powders -lecture Flashcards
gas state
- vancancies
- motion
characteristic properties
gas molecules move among vacancies
- vigorous, chaotic, rapid motion and collide
diffusion and partial pressure are the characterisitc traits
liquid
- vancancy
- motion
- characterisitc properties
- vacancies move among molecules ( vacancies move around )
mobile molecules without orientation nor periodicity
- isotropic ( randomly distributed )
diffusion, surface tension and rheology
solid
movement
characteristic properties
well organised and immobile
molecules have orientation and periodicity ( repeating )
chracteristic properties - melting point and diffraction
describe the 2 mesophases between solid and liquid
and draw
- smectic - soap-like/grease-like
mobile 2d , rotate in 1 axis
orientated & arranged in equispaced planes
no periodicity within the planes
2.nematic - thread-like
mobile 3d, rotate 1 axis
orientated with no periodicity
move up and down and somewhat organised
what are the properties of mesophases
organic
elongated or rectilinear
rigid
strong dipoles and easily polarisable groups
2 grps of mesophases depending on the solvent
- thermotropic ( solvent-free) - temp sensi
2. lyotropic ( with solvent ) - solvent sensitive
what are the uses of mesophases
- temp sensor
- display - liquid crystals provide colours
- stabilisation fo emulsions by inc viscosity
- improve solubilisation of drugs
how does mesophase improve stabilisation of emulsion
inc viscosity
bc there is some crystal order which can help to trap molecules and stabilise it
characteristics of solids
- least amt of kinetic energy
- structurally rigid to resist deformative forces,
bc short int distance, dense and fixed - organised as crystalline or amorphous solids
main physical properties of solids
physical form eg size, shape, flow density mp heat capacity porosity hardness deformability optical properties wettability moisture interaction solubility
liquids vs solids
- shape
- movement
- traits
liquid
- no set shape , takes shape of container
- flow w relative ease
- move freely unrestricted
for solids
- definite mass, volume and shape
- molecules relatively immobile and they oscillate about their mean positions
- mechanically strong and incompressible
oral solid dosage forms
- multiparticulate forms
powders - crystals, nanoparticles, microcapsules, microspheres
granules/agglomerates
pellets spheroids, beads
adv of solid dosage form
- better chem stability shelf life 2-3 yrs
- dry - dosent promote microbial growth
- lower bulk volume
- ease of handling, convenience
- flexible, single or multiple components
what is a
crystal form
- ordered structure w arranged atoms, ions or molecules forming symmetrical and repeating patterns in 3d
basic repeating pattern of a crystal form is called
” unit cell “ of the structure
what is polymorphism
and why is it formed
ability of the solid to exist in more than one form of crystal structure - differences in crystal packing
- different polymorphs are formed to minimise crystal lattice energy under specific thermodynamic conditions
what varies between polymorphs and so what
chemically they r similar but physical properties vary
like solubility , dissolution , bioavailability , morphology , thermal etc
which is a pharmaceutical concern bc it could be unstable
eg of 2 polymorphic forms and their examples
diamond - tetrahedral
atom w 4 covalent equal distanced atoms around
formed under high pressure and temp
graphite - hexagonal arrangement crystalline form of carbon atoms most stable form layers without covalnet bonds between layers can slide
diff between crystalline and amorphous
crystalline
- orderly arrangement
- defined structure
- anisotropic , sharp x ray diffraction patterns
- sharp mp
- definite heat of fusion
- more chemically stable
amorphous
- no arrangmenet
- irregular shape
- isotropic , no well-reoslved x-ray pattern
- mp range
- no definite heat of fusion
- more liable to degradation, less chem stable
between crystalline and amorphous which is more soluble
amorphous is more
crystalline’s limiting factor is solubility , so make it more amorphous to inc solubility
difference between amorphous and nanocrystalline
amorphous is jsut completley disorganised
nanocrystalline is polycrystalline with a crystalline ( rganised ) site of only a new nanometers,
( areas of crystallinity and areas of non isotropic )
also has good solubility
main methods for determining crystallinity / polymorphism
( main ) xray diffractometry melt behaviour -visual - hot stage microscopy - differential scanning calorimetry raman spectrometry
others
- infrared spectroscopy
nuclear magnetic reasonance spectroscopy
what is x ray diffraction for and how does it work
values needed
to determine crystallinity/ polymorphism
for determining solubiloty and thus bioavailability
- planes of atoms in molecules give reflecting layers for
x-rays - capture the outgoing beam and plot - bragg condition / braggs condition , if meets the condition then defraction occurs and outgoing beam can be plotted
visible light - 400-800nm
x-ray: 0.01-10nm
( for crystallography : powder diffraction =0.1nm)
intra-atomic spacing between planes in crystals,
typically a few angstroms’ range 1-100 angstroms 0.1-10nm
from 0-30 mins goes from crystalline to amorphous state
and once broken down , the peaks are no longer like before , orderliness of the material is destroyed
3 results of x ray diffraction
- used to check the crystal form
(a) anhydrous carbamazepine ( beta form ) vv sharp and narrow
(b) anhydrous carbamazepine ( alpha form ) 2 middle same 1 long
(c) carbamazepine dihydrate 1 v long middle
