- A
- Drainage half-life
Time after which 50% of the liquid has drained from the foam. - Maximum foam volume
Maximum value of foam volume during foam formation. - 90%-max. Time
Time after which 90% of the maximum foam volume has formed. - Wetting of surfaces
- Removal of oils and greases from surfaces
- Emulsifying oil in water and dispersing pigments, etc.
- Foam formation or prevention
- Drop formation and adjustment of the drop size
- No wetting: liquid lies on the surface like a drop (contact angle > 90°).
- Partial wetting: liquid lies on the surface like a semicircle (contact angle < 90°)
- Complete wetting: liquid lies flat on the surface
Automated measurement of dynamic Surface tension over a Bubble lifetime range with a SITA Tensiometer. In AUTO mode, the tensiometer varies the bubble lifetime automatically. The AUTO mode is used to characterise the surfactant dynamics and Wetting behaviour, e.g. when comparing different surfactant formulations and surfactant concentrations. The mode is also used to determine the control bubble lifetime for the SINGLE mode as part of preliminary tests and the determination of reference values.
General contamination of cleaning baths. The main components of contamination in the cleaning medium can be production aids as well as particles and chips. If the cleaning bath is too heavily contaminated, the cleaning capacity of the bath can decrease. To counteract this effect, it is necessary to monitor the concentration of the cleaning solution.
Surface tension measurement methods must specifically enlarge the surface area of liquids, for example by pulling or pushing. In the bubble differential pressure method, this is done by creating an air bubble at the tip of a Capillary. All SITA tensiometers work according to this method, making the measured values comparable with each other.
Air flows through a capillary into the liquid, creating an air bubble at the tip of the capillary. This air bubble is the new surface. The surface tension is calculated from the pressure signals that occur during the bubble formation in the volume flow.
The bubble lifetime is the key measurement parameter in the Bubble differential pressure method and indicates the time from the generation to the bursting of the bubble. It is also known as the wetting time or surface age.
In a liquid Foam, spherical and Polyhedral foam can occur. Spherical bubbles form at relatively high liquid content, so Spherical foam is also called wet foam. With Drainage-related loss of liquid, the gas phase takes on a polyhedral shape.
The dimension used to describe the expansion of a foam bubble in a liquid foam, e.g. 0.1 mm.
The plotting of the quantity of different bubble sizes of a monitored Foam volume in a histogram. It is used to describe the homogeneity of a foam. By comparing different Bubble size distributions, the ageing of the foam can be mapped qualitatively.
Builders (Builder salts) are organic or inorganic builders which, in addition to tensides, are contained in aqueous cleaning chemicals. Builder salts are used, for example, to determine the pH value of the washing bath, to adjust the water hardness, to protect material surfaces, to facilitate the removal of solid particles and to increase the cleaning effect of the Surfactants in a kind of synergy effect.
SITA calibration standards are used to check the SITA Fluorescence measuring devices. The Calibration standard N0 has no fluorescence and the standard N1 has a defined fluorescence. By using the calibration standards, the lens is checked for contamination and the offset of the sensor characteristic curve is checked or adjusted.
The capillary generates the air bubbles as interfaces or surfaces in the liquid for the bubble differential pressure method for measuring the surface tension. SITA tensiometers use permanent capillaries made of PEEK (polyether ether ketone) and glass as well as disposable capillaries made of PTFE (polytetrafluoroethylene, ‘Teflon’) for various applications.
Absence of impurities. Like "stillness", Cleanliness cannot be measured. Only the amount of contamination ("noise") is measurably accessible.
The Contact angle, also called the boundary or wetting angle, is the angle formed by a drop of liquid on the surface of a solid.
Contact angle measurement using test liquids offers the possibility of determining an objective value for the Wettability of a surface. The following applies: the smaller the contact angle, the better the examined surface can be wetted by the liquid used.
Surface-active substances in liquids that counteract foam formation or accelerate drainage.
Describes the loss over time of a liquid bound in the foam. The drainage of the liquid leads to a reduction of the lamella thickness. High drainage is synonymous with rapid Foam decay or unstable foam.
Filmic contamination is a thin, coherent non-particulate layer of unwanted, foreign components on component surfaces. Typical filmic contaminants are e.g. oils, greases, cooling lubricants or emulsion residues.
Fluorescence is the spontaneous emission of light shortly after a material is excited by light. Due to energy losses between absorption and emission (Stokes shift), the emitted light has a shorter Wavelength than the excitation light. Fluorescent light is emitted diffusely in every direction.
The measured intensity of the emitted fluorescent light at a defined wavelength in the blue light range on a surface. The intensity is specified in the unit RFU (Relative Fluorescence Unit) and is related to the SITA Fluorescence standard.
Foams are dispersed systems in which gaseous bubbles are enclosed by solid or liquid walls. The gas phase content in the liquid or solid dominates. The internal structure, i.e. the distribution of the individual phases, is very complex due to the high gas content and is structured by foam bubbles. These occur as spherical spheres or polyhedral structures that influence each other. Free bubbles on a surface do not form foam.
As a multiphase mixture, foam is distinguished from an emulsion, a suspension or an aerosol.
Decrease in foam volume over time due to the bursting of individual foam bubbles in liquid foams. Foams are metastable: foam bubbles burst when the foam lamellae surrounding them break or due to thermal and mechanical influences. The foam mixture loses the properties that characterise it as a foam.
Captures the Foam structure and liquid level with a vertically arranged, movable camera system by total reflection.
Liquid foams are strongly time-varying and thermodynamically metastable systems. As a result, the foam volume decreases, the liquid content decreases and changes in the foam structure occur. The foam volume changes due to foam decay. The rate at which the foam volume decreases is considered a measure of the stability of a foam.
Foams are stabilised e.g. by protein compounds, polymers or surfactants. In the field of cleaning and personal care products, the latter are mainly responsible for foam stabilisation. The surfactants attach themselves to the foam lamellae and hold the liquid in the lamella due to their hydrophilic character.
Distribution and characteristics of the gas and liquid phases in liquid foams. Spherical foam and polyhedral foam differ in the shape of the gas phase, the liquid content and the rheological properties. Real foams are polydisperse, i.e. the size of the gas bubbles is uneven. Typically, the structural inhomogeneity is visualised as a histogram of the Bubble size distribution.
Captures the topography of the foam surface and the resulting Total volume using a 3D scanning technique with fringe light (structured light method).
Difference between total volume and liquid volume measured with the SITA FoamTester.
The ability of a liquid to produce a quantity of foam in a certain time. The Foaming behaviour is determined by measuring the foam volume with the SITA FoamTester.
Ratio between the maximum foam volume and the filling volume of liquid foams when measured with the SITA FoamTester.
Gas fraction in the foam phase. Difference between foam volume and liquid volume in the foam.
Interfacial tension is the term used to describe forces that occur between two phases in contact (gaseous, liquid or solid). If the interfacial tension occurs between a liquid and a gaseous phase, it is called surface tension.
Calculated quotient of the liquid volume (in the foam) and the foam volume in liquid foams.
Difference between the filling volume provided in the experiment and the liquid volume below the foam.
Micelles are small aggregates of surfactants in which the hydrophobic ends of the ten-side molecules point inwards and the hydrophilic head groups point outwards. Micelles form spontaneously and represent an energetically more favourable state. The specific concentration at which this process starts is called the critical micelle formation concentration cmc.
Continuous measurement of the dynamic surface tension with the SITA tensiometer at a defined bubble lifetime. The ONLINE mode is used for continuous process monitoring or for analysing external influences, e.g. temperature.
Photobleaching is a dynamic process in which fluorescent structures are photochemically destroyed by UV excitation and their ability to fluoresce diminishes. The extent of the photobleaching effect depends on the substance. An illustrative example is white newsprint, which turns yellow in sunlight.
Polyhedral foam or dry foam in liquid foams is created from a spherical foam by the liquid flowing out of the foam lamellae. Both types usually occur in a foaming liquid, with the spherical foam being located below the polyhedral foam. The liquid flows downwards due to gravity, the foam lamellae become thinner and finally burst at a critical layer thickness - the foam decays.
Surface Roughness (obsolete roughness) refers to the unevenness of the surface height of a solid.
Single-point measurement of the dynamic surface tension with SITA tensiometers at a defined bubble lifetime. This mode is suitable as a target/actual comparison with reference values for controlling the surfactant concentration in process and quality monitoring.
Spherical or wet foam in liquid foams consists of many individual bubbles in the form of spheres (smallest surface area with largest volume), between which there is a lot of liquid.
Surface activation is a chemical or physical process in which the surface of a material becomes more reactive and can interact better with other substances. This is often applied to increase the adhesion e.g. of coatings, adhesives and paints on plastics, metals or glass. Common processes include plasma and corona treatment or the chemical removal of oxide layers.
Surface tension σ (sigma) is a property of a liquid, e.g. water, at the interface with a gas, e.g. air. Cohesive forces between the liquid molecules cause a tension on the surface (similar to a skin), which always tries to keep the surface as small as possible. The effect is particularly clear in the case of water drops, whose round shape is created by precisely these inwardly directed forces. The surface tension is usually given in mN/m or dyne/m. Water has a surface tension of approx. 72 mN/m at room temperature.
Due to the opposing molecule parts, surfactants move towards surfaces in an aqueous environment. This behaviour is called surface-active. This movement of the surfactants is time-dependent and is influenced, among other things, by the type and concentration of surfactant, temperature and the liquid surrounding it (matrix effects). Therefore, the surfactant concentration can be determined indirectly via the measured surface tension.
The surface-active behaviour of surfactants, also called wetting agents, is specifically exploited in technical applications for a variety of effects, for example:
Surfactants are a group of chemicals that consist oftwo opposing molecular parts: a non-polar, hydrophobic hydrocarbon part and a polar, hydrophilic head group. They are classified according to the type of head group into non-ionic, anionic, cationic and amphoteric surfactants.
These two parts of the molecule behave very differently towards water: the hydrophobic part turns away from the water, while the hydrophilic part is inclined towards the water. Because of these opposing components, they move towards surfaces in an aqueous environment. This behaviour is called surface-active.
Tensiometers are measuring instruments for characterising the interfacial or surface tension of liquids by increasing the surface of the liquid by a certain amount, depending on the method, and measuring the force applied. SITA tensiometers use the bubble differential pressure method, in which an air bubble (surface) is generated at a capillary tip. All SITA tensiometers work according to this method, which means that the measured values can be compared with each other.
Sum of foam and liquid volume, measurable by the Foam Surface Scanner and the Foam Interface Scanner of the SITA FoamTester.
The distance between two successive phases of waves. SITA fluorescence meters measure at a fixed wavelength in the range of blue light.
Wettability describes the ability of a surface to be wetted by a liquid. It is particularly important for industrial production, as surfaces with different wettabilities also have different properties. For example, high-energy surfaces are easier to print on. The wettability property can be assessed by measuring the contact angle on the surface.
Wetting describes the behaviour of liquids when they come into contact with a surface. There are three different types of wetting: