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PubMed2005

Nematic liquid crystals at rough and fluctuating interfaces.

Nematic liquid crystals at rough and fluctuating interfaces are analyzed within the Frank elastic theory and the Landau-de Gennes theory. We study specifically interfaces that locally favor planar anchoring. In the first part we reconsider the phenomenon of Berreman anchoring on fixed rough surfaces, and derive new simple expressions for the corresponding azimuthal anchoring energy. Surprisingly, we find that for strongly aligning surfaces, it depends only on the geometrical surface anisotropy and the bulk elastic constants, and not on the precise values of the chemical surface parameters. In the second part, we calculate the capillary waves at nematic-isotropic interfaces. If one neglects elastic interactions, the capillary wave spectrum is characterized by an anisotropic interfacial tension. With elastic interactions, the interfacial tension, i.e., the coefficient of the leading q(2) term of the capillary wave spectrum, becomes isotropic. However, the elastic interactions introduce a strongly anisotropic cubic q(3) term. The amplitudes of capillary waves are largest in the direction perpendicular to the director. These results are in agreement with previous molecular dynamics simulations.

Biophysical Phenomena↗
PubMed1999

Measurement of intracellular triglyceride stores by H spectroscopy: validation in vivo.

We validate the use of 1H magnetic resonance spectroscopy (MRS) to quantitatively differentiate between adipocyte and intracellular triglyceride (TG) stores by monitoring the TG methylene proton signals at 1.6 and 1.4 ppm, respectively. In two animal models of intracellular TG accumulation, intrahepatic and intramyocellular TG accumulation was confirmed histologically. Consistent with the histological changes, the methylene signal intensity at 1.4 ppm increased in both liver and muscle, whereas the signal at 1.6 ppm was unchanged. In response to induced fat accumulation, the TG concentration in liver derived from 1H MRS increased from 0 to 44.9 +/- 13.2 micromol/g, and this was matched by increases measured biochemically (2.1 +/- 1.1 to 46.1 +/- 10.9 micromol/g). Supportive evidence that the methylene signal at 1.6 ppm in muscle is derived from investing interfascial adipose tissue was the finding that, in four subjects with generalized lipodystrophy, a disease characterized by absence of interfacial fat, no signal was detected at 1.6 ppm; however, a strong signal was seen at 1.4 ppm. An identical methylene chemical shift at 1.4 ppm was obtained in human subjects with fatty liver where the fat is located exclusively within hepatocytes. In experimental animals, there was a close correlation between hepatic TG content measured in vivo by 1H MRS and chemically by liver biopsy [R = 0.934; P <.0001; slope 0.98, confidence interval (CI) 0.70-1.17; y-intercept 0.26, CI -0.28 to 0. 70]. When applied to human calf muscle, the coefficient of variation of the technique in measuring intramyocellular TG content was 11.8% in nonobese subjects and 7.9% in obese subjects and of extramyocellular (adipocyte) fat was 22.6 and 52.5%, respectively. This study demonstrates for the first time that noninvasive in vivo 1H MRS measurement of intracellular TG, including that within myocytes, is feasible at 1.5-T field strengths and is comparable in accuracy to biochemical measurement. In addition, in mixed tissue such as muscle, the method is clearly advantageous in differentiating between TG from contaminating adipose tissue compared with intramyocellular lipids.

Adipose Tissue↗
PubMedDate not supplied

Poly n-butylcyanoacrylate (PNBCA) nanocapsules as a carrier for NSAIDs: in vitro release and in vivo skin penetration.

PURPOSE: The aim of this work was to prepare poly n-butylcyanoacrylate (PNBCA) nanocapsules loaded with indomethacin and to evaluate the ability of this carrier system to deliver the drug systemically after its topical application. METHODS: Poly n-butylcyanoacrylate (PNBCA) nanocapsules of indomethacin were prepared by interfacial polymerization. The physicochemical characterization of the PNBCA nanocapsules was performed by measuring the drug content by HPLC and analyzing the particle size using scanning electron microscopy. The in vitro permeation of indomethacin through excised rat skin and an artificial membrane was determined for PNBCA nanocapsules in pH 7.4 phosphate buffer (I), and in PLF-127 gel (II) and were compared against indomethacin incorporated into 25%w/w PLF-127 gel alone (III). The in vivo percutaneous absorption of indomethacin following the application of the PNBCA nanocapsules and a 25%w/w Pluronic F-127 (PLF-127) gel (III) was monitored by the determination of drug plasma levels in rats. RESULTS: The drug loading results indicated that approximately 76.6% of indomethacin was loaded onto the PNBCA nanocapsules; the average particle size was 188 nm. The in vitro results indicated a rank order for the three formulations (I, II and III) in both the flux at steady state and the cumulative amounts permeated at 8 hrs. The higher drug plasma levels over 6 hrs of indomethacin PNBCA nanocapsules are in agreement with the determined in vitro permeation results. CONCLUSION: The presented data show that indomethacin loaded PNBCA nanocapsules can improve the transdermal delivery of indomethacin compared to a conventional gel formulation using Pluronic F-127. This might be due to their ultra fine particle size and their hydrophilic and hydrophobic surface characteristics.

Animals↗
PubMed2006

Effects of exogenous collagenase and cholesterol esterase on the durability of the resin-dentin bond.

PURPOSE: The purpose of this work was to determine microtensile dentin bond strengths (microTBS) of dentin-resin composite bonds after three-month storage in artificial saliva containing either collagenase (COL) or cholesterol esterase (EST). The null hypothesis tested is that the resin-dentin bond strength is equivalent for each storage medium at the tested storage times. MATERIALS AND METHODS: Resin composite was bonded to occlusal dentin, and microTBS specimens were formed and stored in the artificial saliva, COL, EST, or synthetic oil. After 24 h and 12-week storage, microTBS was determined and failure modes were characterized by SEM. The interfacial ultrastructure was evaluated by transmission electron microscopy as unstained and stained sections (phosphotungstic acid/uranyl acetate). Statistical analysis was performed by ANOVA and Weibull survival analyses at the 0.05 level of statistical significance. RESULTS: There were significantly weaker bond strengths after 12 weeks for all experimental storage media (p < 0.001). Artificial saliva containing EST lowered bond strengths to a significantly greater extent than did COL after 12 weeks of storage, while no difference between these groups could be discerned after 24 h. Therefore, the null hypothesis of this experiment is rejected. CONCLUSION: Exogenous enzymatic challenge to resin-dentin bonds decreased bond durability only with EST. However, when further challenges to ideal infiltration of the comonomers into the hybrid layer were carried out using inadequate removal of solvent, additional alterations in hybrid layer ultrastructure were discerned by TEM that may represent different potential degradative processes. The contribution of endogenous enzymatic challenges to the primary degradative process, ie, hydrolysis, is unknown and deserves continued attention.

Acid Etching, Dental↗
PubMed1995

Nuclear magnetic resonance characterization of the Jun leucine zipper domain: unusual properties of coiled-coil interfacial polar residues.

Leucine zippers constitute a widely observed structural motif which serves to promote both homo- and heterodimerization in a number of DNA-binding proteins. As part of our ongoing efforts to characterize both the structure and the dynamical properties of this dimerization domain as they relate to biological function, we report here the secondary structure in solution of a recombinant dimeric peptide (rJunLZ) comprising residues Arg276-Asn314 of the leucine zipper domain of c-Jun. Two- and three-dimensional homo- and heteronuclear NMR experiments have allowed definition of the secondary structure of rJunLZ and have provided a total of approximately 1500 interproton distance and 62 phi dihedral angle constraints for tertiary structure calculations. Amide proton protection factors, calculated from hydrogen-deuterium exchange experiments, have identified 62 hydrogen bonds in the rJunLZ dimer. We have also examined the role of Asn22, the only polar residue situated at the hydrophobic dimer interface. Virtually all leucine zipper sequences contain such a polar residue (usually Asn) near the center of the motif. X-ray crystallographic studies showed that, in the case of the GCN4 homodimer, the polar residue (Asn) adopts an asymmetric conformation in an otherwise essentially symmetric structure. In contrast, all NMR studies of leucine zipper homodimers to date have suggested that the dimers are completely symmetric in solution. We present evidence that the side-chain amide protons of Asn22 are hydrogen-bonded in solution and that this side chain exchanges rapidly between two distinct conformations. On the basis of these observations, we propose a dynamic model which can explain the apparent differences in symmetry observed in NMR and X-ray crystallographic studies of leucine zipper homodimers. We show that mutation of Asn22 to a hydrophobic Leu residue markedly increases the thermal stability of the rJunLZ homodimer, consistent with a destabilizing role for this residue. However, at temperatures below 30 degrees C, the Asn22-->Leu mutant rearranges to form oligomers larger than the dimer, as was previously observed for the corresponding Asn-->Val mutation in the GCN4 leucine zipper. These results are consistent with the hypothesis that the polar Asn residue commonly observed at the interface of leucine zippers imposes specificity for the dimer structure at the expense of stability [Harbury, P.B., Zhang, T., Kim, P.S., & Alber, T. (1993) Science 262, 1401-1407].

Amino Acid Sequence↗
PubMed2001

Interfacial Characteristics and Fracture Toughness of Electrolytically Ni-Plated Carbon Fiber-Reinforced Phenolic Resin Matrix Composites.

The electrolytic plating of metallic nickel on a carbon fiber surface has been carried out in order to improve the interfacial adhesion and the mechanical properties in carbon fiber/phenolic matrix composite systems. The surface and the mechanical interfacial properties of composites are characterized by X-ray photoelectron spectrometry (XPS), surface free energy, and the critical stress intensity factor (K(IC)). From the experimental results, it is clearly revealed that the oxygen functional groups and the metallic nickel on fibers largely affect the mechanical interfacial behavior of the composites, resulting in increased surface polarity, whereas the nitrogen functional groups have no effect. Also, a good correlation between surface oxygen functional groups and mechanical interfacial properties and between wettability and K(IC) is established and it is found that a 10 A m(-2) current density is the optimum condition for this system. Copyright 2001 Academic Press.

Journal Article↗
PubMed2001

Active coatings for SiC particles to reduce the degradation by liquid aluminium during processing of aluminium matrix composites: study of interfacial reactions.

The application of a surface coating on SiC particles is studied as an alternative means of solving problems of reactivity between SiC reinforcements and molten aluminium and problems of low wetting which limit the application of casting routes for fabrication of Al-SiCp composites. The selected active barrier was a ceramic composed of SiO2, which was generated by controlled oxidation of the SiC particles. The coating behaves as an active barrier, preventing a direct reaction between molten aluminium and SiC to form Al4C3 as the main degradation product. At the same time, the SiO2 provokes other interfacial reactions, which are responsible for an improvement in wetting behaviour. Composites were prepared by mixing and compacting SiC particles with Al powders followed by melting in a vacuum furnace, and varying the residence time. Transmission electron microscopy (TEM), high resolution electron microscopy (HREM) and field emission TEM were employed as the main characterization techniques to study the interfacial reactions occurring between the barrier and the molten aluminium. These studies showed that the SiO2 coating behaves as an active barrier which reacts with the molten Al to form a glassy phase Al-Si-O. This compound underwent partial crystallization during the composite manufacture to form mullite. The formation of an outer crystalline layer, composed mainly of Al2O3, was also detected. Participation of other secondary interface reactions inside the active barrier was also identified by HREM techniques.

Journal Article↗
PubMed2005

Probing inhomogeneous vibrational reorganization energy barriers of interfacial electron transfer.

An atomic force microscopy (AFM) and confocal Raman microscopy study of the interfacial electron transfer of a dye-sensitization system, i.e., alizarin adsorbed upon TiO(2) nanoparticles, has revealed the distribution of the mode-specific vibrational reorganization energies encompassing different local sites ( approximately 250-nm spatial resolution). Our experimental results suggest inhomogeneous vibrational reorganization energy barriers and different Franck-Condon coupling factors of the interfacial electron transfer. The total vibrational reorganization energy was inhomogeneous from site to site; specifically, mode-specific analyses indicated that energy distributions were inhomogeneous for bridging normal modes and less inhomogeneous or homogeneous for nonbridging normal modes, especially for modes far away from the alizarin-TiO(2) coupling hydroxyl modes. The results demonstrate a significant step forward in characterizing site-specific inhomogeneous interfacial charge-transfer dynamics.

Journal Article↗
PubMed2000

Capillary interactions between particles bound to interfaces, liquid films and biomembranes.

This article is devoted to an overview, comparison and discussion of recent results (both theoretical and experimental) about lateral capillary forces. They appear when the contact of particles or other bodies with a fluid phase boundary causes perturbations in the interfacial shape. The capillary interaction is due to the overlap of such perturbations which can appear around floating particles, vertical cylinders, particles confined in a liquid film, inclusions in the membranes of lipid vesicles or living cells, etc. In the case of floating particles the perturbations are due to the particle weight; in this case the force decreases with the sixth power of the particle size and becomes immaterial for particles smaller than approximately 10 microm. In all other cases the interfacial deformations are due to the particle wetting properties; the resulting 'immersion' capillary forces can be operative even between very small particles, like protein globules. In many cases such forces can be responsible for the experimentally observed two-dimensional particle aggregation and ordering. An analogy between capillary and electrostatic forces enables one to introduce 'capillary charges' of the attached particles, which characterize the magnitude of the interfacial deformation and could be both positive and negative. Moreover, the capillary interaction between particle and wall resembles the image force in electrostatics. When a particle is moving bound to an interface under the action of a capillary force, one can determine the surface drag coefficient and the surface viscosity supposedly the magnitude of the capillary force is known. Alternative (but equivalent) energy and force approaches can be used for the theoretical description of the lateral capillary interactions. Both approaches require the Laplace equation of capillarity to be solved and the meniscus profile around the particles to be determined. The energy approach accounts for contributions due to the increase of the meniscus area, gravitational energy and/or energy of wetting. The second approach is based on calculating the net force exerted on the particle, which can originate from the hydrostatic pressure, interfacial tension and bending moment. In the case of small perturbations, the superposition approximation can be used to derive an asymptotic formula for the capillary forces, which has been found to agree well with the experiment. Capillary interactions between particles bound to spherical interfaces are also considered taking into account the special geometry and restricted area of such phase boundaries. A similar approach can be applied to quantify the forces between inclusions (transmembrane proteins) in lipid membranes. The deformations in a lipid membrane, due to the inclusions, can be described theoretically in the framework of a mechanical model of the lipid bilayer, which accounts for its 'hybrid' rheology (neither elastic body nor fluid). In all considered cases the lateral capillary interaction originates from the overlap of interfacial deformations and is subject to a unified theoretical treatment, despite the fact that the characteristic particle size can vary from 1 cm down to 1 nm.

Capillary Action↗
PubMed2006

Immobilization of ligands with precise control of density to electroactive surfaces.

We report a broadly applicable surface chemistry methodology to immobilize ligands, proteins, and cells to an electroactive substrate with precise control of ligand density. This strategy is based on the coupling of soluble aminooxy terminated ligands with an electroactive quinone terminated monolayer. The surface chemistry product oxime is also redox active but at a different potential and therefore allows for real-time monitoring of the immobilization reaction. Only the quinone form of the immobilized redox pair is reactive with soluble aminooxy groups, which allows for the determination of the yield of reaction, the ability to immobilize multiple ligands at controlled densities, and the in-situ modulation of ligand activity. We demonstrate this methodology by using cyclic voltammetry to characterize the kinetics of a model interfacial reaction with aminooxy acetic acid. We also demonstrate the synthetic flexibility and utility of this method for biospecific interactions by installing aminooxy terminated FLAG peptides and characterizing their binding to soluble anti-FLAG with surface plasmon resonance spectroscopy. We further show this methodology is compatible with microarray technology by printing rhodamine-oxyamine in various size spots and characterizing the yield within the spots by cyclic voltammetry. We also show this methodology is compatible with cell culture conditions and fluorescent microscopy technology for cell biological studies. Arraying RGD-oxyamine peptides on these substrates allows for bio-specific adhesion of Swiss 3T3 Fibroblasts.

Aminooxyacetic Acid↗
PubMed1998

Influence of different physicochemical conditions on the release of indium oxine from nanocapsules.

The main purpose of this study was to determine the influence of factors (pH, enzymes, etc.) chosen partially to mimic in vivo conditions on the release of a model drug, indium oxine, from polyepsiloncaprolactone (PCL) nanocapsules in vitro. A nanocapsule suspension, an emulsion (O/W), and a solution in olive oil were prepared in order to compare the release of a radioactive tracer, indium oxine, as a function of time by an in vitro dialysis method. Nanocapsules were prepared by interfacial deposition of PCL and characterized by particle size distribution (laser light scattering) and determination of the polymer molecular weight by gel permeation chromatography (GPC). The results of this study suggest that the partition coefficient between the acceptor medium and the olive oil is the major parameter governing the release of the isotope, at least in the absence of significant enzyme activity. The PCL wall of nanocapsules is a barrier that does not seem to retard the release of indium. The addition of porcine liver esterases accelerated the degradation of PCL. This study confirms that the release of a drug from nanocapsules may be very different depending on the in vivo location, that is, the administration site.

Dosage Forms↗
PubMed2002

Interlaminar and ductile characteristics of carbon fibers-reinforced plastics produced by nanoscaled electroless nickel plating on carbon fiber surfaces.

In this work, a new method based on nanoscaled Ni-P alloy coating on carbon fiber surfaces is proposed for the improvement of interfacial properties between fibers and epoxy matrix in a composite system. Fiber surfaces and the mechanical interfacial properties of composites were characterized by atomic absorption spectrophotometer (AAS), scanning electron microscopy (SEM), X-ray photoelectron spectrometry (XPS), interlaminar shear strength (ILSS), and impact strength. Experimental results showed that the O(1s)/C(1s) ratio or Ni and P amounts had been increased as the electroless nickel plating proceeded; the ILSS had also been slightly improved. The impact properties were significantly improved in the presence of Ni-P alloy on carbon fiber surfaces, increasing the ductility of the composites. This was probably due to the effect of substituted Ni-P alloy, leading to an increase of the resistance to the deformation and the crack initiation of the epoxy system.

Journal Article↗
PubMed2006

Bioelectrocatalytic application of titania nanotube array for molecule detection.

A bioelectrocatalysis system based on titania nanotube electrode has been developed for the quantitative detection application. Highly ordered titania nanotube array with inner diameter of 60 nm and total length of 540 nm was formed by anodizing titanium foils. The functionalization modification was achieved by embedding glucose oxidases inside tubule channels and electropolymerizing pyrrole for interfacial immobilization. Morphology and microstructure characterization, electrochemical properties and bioelectrocatalytic reactivities of this composite were fully investigated. The direct detection of hydrogen peroxide by electrocatalytic reduction reaction was fulfilled on pure titania nanotube array with a detection limit up to 2.0 x 10(-4)mM. A biosensor based on the glucose oxidase-titania/titanium electrode was constructed for amperometric detection and quantitative determination of glucose in a phosphate buffer solution (pH 6.8) under a potentiostatic condition (-0.4V versus SCE). The resulting glucose biosensor showed an excellent performance with a response time below 5.6s and a detection limit of 2.0 x 10(-3)mM. The corresponding detection sensitivity was 45.5 microA mM(-1)cm(-2). A good operational reliability was also achieved with relative standard deviations below 3.0%. This novel biosensor exhibited quite high response sensitivity and low detection limit for potential applications.

Biosensing Techniques↗
PubMed2006

Formulation of sustained release nanoparticles loaded with a tripentone, a new anticancer agent.

The purpose of the present work is to develop nanoparticles of a new antitubulin agent of the family of tripentones by means of a phase inversion process. Dynamic light scattering, transmission electron microscopy and zeta-potential measurements were used to characterize tripentone loaded nanoparticles. From interfacial tension measurements and from the study of the rheological interfacial properties of the tripentone at the Labrafac-Solutol interface, the fraction of tripentone initially present in Labrafac would stay in the oily core of nanocapsules. Moreover, the interpenetration of some tripentone molecules within the surfactant units helps to the stabilization of the formulated nanoparticles. The encapsulation efficiency was determined by high performance liquid chromatography (HPLC) and was found to be above 95%. In vitro release studies were carried out in blank nanoparticles containing phosphate buffer, pH 7.4, at 37 degrees C. The drug release kinetics was measured by HPLC. Antiproliferative activity studies on L1210 cells showed that the cytotoxic activity of tripentone was totally recovered after encapsulation of the antitubulin agent in lipid nanoparticles. This study shows that lipid nanocapsules could be a promising and effective carrier for tripentone delivery in the treatment of cancers.

Animals↗
PubMed2000

Imaging and tracking of single GFP molecules in solution.

Visualization and tracking of single fluorescent molecules is a recent development in optical microscopy holding great promise for the study of cell biological processes. However, all experimental strategies realized so far confined the observation to extremely thin interfacial layers. The detection and characterization of single molecules in three-dimensionally extended systems such as living cells has yet to be accomplished. We show, here, for the first time that single protein molecules can be visualized and tracked in three-dimensional (3D) samples at room temperature. Using a wide-field fluorescence microscope equipped with an Ar(+)-laser and a low-light-level CCD camera, single molecules of the green fluorescent protein (GFP) were detected in gels and viscous solutions at depths of up to approximately 10 microm from the interface. A time resolution of 5 ms was achieved by a high-speed framing mode. The two-dimensional localization accuracy was determined to be approximately 30 nm. The number of photons emitted by single GFP molecules before photodestruction was found to be < or = 4 * 10(5). Freely diffusing GFP molecules could be tracked over up to nine images acquired at a frame rate of approximately 80 Hz. From the trajectories, the diffusion coefficients of single GFP molecules were derived and found to agree well with expectation and microphotolysis measurements. Our results imply that the visualization and tracking of single molecules in living cells is possible.

Biophysical Phenomena↗
PubMed2000

Ultrasonic measurement of the diffusion bond strength

This paper presents an ultrasonic method for measurement of diffusion bond strength between two identical materials. The method requires a single normal-incidence ultrasonic measurement. When a diffusion bond is not perfect some ultrasonic energy is reflected from the interface separating the two substrates. Amplitude of a reflected signal correlates qualitatively with the bond strength. However, a quantitative correlation is difficult to establish since reflected signal amplitude depends on parameters of the test equipment. We introduce a spectroscopic analysis of a reflected signal to measure the bond strength. We show experimentally that an imperfect diffusion bond can be characterized by a single parameter: interfacial spring stiffness. The stiffness can be determined from the reflected signal spectrum and does not depend on testing equipment. It is also demonstrated that for a particular diffusion bonding procedure as applied to tool steel the interfacial stiffness correlates quantitatively with bond strength.

Journal Article↗
PubMed1993

The chemical step is not rate-limiting during the hydrolysis by phospholipase A2 of mixed micelles of phospholipid and detergent.

The effect of detergents on the overall catalytic turnover by secreted phospholipase A2 (PLA2) on codispersions of the substrate phospholipid is characterized. The overall rate of interfacial catalytic turnover depends on the effective substrate "concentration" (mole fraction) that the bound enzyme "sees" at the interface. Therefore, besides the intrinsic catalytic turnover rate determined by the Michaelis-Menten cycle in the interface [Berg et al. (1991) Biochemistry 30, 7283], two other interfacial processes significantly alter the overall effective rate of hydrolysis: first, the fraction of the total enzyme at the interface; second, the rate of replenishment of the substrate. At low mole fractions (< 0.3), bile salts promote the binding of pig pancreatic PLA2 to zwitterionic vesicles, and the rate of hydrolysis increases with the fraction of the enzyme in the interface. At higher (> 0.3) mole fractions of the detergent, the bilayer is disrupted, and the rate of hydrolysis decreases by more than a factor of 10. The detergent-dependent decrease in the rate of hydrolysis of the sn-2-oxyphospholipids is much larger than that of sn-2-thiophospholipid, and therefore the element effect (O/S ratio) decreases from about 10 in bilayers to less than 2 in mixed micelles. This loss of the element effect in mixed micelles shows that the chemical step is no longer rate-limiting during the hydrolysis of mixed micelles formed by the disruption of vesicles by the detergent. Such effects were observed with phospholipase A2 from several sources acting on substrates dispersed in a variety of detergents including bile salts, 2-deoxylysophosphatidylcholine, and Triton X-100.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Suppression of instability in liquid flow down an inclined plane by a deformable solid layer.

The linear stability of a liquid layer flowing down an inclined plane lined with a deformable, viscoelastic solid layer is analyzed in order to determine the effect of the elastohydrodynamic coupling between the liquid flow and solid deformation on the free-surface instability in the liquid layer. The stability of this two-layer system is characterized by two qualitatively different interfacial instability modes: In the absence of the deformable solid layer, the free surface of the liquid film undergoes a long-wave instability due to fluid inertia. With the presence of the deformable solid layer, the interface between the fluid and the solid undergoes a finite-wavelength instability when the deformable solid becomes sufficiently soft. The effect of the solid layer deformability on the free-surface instability of the liquid film flow is analyzed using a long-wave asymptotic analysis. The asymptotic results show that for a fixed Reynolds number and inclination angle, the free-surface instability is completely suppressed in the long-wave limit when the nondimensional (inverse) solid elasticity parameter Gamma=Va eta/(GR)increases beyond a critical value. Here, Va is the average velocity of the liquid film flow, eta is the viscosity of the liquid, G is the shear modulus of the solid layer, and is R the thickness of the liquid layer. The predictions of the asymptotic analysis are verified and extended to finite wavelengths using a numerical solution, and this indicates that the suppression of the free-surface instability indeed continues to finite wavelength disturbances. Further increase of Gamma is found to have two consequences: first, the interface between the liquid and the deformable solid layer could become unstable at finite wavelengths; second, the free-surface interfacial mode could also become unstable at finite wavelengths due to an increase in solid layer deformability. However, our numerical results demonstrate that, for a given average velocity, there exists a sufficient window in the value of shear modulus G where both the unstable modes are absent at all wavelengths. Our study therefore suggests that soft solid layer coatings could potentially provide a passive method of suppressing free-surface instabilities in liquid film flows.

Journal Article↗