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44-602: It is possible to create foam balloons with a diameter of more than 1 metre. Identical foam balloons can be manufactured with the same machine in quick repetition. Flogos are most frequently for "skyvertising" or aerial advertising purposes, since they can be manufactured easily in the form of corporate or team logos . In principle, wind conditions in the lower atmosphere can be easily monitored with flogos. Foam balloons are not stable long-term, but decay after some hours. Nevertheless, they can reach heights of several kilometres up. This advertising -related article

88-643: A gill -shaped structure, often with fluid in between though sometimes simply a set of "welded" plates. The term is used in biological contexts for thin membranes of plates of tissue . In the context of materials science , the microscopic structures in bone and nacre are called lamellae. Moreover, the term lamella is often used to describe crystal structure of some materials. In surface chemistry (especially mineralogy and materials science ), lamellar structures are fine layers, alternating between different materials. They can be produced by chemical effects (as in eutectic solidification ), biological means, or

132-432: A deliberate process of lamination , such as pattern welding . Lamellae can also describe the layers of atoms in the crystal lattices of materials such as metals. In surface anatomy , a lamella is a thin plate-like structure, often one amongst many lamellae very close to one another, with open space between. In chemical engineering , the term is used for devices such as filters and heat exchangers . In mycology ,

176-420: A glass of beer are examples of foams; soap foams are also known as suds . Solid foams can be closed-cell or open-cell . In closed-cell foam, the gas forms discrete pockets, each completely surrounded by the solid material. In open-cell foam, gas pockets connect to each other. A bath sponge is an example of an open-cell foam: water easily flows through the entire structure, displacing the air. A sleeping mat

220-402: A lamella (or gill) is a papery hymenophore rib under the cap of some mushroom species, most often agarics . The term has been used to describe the construction of lamellar armour , as well as the layered structures that can be described by a lamellar vector field . In medical professions, especially orthopedic surgery , the term is used to refer to 3D printed titanium technology which

264-565: A larger diffusion time than the bulk of the solution—so the surfactants are less concentrated in the indentation. Also, surface stretching makes the surface tension of the indented spot greater than the surrounding area. Consequentially—since diffusion time for the surfactants is large—the Marangoni effect has time to take place. The difference in surface tension creates a gradient, which instigates fluid flow from areas of lower surface tension to areas of higher surface tension. The second picture shows

308-480: A more accurate model for bubbles rising is: Deviations are due to the Marangoni effect and capillary pressure, which affect the assumption that the bubbles are spherical. For laplace pressure of a curved gas liquid interface, the two principal radii of curvature at a point are R 1 and R 2 . With a curved interface, the pressure in one phase is greater than the pressure in another phase. The capillary pressure P c

352-409: A result of gas diffusing between cells, liquid draining from the foam into a bulk liquid, etc. Theories regarding liquid foams have as direct analogs theories regarding emulsions , two-phase material systems in which one liquid is enclosed by another. In most foams, the volume of gas is large, with thin films of liquid or solid separating the regions of gas. A bath sponge and the head on

396-638: A shallow slope after yielding (plateau stress), and an exponentially increasing regime. The stiffness of the material can be calculated from the linear elastic regime where the modulus for open celled foams can be defined by the equation: ( E ∗ E s ) f = C f ( ρ ∗ ρ s ) 2 {\displaystyle \left({\frac {E^{*}}{E_{s}}}\right)_{f}=C_{f}\left({\frac {\rho ^{*}}{\rho _{s}}}\right)^{2}} where E s {\displaystyle E_{s}}

440-479: A type of colloid . Foam can also refer to something that is analogous to foam, such as quantum foam . A foam is, in many cases, a multi-scale system. One scale is the bubble: material foams are typically disordered and have a variety of bubble sizes. At larger sizes, the study of idealized foams is closely linked to the mathematical problems of minimal surfaces and three-dimensional tessellations , also called honeycombs . The Weaire–Phelan structure

484-403: Is where V {\displaystyle V} is the volume of the bubble, g {\displaystyle g} is the acceleration due to gravity, and ρ 1 is the density of the gas ρ 2 is the density of the liquid. The force working against the buoyancy force is the surface tension force, which is where γ is the surface tension, and r {\displaystyle r}

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528-422: Is a stub . You can help Misplaced Pages by expanding it . Foam Foams are two-phase material systems where a gas is dispersed in a second, non-gaseous material, specifically, in which gas cells are enclosed by a distinct liquid or solid material. The foam "may contain more or less liquid [or solid] according to circumstances", although in the case of gas-liquid foams, the gas occupies most of

572-451: Is an example of a product composed of closed-cell foam. Foams are examples of dispersed media . In general, gas is present, so it divides into gas bubbles of different sizes (i.e., the material is polydisperse )—separated by liquid regions that may form films, thinner and thinner when the liquid phase drains out of the system films . When the principal scale is small, i.e., for a very fine foam, this dispersed medium can be considered

616-412: Is an important factor in foam based technologies. For elastomeric cellular solids, as the foam is compressed, first it behaves elastically as the cell walls bend, then as the cell walls buckle there is yielding and breakdown of the material until finally the cell walls crush together and the material ruptures. This is seen in a stress-strain curve as a steep linear elastic regime, a linear regime with

660-399: Is completed very slowly, then one bubble can be emitted from the orifice at a time as shown in the picture below. One of the theories for determining the separation time is shown below; however, while this theory produces theoretical data that matches the experimental data, detachment due to capillarity is accepted as a better explanation. The buoyancy force acts to raise the bubble, which

704-448: Is derived from assuming an idealized foam with engineering approximations from experimental results. Most energy absorption occurs at the plateau stress region after the steep linear elastic regime. The isotropy of the cellular structure and the absorption of fluids can also have an impact on the mechanical properties of a foam. If there is anisotropy present, then the materials response to stress will be directionally dependent, and thus

748-411: Is given by the equation of: where γ {\displaystyle \gamma } is the surface tension. The bubble shown below is a gas (phase 1) in a liquid (phase 2) and point A designates the top of the bubble while point B designates the bottom of the bubble. At the top of the bubble at point A, the pressure in the liquid is assumed to be p 0 as well as in the gas. At the bottom of

792-432: Is reported in one primary philosophical source to be the best possible (optimal) unit cell of a perfectly ordered foam, while Plateau's laws describe how soap-films form structures in foams. At lower scale than the bubble is the thickness of the film for metastable foams, which can be considered a network of interconnected films called lamellae . Ideally, the lamellae connect in triads and radiate 120° outward from

836-461: Is small. As the stem of the bubble grows in length, it becomes more unstable as one of the radius grows and the other shrinks. At a certain point, the vertical length of the stem exceeds the circumference of the stem and due to the buoyancy forces the bubble separates and the process repeats. The stabilization of a foam is caused by van der Waals forces between the molecules in the foam, electrical double layers created by dipolar surfactants, and

880-444: Is substituted in to the equation above, separation occurs at the moment when Examining this phenomenon from a capillarity viewpoint for a bubble that is being formed very slowly, it can be assumed that the pressure p {\displaystyle p} inside is constant everywhere. The hydrostatic pressure in the liquid is designated by p 0 {\displaystyle p_{0}} . The change in pressure across

924-489: Is the density for a gas and liquid respectively in units of g/cm and ῃ 1 and ῃ 2 is the dynamic viscosity of the gas and liquid respectively in units of g/cm·s and g is the acceleration of gravity in units of cm/s . However, since the density and viscosity of a liquid is much greater than the gas, the density and viscosity of the gas can be neglected, which yields the new equation for velocity of bubbles rising as: However, through experiments it has been shown that

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968-440: Is the density of the solid. The elastic modulus for closed cell foams can be described similarly by: ( E ∗ E s ) f = C f ( ρ ∗ ρ s ) 3 {\displaystyle \left({\frac {E^{*}}{E_{s}}}\right)_{f}=C_{f}\left({\frac {\rho ^{*}}{\rho _{s}}}\right)^{3}} where

1012-455: Is the modulus of the solid component, E ∗ {\displaystyle E^{*}} is the modulus of the honeycomb structure, C f {\displaystyle C_{f}} is a constant having a value close to one, ρ ∗ {\displaystyle \rho ^{*}} is the density of the honeycomb structure, and ρ s {\displaystyle \rho _{s}}

1056-405: Is the radius of the orifice. As more air is pushed into the bubble, the buoyancy force grows quicker than the surface tension force. Thus, detachment occurs when the buoyancy force is large enough to overcome the surface tension force. In addition, if the bubble is treated as a sphere with a radius of R {\displaystyle R} and the volume V {\displaystyle V}

1100-418: Is used in the flooring industry to describe the finished top-layer of an engineered wooden floor. For example, an engineered walnut floor will have several layers of wood and a top walnut lamella. In archaeology , the term is used for a variety of small flat and thin objects, such as Amulet MS 5236 , a very thin gold plate with a stamped text from Ancient Greece in the 6th century BC. In crystallography ,

1144-437: Is used to create implantable medical devices (in this case, orthopedic implants ). In context of water-treatment , lamellar filters may be referred to as plate filters or tube filters . This term is used to describe a certain type of ichthyosis , a congenital skin condition. Lamellar Ichthyosis often presents with a "colloidal" membrane at birth. It is characterized by generalized dark scaling. The term lamella(e)

1188-458: The Marangoni effect , which acts as a restoring force to the lamellae. The Marangoni effect depends on the liquid that is foaming being impure. Generally, surfactants in the solution decrease the surface tension. The surfactants also clump together on the surface and form a layer as shown below. For the Marangoni effect to occur, the foam must be indented as shown in the first picture. This indentation increases local surface area. Surfactants have

1232-411: The surface tension , and the formation of foam faster than its breakdown. To create foam, work (W) is needed to increase the surface area (ΔA): where γ is the surface tension. One of the ways foam is created is through dispersion, where a large amount of gas is mixed with a liquid. A more specific method of dispersion involves injecting a gas through a hole in a solid into a liquid. If this process

1276-420: The bubble at point B, the hydrostatic pressure is: where ρ 1 and ρ 2 is the density for a gas and liquid respectively. The difference in hydrostatic pressure at the top of the bubble is 0, while the difference in hydrostatic pressure at the bottom of the bubble across the interface is gz ( ρ 2  −  ρ 1 ). Assuming that the radii of curvature at point A are equal and denoted by R A and that

1320-403: The cell and stiffness of the matrix material. Another important property which can be deduced from the stress strain curve is the energy that the foam is able to absorb. The area under the curve (specified to be before rapid densification at the peak stress), represents the energy in the foam in units of energy per unit volume. The maximum energy stored by the foam prior to rupture is described by

1364-444: The connection points, known as Plateau borders . An even lower scale is the liquid–air interface at the surface of the film. Most of the time this interface is stabilized by a layer of amphiphilic structure, often made of surfactants , particles ( Pickering emulsion ), or more complex associations. Several conditions are needed to produce foam: there must be mechanical work, surface active components (surfactants) that reduce

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1408-505: The equation: W m a x E s = 0.05 ( ρ ∗ ρ s ) 2 [ 0.975 − 1.4 ( ρ ∗ ρ s ) ] {\displaystyle {\frac {W_{max}}{E_{s}}}=0.05\left({\frac {\rho ^{*}}{\rho _{s}}}\right)^{2}\left[0.975-1.4\left({\frac {\rho ^{*}}{\rho _{s}}}\right)\right]} This equation

1452-439: The film at equilibrium after the Marangoni effect has taken place. Curing a foam solidifies it, making it indefinitely stable at STP. Witold Rybczynski and Jacques Hadamard developed an equation to calculate the velocity of bubbles that rise in foam with the assumption that the bubbles are spherical with a radius r {\displaystyle r} . with velocity in units of centimeters per second. ρ 1 and ρ 2

1496-492: The foam base, which Rybczynski and Hadamar include in their theory; however, foam also destabilizes due to osmotic pressure causes drainage from the lamellas to the Plateau borders due to internal concentration differences in the foam, and Laplace pressure causes diffusion of gas from small to large bubbles due to pressure difference. In addition, films can break under disjoining pressure , These effects can lead to rearrangement of

1540-455: The foam structure at scales larger than the bubbles, which may be individual ( T1 process ) or collective (even of the "avalanche" type). Solid foams, both open-cell and closed-cell, are considered as a sub-class of cellular structures. They often have lower nodal connectivity as compared to other cellular structures like honeycombs and truss lattices, and thus, their failure mechanism is dominated by bending of members. Low nodal connectivity and

1584-406: The interface from gas to liquid is equal to the capillary pressure; hence, where R 1 and R 2 are the radii of curvature and are set as positive. At the stem of the bubble, R 3 and R 4 are the radii of curvature also treated as positive. Here the hydrostatic pressure in the liquid has to take in account z, the distance from the top to the stem of the bubble. The new hydrostatic pressure at

1628-484: The inverse of R A must be larger than the R B . Meaning that from the top of the bubble to the bottom of the bubble the radius of curvature increases. Therefore, without neglecting gravity the bubbles cannot be spherical. In addition, as z increases, this causes the difference in R A and R B too, which means the bubble deviates more from its shape the larger it grows. Foam destabilization occurs for several reasons. First, gravitation causes drainage of liquid to

1672-401: The only difference is the exponent in the density dependence. However, in real materials, a closed-cell foam has more material at the cell edges which makes it more closely follow the equation for open-cell foams. The ratio of the density of the honeycomb structure compared with the solid structure has a large impact on the modulus of the material. Overall, foam strength increases with density of

1716-399: The radii of curvature at point B are equal and denoted by R B , then the difference in capillary pressure between point A and point B is: At equilibrium, the difference in capillary pressure must be balanced by the difference in hydrostatic pressure. Hence, Since, the density of the gas is less than the density of the liquid the left hand side of the equation is always positive. Therefore,

1760-463: The resulting failure mechanism ultimately lead to their lower mechanical strength and stiffness compared to honeycombs and truss lattices. The strength of foams can be impacted by the density, the material used, and the arrangement of the cellular structure (open vs closed and pore isotropy). To characterize the mechanical properties of foams, compressive stress-strain curves are used to measure their strength and ability to absorb energy since this

1804-407: The stem of the bubble is p 0 ( ρ 1  −  ρ 2 ) z . The hydrostatic pressure balances the capillary pressure, which is shown below: Finally, the difference in the top and bottom pressure equal the change in hydrostatic pressure: At the stem of the bubble, the shape of the bubble is nearly cylindrical; consequently, either R 3 or R 4 is large while the other radius of curvature

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1848-550: The stress-strain curve, modulus, and energy absorption will vary depending on the direction of applied force. Also, open-cell structures which have connected pores can allow water or other liquids to flow through the structure, which can also affect the rigidity and energy absorption capabilities. Lamella (materials) A lamella ( pl. : lamellae ) is a small plate or flake, from the Latin, and may also refer to collections of fine sheets of material held adjacent to one another in

1892-537: The term was first used by Christopher Chantler and refers to a very thin layer of a perfect crystal, from which curved crystal physics may be derived. In textile industry , a lamella is a thin metallic strip used alone or wound around a core thread for goldwork embroidery and tapestry weaving . In September 2010, the U.S. Food and Drug Administration (FDA) announced a recall of two medications which contained "extremely thin glass flakes (lamellae) that are barely visible in most cases. The lamellae result from

1936-433: The volume. The word derives from the medieval German and otherwise obsolete veim , in reference to the "frothy head forming in the glass once the beer has been freshly poured" (cf. ausgefeimt ). Theories regarding foam formation, structure, and properties—in physics and physical chemistry —differ somewhat between liquid and solid foams in that the former are dynamic (e.g., in their being "continuously deformed"), as

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