surface tension Flashcards
Surfactants function
can act as emulsifiers by stabilising droplets of an immiscible liquid into the bulk of a liquid, eg: oil in water emulsions
can stabilise air bubbles within a liquid and in this way help to generate and stabilise foams
Food surfactants
fatty acids, proteins
Phosphatidyl choline in lecithin, a widely used food emulsifier
surfactants molecular structure
Polar (hydrophilic) and nonpolar (hydrophobic) parts in the same molecule spacially separated from each other in a balanced way
surfactant (surface active agent) definition
a substance that when present at low concentration in a system has the property of adsorbing onto the surfaces or interfaces of the system and of altering to a marked degree the surface/interfacial energies of those surfaces ie, reducing surface tension
interface
a boundary between any two immiscible phases; the term surface denotes an interface where one phase is a gas, usually air
Cambridge balance
units read from the balance as
The determination of surface tension using the Nouy’s method which is based on the determination of the force
required to tear the ring from the liquid surface.
dyne cm^-1
Drop weight method
At equilibrium forces acting on the surface of the droplet balance out: Forces inwards (due to surface tension acting on the surface of the drop) = Forces outwards (due to weight of the drop)
Capillary rise
The tendency of liquids to rise up a capillary (capillary action) is a consequence of surface tension.
Pressure inside the bubble (in the inside of a cavity) always _______ than outside
higher
In capillary rise, the energy is lowest when
The liquid will rise up till reaching equilibrium where
when a thin film covers as much of the glass as possible.
when forces pulling the liquid up (surface tension) and forces pulling the liquid down balance out
why most droplets are spherical
the shape offers the minimum surface area for a given vol
Which forces oppose surface tension
the effect
gravity
tend to break droplets or flatten spheres into puddles or oceans
surface tension
Force per unit length acting in a particular surface (N m-1), force acting on the surface to minimise it
Molecules interact more strongly with ____________ than with __________. So _______ is required to bring molecules to _______
interact more strongly with the molecules in the interior of the substance than with the gas molecules above (at surface)
work - to bring molecules to surface
Various forces act on molecules in the bulk liquid, such as_________, from all directions effectively _________
VWaals foces
effectively cancelling each other out
