Encapsulation technology: Principles and Applications

Hydrophobic tail . Hydrophilic head . Basic Understanding: ... TEM micrograph of PLGA nanoparticles . produced by ED method. 37 Emulsification Techniq...

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Encapsulation technology: Principles and Applications www.imagico.de

In Woo Cheong, Ph.D. Associate Professor Department of Applied Chemistry, Kyungpook National University 1

Backgrounds Small is not only beautiful but also eminently useful - Prof. JH Fendler

www.digital-photography-school.com

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What are capsules ? Nano- or micron-sized containers !! Core materials: liquid, solid, gas, protein, cell, etc Shell materials: (i) Organics: polymers, lipids, surfactant

(gelatin, urea-urethane, melamine resin, block copolymer, etc)

(ii) Inorganic ceramics (SiO2, TiO2, Al2O3, etc) (iii) O/I hybrids (R-SiO2, R-TiO2, R-Al2O3, etc) Emulsion-based encapsulation (o/w system)

oil

In-situ polymerization

oil

oil

Interfacial polymerization

Complex coacervation

3 KIST From “Smart Capsules for Flexible Electronics” by Dr. S.S. Lee at

Why do we know about capsules ? As reaction container

Nanoparticle formation Polymerization Coupling rxn, etc. Field responsive materials

Protection of vulnerable stuff

Bio-active materials Cell & protein encapsulation Fragrant oils, etc.

Mass transport (release)

Drug delivery Anti-corrosive coating Self-healing Redox rxn, etc. 4

Back to the principle, ”How to make capsules ?” Thermodynamic Consideration Spreading Coefficient

Si = γjk - (γij + γik) where, γjk is interfacial tension between j and k phases.

Condition for complete engulfing of phase 1 by phase 3 S1 < 0(γ23 < γ12), when S2<0 and S3>0 1: hydrophobic liquid, 2: water, 3: polymer Torza S, Mason SG, J Colloid Interface Sci., 33, 6783 (1970)

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Basic Understanding: - Surface Phenomena Why most of the capsules are spherical ? Air

Water

The molecules at the surface must have a higher energy than those in bulk, since they are partially freed from bonding with neighboring molecules !

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Basic Understanding: - Surface Phenomena How to measure the surface tension ? Therefore, work must be done to take fully interacting molecules from the bulk of the liquid to create any new surface  surface tension

Then how about with solid materials ? Wc = 2ⅹsurface energy (2ⅹAⅹγs) Work Wc

A Unfortunately, we can’t define the surface area exactly… 7

Basic Understanding: - Surface Phenomena Measuring contact angle ! vapor

γLV γSV

θ

liquid

γLS

Top-view

θ

dl* dl

solid

dG = γ SL ldl + γ LV ldl * −γ SV ldl dl* = dl cos θ Therefore,

γ SV = γ SL + γ LV cos θ

…Young equation 8

Basic Understanding: - Surface Phenomena Then how to determine γSL and γSV ? • Measure the contact angle of liquids with various surface energy (γLV) and plot γLV vs. cosθ.

•Extrapolate it with the value of θ becomes 0 (we call this value

γc, complete wetting)

and then we can obtain (γc =) γSV. • For specific liquid system, we apply γSV value and get γSL.

1.0

γc = γSV

cosθ

(complete wetting,γSL0)

γc 20

30

40

50

γLV/mJm-2

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Basic Understanding: - Surface Phenomena • Surface energy of solids is closely related to its cohesive energy (The higher the surface energy, the higher its cohesion) • Surrounding (water, vacuum, air, etc.) property significantly affect the force required to make a new surface (i.e., crack propagation) γ SV = γ SL + γ LV cos θ • At the equilibrium, If we add surfactant, drop will spread, γSV - γSL - γLV > 0 Here we can define a parameter (Spreading coefficient);

SLS = γSV - γSL - γLV 10

How to make capsules ? Thermodynamic Consideration Spreading Coefficient

Si = γjk - (γij + γik) where, γjk is interfacial tension between j and k phases.

Condition for complete engulfing of phase 1 by phase 3 S1 < 0(γ23 < γ12), when S2<0 and S3>0 1: hydrophobic liquid, 2: water, 3: polymer Torza S, Mason SG, J Colloid Interface Sci., 33, 6783 (1970)

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Basic Understanding: - Colloidal Phenomena What are Colloids ?

Grind to submicron size

bulk

colloid

“true” solution

Fundamental forces operate on fine particles 1. A gravitational force (settling or creaming depends on density difference) 2. Viscous drag force (resistance to motion) 3. Natural kinetic energy of particles and molecules (Brownian motion) 12

Basic Understanding: - Colloidal Phenomena Type of Colloids

분자Colloid

입자Colloid

Micelle Colloid Detergent, Shampoo, Liposome, etc.

Egg, Protein, PVA, etc.

Natural rubber, Latex paint, milk, ice-cream, etc.

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Basic Understanding: - Colloidal Phenomena Large surface area :Adsorption property

Light scattering : Tyndall phenomena

Electrically charged : Elecrophoresis Etc.: Brownian motion

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Basic Understanding: - Colloidal Phenomena • • • •

Colloidal particles prepared from natural or synthetic process in nano and micron-sizes. Large surface area Various typical properties (surface property) Mineral, metals, protein, polymer, etc.

starch

latex paint

waste water treatment

SEM image of heterocoagulated polymer particles

milk Natural Rubber latex 15

Basic Understanding: - Colloidal Phenomena Thermodynamic aspect Phase transition accompanies change in standard free energy, ∆Gf = γ ∆A ∆Gf > 0

Colloidal stability is poor (Lyophobic) Coagulation

∆Gf < 0

Thermodynamically stable (Lyophilic)

Bulk

∆Gf

Colloids 16

Basic Understanding: - Colloidal Phenomena Thermodynamic aspect Lyophobic colloids, even if they are thermodynamically unstable, can be made “metastable” for long periods of time if an energy barrier of sufficient height can be erected between the bulk and colloidal state.

“Kinetically stable”

Hydrophobic tail Hydrophilic head

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Synthesis

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Historical stuffs • Christopher Columbus discovered natural latex. • 1839-1844 Charles Goodyear – Vulcanized latex was invented.

30-40% 100% cis-Polyisoprene 50-60% Serum Etc. Lipids, Proteins, Inorganics

• Before World War I, synthetic rubbers from emulsion (exactly not from emulsion, but from suspension). • 1920s - World War II, “true” emulsion polymerization was conducted.

Natural rubber tree: Hevea Brasilensis

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Historical stuffs Original reasoning: they assumed they could polymerize emulsion droplets ⇒ polymer latex:

free-radical initiator

Monomer droplet water

Poor quality products because of wrong mechanism

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Historical stuffs surfactant solution

initiator solution

monomer

Polymer particles ~ 100 nm diameter each containing many polymer chains, stabilized by surfactant

water

latex (polymer particles 100 nm diameter)

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Heterogeneous Polymerization Generation of tiny particles From the precept of laborious works on kinetics: Micelles or monomer droplet can be a primary locus of reaction … a state we call “nano- or micro-reactor”

 1018~1021 nano-compartments/L ∆E

Droplets

RXN

Nano-reactor

Small size Protection Mass and heat transfer 22

Heterogeneous Polymerization Why nanoparticle ? – Fast film formation rate and permeability – Better transparency – High reaction rate

– Better storage stability A Problem: Aggregation or flocculation of nanoparticles

Energy of Particle (Etot) = Ei + Es = eiV + γA ei: Energy per unit volume γ: Surface Energy per unit volume

Therefore, Etot/unit volume = ei + γ(A/V) Dp (nm) 1 10 100

A/V(cm-1) 6x107 6x106 6x105

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Heterogeneous Polymerization The differential types of heterogeneous polymerization systems Type

Typical Particle Radius

Droplet size

Initiator water or oil soluble

Emulsion

50 – 300 nm

≈ 1 – 10 µm

Dispersion

≥ 1µm

-

Suspension

≥ 1 µm

≈ 1 – 10 µm

Inverse Emulsion

102 – 103 nm

≈ 1 – 10 µm

Microemulsion

10 – 30 nm

≈ 10 nm

Miniemulsion

30 – 100 nm

≈ 30 nm

Suspension

Emulsion

Continuous Phase

Discrete phase (particles)

Initially absent, monomerWater swollen polymer particles form Organic Initially absent, oil (poor solvent monomersoluble for formed swollen polymer polymer) particles form Monomer + oil formes polymer Water soluble in pre-existing droplets water Monomer, or oil oil cosurfactant + soluble formed polymer Monomer water Water cosurfactant + soluble www.andrew.cmu.edu/user/kemin/Research.htm Formed polymer Monomer, water Water cosurfactant + soluble formed polymer

Miniemulsion

Microemulsion

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Emulsion Polymerization Free-radical polymerization • Usually vinylic: CH2= CR1R2 • R1 = H: – – – – – – –

R2 –Ph –CH=CH2 –Cl –CO2H –CO2Me –OCOCH3

Name styrene butadiene vinyl chloride acrylic acid methyl acrylate (butyl, …) vinyl acetate

• R1 = CH3: –

–CO2Me methyl methacrylate (MMA) (butyl, …)

• R1 = Cl: –

–CH=CH2

chlorobutadiene (neoprene) 25

Emulsion Polymerization • Initiation:

– e.g. R–N=N–R → 2R• + N2 ; R • + M → RM •

rate coefficient kd

• Propagation: (monomer unit M) – –Mn• + M → –Mn+1•

rate coefficient kp

• Termination:

– 2R• → dead polymer

rate coefficient kt

• Transfer, e.g. to monomer: – –Mn• + M → –Mn + M • – M • then starts another chain

rate coefficient ktr

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Emulsion Polymerization Various morphologies: electron microscopic images

Core/shell

Hemisphere

Occlusions 27

Emulsion Polymerization Various morphologies: electron microscopic images

Snowman-like

Rugby ball-like

Porous morphology

Raspberry-like S Omi et al., J Applied Polym Sci., 66, 7, 1327 (1998)

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Emulsion Polymerization Polystyrene Core (20 parts)

S/B Copolymer Shell (80 Parts)

100 nm

Transmission Electron Micrograph Showing the Cross-Sections of OsO4-Stained Two-Stage (20 PS/80 (S/B)) Latex Particles 29

Emulsion Polymerization TEM sample preparation techniques Pt, Cr particles

[RuO4 제조의 예] 2NaIO4 + RuO2  RuO4 + 2NaIO4

Microtoming

Shadowing

Staining

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Microemulsion Polymerization • Microemulsion: transparent liquid system consists of at least ternary mixtures of oil, water, surfactant. • It exhibits continuous or bicontinuous structure with < 100 nm scale. Oil (O)

W II W

W III

W/O

O

Bicontinuous

www.baschem.co.uk

O

WI

O/W Liquid crystalline

Water (W)

Surfactant (S)

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Microemulsion Polymerization • Surfactants – SDS : needs co-surfactants, short chain alcohols – Nonionics, some cationics (e.g., CTAB, DTAB), double chain surfactants (e.g., Aerosol OT) need no co-surfactants

• Features – – – – – –

Thermodynamically stable Enormous inner surface area Various morphologies No steady state reaction rate Inorganic particle formation Large amount of surfactant (7-15wt%)

Andrey J. Zarur and Jackie Y. Ying Nature 403, 65-67

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Microemulsion Polymerization Surfactant system: wet template

N s = v / lao Packing parameter (shape factor)

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Microemulsion Polymerization Making various morphologies

JS Jang et. al., Chem Comm, 2003

Hsiang Y. W. et al, Chem Mat 2005, 17, 6447

Zhaoping Liu, et al, Langmuir 2004, 20, 214

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K. Landfester et al., Macromolecules 2000, 33, 2370

Emulsification Techniques • Features – Post emulsion process – Uncontrollable particle size distribution – Methods: • Direct emulsification – External surfactant assisted emulsification – Neutralization emulsification

• Other emulsification methods – – – – –

Emulsification-diffusion emulsification Nanoprecipitation Dialysis Membrane emulsification Self-assembly technique 35

Emulsification Techniques Emulsification-diffusion emulsification Emulsification Water + Stabilizer

50 nm

PLGA + Solvent

Adding excess water

TEM micrograph of PLGA nanoparticles produced by ED method.

Solvent diffusion 36

Emulsification Techniques Nanoprecipitation and dialysis methods

dialysis tube

polymer solvent drugs

PLGA

microsyringe pump piezoelectric nozzle

water emulsifier

hydrophobic probe

Nanoprecipitation

Dialysis

TEM micrograph of core-type particles produced by nanoprecipitation.

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Emulsification Techniques Membrane emulsification

O/W

W/O/W

Optical micrograph of W/O/W multiple emulsion droplet containing vitamin C by membrane emulsification.

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Emulsification Techniques Self-assembly technique by Block Copolymers worms

lamellae

vesicles

Starfish vesicle

large compound vesicles (LCV)

Micellization of PS-PAA block copolymers under different conditions (i.e., ionic strength, concentration of polymer, MDF/water ratio, etc.)

Amphiphilic block copolymer Micelles vs. Gels 39

Block Copolymers A living free-radical polymerization – – –

No termination or chain transfer Radical chain remains active when all the monomer is used up Propagation continues when additional monomer is added

– –

Block copolymer formation! Example : atom transfer radical polymerization CH3CHCl

+

φ

.

CH3CH

φ

.

+

Cu(I)(bpy) CH2=CH

CH3CHCH2CH + Cu(II)(bpy)Cl

φ

φ

.

CH3CH

φ

+

Cu(II)(bpy)Cl

.

Initiation

CH3CHCH2CH

Propagation

CH3CHCH2CHCl + Cu(I)(bpy)

Atom transfer

φ

φ

φ

φ

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Block Copolymers Formation of block copolymers (a) sequential “controlled/ living “block copolymerization (sequential addition of monomers) (b) coupling of linear chains containing antagonist functions ( X and Y ) (c) switching from one polymerization method to another (d) use of a dual (“doublehead”) initiator consisting of two distinct initiating fragment ( I1 and I2 ) 41

Block Copolymers Crosslinking

Core crosslinking Macromolecules 2000;33: 4780–90.

Shell crosslinking J Am Chem Soc 2000;122:3642–51.

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Block Copolymers Stimuli-responsive nano-assemblies – Intelligent, smart, environmentally sensitive, etc. – Stimuli : light, temp., solvent, pH, chemicals, etc. – Drug release, encapsulation, intelligent switches

PS-co-P2VP-co-PEO Core/shell/corona

2-(dimethylamino)-ethyl methacrylate 2-(diethylamino) ethyl methacrylate Poly(DMAEMA/DEAEMA) diblock copolymer Chem Commun 1997;671–2.

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Applications

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Applications • Anti-corrosive coatings – Sacrificial means: zinc-rich coating

– Barrier effect: polymer coatings, inorganic filler (eg. MMT): increases pathway by parallel arrangement, stainless flakes, glass flakes, etc.

• Self-cleaning coatings – Hydrophobic-hydrophilic effects – Lotus effect – Photo-reactive : TiO2

– Inhibition: Cr and Pb-based pigments  metal phosphate, silicate, titanate or molybdate compounds

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Applications Self-cleaning coating with TiO2

– Photo-catalytic titanium dioxide (TiO2): A strong oxidation power & superhydrophilicity – TiO2 coating cannot be coated directly onto an organic paint surface as this will attack the paint surface, causing a phenomenon so called paint-chalking. : inorganic linker : organic or polymer Substrate

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Applications Encapsulation of Ultra-hydrophobes Copper plating coating

Composite coating

8 days

12 days

24 days

32 days

2 days

16 days

52 days Swapan K G, Functional Coatings, Wiley-VCH, 2006.

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Applications coating with coating without Self-healing Plastics capsule capsule

Matrix: Epoxy Microcapsule : Urea-formaldehyde + dicyclopentadiene (DCPD) Catalyst:

0 hr

24 hrs U of Illinois at UC

S. R. White et al, Nature 2001, 409, 794

48 hrs 48

Applications pH-induced Micellization

Angew. Chem. Int., Ed 2003;42:1516–9. 49

Applications E-paper

Characteristics : • Flexible like news paper • Wide-angular readability • Low energy (No back-light) • Potable (light-weight) 50

Applications ~ 200 nm

+/- charged core-shell particle

20 - 50 µm

Nature, 394, 16, July 1998.

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Applications E-paper 100μm From “Smart Capsules for Flexible Electronics” by Dr. S.S. Lee at KIST

in situ polymerization

interfacial polymerization

prepolymer migration and crosslinking

Characteristics of shell materials

Urethane prepolymer

chain extender

 transparency  durability  flexibility  impermeability  thermal and chemical resistance

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Previous and Current Works on Encapsulation

[email protected] oil

J. Microencapsulation, 19(5), 559 (2002)

[email protected]

Synthetic Metals, 151(3), 246 (2005)

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Previous and Current Works on Encapsulation Phase Change Materials 60% PCM PS Capsule Pure Octadecan Polystyrene

120

Octadecane

100

Weight (%)

80

PCM

60

40

20

Bulk Polystyrene PCM

0 Microencapsulated PCM -20

0

TEM image of PCM nanocapsule prepared by using ultramicrotome

Nanoencapsulated PCM 100 nm600 200 400 Temperature (

800

℃)

TGA curve for capsulation efficiency analysis

[email protected]

Korean Patent 10-061213954 (2005)

Previous and Current Works on Encapsulation Phase Change Materials

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Previous and Current Works on Encapsulation Multi-walled Carbon Nanotubes

Amphiphilic Macromolecules

CNT

Macromol. Res., 14(5), 545 (2006) Korean Patent 2006-94071 56 Korean Patent (출원) 2008-0046401 (2008) Composites Sci. Tech., accepted in 2008

Kyungpook National University

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