
A Langmuir–Blodgett (LB) film is an emerging kind of 2D materials to fabricate heterostructures for nanotechnology, formed when Langmuir films—or Langmuir monolayers (LM)—are transferred from the liquid-gas interface to solid supports during the vertical passage of the support through the monolayers. LB films can contain one or more
monolayers of an organic material, deposited from the surface of a liquid onto a solid by immersing (or emersing) the solid substrate into (or from) the liquid. A monolayer is adsorbed homogeneously with each immersion or emersion step, thus films with very accurate thickness can be formed. This thickness is accurate because the thickness of each monolayer is known and can therefore be added to find the total thickness of a Langmuir–Blodgett film.
The monolayers are assembled vertically and are usually composed either of
amphiphilic
In chemistry, an amphiphile (), or amphipath, is a chemical compound possessing both hydrophilic (''water-loving'', polar) and lipophilic (''fat-loving'', nonpolar) properties. Such a compound is called amphiphilic or amphipathic. Amphiphilic c ...
molecules (see
chemical polarity
In chemistry, polarity is a separation of electric charge leading to a molecule or its chemical groups having an electric dipole moment, with a negatively charged end and a positively charged end.
Polar molecules must contain one or more polar ...
) with a
hydrophilic
A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon'' Oxford: Clarendon Press.
In contrast, hydrophobes are n ...
head and a hydrophobic tail (example:
fatty acids
In chemistry, in particular in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, ...
) or nowadays commonly of
nanoparticle
A nanoparticle or ultrafine particle is a particle of matter 1 to 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 100 nm in only two directions. At ...
s.
Langmuir–Blodgett films are named after
Irving Langmuir
Irving Langmuir (; January 31, 1881 – August 16, 1957) was an American chemist, physicist, and metallurgical engineer. He was awarded the Nobel Prize in Chemistry in 1932 for his work in surface chemistry.
Langmuir's most famous publicatio ...
and
Katharine B. Blodgett, who invented this technique while working in Research and Development for
General Electric Co.
Historical background
Advances to the discovery of LB and LM films began with
Benjamin Franklin
Benjamin Franklin (April 17, 1790) was an American polymath: a writer, scientist, inventor, statesman, diplomat, printer, publisher and Political philosophy, political philosopher.#britannica, Encyclopædia Britannica, Wood, 2021 Among the m ...
in 1773 when he dropped about a teaspoon of oil onto a pond. Franklin noticed that the waves were calmed almost instantly and that the calming of the waves spread for about half an
acre
The acre ( ) is a Unit of measurement, unit of land area used in the Imperial units, British imperial and the United States customary units#Area, United States customary systems. It is traditionally defined as the area of one Chain (unit), ch ...
. What Franklin did not realize was that the oil had formed a monolayer on top of the pond surface. Over a century later,
Lord Rayleigh
John William Strutt, 3rd Baron Rayleigh ( ; 12 November 1842 – 30 June 1919), was an English physicist who received the Nobel Prize in Physics in 1904 "for his investigations of the densities of the most important gases and for his discovery ...
quantified what
Benjamin Franklin
Benjamin Franklin (April 17, 1790) was an American polymath: a writer, scientist, inventor, statesman, diplomat, printer, publisher and Political philosophy, political philosopher.#britannica, Encyclopædia Britannica, Wood, 2021 Among the m ...
had seen. Knowing that the oil,
oleic acid
Oleic acid is a fatty acid that occurs naturally in various animal and vegetable fats and oils. It is an odorless, colorless oil, although commercial samples may be yellowish due to the presence of impurities. In chemical terms, oleic acid is cl ...
, had spread evenly over the water, Rayleigh calculated that the thickness of the film was 1.6
nm by knowing the volume of oil dropped and the area of coverage.
With the help of her kitchen sink,
Agnes Pockels showed that area of films can be controlled with barriers. She added that surface tension varies with contamination of water. She used different oils to deduce that surface pressure would not change until area was confined to about 0.2 nm
2. This work was originally written as a letter to
Lord Rayleigh
John William Strutt, 3rd Baron Rayleigh ( ; 12 November 1842 – 30 June 1919), was an English physicist who received the Nobel Prize in Physics in 1904 "for his investigations of the densities of the most important gases and for his discovery ...
who then helped Agnes Pockels become published in the journal, ''
Nature
Nature is an inherent character or constitution, particularly of the Ecosphere (planetary), ecosphere or the universe as a whole. In this general sense nature refers to the Scientific law, laws, elements and phenomenon, phenomena of the physic ...
'', in 1891.

Agnes Pockels’ work set the stage for
Irving Langmuir
Irving Langmuir (; January 31, 1881 – August 16, 1957) was an American chemist, physicist, and metallurgical engineer. He was awarded the Nobel Prize in Chemistry in 1932 for his work in surface chemistry.
Langmuir's most famous publicatio ...
who continued to work and confirmed Pockels’ results. Using Pockels’ idea, he developed the Langmuir (or
Langmuir–Blodgett) trough. His observations indicated that chain length did not impact the affected area since the organic molecules were arranged vertically.
Langmuir’s breakthrough did not occur until he hired
Katherine Blodgett as his assistant. Blodgett initially went to seek for a job at
General Electric
General Electric Company (GE) was an American Multinational corporation, multinational Conglomerate (company), conglomerate founded in 1892, incorporated in the New York (state), state of New York and headquartered in Boston.
Over the year ...
(
GE) with Langmuir during her
Christmas
Christmas is an annual festival commemorating Nativity of Jesus, the birth of Jesus Christ, observed primarily on December 25 as a Religion, religious and Culture, cultural celebration among billions of people Observance of Christmas by coun ...
break of her senior year at
Bryn Mawr College
Bryn Mawr College ( ; Welsh language, Welsh: ) is a Private college, private Women's colleges in the United States, women's Liberal arts colleges in the United States, liberal arts college in Bryn Mawr, Pennsylvania, United States. Founded as a ...
, where she received a BA in
Physics
Physics is the scientific study of matter, its Elementary particle, fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge whi ...
. Langmuir advised to Blodgett that she should continue her education before working for him. She thereafter attended
University of Chicago
The University of Chicago (UChicago, Chicago, or UChi) is a Private university, private research university in Chicago, Illinois, United States. Its main campus is in the Hyde Park, Chicago, Hyde Park neighborhood on Chicago's South Side, Chic ...
for her MA in
Chemistry
Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...
. Upon her completion of her Master's, Langmuir hired her as his assistant. However, breakthroughs in surface chemistry happened after she received her
PhD degree
A Doctor of Philosophy (PhD, DPhil; or ) is a terminal degree that usually denotes the highest level of academic achievement in a given discipline and is awarded following a course of graduate study and original research. The name of the deg ...
in 1926 from
Cambridge University
The University of Cambridge is a Public university, public collegiate university, collegiate research university in Cambridge, England. Founded in 1209, the University of Cambridge is the List of oldest universities in continuous operation, wo ...
.
While working for GE, Langmuir and Blodgett discovered that when a solid surface is inserted into an aqueous solution containing organic moieties, the organic molecules will deposit a
monolayer
A monolayer is a single, closely packed layer of entities, commonly atoms or molecules.
Monolayers can also be made out of cells. ''Self-assembled monolayers'' form spontaneously on surfaces. Monolayers of layered crystals like graphene and molyb ...
homogeneously over the surface. This is the Langmuir–Blodgett film deposition process. Through this work in
surface chemistry
Surface science is the study of physics, physical and chemistry, chemical phenomena that occur at the interface (chemistry), interface of two phase (matter), phases, including solid–liquid interfaces, solid–gas interfaces, solid–vacuum int ...
and with the help of Blodgett, Langmuir was awarded the
Nobel Prize
The Nobel Prizes ( ; ; ) are awards administered by the Nobel Foundation and granted in accordance with the principle of "for the greatest benefit to humankind". The prizes were first awarded in 1901, marking the fifth anniversary of Alfred N ...
in 1932. In addition, Blodgett used Langmuir–Blodgett film to create 99% transparent anti-reflective glass by coating glass with fluorinated organic compounds, forming a simple
anti-reflective coating
An antireflective, antiglare or anti-reflection (AR) coating is a type of optical coating applied to the surface of lens (optics), lenses, other optical elements, and photovoltaic cells to reduce reflection (physics), reflection. In typical ima ...
.
Physical insight
Langmuir films are formed when amphiphilic (surfactants) molecules or nanoparticles are spread on the water at an air–water interface.
Surfactants
Surfactants are chemical compounds that decrease the surface tension or interfacial tension between two liquids, a liquid and a gas, or a liquid and a solid. The word ''surfactant'' is a blend of "surface-active agent",
coined in 1950. As t ...
(or surface-acting agents) are molecules with hydrophobic 'tails' and hydrophilic 'heads'. When
surfactant
Surfactants are chemical compounds that decrease the surface tension or interfacial tension between two liquids, a liquid and a gas, or a liquid and a solid. The word ''surfactant'' is a Blend word, blend of "surface-active agent",
coined in ...
concentration is less than the minimum surface concentration of collapse and it is completely insoluble in water, the surfactant molecules arrange themselves as shown in Figure 1 below. This tendency can be explained by surface-energy considerations. Since the tails are hydrophobic, their exposure to air is favoured over that to water. Similarly, since the heads are hydrophilic, the head–water interaction is more favourable than head-air interaction. The overall effect is reduction in the surface energy (or equivalently, surface tension of water).

For very small concentrations, far from the surface density compatible with the collapse of the monolayer (which leads to polylayers structures) the
surfactant
Surfactants are chemical compounds that decrease the surface tension or interfacial tension between two liquids, a liquid and a gas, or a liquid and a solid. The word ''surfactant'' is a Blend word, blend of "surface-active agent",
coined in ...
molecules execute a random motion on the water–air interface. This motion can be thought to be similar to the motion of
ideal-gas molecules enclosed in a container. The corresponding thermodynamic variables for the surfactant system are,
surface pressure (
),
surface area
The surface area (symbol ''A'') of a solid object is a measure of the total area that the surface of the object occupies. The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the d ...
(A) and number of
surfactant
Surfactants are chemical compounds that decrease the surface tension or interfacial tension between two liquids, a liquid and a gas, or a liquid and a solid. The word ''surfactant'' is a Blend word, blend of "surface-active agent",
coined in ...
molecules (N). This system behaves similar to a gas in a container. The density of surfactant molecules as well as the surface pressure increases upon reducing the surface area A ('compression' of the 'gas'). Further compression of the surfactant molecules on the surface shows behavior similar to
phase transition
In physics, chemistry, and other related fields like biology, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic Sta ...
s. The ‘gas’ gets compressed into ‘liquid’ and ultimately into a perfectly closed packed array of the surfactant molecules on the surface corresponding to a ‘solid’ state. The liquid state is usually separated in the liquid-expanded and liquid-condensed states. All the Langmuir film states are classified according to the compressionality factor of the films, defined as , usually related to the in-plane elasticity of the monolayer.
The condensed Langmuir films (in surface pressures usually higher than 15 mN/m – typically 30 mN/m) can be subsequently transferred onto a solid substrate to create highly organized thin film coatings.
Langmuir–Blodgett troughs
Besides LB film from surfactants depicted in Figure 1, similar monolayers can also be made from inorganic nanoparticles.
Pressure–area characteristics
Adding a
monolayer
A monolayer is a single, closely packed layer of entities, commonly atoms or molecules.
Monolayers can also be made out of cells. ''Self-assembled monolayers'' form spontaneously on surfaces. Monolayers of layered crystals like graphene and molyb ...
to the surface reduces the
surface tension
Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension (physics), tension is what allows objects with a higher density than water such as razor blades and insects (e.g. Ge ...
, and the surface pressure,
is given by the following equation:
:
where
is equal to the surface tension of the
water
Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...
and
is the surface tension due to the monolayer. But the concentration-dependence of surface tension (similar to
Langmuir isotherm) is as follows:
:
Thus,
:
or
:
The last equation indicates a relationship similar to
ideal gas law
The ideal gas law, also called the general gas equation, is the equation of state of a hypothetical ideal gas. It is a good approximation of the behavior of many gases under many conditions, although it has several limitations. It was first stat ...
. However, the concentration-dependence of surface tension is valid only when the solutions are dilute and concentrations are low. Hence, at very low concentrations of the surfactant, the molecules behave like
ideal gas
An ideal gas is a theoretical gas composed of many randomly moving point particles that are not subject to interparticle interactions. The ideal gas concept is useful because it obeys the ideal gas law, a simplified equation of state, and is ...
molecules.
Experimentally, the surface pressure is usually measured using the
Wilhelmy plate
A Wilhelmy plate is a thin plate that is used to measure equilibrium surface or interfacial tension at an air–liquid or liquid–liquid interface. In this method, the plate is oriented perpendicular to the interface, and the force exerted on ...
. A pressure sensor/electrobalance arrangement detects the pressure exerted by the monolayer. Also monitored is the area to the side of the barrier which the monolayer resides.
Figure 2. A Wilhelmy plate
A simple force balance on the plate leads to the following equation for the surface pressure:
:
only when
. Here,
and
are the dimensions of the plate, and
is the difference in forces. The
Wilhelmy plate
A Wilhelmy plate is a thin plate that is used to measure equilibrium surface or interfacial tension at an air–liquid or liquid–liquid interface. In this method, the plate is oriented perpendicular to the interface, and the force exerted on ...
measurements give pressure – area isotherms that show phase transition-like behaviour of the LM films, as mentioned before (see figure below). In the gaseous phase, there is minimal pressure increase for a decrease in area. This continues until the first transition occurs and there is a proportional increase in pressure with decreasing area. Moving into the solid region is accompanied by another sharp transition to a more severe area dependent pressure. This trend continues up to a point where the molecules are relatively close packed and have very little room to move. Applying an increasing pressure at this point causes the
monolayer
A monolayer is a single, closely packed layer of entities, commonly atoms or molecules.
Monolayers can also be made out of cells. ''Self-assembled monolayers'' form spontaneously on surfaces. Monolayers of layered crystals like graphene and molyb ...
to become unstable and destroy the monolayer forming polylayer structures towards the air phase. The surface pressure during the monolayer collapse may remain approximately constant (in a process near the equilibrium) or may decay abruptly (out of equilibrium - when the surface pressure was over-increased because lateral compression was too fast for monomolecular rearrangements).
Figure 3. (i) Surface pressure – Area isotherms. (ii) Molecular configuration in the three regions marked in the -A curve; (a) gaseous phase, (b) liquid-expanded phase, and (c) condensed phase. (Adapted from Osvaldo N. Oliveira Jr., Brazilian Journal of Physics, vol. 22, no. 2, June 1992)
Applications
Many possible applications have been suggested over years for LM and LB films. Their characteristics are extremely thin films and high degree of structural order. These films have different optical, electrical and biological properties which are composed of some specific organic compounds.
Organic compounds
Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...
usually have more positive responses than
inorganic
An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bondsthat is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemistry''.
Inor ...
materials for outside factors (
pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and eve ...
,
temperature
Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...
or gas change). LM films can be used also as models for half a cellular membrane.
* LB films consisting of nanoparticles can be used for example to create functional coatings, sophisticated sensor surfaces and to coat silicon wafers.
* LB films can be used as passive layers in
MIS (metal-insulator-semiconductor) which have more open structure than
silicon oxide Silicon oxide may refer to either of the following:
*Silicon dioxide
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the maj ...
, and they allow gases to penetrate to the interface more effectively.
* LB films also can be used as
biological membranes.
Lipid
Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...
molecules with the fatty acid moiety of long carbon chains attached to a polar group have received extended attention because of being naturally suited to the Langmuir method of film production. This type of biological membrane can be used to investigate: the modes of
drug action, the permeability of biologically active molecules, and the chain reactions of biological systems.
* Also, it is possible to propose field effect devices for observing the
immunological response and enzyme-substrate reactions by collecting biological molecules such as antibodies and enzymes in insulating LB films.
* Anti-reflective glass can be produced with successive layers of fluorinated organic film.
* The
glucose
Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...
biosensor
A biosensor is an analytical device, used for the detection of a chemical substance, that combines a biological component with a physicochemical detector.
The ''sensitive biological element'', e.g. tissue, microorganisms, organelles, cell rece ...
can be made of poly(3-hexyl thiopene) as Langmuir–Blodgett film, which entraps glucose-oxide and transfers it to a coated
indium
Indium is a chemical element; it has Symbol (chemistry), symbol In and atomic number 49. It is a silvery-white post-transition metal and one of the softest elements. Chemically, indium is similar to gallium and thallium, and its properties are la ...
-
tin
Tin is a chemical element; it has symbol Sn () and atomic number 50. A silvery-colored metal, tin is soft enough to be cut with little force, and a bar of tin can be bent by hand with little effort. When bent, a bar of tin makes a sound, the ...
-
oxide
An oxide () is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of −2) of oxygen, an O2− ion with oxygen in the oxidation st ...
glass plate.
* UV resists can be made of poly(N-alkylmethacrylamides) Langmuir–Blodgett film.
*
UV light
Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of t ...
and
conductivity of a Langmuir–Blodgett film.
* Langmuir–Blodgett films are inherently 2D-structures and can be built up layer by layer, by dipping hydrophobic or hydrophilic substrates into a liquid sub-phase.
* Langmuir–Blodgett patterning is a new paradigm for large-area patterning with mesostructured features
* Recently, it has been demonstrated that Langmuir–Blodgett is an effective technique even to produce ultra-thin films of emerging two-dimensional layered materials on a large scale.
See also
*
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References
Bibliography
* R. W. Corkery, Langmuir, 1997, 13 (14), 3591–3594
* Osvaldo N. Oliveira Jr., Brazilian Journal of Physics, vol. 22, no. 2, June 1992
* Roberts G G, Pande K P and Barlow, Phys. Technol., Vol. 12, 1981
* Singhal, Rahul. Poly-3-Hexyl Thiopene Langmuir-Blodgett Films for Application to Glucose Biosensor. National Physics Laboratory: Biotechnology and Bioengineering, p 277-282, February 5, 2004. John and Wiley Sons Inc.
* Guo, Yinzhong. Preparation of poly(N-alkylmethacrylamide) Langmuir–Blodgett films for the application to a novel dry-developed positive deep UV resist. Macromolecules, p1115-1118, February 23, 1999. ACS
* Franklin, Benjamin, Of the stilling of Waves by means of Oil. Letter to William Brownrigg and the Reverend Mr. Farish. London, November 7, 1773.
* Pockels, A., Surface Tension, Nature, 1891, 43, 437.
* Blodgett, Katherine B., Use of Interface to Extinguish Reflection of Light from Glass. Physical Review, 1939, 55,
* A. Ulman, An Introduction to Ultrathin Organic Films From Langmuir-Blodgett to Self-Assembly, Academic Press, Inc.: San Diego (1991).
* I.R. Peterson, "Langmuir Blodgett Films ", J. Phys. D 23, 4, (1990) 379–95.
* I.R. Peterson, "Langmuir Monolayers", in T.H. Richardson, Ed., Functional Organic and Polymeric Materials Wiley: NY (2000).
* L.S. Miller, D.E. Hookes, P.J. Travers and A.P. Murphy, "A New Type of Langmuir-Blodgett Trough", J. Phys. E 21 (1988) 163–167.
* I.R.Peterson, J.D.Earls. I.R.Girling and G.J.Russell, "Disclinations and Annealing in Fatty-Acid Monolayers", Mol. Cryst. Liq. Cryst. 147 (1987) 141–147.
* Syed Arshad Hussain, D. Bhattacharjee, "Langmuir-Blodgett Films and Molecular Electronics", Modern Physics Letters B vol. 23 No. 27 (2009) 3437–3451.
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