Dispersion colloidsII.

Levente NovákIstván BányaiZoltán Nagy

Department of Physical Chemistry

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)

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)

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:

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)

• 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

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

● 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

Example: ceria (Ce2O3) nanoparticles

LaMer diagram: nucleation, precipitation

Yugang Sun, Chem. Soc. Rev. 42: 2497—2511 (2013)

LaMer diagram: nucleation, precipitation

minimal nucleationsupersaturation

saturation

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

Coherent systems (gels)

• 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

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.

a) reversible polymer fibrillar gelb) reversible porodin gelc) irreversible polymer fibrillar geld) irreversible solid-gas porodin xerogel

Typical gels

Cohesive interactions in gelsa) Ionic, b) hydrophobic, c) H-bridge, d) van der Waals, e) hairy micelles, f-g) coordination bond

pregel

gelapolarsolvent

Silica gel (SiO2 · n H2O)

Silica gel: a porodin system

Hydrated silica (hydrogel)

Silica particles

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

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

Sol-gel technology

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

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

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.

aerogel

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)

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

By addition of salt water flows out.

Disposable diapers

• Easier to handle• Storage• Destruction is easier

Solidification of liquid waste

PDMS: poly(dimethyl-siloxane) elastomers

Magnetic nanoparticles

Intelligent gels

Non-ionized in acidic medium: shrinks

Polyaspartic acid gel: artificial muscleD

egre

e of

exp

ansi

on

N-isopropylacrylamide (NIPA) gel: transition at 34 oC

Temperature-sensitive gels (e.g. NIPA)

32

PEM (proton exchange membrane)

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

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

htp://www.molecularexpressions.com/primer/lightandcolor/interferenceintro.html