I – Nano- and Microtechnology from A – Z: From Nanosystems to Colloids and Interfaces



See Ion Beam Analysis.

IBB Rheometer

See Two-Point Test.

Ideal Fluid

See Inviscid Fluid.


See Imbedded Disc Retraction Method.


See Inorganic Fullerene-Like Material.


See Imbedded Fibre Retraction Method.


Inner Helmholtz plane, see Helmholtz Double Layer.

Iijima, Sumio (1939–)

A Japanese physicist and industrial scientist best known for coining the term carbon nanotube and demonstrating double-walled carbon nanotubes, both in 1991. He also discovered single-walled nanotubes in 1993. References [36, 172].

Illuminating Lens

(Microscopy) There are several kinds of illuminating lenses in microscopy. Their purpose is to focus the illuminating light onto a specimen in a particular way. For example, Köhler illumination refers to a condenser lens and diaphragm system designed and adjusted so as to provide bright, uniform illumination of a specimen across the full field of view. A condenser lens is a lens placed below (or in) a microscope stage but in the light path, in order to concentrate the illumination on the sample being studied. An Abbe condenser is used to provide a concentrated cone of light that illuminates the specimen being examined with uniform intensity over the entire field of view. See also Abbe Condenser. A dark-field condenser lens provides a specific kind of cone-shaped illuminating light needed for dark-field microscopy. See Dark-Field Microscopy. An illuminating lens is usually also associated with one or more diaphragms, which are typically iris-style sets of overlapping leaves or plates that can be opened or closed in order to regulate the amount of light illuminating a lens and/or the specimen under examination. See also Phase Contrast Microscopy.


See Ionization-Loss Spectroscopy.

Imaging Contrast Agent

See Contrast Agent.

Imbedded Disc Retraction Method

(IDR) A method for determining the interfacial tension between two polymer melts. A disc of one polymer is imbedded in a second polymer. Temperature is then increased so that the polymers melt and the disc retracts into the shape of a sphere. The shape changes are monitored as a function of time, and the interfacial tension is calculated from the analysis of the viscous and interfacial forces. See also Imbedded Fibre Retraction Method (IFR).

Imbedded Fibre Retraction Method

(IFR) A method for determining the interfacial tension between two polymer melts. A short, uniform fibre of one polymer is imbedded in a second polymer. Temperature is then increased so that the polymers melt and the fibre retracts into the shape of a sphere. The shape changes are monitored as a function of time, and the interfacial tension is calculated from the analysis of the viscous and interfacial forces. See also Imbedded Disc Retraction Method (IDR).


The displacement of a nonwetting phase by a wetting phase in a porous medium or a gel; the reverse of drainage.

Immersional Wetting

The process of wetting when a solid (or liquid) that is initially in contact with gas becomes completely covered by an immiscible liquid phase. See also Wetting, Spreading Wetting, and Adhesional Wetting.


An older term usually meaning injection. In the atmospheric sciences, it has been used to refer to the transfer of pollutants to a receptor, such as from the atmosphere into human lungs. The term generally refers, in some context, to the opposite of emission.


A device for the separation of larger-sized, heavier particles from smaller-sized, lighter particles in a gas stream by having the former strike a plate positioned in the flow path. The lighter particles follow the gas flow around the plate, which is called a collector. For a given set of operating conditions, particles larger than a certain size will be impacted and caught on the collector. The particle-size cutoff is not exact due to the effects of turbulence and the existence of velocity gradients. Particles smaller than the cutoff size will remain in the gas stream. A series of impactors, used to separate particles into several size fractions, is called a cascade impactor. Impactors employing a narrow nozzle or jet are sometimes called jet impactors. Impactors are sometimes referred to as koniometers. Elutriation and cyclones operate on a similar principle. See Reference [173]. See also Cascade Impactor.

Impingement-Plate-Tower Scrubber

A separation device used to remove fine aerosol particles, and/or aerosol droplets, from a gas stream. The scrubber has a number of horizontal plates or trays mounted in a tower, and the gas stream is made to flow upwards, counter-current against a downward flow of scrubbing liquid against which the desired aerosol particles and/or droplets are made to impact. The scrubbing liquid is usually an absorbent, or reactive, or solvent liquid. Such devices are widely used in industry. Impingement-Plate-Tower scrubbers are sometimes referred to as Acid-Gas Scrubbers, or Impingement-Tray-Tower Scrubbers. See also Mist Eliminator, Packed-Bed Scrubber, and Wet Scrubber.

Impingement Separator

See Separator.

Impingement-Tray-Tower Scrubber

See Impingement-Plate-Tower Scrubber.

Incidental Nanoparticles

Nanoparticles that have been formed as a by-product of a natural or artificial process, as opposed to being formed by design. Examples include nanoparticles formed during welding, milling, grinding, or combustion.

Inclined-Plate Settling

See Lamella Settling.

Increase of Volume upon Foaming

In foaming, 100 times the ratio of gas volume to liquid volume in a foam. Also termed the foaming power.

Indentation Hardness

See Hardness.

India Ink

A black ink comprising a colloidal dispersion of lampblack or carbon black particles, as the pigment, stabilized by a natural gum, and dispersed in an aqueous adhesive solution. Also termed Indian ink or Chinese ink. See also Lampblack and Carbon Black.

Indian Ink

See India Ink.

Indifferent Electrolyte

An electrolyte whose ions have no significant effect on the electric potential of a surface or interface, as opposed to potential-determining ions that have a direct influence on surface charge. This distinction is most valid for low electrolyte concentrations. Example: for the AgI surface in water, NaNO3 would be an indifferent electrolyte, but both Ag+ and I would be potential-determining ions.

Indirect Flotation

See Reverse Flotation.

Induced Gas Flotation

See Froth Flotation.

Induction Forces

Debye forces. See van der Waals Forces.

Inelastic Scattering

See Light Scattering.

Infinite Clusters

See Percolation.

Infinity Microscope

A microscope that incorporates a special lens (tube lens) in the optical path, between the objective lens and the eyepiece lens, in order to provide a region in the tube where the light rays are parallel to each other. This in turn provides a region into which can be inserted any of a number of accessories (such as polarizers) without causing optical aberrations or changes in focus. Infinity microscopes also use dedicated “infinity” objective lenses.

Infrared Reflection–Absorption Spectroscopy

(IRAS) A surface vibrational spectroscopic technique for studying adsorbed molecules on crystals. The absorption of infrared radiation due to the adsorbates is determined after reflection from a plane substrate surface. See also Table 15.

Inhalable Particulate Matter

Particulate matter that is hazardous when deposited anywhere in the respiratory tract. Operationally, this is often taken to be any particles with sizes up to 100 μm diameter. See also Respirable Particulate Matter, Thoracic Particulate Matter, and Table .9.

Inherent Viscosity

In solutions and colloidal dispersions, the natural logarithm of the relative viscosity, all divided by the solute or dispersed-phase concentration. ηInh = C–1 ln(η/ηo). In the limit of vanishing concentration, it reduces to the intrinsic viscosity. Also termed the logarithmic viscosity number. See Table .11.

Initial Knockdown Capability

See Knockdown Capability.

Initial Spreading Coefficient

See Spreading Coefficient.

Ink Bottle Pore

Describes a shape of dead-end pore, in which a narrow throat is connected to a larger pore body, in a porous medium. See also Porous Medium.

Inner Helmholtz Plane

(IHP) See Helmholtz Double Layer.

Inner Potential

  1. In the diffuse electric double layer extending outward from a charged interface, the electrical potential at the boundary between the Stern and the diffuse layer is termed the inner electrical potential. Synonyms include the “Stern layer potential” or “Stern potential.” See also Electric Double Layer and Zeta Potential.
  2. The electric potential inside a phase, in this case termed the Galvani potential. See also Galvani Potential, Outer Potential, and Jump Potential.

Inorganic Nanotube

A noncarbon nanotube. Such nanotubes have been made from a wide range of materials, including pure metals, and transition metal oxides and halides. It is expected that inorganic nanotubes may have advantages over carbon nanotubes where high loads, pressures, or temperatures are involved [174]. See also Carbon Nanotube.

Inorganic Fullerene-Like Material

(IFLM) A noncarbon nanoparticle having a fullerene-like structure. See also Fullerene.

Inorganic Nanotube

A noncarbon nanotube.


See Ion-Neutralization Spectroscopy.

In Silico

In science and engineering, the Latin-based term in silico generally refers to an experiment, calculation, or process simulation conducted by numerical (computer) simulation.

In Situ

In science and engineering, the Latin term in situ generally refers to an aspect of a reaction or process taking place where it normally occurs, as opposed to moving it to some other place. Examples include studying a phenomenon where it occurs, in a reaction mixture or in a process vessel. See also Ex Situ.

In Situ Method

(Emulsions) See Nascent Soap Method.

Integral Capacitance of the Electric Double Layer

See Capacitance of the Electric Double Layer.

Intelligent Materials

See Smart Materials.

Intelligent Textiles

See Smart Textiles.


(Photography) A formulated solution used in photographic film, plate, or paper processing to correct for under-exposure. Typical intensifiers for permanent images are based on the precipitation of silver (e.g., from silver nitrate) or chromium (e.g., from potassium dichromate). See also Developer and Latent Image.


The formation of a layer of one material between layers of another. Certain compounds can expand clay crystals through intercalation. With salts that are intercalated as the total salt, the process is termed intersalation. Clay minerals containing an intercalation layer are also termed pillar interlayered clay minerals, pillared inorganic layered compounds (PILC), or composite clay nanostructures.


The boundary between two immiscible phases, sometimes including a thin layer at the boundary within which the properties of one bulk phase change over to become the properties of the other bulk phase. An interfacial layer of finite specified thickness can be defined. When one of the phases is a gas, the term “surface” is frequently used.

Interface Emulsion

An emulsion occurring between oil and water phases in a process separation or treatment apparatus. Such emulsions can have a high solid content and are frequently very viscous. In this case, the term “interface” is used in a macroscopic sense and refers to a bulk phase separating two other bulk phases of higher and lower density. Other terms: “cuff layer,” “pad layer,” or “rag layer emulsions.”

Interfacial Film

A thin layer of material positioned between two immiscible phases, usually liquids, whose composition is different from either of the bulk phases.

Interfacial Layer

The layer at an interface that contains adsorbed species. Also termed the surface layer. See also Adsorption Space.

Interfacial Polymerization

A means to microencapsulate species. For example, a lipophilic drug in an oil phase can be microencapsulated by adding a hydrophobic monomer and then using water and a surfactant to prepare an oil-in-water emulsion. Next, a hydrophilic monomer is dissolved in the aqueous phase. The two different monomers interact at the oil/aqueous interface to create polymer films that form the microcapsule walls. The inverse applies to the microencapsulation of a hydrophilic drug.

Interfacial Potential

See Surface Potential.

Interfacial Rheology

See Surface Viscosity.

Interfacial Rheometer

See Surface Viscometer.

Interfacial Tension

See Surface Tension.

Interfacial Tension Methods

See Table 25.

Interfacial Viscometer

See Surface Viscometer.

Interfacial Viscosity

See Surface Viscosity.

Interference Filter

A filter designed to transmit or reflect a particular range of wavelengths of light. Interference filters are used in classical light microscopy to block certain colours of light, and they are used in fluorescence microscopy to pass any fluorescent light emitted by a specimen while blocking the excitation light originally cast onto the specimen. See also Neutral Density Filter, Polarized Light Microscopy, and Shortpass Filter.


An experimental technique in which a beam of light is reflected from a film. Light reflected from the front and back surfaces of the film travels different distances and produces interference phenomena, a study of which allows calculation of the film thickness.

Intermediate Pore

An older term, now replaced by “mesopore.”

Intermicellar Liquid

An older term for the continuous (external) phase in micellar dispersions. See also Continuous Phase and Micelle.

Internal Phase

See Dispersed Phase.

Internal Surface

In porous media, the surface contained in pores and throats that are in communication with the outside space. See also Molecular Sieve Effect. Media having internal porosity also have internal surface area that can be available for sorption reactions. See also Activated Carbon.


See Intercalation.

Intramolecular Circuitry

See Molecular Circuitry.

Intravenous Fat Emulsion

See Lipid Drug Emulsion.

Intrinsic Fluorophore

See Fluorochrome.

Intrinsic Viscosity

The specific viscosity divided by the dispersed-phase concentration in the limits of both the dispersed-phase concentration approaching infinite dilution, and the shear rate approaching zero (). Also termed limiting viscosity number. See Table .11.

In-Tube Lens

(Microscopy) There are several kinds of in-tube lenses. A Tube Lens is used to enable the use of a variety of in-tube accessories in the observation tube of a microscope, without causing optical aberrations or changes in focus (see Infinity Microscope). A Bertrand Lens is a small lens that is positioned inside the observation tube of (i) a polarized light microscope in order to observe the interference patterns produced by the objective lens, or (ii) a differential interference contrast microscope to assist in adjustments of the condenser lens and Wollaston or Nomarski prisms.


See Polymeric Surfactant.

In Vacuo

In science and engineering, the Latin term in vacuo generally refers to a process or procedure conducted in a vacuum.

Inverse Micelle

A micelle that is formed in a nonaqueous medium, thus having the surfactants' hydrophilic groups oriented inward away from the surrounding medium.


The process by which one type of emulsion is converted to another, as when an O/W emulsion is transformed into a W/O emulsion, and vice versa. Inversion can be accomplished by a wide variety of physical and chemical means.

Invert Emulsion

A water-in-oil emulsion. This term differs from the term “reverse emulsion,” which is used in the petroleum field.

Inverting Surfactant

A surfactant that can be added to an emulsion to quickly invert it.

Invert-Oil Mud

An emulsion drilling fluid (mud) of the water-in-oil (W/O) type that has a high water content. See also Oil-Base Mud and Oil Mud.

Inviscid Fluid

An ideal fluid that has no viscosity. Such a fluid cannot support any applied shear stress and flows without any dissipation of energy. Also referred to as an Euler Fluid, Ideal Fluid, Pascalian Fluid, or a Nonviscous Fluid.

In Vitro

In science and engineering, the Latin term in vitro generally refers to a process or procedure conducted in an artificial environment such as a laboratory, as opposed to the “natural” setting. Example: growing biological cells in a laboratory culture, rather than within an organism (which is in vivo).

In Vivo

In science and engineering, the Latin term in vivo generally refers to a process or procedure conducted in its natural environment, as opposed to in an artificial environment. Example: growing biological cells in a living organism, rather than in a laboratory culture (which is in vitro).

Ion Beam Analysis

(IBA) A nondestructive, surface- and near-surface analysis technique in which a high-energy ion beam is used to probe elemental composition at depths of up to several micrometres, with depth resolution of about 10–20 nm. The energy distributions of scattered ions, and emitted X-rays and gamma rays, can be used to determine elemental compositions and their distributions with depth in the near-surface region. There are several basic method variations depending upon which scattered ions or emitted energy rays are detected and analyzed: nuclear reaction analysis (NRA, nuclear reaction producing charged particles), particle-induced gamma-ray emission analysis (PIGEA, nuclear reaction producing gamma rays), particle-induced X-ray emission analysis (PIXEA, atomic fluorescence producing X-rays), and ion-scattering spectroscopy (ISS, charged scattered particles). See also Ion-Scattering Spectroscopy and Table 15.

Ion Beam Lithography

The use of an ion beam to scan a surface in a particular pattern. The ions either interact directly with the surface to create a pattern or, in the case of a coated surface, one can next selectively remove the coating from either the scanned or unscanned region. This is one of the techniques used in making nanoelectromechanical systems. See also Nanolithography.

Ion Exchange

A special kind of adsorption in which the adsorption of an ionic species is accompanied by the simultaneous desorption of an equivalent charge quantity of other ionic species. Ion exchange is commonly used for removing hardness and other metal ions in water treatment. The ion-exchange media can be arranged to provide a specific selectivity. See also Sorbent-Motivated Sorption.

Ionic Strength

A measure of electrolyte concentration given by I = ½Σcizi2, where ci are the concentrations, in moles per litre, of the individual ions, i, and zi are the ion charge numbers.


A term applied to the founders of the discipline of physical chemistry (Ostwald, van't Hoff, and Arrhenius) and their students, who opened up new areas of research with their theory of electrolytic dissociation. See Reference [175].

Ionization-Loss Spectroscopy

(ILS) A technique related to photoelectron spectroscopy in which the emission of secondary electrons is studied and used for the determination of surface composition. See also Table 15.

Ion-Neutralization Spectroscopy

(INS) A surface technique in which low-energy inert gas ions are made to strike a surface and become neutralized by a charge-transfer process that leads to the ejection of electrons, which are detected. Information about both the surface and the adsorbed material can be gained. See also Table 15.


See Chromism.


A polymer molecule that contains pendant ionic groups, usually at a level of 10–15 mass%. The polymer backbone can be hydrocarbon or fluorocarbon. Used in plastics, and membranes and as surface coatings.


A large polymer molecule capable of solubilizing specific inorganic ions in organic media. By essentially encapsulating an inorganic ion, an ionophore can provide a vehicle for the transport into and across a bilayer membrane. Example: the antibiotic valinomycin selectively transports potassium ions through lipid membranes.


See Atmospheric Regions.

Ion-Scattering Spectroscopy

(ISS) A scattering technique used for the determination of surface composition by scanning the surface with a monoenergetic ion beam. The energy of the scattered ions is related to the mass of the scattering atoms at the surface so that the masses of the surface atoms can be determined. The techniques employing low-energy ions (less than 10 keV) are termed low-energy ion-scattering spectroscopy (LEIS), for medium-energy ions (100–200 keV) they are termed medium-energy ion-scattering spectroscopy (MEIS) and for high-energy ions (1–2 MeV) they are termed high-energy ion-scattering (HEIS) spectroscopy or Rutherford backscattering analysis (RBSA). Ion-scattering spectroscopy was originally termed Energetic Ion Analysis or Energetic Ion Backscattering. See also Ion Beam Analysis and Table 15. See Reference [69] for specific terms in ISS.

Ion-Selective Membrane

A membrane that is permeability-selective (permselective) for certain ions. Typically, such a membrane will carry an electric charge and therefore tend not to be permeable to ions of like charge. Selectivity among ions of opposite charge to the membrane but like charge among each other can sometimes be achieved through adjustment of a membrane's pore sizes.


An electrokinetic technique in which a small electric charge is used to cause a charged species to move transdermally through skin. This enables the noninvasive injection of drugs. Example: the injection of antiinflammatory drugs. Also termed Electromotive Drug Administration (EMDA). Reverse iontophoresis refers to the electrokinetic removal through the skin of species (molecules). This enables the removal of selected species for detection and/or measurement. Example: blood glucose monitoring.


See Infrared Reflection–Absorption Spectroscopy.


The phenomenon by which the colour of a material changes with the angle of view (or the angle of illumination) due to multiple reflections from surfaces within the material. Example: iridescence in soap bubbles, and in pearls. Sometimes termed Pearlescence.

Iridescent Layers

See Schiller Layers.

Isaphroic Lines

Contours of equal foam stability plotted on foam-phase diagrams. Example: see page 312 in Reference [8].


The mathematical representation of a phenomenon occurring at constant pressure. See Adsorption Isotherm.


See Monodisperse.


An ionic macromolecule that exhibits no electrophoretic or electro-osmotic motion.

Isoelectric Focusing

A method for the separation of charged colloidal particles or large molecules. An electric field gradient is imposed along a supporting medium as in zone electrophoresis. In this case, however, the supporting medium also supports a pH gradient. A sample of mixture to be separated is applied to one end of the supporting medium, and electrophoretic motion of each species occurs until it comes to rest at a pH corresponding to its isoelectric point. Regions of different components separate along the direction of the electric field and pH gradient according to the different isoelectric points of the components (typically the cathode end is held at the most basic pH). See also Zone Electrophoresis.

Isoelectric Point

The solution pH or condition for which the electrokinetic or zeta potential is zero. Under this condition, a colloidal system will exhibit no electrophoretic or electro-osmotic motions. See also Point of Zero Charge.


An ionic macromolecule system is isoionic if the only other ions in the system are the ions of the solvent, such as H+ and OH in water.

Isoionic Point

The solution pH or condition for which a species has a zero net charge. Under this condition, the species cannot have zero charge, but rather regions of opposite charges that balance. Example: Proteins and kaolinite clay particles can exhibit isoionic points.

Isokinetic Sampling

Collecting samples of a flowing dispersion using a method in which the sampling velocity (in the sampling probe) is equal to the upstream local velocity. If these velocities are not the same (anisokinetic sampling), then fluid streamlines ahead of the probe will be distorted; collection of particles or droplets will be influenced by their inertia, which varies with particle size, and sampling will not be representative.

Isometric Particle

A particle that yields the same measurement in all three dimensions.


Isomorphic sets are essentially identical in structure. In mineralogy, isomorphic substitution refers to the substitution of one cation for another in the mineral structure, when the mineral is forming. Example: isomorphic substitutions of Al for Si in the tetrahedral sheet and Mg for Al in the octahedral sheet are important in the formation of the clay mineral montmorillonite and represent the major source of permanent negative charge in this mineral's structure.


The mathematical representation of a phenomenon occurring at constant volume. See also Adsorption Isostere and Adsorption Isotherm.


A kind of capillary electrophoresis involving selected leading and trailing ions (cationic or anionic) chosen such that the mobilities of solutes of interest are intermediate with respect to those of the leading and trailing ions. Solutes become concentrated in a zone behind the leading ion front. Also termed displacement electrophoresis. Used to analyze charged molecules in complex mixtures. See Reference [176].

Isotactic Polymer

See Atactic Polymer, and Tacticity.


The mathematical representation of a phenomenon occurring at constant temperature. See also Adsorption Isotherm.

Israelachvili, Jacob (Nissim) (1944–)

An Israeli-born American chemical engineer and colloid scientist known for his work on intermolecular and intersurface forces. He developed the Surface Forces Apparatus for directly measuring the forces between surfaces in fluids. He is the author of the classic textbook “Intermolecular and Surface Forces” (1991).


See Ion-Scattering Spectroscopy.