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90-494: The PVF-based film was first commercialised in 1961 by DuPont under the name Tedlar. The most widely used polymerizations of VF are in aqueous suspensions or emulsions . High pressures are required because of the VF volatility . The high electronegativity of fluorine makes the polymerization more difficult when compared to other vinyl halides . The polymerization temperatures range from 50 °C to 150 °C and can affect

180-671: A [ 1 − exp ⁡ ( − t τ a ) ] n = J σ τ a [ exp ⁡ ( − t τ a ) ] {\displaystyle n=J\sigma \tau _{a}\left[1-\exp \left({-t \over \tau _{a}}\right)\right]n=J\sigma \tau _{a}\left[\exp \left({-t \over \tau _{a}}\right)\right]} Adsorption can also be modeled by different isotherms such as Langmuir model and BET model . The Langmuir model derives an equilibrium constant b {\displaystyle b} based on

270-438: A halide or hydride of the element to be deposited. In the case of metalorganic vapour phase epitaxy , an organometallic gas is used. Commercial techniques often use very low pressures of precursor gas. Plasma Enhanced Chemical Vapor Deposition uses an ionized vapor, or plasma , as a precursor. Unlike the soot example above, this method relies on electromagnetic means (electric current, microwave excitation), rather than

360-414: A noble gas , such as argon ) to knock material from a "target" a few atoms at a time. The target can be kept at a relatively low temperature, since the process is not one of evaporation, making this one of the most flexible deposition techniques. It is especially useful for compounds or mixtures, where different components would otherwise tend to evaporate at different rates. Note, sputtering's step coverage

450-427: A chemical-reaction, to produce a plasma. Atomic layer deposition and its sister technique molecular layer deposition , uses gaseous precursor to deposit conformal thin film's one layer at a time. The process is split up into two half reactions, run in sequence and repeated for each layer, in order to ensure total layer saturation before beginning the next layer. Therefore, one reactant is deposited first, and then

540-472: A decrease in head-to-head linkages and subsequently increase in melting point since the highly regular structures display higher crystallinity . As for stereoregularity , PVF is mostly atacic , but this does not significantly affect the melting point . The commercial atactic PVF film shows a melting point peak at 190 °C. Several transition phases occur below the melting point , mainly at lower T g from -15 to ‑20 °C, and at upper T g with

630-448: A dielectric constant (more accurately, relative static permittivity ) greater than 15 (i.e. polar or polarizable) can be further divided into protic and aprotic. Protic solvents, such as water , solvate anions (negatively charged solutes) strongly via hydrogen bonding . Polar aprotic solvents , such as acetone or dichloromethane , tend to have large dipole moments (separation of partial positive and partial negative charges within

720-422: A fluid precursor undergoes a chemical change at a solid surface, leaving a solid layer. An everyday example is the formation of soot on a cool object when it is placed inside a flame. Since the fluid surrounds the solid object, deposition happens on every surface, with little regard to direction; thin films from chemical deposition techniques tend to be conformal , rather than directional . Chemical deposition

810-492: A high rate of reaction even after 40% conversion , they are thermally and chemically stable and their incorporation does not impair PVF properties. Other emulsifiers ( fatty alcohol sulfates , alkane sulfonates etc) are not as effective. PVF is usually converted into thin films and coatings . However, due to its hydrogen bonds and crystallinity , a temperature above 100 °C is necessary to dissolve PVF in latent solvents . The processing by melt extrusion depends on

900-472: A high level of ionization (30–100%), multiply charged ions, neutral particles, clusters and macro-particles (droplets). If a reactive gas is introduced during the evaporation process, dissociation , ionization and excitation can occur during interaction with the ion flux and a compound film will be deposited. Electrohydrodynamic deposition (electrospray deposition) is a relatively new process of thin-film deposition. The liquid to be deposited, either in

990-407: A layer on top of water. Important exceptions are most of the halogenated solvents like dichloromethane or chloroform will sink to the bottom of a container, leaving water as the top layer. This is crucial to remember when partitioning compounds between solvents and water in a separatory funnel during chemical syntheses. Often, specific gravity is cited in place of density. Specific gravity

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1080-417: A liquid precursor, or sol-gel precursor deposited onto a smooth, flat substrate which is subsequently spun at a high velocity to centrifugally spread the solution over the substrate. The speed at which the solution is spun and the viscosity of the sol determine the ultimate thickness of the deposited film. Repeated depositions can be carried out to increase the thickness of films as desired. Thermal treatment

1170-450: A neutral process. When one substance dissolves into another, a solution is formed. A solution is a homogeneous mixture consisting of a solute dissolved into a solvent. The solute is the substance that is being dissolved, while the solvent is the dissolving medium. Solutions can be formed with many different types and forms of solutes and solvents. Solvents can be broadly classified into two categories: polar and non-polar . A special case

1260-421: A peroxide compound. The process of peroxide formation is greatly accelerated by exposure to even low levels of light, but can proceed slowly even in dark conditions. Unless a desiccant is used which can destroy the peroxides, they will concentrate during distillation , due to their higher boiling point . When sufficient peroxides have formed, they can form a crystalline , shock-sensitive solid precipitate at

1350-424: A solute during a chemical reaction. Kosower 's Z scale measures polarity in terms of the influence of the solvent on UV -absorption maxima of a salt, usually pyridinium iodide or the pyridinium zwitterion . Donor number and donor acceptor scale measures polarity in terms of how a solvent interacts with specific substances, like a strong Lewis acid or a strong Lewis base. The Hildebrand parameter

1440-401: A spreadsheet of values, or HSP software. A 1:1 mixture of toluene and 1,4 dioxane has δD, δP and δH values of 17.8, 1.6 and 5.5, comparable to those of chloroform at 17.8, 3.1 and 5.7 respectively. Because of the health hazards associated with toluene itself, other mixtures of solvents may be found using a full HSP dataset. The boiling point is an important property because it determines

1530-456: A substrate, which is also heated via a laser beam. The vast range of substrate and deposition temperatures allows of the epitaxial growth of various elements considered challenging by other thin film growth techniques. Cathodic arc deposition (arc-physical vapor deposition), which is a kind of ion beam deposition where an electrical arc is created that blasts ions from the cathode. The arc has an extremely high power density resulting in

1620-449: A tool for the selection of solvents based on a principal component analysis of solvent properties. The Hansen solubility parameter (HSP) values are based on dispersion bonds (δD), polar bonds (δP) and hydrogen bonds (δH). These contain information about the inter-molecular interactions with other solvents and also with polymers, pigments, nanoparticles , etc. This allows for rational formulations knowing, for example, that there

1710-901: A united manner. The polarity, dipole moment, polarizability and hydrogen bonding of a solvent determines what type of compounds it is able to dissolve and with what other solvents or liquid compounds it is miscible . Generally, polar solvents dissolve polar compounds best and non-polar solvents dissolve non-polar compounds best; hence " like dissolves like ". Strongly polar compounds like sugars (e.g. sucrose ) or ionic compounds, like inorganic salts (e.g. table salt ) dissolve only in very polar solvents like water, while strongly non-polar compounds like oils or waxes dissolve only in very non-polar organic solvents like hexane . Similarly, water and hexane (or vinegar and vegetable oil) are not miscible with each other and will quickly separate into two layers even after being shaken well. Polarity can be separated to different contributions. For example,

1800-551: Is dissolved into another, a solution is formed. This is opposed to the situation when the compounds are insoluble like sand in water. In a solution, all of the ingredients are uniformly distributed at a molecular level and no residue remains. A solvent-solute mixture consists of a single phase with all solute molecules occurring as solvates (solvent-solute complexes ), as opposed to separate continuous phases as in suspensions, emulsions and other types of non-solution mixtures. The ability of one compound to be dissolved in another

1890-403: Is a fundamental step in many applications. A familiar example is the household mirror , which typically has a thin metal coating on the back of a sheet of glass to form a reflective interface. The process of silvering was once commonly used to produce mirrors, while more recently the metal layer is deposited using techniques such as sputtering . Advances in thin film deposition techniques during

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1980-555: Is a good HSP match between a solvent and a polymer. Rational substitutions can also be made for "good" solvents (effective at dissolving the solute) that are "bad" (expensive or hazardous to health or the environment). The following table shows that the intuitions from "non-polar", "polar aprotic" and "polar protic" are put numerically – the "polar" molecules have higher levels of δP and the protic solvents have higher levels of δH. Because numerical values are used, comparisons can be made rationally by comparing numbers. For example, acetonitrile

2070-464: Is a quantum chemically derived charge density parameter. This parameter seems to reproduce many of the experimental solvent parameters (especially the donor and acceptor numbers) using this charge decomposition analysis approach, with an electrostatic basis. The ϸ parameter was originally developed to quantify and explain the Hofmeister series by quantifying polyatomic ions and the monatomic ions in

2160-673: Is a relative term, but most deposition techniques control layer thickness within a few tens of nanometres . Molecular beam epitaxy , the Langmuir–Blodgett method , atomic layer deposition and molecular layer deposition allow a single layer of atoms or molecules to be deposited at a time. It is useful in the manufacture of optics (for reflective , anti-reflective coatings or self-cleaning glass , for instance), electronics (layers of insulators , semiconductors , and conductors form integrated circuits ), packaging (i.e., aluminium-coated PET film ), and in contemporary art (see

2250-442: Is also being applied to pharmaceuticals, via thin-film drug delivery . A stack of thin films is called a multilayer . In addition to their applied interest, thin films play an important role in the development and study of materials with new and unique properties. Examples include multiferroic materials , and superlattices that allow the study of quantum phenomena. Nucleation is an important step in growth that helps determine

2340-604: Is also known as the sol-gel method because the 'sol' (or solution) gradually evolves towards the formation of a gel-like diphasic system. The Langmuir–Blodgett method uses molecules floating on top of an aqueous subphase. The packing density of molecules is controlled, and the packed monolayer is transferred on a solid substrate by controlled withdrawal of the solid substrate from the subphase. This allows creating thin films of various molecules such as nanoparticles , polymers and lipids with controlled particle packing density and layer thickness. Spin coating or spin casting, uses

2430-510: Is an acceptable predictor of the solvent's ability to dissolve common ionic compounds , such as salts. Dielectric constants are not the only measure of polarity. Because solvents are used by chemists to carry out chemical reactions or observe chemical and biological phenomena, more specific measures of polarity are required. Most of these measures are sensitive to chemical structure. The Grunwald–Winstein m Y scale measures polarity in terms of solvent influence on buildup of positive charge of

2520-418: Is associated with the highest atomic mobility and deposition temperature. There is also a possibility of developing a mixed Zone T/Zone II type structure, where the grains are mostly wide and columnar, but do experience slight growth as their thickness approaches the surface of the film. Although Koch focuses mostly on temperature to suggest a potential zone mode, factors such as deposition rate can also influence

2610-568: Is below 100 °C (212 °F), so objects such as steam pipes, light bulbs , hotplates , and recently extinguished bunsen burners are able to ignite its vapors. In addition some solvents, such as methanol, can burn with a very hot flame which can be nearly invisible under some lighting conditions. This can delay or prevent the timely recognition of a dangerous fire, until flames spread to other materials. Ethers like diethyl ether and tetrahydrofuran (THF) can form highly explosive organic peroxides upon exposure to oxygen and light. THF

2700-409: Is characterized by low grain growth in subsequent film layers and is associated with low atomic mobility. Koch suggests that Zone I behavior can be observed at lower temperatures. The zone I mode typically has small columnar grains in the final film. The second mode of Volmer-Weber growth is classified as Zone T, where the grain size at the surface of the film deposition increases with film thickness, but

2790-827: Is defined as the density of the solvent divided by the density of water at the same temperature. As such, specific gravity is a unitless value. It readily communicates whether a water-insoluble solvent will float (SG < 1.0) or sink (SG > 1.0) when mixed with water. Multicomponent solvents appeared after World War II in the USSR , and continue to be used and produced in the post-Soviet states. These solvents may have one or more applications, but they are not universal preparations. Most organic solvents are flammable or highly flammable, depending on their volatility . Exceptions are some chlorinated solvents like dichloromethane and chloroform . Mixtures of solvent vapors and air can explode . Solvent vapors are heavier than air; they will sink to

Polyvinyl fluoride - Misplaced Pages Continue

2880-468: Is elemental mercury , whose solutions are known as amalgams ; also, other metal solutions exist which are liquid at room temperature. Generally, the dielectric constant of the solvent provides a rough measure of a solvent's polarity. The strong polarity of water is indicated by its high dielectric constant of 88 (at 0 °C). Solvents with a dielectric constant of less than 15 are generally considered to be nonpolar. The dielectric constant measures

2970-440: Is further categorized by the phase of the precursor: Plating relies on liquid precursors, often a solution of water with a salt of the metal to be deposited. Some plating processes are driven entirely by reagents in the solution (usually for noble metals ), but by far the most commercially important process is electroplating . In semiconductor manufacturing, an advanced form of electroplating known as electrochemical deposition

3060-446: Is known as solubility; if this occurs in all proportions, it is called miscible . In addition to mixing, the substances in a solution interact with each other at the molecular level. When something is dissolved, molecules of the solvent arrange around molecules of the solute. Heat transfer is involved and entropy is increased making the solution more thermodynamically stable than the solute and solvent separately. This arrangement

3150-412: Is mediated by the respective chemical properties of the solvent and solute, such as hydrogen bonding , dipole moment and polarizability . Solvation does not cause a chemical reaction or chemical configuration changes in the solute. However, solvation resembles a coordination complex formation reaction, often with considerable energetics (heat of solvation and entropy of solvation) and is thus far from

3240-411: Is more or less conformal. It is also widely used in optical media. The manufacturing of all formats of CD, DVD, and BD are done with the help of this technique. It is a fast technique and also it provides a good thickness control. Presently, nitrogen and oxygen gases are also being used in sputtering. Pulsed laser deposition systems work by an ablation process. Pulses of focused laser light vaporize

3330-483: Is much more polar than acetone but exhibits slightly less hydrogen bonding. If, for environmental or other reasons, a solvent or solvent blend is required to replace another of equivalent solvency, the substitution can be made on the basis of the Hansen solubility parameters of each. The values for mixtures are taken as the weighted averages of the values for the neat solvents. This can be calculated by trial-and-error ,

3420-440: Is normally more likely to form such peroxides than diethyl ether. One of the most susceptible solvents is diisopropyl ether , but all ethers are considered to be potential peroxide sources. The heteroatom ( oxygen ) stabilizes the formation of a free radical which is formed by the abstraction of a hydrogen atom by another free radical. The carbon-centered free radical thus formed is able to react with an oxygen molecule to form

3510-483: Is now used to create the copper conductive wires in advanced chips, replacing the chemical and physical deposition processes used to previous chip generations for aluminum wires Chemical solution deposition or chemical bath deposition uses a liquid precursor, usually a solution of organometallic powders dissolved in an organic solvent. This is a relatively inexpensive, simple thin-film process that produces stoichiometrically accurate crystalline phases. This technique

3600-451: Is often carried out in order to crystallize the amorphous spin coated film. Such crystalline films can exhibit certain preferred orientations after crystallization on single crystal substrates. Dip coating is similar to spin coating in that a liquid precursor or sol-gel precursor is deposited on a substrate, but in this case the substrate is completely submerged in the solution and then withdrawn under controlled conditions. By controlling

3690-598: Is placed in an energetic , entropic environment, so that particles of material escape its surface. Facing this source is a cooler surface which draws energy from these particles as they arrive, allowing them to form a solid layer. The whole system is kept in a vacuum deposition chamber, to allow the particles to travel as freely as possible. Since particles tend to follow a straight path, films deposited by physical means are commonly directional , rather than conformal . Examples of physical deposition include: A thermal evaporator that uses an electric resistance heater to melt

Polyvinyl fluoride - Misplaced Pages Continue

3780-401: Is the applied vapor pressure of adsorbed adatoms: θ = X p ( p e − p ) [ 1 + ( X − 1 ) p p e ] {\displaystyle \theta ={Xp \over (p_{e}-p)\left[1+(X-1){p \over p_{e}}\right]}} As an important note, surface crystallography and differ from

3870-481: Is the net flux, τ a {\displaystyle \tau _{a}} is the mean surface lifetime prior to desorption and σ {\displaystyle \sigma } is the sticking coefficient: d n d t = J σ − n τ a {\displaystyle {dn \over dt}=J\sigma -{n \over \tau _{a}}} n = J σ τ

3960-497: Is the square root of cohesive energy density . It can be used with nonpolar compounds, but cannot accommodate complex chemistry. Reichardt's dye, a solvatochromic dye that changes color in response to polarity, gives a scale of E T (30) values. E T is the transition energy between the ground state and the lowest excited state in kcal/mol, and (30) identifies the dye. Another, roughly correlated scale ( E T (33)) can be defined with Nile red . Gregory's solvent ϸ parameter

4050-394: Is the vapor pressure of adsorbed adatoms: θ = b P A ( 1 + b P A ) {\displaystyle \theta ={bP_{A} \over (1+bP_{A})}} BET model where p e {\displaystyle p_{e}} is the equilibrium vapor pressure of adsorbed adatoms and p {\displaystyle p}

4140-458: Is used on their bottom surface. PVF films are non- adhering to phenolic , acrylic and epoxy resins and can be therefore used as release films , usually in high-temperature processing of these resins . Thin film A thin film is a layer of materials ranging from fractions of a nanometer ( monolayer ) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition)

4230-578: The HF loss occurs at 350 °C. Since PVF has exceptional thermal stability , it is far safer than PVC , which degrades more easily. If PVF degradation happens, the highly reactive HF acid is generated but is quickly absorbed into the surrounding materials and dissipates. The monomer , VF is flammable and highly reactive, forms an explosive mixture with air and is classified as "probably carcinogenic to humans ". PVF has not caused any skin reaction or toxic effects , although after excessive exposure

4320-538: The Kamlet-Taft parameters are dipolarity/polarizability ( π* ), hydrogen-bonding acidity ( α ) and hydrogen-bonding basicity ( β ). These can be calculated from the wavelength shifts of 3–6 different solvatochromic dyes in the solvent, usually including Reichardt's dye , nitroaniline and diethylnitroaniline . Another option, Hansen solubility parameters , separates the cohesive energy density into dispersion, polar, and hydrogen bonding contributions. Solvents with

4410-1017: The Latin solvō , "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution . A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid . Water is a solvent for polar molecules , and the most common solvent used by living things; all the ions and proteins in a cell are dissolved in water within the cell. Major uses of solvents are in paints, paint removers, inks, and dry cleaning. Specific uses for organic solvents are in dry cleaning (e.g. tetrachloroethylene ); as paint thinners ( toluene , turpentine ); as nail polish removers and solvents of glue ( acetone , methyl acetate , ethyl acetate ); in spot removers ( hexane , petrol ether); in detergents ( citrus terpenes ); and in perfumes ( ethanol ). Solvents find various applications in chemical, pharmaceutical , oil, and gas industries, including in chemical syntheses and purification processes When one substance

4500-460: The UV radiation decomposes the VF into acetylene and HF . Emulsion polymerization can be done at highly reduced pressures and lower temperatures compared to suspension polymerization . The improved process control and reaction heat removal lead to increase in molecular weight , rate of reaction and yield . Fluorinated surfactants such as perfluorinated carboxylic acids maintain

4590-466: The automotive industry , PVF primer is used to improve paint adhesion , while in the aerospace engineering industry, the PVF film is applied to insulating bags containing glass fibre , which are used on exterior airplane walls, in cargo space and air condition ducts . On the top of photovoltaic cells , the transparent PVF film protects against moisture , while the white - pigmented film

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4680-463: The carbon monoxide created by the combustion of other construction materials is far more dangerous. The main applications of PVF are protective and decorative coatings , thanks to its thermal stability , and general inertness towards chemicals , corrosives and staining agents . There are two ways to apply PVF, either as a preformed film ( laminating ) or from dispersion ( coating ). These coatings can be transparent or pigmented . In

4770-399: The crystallinity , melting point and branching of the product. Initiation is done by peroxides or azo compounds . The resonance stabilization of the propagating intermediate ( VF radical ) is poor, which often leads to monomer reversals, branching and chain-transfer reactions . The presence of impurities greatly affects the molecular weight and thermal stability of

4860-539: The fluoride content in urine increased. The overheating of PVF products may result in interaction with the additives such as pigments or fillers , which may pose as an additional risk. Some formulations of the Tedlar films may contain heavy metal compounds, which can be present in dust created by secondary operations (eg sanding ). Exterior and interior PVF finishes do not create an additional danger regarding fire in residential and industrial buildings, because

4950-399: The 20th century have enabled a wide range of technological breakthroughs in areas such as magnetic recording media , electronic semiconductor devices , integrated passive devices , light-emitting diodes , optical coatings (such as antireflective coatings), hard coatings on cutting tools, and for both energy generation (e.g. thin-film solar cells ) and storage ( thin-film batteries ). It

5040-401: The adsorbate-surface interactions are stronger than adsorbate-adsorbate interactions. Volmer–Weber ("isolated islands"). In this growth mode the adsorbate-adsorbate interactions are stronger than adsorbate-surface interactions, hence "islands" are formed right away. There are three distinct stages of stress evolution that arise during Volmer-Weber film deposition. The first stage consists of

5130-407: The adsorption reaction of vapor adatom with vacancy on the substrate surface. The BET model expands further and allows adatoms deposition on previously adsorbed adatoms without interaction between adjacent piles of atoms. The resulting derived surface coverage is in terms of the equilibrium vapor pressure and applied pressure. Langmuir model where P A {\displaystyle P_{A}}

5220-456: The bottom and can travel large distances nearly undiluted. Solvent vapors can also be found in supposedly empty drums and cans, posing a flash fire hazard; hence empty containers of volatile solvents should be stored open and upside down. Both diethyl ether and carbon disulfide have exceptionally low autoignition temperatures which increase greatly the fire risk associated with these solvents. The autoignition temperature of carbon disulfide

5310-412: The bulk to minimize the overall free electronic and bond energies due to the broken bonds at the surface. This can result in a new equilibrium position known as “selvedge”, where the parallel bulk lattice symmetry is preserved. This phenomenon can cause deviations from theoretical calculations of nucleation. Surface diffusion describes the lateral motion of adsorbed atoms moving between energy minima on

5400-402: The evaporant flux. Typical deposition rates for electron beam evaporation range from 1 to 10 nanometres per second. In molecular beam epitaxy , slow streams of an element can be directed at the substrate, so that material deposits one atomic layer at a time. Compounds such as gallium arsenide are usually deposited by repeatedly applying a layer of one element (i.e., gallium ), then a layer of

5490-412: The film. Molecular beam epitaxy is a particularly sophisticated form of thermal evaporation. An electron beam evaporator fires a high-energy beam from an electron gun to boil a small spot of material; since the heating is not uniform, lower vapor pressure materials can be deposited. The beam is usually bent through an angle of 270° in order to ensure that the gun filament is not directly exposed to

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5580-512: The final film microstructure. A subset of thin-film deposition processes and applications is focused on the so-called epitaxial growth of materials, the deposition of crystalline thin films that grow following the crystalline structure of the substrate. The term epitaxy comes from the Greek roots epi (ἐπί), meaning "above", and taxis (τάξις), meaning "an ordered manner". It can be translated as "arranging upon". Solvent A solvent (from

5670-404: The final structure of a thin film. Many growth methods rely on nucleation control such as atomic-layer epitaxy (atomic layer deposition). Nucleation can be modeled by characterizing surface process of adsorption , desorption , and surface diffusion . Adsorption is the interaction of a vapor atom or molecule with a substrate surface. The interaction is characterized the sticking coefficient ,

5760-467: The form of nanoparticle solution or simply a solution, is fed to a small capillary nozzle (usually metallic) which is connected to a high voltage. The substrate on which the film has to be deposited is connected to ground. Through the influence of electric field, the liquid coming out of the nozzle takes a conical shape ( Taylor cone ) and at the apex of the cone a thin jet emanates which disintegrates into very fine and small positively charged droplets under

5850-475: The fraction of incoming species thermally equilibrated with the surface. Desorption reverses adsorption where a previously adsorbed molecule overcomes the bounding energy and leaves the substrate surface. The two types of adsorptions, physisorption and chemisorption , are distinguished by the strength of atomic interactions. Physisorption describes the Van der Waals bonding between a stretched or bent molecule and

5940-402: The grain size in the deposited layers below the surface does not change. Zone T-type films are associated with higher atomic mobilities, higher deposition temperatures, and V-shaped final grains. The final mode of proposed Volmer-Weber growth is Zone II type growth, where the grain boundaries in the bulk of the film at the surface are mobile, resulting in large yet columnar grains. This growth mode

6030-497: The influence of Rayleigh charge limit. The droplets keep getting smaller and smaller and ultimately get deposited on the substrate as a uniform thin layer. Frank–van der Merwe growth ("layer-by-layer"). In this growth mode the adsorbate-surface and adsorbate-adsorbate interactions are balanced. This type of growth requires lattice matching, and hence considered an "ideal" growth mechanism. Stranski–Krastanov growth ("joint islands" or "layer-plus-island"). In this growth mode

6120-621: The latent solvation of PVF in highly polar solvents and its subsequent coalescence . The incorporation of additives ( plasticizers , pigments , stabilizers etc.) is done by dispersion with PVF in the latent solvent . The solvent is evaporated after extrusion . To create biaxially oriented films , the PVF dispersed in solvent must be trailed by both transverse directions and biaxial orientations, which results in higher tensile strength . The unoriented films are also slightly stretched after casting . They are more compliant and formable and exhibit higher elongation at break than

6210-430: The material and raise its vapor pressure to a useful range. This is done in a high vacuum, both to allow the vapor to reach the substrate without reacting with or scattering against other gas-phase atoms in the chamber, and reduce the incorporation of impurities from the residual gas in the vacuum chamber. Only materials with a much higher vapor pressure than the heating element can be deposited without contamination of

6300-590: The morphology of the film’s surface is unchanging with film thickness. During this stage, the overall stress in the film can remain tensile, or become compressive.   On a stress-thickness vs. thickness plot, an overall compressive stress is represented by a negative slope, and an overall tensile stress is represented by a positive slope. The overall shape of the stress-thickness vs. thickness curve depends on various processing conditions (such as temperature, growth rate, and material). Koch states that there are three different modes of Volmer-Weber growth. Zone I behavior

6390-412: The mouth of a container or bottle. Minor mechanical disturbances, such as scraping the inside of a vessel, the dislodging of a deposit, or merely twisting the cap may provide sufficient energy for the peroxide to detonate or explode violently. Peroxide formation is not a significant problem when fresh solvents are used up quickly; they are more of a problem in laboratories which may take years to finish

6480-467: The newly formed grain boundaries. The magnitude of this generated tensile stress depends on the density of the formed grain boundaries, as well as their grain-boundary energies. During this stage, the thickness of the film is not uniform because of the random nature of the island coalescence but is measured as the average thickness. The third and final stage of the Volmer-Weber film growth begins when

6570-445: The nucleation of individual atomic islands. During this first stage, the overall observed stress is very low. The second stage commences as these individual islands coalesce and begin to impinge on each other, resulting in an increase in the overall tensile stress in the film. This increase in overall tensile stress can be attributed to the formation of grain boundaries upon island coalescence that results in interatomic forces acting over

6660-440: The oriented films. The majority of linkages in PVF are head-to-tail, and only 12-18 % of linkages are head-to-head. These irregularities are probably the cause of the variations in melting point , which ranges from 185 °C to 210 °C. The crystallinity of PVF ranges from 20 to 60%, depending on the polymerization method and thermal history of the polymer . It has been found that lower polymerization temperature leads to

6750-413: The other (i.e., arsenic ), so that the process is chemical, as well as physical; this is known also as atomic layer deposition . If the precursors in use are organic, then the technique is called molecular layer deposition . The beam of material can be generated by either physical means (that is, by a furnace ) or by a chemical reaction ( chemical beam epitaxy ). Sputtering relies on a plasma (usually

6840-552: The overall free energy. These stable sites are often found on step edges, vacancies and screw dislocations. After the most stable sites become filled, the adatom-adatom (vapor molecule) interaction becomes important. Nucleation kinetics can be modeled considering only adsorption and desorption. First consider case where there are no mutual adatom interactions, no clustering or interaction with step edges. The rate of change of adatom surface density n {\displaystyle n} , where J {\displaystyle J}

6930-518: The polymer chains. Physical deposition uses mechanical, electromechanical or thermodynamic means to produce a thin film of solid. An everyday example is the formation of frost . Since most engineering materials are held together by relatively high energies, and chemical reactions are not used to store these energies, commercial physical deposition systems tend to require a low-pressure vapor environment to function properly; most can be classified as physical vapor deposition . The material to be deposited

7020-499: The potential energy as a function of distance. The equilibrium distance for physisorption is further from the surface than chemisorption. The transition from physisorbed to chemisorbed states are governed by the effective energy barrier E a {\displaystyle E_{a}} . Crystal surfaces have specific bonding sites with larger E a {\displaystyle E_{a}} values that would preferentially be populated by vapor molecules to reduce

7110-569: The product, as the VF radical is highly reactive. This also limits the choice of polymerization mediums, surfactants , initiators or other additives. The liquid VF is suspended in water and stabilized either by water-soluble polymers based on cellulose or polyvinyl alcohol . Inorganic salts can also act as stabilizers. The suspension polymerization is usually initiated by organic peroxides (eg diisopropyl peroxydicarbonate), but UV light or ionizing radiation can also be used. However, when there are no radicals present,

7200-1043: The same molecule) and solvate positively charged species via their negative dipole. In chemical reactions the use of polar protic solvents favors the S N 1 reaction mechanism , while polar aprotic solvents favor the S N 2 reaction mechanism. These polar solvents are capable of forming hydrogen bonds with water to dissolve in water whereas non-polar solvents are not capable of strong hydrogen bonds. The solvents are grouped into nonpolar , polar aprotic , and polar protic solvents, with each group ordered by increasing polarity. The properties of solvents which exceed those of water are bolded. CH 3 CH 2 CH 2 CH 2 CH 3 CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 H 3 C(CH 2 ) 5 CH 3 C 6 H 5 -CH 3 CH 3 CH 2 -O-CH 2 CH 3 CHCl 3 CH 2 Cl 2 CH 3 -C≡N CH 3 -NO 2 C 4 H 6 O 3 NH 3 (at -33.3 °C) CH 3 CH 2 CH 2 CH 2 OH CH 3 CH 2 CH 2 OH CH 3 CH 2 OH CH 3 OH The ACS Green Chemistry Institute maintains

7290-448: The second reactant is deposited, during which a chemical reaction occurs on the substrate, forming the desired composition. As a result of the stepwise, the process is slower than chemical vapor deposition; however, it can be run at low temperatures. When performed on polymeric substrates, atomic layer deposition can become sequential infiltration synthesis , where the reactants diffuse into the polymer and interact with functional groups on

7380-399: The solvent's tendency to partly cancel the field strength of the electric field of a charged particle immersed in it. This reduction is then compared to the field strength of the charged particle in a vacuum. Heuristically, the dielectric constant of a solvent can be thought of as its ability to reduce the solute's effective internal charge . Generally, the dielectric constant of a solvent

7470-436: The speed of evaporation. Small amounts of low-boiling-point solvents like diethyl ether , dichloromethane , or acetone will evaporate in seconds at room temperature, while high-boiling-point solvents like water or dimethyl sulfoxide need higher temperatures, an air flow, or the application of vacuum for fast evaporation. Most organic solvents have a lower density than water, which means they are lighter than and will form

7560-659: The substrate surface. Diffusion most readily occurs between positions with lowest intervening potential barriers. Surface diffusion can be measured using glancing-angle ion scattering. The average time between events can be describes by: τ d = ( 1 / v 1 ) exp ⁡ ( E d / k T s ) {\displaystyle \tau _{d}=(1/v_{1})\exp(E_{d}/kT_{s})} In addition to adatom migration, clusters of adatom can coalesce or deplete. Cluster coalescence through processes, such as Ostwald ripening and sintering, occur in response to reduce

7650-495: The surface characterized by adsorption energy E p {\displaystyle E_{p}} . Evaporated molecules rapidly lose kinetic energy and reduces its free energy by bonding with surface atoms. Chemisorption describes the strong electron transfer (ionic or covalent bond) of molecule with substrate atoms characterized by adsorption energy E c {\displaystyle E_{c}} . The process of physic- and chemisorption can be visualized by

7740-419: The surface of the target material and convert it to plasma; this plasma usually reverts to a gas before it reaches the substrate. Thermal laser epitaxy uses focused light from a continuous-wave laser to thermally evaporate sources of material. By adjusting the power density of the laser beam, the evaporation of any solid, non-radioactive element is possible. The resulting atomic vapor is then deposited upon

7830-529: The temperature range of 40 to 50 °C. PVF is insoluble in common solvents below 100 °C. When the temperature is raised, it becomes soluble in polar solvents ( amides , ketones etc.). At room temperature , the PVF films are resistant to both acids and bases as well as aliphatic , aromatic and alcohol liquids . The thermal stability of PVF is better than that of other vinyl halide polymers , reporting backbone cleavage and HF loss in an inert atmosphere at 450 °C, while in air

7920-445: The total surface energy of the system. Ostwald repining describes the process in which islands of adatoms with various sizes grow into larger ones at the expense of smaller ones. Sintering is the coalescence mechanism when the islands contact and join. The act of applying a thin film to a surface is thin-film deposition – any technique for depositing a thin film of material onto a substrate or onto previously deposited layers. "Thin"

8010-419: The withdrawal speed, the evaporation conditions (principally the humidity, temperature) and the volatility/viscosity of the solvent, the film thickness, homogeneity and nanoscopic morphology are controlled. There are two evaporation regimes: the capillary zone at very low withdrawal speeds, and the draining zone at faster evaporation speeds. Chemical vapor deposition generally uses a gas-phase precursor, often

8100-425: The work of Larry Bell ). Similar processes are sometimes used where thickness is not important: for instance, the purification of copper by electroplating , and the deposition of silicon and enriched uranium by a chemical vapor deposition -like process after gas-phase processing. Deposition techniques fall into two broad categories, depending on whether the process is primarily chemical or physical . Here,

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