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Evaporation suppressing monolayers are materials that when applied to the air/water interface, will spread (or self-assemble) and form a thin film across the surface of the water. The purpose of these materials is to reduce evaporative water loss from dams and reservoirs.
The specific mechanism that underlies monolayer evaporation resistance has been attributed to the physical barrier formed by the presence of these materials on the surface of the water (see figure). [1] The extent to which a material can resist the evaporation of water is best treated on a case-by-case basis, however, a number of empirically derived formulas have been reported. Before the advent of surface spectroscopic techniques such as Brewster Angle Microscopy (BAM) and Glancing Incidence X-Ray reflectrometry (GIXD), it was thought that the intermolecular spacing between monolayer molecules was the largest determinant factor governing evaporation suppression. When the surface density of the monolayer was sufficiently small, water molecules were presumed to pass through the space between molecules. [2] [3] [4] [5] Scattering and imaging results, however, revealed that the intermolecular distance between monolayer molecules was essentially constant, and that evaporation was more likely at domain boundaries. [6] The factors governing the efficacy of an evaporation suppressing monolayer are the ability to remain tightly packed despite changes in surface pressure, the ability to adhere to the surface of water, and to neighbouring molecules. [7]
Irving Langmuir accurately described the geometric structure of a monolayer film on water in 1917, work for which he would be later awarded the Nobel prize in chemistry. [8] The evaporation suppressing properties of these materials were first reported by Rideal in the 1920s [9] In the 1940s Langmuir and Schaefer quantified the evaporation resistance and its dependence on temperature. [10] This work was extended by Archer and La Mer in the following decade, who observed a dependence on surface pressure, chain length, monolayer phase, subphase composition and surface temperature. [4] Large scale field trials were being conducted at this time in Australia by Mansfield [11] He reported that the results seen in the laboratory setting could not be replicated in real world conditions, with dust and wind being cited as adversely affecting evaporation suppressing performance.
In later decades, research efforts focussed on multicomponent monolayer materials such as hexadecanol + octadecanol, [12] altering the number of carbons in the aliphatic chain, [13] and later on, the addition of polymerised surfactants to increase monolayer stability. [14]
Better monolayer materials are required as are better methods of monolayer distribution methods, although no resolution of these difficulties presently exists. [15]
Despite research in this area for most of the 20th century, no durable, effective and inexpensive product has come to market. Recently, advances in experimental and modelling techniques have increased the understanding of these materials.
During a prolonged drought in Australia at the start of this century, scientists there from a number of research institutions, including Pr. David Solomon, inventor of the polymer banknote, [16] set about developing a product that is efficacious, resistant to the deleterious effects of wind, and affordable. In addition to small and large scale field trials, new techniques were utilised including a novel evaporation tank with a controlled climate system to mimic the effects of wind and waves, [17] and computational modelling was for the first time employed to relate dynamic and geometric properties at the atomistic level, with evaporation suppressing performance at the macroscopic level. [18] [19] [20] The use of ethylene glycol monooctadecyl ether was found to substantially decrease evaporation resistance in the presence of wind, and the addition of a water-soluble polymer further enhanced its effectiveness. [7] [21]
WaterGuard manufactured by Aquatain advertises a polymer based material that reduces water evaporation. [22] Other products include Solarpill [23] and Water$aver. [24] The efficacy of these products has not been shown.[ citation needed ]
A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. However, some definitions specify that the particles must be dispersed in a liquid, and others extend the definition to include substances like aerosols and gels. The term colloidal suspension refers unambiguously to the overall mixture. A colloid has a dispersed phase and a continuous phase. The dispersed phase particles have a diameter of approximately 1 nanometre to 1 micrometre.
Surface science is the study of physical and chemical phenomena that occur at the interface of two phases, including solid–liquid interfaces, solid–gas interfaces, solid–vacuum interfaces, and liquid–gas interfaces. It includes the fields of surface chemistry and surface physics. Some related practical applications are classed as surface engineering. The science encompasses concepts such as heterogeneous catalysis, semiconductor device fabrication, fuel cells, self-assembled monolayers, and adhesives. Surface science is closely related to interface and colloid science. Interfacial chemistry and physics are common subjects for both. The methods are different. In addition, interface and colloid science studies macroscopic phenomena that occur in heterogeneous systems due to peculiarities of interfaces.
A monolayer is a single, closely packed layer of atoms, molecules, or cells. In some cases it is referred to as a self-assembled monolayer. Monolayers of layered crystals like graphene and molybdenum disulfide are generally called 2D materials.
Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. This process differs from absorption, in which a fluid is dissolved by or permeates a liquid or solid. Adsorption is a surface phenomenon, while absorption involves the whole volume of the material, although adsorption does often precede absorption. The term sorption encompasses both processes, while desorption is the reverse of it.
Polyelectrolytes are polymers whose repeating units bear an electrolyte group. Polycations and polyanions are polyelectrolytes. These groups dissociate in aqueous solutions (water), making the polymers charged. Polyelectrolyte properties are thus similar to both electrolytes (salts) and polymers and are sometimes called polysalts. Like salts, their solutions are electrically conductive. Like polymers, their solutions are often viscous. Charged molecular chains, commonly present in soft matter systems, play a fundamental role in determining structure, stability and the interactions of various molecular assemblies. Theoretical approaches to describing their statistical properties differ profoundly from those of their electrically neutral counterparts, while technological and industrial fields exploit their unique properties. Many biological molecules are polyelectrolytes. For instance, polypeptides, glycosaminoglycans, and DNA are polyelectrolytes. Both natural and synthetic polyelectrolytes are used in a variety of industries.
Self-assembled monolayers (SAM) of organic molecules are molecular assemblies formed spontaneously on surfaces by adsorption and are organized into more or less large ordered domains. In some cases molecules that form the monolayer do not interact strongly with the substrate. This is the case for instance of the two-dimensional supramolecular networks of e.g. perylenetetracarboxylic dianhydride (PTCDA) on gold or of e.g. porphyrins on highly oriented pyrolitic graphite (HOPG). In other cases the molecules possess a head group that has a strong affinity to the substrate and anchors the molecule to it. Such a SAM consisting of a head group, tail and functional end group is depicted in Figure 1. Common head groups include thiols, silanes, phosphonates, etc.
A Langmuir–Blodgett trough is a laboratory apparatus that is used to compress monolayers of molecules on the surface of a given subphase and measures surface phenomena due to this compression. It can also be used to deposit single or multiple monolayers on a solid substrate.
Stearyl alcohol, or 1-octadecanol, is an organic compound classified as a saturated fatty alcohol with the formula CH3(CH2)16CH2OH. It takes the form of white granules or flakes, which are insoluble in water. It has a wide range of uses as an ingredient in lubricants, resins, perfumes, and cosmetics. It is used as an emollient, emulsifier, and thickener in ointments, and is widely used as a hair coating in shampoos and hair conditioners. Stearyl heptanoate, the ester of stearyl alcohol and heptanoic acid (enanthic acid), is found in most cosmetic eyeliners. Stearyl alcohol has also found application as an evaporation suppressing monolayer when applied to the surface of water.
A Langmuir–Blodgett (LB) film is a nanostructured system 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 the solid substrate into 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.
In physics, a "coffee ring" is a pattern left by a puddle of particle-laden liquid after it evaporates. The phenomenon is named for the characteristic ring-like deposit along the perimeter of a spill of coffee. It is also commonly seen after spilling red wine. The mechanism behind the formation of these and similar rings is known as the coffee ring effect or in some instances, the coffee stain effect, or simply ring stain.
Inverse gas chromatography is a physical characterization analytical technique that is used in the analysis of the surfaces of solids.
Octadecyltrimethoxysilane (OTMS) is an organosilicon compound. This colorless liquid is used for preparing hydrophobic coatings and self-assembled monolayers. It is sensitive toward water, irreversibly degrading to a siloxane polymer. It places a C18H39SiO3 "cap" on oxide surfaces. The formation of OTMS monolayers is used for converting hydrophilic surfaces to hydrophobic surfaces, e.g. for use in certain areas of nanotechnology and analytical chemistry.
Adsorption is the adhesion of ions or molecules onto the surface of another phase. Adsorption may occur via physisorption and chemisorption. Ions and molecules can adsorb to many types of surfaces including polymer surfaces. A polymer is a large molecule composed of repeating subunits bound together by covalent bonds. The adsorption of ions and molecules to polymer surfaces plays a role in many applications including: biomedical, structural, coatings, environmental and petroleum.
Silanization of silicon and mica is the coating of these materials with a thin layer of self assembling units.
Milliana Kroumova Kaisheva was a Bulgarian physical chemist, internationally known for her work in electrochemistry and colloid chemistry.
Bovine submaxillary mucin (BSM) coatings are a surface treatment provided to biomaterials intended to reduce the growth of disadvantageous bacteria and fungi such as S. epidermidis, E. coli, and Candida albicans. BSM is a substance extracted from the fresh salivary glands of cows. It exhibits unique physical properties, such as high molecular weight and amphiphilicity, that allow it to be used for many biomedical applications.
Edward Bormashenko is a professor of Materials Science and the Head of the Laboratory of Interface Science of the Ariel University in Israel. He was born in 1962 in Kharkiv, Ukraine and lives in Israel since 1997. He studied in the V. N. Karazin Kharkiv National University. His research is in the polymer science and surface science. He accomplished his PhD in Moscow Institute of Plastics in 1990.
Nanosphere lithography (NSL) is an economical technique for generating single-layer hexagonally close packed or similar patterns of nanoscale features. Generally, NSL applies planar ordered arrays of nanometer-sized latex or silica spheres as lithography masks to fabricate nanoparticle arrays. NSL uses self-assembled monolayers of spheres as evaporation masks. These spheres can be deposited using multiple methods including Langmuir-Blodgett, Dip Coating, Spin Coating, solvent evaporation, force-assembly, and air-water interface. This method has been used to fabricate arrays of various nanopatterns, including gold nanodots with precisely controlled spacings.
Irshad Hussain is a Pakistani Scientist in the field of chemistry and among the few pioneers to initiate nanomaterials research in Pakistan.
Interfacial rheology is a branch of rheology that studies the flow of matter at the interface between a gas and a liquid or at the interface between two immiscible liquids. The measurement is done while having surfactants, nanoparticles or other surface active compounds present at the interface. Unlike in bulk rheology, the deformation of the bulk phase is not of interest in interfacial rheology and its effect is aimed to be minimized. Instead, the flow of the surface active compounds is of interest.