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Interfaces & Particles - Coggle Diagram

- - - - Antiferromagnetic
        
        Atoms correlated, but antiparralel
        
        No net magnetic moment
      - Paramagnetic
        
        No atomic correlation in absence of B
        
        Atomic correlation if B is applied
      - Ferrimagnetic
        
        Atomic correlation, but alternating direction of different magnitude
        
        Small nett magnetic moment
      - Canted antiferro
        
        Correlated, but now with different angles
        
        small nett magnetic moment
      - Ferromagnetic
        
        Correlated atomic movement
        
        Behaves paramagnetically above the curie temperature
    - - Spin angular momentum
      - Orbital angular momentum
      - Summutation over all atoms
    - - Single domain particles
        
        10-100 nm
        
        Have spontaneous structure formation
      - Multi domain particles
        
        No nett magnetic moment, becauses domains cancel eachother
      - Domain in wich atoms are correlated in one specific way
  - - - Dipole dipole interaction Ud
        
        Depends on
        
        Magnetic moment particles
        
        Standard magnetisation material Ms
        
        mu = Ms*V
        
        Volume of magnetic part
        
        Distance between the two dipole centers
        
        Direction of their magnetic field
        
        Max interaction energy
        
        Head to tail configuration
        
        r is the distance between centers
      - Can be tuned depositiong inert material
        
        Increasing the center distance
        
        To stabilise ferrofluid
        
        For example using silica
      - Total energy = Ud + Ue
    - - Gravity
      - Surface tension
      - Magnetic field strength
      - Field lines
      - Concentration
    - - When rotating in magnetic field
      - Torque = |mu||B|sin(theta)
  - - - To form structures
      - To form strings of colloids like polymers
      - Lubricant
      - Seal
    - - Seperation of biological material
        
        Attach magnetic label to biological material
        
        Seperate using a magnet or magnetic column
      - Hyperthermea treatment
        
        Alternating magnetic field causes the particles to locally heat up.because of relaxation--> kill cancer cells
      - Magnetic density seperation (plastics)
      - Self replication
  - - - Apolar for the steric stabilisation
  - - - Standard magnetisation
      - Size of single magnetic domain
      - Usually transition metal oxides
    - - Magnetic nanoparticles embedded in larger inter particle
      - Inert particle still moves under an electric field
      - Can also bond if magnetic part is on the outside (polymer)
- - - - Applying high shear stress
      - Addition of surfactants
      - High pressure piston
    - - Exact size control
      - Usually gives low amount of particles
      - Uv crosslinks substrate
    - - Particles are grinded into smaller particles
      - Unwanted: give low size/shape controlability
  - - - Can be done with every insoluble material via precipitation using supersaturated solution
      - Nucleation
        
        Homogeneous
        
        Nucleation in pure solution
        
        Hard to reach
        
        Heterogeneous
        
        Nucleation aided by the presence of external surfaces and defects
        
        Thermodynamics
        
        dG<0 for growth + nucleation
        
        dG = bulk interaction + interface formation = -Ndmu + yBN^2/3
        
        After critical particles size, bulk interaction are greater than interace energy and growth is spontaneous. Because N > N^2/3
        
        Stopping of particle growth is then needed
        
        Can be done with charge/steric
      - Growth
        
        Always make sure that during particle growth, supersataration is not reached again (seeded growth) --> unwanted nucleaction --> varying particles size
    - - Particles in evaporating droplets
      - Reactive emulsions
        
        UV --> polymerisation --> solid particles
        
        Oil precursor --> nucleation --> spontaneous emulsification
      - Multicomposition particles
      - Look up on intenet for all possible variants
      - Controlled aggregation
        
        Opposite charge colloids
        
        One type must be in surplus
      - Dewetting techniques
- - - - Oil dispersed in water (O/W) emulsion, water = continious phase
      - Water dispersed in oil (W/O) emulsion, oil = continious phase
      - Determined by
        
        The type and conc of surfactant used
        
        Low hydrophilic/lyophilic balance (hlb), oli cont
        
        High hlb, water cont
        
        Bancroft rule of thumb: Phase where surfactant is more soluble in becomes the continious phase.
        
        The viscosity ratio of the two liquids
        
        Higher viscosity = more chance to be dispersed
        
        Volume ratio of inner/outer phase
      - Examples
        
        O/W = mayonaise
        
        Paint
  - - - Creaming/Sedimentation
        
        Reduce particle size
        
        Alter viscosity continious phase
        
        Settling velocity = 2gr^2*(pi-p0)/9eta0
      - Aggregation/flocculation
        
        When particles clump together
        
        Steric hindrance
        
        But to high polymer conc = depletion
        
        To low polymer conc = flocculation
        
        Electric repulsion
      - Coalescence
        
        Physical barrier at interface
        
        Full surface covarage of surfactant
        
        Is the fusion of particles
      - Oiling off
    - - Lowering surface tension
      - Provide physical stabilisation
  - - - Dilute emulsion
        
        eta = eta0*(1+5/2phi)
        
        Phi is volume fraction
        
        For phi>0.64 random closed packing occurs
      - Concentrated emulsion
        
        Exhibit non-newtonian behaviour
        
        Viscosity depends on
        
        Viscosities
        
        droplet deformability
        
        Interactions droplets
        
        Droplet size
        
        Volume fraction
        
        Sedimentation plays a smaller role
      - Ranges from viscous liquid to elastic solid
    - - Mechanical energy
        
        Two overcome y*dA
      - Surfactants
      - Two or more immiscable liquids
    - - Extensional flow
        
        Lower weber number needed
        
        Elongation flow
      - Laminar emulsification
        
        Weber number must be higher than the critical weber number
        
        Weber number = external forces / interfacial forces = etaeR/2*y
        
        Critical weber number
        
        Dependent on viscosity ratio
        
        Shear stress must elongate particle before two smaller particles are formed. e = shear rate
  - - - Examples
        
        Insoluble phytosterols
        
        Low bioavailability
        
        Form needle like crystals
        
        Key is to disperse them into many droplets such that there are less nucleation points: undercooling
        
        Translucent emulsions
        
        Volume fraction
        
        Particle size
        
        Edible colloidal emulsions
        
        Some tast soapy in high conc
        
        Try modified starch, proteins as emulsifier
      - Benefits
        
        More stable against sedimentation, aggregation, etc
        
        Stable enough to dry and form powder
        
        More soluble, size control, morphology control
      - Downsides
        
        Expensive, novel technology
        
        More reactive
      - Are emulsions of nano size (100 nm)
    - - Colloidal emulsions
      - Liposomes
      - Micellar solutions
      - Smaller particles = more soluble and bioavailable, but more reactive. Larger particles = can cream more
    - - Neutraceuticals
      - Colarants
      - Microneutrients
      - Flavours
      - Macroneutrients
      - Functional ingredients in food + bevarages
    - - Chemical
        
        Oxidation/ colour change
        
        Reactions
      - Organoleptice
        
        Colour
        
        Transparancy loss if lamda - d. So lamba>>d
        
        Taste/flavour
      - Physical
        
        Aggregation/gellation/creaming/coalescence
        
        Solubility
    - - Texture and taste
      - Bioavailibility
      - Stability
      - Appearance
      - Safety
      - Sometimes, tradeoffs should be made
- - - - Interfaces
        
        Liquid-solid
        
        surface energy (ysl)
        
        Solid-air
        
        surface energy (ysa)
        
        Air(fluid)-liquid
        
        Surface tension (yal)
      - This three interfaces (+other forces) determine the shape of the drop --> free energy minimisation. dE=0
        
        Energy can be written as function radius cap, contact angle and surface tension/energies
    - - Dynamic contact angle
        
        Reversing fluid contact angle tr
        
        Advancing fluid contact angle ta
        
        During flow of liquid on solid, by pressure or gravity
        
        Reason why drops can stick to windows
        
        Contact angle left and right differ
        
        To compensate for gravity
        
        When drops get to large, maximum angles are reached.
        
        Force needed to make drop slide f = yla(cos(tr)-cos(ta))/2
        
        Contact angle hysterisis = ta-tr
        
        Origin
        
        During fluid receding or advancing, the fluid close to surface gets partially stuck by surface roughness. It stays stuck until the contact angle has decreased/increased such that they overcome the surface resistance.
      - Influencing the contact angle
        
        Wenzel method
        
        Increasing surface roughness to increase contact angle
        
        cos(tw) = Rw * cos(t)
        
        Rw = surface roughness = Atrue/Aapp
        
        Cassie baxter method
        
        Two different underlying substance = two contact angles
        
        Cos(tcb) = f1cos(t1) + f2cos(t2)
        
        If the other substance is air ysa = 0, ysl = yla
        
        Can be utilized for example for coatings
      - Equilibrium contact angle
        
        Young equation, cos(t) = (ysa-yls)/(yal)
        
        High yal results mostly in large contact angle
        
        Derive with force balance
    - - partial wetting
        
        0<t<90, hydrofilic surface
        
        90<t<180 hydrofobic surface
      - Non-wetting
        
        t = 180, superhydrofobic surface
      - full wetting t = 0
  - - - Molecular description
        
        The free energy of interfacial molucules is higher than that of the bulk molecules.
        
        Cohesive forces towarard the liquid bulk are not balanced at the interface, causing the molecules to attract inwards.
      - Having a large surface area costs lots of energy
      - Surface tension tries to minimize the interfactial area, y = J/m^2, N/m
    - - Energy
        
        y*A
        
        dE = yLdx
      - Pressure
        
        Laplace pressure, dP = 2y/R
        
        Pressure inside bubble increases for smaller bubbles due to surface tension
        
        Cappillary pressure, P = P0 +dP
      - Force
        
        Rolling bar
        
        F = y*L
    - - Wilhelm plate method
        
        Force on a vertically immersed plate
        
        y = F/((cos(t)*L) with cos(t)=1
      - Pendant drop method
        
        Drop of heavier density is dropped in lighter liquid with, Shape is determined by weight, shape and surface tension forces.
        
        Via the bond number, the surface tension can be determined
- - - - Hydrofobic tails
        
        Length determines hydrofobicity
      - Polar head group
        
        anionic
        
        cationic
        
        nonionic
        
        less affected by ph
    - - Bulk (M/m^3)
      - Surface (M/m^2)
    - - Equilibrium contact angle controls depth of immersion
      - Practically stuck at inteface because of energy min
      - Can thus be used to form structures
  - - - Gibbs absorption isotherm
        
        dy = -cs*dmu
        
        Relates change is surface tension to change in surface concentration and change in chemical potential of bulk chemical surfactant.
        
        cs = -(1/RT)*dy/dlnc = max conc surface
    - - At the critical micelle concentration it becomes more favourable to form micelles than adsorb at surface --> increase in bulk conc does not result anymore in reduction of surface tension.
  - - - ideal gas like equation that can be extended by finite volume and interactions (VDW)
      - May not be used in real life application
    - - pi = surface pressure of surfactant
      - Pi is in opposite direction of surface tension
- - - - Spontaneous and undesired formation of a coherent mass form individual powders
      - Contributing factors
        
        Moisture
        
        High RH will for example partly soluble NaCl --> formation of larger crystals
        
        Phase change/crystallisation
        
        Pressure
        
        Any proces that stimulates attractions
        
        Temperature
        
        Higher T --> rubbery regime
      - Measurement
        
        Uniaxial compression
        
        Breukline goes always diagonal troughout the clump
      - Use anti caking agents to avoid this
    - - Causes
        
        Movement
        
        Is also the most common reason for seggregation of particles
        
        So avoid motion after mixing
        
        Is needed to mix particles
        
        Different particle size
        
        Larger particles will move on top
        
        Brazilian nut experiment
        
        Because smaller particles fill the gap below
        
        Metal ball comes on top after tapping the bottem
        
        Smaller angle of repose
        
        Rotating drum example
        
        Have other angle of repose
        
        Forces acting on particles differ for its size
        
        Others
        
        Fines fluidisation
        
        Air current
        
        Sifting
        
        Chute directory
      - There is a formula to determine the amount of unmixing
    - - Angle of repose
        
        Static
        
        Smaller angle: more flowable
        
        Higher angle: concave structur: less flowable
        
        Adding water will highly increase AoR for small particles
        
        A tap will decrease the angle
        
        Dynamic
        
        Angle of repose also visible in rotating drum
        
        A measure on flowability of particles
        
        Measured after the weight of the particles collapsed on itself
      - Determined by interparticular interactions
        
        Is for example altered when aerated, less locking
        
        Mechanical locking, cohesive forces
      - Powder flow from silos
        
        Core flow
        
        The last filled powder will flow first
        
        Unwanted
        
        Mass flow
        
        The first filled powder comes out first
        
        Depends on silo shape and type of particles
  - - - Use size/shape/density distribution functions
        
        Gives difficulties in describing behaviour of particles
      - Particles are most of the time not round
        
        Use equivalent diameter to model as round spheres
        
        Stokes or Aerodynamic equivalent
    - - Different type of interactions dominate for each particle size
        
        Large particles
        
        Inertia
        
        Gravity
        
        Small particles <1micm
        
        Diffussion
        
        Electrostatic
      - Particles of different sizes behave differently
    - - Vts = pd^2gCc/18eta
      - Smaller particles move relatively faster because of the Cc term --> when they are smaller they find the gaps between molecules
- - - - Transmission electron microscope
        
        Much greater resolution in 2D
      - Scanning electron microscope
        
        Scanning enables for 3d images to determine shape
      - Optical microscope
        
        Functions up to the diffraction limit
        
        Great for particles down to 1 micrometer
      - All instruments are complementary
    - - Size
        
        Particles sizes usually vary in a dispersion and follow a normal distribution.
        
        With PD = 100*(sigma/x) can the particles distrubution be calculated. PD low = monodispersed, PD high polydispersed
        
        What is a large Polydispersity depends on the usage: crystal formation + good stacking (low PD), industry (60% is oké)
        
        Particles size partyly determines properties
      - Shape
  - - - Charged surfaces
        
        Repulsive coulomb forces (dGrep)
        
        Repulsion also depends on ion conc/ debye length
        
        Ionisation of surface groups
      - Steric hindrance
        
        Will result in steric hindrance between particles
        
        Must be a dense polymer brush to function
        
        Polymers grafted on particles
    - - Adding depletants
        
        Adsorbing polymers
        
        Polymers will bridge particles and result in flocculation
        
        Non-adsorbing polymers
        
        Polymers will collide with particles
        
        If the distance between particles < 2 Rg there will be a nett osmotic force that pushes the particles together
        
        Depletant interaction, depends on size/shape particle, size depletant, temperature. W = -dVP= -dVnKbT
        
        dv = overlap volume, dot line = exclusion zone
        
        Depletent interaction can also be combined with steric hindrance, such that the particles stay at a certain distance from eachother.
        
        Used for
        
        Shape and size selection
        
        Directing colloid assembly, with tuning Rg or lock-key
        
        To obtain colloidal crystals from disperse solutions
      - Adding addtional ions
        
        Will shield charge of particles
    - - Van der waals force (dGatt)
      - Also depends on shape particles
  - - - Non-spherical colloids (inorganic, designer)
      - Isotropic
      - Spherical colloids (emulsions)
      - Anisotropic
        
        Properties of colloid differ troughout the colloid
        
        Dipole
        
        Rod-like shape
        
        Density
    - - Foam
      - Aerosol
      - Mayonaise
      - Milk
      - Paint
    - - Solute is dispersed (aggregate)
    - - Solute is dissolved