This page provides a glossary of the terms that we commonly use on the BTG Labs website. We developed this resource because many visitors to our website may not know what some of the terms mean and we wanted to ensure that the educational content we provided was not obscured because of a technical term that was used.
Abrasion is the result of sliding contact and/or impingement of hard, sharp-edged particles onto a softer material. It results in material deformation by plastic flow and material removal by fracture. Material removal can create a clean, high-energy surface that is receptive to coating or adhesive bonding. Typical types of abrasion used in manufacturing include manual or automated sanding with abrasive coated paper or cloth and media blasting.
Adhesion is the attraction that exists between all dissimilar materials due to surface energy.
Adhesion failure is an interfacial bond failure between an adhesive or coating and the substrate.
Adhesive bonding is the process by which two surfaces are joined together utilizing the intermolecular attractions between the surfaces and an intermediate substance (adhesive).
Advancing contact angle is established by a liquid front that is advancing slowly over a surface. It is related to the free energy of wetting. The advancing contact angle is the largest equilibrium contact angle that exists between a given surface and liquid.
Anti-fog coating creates a hydrophilic surface such that condensation results in a uniform film of moisture rather than discrete droplets (which scatter light and create a 'foggy' appearance).
Ballistic deposition is a process in which one or more droplets of a liquid are impinged onto a surface with non zero velocity. When used to deposit a liquid drop for contact angle measurement, The kinetic energy imparted to the deposited drop can be used to overcome barriers to establishing an equilibrium drop shape on a rough or heterogeneous surface. Adjustment of the amount of kinetic energy can be used to achieve an advancing or receding contact angle.
Blooming is the migration of a mobile component from within a polymer to the surface. Blooming is desirable in the case of antistatic or scratch/mar and lubricant additives whose presence on the surface is necessary for function. Blooming is undesirable when it leads to degradation of desirable surface properties. An example of undesirable blooming is plasticizer migration to a polymer surface which can lead to low surface energy and poor paint adhesion.
A bond is the chemical attraction between two contacting surfaces that results from attractions between the atoms, molecules, or ions present in the surfaces.
A “bond unit” represents a portion of a surface that has been prepared consistently at every point in the processing stage. Bond units are not defined by physical dimensions. A bond unit might be one square inch, 20 square feet, or any other shape and perimeter combination. It represents a discrete surface area defined by uniform processing occurring on a specific material surface.
A bond unit has been prepared all at the same time. It has been prepared by one person. The same cleaning process was used consistently throughout the surface preparation process – including the same detergents, wipes, or plasma treatment. Any deviation from this definition results in a distinct, separate bond unit being prepared. Triggers for transitioning from one bond unit to a new bond unit include:
A coating is a substance applied to the surface of an object that either functions as a protective barrier to contact with detrimental substances, provides functional properties (such as lubricity or reflectivity), improves aesthetic qualities, or a combination of these functions.
Chemical cleanliness is the absence of chemical contaminants on the surface of an object. The presence of chemical contaminants can interfere with adhesion of a desired substance such as a coating or adhesive.
Cohesive failure is an adhesive joint failure where the crack propagates within the adhesive. Cohesive failure indicates that bond strength is being controlled by the adhesive properties, not the interface. It is the most desirable failure mode in an adhesive joint, as it occurs at a load that is generally predictable.
Conformal coatings are thin (25-250 microns) polymeric films that are applied to PCBs to protect against moisture, dust, and chemicals.
Contact angle is the angle formed between a surface and a liquid in contact with the surface at the line of contact.
A contact angle goniometer is typically a laboratory instrument for measuring contact angles.
Contaminants are undesirable substances on a surface. Contaminants can be chemical (e.g. oils, fingerprints) or particulate (e.g.dust, machining debris).
Corona treatment is a type of plasma that utilizes high voltage electrodes at atmospheric pressure to excite gas molecules by ionization. Corona treatment is a low-temperature process. The excited gas can be used to effectively oxidize the surface of polymeric materials to achieve improved adhesion of inks, coatings, and adhesives.
A critical control point is a point in a manufacturing process where the surface properties of the materials being processed has the opportunity to change either intentionally or unintentionally, with positive or negative effects.
The dispersive component of surface energy is a measure of the attractions of the temporary dipoles created by random electron cloud fluctuations. Dispersion forces scale with electron cloud size and are not a strong function of specific functional groups. Surface treatments can decrease the dispersive component of surface energy (for example by disrupting aromatic structure), but not increase it. Dispersive interactions are weak but largely responsible for the adhesion of pressure sensitive tapes.
Dyne inks are mixtures of different solvents (frequently either 2-ethoxyethanol and formamide, or ethanol and water) that display known surface tension values and are used to determine wetting tension of a polyethylene and polypropylene films via ASTM D2578.
Dyne pens are a method for applying dyne inks routinely used in polymer and automotive industries.
Flame treatment is a type of plasma treatment where the gas is excited chemically rather than electrically. The gas phase species are high temperature. Flame treatment is commonly used to prepare the surfaces of polymeric materials such as packaging films and automotive body and interior components for improved adhesion to paints, inks, and adhesives.
Formed in place gaskets (FIPG) are liquid gaskets that cure after part assembly. FIPG can be more economical than traditional gaskets and allow for easier automated assembly.
Hydrophilicity is the tendency for a surface to attract water molecules. A hydrophilic surface exhibits attractive forces towards water molecules that are similar to or greater than the attraction of water molecules towards each other.
Hydrophobicity is the inability of a surface to attract water molecules. Water molecules are more strongly attracted to each other than to a hydrophobic surface, hence a water drop will 'bead up' (form a high contact angle) on a hydrophobic surface.
Interfacial failure is an adhesive joint failure where the crack propagates at the interface of the adhesive and the substrate. Interfacial failure is usually indicative of poor surface preparation or degradation due to chemical attack. It is the least desirable failure mode in an adhesive joint, as it occurs at a load that is generally unpredictable.
A joint is the interface formed between two substrates that are fastened either mechanically via bolts, rivets, or screws; metallurgically via soldering, brazing or welding; or chemically, via adhesives.
Material science is the study of the relationship between the molecular structure of a material and its properties. It can involve the design and discovery of new materials as well as the influence of manufacturing processes on the material’s structure and properties.
A metal is a material that conducts electricity and, in comparison to polymers, is generally hard, malleable, and ductile. Metals tend to have surfaces that are highly reactive (high surface energy) and therefore tend to react with other substances: they tend to oxidize and corrode, adsorb contaminants, and bond strongly to other substances such as polymers.
Oleophobic coatings are oil-repellent and often used on consumer electronic devices to make them easier to clean off skin oils.
Parylene coatings are thin polymer layers applied to a surface from vapor phase that can act as moisture barriers, corrosion barriers, and protect from chemical contamination. Parylene coatings are commonly used on medical devices and PCBs in demanding applications.
Plasma treatment is a surface treatment technique using a chemically or electrically excited gas to alter the composition and properties of a surface. Flame treatment, corona treatment, vacuum plasma treatment, and atmospheric pressure plasma treatment are all types of plasmas. Plasma treatments can be used to clean surfaces by oxidizing contaminants to volatile species, dehydrate and reduce oxides on metals, increase surface energy of polymers by introduction of oxidized functional groups, and deposit functional coatings.
Polar component of surface energy is a measure of the intermolecular attractions in a substance due to hydrogen bonding and the interactions of permanent dipoles, either with other dipoles (Keesom forces) or with induced dipoles (Debye forces). Because the polar component of surface energy depends on the specifics of molecular structure (i.e. the type and amount of functional groups), it is readily increased by surface treatments. The polar component of surface energy is responsible for many of the strong interactions responsible for adhesion of inks, paints, and coatings.
Polypropylene (PP) is a non-polar, partially crystalline thermoplastic polymer. It is used in a wide variety of medical, automotive, and clothing. It frequently requires surface treatment prior to painting, printing, or bonding.
A polymer is a material made up of long molecular chains whose behavior is determined by the tendency of these chains to move under the influence of heat and pressure.
Polytetrafluoroethylene (PTFE) is a thermoplastic, synthetic fluoropolymer characterized by its hydrophobicity, low coefficient of friction, high temperature resistance, and chemical resistance. PTFE is commonly used for non-stick coatings, bearings, chemical process hardware, and wire insulation.
Primer is a preparatory coating applied to a surface prior to bonding or coating to aid in adhesion and/or improve durability. Primers can also be used to protect a prepared surface during storage if it cannot be immediately coated or bonded.
Receding contact angle is established as a liquid front is slowly retracted across a surface. It is related to the free energy of dewetting (liquid-solid adhesion) and is affected strongly by the presence of high-energy functional groups on a surface. The receding contact angle is the smallest equilibrium contact angle that exists between a given liquid/solid pair.
Spectroscopy is the study of the absorption, emission, reflection, refraction, and resonance of electromagnetic radiation by matter. Depending on the type of spectroscopy, the specific behavior of the substance can be used to characterize the atomic composition and molecular structure.
A surface is the part of a substance with properties different from the bulk due to the lack of bonds on one side (i.e. the part that has surface energy). Typically the surface includes the outermost 2-5 molecular layers of a material.
Surface cleanliness refers to the amount of contaminants on the surface of a material.
Surface energy While molecules in the bulk of a substance have bonds with nearest neighbors on all sides, those present in a surface are missing those bonds on one side. Because of these missing bonds, a surface has the potential to react chemically and physically with other substances. This potential is called Surface Energy. It is expressed in units of energy/area (e.g. millijoules/m2) or force/length (e.g. dyne/cm).
Surface preparation is the process of generating a surface that is acceptable to the application of an adhesive or coating. Surface preparation techniques include plasma treatment, abrasion, washing, vapor degreasing, etc.
Surface tension is the surface energy of a liquid, usually expressed in dynes/cm. It is the excess chemical potential of molecules in the surface of the liquid compared to the bulk of the liquid. Surface tension is a measure of the strength of attraction of liquid molecules for each other: high surface tension liquids have strong intermolecular attractions.
Surface treatment is any process applied to a surface of a material to obtain desired surface properties, such as improved adhesion or corrosion resistance. Surface treatments include processes such as anodizing of metals or corona, plasma, and flame treatment of polymers.
Surfactant is a compound that tends to migrate to the surface of a liquid or to the interface of a liquid with another liquid or solid, and acts to lower the liquid surface tension and improve wetting. Surfactants are a major component of most aqueous cleaners. Improper rinsing tends to leave surfactant residue on surfaces that can interfere with downstream processing, such as coating or bonding.
Thermoplastic polymers have chains that are connected to each other only by physical entanglements. They are frequently processable by heat (e.g. injection molding, thermoforming).
Thermoset polymers have chains that are connected to each other by covalent bonds as well as physical entanglements. Once these covalent bonds are established (by curing) they are no longer thermally processable.
A water break test involves observing how water flows over a surface. If the surface is sufficiently hydrophilic, the water will flow in a continuous sheet. If sufficient hydrophobic contaminants are present, the water flow will break up into rivulets.
Wettability is the tendency of a surface to be wet by a liquid. In general, high energy surfaces have high wettability: the attraction of the liquid towards the surface is large compared with the attraction of the liquid towards itself.
Wetting is the tendency of a liquid to spread across a surface to maximize the interfacial area. Wetting is driven by the relative strength of the self-attractive forces of the liquid molecules compared to their attractions to the solid surface. If the self-attractive forces are greater, the liquid will be non-wetting and tend to remain beaded up (establish a high contact angle). If the attractions to the solid surface are greater, the liquid will wet and tend to spread out (establish a low contact angle).
This list is an index of the terms on this page. They link to each term.