A Study of Impacting Droplets of an Emulsion or Surfactant Solution on Solid Substrates

ABSTRACTCoating of solid surfaces with uniform, thin liquid films occurs in many industrial processes. A common process consists of spraying some liquids or emulsions on a freshly created solid surface. In this context, we have investigated the impact of a single droplet of various emulsions and surface-active solutions on a solid substrate using a high frequency fluorescent visualization technique (1 picture every 0.25 ms). Whatever the materials in presence, the drop spreads and then retracts under the action of inertia and capillarity respectively. Inertia induces spreading and generates a peripheral rim which is unstable to fingering. Then contact line instabilities appear under the form of festoons with pure liquids which are damped with surface-active solutions and amplified with emulsions. When the adsorption kinetics of the surfactant is slow, the equilibrium surface tension is not restored during the duration of the experiment and the drop can bounce back.

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Rupture of thin films formed during droplet impact

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2009.0425 ◽

2009 ◽

Vol 466 (2116) ◽

pp. 1229-1245 ◽

Cited By ~ 26

Author(s):

Rajeev Dhiman ◽

Sanjeev Chandra

Keyword(s):

Impact Velocity ◽

Liquid Films ◽

Solid Substrate ◽

Contact Angles ◽

Droplet Impact ◽

Film Rupture ◽

Droplet Spreading ◽

Spreading Model ◽

Wide Range ◽

The Impact

Rupture of liquid films formed during droplet impact on a dry solid surface was studied experimentally. Water droplets (580±70 μm) were photographed as they hit a solid substrate at high velocities (10–30 m s −1 ). Droplet–substrate wettability was varied over a wide range, from hydrophilic to superhydrophobic, by changing the material of the substrate (glass, Plexiglas, wax and alkylketene dimer). Both smooth and rough wax surfaces were tested. Photographs of impact showed that as the impact velocity increased and the film thickness decreased, films became unstable and ruptured internally through the formation of holes. However, the impact velocity at which rupture occurred was found to first decrease and then increase with the liquid–solid contact angle, with wax showing rupture at all impact velocities tested. A thermodynamic stability analysis combined with a droplet spreading model predicted the rupture behaviour by showing that films would be stable at very small or at very large contact angles, but unstable in between. Film rupture was found to be greatly promoted by surface roughness.

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The Colloidal Chemical Properties and Features of the Adsorption of Functional Oligoperoxides on to Liquid and Solid Surfaces

Adsorption Science & Technology ◽

10.1260/02636170260504332 ◽

2002 ◽

Vol 20 (7) ◽

pp. 647-656 ◽

Cited By ~ 1

Author(s):

A.S. Zaichenko ◽

N.E. Mitina ◽

M.O. Kovbuz ◽

O.M. Hertsyk

Keyword(s):

Chemical Properties ◽

Solid Surfaces ◽

Ion Content ◽

Molar Ratios ◽

Glass Carbon ◽

Kinetics Of Formation ◽

Surface Active ◽

Inorganic Fillers ◽

Adsorption Layers ◽

Kinetics Of

The study of the sorption processes of polyfunctional initiating systems on to organic and inorganic fillers has arisen because of the development of new filled copolymer composites. In the present study, the kinetics of formation of adsorption layers by surface-active functional oligoperoxides (FSAP) based on vinyl acetate (VA), 2-t-butylperoxy-2-methyl-5-hexene-3-yne (VEP), maleic anhydride (MAN) or maleic acid (MA) at molar ratios of VA/VEP/MA and VA/VEP/MAN equal to 1:1:1 and derived metal complexes (OMC) with a Cu2+ ion content of 0.45% and 0.80% on the surface of glass–carbon plates were examined.

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The Impact of Bioconjugation on the Interfacial Activity of a Protein Biosurfactant

10.26434/chemrxiv.7497053.v1 ◽

2018 ◽

Author(s):

Hossam H Tayeb ◽

Marina Stienecker ◽

Anton Middelberg ◽

Frank Sainsbury

Keyword(s):

Polyethylene Glycol ◽

Colloidal Stability ◽

Point Mutations ◽

Pharmaceutical Formulations ◽

Industrial Processes ◽

Parent Molecule ◽

Site Specific ◽

Interfacial Activity ◽

Surface Active ◽

The Impact

Biosurfactants, are surface active molecules that can be produced by renewable, industrially scalable biologic processes. DAMP4, a designer biosurfactant, enables the modification of interfaces via genetic or chemical fusion to functional moieties. However, bioconjugation of addressable amines introduces heterogeneity that limits the precision of functionalization as well as the resolution of interfacial characterization. Here we designed DAMP4 variants with cysteine point mutations to allow for site-specific bioconjugation. The DAMP4 variants were shown to retain the structural stability and interfacial activity characteristic of the parent molecule, while permitting efficient and specific conjugation of polyethylene glycol (PEG). PEGylation results in a considerable reduction on the interfacial activity of both single and double mutants. Comparison of conjugates with one or two conjugation sites shows that both the number of conjugates as well as the mass of conjugated material impacts the interfacial activity of DAMP4. As a result, the ability of DAMP4 variants with multiple PEG conjugates to impart colloidal stability on peptide-stabilized emulsions is reduced. We suggest that this is due to constraints on the structure of amphiphilic helices at the interface. Specific and efficient bioconjugation permits the exploration and investigation of the interfacial properties of designer protein biosurfactants with molecular precision. Our findings should therefore inform the design and modification of biosurfactants for their increasing use in industrial processes, and nutritional and pharmaceutical formulations.

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Multiple interactions in riverine biofilms - surfactant adsorption, bacterial attachment and biodegradation

Water Science & Technology ◽

10.2166/wst.1995.0015 ◽

1995 ◽

Vol 31 (1) ◽

pp. 61-70 ◽

Cited By ~ 6

Author(s):

Graham F. White

Keyword(s):

Organic Pollutants ◽

Bacterial Attachment ◽

Solid Surfaces ◽

Sediment Surface ◽

Liquid Interfaces ◽

Polluted Soils ◽

Biofilm Bacteria ◽

The Impact ◽

Multiple Interactions

Many organic pollutants, especially synthetic surfactants, adsorb onto solid surfaces in natural and engineered aquatic environments. Biofilm bacteria on such surfaces make major contributions to microbial heterotrophic activity and biodegradation of organic pollutants. This paper reviews evidence for multiple interactions between surfactants, biodegradative bacteria, and sediment-liquid interfaces. Biodegradable surfactants e.g. SDS, added to a river-water microcosm were rapidly adsorb to sediment surface and stimulated the indigenous bacteria to attach to the sediment particles. Recalcitrant surfactants and non-surfactant organic nutrients did not stimulate attachment Attachment of bacteria was maximal when biodegradation was fastest, and was reversed when biodegradation was complete. Dodecanol, the primary product of SDS-biodegradation, markedly stimulated attachment. When SDS was added to suspensions containing sediment and either known degraders or known non-degraders, only the degraders became attached, and attachment accelerated surfactant biodegradation to dodecanol. These cyclical cooperative interactions have implications for the design of biodegradability-tests, the impact of surfactant adjuvants on biodegradability of herbicides/pesticides formulated with surfactants, and the role of surfactants used to accelerate bioremediation of hydrocarbon-polluted soils.

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Ice Coverage Induced by Depositing a Water Drop onto the Supercooled Substrate at Extreme Low Vapor Pressure

Crystals ◽

10.3390/cryst11060691 ◽

2021 ◽

Vol 11 (6) ◽

pp. 691

Author(s):

Yugang Zhao ◽

Zichao Zuo ◽

Haibo Tang ◽

Xin Zhang

Keyword(s):

Vapor Pressure ◽

Substrate Temperature ◽

Water Drop ◽

Industrial Processes ◽

Aircraft Icing ◽

Ice Coverage ◽

Fundamental Understanding ◽

Order Of Magnitude ◽

The Impact ◽

Kinetics Of

Icing/snowing/frosting is ubiquitous in nature and industrial processes, and the accretion of ice mostly leads to catastrophic consequences. The existing understanding of icing is still limited, particularly for aircraft icing, where direct observation of the freezing dynamics is inaccessible. In this work, we investigate experimentally the impact and freezing of a water drop onto the supercooled substrate at extremely low vapor pressure, to mimic an aircraft passing through clouds at a relatively high altitude, engendering icing upon collisions with pendant drops. Special attention is focused on the ice coverage induced by an impinging drop, from the perimeter pointing outward along the radial direction. We observed two freezing regimes: (I) spread-recoil-freeze at the substrate temperature of Ts = −15.4 ± 0.2 °C and (II) spread (incomplete)-freeze at the substrate temperature of Ts = −22.1 ± 0.2 °C. The ice coverage is approximately one order of magnitude larger than the frozen drop itself, and counterintuitively, larger supercooling yields smaller ice coverage in the range of interest. We attribute the variation of ice coverage to the kinetics of vapor diffusion in the two regimes. This fundamental understanding benefits the design of new anti-icing technologies for aircraft.

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Morphology and crystallization kinetics of Rubber-modified Nylon 6 Prepared by Anionic In-situ Polymerization

Science and Engineering of Composite Materials ◽

10.1515/secm-2020-0020 ◽

2020 ◽

Vol 27 (1) ◽

pp. 204-215

Author(s):

Hongkai Zhao ◽

Dengchao Zhang ◽

Yingshuang Li

Keyword(s):

Crystallization Kinetics ◽

In Situ Polymerization ◽

Good Description ◽

Nylon 6 ◽

Avrami Equation ◽

Infrared Analysis ◽

Chain Segment ◽

The Impact ◽

Kinetics Of

AbstractIn this work, we modified nylon 6 with liquid rubber by in-situ polymerization. The infrared analysis suggested that HDI urea diketone is successfully blocked by caprolactam after grafting on hydroxyl of HTPB, and the rubber-modified nylon copolymer is generated by the anionic polymerization. The impact section analysis indicated the rubber-modified nylon 6 resin exhibited an alpha crystal form.With an increase in the rubber content, nylon 6 was more likely to generate stable α crystal. Avrami equation was a good description of the non-isothermal crystallization kinetics of nylon-6 and rubber-modified nylon-6 resin. Moreover, it is found that the initial crystallization temperature of nylon-6 chain segment decreased due to the flexible rubber chain segment. n value of rubber-modified nylon-6 indicated that its growth was the coexistence of two-dimensional discoid and three-dimensional spherulite growth. Finally, the addition of the rubber accelerated the crystallization rate of nylon 6.

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Controlling the breakup of toroidal liquid films on solid surfaces

Scientific Reports ◽

10.1038/s41598-021-87549-5 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Andrew M. J. Edwards ◽

Élfego Ruiz-Gutiérrez ◽

Michael I. Newton ◽

Glen McHale ◽

Gary G. Wells ◽

...

Keyword(s):

Fluid Dynamics ◽

Mode Selection ◽

Liquid Films ◽

Solid Surfaces ◽

Final States ◽

Digital Microfluidic ◽

Insulating Liquid ◽

Solid Liquid Interface ◽

Solid Liquid ◽

Dynamics Stability

AbstractThe breakup of a slender filament of liquid driven by surface tension is a classical fluid dynamics stability problem that is important in many situations where fine droplets are required. When the filament is resting on a flat solid surface which imposes wetting conditions the subtle interplay with the fluid dynamics makes the instability pathways and mode selection difficult to predict. Here, we show how controlling the static and dynamic wetting of a surface can lead to repeatable switching between a toroidal film of an electrically insulating liquid and patterns of droplets of well-defined dimensions confined to a ring geometry. Mode selection between instability pathways to these different final states is achieved by dielectrophoresis forces selectively polarising the dipoles at the solid-liquid interface and so changing both the mobility of the contact line and the partial wetting of the topologically distinct liquid domains. Our results provide insights into the wetting and stability of shaped liquid filaments in simple and complex geometries relevant to applications ranging from printing to digital microfluidic devices.

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A Study of the Effects of Rain, Snow and Hail on the Atmospheric Electric Field near Ground

Atmosphere ◽

10.3390/atmos12080996 ◽

2021 ◽

Vol 12 (8) ◽

pp. 996

Author(s):

Athanasios Karagioras ◽

Konstantinos Kourtidis

Keyword(s):

Frequency Distribution ◽

Complex Structure ◽

Potential Gradient ◽

Weather Conditions ◽

The Other ◽

Fair Weather ◽

Northern Greece ◽

Rain Events ◽

The Impact ◽

Bounce Back

The purpose of the present study is to investigate the impact of rain, snow and hail on potential gradient (PG), as observed in a period of ten years in Xanthi, northern Greece. An anticorrelation between PG and rainfall was observed for rain events that lasted several hours. When the precipitation rate was up to 2 mm/h, the decrease in PG was between 200 and 1300 V/m, in most cases being around 500 V/m. An event with rainfall rates up to 11 mm/h produced the largest drop in PG, of 2 kV/m. Shortly after rain, PG appeared to bounce back to somewhat higher values than the ones of fair-weather conditions. A decrease in mean hourly PG was observed, which was around 2–4 kV/m during the hail events which occurred concurrently with rain and from 0 to 3.5 kV/m for hail events with no rain. In the case of no drop, no concurrent drop in temperature was observed, while, for the other cases, it appeared that, for each degree drop in temperature, the drop in hourly mean PG was 1000 V/m; hence, we assume that the intensity of the hail event regulates the drop in PG. The frequency distribution of 1-minute PG exhibits a complex structure during hail events and extend from −18 to 11 kV/m, with most of the values in the negative range. During snow events, 1-minute PG exhibited rapid fluctuations between high positive and high negative values, its frequency distribution extending from −10 to 18 kV/m, with peaks at −10 and 3 kV/m.

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Single entity electrochemistry and the electron transfer kinetics of hydrazine oxidation

Nano Research ◽

10.1007/s12274-021-3353-8 ◽

2021 ◽

Cited By ~ 1

Author(s):

Ruiyang Miao ◽

Lidong Shao ◽

Richard G. Compton

Keyword(s):

Electron Transfer ◽

Bulk Solution ◽

Relative Contribution ◽

Rate Determining Step ◽

Multistep Process ◽

Ph Range ◽

Electro Catalytic Oxidation ◽

Single Particle Impact ◽

The Impact ◽

Kinetics Of

AbstractThe mechanism and kinetics of the electro-catalytic oxidation of hydrazine by graphene oxide platelets randomly decorated with palladium nanoparticles are deduced using single particle impact electrochemical measurements in buffered aqueous solutions across the pH range 2–11. Both hydrazine, N2H4, and protonated hydrazine N2H5+ are shown to be electroactive following Butler-Volmer kinetics, of which the relative contribution is strongly pH-dependent. The negligible interconversion between N2H4 and N2H5+ due to the sufficiently short timescale of the impact voltammetry, allows the analysis of the two electron transfer rates from impact signals thus reflecting the composition of the bulk solution at the pH in question. In this way the rate determining step in the oxidation of each specie is deduced to be a one electron step in which no protons are released and so likely corresponds to the initial formation of a very short-lived radical cation either in solution or adsorbed on the platelet. Overall the work establishes a generic method for the elucidation of the rate determining electron transfer in a multistep process free from any complexity imposed by preceding or following chemical reactions which occur on the timescale of conventional voltammetry.

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