Glossary of Terms
This page provides a glossary of the terms that we commonly use on the Brighton Science 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
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
The 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 the 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:
- There is a shift change and A Different Person Prepares a Surface for Adhesion
- The Surface Preparation Process is Stopped for a Period of Time and Then Restarted
- A Different Cleaning Process was Used to Clean the Surface
- A cleaning solution or supplies have been changed
A Coating is a substance applied to the surface of an object that 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 the adhesion of the desired substance such as a coating or adhesive.
Cohesion is the interatomic or intermolecular attraction that holds a substance together.
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 Goniometer
A Contact Angle Goniometer is typically a laboratory instrument for measuring contact angles.
Contact Angle Hysteresis
The Contact Angle Hysteresis is the difference between the advancing and receding angles.
Contact Angle Measurement
Contact Angle is the angle formed between a surface and a liquid in contact with the surface at the line of contact. This angle can be measured using a contact angle meter. Angle measurements can be labeled using Greek symbols, like Theta (Θ).
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.
Critical Control Point
A Critical Control Point is a point in a manufacturing process where the surface properties of the materials being processed have the opportunity to change either intentionally or unintentionally, with positive or negative effects.
Design Failure Mode and Effect Analysis or (DFMEA) is similar to FMEA, or Failure Mode and Effects Analysis, but with an added design element. It is an analysis processes used to find possible risks arising from a new or updated product.
DFMEA is necessary for all manufacturing processes, but especially those involving high-risk products, like medical devices. Failure to perform a proper DFMEA could results in loss of life first and foremost, along with additional costs, product dissatisfaction, or a slew of other public-facing issues.
Dispersive Component of Surface Energy
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.
Dynamic Contact Angle
Dynamic Contact Angle can either be:
- The contact angle of a liquid relative to a moving surface
- A contact angle that varied with time due to changes in the surface tension of the liquid, the surface energy of the substrate, or both.
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 the wetting tension of 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.
Failure Modes and Effects Analysis or (FMEA) is an analysis processes used to identify all possible risks arising from a new or update to a product. For more information, check out our eBook, The Strength of FMEA (Failure Modes & Effects Analysis) is Predictability.
Formed in Place Gaskets
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.
Fourier Transform Infrared Spectroscopy
Fourier Transform Infrared Spectroscopy (FTIR) measures the absorption of infrared light by a substance. Because the wavelengths of infrared light absorbed and the strength of absorption depends on the mass of the atoms, the strength of the bonds between atoms, and the polarity of the bonds; FTIR allows the identification of the specific molecular structures of a substance.
Hydrophilicity is the tendency for a surface to attract water molecules. A hydrophilic surface exhibits attractive forces toward water molecules that are similar to or greater than the attraction of water molecules toward 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 a chemical attack. It is the least desirable failure mode in an adhesive joint, as it occurs at a load that is generally unpredictable.
Interfacial Tension is the surface tension (or surface energy) remaining at the interface of two substances after they come into contact.
A Joint is an 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.
The Lotus Effect refers to the ultra-hydrophobicity properties of the lotus leaf which is due to a combination of a waxy hydrophobic composition along with a surface that is rough on a microscopic scale
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.
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 the 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 the surface energy of polymers by the introduction of oxidized functional groups, and deposit functional coatings.
Polar Component of Surface Energy
The 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 the 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.
A 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 they cannot be immediately coated or bonded.
Receding Contact Angle
A receding Contact Angle is established as a liquid front is slowly retracted across a surface. It is related to the free energy of de-wetting (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.
A Sessile Drop is a drop formed on the end of a syringe needle or other tube that is subsequently transferred to a surface for a contact angle measurement. A gentle transfer can achieve a contact angle that is close to the true advancing angle.
Sessile Drop Method
The Sessile Drop Method is the most common approach for contact angle measurements whereby the contact angle is estimated by averaging the contact angle of two diametrically opposed points on a sessile drop. These angles are generally measured either directly by constructing a tangent to the drop at the three-phase point, or indirectly by drop shape analysis. Obtaining precision and accuracy with this method requires a flat, smooth, horizontal surface and a uniformly round drop.
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.
Static Contact Angle
Static Contact Angle is the contact angle determined from a stationary drop.
Superhydrophobic (or Ultra-hydrophobic)
Superhydrophobic refers to surfaces that are highly hydrophobic and repel liquid droplets when placed onto the surface. One definition is a surface that demonstrates a water contact angle of 150° or more.
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 material.
Surface Cleanliness refers to the amount of contaminants on the surface of a material.
While molecules in the bulk of a substance have bonds with nearest neighbors on all sides, those present on 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 Intelligence is surface science applied to real-life adhesion, manufacturing, product development, and supply chain challenges.
This intelligence offers manufacturers:
- Convenience: clear and fast answers, right on site
- Consistency: the ability to anticipate and assure material performance
- Confidence: proven ways to improve quality and processes and deliver better products).
Surface Intelligence is about measurement, but also about alignment. It gives organizations a common language, data to innovate, and the ability to continually improve.
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 on 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.
TACT is an acronym that stands for, "Temperature, Agitation, Chemistry, and Time." It is known in the world of surface cleanliness as a simplified way to organize the most controllable parameters of most cleaning processes
Tensiometer is a metrology instrument used to measure the surface tension of liquids.
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.
Three-phase Contact Point
A three-phase contact point is a point where the perimeter of a liquid drop meets the gas interface and solid-liquid interface. The contact angle is defined as the angle between a tangent to the liquid surface and the solid surface at this point.
Water Break Test
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 attraction 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. Each term links to the definition.
Dispersive Component of Surface Energy
Fourier Transform Infrared Spectroscopy
Polar Component of Surface Energy