vapor sorption characterisation of materials...overview 1. vapor sorption techniques •molecules as...
TRANSCRIPT
Vapor Sorption Characterisation of Materials
Dr. Daryl Williams
Surface Measurement Systems
Overview
1. Vapor Sorption Techniques • Molecules as Probes (DVS, iGC)
• Sorption Mechanisms
2. DVS Applications • Isotherms and Isotherm Shape
• Phase Transitions
• Sorption Kinetics
3. IGC/SEA Applications • Surface Energy
• Adhesion/Cohesion
• Bulk Properties
2
The Company
• Based in London
• Invented the Dynamic Vapor Sorption Instrument in 1993
• Currently 50 staff- London, USA, France, Germany- 7 PhD scientists
• Installed base >1000 instruments
• Technological market leader in sorption instrumentation
Characterisation of Solids
1. Radiation as a Probe • Raman, NMR, FTIR Spectroscopy • Light, x-rays, lasers, etc.
• Analytical and structural information- what where how much
2. Heat as a Probe • Calorimetry and Thermal Methods
• Thermodynamic information- rates DH DS DG
3. Molecule as a Probe • Sorption and wetting techniques
• Thermodynamic, chemical, and structural information
• Process rates, DH DS DG, diffusion constants, surface energy
4
Radiation as a Probe
1. Structural Information • XRD, XRPD
2. Chemical Information • XPS (ESCA), NMR, FTIR
3. Visual Information • Light Microscopy (polarized)
• AFM, SEM
• Particle size measurements (laser diffraction)
• Particle shape
5
Heat as a Probe
1. Thermodynamic Information • DSC (modulated; hyper)
• TGA
• DMA
• TAM
2. Chemical Reactions • Reaction Calorimetry
6
Molecule as a Probe
1. Chemical Interactions • IGC, DVS, Wetting, TAM, Chemisorption analyzers
2. Physical Structure (surface area, pore size, density, etc.) • DVS, IGC, Volumetric sorption (i.e. BET analyzers), Chemisorption,
Pycnometer
3. Thermodynamic Information • IGC, DVS, TAM
7
Types of Molecule-Solid Interactions
Adsorption
• Physisorption
• Chemisorption
Absorption
• Bulk absorption
• Absorption into lattice structure
Reactions
• Hydration and solvation
Condensation
• Pore filling
8
Adsorption
Molecules In Molecules Out
Adsorption-Physisorption
Molecules Weakly Adsorbed
9
Physisorption
•Weak interactions
•Molecules only on surface
•Probe molecules not chemically bound to surface
•Reversible sorption
•Associated properties measured
• Physical Structure: surface area, pore size, surface roughness
• Chemical Interactions: surface sorption capacity, surface energy, hydrophilicity, Lewis acidity-basicity, surface heterogeneity
• Thermodynamic: heat of sorption, free energy
10
Adsorption
Molecules In
Adsorption-Chemisorption
Molecules Covalently Bonded to Surface
11
Chemisorption
•Strong interactions
•Molecules only on the surface
•Probe molecules are covalently bound to surface
•Can be reversible or irreversible sorption
•Associated properties measured
• Titrate acid-base sites
• Active surface area
• Catalyst Dispersion
12
Absorption-Bulk
Molecules In Molecules Out-Diffusion Limited
Bulk Absorption
Molecules Absorbed
Molecules Interact with Bulk
13
Absorption-Bulk
•Penetrate surface
•Desorption is often diffusion limited
•Reversible or irreversible sorption
•Associated properties measured
• Physical Structure: vapor-induced phase changes (glass transition, crystallization, deliquescence), glass transition temperatures, crosslink density
• Chemical: total sorption capacity, solubility parameters
• Kinetic: diffusion coefficients, solid-solid phase transformation, drying kinetics
14
Dynamic Vapour Sorption
• Dynamic Gravimetric Vapor Sorption (DVS)
• Invented by SMS in 1993
• Long–Term Baseline Balance Stability is Key
• Controlled humidity and temperature
• Dynamic Flowing Gas System means Fast Thermal and Mass Equilibrium
• Conceptual similarities to TGA- but RH the key variable
15 Static Sorption Dynamic Sorption
DVS Introduction
16
DVS Introduction
Dynamic gravimetric Vapor Sorption (DVS)
• Fully automatic sorption instrument
• Fast equilibrium: significantly improved kinetics over static sorption systems
• SMS pioneer in vapor sorption technology
SMS UltraBalance
• Up to 0.1 µg sensitivity; unrivaled long-term baseline stability
• Allows use of small samples 1-10 mg
‘Real-world’ conditions
• Wide range of temperatures: measurement and preheat conditions
• Wide range of vapors: water and organic vapors
17
DVS Advantage
18
Experimental temperatures
System incubator: 5°C to 60°C Upper local sample temp: up to 125°C
Optional modular coil pre-heaters (large and small for temperatures up to 150°C)
Optional modular high-temperature pre-heater (for temperatures up to 350°C)
Pre-experimental temperatures
Microbalance Sample mass: up to 1g Mass change: up to ±150mg Resolution: 0.1µg High-mass option also available
Additional optional modular features Modular color video microscope for qualitative sample data
(use with a limited temperature range)
Dual fiber-optic probe adaptors for coupling with Raman/NIR spectrometers
(use with a limited temperature range)
Modular expandable manifold for use with large-sized samples
• Preconditioning with preheater 150° C or 350°C
• Vapor sorption till 85°C optional till 125°C/20%RH using 150°C preheater
• Humidity or solvent vapor steps, ramps and Isohum/Isochore measurements
• Diffusion / activation energy of diffusion
• Permeation (with Payne Cell)
• Tg versus RH or temperature
• Heat of sorption/Micro/Mesopore size distribution
• Stability tests
DVS Advantage Family
Isotherm Types (BDDT)
20
• Type I: Langmuir isotherm; chemisorption
• Type II: Monolayer formation, BET equation
• Type III: Strong sorbate-sorbate interactions; water often has this behavior
• Type IV: Monolayer formation, BET equation, capillary condensation at high pressures
• Type V: Strong sorbate-sorbate interacitons; capillary condensation at high pressures
• Type VI: only at liquid Kr temperatures
DVS-Typical Data- Kinetics
21
DVS Change In Mass (dry) Plot
-5
0
5
10
15
20
25
0 2000 4000 6000 8000 10000 12000 14000
Time/mins
Ch
an
ge
In
Ma
ss
(%
) -
Dry
0
10
20
30
40
50
60
70
80
90
100
Ta
rget
RH
(%
)
dm - dry Target RH
© Surface Measurement Systems Ltd UK 1996-2001DVS - The Sorption Solution
Date: 07 Dec 2001 Time: 4:14 pm File: ricestarch071201_reduced.XLS Sample: rice starch
Temp: 24.8 °C Meth: duncan.sao M(0): 40.5303
Moisture sorption behavior of rice starch at 25 °C- 2 cycle experiment
DVS-Typical Data-Equilibrium
22
DVS Isotherm Plot
0
5
10
15
20
25
0 10 20 30 40 50 60 70 80 90 100
Target RH (%)
Ch
an
ge
In
Ma
ss
(%
) -
Dry
Cycle 1 Sorp Cycle 1 Desorp
© Surface Measurement Systems Ltd UK 1996-2001DVS - The Sorption Solution
Date: 07 Dec 2001 Time: 4:14 pm File: ricestarch071201_reduced.XLS Sample: rice starch
Temp: 24.8 °C Meth: duncan.sao M(0): 40.5303
Norit GAC-Mesopore Sorption
• Hysteresis gap suggests mesoporosity (2 to 50 nm)
23
0
5
10
15
20
25
30
35
40
0 10 20 30 40 50 60 70 80 90 100
Ch
an
ge
In M
as
s (
%)
-R
ef
Target % P/Po
DVS Isotherm Plot
Cycle 1 Sorp Cycle 1 Desorp
© Surface Measurement Systems Ltd UK 1996-2009DVS - The Sorption Solution
Date: 11 Mar 2010Time: 14-28File: 1 - Norit GAC - Thu 11 Mar 2010 14-28-15.xlsSample: Norit GAC
Temp: 25.0 CMeth: GAC 0-95 B.saoMRef: 7.944
Channel Hydrate
• Water sorption on Channel Hydrate
• 0.2% RH steps: 0 to 10% RH
24
0
0.5
1
1.5
2
2.5
3
3.5
4
0 10 20 30 40 50 60 70 80 90 100
Ch
an
ge
In M
as
s (
%)
-R
ef
Target RH (%)
DVS Isotherm Plot
Cycle 1 Sorp Cycle 1 Desorp
© Surface Measurement Systems Ltd UK 1996-2007DVS - The Sorption Solution
Date: 15 Dec 2011Time: 16-13File: Channel Hydrate -
Thu 15 Dec 2011 16-13-33.xlsSample: Channel Hydrate
Temp: 25.0 °CMeth: Channel Hydrate small steps 2.sao
MRef: 13.4291
Quartz-Surface Adsorption
• Isotherm shape (Type II) and low uptake indicate surface dominated sorption
25
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 10 20 30 40 50 60 70 80 90 100
Ch
an
ge
In M
as
s (
%)
-D
ry
Target RH (%)
DVS Isotherm Plot
Cycle 1 Sorp
© Surface Measurement Systems Ltd UK 1996-2001DVS - The Sorption Solution
Date: 05 Mar 2003Time: 3:47 pmFile: 03-05-03-quartz-gt-106.xlsSample: Quartz > 106 microns
Temp: 24.9 CMeth: BEToctane.SAOM(0): 5.9975
Fuel Cell Proton Exchange Membranes
26
Nafion-1135 sample sorbs less water than BPSH-30 sample across humidity range
DVS Isotherm Plot
0
2
4
6
8
10
12
14
16
18
0 10 20 30 40 50 60 70 80 90 100
Target RH (%)
Ch
an
ge
In
Ma
ss
(%
) -
Dry
BPSH-30 Sorp BPSH-30 Desorp Nafion 1135 Sorp Nafion 1135 Desorp
© Surface Measurement Systems Ltd UK 1996-2005DVS - The Sorption Solution
Temp: 25.0 °C
Water Sorption on Hair
27
Moisture sorption behavior of three hair samples at 25 °C
DVS Change In Mass (ref) Plot
0
2
4
6
8
10
12
14
16
18
20
0 500 1000 1500 2000 2500 3000 3500
Time/mins
Ch
an
ge
In
Ma
ss
(%
) -
Re
f
0
10
20
30
40
50
60
70
80
90
100
Ta
rg
et
% P
/Po
© Surface Measurement Systems Ltd UK 1996-2010DVS - The Sorption Solution
Water Sorption on Keratinized Tissues
28
GK Johnsen, ØG Martinsen, and S Grimmes, J of Physics: Conference Series, 224 (2010) 1-4.
SC: Stratum Corneum Nail: Human Nail Hair: Human Hair
Sorption Isotherms of three different cellulose
Yanjun Xie, Callum A. S. Hill, Zaihan Jalaludin, Dongyang Sun. The water vapour sorption behaviour of three celluloses: analysis using parallel exponential kinetics and interpretation using the Kelvin-Voigt viscoelastic model. Cellulose. June 2011, Volume 18, Issue 3, pp 517-530.
sorption isotherms
Water kinetics: mass uptake vs time
-cellulose
linter
MCC
Vapor-Induced Phase Transitions
30
• Water vapor is a strong plasticiser
• Glass transitions
• Transition kinetics from glassy to crystalline phases
Material Morphology and Vapour Sorption
Amorphous- Glassy Solid
T <Tg
Mainly surface adsorption
Fast kinetics and low uptake levels
Amorphous- Rubbery Solid
T >Tg
Deep bulk sorption
Slow kinetics and large uptake levels
Crystalline
No Tg
Surface adsorption
Fast kinetics and very low uptake
Vapor-Induced Transitions
32
• RH ramping experiment (similar to DSC temperature ramp)
• Gravimetric data clearly shows moisture-induced glass transition and crystallization
DVS Change In Mass (dry) Plot
0
2
4
6
8
10
12
14
-100 100 300 500 700 900 1100 1300 1500
Time/mins
Ch
an
ge
In
Ma
ss
(%
) -
Dry
0
10
20
30
40
50
60
70
80
90
100
Ta
rge
t R
H (
%)
% Change in Mass Target RH
© Surface Measurement Systems Ltd UK 1996-2001DVS - The Sorption Solution
Date: 05 Dec 2002 Time: 11:58 am File: 12-05-02-lactoseramp900.XLS Sample: amorphous lactose
Temp: 25.1 °C Meth: lactoseramp0-90-900min.SAO M(0): 93.2048
Glass Transition
Surface Adsorption
Bulk Absorption andSurface Adsorption
Recrystallization
Spray Dried Lactose
Spray dried Lactose powder at 25C shown at a range of humidities: A: 0%RH B: 50%RH C: 60%RH D: 90%RH The formation of a gel, a solution followed by crystallisation is clearly shown.
Color Video Microscope
34
Colour Video Microscope The DVS colour vide microscope is fully
detachable with improved specifications,
coupling qualitative sample information with
DVS isotherm data.
The microscope shows visual sample changes
including swelling, deliquescence events,
cracking and phase changes.
This optional feature can also be used in
combination with some other DVS advantage
modular features.
Key Specifications • 1.3 Megapixel colour images (1280x1024)
• Adjustable focus.
• Adjustable magnification of 50x to 200x
• Picture overlay information includes: date,
sample info, experimental info, adjustable
scale marker, and overlay grid.
• Images exportable to .bmp, .tiff, and .jpeg
file formats
DVS-Microscope Accessory
35
Maltodextrin – 0% RH Maltodextrin – 95% RH, 0 minutes
Maltodextrin – 95% RH, 30 minutes Maltodextrin – 95% RH, 50 minutes
Vapor-Induced Transitions
36
• Ramping experiments at different temperatures
• 2-D stability ‘map’ for meta-stable materials
15
20
25
30
35
40
45
50
55
60
65
15 20 25 30 35 40 45 50 55
Re
lati
ve H
um
idit
y (%
)
Temperature (°C)
Humidity Induced Transitions for Spray-Dried Lactose
Humidity at Glass Transition (%) Humidity at Crystallization (%)
Stable Amorphous Region
Crystalline Region
Unstable Amorphous Region
Sorption Kinetics
37
• Bulk diffusion coefficients with fixed geometries • Film geometry (one-sided/two-sided)
• Spherical (powder) geometry
• Packaging applications • Payne style cell – MVTR determination
• Electronic packaging
Kinetics of Transitions
38
• Monitor mass loss as sample dehydrates
• Study and model drying conditions
Fraction Dehydrated
0
0.2
0.4
0.6
0.8
1
1.2
0 100 200 300 400 500 600 700 800 900 1000
Time/mins
Fra
cti
on
De
hy
dra
ted
30 °C 27.5 °C 25 °C 22.5 °C 20 °C 17.5 °C 15 °C
© Surface Measurement Systems Ltd UK 1996-2005DVS - The Sorption Solution
Two-Sided Film Diffusion
39
• Moisture gain and loss with polymer film; moisture access from both sides
• 1-D Fickian Diffusion coefficient at each step change in RH
Polyimide films
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 10000 20000 30000 40000 50000 60000
Sqrt(t)/d
Mt/M
infin
ity
20% RH
20% RH (fitted)
Previous RH (%)
Target RH (%)
Diffusion Coeff. (cm²/s)
R-sq. (%)
0.0 20.0 7.63E-10 99.55 20.0 0.0 4.38E-10 99.58 0.0 40.0 9.04E-10 99.52
40.0 0.0 6.05E-10 99.59 0.0 60.0 9.30E-10 99.54
60.0 0.0 6.55E-10 99.57
Dt
dM
Mt 4
Payne-Style Cell
40
• Payne-style cell allows MVTR determination
• Can be run in dry (a) or wet (b) mode
Test Specimen
Lower O’ring
Drying Agenti.e. Zeolite, Silica Gel
Cell Lid
Cell Cup
Cell opening
Upper O’ring
Temperature & RH controlled environment
(b)(a)
100%RH
0%RH
Payne-Style Cell
41
• Payne-style cell allows MVTR determination
• Investigate surrounding RH effects
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
60 61 62 63 64 65 66 67 68 69 70
Chan
ge In
Mas
s (%
w/d
ry w
)
Time (min)
100 %RH
80 %RH
50 %RH
30 %RH
DVS Vapor Permeability-Membranes
42
DVS-Organic Vapors
• Water and Organic Vapor Control
• Proprietary optical sensor allows for real-time measurement and control of organic vapors
• Does not predict organic vapor concentration like competitive products
• Allows accurate determination of BET surface area, solvate formation, surface energetics, porosity, solid-solvent interactions
• Ethanol, Methanol, IPA, Cyclohexane, Heptane, Octane, Nonane, DCM, Ethyl Acetate, and Toluene commonly used
43
DVS-Organic Vapors
44
0
10
20
30
40
50
60
70
80
90
100
0 50 100 150 200 250
% P
art
ial
Pre
ss
ure
Time/mins
DVS Octane Partial Pressure PlotTarget % P/Po Actual % P/Po
BET Surface Area for Hydrophobic Drug
45
0
10
20
30
40
50
60
70
0 5 10 15 20 25 30 35 40 45 50
(P/P
o) / [(
1 -
(P/P
o) )
* M
]
Octane P/Po (%)
DVS BET Plot for Metformin Hydrochloride Fines (less thane 140 mesh)
BET Data Line Fit
© Surface Measurement Systems Ltd UK 1996-2009DVS - The Sorption Solution
Methanol Sorption on Nafion
46
Methanol sorption on different Nafion samples at 25 °C
0
2
4
6
8
10
12
14
16
18
20
0 20 40 60 80 100
Ne
t C
ha
ng
e in
Ma
ss
(w
t%)
Methanol P/Po (%)
Methanol Sorption Isotherm at 25 °C
N117 SampleN112 SampleNR112 Sample
Amorphous Content by DVS
47
DVS Isotherm Plot
0
0.05
0.1
0.15
0.2
0.25
0 10 20 30 40 50 60 70 80 90 100
Target p/po (%)
Ch
an
ge In
Mass (
%)
- D
ry
100% Crystalline Lactose 2.1700% Amorphous 6.017% Amorphous 24.801% Amorphous 100% Amorphous
© Surface Measurement Systems Ltd UK 1996-2000DVS - The Sorption Solution
Temp: 25.0 °C
Octane adsorption on mixtures of amorphous lactose and
-lactose monohydrate
Amorphous Content by DVS
48
Amorphous content
for mixtures of
crystalline and
amorphous (spray-
dried) Salbutamol
Sulfate
DVS-Raman Accessory
49
1. Raman spectroscopy is the measurement & detection of the wavelength and intensity of inelastically scattered light from molecules. When electromagnetic radiation passes through matter, most of the radiation continues in its original direction but a small fraction is scattered.
2. Rayleigh scattering: Light that is scattered at the same wavelength as the incoming light.
3. Raman scattering: Light that is scattered due to vibrations in molecules or optical phonons in solids.
4. The majority of scattered light is elastic and only one in 106 optical photons are scattered at frequencies different to the incident light – This is the weaker Raman scattered light.
Sample
Incident Laser Light
Rayleigh Scattering
Raman Scattering
DVS Advantage– Video and Raman
50
DVS-Raman Spectroscopy
51
DVS water sorption/desorption results (a.) and in-situ Raman spectra (b.) for MCC at 25 °C.
IGC – Surface Energy
• Surface energy is the most commonly measured property by IGC
• Analogous to surface tension of liquids
• Defined as the excess energy at the surface of a material compared to the bulk
• Directly related to the thermodynamic work of adhesion
• Can be divided into dispersive, acidic, and basic components
Measuring Surface Energy of Solids
Comparisons to Contact Angle
• Contact angle measurements are a common surface energy method
γLV
γ0SV γSL
θY Clean surface
Solid surface
• Sessile drop contact angle performed on powder compacts
• High pressure causes surface deformation; Rough surface topography
• Porous surface leading to penetration of liquid; Swelling; Dissolution
Fast penetration of water droplet into 400 MPa mannitol compacts.
Incr
easi
ng S
urfa
ce E
nerg
y
Wettability Cohesion Process-induced Disorder
Adhesion
What Does Surface Energy Affect?
IGC Principles
Animation by L. Teng, Surface Measurement Systems
iGC-SEA Instrument Overview
• Small footprint: 450 mm (18”) x 450 mm (18”) x 700 mm (27.5”)
• Variable injection sizes; wider concentration range; 1:4000 injection ratio
• 12 vapor reservoirs (50ml)
• 2 column oven design: 20 to 180 °C
• Flame Ionization Detector (FID)
• Humidity control (optional)
58
IGC Sample Preparation
Silane-treated glass tube 30cm long & 6 mm O.D. 2, 3 , 4 and 10 mm I.D. 10 mg – 500 mg of material typically
0.5 m2 of surface area
Glass wool
Sample
Schematic of IGC
IGC Principle: Retention Time
• Single pulse of probe molecule
• t0 is the retention time for an inert molecule (distribution coefficient KR = 0, CH4, Ar, N2 & H2)
• tR is the retention time for the interacting probe
• Net retention time tN = tR - t0
Detector response
Time
Methane Hexane Heptane Octane
t0 tR,OctanetR,Heptane
tR,Hexane
Detector response
Time
Methane Hexane Heptane Octane
t0 tR,OctanetR,Heptane
tR,Hexane
Detector response
Time
Methane Hexane Heptane Octane
t0 tR,OctanetR,Heptane
tR,Hexane
Isotherms
Det
ecto
r Res
pons
e
Time
Det
ecto
r Res
pons
e
Time
Det
ecto
r Res
pons
e
Time
Am
ount
Ads
orbe
d
Partial Pressure
Am
ount
Ads
orbe
d
Partial Pressure
Am
ount
Ads
orbe
d
Partial Pressure
a) b) c)
The retention time is directly related to the first derivation of the amount adsorbed
The height is related to the partial pressure
Dispersive Surface Energy
Dispersive Component of Surface Energy
Sequential injection of alkanes with increasing C-chain length at specific
surface coverage
Plot RTlnVN vs. a(γdL)
1/2 then γds = (slope/2NA)2
d
L
d
SmAN aNConstVRTG 2ln0 D
Surface Energy Heterogeneity
Decane
Nonane
Octane
Heptane
Surface Coverage
Known sample BET surface area
Known molecular size of probes
Amount/Mole of probes needed to achieve certain coverage can
be determined
Retention volumes at this coverage can be used to
determine surface energy 30% 60% 70% 75%
Surface Energy Methodology
• Specific Free Energy DGSP Measured Directly • Use polar or acid-base probes
• Use probes of specific functional groups to probe interactions with the surface
• Apply Various Acid-Base Theories • Allows determination of specific component of surface energy (using
Good-van Oss Chadury approach)
• Measurement of the Lewis acidity and basicity of the surface (using Gutmann approach)
Origins of Surface Chemistry Heterogeneity
• Almost all solid surfaces possess heterogeneous properties
• Chemical heterogeneity • Surface contaminants and impurities • Different crystal planes can exhibit different chemistry • Degree of crystallinity/amorphicity • Morphological state: polymorphs, hydrates and solvates • Surface groups/Inhomogeneous surface modification
• Structural heterogeneity • Crystals may have several defect sites
• Growth steps, crystal edges, surface pores, etc. • Irregularities of crystal lattice • Pore of different sizes and shapes
• Heterogeneous properties cause differences in adsorption energies, thus vapour sorption capacity and surface energies
Anisotropic Surface Chemistry of Crystals
• Crystallisation of macroscopic pharmaceutical crystal (Excipient) D-mannitol (AR as received D-mannitol) Silanised D-mannitol
• Characterisation of surface energy using sessile drop contact angle Following crystallisation of macroscopic crystals
• Preparation of D-mannitol powders with same particle size (45-63 m), density, shape but different surface chemistries and thus energies.
HO
OH
OH OH
OH
OH
C6H14O6(D-mannitol)
D-mannitol
5mm
(011)
(010)(120)
Contact Angle Measurement on D-mannitol Crystals
Facet Advancing Contact Angle, a(°) Surface Energy (mJ/m2) Hydrophilicity
DIM H2O d p p/
(010) 30.3 2.4 56.2 1.9 44.1 12.8 56.9 0.23
(120) 31.9 2.9 46.2 2.2 43.3 18.6 61.9 0.30
(011) 40.1 1.5 12.8 4.6 39.5 35.4 75.9 0.47
Monographs of macroscopic β mannitol crystal. Size: 8 × 8 × 60 mm.
R. Ho, S.J. Hinder, J.F. Watts, S.E. Dilworth, D.R. Williams and J.Y.Y. Heng. Int. J. Pharm (2010) 387: 1-2 pp. 79-86
D-mannitol
5mm
(011)
(010)(120)
γLV
γSV
γSL
θ Clean solid surface
Liquid drop
(cos22 LV
p
SV
p
LV
d
SV
d
LVAW
SVSLLV cosYoung’s equation:
Owens-Wendt:
282283284285286287288289290Binding Energy (eV)
C 1
s X
P S
igna
l (a.
u.)
282283284285286287288289290Binding Energy (eV)
C 1
s X
P S
igna
l (a.
u.)
ba
Facet (120)
Facet (011)
CHx
CHx
C-OH
C-OH
Surface Chemistry by XPS
SEA surface energy profile measurements
– ability to distinguish homogeneity and heterogeneity in surface free energy
SEA Dispersive Surface Energy
D-Mannitol
γ D
max γ D
min γ D
50
Silanised 33.29 33.45 33.38
AR 37.51 52.63 40.34
25.0
30.0
35.0
40.0
45.0
50.0
55.0
0.00 0.04 0.08 0.12 0.16 0.20 0.24
Dis
pe
rsiv
e S
.E.
[mJ/
m2]
Surface Coverage [n/nm]
Silanised D-Mannitol
AR D-Mannitol
SEA Specific Surface Energy Profiles
D-Mannitol γ AB
max γ AB min
γ AB50
Silanised 1.54 1.59 1.57
AR 2.67 4.93 3.09
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0.00 0.04 0.08 0.12 0.16 0.20 0.24
Spe
cifi
c S.
E.
[mJ/
m2]
Surface Coverage [n/nm]
Silanised D-Mannitol
AR D-Mannitol
Changes in surface chemical environment - To an isotropic hydrophobic surface property
Surface Modification: Silanisation
Work required to reversibly separate an interface between two bulk phases.
WCohtotal = 2[(s
D * sD)½ + (s
+ * s-)½ +(s
- * s+)½]
0
50
100
150
200
250
300
350
400
0 2 4 6 8 10 12 16 20 24
Tota
l Flo
w E
ner
gy [
mJ]
Air Velocity [mm/s]
Silanised D-Mannitol
AR D-Mannitol
Free flowing materials fully aerate when flow energy stabilises
- Silanisation influences the dynamic flow properties, but not under consolidated conditions
Surface Modification for Improved Flow Properties
Effect of Cleaning Process on Surface Energy Heterogeneity
• Surface energy distribution of Aluminum and Teflon measured using iGC-SEA
film cell (sample area ~2” x 8”)
• Investigated cleaning proceedures effects on surface energy
• Ability to measure heterogeneity of entire surface unique to iGC-SEA
• Even simple films can be highly energetically heterogeneous
• Contact angle would require numerous droplets across the film surface. Even this would only be a gross approximate measure of heterogeneity
Dispersive Surface Energy of Aluminium
Acid-cleaned aluminium surface was energetically more active and heterogeneous, having higher mean γs
d.
Dispersive Surface Energy of Teflon®
Though bleached Teflon surface possessed higher mean γsd, nitric acid
solution has roughened the surface, inducing more surface defects and a variation of γs
d.
Planar Sample γs
d
[ mJ/m2 ]
γsab
[ mJ/m2 ]
γst
[ mJ/m2 ] γs
ab / γst
Aluminium 40.83 3.44 44.27 0.0777
Al Bleached 40.57 6.26 46.84 0.1337
Al Nitric Acid 46.15 7.24 53.39 0.1356
Teflon 38.15 2.51 40.66 0.0617
Teflon Bleached 38.96 3.84 42.80 0.0897
Teflon Nitric Acid 36.90 4.02 40.92 0.0982
Surface Energy Values (γ50) by iGC SEA
Isotherms-BET Surface Area
CnP
P
Cn
C
PPn
P
mm
11][ 00
0
5
10
15
20
25
30
35
40
45
50
0.00 0.05 0.10 0.15 0.20 0.25P/P0
P/[
n(P
0-P
)] [
g/m
Mo
l]
SEA Calculated Results : Selected P/P0 range 0.14 to 0.20 C constant 7.109 BET Surface Area: 2.9524 m2/g CRM 171 BET Surface Area = 2.95 m2/g
Selected linearization P/P0 range
IGC-BET Surface Area Standards
0% RH: IGC value of 2.95 m2/g 50% RH: IGC value of 2.73 m2/g 90% RH: IGC value of 1.45 m2/g
• As humidity increases, measured BET surface area decreases
• Water competing for sites or blocking available surface area
• Example AFM image on Graphene: JACS, 2011, 133(8), 2334-2337.
• Various pretreatments used to improve adhesion to polyolefins • Low pressure plasma
• Corona treatment
• Flame treatment
• UV irradiation
• Mechanical etching
• Priming techniques • Adhesion promoters to introduce polar functionality to TPO
• Chlorine donors
78
Polyolefin-Challenges
79
Polyolefin-Challenges
Polymer Samples Thermoplastic polyolefins (TPO) and elastomers
Different elastomer loadings (12 and 25 wt %)
Different elastomer densities
Measure mechanical adhesion to paint and compare to IGC surface energies
Polyolefin-Case Study
Dispersive Surface Energy
• TPO samples were painted with topcoat
• Comprehensive Shear Delamination Apparatus (SLIDO) as a measure of mechanical adhesion
• Traction force (or frictional force) measured by taking the peak load in compression
Mechanical Testing
Traction Force
Compressive Force
Run Length
S= v2
a
Sliding Frictional
Friction in Painted TPO
Plowing
Cohesive Failure
Mechanical Adhesion Versus Surface Energy
• Higher surface energies lead to higher practical adhesion to paint
• Higher surface energies lead to lower microhardness (lower crystallinity)
• Increase in amorphous content (lower crystallinity) allows greater penetration of paint into TPO, thus greater adhesion
• Thermodynamic adhesion agrees with practical adhesion
Polyolefin Case Study Summary
Properties measured by IGC
• Surface Energy Analysis
• Dispersive, acid-base components & total surface energy
• Acid-base Free Energy of Desorption Analysis
• Heterogeneity Mapping
• Heterogeneity profiles, heterogeneity distributions
• Gutmann Acid/Base Properties
• Isotherm Analysis
• Vapour uptake, Henry’s constant
• BET Specific Surface Area
• Thermodynamic Work of Adhesion/Work of Cohesion
• Heat of Sorption
• Bulk Solid Properties
• Glass Transition Temperature
• Solubility Parameter (Hildebrand 1D, Hansen 3D)
• Cross-linking Density
Acknowledgements
• Thank you to SMS collaborators
• SMS Colleagues: current and former team members
• London Imperial College SPEL Group
• Thank you for your time and attention
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