What is Surface Energy (SE)?
Surface energy γ, is the principal characteristic measured by the IGC-SEA. For a solid to exist, it must be energetically favorable (of lower energy) for its molecules to form bonds with each other. It follows that the molecules at the solid’s surface are in a less favorable state (of higher energy), as they are not surrounded by other bulk molecules. It is the same intermolecular forces which are responsible for the attraction between powder particles and other solids, liquid and vapor molecules which can occur via long range van der Waals forces (dispersion forces) and short range chemical forces (polar forces). Thus, surface energy values (dispersive and polar) correlate to several key solid properties including wetting, dispersability, powder flowability, agglomeration, process-induced disorder, adhesion/cohesion, static charge, adsorption capacity and surface chemistry.
Experimental Technique for Measuring Surface Energy
There are a range of techniques available for measuring the surface energy of solid particulate materials. Though contact angle measurement is by far the most common method, it is rarely used for particle and other non-planar materials due to experimental limitations leading to inaccurate and unreliable results. Inverse gas chromatography is now the proven and preferred method for surface energy measurements, and surface energy heterogeneity in particular.
Inverse Gas Chromatography
Inverse Gas Chromatography (iGC) is a gas-solid technique for characterizing surface and bulk properties of powders, particulates, fibers, films and semi solids. A series of vapor pulses are injected through a column packed with the sample of interest. Unlike traditional analytical gas chromatography, iGC is a physical chemistry technique using vapor probes with known properties to characterize the unknown surface/ bulk properties of the solid sample.
What is iGC-SEA (Inverse Gas Chromatography-Surface Energy Analyzer)?
iGC- SEA or Inverse Gas Chromatography-Surface Energy Analyzer is an instrument that uses the iGC principle. The heart of its innovation is the patented injection manifold system which generates accurate solvent pulse sizes across a large concentration range, resulting in isotherms at unprecedented high and low sample surface coverages. This allows for the accurate determination of surface energy heterogeneity distributions. The fully automated iGC-SEA can be operated at different solvent vapor, flow rate, temperature, humidity and column conditions.
iGC-SEA has a unique data analysis software called Cirrus Plus, specifically designed to measure surface energy heterogeneity, isotherm properties and related physical characterization parameters. Further, bulk solid property experiments resulting from probe-bulk interaction and using solubility theory are now possible. It automatically and directly provides a wide range of surface and bulk properties of the solid samples and gives more accurate and reliable data than manual calculations. It also has a humidity control option. The impact of humidity and temperature can be determined for the physicochemical properties of solids such as moisture induced Tg, BET specific surface area, surface energy, wettability, adhesion and cohesion. Read product information or request application notes.
Founding Principle of iGC-SEA
iGC is a gas-phase technique for characterizing surface and bulk properties of powders, particulates, fibers, films and semi-solids. An experiment consists of a series of vapor pulses or frontal injections eluting through a column packed with the sample under examination.
The vapor’s retention time is measured by a Flame Ionization Detector (FID). Varying the vapor probe molecule, flow rate, temperature, or column conditions elucidates a wide range of surface and bulk properties of the sample.