Property testers are used to determine various physical properties of samples, including cloud point, distillation, flash point, freezing point, melting point, pour point, and vapor pressure.
Adsorption is the physicochemical adhesion of a substance (liquid, gas or dissolved solids sorbate) onto the surface of a solid or liquid. Adsorption results in the accumulation of molecules of gases, or ions or molecules of liquids, at the surfaces of contacting solids or liquids. Desorption is the release of the molecular layer of adsorbed on the surface of an absorbent. Desorption can be caused by high temperature, high humidity or scalping. Chemisorption is the process where sorbates are adsorbed and chemically changed by a reaction with the sorbent material. Physisorption is the process where molecules are physically bonded to the surface by Van der Vals and weak dipole forces. Physisorption processes are more reversible and weaker bonds are formed compared to chemisorption processes. Sorption, adsorption and desorption can be determined by measuring weight changes of the sorbate material. Absorption is the taking up or retention of one material by another by chemical or molecular action. Absorption is measured based on time and the amount of fluid displaced from a fluid reservoir.
The temperature at which the sample and water separate is known as the “cloud point temperature”; or simply “cloud point” because, at separation a previously clear solution becomes cloudy. Deflection or softening point instruments measure the temperature that reflects the point of softening to be expected when a material is used in an elevated temperature application. Distillation is a process in which a liquid or vapor mixture of two or more substances is separated into its component fractions of desired purity, by the application and removal of heat. Flash point is the lowest temperature at which a liquid can form an ignitable mixture in air near the surface of the liquid. The lower the flash point, the easier it is to ignite the material. Freezing point is the temperature at which a liquid becomes a solid at normal atmospheric pressure. Friction or wear testers test friction force, the resisting force tangential to the interface between two bodies when, under the action of an external force, one body moves or tends to move relative to the other. Gelation refers to the amount of time a sample requires to form a gel. A melting point is the temperature at which a solid becomes a liquid at normal atmospheric pressure. Gas permeability is the ability, or measurement of a sample's ability, to transmit vapors or gases. Liquid permeability is the ability, or measurement of a sample's ability, to transmit liquids. Densometers or porosimeters are used for measuring porosity, air-permeability or air resistance of sheet-like or bulk materials. It is often necessary to know how cold a particular sample can become before it loses its fluid characteristics; this is why pour point is an important measurement. Texture analysis is primarily concerned with the evaluation of mechanical characteristics where a food is subjected to a controlled force from which a deformation curve of its response is generated. All solids and liquids, that is, all substances in condensed phases, exhibit a vapor pressure. Vapor pressure is defined as the pressure of the vapor of a liquid or solid in equilibrium with the liquid or solid state.