Interfaces Flashcards
interface formed by
Ex: (4)
Formed by two phases that are mutually insoluble (immiscible)
G/G S/L
L/L G/S
Gas/liquid interface formed while _____ existed
surface tension
–> liquid interface with gas (e.g. air and water) = surface tension
= unbalanced forces at the surface of molecules
attracted inwards
surface tension or interfacial tension
- -> lead to ____?
- -> require ____ to overcome?
- -> Units?
Unbalanced forces at the surface lead to a net inward force of attraction on surface molecules that tends to minimise the area of the surface
Contraction of the surface therefore leads to a minimum free energy state and work is required to increase the surface area
Free energy and surface tension are numerically equal with units N m-1 (usually quoted as mN m-1)
What is require to increase surface area
Equation?
Work / Energy
ΔE = γΔA
Continuous phase define?
can also called ?
That phase in a two or more phase mixture which is continuously interconnected
dispersing medium or external phase
surface free energy is
Units?
the ‘work’ required to increase the surface area by 1 m^2
Free energy and surface tension are numerically equal with units N m-1 (usually quoted as mN m^-1)
liquid interface with a solid surface (e.g. water droplet on glass) = surface free energy
Energy (ΔE) required to increase surface area (ΔA) of
liquid interface with gas (e.g. air and water)
surface tension
Energy (ΔE) required to increase surface area (ΔA) of liquid interface with a solid surface (e.g. water droplet on glass)
= surface free energy
Energy (ΔE) required to increase surface area (ΔA) of interface between immiscible liquids (e.g. oil and water)
interfacial tension
Colloid aka ?
define
colloidal system - have a dispersed phase and a continuous phase (X/Y)
state of subdivision such that molecules or particles dispersed in a medium have at least one dimension between 1 nm and 1000 nm (1 μm)
Three types of solutions
differences?
true solution = dispersed molecules or particles < 1nm
Colloidal solution = molecules or particles dispersed in a medium have at least one dimension between 1 nm and 1000 nm (1 μm)
Suspensions = dispersed molecules or particles > 1um
colloidal can be seen by optical microscopy
T/F ?
False
Colloids can have what effects? why ?
Tyndall effect as particles (size) scatter light
Colloids has [Large/ Small?] surface area
important factor ?
Large surface area - almost entirely surface rather than bulk
interfacial properties are important
example of phase inversion in colloidal systems
dispersed phase and a continuous phase (X/Y)= O/W oil in water
turning cream (o/w) into butter (w/o) described as phase inversion
Dispersed phase- define?
may also be described as ____?
the phase in a two-phase system that consists of finely divided particles
discontinuous phase or internal phase
Different Colloidal systems (9)
miscible (G/G ) foam (G/L) Solid foam (G/S) Liquid aerosol (L/G) Emulsion (L/L) Gel or Solid emulsion (L/S) Solid aerosol (S/G) Suspension or Sol (S/L) Solid sol (S/S)
Food colloids (L/G)
Liquid aerosol : fog, mist, spray cooking oil
Food colloids (S/G)
Solid aerosol : smoke, dust
Food colloids (G/L)
Foam : whipped cream, beer foam
Food colloids (L/L)
Emulsion : milk, mayonnaise
Food colloids (S/L)
Suspension / Sol : paint, ink, detergents, gum, thick sauces (e.g. custard)
Food colloids (G/S)
Solid foam :marshmallow, honeycomb, “aero” chocolate, meringue, bread
Food colloids (L/S)
Gel / Solid emulsion: jelly, butter, cheese
