Encapsulation technology: Principles and Applications

Size: px

Start display at page:

Download "Encapsulation technology: Principles and Applications"

Bernard Dennis
5 years ago
Views:

Encapsulation technology: Principles and Applications www.imagico.de In Woo Cheong, Ph.

1 Encapsulation technology: Principles and Applications In Woo Cheong, Ph.D. Associate Professor Department of Applied Chemistry, Kyungpook National University 1

2 Backgrounds Small is not only beautiful but also eminently useful - Prof. JH Fendler 2

3 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 (SiO 2, TiO 2, Al 2 O 3, etc) (iii) O/I hybrids (R-SiO 2, R-TiO 2, R-Al 2 O 3, etc) Emulsion-based encapsulation (o/w system) oil oil oil In-situ polymerization Interfacial polymerization Complex coacervation From Smart Capsules for Flexible Electronics by Dr. S.S. Lee at KIST 3

4 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

5 Back to the principle, How to make capsules? Thermodynamic Consideration Spreading Coefficient S i = γ jk - (γ ij + γ ik ) where, γ jk is interfacial tension between j and k phases. Condition for complete engulfing of phase 1 by phase 3 S 1 < 0(γ 23 < γ 12 ), when S 2 <0 and S 3 >0 1: hydrophobic liquid, 2: water, 3: polymer Torza S, Mason SG, J Colloid Interface Sci., 33, 6783 (1970) 5

6 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! 6

liquid to create any new surface surface tension Then how about with solid materials?

7 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? W c = 2ⅹsurface energy (2ⅹAⅹγ s ) Work W c A Unfortunately, we can t define the surface area exactly 7

8 Basic Understanding: - Surface Phenomena Measuring contact angle! vapor γ SV γ LV θ γ LS dl* θ liquid Top-view dl solid Therefore, dg = γ ldl + γ ldl * γ SL dl * = dl cosθ γ SV = γ SL + γ LV LV cosθ SV ldl Young equation 8

9 Basic Understanding: - Surface Phenomena Then how to determine γ SL and γ SV? Measure the contact angle of liquids with various surface energy (γ LV ) and plot γ LV vs. cosθ. Extrapolate it with the value of θ becomes 0 (we call this value γ c, complete wetting) and then we can obtain (γ c =) γ SV. For specific liquid system, we apply γ SV value and get γ SL. 1.0 cosθ γ c = γ SV (complete wetting, γ SL 0) γ c γ LV /mjm -2 9

10 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 = γ γ cosθ At the equilibrium, SV SL + If we add surfactant, drop will spread, γ SV - γ SL - γ LV > 0 Here we can define a parameter (Spreading coefficient); LV S LS = γ SV - γ SL - γ LV 10

How to make capsules? Thermodynamic Consideration Spreading Coefficient S i = γ jk - (γ ij + γ ik ) where, γ jk is interfacial tension between j and k phases.

11 How to make capsules? Thermodynamic Consideration Spreading Coefficient S i = γ jk - (γ ij + γ ik ) where, γ jk is interfacial tension between j and k phases. Condition for complete engulfing of phase 1 by phase 3 S 1 < 0(γ 23 < γ 12 ), when S 2 <0 and S 3 >0 1: hydrophobic liquid, 2: water, 3: polymer Torza S, Mason SG, J Colloid Interface Sci., 33, 6783 (1970) 11

12 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

13 Basic Understanding: - Colloidal Phenomena Type of Colloids 분자 Colloid 입자 Colloid Micelle Colloid Egg, Protein, PVA, etc. Detergent, Shampoo, Liposome, etc. Natural rubber, Latex paint, milk, ice-cream, etc. 13

14 Basic Understanding: - Colloidal Phenomena Large surface area :Adsorption property Light scattering : Tyndall phenomena Electrically charged : Elecrophoresis Etc.: Brownian motion 14

synthetic process in nano and micron-sizes.

15 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 milk treatment SEM image of heterocoagulated polymer particles Natural Rubber latex 15

16 Basic Understanding: - Colloidal Phenomena Thermodynamic aspect Phase transition accompanies change in standard free energy, G f = γ A G f G f > 0 < 0 Colloidal stability is poor (Lyophobic) Coagulation Thermodynamically stable (Lyophilic) Bulk G f Colloids 16

17 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 17

18 Synthesis 18

Historical stuffs Christopher Columbus discovered natural latex. 1839-1844 Charles Goodyear Vulcanized latex was invented. 30-40% 100% cis-polyisoprene 50-60% Serum Etc.

19 Historical stuffs Christopher Columbus discovered natural latex Charles Goodyear Vulcanized latex was invented % 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 19

20 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 20

21 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) 21

22 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 ~10 21 nano-compartments/l E RXN Droplets Nano-reactor Small size Protection Mass and heat transfer 22

23 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 (E tot ) = E i + E s = e i V + γa e i : Energy per unit volume γ: Surface Energy per unit volume Therefore, E tot /unit volume = e i + γ(a/v) Dp (nm) A/V(cm -1 ) 1 6x x x

Heterogeneous Polymerization The differential types of heterogeneous polymerization systems Type Typical Particle Radius Droplet size Emulsion 50 300 nm 1 10 µm Dispersion 1µm - Suspension 1 µm 1 10

24 Heterogeneous Polymerization The differential types of heterogeneous polymerization systems Type Typical Particle Radius Droplet size Emulsion nm 1 10 µm Dispersion 1µm - Suspension 1 µm 1 10 µm Inverse Emulsion nm 1 10 µm Microemulsion nm 10 nm Miniemulsion nm 30 nm Initiator water or oil soluble oil soluble oil soluble water or oil soluble Continuous Phase Water Organic (poor solvent for formed polymer) Water oil Discrete phase (particles) Initially absent, monomerswollen polymer particles form Initially absent, monomerswollen polymer particles form Monomer + formes polymer in pre-existing droplets Monomer, cosurfactant + formed polymer Monomer cosurfactant + Formed polymer Monomer, cosurfactant + formed polymer Suspension Emulsion Miniemulsion Microemulsion water Water soluble water soluble Water 24

25 Emulsion Polymerization Free-radical polymerization Usually vinylic: CH 2 = CR 1 R 2 R 1 = H: R 2 Name Ph styrene CH=CH 2 butadiene Cl vinyl chloride CO 2 H acrylic acid CO 2 Me methyl acrylate (butyl, ) OCOCH 3 vinyl acetate R1 = CH 3 : CO 2 Me methyl methacrylate (MMA) (butyl, ) R1 = Cl: CH=CH 2 chlorobutadiene (neoprene) 25

26 Emulsion Polymerization Initiation: e.g. R N=N R 2R + N 2 ; rate coefficient k d R + M RM Propagation: (monomer unit M) M n + M M n+1 rate coefficient k p Termination: 2R dead polymer rate coefficient k t Transfer, e.g. to monomer: M n + M M n + M rate coefficient k tr M then starts another chain 26

27 Emulsion Polymerization Various morphologies: electron microscopic images Core/shell Hemisphere Occlusions 27

28 Emulsion Polymerization Various morphologies: electron microscopic images Snowman-like Porous morphology Rugby ball-like Raspberry-like S Omi et al., J Applied Polym Sci., 66, 7, 1327 (1998) 28

29 Emulsion Polymerization Polystyrene Core (20 parts) S/B Copolymer Shell (80 Parts) 100 nm Transmission Electron Micrograph Showing the Cross-Sections of OsO 4 -Stained Two-Stage (20 PS/80 (S/B)) Latex Particles 29

30 Emulsion Polymerization TEM sample preparation techniques Pt, Cr particles [RuO 4 제조의예 ] 2NaIO4 + RuO2 RuO 4 + 2NaIO4 Microtoming Shadowing Staining 30

31 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/O W III O Bicontinuous W I O O/W Liquid crystalline Water (W) Surfactant (S) 31

32 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,

33 Microemulsion Polymerization Surfactant system: wet template N = v / s la o Packing parameter (shape factor) 33

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

35 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

36 Emulsification Techniques Emulsification-diffusion emulsification Emulsification Water + Stabilizer 50 nm PLGA + Solvent Adding excess water Solvent diffusion TEM micrograph of PLGA nanoparticles produced by ED method. 36

Emulsification Techniques Nanoprecipitation and dialysis methods polymer solvent drugs microsyringe pump piezoelectric nozzle dialysis

37 Emulsification Techniques Nanoprecipitation and dialysis methods polymer solvent drugs microsyringe pump piezoelectric nozzle dialysis tube PLGA water emulsifier hydrophobic probe Nanoprecipitation Dialysis TEM micrograph of core-type particles produced by nanoprecipitation. 37

38 Emulsification Techniques Membrane emulsification O/W W/O/W Optical micrograph of W/O/W multiple emulsion droplet containing vitamin C by membrane emulsification. 38

Emulsification Techniques Self-assembly technique by Block Copolymers worms vesicles Starfish vesicle lamellae large compound vesicles (LCV) Amphiphilic block

39 Emulsification Techniques Self-assembly technique by Block Copolymers worms vesicles Starfish vesicle lamellae large compound vesicles (LCV) Amphiphilic block copolymer Micellization of PS-PAA block copolymers under different conditions (i.e., ionic strength, concentration of polymer, MDF/water ratio, etc.) Micelles vs. Gels 39

Example : atom transfer radical polymerization CH 3 CHCl + Cu(I)(bpy) CH 3 CH + Cu(II)(bpy)Cl φ.

40 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 CH 3 CHCl + Cu(I)(bpy) CH 3 CH + Cu(II)(bpy)Cl φ.. CH 3 CH + CH 2 =CH CH 3 CHCH 2 CH φ. CH 3 CHCH 2 CH + Cu(II)(bpy)Cl φ φ φ φ φ. φ φ CH 3 CHCH 2 CHCl + Cu(I)(bpy) Initiation Propagation Atom transfer 40

41 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 ( I 1 and I 2 ) 41

42 Block Copolymers Crosslinking Core crosslinking Macromolecules 2000;33: Shell crosslinking J Am Chem Soc 2000;122:

43 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;

44 Applications 44

MMT): increases pathway by parallel arrangement, stainless flakes, glass flakes, etc.

45 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 : TiO 2 Inhibition: Cr and Pb-based pigments metal phosphate, silicate, titanate or molybdate compounds 45

directly onto an organic paint surface as this will attack the paint surface, causing

46 Applications Self-cleaning coating with TiO 2 Photo-catalytic titanium dioxide (TiO 2 ): A strong oxidation power & superhydrophilicity TiO 2 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 46

47 Applications Encapsulation of Ultra-hydrophobes Copper plating coating Composite coating 2 days 8 days 12 days 16 days 24 days 32 days 52 days Swapan K G, Functional Coatings, Wiley-VCH,

48 Applications coating without capsule Self-healing Plastics Matrix: Epoxy Microcapsule : Urea-formaldehyde + dicyclopentadiene (DCPD) Catalyst: 0 hr coating with capsule 24 hrs U of Illinois at UC S. R. White et al, Nature 2001, 409, hrs 48

49 Applications ph-induced Micellization 49 Angew. Chem. Int., Ed 2003;42:

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

51 Applications ~ 200 nm +/- charged core-shell particle µm Nature, 394, 16, July

S. Lee at KIST interfacial polymerization prepolymer migration and crosslinking

52 Applications E-paper in situ polymerization 100μm From Smart Capsules for Flexible Electronics by Dr. S.S. Lee at KIST interfacial polymerization prepolymer migration and crosslinking Urethane prepolymer chain extender Characteristics of shell materials transparency durability flexibility impermeability thermal and chemical resistance 52

53 Previous and Current Works on Encapsulation oil J. Microencapsulation, 19(5), 559 (2002) Synthetic Metals, 151(3), 246 (2005) 53

Previous and Current Works on Phase Change Materials Encapsulation Octadecane 120 60% PCM PS Capsule Pure

prepared by using ultramicrotome 20 Microencapsulated 0 PCM -20 Nanoencapsulated PCM 100 nm 0 200 400 600

54 Previous and Current Works on Phase Change Materials Encapsulation Octadecane % PCM PS Capsule Pure Octadecan Polystyrene 100 PCM Weight (%) Polystyrene Bulk PCM TEM image of PCM nanocapsule prepared by using ultramicrotome 20 Microencapsulated 0 PCM -20 Nanoencapsulated PCM 100 nm Temperature ( ) TGA curve for capsulation efficiency analysis Octadecane@PS 54 Korean Patent (2005)

55 Previous and Current Works Phase Change Materials on Encapsulation 55

, 14(5), 545 (2006) Korean Patent 2006-94071 Korean Patent (

56 Previous and Current Works on Multi-walled Carbon Nanotubes Encapsulation Amphiphilic Macromolecules CNT Macromol. Res., 14(5), 545 (2006) Korean Patent Korean Patent ( 출원 ) (2008) 56 Composites Sci. Tech., accepted in 2008

57 Kyungpook National University 57

Applied Surfactants: Principles and Applications

Applied Surfactants: Principles and Applications Tadros, Tharwat F. ISBN-13: 9783527306299 Table of Contents Preface. 1 Introduction. 1.1 General Classification of Surface Active Agents. 1.2 Anionic Surfactants.