Self-similar finite-time singularity formation in degenerate parabolic equations arising in thin-film flows

A thin liquid film coating a planar horizontal substrate may be unstable to perturbations in the film thickness due to unfavourable intermolecular interactions between the liquid and the substrate, which may lead to finitetime rupture. The self-similar nature of the rupture has been studied before by utilising the standard lubrication approximation along with the Derjaguin (or disjoining) pressure formalism used to account for the intermolecular interactions, and a particular form of the disjoining pressure with exponent n = 3 has been used, namely, Π(h) ∝ −1/h3, where h is the film thickness. In the present study, we use a numerical continuation method to compute discrete solutions to self-similar rupture for a general disjoining pressure exponent n (not necessarily equal to 3), which has not been previously performed. We focus on axisymmetric point-rupture solutions and show for the first time that pairs of solution branches merge as n decreases, starting at nc ≈ 1.485. We verify that this observation also holds true for plane-symmetric line-rupture solutions for which the critical value turns out to be slightly larger than for the axisymmetric case, nplane c ≈ 1.499. Computation of the full time-dependent problem also demonstrates the loss of stable similarity solutions and the subsequent onset of cascading, increasingly small structures

Axisymmetric self-similar rupture of thin films with general disjoining pressure

A thin film coating a dewetting substrate may be unstable to perturbations in the thickness, which leads to finite time rupture. The self-similar nature of the rupture has been studied by numerous authors for a particular form of the disjoining pressure, with exponent n = 3. In the present study we use a numerical continuation method to compute discrete solutions to self-similar rupture for a general disjoining pressure exponent n. Pairs of solution branches merge when n is close to unity, indicating that a more detailed examination of the dynamics of a thin film in this regime is warranted. We also numerically evaluate the power law behaviour of characteristic quantities of solutions in the limit of large branch number

Healing capillary films

Consider the dynamics of a healing film driven by surface tension, that is, the inward spreading process of a liquid film to fill a hole. The film is modelled using the lubrication (or thin-film) approximation, which results in a fourth-order nonlinear partial differential equation. We obtain a self-similar solution describing the early-time relaxation of an initial step-function condition and a family of self-similar solutions governing the finite-time healing. The similarity exponent of this family of solutions is not determined purely from scaling arguments; instead, the scaling exponent is a function of the finite thickness of the prewetting film, which we determine numerically. Thus, the solutions that govern the finite-time healing are self-similar solutions of the second kind. Laboratory experiments and time-dependent computations of the partial differential equation are also performed. We compare the self-similar profiles and exponents with both measurements in experiments and time-dependent computations near the healing time, and we observe good agreement in each case

Healing capillary films

We investigate, by means of theoretical arguments, numerical simulation and numerics, the closing of a circular cavity (healing) in a thin liquid film. We assume that the process is dominated by capillary forces. The final stages of the evolution can be described by means of self-similar solutions to the problem. A comparison with experimental data is also presented

Noncircular Stable Displacement Patterns in a Meshed Porous Layer

We report noncircular, stable liquid propagation patterns in a displacement process in a confined thin patterned porous layer. For constant fluid injection rates, the average front location of the interface <i>r</i>(<i>t</i>) exhibits a power-law behavior <i>r</i> ∝ <i>t</i>^1/2; however, when surface tension effects become important, the interface displays noncircular shapes, e.g., square, rectangular, or octagonal, and maintains the same shape during most of the injection process. The interface shape is controlled by the value of a dimensionless group representing the strength of surface tension stresses relative to stresses accompanying injection. Furthermore, we show that the propagation patterns of the interface can be controlled by the relative orientation of the different porous layers

Thickening of the Immobilized Polymer Layer Using Trace Amount of Amine and Its Role in Promoting Gelation of Colloidal Nanocomposites

Immobilized polymer layers surrounding nanoparticles are proposed to be of essentially vital importance for the reinforcement of nanofiller to polymer matrices, but there is still a need to clarify its contribution to diverse rheological performance like colloidal stability and gelation. In this study, we find for the first time that introducing a trace amount of secondary/tertiary amine efficiently thickens the immobilized glassy layer in hydrophilic fumed silica (FS) filled polypropylene glycol (PPG) from 1.5 to 4.5 nm, which simultaneously promotes gelation of the liquid-like dispersion even containing extremely low contents of FS (<2 vol %). By coordinately using modulated differential scanning calorimetry and rheology methods, we find strong evidence that (1) the amine-promoted gelation is due to thickening and easy-percolation of the inner glassy layer converted from an outer uncrystallizable layer, and (2) the dispersion rheology could be well normalized within the framework of a two-phase model incorporating effective volume fraction of nanoparticles plus the glassy layers. We also highlight the importance of the surface chemistry of FS for adjusting the polymer immobilization and dispersion rheology

Noncircular Stable Displacement Patterns in a Meshed Porous Layer

We report noncircular, stable liquid propagation patterns in a displacement process in a confined thin patterned porous layer. For constant fluid injection rates, the average front location of the interface <i>r</i>(<i>t</i>) exhibits a power-law behavior <i>r</i> ∝ <i>t</i>^1/2; however, when surface tension effects become important, the interface displays noncircular shapes, e.g., square, rectangular, or octagonal, and maintains the same shape during most of the injection process. The interface shape is controlled by the value of a dimensionless group representing the strength of surface tension stresses relative to stresses accompanying injection. Furthermore, we show that the propagation patterns of the interface can be controlled by the relative orientation of the different porous layers

Enhanced Dielectric Breakdown Property of Polypropylene Based on Mesoscopic Structure Modulation by Crystal Phase Transformation for High Voltage Power Cable Insulation

As an environmentally friendly polymer material, isotactic polypropylene (pp), possesses excellent dielectric properties while it can be recycled, so it is regarded as having promising application prospects in the field of high voltage power cable insulation. However, the increasing operating voltage rating also puts higher demands on its insulation reliability. In this study, an intrinsic modulation method for pp insulation based on mesoscopic structure modulation by crystal phase transformation is proposed, which not only effectively improved the dielectric properties but also enhanced the mechanical toughness synergistically. The transformation of the crystal phase from the α-crystal to β-crystal within the PP/β-NA samples was successfully achieved by the solution blending method. The crystallization efficiency is greatly promoted, and the crystal structure is further improved at the same time. As the proportion of β-crystal gradually increases, the elongation at break could be raised to 451% at maximum. The difference in dielectric parameters between the crystal and amorphous regions is caused by the variation in the molecular chain density and arrangement, which is also the main reason for further triggering the high-intensity partial discharges and large-area electrical tree degradation in the amorphous region between the spherocrystal boundary at the mesoscopic scale. Compared with the premodification, the introduction of β-crystal effectively alleviated the problem of electric field distortion. Among them, the modified PP-β-0.2 sample had 16.8 kV/mm lower maximum electric field, 2258 fewer total partial discharges, 420 μm2 less electrical tree cumulative damage area, and 28% higher breakdown strength. Accordingly, it also has promising applications in the manufacturing of high-voltage power cable insulation

Spectroscopic data.docx from One-pot domino syntheses of 3-alkyl-3-<i>N</i>-substituted aminobenzofuran- 2(3<i>H</i>)-ones based on alkali-promoted Michael addition and lactonization

In this paper, a novel cascade reaction of caesium carbonate-promoted Michael addition and lactonization for the one-pot synthesis of 3-alkyl-3-N-substituted aminobenzofuran-2(3H)-one derivatives has been established based on the screening of the alkaline catalysts and optimization of reaction conditions, in which the N-substituted (ortho-hydroxy) aryl glycine esters were used as the Michael donors to react with different α, β-unsaturated carbonyl compounds. Besides racemic enantiomers, the obtained epimers were successfully separated by conventional chromatography in the case of using the asymmetric raw material. In addition, the possible reaction mechanisms were suggested and the absolute configuration of the epimer was analysed. All the chemical structures of unreported benzofuran- 2(3H)-one derivatives were characterized by IR, 1H NMR, 13C NMR spectra and HRMS spectra

1H and 13C of compound from One-pot domino syntheses of 3-alkyl-3-<i>N</i>-substituted aminobenzofuran- 2(3<i>H</i>)-ones based on alkali-promoted Michael addition and lactonization

In this paper, a novel cascade reaction of caesium carbonate-promoted Michael addition and lactonization for the one-pot synthesis of 3-alkyl-3-N-substituted aminobenzofuran-2(3H)-one derivatives has been established based on the screening of the alkaline catalysts and optimization of reaction conditions, in which the N-substituted (ortho-hydroxy) aryl glycine esters were used as the Michael donors to react with different α, β-unsaturated carbonyl compounds. Besides racemic enantiomers, the obtained epimers were successfully separated by conventional chromatography in the case of using the asymmetric raw material. In addition, the possible reaction mechanisms were suggested and the absolute configuration of the epimer was analysed. All the chemical structures of unreported benzofuran- 2(3H)-one derivatives were characterized by IR, 1H NMR, 13C NMR spectra and HRMS spectra