVA was added to the mortar. While Scanning electron microscope studies were conducted for analysing the internal structure of EVA-added mortar, it was discovered that the EVA-cement composite had a three-dimensional net structure. Consequently, the mortar's cohesive strength rose. Also, Samples incorporated with EVA polymer waste had shown the ability of noise insulation. Incorporating EVA with CaO showed a positive effect on mortar performance. The risk of cracking was reduced in EVA-incorporated mortar. Thus, reviewing all the research papers it was found that the addition of EVA can considerably enhance the mortar’s physical as well as mechanical properties.

Cyrene™, a Sustainable Solution for Graffiti Paint Removal

Graffiti can create detrimental aesthetic and environmental damage to city infrastructure and cultural heritage and requires improved removal methods. Incumbent laser, mechanical and chemical removal techniques are often not effective, are expensive or damage the substrate. Solvents are generally hazardous and not always effective because of the insolubility of the graffiti paint. This study proposes a simple strategy for safe and effective graffiti removal, using the bio-based, non-toxic and biodegradable solvent dihydrolevoglucosenone (Cyrene™). The results showed that the type of substrate influenced the cleaning performance; in benchmark studies a non-porous substrate was easy to clean, while porous ceramic showed the presence of residual paint and yellowing when the conventional polar aprotic solvents were used. Cyrene, however, showed good removability of graffiti paint from both glazed and porous substrates, with little paint remaining in the pores of ceramic tiles. The paint suffered a reversible change in colour and a selective solubility of its components when using N-methyl-2-pyrrolidone; no changes occurred when Cyrene was used. While N-methyl-2-pyrrolidone and N,N′-dimethylformamide were only effective when neat, a Cyrene–water mixture showed some cleaning results. The performance of Cyrene was validated with Hansen solubility parameters and represents a greener and more sustainable solvent for paint removal.

Edge cracking behavior of Y2O3 coatings by the solution deposition planarization method

As an efficient flattening technique for surface smoothing, solution deposition planarization (SDP) has recently drawn more attention as a fabrication method for second generation high temperature superconducting (2G-HTS) tapes. However, at present, it is still challenging to achieve edge crack-free surfaces while preparing a Y2O3 coating via SDP processing, especially during drying and heat treatment. Experimental results show that as the colloidal dispersion is coated and dried on a nonporous rigid substrate, the enormous stresses developed during the drying process can fracture the thin film. The finite element simulation results show that coating thickness, which is affected by the differences in pulling rate and solution concentration, is a critical factor determining the crack sies may be initiated. After optimizing the coating parameters, a 10-m long Hastelloy C-276 alloy base was successfully prepared. The average value of Ra was 1.28 nm, which is less than 5 nm (5 × 5 μm2), satisfying the industrial requirements for the preparation of superconducting materials using the IBAD (lon Beam Assisted Deposition) technology route.

Dielectrophoretic Trapping for Nanoparticles, High-Molecule-Weight DNA, and SYBR Gold Using Polyimide-Based Printed Circuit Board

Microelectrodes for electrokinetic detection have been employed to manipulate and collect nanomaterials and biomaterials. However, the process of microelectrode patterning has been researched in the semiconductor fabrication process, which is expensive and time-consuming. Here, we demonstrate dielectrophoretic trapping of 200 nm fluorescent polystyrene nanoparticles and λ-deoxyribonucleic acid with SYBR gold using dielectrophoretic trapping onto an interdigitated circular electrode (ICE). For dielectrophoretic trapping, an ICE is designed and an ordered flexible printed circuit board (FPCB), possessing a non-porous polyimide substrate, is constructed. The ICE FPCB could identify the dielectrophoretic trapping conditions and simulate them by the finite element method. The fluorescent molecules in the ICE FPCB are dielectrophoretically trapped at the finger edges of the ICE when a peak-to-peak voltage of 12 V is applied at 6 kHz for 15-20 min. Moreover, monitoring of the dielectrophoretic trapping effect of SYBR gold eliminated the false negative detection error.

Design and Development of High-Loading Carbon-Sulfur Nanocomposite Cathodes with Drop-Casting Method

Advanced rechargeable batteries that can be widely applied in different energy-storage systems require a high energy density, a stable cyclability, and low costs in materials and fabrications. The commercial lithium-ion batteries exhibit high discharge capacity with a long cycle life, which allows them to dominate the current rechargeable battery markets. With the continuous development, the lithium-ion battery chemistry would soon encounter the theoretical material limitations. The mature fabrication technique and materials science have promoted the lithium-ion battery cathodes to meet their theoretical charge-storage capacity values. Moreover, the lithium insertion compounds have to maintain a stable crystal structure by limiting the full electrochemical utilization of the active material during cycling. Furthermore, with an increasing demand for lithium-ion battery products, the high prices and limited availability of the raw materials impact the market and the development of future lithium-ion batteries.To address these issues, a conversion-reaction cathode bypasses the limitation of low theoretical charge-storage capacity and limited electrochemical utilization garner significant attention. Among various conversion-reaction cathodes, the lithium-sulfur system is the most promising candidate for developing the post-lithium-ion technology with higher energy density at an affordable cost. This is primarily due to its naturally-abundant and low-cost sulfur cathode possesses a high charge-storage capacity of 1,672 mA∙h g-1, which makes the lithium-sulfur cells to approach a high energy density of about two to three times higher than that of current lithium-ion batteries. However, many obstacles limit the fast commercialization of lithium-sulfur technology. The low electronic conductivity values of sulfur and its end-discharged sulfides affect the electrochemical utilization of the active material and the development of a high-loading sulfur cathode for demonstrating a high energy density. In between sulfur and sulfides, the polysulfide intermediates generated during charge and discharge states are liquid-state active materials and have high solubility toward the liquid electrolyte. The dissolution of polysulfides would irreversibly diffuse out from the cathode and uncontrollably migrate in the cell, which causes the loss of active material from the cathode, the contamination of electrolyte, and the corrosion of the lithium metal anode. Consequently, the polysulfide issues result in poor electrochemical stability and further impact the high-loading cathode performance.This presentation will focus on the use of a drop-casting method to fabricate a high-loading carbon-sulfur nanocomposite cathode. Subsequently, we apply the developed high-loading nanocomposite cathode for exploring the effect of carbons’ nanopore sizes toward the electrochemical performance of sulfur cathodes. First, the drop-casted carbon-sulfur nanocomposite cathodes are fabricated with various carbon-sulfur nanocomposites. Super P-Sulfur, Ketjenblack-Sulfur, Black Pearl-Sulfur, and Vulcan Black-Sulfur nanocomposites featuring the nonporous Super P carbon, the mixed micro/mesoporous Ketjenblack carbon, the microporous Black Pearl carbon, and the macroporous Vulcan Black carbon are synthesized by the melt-sulfur diffusion method. The carbon-sulfur nanocomposites are mixed with liquid electrolyte to form a paste, followed by drop-casting on the current collector. These carbon-sulfur nanocomposite cathodes attain and are fixed at a high sulfur loading and sulfur content of 4 mg cm-2 and 60 wt%, respectively. Our findings indicate that the Black Pearl-sulfur nanocomposite cathode exhibits the best overall electrochemical performances featuring the high rate capability from C/20 to C/3 rates, stable long-term cyclability, and high capacity retention of above 80% after 100 cycles. The Ketjenblack-sulfur nanocomposite cathode with mixed micro/mesoporous carbon shows similar performances, while relatively lower than those obtained by Black Pearl-sulfur nanocomposite. With no nanopores and with macropores, Super P-Sulfur and Vulcan Black-sulfur nanocomposites display short cycle life in 40 cycles and low electrochemical utilization of sulfur, respectively. As a result, a carbon-sulfur nanocomposite with microporous carbon as the host would give the excellent polysulfide retention and the active-material utilization. With a nonporous carbon substrate, the carbon-sulfur nanocomposite might encounter the diffusion of polysulfides from the cathode electrode during cycling. With a macroporous carbon, the carbon-sulfur nanocomposite might also face the polysulfide diffusion issue, while mainly the diffusion of polysulfides from the composite. All these results demonstrate that the drop-casting method is a promising solution to develop high-loading sulfur cathode. Moreover, the further optimization of the nanocomposite might improve the electrochemical performance of the resulting high-loading nanocomposite sulfur cathode.

Impact of surface roughness on the deposition of saliva and fingerprint residue on non-porous substrates

A diverse range of non-porous substrate surfaces routinely encountered in crime scene settings were evaluated for their affinity towards deposited saliva and fingerprint residue. Raman spectroscopy, atomic force microscopy (AFM), field-emission scanning electron microscopy (FE-SEM) and water contact angle measurements were employed to quantitatively and qualitatively evaluate the physicochemical variables impacting the deposition of touch and salivary deposits. It was established that small changes in surface roughness and physicochemical interactions, including hydrophobicity, resulted in observable impacts on the spread of salivary deposits and deposition of fingerprint residue. It was further identified that not only did the surface free energy (SFE) available to the deposit, measured through water contact angles, influence the deposition and spread of the material on the surface, but that the nature of the deposit further impacted these dynamics. This preliminary study has developed a platform to gain a better understanding of the importance of surface roughness as a consideration, when interrogating how forensically relevant deposits such as saliva and fingerprint residue interact with non-porous surfaces. This better understanding is necessary when reflecting on the successfulness of recovering DNA, when considering means to improve recovery of trace samples from crime scenes, and when improving assessment of the likelihood of transfer of a deposit from one substrate to another upon contact.

Hydrothermal growth of overlapping ZnO nanorod arrays on the porous substrate and their H2 gas sensing

ZnO nanorod arrays (ZNAs) were prepared on a metakaolin (MK)-based porous substrate via a seeding-hydrothermal method. The spherical poly methyl methacrylate (PMMA) microspheres were employed as the pore former to obtain homogeneous porous structure on the MK-based substrates. Various characterization methods were used to investigate the effects of the porous structure on the morphological and structural properties of the ZNAs. The results indicated that the alignment degree of the ZNAs decreased significantly with the enhancement of the apparent porosity of the substrate. The ZNAs prepared on the MK-based substrate with the PMMA content of 30 wt% exhibited an overlapping morphology with an average diameter and length of 88 nm and 570 nm, respectively. Gas sensing measurements revealed that the response value of the overlapping ZNAs to 1000 ppm H2 at the operating temperature of 225 °C was 9.2, which is four times higher than that of the vertical ZNAs grown on the MK-based non-porous substrate. It confirms that the porous structure of the as-prepared substrates favors for the growth of the overlapping ZNAs, and the enhanced H2 gas sensing performance might be primarily related to the more effective adsorption sites and the modulation of the potential barrier at the junctions of the overlapping morphology.

Mid-infrared optimized electroreflective device based on PEDOT/PSS

A new type of device with adjustable reflective capabilities in the mid-IR is elaborated from the combination of Poly (3,4-ethylenedioxythiophene)/Poly (styrenesulfonate) (PEDOT/PSS), gold-coated non-porous polyimide substrate and gel electrolyte. Prior to device characterization, the influence of polymer thickness and gold substrate types on reflectance modulation of PEDOT-Au films is scrutinized to obtain the film with optimum quality. A combination of SEM images and reflectance curves confirms that adopting thin PEDOT/PSS on the non-porous substrate can achieve large amplitude reflectance regulation. Further, a mechanical perforating method is developed to address the issue that ions cannot transport between the polymer film and the counter electrode when this PEDOT/non-porous film assembled into device. An in-depth study shows that by varying the punching side, porosity and aperture, a device with front holes of porosity 12.77% affords the highest reflectance contrast of 0.566 over the wavelength range of 3-5 μm, meanwhile exhibits effective temperature changes of approximately 16 °C. These results inspire interesting perspectives regarding the fabrication of PEDOT-based devices with controllable IR electroreflective performance.

Development of environmentally insulted fingermarks on nonporous forensically relevant substrates with conformal columnar thin films

A systematic study was undertaken on the influence of environmental insult on the efficacy of developing a latent fingermark on a nonporous substrate by the deposition of a conformal nanoscale columnar thin film (CTF) on it. Four warm-weather and one cold-weather environmental conditions were chosen as representative for Pennsylvania. Three durations of environmental insult were selected: a day, seven days, and 30 days. Fingermarks were collected from one male donor and one female donor on five different types of substrates. The evaporant material for the deposition of a CTF on a specific fingermark sample was specifically chosen based on a prior study. Photographs of every fingermark were graded for quality after collection, after enduring the chosen environmental insult for a particular duration, and after CTF development. The results of the study on 750 fingermark samples indicate that environmental insult does not always degrade and can even improve the quality of fingermarks, and CTF deposition thereafter may considerably enhance the insulted fingermarks for visualization.

Nanoporous Silica Preconcentrator for Vapor-Phase DMNB, a Detection Taggant for Explosives.

The detection of trace amounts of explosives in the vapor phase is of great importance. Preconcentration of the analyte is a useful technique to lower the detection limit of existing sensors. A nanoporous silica (pSiO2) substrate was evaluated as a preconcentrator for gas-phase 2,3-dimethyl-2,3-dinitrobutane (DMNB), a volatile detection taggant added by law to plastic explosives. After collection in pSiO2, the DMNB vapor was thermally desorbed at 70 °C into a gas chromatography–mass spectrometry sorbent tube. This was analyzed for the total mass of DMNB collected in pSiO2. The loading time and loading temperature of pSiO2 were varied systematically between 15 and 60 min and 5–20 °C, respectively. The preconcentrator’s performance was compared to that of a nonporous substrate of the same material as a control. The collection efficiency of pSiO2 was calculated as approximately 20% of the total DMNB that passed over it in 30 min, at a concentration of 0.5 ppm in N2 carrier gas. It had enhancement factors compared to the nonporous substrate of 12 and 16 for 0.5 and 4.1 ppm DMNB, respectively, under the same conditions. No advantage was found with cooling pSiO2 below room temperature during the loading phase, which removes any need for a cooling system to aid preconcentration. The low desorption temperature of 70 °C is an advantage over other preconcentration systems, although a higher temperature could decrease the desorption time.

Surface and optical characteristics of polycrystalline GaN layer with different pores profile of porous GaAs/GaAs substrate

This work investigated the influence of pores profile of a porous GaAs/GaAs substrate on surface and optical characteristics of an over-deposited GaN layer. Different pores profile of the porous GaAs/GaAs substrate was introduced by varying the DMF concentration of 50%, 75% and 90%. The pores distribution is more uniform, while the pores size is bigger with higher DMF concentration. In contrast, the pores depth is less deep when the DMF concentration was higher than 75%. Next, the GaN layer was deposited onto the porous GaAs/GaAs substrate using an e-beam evaporator system, followed by thermal annealing in ammonia ambient. It was found that the porous GaAs/GaAs substrate, etched by the DMF concentration above 75% gave lower surface roughness to the polycrystalline GaN layer although the surface morphology showed no significant changes. XRD measurement showed on non-porous substrate favoured hexagonal growth in the polycrystalline GaN layer. Instead, the porous GaAs/GaAs substrate favoured the cubic growth, especially the porous GaAs/GaAs substrate etched by 75% DMF concentration. Moreover, the GaN layer on the porous GaAs/GaAs substrate etched by 75% DMF concentration showed the smallest FWHM of NBE peak emission, while exhibited a relaxation level closer to a reported stress-free bulk GaN, as compared to other samples. After all, the porous GaAs/GaAs substrate, etched by 75% DMF concentration has improved the surface and optical characteristics of the layer due to its better porosity.

An Implantable Transparent Conductive Film with Water Resistance and Ultrabendability for Electronic Devices.

Recently, instead of indium tin oxide, the random mesh pattern of metallic nanowires for flexible transparent conducting electrodes (FTCEs) has received a great amount of interest due to its flexibility, low resistance, reasonable price, and compliant processes. Mostly, nanowires for FTCEs are fabricated by spray or mayer coating methods. However, the metallic nanowire layer of FTCEs, which is fabricated by these methods, has a spiked surface roughness and low junction contact between the nanowires that lead to their high sheet resistance value. Also, the nanowires on FTCEs are easy to peel-off through exterior forces such as bending, twisting, or contact. To solve these problems, we demonstrate novel methods through which silver nanowires (AgNWs) are deposited onto a nanosize porous nitrocellulose (NC) substrate by electrophoretic deposition (EPD) and an opaque and porous substrate. Respectively, through dimethyl sulfoxide treatment, AgNWs on NC (AgNW/NC) is changed to the transparent and nonporous FTCEs. This enhances the junction contact of the AgNWs by EPD and also allows a permanent attachment of AgNWs onto the substrate. To show the mechanical strength of the AgNWs on the transparent nitrocellulose (AgNW/TNC), it is tested by applying diverse mechanical stress, such as a binding test (3M peel-off), compressing, bending, twisting, and folding. Next, we demonstrate that AgNW/TNC can be effectively implanted onto normal newspapers and papers. As paper electronics, light-emitting diodes, which are laminated onto paper, are successfully operated through a basic AgNW/TNC strip circuit. Finally, it is demonstrated that AgNW/TNC and AgNW/TNC on paper are water resistant for 15 min due to the insulation properties of the nonporous substrate.

An AIE based fluorescent probe for digital lifting of latent fingerprint marks down to minutiae level

Abstract Acridinediones, a new addition to the family of dyes having aggregation induced emission characteristics have been reported. Facile hydrophobic interactions between the acridinedione aggregates and fingerprint residues were exploited to lift the latent fingerprint marks on a non-porous substrate. By employing this preferential adhesion approach, a portable wet method for the enhancement and visualization of latent fingerprint marks using hand held UV light and mobile camera was demonstrated. Using this simple, rapid, cost effective, eco and user friendly method the latent fingerprints, its primary and secondary level of information’s can be easily decoded. These acridinedione derivatives also show strong blue luminescence in solid state with high fluorescence quantum yield.

Effect of hand sanitizer on the performance of fingermark detection techniques

Hand sanitizers have seen a rapid increase in popularity amongst the general population and this increased use has led to the belief that hand sanitizers may have an effect on subsequent fingermark detection. Based on this hypothesis, three alcoholic and two non-alcoholic hand sanitizers were evaluated to determine the effect they had on the detection of fingermarks deposited after their use. The following fingermark detection methods were applied: 1,2-indanedione-zinc, ninhydrin, physical developer (porous substrate); and cyanoacrylate, rhodamine 6G, magnetic powder (non-porous substrate). Comparison between hand sanitized fingermarks and non-hand sanitized fingermarks showed that the alcohol-based hand sanitizers did not result in any visible differences in fingermark quality. The non-alcoholic hand sanitizers, however, improved the quality of fingermarks developed with 1,2-indanedione-zinc and ninhydrin, and marginally improved those developed with magnetic powder. Different parameters, including time since hand sanitizer application prior to fingermark deposition and age of deposited mark, were tested to determine the longevity of increased development quality. The non-alcoholic hand sanitized marks showed no decrease in quality when aged for up to two weeks. The time since sanitizer application was determined to be an important factor that affected the quality of non-alcoholic hand sanitized fingermarks. It was hypothesized that the active ingredient in non-alcoholic hand sanitizers, benzalkonium chloride, is responsible for the increase in fingermark development quality observed with amino acid reagents, while the increased moisture content present on the ridges resulted in better powdered fingermarks.

Inkjet printing of alumooxide sol for deposition of antireflecting coatings

Subject of Research. This work describes for the first time the formation of antireflective coating on the base of boehmite phase of AlOOH with low refractive index (1.35) by inkjet printing on the nonporous substrate. This method gives the possibility to increase the contrast of colorful interfering images by 32% obtaining by inkjet printing of titanium dioxide sol. The usage of this technology enables to obtain patterns with wide viewing angle and makes them highly stable. Methods. Traditional sol-gel method with peptizing agents and heating for 90oC was applied for sol synthesis. Then the mixture was under sonic treatment for the obtaining of viscous sol. The viscosity was determined by Brookfield HA/HB viscometer, and the surface tension by Kyowa DY-700 tensiometer. Aluminum oxide ink was deposited on polished slides (26×76 mm2, Paul Marienfeld, Germany), over titanium oxide layer. To print titania ink, we use a desktop office printer Canon Pixma IP 2840 and Dimatix DMP-2831. The thickness of an inkjet AlOOH layer after drying in the air and removal of the solvents did not exceed 150 nm with an RI not less than 1.35 in the entire visible range. Results. The stable colloidal ink was obtained for the first time on the base of aluminum oxide matrix with neutral pH. The rheology was regulated by controlling parameters of sol-gel method in the system of aqueous titanium dioxide sol and by adding ethanol that affects the charge of double electrical layer of disperse phase. The controllable coalesce of drops enables to apply antireflection coating within the thickness accuracy of 10 nm. The morphology of particles and the topology of printed structures were analyzed by optical, scanning electron and atomic-force microscopes. Practical Relevance. We have proposed the approach to obtain colorful, interference patterns using two types of high refractive inks with different refractive indexes. The inkjet printing method opens new opportunities for preparing optical waveguides and forming photon-induction panels for new generation of computers.

Painting cracks: A way to investigate the pictorial matter

An old painting generally exhibits a wide variety of crack patterns. From a strictly aesthetic point of view, cracks are undesirable; nevertheless, they can be seen as the fingerprints of the painting and provide valuable knowledge about the art piece. Precisely, the morphology of crack patterns can be related to the mechanical properties of the pictorial matter or they can reveal information about the methods used by the artist or the conditions of conservation. In the present paper, we show how drying dispersions of colloidal particles in a volatile solvent on a non-porous substrate provides a good candidate to study crack formation in a solid layer. We recover the crack patterns observed in paintings, and we investigate the role of the substrate, e.g., the sub-layer, and of the thickness of the layer in the crack spacing. We show how to deduce mechanical properties of a sub-layer, provided the thickness and the elastic modulus of the layer are known. These experiments aim to propose a potentially non-invasive method to deduce quantitative information about mechanical properties of a pictorial matter which could be of great interest for cultural heritage.

Drop impact on natural porous stones

Drop impact and spreading on three natural porous stones are experimentally determined using high-speed imaging and compared with spreading over an impermeable steel surface. The dynamic non-wetting behavior during spreading and the hydrophobic contact angle >90° is attributed to the presence of an air layer between the droplet and the porous substrate. As the contact line pins at maximum spreading on the porous stone, the maximum spreading determines the liquid contact area on such substrate. The droplet gets pinned when the air layer is broken at the contact line and capillary forces develop in fines pores at the droplet edge, pinning the droplet. Maximum spreading on porous stones increases with impact velocity but does not scale with Weber number at low impact velocity. It is demonstrated that dynamic wetting plays an important role in the spreading at low velocity and that the dynamic wetting as characterized by the dynamic contact angle θD has to be taken into account for predicting the maximum spreading. Correcting the maximum spreading ratio with the dynamic wetting behavior, all data for porous stones and non-porous substrate collapse onto a single curve.

Stability analysis of non-inertial thin film flow over a heterogeneously heated porous substrate

The dynamics and linear stability of a gravity drive thin film flowing over non-uniformly heated porous substrate are studied. A governing equation for the evolution of film-thickness is derived within the lubrication approximation. Darcy-Brinkman equation is used to model flow in the porous medium along with a tangential stress-jump condition at the interface of the porous layer and the fluid film. A temperature profile is imposed at the solid wall to model an embedded heater beneath the porous layer. At the upstream edge of the heater, an opposing thermocapillary stress at the liquid-air interface leads to the formation of a thermocapillary ridge. The ridge becomes unstable beyond a critical Marangoni number leading to the formation of rivulets that are periodic in the spanwise direction. Increase in the values of parameters such as Darcy number, stress jump coefficient, and porosity is shown to have stabilizing effect on the film dynamics. The critical Marangoni number is shown to increase monotonically with Darcy number for various values of porosity. At large values of stress-jump coefficient, a non-monotonic variation in critical Marangoni number versus Darcy number is shown. A correlation is developed numerically for the ratio of critical Marangoni number at large Darcy number to that for a non-porous substrate as a function of porosity and thickness of the porous substrate. A transient growth analysis is carried out followed by non-linear stability analysis. The non-modal growth is found to be negligible thus indicating that the eigenvalues are physically determinant.