Final Exam Flashcards
What are then most common shapes for micelles to take?
Spherical
Worm Like
Vesicles
Planar Bilayers
Inverted
What is the key packing parameter value for spherical micelles?
<1/3
What is the key packing parameter value for worm like micelles?
1/3-1/2
What is the key packing parameter value for vesicle micelles?
1/2-1
What is the key packing parameter value for planar micelles?
1
What is the key packing parameter value for inverted micelles?
> 1
Which type of micelle head group is more bulky?
Ionic
What is the cloud point?
The temperature at which an oily mixture beings to separate when chilled
What is the Krafft temperature?
The temperature at which the CMC and solubility of a surfactant are the same
What are the 3 extremes of polymer configuration in a solvent?
Rod, Random coil and Spherical Globule
What are the mechanisms of steric repulsion?
Osmotic Pressure and Elastic recoil
What is the mechanism of depletion flocculation? Can it be reversed?
Osmotic Pressure, yes
What are the mechanisms of bridging flocculation?
Favourable particle polymer binding interactions, low surface concentration of polymer, high polymer MW
What polymer attributes are required for steric stabilisation?
Sufficiently thick coating
MW approx. 3000 Da
Bulk concentration to ensure high surface concentration
What polymer attributes are required for depletion flocculation?
Non adsorbent polymer
What are the 4 modes of emulsion failure?
Creaming/Sedimentation
Phase inversion
Coalescence
Ostwald ripening
What is the mechanism of creaming/sedimentation?
Gravity driven separation depending on buoyancy
What is the mechanism of phase inversion?
Inversion of continuous and dispersed phase in near 50/50 emulsion when exposed to heat or mechanical shock
Ostwald ripening mechanism
In a polydisperse emulsion the higher Laplace pressure in small droplets drives molecules into solution, which then precipitate into larger drops
What is the mechanism of coalescence?
Surface forces fail to keep droplets apart. Upon collision drops combine
Provide a list of typical rheological features?
Yield stress
First Newtonian Plateau
Transition
Second Newtonian Plateau
Recovery rate
What are the basic drug release kinetics?
first order
t^1/2
zero order
What structures can give zero order kinetics?
Saturated solution with solid crystals inside permeable membrane capsule
Open hole in hemisphere
Initial concentration profile
Provide the meaning of G’ and G’’
G’=Elastic (storage) modulus
G’‘=Viscous (loss) modulus
Give the quantity and formula for the measure of material damping in yield stress materials
tan(delta)=G’‘/G’
What are the two main types of hydrogels and value of the defining quantity?
Honey like, tan(delta)>1
Jelly like, tan(delta)<1
Accelerating voltage range for TEM?
80-300 kV
What are BSE and what information do they provide in SEM?
Electrons that penetrate deeper into the surface before reflecting. The give information on composition or crystallography
What is spot size/probe current in SEM?
The allowed spread of electrons hitting the sample
What are some issues with excessively small spot size in SEM?
Reduced beam current results in less electrons being scattered, and the signal to noise ratio becomes too low
What is the benefit of increased working distance in SEM?
Improved depth of field
What are the requirements for a sample to be analysed using TEM?
-Very clean sample
-Very thin sample
-Inert
-Dry
What are the requirements for a sample to be analysed using SEM?
-Conductive sample
-Dry Sample
-Fully adhered to stub
What causes astigmatism in TEM?
-Non uniform magnetic field
-Off centre aperture
What is the effect of astigmatism on TEM images?
Image distortion
Why is a TEM beam diverged?
-Increase resolution without decreasing sampled area
-Avoid film damage
What is the wobbler used for in TEM?
The wobbler is a focus assist that allows easy positioning of the sample in the eucentric position
What causes gelling at low salt concentration in dispersed systems?
Repulsive forces between particles keeping them ordered near the average particle spacing
What key property can reduce viscosity at a constant volume fraction in a dispersed suspension?
Polydispersity
What is the stokes shift?
Fluorescence occurs at lower energies than incident radiation
What is the Raman shift?
A shift in the wavelength of emitted light from excited samples due to excitation of short lived virtual states
What is required for a molecule to be Raman active?
Symmetrical molecules with a vibration resulting in a change in polarizability.
What is required for a molecule to be IR spectroscopy active?
Asymmetrical molecules with a vibration resulting in a change in dipole moment
What is the mutual exclusion rule?
Molecules with a centre of symmetry have no
coincident IR and Raman bands
How should fluorescent samples be prepared for Raman spectroscopy?
Photobleaching
What are the advantages of confocal microscopy?
Reduced Blur
Can examine internal structures
Allows for imaging of optical sections via alteration of focal plain
What are the key components of a confocal microscope?
Pinhole
Dichroic mirror
Objective
Laser
What is the operating principle of confocal microscopy?
The pinhole and focal point of the objective form a conjugate pair of points, and any light originating from other points will be excluded by the pinhole
What are the key components of an AFM?
-Cantilever
-Tip
-Feedback Loop
-Piezoelectric scanner
-Laser
-Photodiode
What AFM mode should be used to study hard samples?
Contact mode
What AFM mode should be used to study soft samples?
Tapping mode
What AFM mode should be used to study material phase?
Tapping mode
What is the key property to control in tapping mode AFM measurements?
Cantilever spring constant
Which type of surfactant has a lower CMC? Why?
Non ionic surfactants, decreased head group repulsion favours micelle formation
What is the ideal range of absorbance in UV-vis spectroscopy and why?
0.4<A<0.9. minimise relative error
What properties can be used to increase the viscosity of a coagulated suspension?
Polydispersity
Decrease particle size
What property can be used to increase the yield stress of a coagulated suspension?
Decrease particle size
What is the working principle of DLS?
Rate of chance of noise in scattered light can be used to measure Brownian velocity
What are some advantages of DLS?
Fast
Non invasive
Requires a small amount of sample
What are some disadvantages of DLS?
Mean particle size is volume weighted
measures hydrodynamic diameter
does not provide information on particle shape
What is the appropriate size range for DLS?
1nm - 1 micron
What is the appropriate size range for Laser diffraction?
1 micron to mm
What are some advantages of laser diffaction?
Well established with regulatory approval
High throughput
What is the formula for D.O.F in a molecule
Linear: 3n-5
Non-liner: 3n-6
What key factors must be accounted for when calculating collisions per second?
Both particles are moving
distance travelled is 2r less than centre to centre distance
Give some methods of particle formation and size cuts
Grinding (1 micron-1mm)
Precipitation (10s of nanometres)
Atomisation/Spray Drying (10-200 micron)
Sol Gel
If sodium chloride is added to sodium dodecyl sulphate (SDS) what
happens to the CMC of the solution?
The sodium ions bind to the anionic surfactant headgroup and decrease the head
group interactions (spacing) decreasing the CMC. In other words, adding a salt decreases
the CMC by decreasing repulsions between the charged heads of the surfactant molecule
What value does the length scale of depletion flocculation vary with?
Polymer Rg
What parameter does the force magnitude of depletion flocculation vary with?
Polymer concentration
What change in CMC is expected for a longer hydrophobic group?
Decreased CMC. Increased hydrophobic interactions favours micelle formation
What is the relationship between particle size and scattering angle?
Larger particle size reduces scattering angle
What is the baseline in fluorescence techniques?
The emission of light from the sample without incident light
What does the signal refer to in analytical techniques?
The radiation of interest, noise is not included
What formulation change can reduce Ostwald ripening?
Addition of a small amount of insoluble oil
What is the most significant effect of increased particle diameter at constant weight fraction?
Increased particle spacing/reduced number concentration
What measurement can be used to measure the strength of intermolecular forces? What is the direction of the correlation?
Refractive index, increased refractive index->increased intermolecular forces
What is the formula for CPP?
Vhc/ae.Lc
What forces are competing in rayleigh-taylor breakup?
Shear force and surface tension
What size distribution is produced via homogeniser emulsion formation?
Polydisperse
Why does reduced particle size increase shear thinning behaviour in dispersed suspensions?
At a smaller particle size the distance between particles is smaller, and hence double layer effects are more pronounced.
