Principles of Video Contact Angle Analysis

Principles of Video Contact Angle Analysis

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Description: Applications of Contact Angle Analyzer, Contact Angle Analysis, Observing Contact Angle, Video Contact Angle Analyzer, Surface Energy Calculations, Fox-Zisman Theory, Geometric-Mean Method, Harmonic-Mean Method, Acid-Base Theory, Contact Angle Theories, Advancing and Receding Contact Angles, Angle Measurements, Tilting Stage assembly, Motorized Syringe, Industry Standards of Contact Angle Measurements.

 
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Contents:
Principles of Video Contact Angle Analysis

AST Products, Inc.

Phone: (978) 667-4500 Fax: (978) 667-9778

AST Products, Inc., Billerica, MA 01821.

Web: www.astp.com E-mail: inquiry2006@astp.com

What is Contact Angle Analysis?
To Determine surface energy indirectly with the shape of a drop placed on the surface
� Three interfacial forces balance at the edge of a drop. � Two are in opposite directions and the third one forms a particular angle to the surface. � That particular angle is called Contact Angle. LV
Vapor Phase Liquid Phase

cos

f VS - f LS f LV

Young' s Equation


Solid Phase

VS

LS

interfacial force of drop and vapor LV interfacial force of drop and test surface LS interfacial force of test surface and vapor VS

Phone: (978) 667-4500 Fax: (978) 667-9778

AST Products, Inc., Billerica, MA 01821.

Web: www.astp.com E-mail: inquiry2006@astp.com

Applications of Contact Angle Analyzer
� Bio-medical
� Wettability improvement of contact lens and product quality assurance. � Bio-compatibility of human implants � Micro-fluidity studies of bio-chips

� Hard Disk Drives
� Wettability and Spreading of Lubricant on Disk Surface � Surface Cleanliness

� Interfacial Chemistry
� Surface Tension and Wettability of Detergents and Surfactants � Adhesive strengthen and pre-adhesion treatment studies � Studies on Waterproof Agents � Die and color fastenization

� Plating, Painting, and Printing
� � � � Surface cleanliness quality assurance Surface adhesion quality assurance Ink speading and adhesion studies Color ink-jet tranparency development

� Plastics Inductry
� Surface modification of polymers and process quality assurance

� TFT-LCD Display Panel Industry
� Glass panel cleanliness inspection and process quality assurance. � Pre-coating surface quality assurance of TFT printed circuitry, color filter, ITO conducting films.

� Semiconductors
� � � � � � � � Wafer cleanliness HMDS process control Photo-resist and developer studies CMP process development Substrate cleanliness BGA welding surface Epoxy adhesion Oxidation identification of bonding

� Erosion Control Studies
� Studies of Surface Corrosion Factors � Surface Water Repellency Studies

� IC Packaging

� Cosmetics
� Skin wettability and spreading of lotions � Wettability studies on powders

� Nano Technology
� Lotus effect on surface nano-structure � Surface Repellency of Nano-composites

Phone: (978) 667-4500 Fax: (978) 667-9778

AST Products, Inc., Billerica, MA 01821.

Web: www.astp.com E-mail: inquiry2006@astp.com

Observing Contact Angle
What one observes is actually a 2D projection of 3D drop
Observation plane Intersection of observation plane and the drop Slope at Tri-point

�At least one is liquid phase �Test surface is solid phase or another liquid phase �Third phase is vapor phase (drop vapor and air) or another liquid phase
Tri-phase Point on the observation plane Observer



Intersection ring of tri-phase

Phone: (978) 667-4500 Fax: (978) 667-9778

AST Products, Inc., Billerica, MA 01821.

Web: www.astp.com E-mail: inquiry2006@astp.com

Drop Surface Tension and Surface Energy of Test Surface

Low Surface Energy, non-wetting

Phone: (978) 667-4500 Fax: (978) 667-9778

Drop Surface Tension

High Surface Energy, good wettability and adhesion

Surface Energy of Test Surface

AST Products, Inc., Billerica, MA 01821.

Web: www.astp.com E-mail: inquiry2006@astp.com

Diagram of Video Contact Angle Analyzer
Push Block Screw Stepping Motor Controller Motorized Syringe Assembly

Hi-Mag Lens Stepping Motor

LED Back Light

CCD Camera
Syringe Control Image Process Calculations

Sample Stage Workstation Image Grabber Focusing
Phone: (978) 667-4500 Fax: (978) 667-9778 AST Products, Inc., Billerica, MA 01821.

Elevation

Web: www.astp.com E-mail: inquiry2006@astp.com

Simple Theoretical Model
Assume the drop is part of a sphere

b


r
r-b - tan-1 90 2 2rb-b

� Contact angle analysis software in general assume the drop is part of a sphere. � However, due to gravitation and molecular dispersion, the shape of a drop is close but not exactly a part of a sphere. � The hidden assumption: when the drop volume is small, the gravitational effect can be ignored. � Improved on sphere model has been replaced by ellipsoid model to simulate gravitational effect. But, what about the molecular dispersion?
Phone: (978) 667-4500 Fax: (978) 667-9778 AST Products, Inc., Billerica, MA 01821. Web: www.astp.com E-mail: inquiry2006@astp.com

Drop Shape Determination by AutoFAST Algorithm
To keep the calculation objective, AutoFAST algorithm uses second-order binary curves to simulate the shape of drop without any theoretical modeling Algorithm: � Find points at the edge of drop � Fit a curve to the drop edge. � Find points at the contact boundary � Fit a curve to the contact boundary � Find the intersections of the two curves and calculate the slopes at the two intersections
Second-order Binary Equation

The AutoFAST algorithm automatically determines drop edge and contact boundary. The RED lines are the actual simulated curves. Mark L and R are left and right intersections of curves, respectively.

a5 x 2 4 xy 3 y 2 2 x 1 y 0 a a a a a 0
Phone: (978) 667-4500 Fax: (978) 667-9778 AST Products, Inc., Billerica, MA 01821. Web: www.astp.com E-mail: inquiry2006@astp.com

Interactions Between Drop and Testing surface
Surface energy is the combination of dispersion (non-polar) and polar energy
� Coulomb interactions of polar groups
Dipole-Dipole Interactions Dipole-Induced Dipole Interaction Hydrogen Bonding Acid-Base Interactions

Dispersion Energy : Surface energy that results from nonpolar interactions of molecules Polar Energy : Surface energy that results from interactions of polar groups

Testing Drop Changed Contact Angle

Polar Group in Drop

Surface Contamination Surface Polar Group Hydrogen Bonding Acid-base Interactions
Phone: (978) 667-4500 Fax: (978) 667-9778 AST Products, Inc., Billerica, MA 01821.

Dispersion energy exists between all molecules but polar energy exists only when polar groups are present.

Web: www.astp.com E-mail: inquiry2006@astp.com

Surface Energy Calculations
� Fox-Zisman Theory
� Free energy of adhesion is equal to the projection of surface tension of drop at testing surface. � Assume that the interaction between the drop and the testing surface is greater than the internal force of drop (low contact angle). � Suitable for low contact angle surfaces.

� Geometric Mean Theory
� Free energy of adhesion is equal to the Geometric Mean of cohesive energy of separated phases � Suitable for testing surfaces with similar ionization potential.

� Harmonic Mean Theory
� Free energy of adhesion is equal to the Harmonic Mean of cohesive energy of separated phases � Suitable for non-polar low-energy testing surfaces.

� Acid-Base Theory
� Evaluate polar energy based on energy interchange model of acid and base.

Phone: (978) 667-4500 Fax: (978) 667-9778

AST Products, Inc., Billerica, MA 01821.

Web: www.astp.com E-mail: inquiry2006@astp.com

Fox-Zisman Theory
� Free energy of adhesion is equal to the projection of surface tension of the drop at testing surface. � Assume that the interaction between the drop and the testing surface is greater that the internal force (low contact angle), and energy of the interaction is negligible compared to testing surface energy � Suitable for testing surfaces with low contact angle. � Requires at least two drops of low contact angle.

cos s i i

i 2 1,

: contact angle of testing drop i : surface tension of testing drop i : surface tension of testing surface s

Phone: (978) 667-4500 Fax: (978) 667-9778

AST Products, Inc., Billerica, MA 01821.

Web: www.astp.com E-mail: inquiry2006@astp.com

Geometric-Mean Method
� Free energy of adhesion between phases is equal to the Geometric Mean of two separated phases. � Owen, Wendt, Rabel and Kaelble (OWRK) Method � Suitable for testing surfaces with similar ionization potential. � Require at least two kinds of drops that have similar ionization potential with the testing surface
p p (1 cos i ) 2 id d i s i s



i 1, 2

d ip i 2 1, i i d p s s s

: contact angle of testing drop i i : surface tension of testing drop i i
d p , : dispersion and polar energy of testing drop i i i d p , : dispersion and polar energy of testing surface s s

Phone: (978) 667-4500 Fax: (978) 667-9778

AST Products, Inc., Billerica, MA 01821.

Web: www.astp.com E-mail: inquiry2006@astp.com

Harmonic-Mean Method
� Free energy of adhesion between phases is equal to the Harmonic Mean of two separated phases. � Wu's Method � Suitable for non-polar low energy surfaces. � Require at least two kinds of drops with different surface tensions.
d d p p d i s d p i s p i 2 4 1, i (1 cos i ) i i s s

d ip i 2 1, i i

: contact angle of testing drop i i : surface tension of testing drop i i
d p , : dispersion and polar energy of testing drop i i i d p , : dispersion and polar energy of testing surface s s

s
d s p s

Phone: (978) 667-4500 Fax: (978) 667-9778

AST Products, Inc., Billerica, MA 01821.

Web: www.astp.com E-mail: inquiry2006@astp.com

Acid-Base Theory
� Evaluate polar energy based on energy interchange model of acid and base. � Suitable for materials with polar surface � Requires at least three drops of different surface tensions, at least two of them must be polar fluid.

(1 cos i ) 2 d d i i s i s i s





d 2 i i i i 2 s
d s s s

: surface tension of testing drop i i
d : dispersion portion of surface tension i : surface tension contributed by acid i : surface tension contributed by base i

Phone: (978) 667-4500 Fax: (978) 667-9778

AST Products, Inc., Billerica, MA 01821.

Web: www.astp.com E-mail: inquiry2006@astp.com

References on Contact Angle Theories �S. Wu, "Polymer Interface and Adhesion," Marcel Dekker, New York (1982). �R.J. Good, in "Modern Approaches to Wettability: Theory and Applications," Eds. M.E. Schrader and G.I. Loeb, p. 1-27, Plenum Press, New York, (1992). � K.L. Mittal, Ed., "Contact Angle, Wettability and Adhesion," VSP BV, The Netherlands, (1993).
Phone: (978) 667-4500 Fax: (978) 667-9778 AST Products, Inc., Billerica, MA 01821. Web: www.astp.com E-mail: inquiry2006@astp.com

AutoFAST Options
"Reflective Surface" Option
� Assumes the drop image possesses horizontal mirror symmetry and the axis of symmetry is the contact boundary

"Low Contact Angle" Option
Drop on a reflective surface

� Assume at low contact angle, the drop image possess vertical mirror symmetry

When measuring advancing and receding contact angles with tilting stage, do not choose either " Reflective Surface" or " Low Contact Angle" Option.

Phone: (978) 667-4500 Fax: (978) 667-9778

AST Products, Inc., Billerica, MA 01821.

Web: www.astp.com E-mail: inquiry2006@astp.com

Advancing and Receding Contact Angles
When the testing surface is tilted, contact angles at either sides of the drop differ.
Advancing Contact Angle relates to surface energy and wettability. Receding Contact Angle relates to surface roughness and repellency.

Receding Contact Angle

r

a

Advancing Contact Angle

Phone: (978) 667-4500 Fax: (978) 667-9778

AST Products, Inc., Billerica, MA 01821.

Web: www.astp.com E-mail: inquiry2006@astp.com

Measuring Advancing and Receding Contact Angle with the Tilting Stage assmebly

VCA Optima software calculates as ymmetrical drop image with accuracy. The advancing contact angle at right is 27.9� while the receding contact angle at left, 16.7�. The critical titling angle is 87�.

Tilting Stage Control Interface
Web: www.astp.com E-mail: inquiry2006@astp.com

Phone: (978) 667-4500 Fax: (978) 667-9778

AST Products, Inc., Billerica, MA 01821.

Measuring Advancing and Receding Contact Angle with Motorized Syringe

Edge of Contact

Edge of Contact

Advancing Contact Angle The critical angle at which the edge of contact expands

Receding Contact Angle The critical angle at which the edge of contact retracts

Phone: (978) 667-4500 Fax: (978) 667-9778

AST Products, Inc., Billerica, MA 01821.

Web: www.astp.com E-mail: inquiry2006@astp.com

Industry Standards of Contact Angle Measurements
� ASTM D724-99 Standard Test Method for Surface Wettability of Paper (Angle-of-Contact Method) � ASTM D5725-99 Standard Test Method for Surface Wettability and Absorbency of Sheeted Materials Using an Automated Contact Angle Tester � ASTM C813-90(1994)e1 Standard Test Method for Hydrophobic Contamination on Glass by Contact Angle Measurement � ASTM D5946-96 Standard Test Method for Corona-Treated Polymer Films Using Water Contact Angle Measurements � TAPPI T458 Surface Wettability of Paper (Angle of Contact Method) (TAPPI web site: www.tappi.org)

Phone: (978) 667-4500 Fax: (978) 667-9778

AST Products, Inc., Billerica, MA 01821.

Web: www.astp.com E-mail: inquiry2006@astp.com

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