dispersion colloids ii.kolloid.unideb.hu/en/files/2010/11/9-lyophobic_colloids...2010/11/09 ·...
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Dispersion colloidsII.
Levente NovákIstván BányaiZoltán Nagy
Department of Physical Chemistry
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Dispersions (lyophobic sols)
● Dispersions are colloidal size particles (dispersed phase) dispersed in a continuous phase (dispersion medium)
● Lyophobic colloids consist of bubbles, droplets or parti-cles partially weted or unweted by the dispersion medium → weak adhesive forces, interparticle cohesive forces predominate
● Lyophobic sols are named afer the dispersion medium
– Gas phase → Aerosols (L/G and S/G systems)– Liquid phase → Lyosols (L/G, L/L, S/L systems)– Solid phase → Xerosols (G/S, G/L, S/S systems)
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Does not exist Gas lyosol (G/L)
● Foam● Sparkling liquid
Gas xerosol (G/S)
● Solid foam● Xerogel● Aerogel
Liquid aerosol (L/G)
● Mist● Fog
● Spray
Liquid-liquid lyosol (L/L)
● Emulsion
Liquid xerosol (L/S)
● Lyogel (or gel)● Solid emulsion
Aerosol (S/G)
● Smoke
Solid lyosol (S/L)
● Colloidal suspension or sol
Solid xerosol (S/S)
● Solid smoke● Solid dispersion
CONTINUOUS PHASED
ISPE
RSE
D P
HA
SE
GA
SLI
QU
IDSO
LID
GAS(AEROSOL)
LIQUID(LYOSOL)
SOLID(XEROSOL)
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Types of colloidson the basis of structure (appearance)
Porodin
colloids
Incoherent (fluid-like) Coherent (solid-like) = gel
ColloidalDispersions (sols)
Macromolecular solutions
Association Colloids
Colloidal solutions
(porous)Reticular Spongoid
corpuscular fibrillar lamellardispersion macromolecular association lyophobic lyophilic lyophilic
Forms from the following particle types:
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categorized by inner / outer phases
Types of sols (incoherent)
aerosols lyosols xerosols
● L/G liquid in air: fog, mists, spray
● S/G solid aerosol, solid in gas: smoke, colloidal powder
● Complex, smog
● G/L gas phase in liquid (sparkling water, foam, whipped cream)
● L/L emulsion, liquid in liquid, milk
● S/L colloid suspension (gold sol, toothpaste, paint, ink)
● G/S solid foams (polystyrene foam)
● L/S solid emulsion (opals, pearls)
● S/S solid suspensions (pigmented plastics)
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• Sol stability: property of a lyophobic sol to remain unaggregated → only kinetic stability is possible (see DLVO theory & steric stabilization), lyophobic sols are thermodynamically unstable
• Sol: incoherent, dispersion colloidal system
• Xerosol: solidified sol, does not aggregate (the solid matrix makes this impossible), no skeleton structure between dispersed particles/droplets/bubbles → not a gel!
• Gel: coherent colloidal system, has a skeleton (scafold) structure.
• Cream: concentrated emulsion (L/L), o/w type.
• Grease: high viscosity gel, with shear-thinning properties (transition from gel to sol state).
Definitions
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It is important to make sols with well controlled particle size and size distribution for most uses.
● Top down technique (dispersion) → it is almost impossible to achieve this.
● Botom up technique → precipitation resulting from a chemical reaction ofen works
– AgX sol (X=halogen)
AgNO3+ KX → KNO3 + AgX
– Gold sol
2 AuCl4- + 3 C6H5O7
3- → 3 C5H4O52- + 3 CO2 + 8 Cl- + 3 H+ + 2 Au
– Sulfur sol
Na2S2O3 + 2 HCl → 2 NaCl + SO2 + H2O + S
– Iron(III) hydroxide sol
FeCl3 + 3 H2O → + 3 HCl + Fe(OH)3
Preparation of monodisperse sols
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● Depending on the reducing agent, its concentration, the pH and the temperature used, almost monodisperse gold sols can be prepared:
– With citrate: diameter of 15 to >50 nm.
– With citrate + tannic acid: 5 to 20 nm.
– With borohydride: 1 to 10 nm.
● These methods act by modifying the nucleationand growth rates.
● Monodisperse gold colloids have a specific visual absorption spectrum (=color).
● These nanoparticles are stabilized by the adsorbed charges (e.g. citrate) or a layer of stabilizer (e.g. tannic acid).
● By adsorption of a sulfur-containing stabilizer monolayer, the gold nanoparticles can even be dried and redispersed.
Gold nanoparticles
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Example: ceria (Ce2O3) nanoparticles
LaMer diagram: nucleation, precipitation
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Yugang Sun, Chem. Soc. Rev. 42: 2497—2511 (2013)
LaMer diagram: nucleation, precipitation
minimal nucleationsupersaturation
saturation
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Ageing and Ostwald ripening (slow change until equilibrium)
Lyophobic colloid systems are thermodynamically unstable → ageing (spontaneous slow, irreversible change) → coarsening (particle growth)
ln(pr
p)=
2 γV M
R T rln(
Lr
L)=
2 γV M
R T r
Kelvin equation Ostwald equation
pr : vapor pressure over surface of radius r (Pa) Lr : pr, cr, or μr in the droplet of radius rp : saturation vapor pressure in gas phase (Pa) L : p, c, or μ in the mediumγ : surface tension (N/m)r : radius of curvature (m)V : molar volume (m3/mol)
Post-preparation phenomena
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Coherent systems (gels)
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• Definition– Coherent colloid system is a system in which one of the
components forms a skeleton (network made with primary or secondary bonds) and contains a fluid (=gas or liquid) dispersion medium
– State of transition between liquids (→ similar vapor pressure, conductivity) and solids (→ defined shape)
• Types– Porodin gels: consist of a skeleton of particles– Reticular gels: skeleton of fibers, coarse fibers, bunch of
fibers – Spongoid gels: skeleton of lamellae or films
Coherent systems
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Definition by IUPAC (reading)Gel: Nonfluid colloidal network or polymer network that is expanded throughout its wholevolume by a fluid.[3]
Note 1: A gel has a finite, usually rather small, yield stress.Note 2: A gel can contain:(i) a covalent polymer network, e.g., a network formed by crosslinking polymer chains or by nonlinear polymerization;(ii) a polymer network formed through the physical aggregation of polymer chains, caused by hydrogen bonds, crystallization, helix formation, complexation, etc., that results in regions of local order acting as the network junction points. The resulting swollen network may be termed a “thermoreversible gel” if the regions of local order are thermally reversible;(iii) a polymer network formed through glassy junction points, e.g., one based on block copolymers. If the junction points are thermally reversible glassy domains, the resulting swollen network may also be termed a thermoreversible gel;(iv) lamellar structures including mesophases, e.g., soap gels, phospholipids, and clays;(v) particulate disordered structures, e.g., a flocculent precipitate usually consisting of particles with large geometrical anisotropy, such as in V2O5 gels and globular or fibrillar protein gels. (above) rather than of the structural characteristics that describe a gel.Hydrogel: Gel in which the swelling agent is water.Note 1: The network component of a hydrogel is usually a polymer network.Note 2: A hydrogel in which the network component is a colloidal network may be referredto as an aquagel.
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a) reversible polymer fibrillar gelb) reversible porodin gelc) irreversible polymer fibrillar geld) irreversible solid-gas porodin xerogel
Typical gels
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Cohesive interactions in gelsa) Ionic, b) hydrophobic, c) H-bridge, d) van der Waals, e) hairy micelles, f-g) coordination bond
pregel
gelapolarsolvent
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Silica gel (SiO2 · n H2O)
Silica gel: a porodin system
Hydrated silica (hydrogel)
Silica particles
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During formation, the size of silica gel particles is determined by the pH of the reaction medium.
In acidic medium: The hydrolysis is fasterThe condensation is slow → small particles form.
In alkaline medium: Bigger particles, loose structure
TEM pictures
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Example: (Na,Ca)0.33(Al,Mg)2Si4O10(OH)2·(H2O)n (montmorillonite)
Drilling mud:
1. Viscosity is high: takes up solids and keeps them in suspension
2. Cools and lubricates the borehead3. Increases pressure to keep away
liquids (density)4. Cover the pores of the borehole wall5. Keeps the stability of the wall
Takes 4-5 times its weight of water Composition: water + clay + baryte (for its weight) + xanthan or carboxymethyl cellulose (for their viscosity increasing efect)
Clays
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Sol-gel technology
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Aerogel („frozen smoke”)
Aerogels are the lightest solid materials. They are very good insulators. Silica based aerogel was the first to make, but today Al, Cr, Zn or carbon are also used for synthesizing aerogels.
htp://www.youtube.com/watch?cv=mAJWWyRIDDVQhtp://www.youtube.com/watch?cv=HoCAxS4vqwQ Structure of an aerogel
htp://stardust.jpl.nasa.gov/photo/aerogel.html
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htp://www.resonancepub.com/aerogel.htm
htp://en.wikipedia.org/wiki/Aerogel
Exchange the liquid to gas!
Si or Al are biocompatible
Preparation of silica aerogels
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Effect of the surface tension:● spreading of the liquid on the surface, filling the voids (→ possible collapse of the structure)● at evaporation: complete break-up of the gel structure when the liquid volume shrinks
Solution: gradual solvent change, then supercritical drying.There is no surface tension in a supercritical fluid, as there is no liquid/gas phase boundary. By changing the pressure and temperature of the fluid, the properties can be “tuned” to be more liquid- or more gas-like.
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aerogel
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Polymer gels (e.g. “intelligent” gels) → reversible transformations(as a function of T, pH, salt content, etc.)
Disposable diapers
Example:
drug delivery
gel
solvent
syneresis swelling
Lyogels (solvent in the skeleton)
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htp://www.gcsescience.com/o69.htm
Poly (sodium propenoate): poly acrylic acid.
The monomer:
Randomly coiled molecules, swelling in water
Examples of hydrogels: gelled foods, fruit jellies, etc.
Hydrogels
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By addition of salt water flows out.
Disposable diapers
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• Easier to handle• Storage• Destruction is easier
Solidification of liquid waste
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PDMS: poly(dimethyl-siloxane) elastomers
Magnetic nanoparticles
Intelligent gels
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Non-ionized in acidic medium: shrinks
Polyaspartic acid gel: artificial muscleD
egre
e of
exp
ansi
on
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N-isopropylacrylamide (NIPA) gel: transition at 34 oC
Temperature-sensitive gels (e.g. NIPA)
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32
PEM (proton exchange membrane)
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Low temperature synthesis of oxide layers with ordered structure and thickness on nanometer scale
Sodium borosilicate layer on glass at near room temperature
Xerogel coating
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htp://www.prinzoptics.de/en/home/index.php
htp://www.variotrans-glas.de/htdocs_en/home/index.html
● Light interference (e.g. anti-reflection coatings for the areas of UV, VIS and NIR).
● Applications: From architectural application to UV protection
● 1992, Prinz Optics (Sol-Gel Dip Coating Process).
Xerogel coating: applications,modern artificial opal
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htp://www.molecularexpressions.com/primer/lightandcolor/interferenceintro.html