Powder Flashcards
(37 cards)
Solids
- Mobility
- Degree of order
Mobility:
Immobile
Degree of order
Anisotropic
Has periodicity & orientation
Liquids
- Mobility
- Degree of order
Mobility:
Mobile 3D, rotate 3 axes
Move about randomly
Degree of order
Isotropic
No periodicity & orientation
Mesophase
State of matter intermediate between solid & liquid
Smectic, nemactic
Smectic phase
- Mobility
- Degree of order
Mobility:
Mobile 2D, rotate 1 axis
Degree of order:
Anisotropic
Has orientation, arranged in equispaced planes
No periodicity within planes
Nematic phase
- Mobility
- Degree of order
Mobility:
Mobile 3D, rotate 1 axis
Degree of order
Anisotropic
Has orientation
No periodicity
Properties of mesophase molecules
1) Organic
2) Elongated/Rectilinear
3) Rigid
4) Possess strong dipole or easily polarizable groups
- Gives certain orientation
Mesophase molecules are classified as
1) Thermotropic (solvent-free)
- Transition by temperature change
2) Lyotropic (with solvent)
- Responsive to solvent
Applications of mesophase molecules
1) Temperature sensor (thermotropic)
2) Display - Liquid crystals provide colours
3) Stabilize emulsions by increasing viscosity
4) Improve solubilization of drugs
5) Pharmaceutics –> can make rigid gels/emulsions
Characteristics of solids
1) Solid molecules are closely packed & immobile
2) Least amount of kinetic energy (stable)
3) Structural rigidity, resists deformative forces
- Short intermolecular distance
- Dense & fixed
Physical properties of solids
1) Physical form
- Size, shape, flow
2) Density
3) Melting point
4) Porosity
5) Heat capacity
6) Hardness
7) Deformability
8) Optical properties
9) Wettability
10) Moisture interaction
11) Solubility
Calculated paths of molecules - Solids
Definitive mass, volume, shape
Molecules relatively immobile
- May oscillate in fixed position
Mechanically strong, incompressible
Calculated paths of molecules
No set shape Flow with relative ease Molecules move freely, unrestricted - Via Brownian motion - Speed of molecules can be calculated / mapped out
Types of solid oral dosage forms
Microparticulates
1) Powders
- Crystals, nanoparticles, microcapsules, microspheres
2) Pellets/Spheroids/Beads
3) Granules/Agglomerates
Final dosage forms:
1) Tablets/Caplets
2) Capsules
3) Others e.g. films, gums
Advantages of solid dosage forms
1) Markedly better chemical stability
- Longer shelf-life
2) Lower bulk volume
3) Ease of handling, convenient
4) Does not promote microbial growth (when dry)
5) Flexible
- Allows single or multiple chemical components
Structure of solids
Crystalline or amorphous
Crystal form
Atoms / Ions / Molecules arranged in symmetrical and repeating patterns in 3D
Unit cell: Basic repeating pattern in crystal
What is polymorphism
Ability of a solid to exist as more than one form/crystal structure
Solids form different polymorphs when
They are under specific thermodynamic conditions –> so as to minimize crystal lattice energy
E.g. Different polymorphs formed at different temperatures
Characteristics of polymorphs
1) Chemically similar
2) Different physical properties
- E.g. Solubility, dissolution, bioavailability, morphology thermal
3) Different stability
Application in pharmaceutics
Different polymorphs have different physical properties –> affect therapeutic effect
- E.g. Often prepared as more soluble metastable form –> if change to more stable form –> decrease solubility –> affect bioavailability
Manufacturers must ensure that polymorphic form does not change throughout product life
- E.g. Temperature control throughout supply chain
Carbon polymorphs
1) Diamond
- Tetrahedral structure
- Each C atom is surrounded by 4 other covalently-bound equidisant neighbouring C atoms
- Formed under high temperature & pressure
- Cannot conduct electricity
2) Graphite
- Most stable polymorph
- Hexagonally arranged crystalline form
- Arranged in layers (graphene) that are not covalently bound
- Allows slippage between layers
- Conducts electricity
Crystalline VS Amorphous form
1) Arrangement of constituents
2) Degree of order
3) Melting point
4) Heat of fusion
5) Stability
6) Solubility
Crystalline:
1) Orderly arrangement of constituents; Defined structure
2) Anisotropic; Sharp X-ray diffraction patterns
3) Sharp melting point
4) Defined heat of fusion
5) More chemically stable
- Only surface molecules available for attack
6) Lower solubility
- Less surface area available for dissolution
Amorphous:
1) No arrangement; Irregular, undefined structure
2) Isotropic; No well-resolved X-ray pattern
3) Melts over a range
4) No definite heat of fusion
5) More liable for degradation
6) Markedly more soluble
Preparation methods of amorphous solids
1) Milling (common)
- E.g. Vibratory ball mill
- Difficult to scale up –> limited to small scale operations
- Requires large temperature change (a lot of energy needed)
2) Precipitation
3) Compaction
4) Dehydration
5) Spray drying (common)
6) Supercooling
7) Vapor condensation
8) Freeze-drying (common)
Nanocrystalline
Structure:
Polycrystalline material, with a crystallite size of only a few nanometers
I.e. Amorphous with small area of crystalline structure
Properties:
Good solubility due to amorphous structure
Increased stability due to nanocrystalline spots
