Colloids and Gels

?
  • Created by: LBCW0502
  • Created on: 19-01-18 09:50
What is a colloid?
A two phase system of matter (intermediate between homogeneous and heterogenous mixtures (>1 micron)
1 of 61
What is the main difference between a colloid and a suspension?
The size
2 of 61
Describe what happens in a phase colloid
Small droplets in the dispersed phase are dispersed in continuous solution
3 of 61
Describe what happens in a molecular colloid
Macromolecules are dispersed in continuous phase (dispersion medium)
4 of 61
Give examples of systems which are not colloids
100 micron suspension, suspension MDI, emulsion, milk, HA gel
5 of 61
Give an example of a colloid system
Insulin solution (proteins/large particles dispersed in solution)
6 of 61
Can a colloid be seen with the naked eye?
No
7 of 61
Describe how a colloid can be viewed
A laser beam is used to produce high resolution images (colloid powered by passive diffusion/behave independently)
8 of 61
In a suspension, are large particles powered by passive diffusion?
No, they are powered by gravity
9 of 61
What are the properties of colloids?
Tyndall effect, brownian movements, adsorption, dialysis, electrophoresis and thixotropy
10 of 61
Describe the Tyndall effect
A light beam is passed through the colloid, causing light scattering. A solution cannot scatter light (only colloids)
11 of 61
What is the Brownian movement?
Random movement of particles in fluid due to continuous collisions from molecules in surrounding solution
12 of 61
Describe the process of adsorption
Chemical associated to surface of second agent. Reversible/conformational change/able to manipulate physicochemical properties. Colloids have a strong capacity to adsorb at the interphase
13 of 61
Describe the process of dialysis
Process when colloids are separated and purified. Drives a concentration gradient (applies to colloids, not solutions)
14 of 61
Describe the process of electrophoresis
Charged molecules migrate across depending on size. Surface dependent and involves light scattering
15 of 61
What is thixotropy?
Colloids and gels exhibit a stable form at rest, become fluid when agitated (formation of large chains)
16 of 61
What are the four main types of colloids?
Sols (solid in liquid), emulsions (liquid in liquid), foams (gas in liquid) and aerosols (in gas)
17 of 61
Give examples of a liquid aerosol
Fogs, mist (liquid in dispersed phase and gas in dispersed medium)
18 of 61
Give an example of solid aerosol
Smoke (solid in dispersed phase and gas in dispersed medium)
19 of 61
Give an example of a foam
Soap foam (gas in dispersed phase and liquid in dispersed medium)
20 of 61
Give examples of emulsions
Milk, mayonnaise (liquid in dispersed phase and liquid in dispersed medium)
21 of 61
Give examples of sol, suspension
AgI sol, toothpaste (solid in dispersed phase and liquid in dispersed medium)
22 of 61
Give an example of a solid foam
Expanded polystyrene (gas in dispersed phase and solid in dispersed medium)
23 of 61
Give examples of solid emulsions
Opal, pearls (liquid in dispersed phase and solid in dispersed medium)
24 of 61
Give an example of solid suspension
Pigmented plastics (solid in dispersed phase and solid in dispersed medium)
25 of 61
What are the four types of sols?
Lyophobic colloids (solvent-hating), lyophilic (solvent-loving), association and gels
26 of 61
Describe features of lyophobic colloids
Hydrophobic in aqueous media (e.g. inorganic particles in water: Au/Ag/S), thermodynamically unstable, insoluble/no interaction with dispersion media
27 of 61
What are the preparation techniques for lyophobic colloids
Dispersion, milling, ultrasonics, electric arc or condensation from solution e.g. sulphur or chemical reaction
28 of 61
Why is it important that formulations are homogeneous systems?
In order for the formulation to have a equal concentration throughout the formulation
29 of 61
Describe features of lyophilic colloids
Hydrophilic sols in aqueous media. Large organic molecules dispersed in aqueous media e.g. acacia, gelatin, albumin, polymers.
30 of 61
What are the preparation techniques for lyophilic colloids?
In aqueous media, molecules become hydrated by interacting with water. Rubber and polystyrene are solvated by non-aqueous organic solvents to form lyophilic sols
31 of 61
Describe features of association solloids (solvent loving)
Aggregates of molecules. Molecules in solution at low concentrations. Aggregates form micelles of colloid size at high concentrations. Lyophilic (e.g. soap/surfactants). Lyophilic head group/lyophilic tail (amphiphiles)
32 of 61
What are gels?
Viscous semi-solid. A type of sol. Solid particles form a 3D arrangement in liquid solvent, giving the solution a rigid/definite shape
33 of 61
What is an emulsion?
Mixture of two immiscible substances e.g. oil in water, water in oil (homogenity)
34 of 61
How are foams formed?
Trap gas particles in liquid or solid. Also produced as unwanted by-product in manufacture of various substances
35 of 61
What are aerosols?
Can be liquid or solid that will dry to form a solid. Provides propulsion. Gas can be liquid under pressure
36 of 61
Why do pharmacists need to understand the major principles of colloid science?
Formulation tool for drug delivery. Hydrophobic drugs in aqueous solvents. Cosmetically acceptable topicals. Aerosols for inhalation. Manufacture. Formulation must deliver a safe reproducible dose
37 of 61
What can go wrong with a formulation once manufactured?
Contamination (microbial), chemical instability (impurities/toxic adducts) and physical instability (poor dosing reproducibility)
38 of 61
Is a colloid always homogeneous?
Lyophobic systems have poor interaction with the solvent. Physical stability can be problematic. Control of reversible/irreversible aggregation. Sols - thermodynamically unstable 2 phase systems
39 of 61
What are the properties of colloids which influence physical stability?
Kinetic (Brownian motion, diffusion/Fick's first law, sedimentation/stoke's law, osmotic pressure, viscosity), electrical properties, size/shape
40 of 61
Describe features of electrical properties
Electrical double layer, particle surface charge, negative stern layer, negativity reduces with distance, shear plane is where the zeta potential is measured and provides an estimate of surface potential
41 of 61
What is polydiversity?
Mw/Mn
42 of 61
Describe features of shape as a property of colloids
Many types of colloids are spherical. Small deviations (ellipsoidal). Large deviations (clay suspension/plates, polymers in solution/coil)
43 of 61
Describe features of physical stability
Important to lyophobic colloid systems. Coagulation/flocculation, interactions
44 of 61
What is aggregation?
Particles in groups
45 of 61
What is coagulation?
Closely aggregated and difficult to disperse
46 of 61
What is flocculation?
Aggregates have an open structure with particles a small distance apart
47 of 61
Describe features of the DVLO theory
Assumes that the interactions involved are attractive (van der Waals) and repulsive (electrical). Vt = Va + Vr. Graph with primary maximum
48 of 61
Describe features of lyophilic colloids
Thermodynamically stable systems. Strong/extensive interactions between dispersed phase and dispersed medium. No physical instability. Hydrophilic sols in aqueous media. Large organic molecules in water e.g. polymers, albumin
49 of 61
Describe features of albumin in water
Nm size, invisible, charge stabilised, pH dependency, isoelectric point
50 of 61
Describe the preparation techniques for lyophilic colloids
In aqueous media, molecules become hydrated by interacting with water, rubber/polystyrene are solvated by non-aqueous organic solvents to form lyophilic sols. Pharmaceutical uses (suspending and emulsifying agents/binders)
51 of 61
Describe features of lyophobic colloids
Inorganic/insoluble particles, no/little interaction with dispersion medium, don't disperse spontaneously, no effect on viscosity, low concentration of electrolytes lead to stability (high conc./instability)
52 of 61
Describe features of lyophilic colloids
Organic molecules in colloidal range, solvated in medium, disperses spontaneously, increases viscosity to form gels at high concentrations, electrolytes salted out at high concentrations due to solvation
53 of 61
What is a gel?
A colloidal system which under a set of conditions of concentration and temperature, sets into a solid or semi-solid. Rigidity of a gel is due to the aggregation of the colloidal system
54 of 61
Describe features of gels
Can be formed with lyophobic or lyophilic sols, only small concentration of colloid required to form network, jelly formed if gel-rich, xerogel formed when water is removed from jelly
55 of 61
Describe features of lyophobic sols
Loosely aggregated flocculated systems, aluminium/magnesium hydroxide gels, bentonite, colloids are plates with + charge edge from inorganic and face - charge from hydrated crystal, forces
56 of 61
What is thixotropy?
Reversible aggregate system. Property of some non-newtonian pseudoplastic fluids to show a time-dependent change in viscosity; the longer the fluid undergoes shear, the lower its viscosity. Gel-sol-gel. Shear breaks weak bonds. Bentonite/calamine
57 of 61
What are type I lyophilic sols?
Irreversible systems with a 3D network formed from covalent bonds. Focal gel, implants, biocompatible, lower solvent intake, must be hydrolysed e.g. silicone hydrogels
58 of 61
What are type II lyophilic sols?
Heat reversible gels held under much weaker intermolecular bonds (e.g. H bonds). Reform on cooling. Gel point. Large fluid intake. E.g. cellulose gels
59 of 61
Can lyophilic sols be thixotropic?
Yes e.g. tomato ketchup
60 of 61
Give examples of pharmaceutical colloids
Diclofenac sodium, Amphotericin B, Human Recombinant DNase, Ciclosporine, Gold. Future - PEG, nanoparticles,
61 of 61

Other cards in this set

Card 2

Front

What is the main difference between a colloid and a suspension?

Back

The size

Card 3

Front

Describe what happens in a phase colloid

Back

Preview of the front of card 3

Card 4

Front

Describe what happens in a molecular colloid

Back

Preview of the front of card 4

Card 5

Front

Give examples of systems which are not colloids

Back

Preview of the front of card 5
View more cards

Comments

No comments have yet been made

Similar Pharmacy resources:

See all Pharmacy resources »See all Colloids and Gels resources »