Application on surfactants
Wettability
• Wettability and repellency are important properties of solid surfaces from
both fundamental and practical aspects.
• Wettability is the ability of a substrate to be covered with water or other
liquids.
• wettability can be determined by measuring the contact angle of a water
drop resting on a solid substrate
• the wettability of the solid surface is a characteristic material property and
strongly depends on both the surface energy arising from the surface
chemical structure and the surface roughness.
• The determination of wettability is important in adhesion, detergency,
lubrication, friction, coating operations, flotation, catalysis and many other
processes in chemical, mechanical, mineral, metallurgy, microelectronics,
biomedical and biological industries.
Contact Angle of Liquid Drops on Solids
❑If we consider a liquid drop resting on a solid surface
as shown in Figure , the drop is in equilibrium by
balancing three forces, namely, the interfacial
tensions between
➢solid and liquid, SL;
➢solid and vapor, SV;
➢liquid and vapor, LV.
❑ The contact angle, q, is the angle formed by a liquid
drop at the three-phase boundary where a liquid, gas
and solid intersect, and it is included between the
tangent plane to the surface of the liquid and the
tangent plane to the surface of the solid, at the point
of intersection.
❑The contact angle is a quantitative measure of the
wetting of a solid by a liquid.
• Low values of q indicate a strong liquid–solid interaction such that the
liquid tends to spread on the solid, or wets well, while high q values
indicate weak interaction and poor wetting.
Increase contact angle decrease wettability
The degree of wettability is determined by force
balance between adhesive and cohesive forces.
Young’s Equation
• T. Young was the first to describe contact angle equilibrium, in 1805.
The vectorial summation of forces at the three-phase intersection
point (the so-called three-phase contact point) gives
gSV = gSL + gLV cos q
Industrial applications of contact angles
➢Measurement of contact angles provides a better
understanding of the interactions between solids and
liquids, or between immiscible liquids.
➢the wetting of adhesive on a substrate
➢the paints and coatings industries
The motivation for new preparation methods is to
obtain long-lasting adhesion between the coating and
substrate surfaces (paper, metal, wood, plastic etc
➢the automotive and building industries
Surface and interfacial tension directly
influence the quality of coatings
• the textiles industry
• The medical, pharmaceutical and cosmetic industries also use contact
angle measurements in their research and quality control
laboratories. Biocompatibility is an important issue in the medical and
dental industries.
Wetting agent and
anti wetting agent
Wetting agent ..
◘Wetting agent are substances that reduce the surface tension
of water to allow it to spread drops onto a surface, increasing
the spreading abilities of a liquid.
◘Wetting agent is known as surfactant.
◘Lowering the surface tension lowers the energy
required to spread drops onto a film.
◘Thus weakening the cohesive properties of the
liquid and strengthening its adhesive properties.
◘Lowering the surface tension lowers
the energy required to spread drops
onto a film.
◘Thus weakening the cohesive
properties of the liquid and
strengthening its adhesive properties.
How wetting agents work !
is in the formation of micelles. Micelles consist of hydrophilic
heads forming an outer layer around lipophilic tails. When in
water, the micelles' tails can surround an oil droplet while the
heads are attracted to the water.
Anti-wetting agent ..
◘Anti wetting agent increase the
surface tension.
◘Increase the intermolecular force.
◘increase the cohesive force and
decrease the adhesive force.
◘so the ability of spreading decrease.
KRÜSS Force Tensiometer TenssiowithMicro Dispenser
Detergency
Detergency
• Detergency is the removal of solid or liquid dirt particles from the
adsorbed (or attached) solid surfaces by using surfactants in an
aqueous solution.
• The sole detergent action can independently remove all oily
substances and solid particles such as dust, soot etc. from a solid
surface in a washing process; but it is usually supported by
mechanical agitation in washing machines to speed up the cleaning
process.
• The washing of textiles by the application of detergents accounts for
the bulk of all surfactant usage, but detergent action is not limited to
textiles. There is a wide variety of possible substrates to be cleaned by
detergents, including hard materials such as plastic, metal, glass,
ceramic; soft natural materials such as body skin and hair etc.
• On the other hand, the dirt materials are versatile; they may be liquid
or solid (usually a combination of both), polar or non-polar, of small
or large particle size, and chemically reactive or inert towards the
substrate and/or the detergent.
Mechanisms of detergent action
• It is clear that the solid or liquid dirt particles are adsorbed on a
substrate, because it is energetically more favorable to adsorb.
• If we can reverse the process, so that it is energetically more
favorable for dirt material to leave the substrate surface and to
suspend or to dissolve in the solution, then the cleaning action will be
accomplished spontaneously.
• In thermodynamic terms, when a dirt particle is adsorbed on a
substrate surface, it forms a solid–dirt interface (SD) with an
interfacial tension of g .
SD
• When the dirt is removed from this solid surface in aqueous solution,
two new surfaces will be created;
• one is the solid–water solution interface (SWs) having an interfacial
tension of g , and
SWs
• the other is the dirt–water solution interface (DWs) with an interfacial
tension of g
DWs
• then the work of adhesion between a dirt particle and a solid surface
per unit area can be expressed from Equation
• In microscopic terms, the water molecules with a high surface tension
( 72.8mJm ) cannot enter the dirt–solid interfacial region to dislodge
2
the dirt in detergent-free conditions.
• However, when a suitable surfactant with detergency properties is
dissolved in water, it decreases the surface tension of water near the
surface tension of the dirt ( 20– 40mJm ), and the hydrophobic parts
2
of the detergent molecules line up both on the solid surface and on
the dirt particles, thus increasing the surface excess of detergent
molecules in these interfaces, and reducing the adhesion of the dirt
to the solid.
• Afterwards, the dirt may be removed by mechanical action and will
be held suspended in the aqueous solution due to detergent
adsorption on the dirt particles. Meanwhile, several other detergent
molecules form an adsorbed layer on the cleaned solid surface.
Soap
Soap normally consists of the sodium or potassium salts of various long
chain fatty acids and is manufactured by the saponification of glyceride
oils and fats (e.g. tallow) with NaOH or KOH, giving glycerol as a by-
product:
DETERGENTS Surfactants are one of the major
components of cleaning products and Detergents are
composed of physical or chemical active ingredients
such as :
1. Surfactants.
2. Chelating/Sequestering Agents.
3. Builders.
4. Solvents.
5. Preservatives.
6. Bleaches.
7. Enzymes.
Applications
• laundry washing
• Dish-washing liquids
• Industrial cleaners
• Glass and bottle cleaning
