en>Joel B. Lewis: Make formula prettier

2013-03-07T15:45:43Z

Make formula prettier

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{{main|Paint}}
[[Paint]] has four major components: [[pigments]], binders, [[solvents]], and other additives. [[Pigments]] serve to give paint its color, texture, toughness, as well as determining if a paint is opaque or not. Common white pigments include [[titanium dioxide]] TiO2 and [[zinc oxide]] ZnO. Binders are the film that forms as a paint dries and they affect the durability, gloss, and flexibility of the coating. Polyurethanes, polyesters, and acrylics are all examples of common binders. The [[solvent]] helps adjust the curing rate and viscosity of the paint in its liquid state. The solvent evaporates off as the paint dries. There are two types of solvents: solvent-borne and water-borne. The additives that are incorporated into paints are a wide range of things which help to effect the properties of the paint and the final coating. The main additives added to many paints are surfactants.
{{main|Surfactant}}
The word ''surfactant'' is short for ''surface active agent''.<ref name="Rosen MJ">{{Cite book|author=Rosen MJ |title=Surfactants and Interfacial Phenomena |edition=3rd |year=2004 |location=Hoboken, New Jersey |publisher=John Wiley & Sons |page=1| date=September 2010}}</ref> [[Surfactants]] are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or the interfacial tension between a liquid and a solid. In solutions this behavior is known as [[wetting]], and it occurs as a result of surfactants adsorbing to the air/water interface.<ref>{{cite journal | author = M. R. Bresler and J. P. Hagen | title = Diethyl Surfactant Adsorption: A Revised Physical Chemistry Lab | year = 2008 | journal = [[Journal of Chemical Education]] | volume = 82 | issue = 2 | pages = 269–271 | doi = 10.1021/ed085p269}}</ref> Soluble surfactants are also capable of forming [[micelles]] and other aggregate structures in solution, leading to a stabilizing effect in latex paints. Surfactants in paint are used to change many end properties of a dried paint, as well as to emulsify paints in their liquid state.

== Role of surfactants in paint ==

{| class="wikitable sortable" style="float: right;"
|-
! % TiO2 by volume !! Modulus of Elasticity (MPa) !! Modulus of Elasticity: Surfactant Removed (MPa)
|-
| 0 ||8.9 || 6.0
|-
| 13 || 22.9 || 22.4
|-
| 25 || 60.2 || 89.1
|-
| 38 || 169.8 || 416.8
|-
| colspan="3" style="text-align: left;" | Elasticity of a latex paint is affected by presence of surfactant.<ref name="EWS Hagan ; MN Charalambides ; CRT Young ; TJS Learner ; S Hackney 2010 73–81">{{cite journal | author = EWS Hagan ; MN Charalambides ; CRT Young ; TJS Learner ; S Hackney | title = Viscoelastic properties of latex paint films in tension: Influence of the inorganic phase and surfactants | year = 2010 | journal = [[Progress in Organic Coatins]] | volume = 69 | issue = 1 | pages = 73–81 }}</ref> Note the effect changes dependent on TiO2 concentration.
|}

=== Positive Effects ===

Surfactants affect a wide array of physical properties in paints. Surfactants affect the behavior of a paint not only during the lifetime of the formed coating but also the initial aggregation and film formation of the paint. Surfactants are also used to stabilize the dispersion of polymer particles during emulsion polymerization in paints and other applications. The mechanical stability, freeze-thaw stability and shelf-life of paints are all improved by the addition of surfactants. The addition of surfactants to paint also allow the paint to coat a surface more easily because surfactants increase the wetting of a solution.<ref name="RE Skokina ; LI Voronchikhina 2003 288–290">{{cite journal | author = RE Skokina ; LI Voronchikhina | title = Protective Properties of Surfactants Based on Dimethylaminoethanol | year = 2003 | journal = [[PROTECTION OF METALS]] | volume = 39 | issue = 3 | pages = 288–290 | doi=10.1023/A:1023979523413}}</ref>

=== Negative Effects ===

The addition of surfactants does not always have a positive effect on all properties. The water resistance of the coating can be decreased with surfactant addition since surfactants can be very water soluble and will easily wash out of a coating.<ref name="EWS Hagan ; MN Charalambides ; CRT Young ; TJS Learner ; S Hackney 2010 73–81"/> While the type and amount of surfactant determine what properties will be affected, other chemicals in a paint can alter the overall effect the surfactants may have on the paint.<ref>{{cite journal | author = LN Butler ; CM Fellows ; RG Gilbert | title = Effect of surfactants used for binder synthesis on the properties of latex paints | year = 2005 | journal = [[Progress in Organic Coatings]] | volume = 53 | issue = 2 | pages = 112–118 | doi=10.1016/j.porgcoat.2005.02.001}}</ref> Elasticity has been found to either increase or decrease in latex paints depending on the amount of TiO2 present.<ref name="EWS Hagan ; MN Charalambides ; CRT Young ; TJS Learner ; S Hackney 2010 73–81"/>

=== Emulsification ===
[[File:Latexemulsion.png|thumb|250px|Surfactants are used to stabilize polymer emulsions in latex paints.]]

Latex paints are an emulsion of polymer particles dispersed in water. [[Macroemulsion]]s in latex paint are inherently unstable and phase separate, so surfactants are added to lower interfacial tension and stabilize polymer particles to prevent demulsification.<ref name="Butt 2006">{{cite book |last= Butt |first= Hans-Jurgen |coauthors= Michael Kappl, Karlheinz Graff |title= [[Physics and Chemistry of Interfaces]] |publisher= [[Wiley-VCH]] |year= 2006 |isbn= 3-527-40629-8}}</ref>

The thermodynamic explanation for demulsification is the gain in Gibbs Free Energy resulting from lowering the total area of high energy surface interactions.

:<math>\Delta G_{\text{em}}=\gamma{3V\ \over R}</math>

The energy gained from demulsification is dependent on the total area of interface and the surface tension of that interface. Surfactants lower the surface tension (γ) and thus gibbs energy is gained from demulsification. This slows the process of demulsification and stabilizes the latex paint.

The size of the droplets of dispersed polymer in a latex paint can be modeled with the following equation:

:<math> R={3L_{\text{s}}\phi_{\text{d}} \over \phi_{\text{s}}}</math>

The radius of a droplet in the emulsion is dependent on surfactant length, Ls, volume fraction of dispersed phase, φd, and volume fraction of surfactant, φs.<ref name="Butt 2006"/>

== Classification of surfactants ==
There are three main categories of surfactants used in paint —ionic, polymeric and electrosteric.<ref name="L. N. Butler, C. M. Fellows and R. G. Gilbert 2005 112–118">{{cite journal | author = L. N. Butler, C. M. Fellows and R. G. Gilbert | title = Effect of surfactants used for binder synthesis on the properties of latex paints | year = 2005 | journal = [[Progress in Organic Coatings]] | volume = 53 | issue = 2 | pages = 112–118 | doi = 10.1016/j.porgcoat.2005.02.001}}</ref>

=== According to head group composition ===

[[File:SDS surfactant.png|thumb|350px|Sodium Dodecyl Sulfate, a common anionic surfactant.]]

The head group classification of a surfactant is determined by the head group ion type. Ionic surfactants derive their amphiphilicity from a charged hydrophilic head group and tend to be small, low molecular weight molecules. Ionic surfactants will stabilize particles suspended in a paint by electrostatic repulsion and are easily adsorbed and desorbed from a surface due to their small size.<ref name="L. N. Butler, C. M. Fellows and R. G. Gilbert 2005 112–118"/>

Anionic head groups are negatively charged, and commonly used in cleaning products. Anionic surfactants can be found in products such as shampoos, laundry detergents, and soaps because of their ability to remove dirt from soft mediums such as fabric. Anionic surfactants are easily suspended in water due to the polarity of the charged head group. However, hard water can deactivate the molecule. Some of the more commonly used anionic head groups are [[sulfates]] and ethoxylates.

Cationic head groups have a positive charge and cationic surfactants are used in several different applications. One common use for cationic surfactants is in fabric softeners. Cationic head groups are also added to laundry detergent in conjunction with anionic surfactants because they help to improve the dirt removal properties of the anionic surfactants. Cationic head groups also increase the disinfecting properties of household cleaners. Some common cationic surfactants head groups include [[amines]] and quaternary [[ammonium]] ions.
Among the many types of surfactants, cationic surfactants are very useful as corrosion inhibitors due of their protective effectiveness in neutral and acidic media.<ref>{{cite journal | author = R. E. Skokina and L. I. Voronchikhina |ntitle = Protective Properties of Surfactants Based on Dimethylaminoethanol | year = 2003 | journal = [[Protection of Metals]] | volume = 39 | issue = 3 | pages = 288–290 | doi = 10.1023/A:1023979523413}}</ref>

Nonionic head groups have no charge and they function very well as grease removers. Nonionic surfactants are commonly used in detergents, soaps, and household cleaners. In solutions of hard water, nonionic surfactants are used to help limit the deactivation of ionic surfactants caused by the calcium and magnesium ions. Some common nonionic surfactant head groups include [[fatty acids]] and [[glycols]].

=== According to tail composition ===

Hydrocarbon chains are long chains which consist of a carbon backbone hydrogen substituents, making them very hydrophobic. Hydrocarbon chains alone form waxes and oils and retain these characteristics when they are incorporated into surfactant. A good example of surfactants containing a hydrocarbon chain are lipids, which form cell membranes.

Alkyl ether chains are similar to hydrocarbon chains, except with oxygens incorporated within the backbone as well as carbons. There are two alkyl chains commonly used in surfactants: polyethylene oxide and polypropylene oxide. Polyethylene oxide chains have an oxygen and two carbon (-O-C-C-)n repeating unit and has an increased hydrophilic character compared to hydrocarbons. Polypropylene oxide has the same backbone structure as polyethylene oxide but with a methyl group substituent of one of the carbons, and this structure has hydrophobicity between hydrocarbons and polyethylene oxides.
[[File:Siloxanechain.png|thumb|Silicon - Oxygen bonds resist chain breakdown from hydrolysis and will prevent cracking in paints.]]

Fluorocarbon chain tails consist of a carbon backbone that has fluorine substituents instead of hydrogens. Fluorocarbons help to lower the surface tension of water and other solvents because of their lypophobic nature even in harsh conditions such as low pH. When fluorocarbons are incorporated into surfactants they are used as stain repellents and incorporated into coatings in order to decrease surface defects.

Siloxane chains consist of a backbone which contains alternating oxygen and silicon atoms. Surfactants with siloxane tails have been found to resist hydrolysis and prevent breakdown polymer chains which can cause cracking in the paint and are thus used in products such as cosmetics, deodorants, defoamer, and soap.
(Syntheses and Properties of New Double-tail Trisiloxane Surfactants with Both Hydrolysis Resistance and High Spreading Ability)

== Problems with surfactant use ==

=== Environmental issues ===
Surfactants can destabilize toxic organic compounds in paint which can enter the environment and have negative effects.<ref name="RE Skokina ; LI Voronchikhina 2003 288–290"/> Water soluble surfactants can wash out of dried paints and enter the environment. Some of these surfactants are directly toxic to animals and the environment as well as increase the ability of other toxic contaminants present to enter the environment.<ref name="Metcalfe TL, Dillon PJ, Metcalfe CD">{{cite journal |last1=Metcalfe |first1=Tracy L. |last2=Dillon |first2=Peter J. |last3=Metcalfe |first3=Chris D. |title=DETECTING THE TRANSPORT OF TOXIC PESTICIDES FROM GOLF COURSES INTO WATERSHEDS IN THE PRECAMBRIAN SHIELD REGION OF ONTARIO, CANADA |journal=Environmental Toxicology and Chemistry |volume=27 |issue=4 |pages=811–8 |year=2008 |pmid=18333674 |doi=10.1897/07-216.1}}</ref>

=== Cost ===
The cost of surfactants is partially dependent on the crude oil market. As a stock ingredient for production of surfactants, paints highly dependent on surfactants will be affected by this market.<ref>{{cite web | title = Market Report: World Surfactant Market | publisher = [http://www.acmite.com Acmite Market Intelligence] | url = http://www.acmite.com/market-reports/chemicals/world-surfactant-market.html }}</ref> More intricate surfactants with larger, more difficult to synthesize structure are more expensive to produce and have a greater effect on end market price of their applications. As a result, simple, easy to produce and more environmentally friendly surfactants are used more widely.
<ref>{{cite journal | author = U Schoenkaes | title = LAS - a Modern Classic Surfactant | year = 2005 | journal = [[CHIMICA OGGI-CHEMISTRY TODAY]] | volume = 16 | issue = 9 | pages = 9–13 }}</ref>

== References ==
{{Reflist}}

[[Category:Surfactants]]

Stanley symmetric function - Revision history

en>Joel B. Lewis: Make formula prettier