Contents
Cover
Title page
Copyright page
Preface
Part 1: Contact Angle Measurement and Analysis
Chapter 1: A More Appropriate Procedure to Measure and Analyse Contact Angles/Drop Shape Behaviours
1.1 Introduction
1.2 Experimental
1.3 Obtaining “Continuous” Drop Shapes and Independent Contact Angles
1.4 Different Contact Angles Analyses
1.5 Summary/Outlook
Acknowledgements
Glossary of Symbols
Copyrights
References
Chapter 2: Optical Contact Angle Measurement Considering Spreading, Evaporation and Reactive Substrate
2.1 Introduction
2.2 Experimental Setup for Contact Angle Measurement
2.3 Summary
2.4 Supplementary Media Material
Acknowledgement
References
Chapter 3: Method Development for Measuring Contact Angles of Perfluoropolyether Liquid on Fomblin HC/25
®
PFPE Film
3.1 Introduction
3.2 Experimental
3.3 Results and Discussion
3.4 Summary
Acknowledgements
References
Chapter 4: Characterizing the Physicochemical Processes at the Interface through Evolution of the Axisymmetric Droplet Shape Parameters
4.1 Introduction
4.2 The Relationships between the Contact Angle and the Thermodynamic and Geometric Characteristics of the Surface
4.3 Experimental Methods for Determination of the Contact Angle and the Surface Tension for a Sessile Droplet on the Surface
4.4 Determination of the Wetting Tension and the Wetted Area Fraction on the Basis of Temporal Evolution of Contact Angle and Surface Tension in Sessile Drop Method
4.5 Testing the Mechanical Durability of Superhydrophobic Coatings
4.6 Summary
References
Chapter 5: The Interfacial Modulus of a Solid Surface and the Young’s Equilibrium Contact Angle Using Line Energy
5.1 Introduction
5.2 The Young Equation Obtained with a Three-Dimensional Description
5.3 Incorporating the Contact Line into the Young Equation
5.4 Finding the Young Thermodynamic Contact Angle from Advancing/Receding Data
5.5 Interfacial Modulus G
s
Associated with the Solid Surface
5.6 Summary
References
Part 2: Wettability Behavior
Chapter 6: Patterned Functionalization of Textiles Using UV-Based Techniques for Surface Modification – Patterned Wetting Behavior
6.1 Introduction
6.2 UV-Based Processes for Surface Modification
6.3 Experimental
6.4 Results
6.5 Summary and Outlook
References
Chapter 7: Wettability Behavior of Oleophilic and Oleophobic Nanorough Surfaces in Air or Immersed in Water
7.1 Introduction
7.2 Sample Preparation
7.3 Characterization Methods
7.4 Surface Roughness of Al
2
O
3
Coatings
7.5 Wetting Behavior of Al
2
O
3
Coatings
7.6 Wetting Behavior of Al
2
O
3
Coatings Overcoated with a Thin Top Layer
7.7 Summary
Acknowledgements
References
Chapter 8: Effect of Particle Loading and Stability on the Wetting Behavior of Nanofluids
8.1 Introduction
8.2 Review on Wetting Behavior and Stability of Nanofluids
8.3 Summary
References
Chapter 9: Dielectrowetting for Digital Microfluidics
9.1 Introduction
9.2 Electrowetting on Dielectric (EWOD)
9.3 Liquid-Dielectrophoresis (L-DEP)
9.4 L-DEP in Microfluidics
9.5 Dielectrowetting
9.6 Droplet Manipulations by Dielectrowetting
9.7 Concluding Remarks and Outlook
References
Part 3: Superhydrophobic Surfaces
Chapter 10: Development of a Superhydrophobic/Superhydrophilic Hybrid Surface by Selective Micropatterning and Electron Beam Irradiation
10.1 Introduction
10.2 Selective Micropatterning Using Ultrasonic Imprinting
10.3 Selective Wettability Control
10.4 Development of Hybrid Surfaces with Versatile Wettability
10.5 Summary
Acknowledgements
References
Chapter 11: Hydrophobicity and Superhydrophobicity in Fouling Prevention in Sea Environment
11.1 Introduction
11.2 Antifouling Options
11.3 Problem Statement
11.4 Coatings with Special Wettability and Performance Against Biofouling
11.5 General Discussion
11.6 Summary
References
Chapter 12: Superhydrophobic Surfaces for Anti-Corrosion of Aluminum
12.1 Introduction
12.2 Fundamentals of Superhydrophobic Surface for Anti-Corrosion
12.3 Applications of Superhydrophobized Aluminum Surfaces for Anti-corrosion
12.4 Summary
References
Part 4: Wettability, Surface Free Energy and Adhesion
Chapter 13: Determination of the Surface Free Energy of Solid Surfaces: Statistical Considerations
13.1 Introduction
13.2 Data Analysis
13.3 Summary and Conclusions
References
Chapter 14: Equilibrium Contact Angle and Determination of Apparent Surface Free Energy Using Hysteresis Approach on Rough Surfaces
14.1 Introduction
14.2 Experimental
14.3 Results and Discussion
14.4 Conclusions
Acknowledgment
References
Chapter 15: Contact Angle and Wettability Correlations for Bioadhesion to Reference Polymers, Metals, Ceramics and Tissues
15.1 Introduction
15.2 Materials and Methods
15.3 Results
15.4 Discussion
15.5 Summary and Conclusions
15.6 Future Scope
References
Chapter 16: The Efficacy of Laser Material Processing for Enhancing Stem Cell Adhesion and Growth on Different Materials
16.1 Introduction
16.2 Surface Engineering Techniques in Stem Cell Technologies
16.3 Laser Surface Engineering of Polymeric Materials
16.4 Laser Welding of NiTi Alloys
16.5 Summary and Future Considerations
References
Index
End User License Agreement
Guide
Cover
Copyright
Contents
Begin Reading
List of Illustrations
Chapter 1
Figure 1.1
Superposition of the drop image with the calculated coordinates before and after the weighting procedure. The image is converted into coordinates with a sub-pixel resolution. In this figure, the surface of the solid corresponds to the
y
-axis due to the rotation of the coordinates and the definition of the BMP file format [3].
Figure 1.2
The baseline detection, the fitting, the determination of the intersection point with a semicircle = triple point (baseline (length 7.8 mm)) and the calculation of the contact angle using a right-angled triangle. For the purpose of visualization, the camera is slightly tilted by 0.57° and every 20
th
data point is individually marked (the fit range of approximately 0.5 mm contains 37 data points).
Figure 1.3
Examples of different coordinate transformations and drop contours obtained by the coordinate transformation of HPDSA for (a) mono (1H,1H,2H,2H-perfluorooctyl) siloxane (FOS-layer) / fluorinated ionic liquid; (b) FOS-layer/water. Between two drawn point symbols 18 data points are not individually marked by symbols. The strong pinning in (a) can even be analysed.
Figure 1.4
Examples of different coordinate transformations and drop contours obtained by the coordinate transformation of HPDSA: (a) structured SiO
2
surface/water; (b) modified GDL/water; (c) FOS-layer/water; (d) GDL/water. Between two drawn point symbols 18 data points are not individually marked by symbols. “Continuous” data points are clearly recognisable.
Figure 1.5
left
: Image of a drop resting on a hydrophobically modified, structured silicon wafer test surface;
right
: Transformed coordinates, including the excluded area of the inner reflection (0 s, 16 s, 32 s), for a drop on a hydrophobically modified, structured silicon wafer.
Figure 1.6
Illustration of the point definition in one of two dimensions depending on the colour gradient
p
for every pixel. The points obtained are marked by arrows. For identification, calculations of the absolute values are considered. Note that events like the first two are often a result of an overlapping reflection, which is identified by different colour changes[4].
Figure 1.7
Example of experiments analysed by HPDSA and SCA20 software (within the images);
top
: Pictures from video files of OCA experiments on inclined surfaces (first and one of the last pictures). The systems are ionic liquid on perfluorinated silicon oxide surface (right), water droplet on superhydrophobic graphite GDL felt (middle) and water droplet on rose petal surface = coated graphite GDL felt (left). Mismatch of the ellipse fitting is clearly recognisable;
bottom:
Measured contact angles analysed by HPDSA of the same experiments. All angles are measurable (smooth continuous slopes, range 0° to > 170°) even in case of strong pining (left) or the motor induced vibrations (“noise” in-between 0 and 1° inclination of the CA on the GDL felt(middle)).
Figure 1.8
Example of the static contact angle analysis of ionic liquids on flat solid surfaces [11] using the positions of the triple points (right = uphill, left = downhill) relative to the first triple point Δ
X
Bl
0
as reference. The specific static angles can be obtained on the position where the first motion is monitored. This definition does not clearly lead to a limiting value (largest or smallest CA).
Figure 1.9
(a, b) Gompertzian analysis and selected residuals for the rinsed wafer. Specific angles with the lowest standard deviations are marked; (c, d) Gompertzian analysis and selected residuals for the RCA-cleaned surface. For the RCA-cleaned surface, an acceleration of the drop motion is recognisable by the large variance from the fitted curve. In addition to the specific angles with the lowest standard deviations, the ones at the fitting limit before the discontinuity are marked.
Figure 1.10
Different examples of overall analyses performed on solid/liquid systems: (a) FOS-layer/ionic liquid (fluorinated); (b) siloxane surface(transition from hydrophilic to FOS/hydrophobic)/water; (c) APS/water; (d) silicon oxide (0.150 mm, blue)/water. The slopes of the averaged data are very well fitted to the final Gompertzian functions and in all cases specific angles can be identified independent of human subjectivity.
Figure 1.11
(a, b) Gompertzian analysis and selected residuals for advancing motion. The advancing angle with the lowest standard deviation is marked by arrows; (c, d) Gompertzian analysis and selected residuals for receding motion (Δ
V
(
t
start
) ≈ 11 µL and Δ
V
(
t
end
) ≈ –20 µL). Specific variance from the fit function can result in the identification of surface effects for example the receding angle (d) is affected by some pinning events (receding experiment from right to left = removing of liquid).
Figure 1.12
Examples of the identified downhill contact angle events (marked as vertical lines;
lv
= 40 µm/°) and velocity relative to the inclination of the rinsed wafer (a) and of the cleaned wafer (b). The markings of the statistical contact angle events “before acceleration” and “during acceleration” are shown for (a), whereas in (b) the markings of the statistical contact angle events “after acceleration” and during “constant speed” are presented. The difference in motion behaviour (strong acceleration for (b)) is found in all experiments and indicates a self-induced heterogeneity of the cleaned wafer. Similar but smaller differences exist for the motion on the uphill side of the droplet. A slow movement of the triple line is evident for both surfaces (φ<9°) and sides of the drops.
Figure 1.13
Blown-up visualization of the slow-moving range of the drop on two hydrophobically modified silicon wafers with FOS (top and bottom) at 0° (initial), at 10° and at 20° inclination. For both identically prepared surfaces the covered distance is smaller than 0.52 mm which is hardly analysable by a human being.
Figure 1.14
Examples of the calculation of the relative density distribution (relative numbers) with
θ
(a, c) or
φ
(b, d) as independent parameter for a freshly received Si wafer; similar results can be found for mono-aminopropyl siloxane surface (“wet” preparation) [7]. The expected values and the standard deviations of the global analysis are also shown by solid vertical lines to visualise how a class (= the width of one column is 0.5·
σ
) is defined. Neither the uphill (a) and the downhill (c) angles nor their velocities (b, d) are normal distributed. This also demonstrates that a simple analysis leads to unsatisfactory results.
Figure 1.15
a, b
left
:
φ
d
/ velocity-dependent analysis of
θ
d
for the event “before acceleration” of the rinsed wafer. E(
p
) and
σ
(
p
) are marked by lines, whereas the
σ
(
p
)’s in the classes are marked by error bars and by the broadness of the columns for f
p
(
p
). A bimodal distribution for E(
φ
d
) and a domination of events with low
vel
d
. can be easily observed; a, b
right
:
φ
u
/ velocity-dependent analysis of
θ
u
for the event “before acceleration” of the rinsed wafer. Two maxima in the distribution of
φ
u
can be easily observed.
Scheme 1.1
Summary and history of the methods developed and their applications. Development of the super-resolution drop shape analysis is mainly focused in contribution [3], the application/development of the statistical CA analyses was finally developed/conceived in contribution [9]. The aims of statistical procedures are
inter alia
reproducible CA definitions (advancing/receding, up-/downhill) and motion behaviour analysis. Uncited applications are experimentally confirmed but not published, and applications and questions in dashed boxes are most likely possible but due to hardware or time aspects were not performed until now.
Chapter 2
Figure 2.1
Different scenarios during contact angle measurements: Panel (a): complete spreading/wetting with equilibrium contact angle,
θ
e
≈ 0°; Panel (b) partial wetting,
θ
e
< 90°; Panel (c) partial non-wetting,
θ
e
> 90°; (d) complete non-wetting,
θ
e
≈ 180°.
Figure 2.2
Ideal spreading of a liquid (silicone oil) drop under water medium. Experimental evidences for four different stages of drop spreading are shown in the inset figures with scale bar on the right bottom corner. (i) complete non-spreading; (ii) partial non-spreading with CA > 90° (increase of base diameter with decrease of contact angle); (iii) partial non-spreading with CA< 90° (further increase of base diameter with decrease of contact angle); and (iv) attainment of constant base diameter and contact angle after a certain time,
e.g.,
in this case after ~225 seconds.
Figure 2.3
Non-ideal drop spreading on a substrate during evaporation of the liquid drop with the images showing the temporal variations in drop shapes at appropriate stages. The scale bars in the right bottom corner for each case represent 1mm. Here: (a) water drop spreading on Cu substrate. We observe initial decrement of contact angle with fixed DBD up to a certain time (stage (i) to (ii)) and later the DBD decreases over time (stage (iii)); (b) ethanol drop spreading and evaporation on a PDMS substrate: (i) initial stage of drop deposition; (ii) fast decrease of contact angle with gradual decrease of DBD after a certain time; (c) diiodomethane (DIM) spreading on a PTFE substrate: (i) initial stage of drop deposition; (ii) after a certain time, fast decrement of contact angle with gradual decrease of DBD; (iii) At the final stage, we observe faster spreading rate due to the increment of evaporation rate.
Figure 2.4
Holder for attaining the saturated condition required to obtain ideal/static contact angle (saturated condition chamber).
Figure 2.5
Ideal spreading of a liquid drop in saturated condition. Experimental observations (with the scale bar at right bottom corner) are shown in the inset image for each case, where: (a) ethanol on a PDMS substrate; (b) water on a Cu substrate. For both cases, we observe constant contact angle and base diameter after instantaneous spreading.
Figure 2.6
Drop spreading on reactive (paper) substrates. We observe significant variation in DBD (as well as contact angle, i.e., stage (i) to (ii)) due to absorption and percolation. Cu-paper and PDMS-paper combinations show different behaviors of drop spreading which indicates the significance of the material underneath the substrate.
Figure 2.7
Drop spreading on reactive (paper) substrate. (a) experimental setup to fix the paper substrate with the holder arrangement in the surrounding medium without direct contact to any other substrate; (b) variations of drop base diameter and contact angle with time. We observed an increment of drop diameter and thus a continuous decrement of contact angle (stage (i) to stage (ii)).
Chapter 3
Figure 3.1
Schematic preparation procedure for a “liquid film” of Fomblin HC-25
®
PFPE (PFPEf) (by D. Rossi).
Figure 3.2
Formation process of a stable Fomblin HC-25
®
PFPE “liquid film” (PFPEf) as a function of the relaxation time of the drop of the same PFPE (PFPEd) on the PermaFoam surface (by D. Rossi).
Figure 3.3
Comparison between SFE (surface free energy), DC (dispersion component), PC (polar component) of PermaFoam and Fomblin HC-25
®
PFPE (PFPEf). By merging the values reported on the axes it is possible to obtain representative areas (“imprints”) of the two materials and compare them to each other.
Figure 3.4
The Owens-Wendt approach for the evaluation of the applicability of the tensiometric model developed for the calculation of the surface free energy of PermaFoam using drops of PFPE (PFPEd), ethylene glycol (EG), and water milliQ (WmQ) as test liquids.
Figure 3.5
(a) Glycerol (gly) drop image on the PFPE “liquid film” (PFPEf) surface and (b) schematic view of fitted line obtained by applying the sessile drop method for measurement of glycerol (gly) contact angle (CA) at the point of intersection between the dashed fitted line and baseline
.
Figure 3.6
Influence of PermaFoam support on the measurement of contact angles of test liquids on the PFPE “liquid film”.
Figure 3.7
Correlations between the contact angles (CAs) of drops of PFPE (PFPEd), diiodomethane (dim), and glycerol (gly) measured on “liquid film” of Fomblin HC-25
®
PFPE (PFPEf) and PermaFoam, and the molecular weights (MW) of test liquids. The higher correlation degree for PFPEf (R
2
=0.9331) means a greater sensitivity of CA measurements performed at the interface with PFPEf than of those performed at the interface with PermaFoam (R
2
=0.3313).
Figure 3.8
Comparison between contact angle (CA) values of perfluoropolyether drop (PFPEd), diiodomethane (dim), and glycerol (gly) measured onto PermaFoam and Fomblin HC/25
®
PFPE “liquid film” (PFPEf) depending on the time available to make each CA measurement that in the case of PFPEf (dim, 3.7 min: PFPEd, 2.8 min; gly, 7.8 min) appear longer than in the case of PermaFoam (dim, 1.1 min; PFPEd, 2.3 min; gly, 2.06 min).
Figure 3.9
Relationships between measurement time for contact angles and drop volume of each test liquid used for the surface free energy characterization of the PFPE “liquid film” (PFPEf).
Figure 3.10
No effect of the volume of the glycerol drop on contact angle measurements performed on the PFPE “liquid film” (PFPEf) as demonstrated by a large variation in the drop volume but only a very minor change in the contact angle (CA).
Figure 3.11
Vertical movement of drops of test liquids into the “liquid film” of PFPE (PFPEf) studied by the vertical dynamic contact angle (VDCA) method applied for the analysis of the diffusion rate of gly, dim, and water through PFPEf.
Figure 3.12
(A) formation of a liquid film of Fomblin HC/25
®
PFPE (PFPEf) on a polyurethane support, (B) contact angle measurements between a PFPE drop and the PFPE “liquid film” by the sessile drop method, (C) conversion of contact angles into surface free energy by the Owens-Wendt model, and (D) graphical comparison between Fomblin HC-25
®
PFPE drop and Fomblin HC-25
®
PFPE “liquid film” (“imprints”) which demonstrates the applicability of the Solid-Like Method (SLM).
Chapter 4
Figure 4.1
The scheme for the determination of the Young contact angle on a flat smooth solid surface (a). Note that at equilibrium the solid surface is not dry but covered with a thin wetting or adsorption film (b).
Figure 4.2
Experimental setup for studying the evolution of the droplet parameters in saturated vapor atmosphere.
Figure 4.3
A typical set of raw experimental data collected during long-term contact between a substrate and the aqueous droplet: temporal evolution of contact angle (1), surface tension (2) and contact diameter (3).
Figure 4.4
The evolution of contact angle and the product
σ
LV
cos
θ
with time after deposition of brine droplet on the composite hydrophobic coating on the titanium substrate. Solid lines are used to guide the eye.
Figure 4.5
The evolution of the contact angle (triangles) and the surface tension (diamonds) for deionized water droplet (open symbols) or for a droplet of 0.05M H
2
SO
4
solution (full symbols) at prolonged contact with the superhydrophobic coating fabricated by laser texturing of aluminum alloy AMG2 followed by chemisorption of stearic acid.
Figure 4.6
Analysis of wettability evolution on the basis of Eq. (4.8) for the droplet of the acidic solution on the superhydrophobic surface obtained by chemisorption of stearic acid on the laser-textured aluminum surface.
Figure 4.7
The details of the surface morphology for an aluminum substrate of type 1, textured by nanosecond laser treatment (a) and for a substrate of type 2, textured by anodic oxidation (b).
Figure 4.8
Temporal evolution of the surface tension (1, 2) and the contact angle (1′, 2′) for the water droplet under prolonged contact with superhydrophobic substrates of type 1 (1, 1′) and type 2 (2, 2′).
Figure 4.9
Analysis of wettability evolution on the basis of Eq. (4.8) for superhydrophobic substrates of type 1 (a) and type 2 (b). The parameters characterizing the linear sections I, II, and III for each of substrates are given in Table 4.1.
Figure 4.10
Variations of contact and rolling angles for superhydrophobic coatings subjected to cavitation (1, 1′) or abrasion (2, 2′) tests for different times.
Figure 4.11
Variations of water contact angle and rolling angle as functions of the number of freeze/thaw cycles for the aluminum sample with the superhydrophobic coating immersed into deionized water.
Figure 4.12
Dependences of contact (lines 1–3) and rolling (lines 1′-3′) angles on the number of icing/de-icing cycles. 1 and 1′ correspond to angles measured just after taking out the sample from the aqueous phase, 2 and 2′ to those after drying in the laboratory air for 2 h, and 3 and 3′ to angles after heat treatment in the oven at 140 °C for 2 h.
Figure 4.13
The restoration of initial properties of superhydrophobic coatings with time of laboratory storage indicating their self-healing after 2 h cavitation (1, 1′) or 2 h abrasion (2, 2′) tests.
Chapter 5
Figure 5.1
(a) Two-dimensional representation of a drop on a surface describing interfacial tensions as forces balanced along the x axis which results in Eq. (5.1). For this, the contact line is viewed as a point object on which the force balance is made. (b) Three-dimensional representation of a drop on a surface. Here the drop is three-dimensional, and the surface tensions can be viewed as surface energies. Then we can obtain the Young equation from surface energy minimization.
Figure 5.2
K
dependence on the contact angle,
θ
, for Young equilibrium contact angles,
θ
0
,
smaller than 90°. The five different lines represent five different Young equilibrium contact angles
θ
0
: contact angles (clockwise direction) correspond to 1/cos(
θ
0
) 1.01, 1.2, 2, 14.3, and 107 which roughly correspond to
θ
o
= 9°, 30°, 60°, 86°, and 89.99999°, respectively. The dashed line corresponding to
θ
o
=89.99999° and for the scale of the figure it coincides with a vertical line along
θ
o
= 90°. Note that the slope at which
K
intersects the x axis increases as
θ
o
approaches 90°.
Figure 5.3
K
dependence on the contact angle,
θ
, for four different Young equilibrium contact angles,
θ
o
, at two angular intervals away from straight angle (i.e.
θ
o
= 90°):
θ
o
= 90° ± 30° and
θ
o
= 90° ± 0.00001°. The two
θ
o
values which are closer to 90° cannot be resolved on the scale of this figure and are both represented as an overlapping dashed line (the vertical dashed line along
θ
=
π
/2). On a larger scale they would look qualitatively as the other pair shown.
Chapter 6
Figure 6.1
The concept of water collection (“water harvesting”) on the shell of the Namib Desert beetle
Stenocara gracilipes
: Water from ambient humidity adsorbs on the hydrophilic islands (bumps) on the beetle’s superhydrophobic shell until the accumulating droplets lose adhesion and roll over the shell to the beetle’s head.
Figure 6.2
Self-driven drop motion due to variation in local wettability; the droplet moves from a hydrophobic area on the substrate surface to a more hydrophilic domain due to the force gradient dF/dy originating from the difference of the advancing contact angle on the more hydrophilic area Θ
a
and the receding contact angle on the more hydrophobic area Θ
r
. γ is the surface tension of the liquid.
Figure 6.3
(a) Patterned wettability of a fabric visualized by the behavior of droplets of an aqueous dyestuff solution; the six droplets – three in hydrophilic, three in hydrophobic domains – were applied simultaneously! Confined hydrophobic domains on a technical PET fabric were attained by local deposition of poly-DAP layers on fiber surfaces. The effect was achieved by finishing the fabric with DAP monomer solution and masking certain areas during irradiation at 222 nm. Irradiation was allowed only in the areas indicated by the dashed circles. (b) SEM micrograph of fibers in the irradiated area; UV-grafted poly-DAP layers are clearly visible.
Figure 6.4
Patterning wettability for local accumulation of collected liquid on a porous textile by masked UV-grafting. (a) Photograph of a Teflon
®
mask for the generation of a wedge-shaped pattern. (b) Local wetting of mineral oil on the modified nonwoven; the oleophobic areas on the oleophilic nonwoven were produced by local photo-grafting of poly-PFDA.
Figure 6.5
SEM micrograph of a multifilament yarn made of regenerated cellulose (viscose) fibers. Grey lines indicate the outer part of the yarn where fibers can be assumed to be affected by UV-grafting and UV laser irradiation. “Inner” surfaces in the capillary marked in red will remain unmodified, thus will be oleophilic in the presented example.
Chapter 7
Figure 7.1
Photograph of experimental setup for underwater investigation.
Figure 7.2
Surface topography and rms roughness of nanorough Al
2
O
3
coatings (upper row: scan size 1 × 1 µm
2
, lower row: scan size 10 × 10 µm
2
).
Figure 7.3
PSD functions of nanorough Al
2
O
3
coatings and untreated substrate.
Figure 7.4
CA behavior as a function of wetting time t
w
of Al
2
O
3
coatings with varying roughness and an untreated substrate.
Figure 7.5
Advancing CA and receding CA of Al
2
O
3
coatings with varying roughness and an untreated substrate. Insets show: (a) underwater oleophobicity of sample #1 and (b) underwater superoleophobicity of sample #3.
Figure 7.6
Advancing CA and receding CA of Al
2
O
3
coatings with additional top layer and an untreated substrate.
Figure 7.7
Samples immersed in water: Advancing CAs of Al
2
O
3
coatings and an untreated substrate with top layer minimizing surface energy. Two wetting cases for sample #4 under water are oleophobic (1
st
) and oleophilic (2
nd
).
Chapter 8
Figure 8.1
Aqueous MWCNT nanofluids (a) immediately after synthesis (b) after 1 week of preparation.
Chapter 9
Figure 9.1
(a) Configuration of electrowetting on dielectric (EWOD). (b) Enlarged view of the three-phase contact line and charge distribution upon applying voltage.
θ
is contact angle,
γ
SL
, γ
SG
and
γ
LG
are interfacial tensions of solid-liquid, solid-gas and liquid-gas interfaces, respectively.
Figure 9.2
Water droplet actuation by EWOD in parallel-plate configuration.
Figure 9.3
Schematic of liquid-dielectrophoresis (L-DEP).
Figure 9.4
Microfluidic L-DEP by Jones [21]. The liquid drop is elongated in the direction out of the paper when a voltage is applied to the two electrode strips.
Figure 9.5
(a) Schematic of discrete dielectric droplet transport driven by L-DEP force. (b)–(g) Dielectric droplet splitting, transporting and merging (from Ref [40]).
Figure 9.6
(a) Schematic of parallel-plate configuration, where dielectric and water droplets are actuated by L-DEP and EWOD, respectively. (b) Electrical circuit model for the system.
Figure 9.7
Top and side views of droplet spreading by dielectrowetting. Upon applying voltage, (a) the droplet is elongated along the electrodes; (b) the contact angle decreases.
Figure 9.8
The contact angle change of propylene carbonate sessile droplet by dielectrowetting. The solid line is from Equation (9.6). The inserts show the side views of droplet at (a) 0 V, (b) 180 V and (c) 236 V. The frequency of the applied voltage is 20 kHz.
Figure 9.9
Top views of a droplet (~1.5 µL) spreading at different voltages: (a)–(d) 0 V, 180 V, 220 V, 240 V, (e)-(h) 280 V, 320 V, 360 V and back to 0 V. The scale bar is 2 mm.
Figure 9.10
Contact angle versus voltage under the effect of dielectrowetting for DI water with and without surfactant at 55 kHz.
Figure 9.11
(a) Schematic of periodic wrinkle at the air-liquid interface generated by dielectrowetting. (b) Increasing amplitudes with voltages. The device was under an optical interferometer, and the optical interference fringes were produced by the wrinkle. (from Ref [27])
Figure 9.12
Schematic of dielectrowetting microfluidic device for droplet manipulations.
Figure 9.13
Sequential images of droplet splitting and transporting (dielectric fluid). The voltage is 360 V. The scale bar is 2 mm.
Figure 9.14
Splitting and merging of multiple (three) droplets in one operation for dielectric liquid (360 V). The scale bar is 2 mm.
Figure 9.15
Procedure for droplet generating. (a) place a droplet (~ 22 pL) of propylene carbonate on the reservoir pad; (b) turn on the three electrode pads (360 V, 20 kHz) to stretch the fluid on them; (c) turn off the middle one to cause necking of the stretched fluid; (d) turn off all the pads to attain a small droplet (~0.9 pL) on the right. The voltage is 360 V, 20 kHz. Scale bar: 2 mm.
Figure 9.16
(A) Sequential images of DI water splitting. (B) Sequential images of DI water transporting. Scale bars are 2 mm. (55 kHz, 340 V)
Figure 9.17
Volume effect on droplet splitting for three different liquids: DI water with surfactant (red triangles), propylene carbonate (blue circles), DI water (black squares). The three broken lines show the threshold volumes where splitting occurs for the respective liquids. The left region of each threshold line means “split” while the right region means “no split”. All the experiments were carried out at 340 V, 55 kHz without top cover plate.
Chapter 10
Figure 10.1
Configuration of the ultrasonic imprinting process for micropattern replication, in which micropatterns are replicated on the whole region of the target film [42].
Figure 10.2
Stepwise description of the ultrasonic imprinting process [43].
Figure 10.3
Configuration of the selective ultrasonic imprinting process using a profiled mask, in which micropatterns are replicated on the masked region (H-shape) only [42].
Figure 10.4
Comparison of ultrasonic wave propagation characteristics according to the mask shape: (a) positive mask, and (b) negative mask [42].
Figure 10.5
Fabrication of a nickel micromold using MEMS process: (a) fabrication procedure; (b) SEM micrograph of the fabricated nickel stamp [45].
Figure 10.6
Configuration of selective ultrasonic imprinting using a profiled mask film with a negative ‘#’-shape: (a) top view; and (b) side view.
Figure 10.7
Temperature distributions after ultrasonic imprinting: (a) normal imprinting; and (b) selective imprinting.
Figure 10.8
Replicated micropatterns by selective ultrasonic imprinting: (a) Replicated micropatterns in different regions (A, B and C); and (b) SEM images of the replicated micropillars in Region B (isometric, top and side views).
Figure 10.9
Surface treatments for the selected regions: (a) hydrophobic silane coating for the negative region; (b) e-beam irradiation for the positive region.
Figure 10.10
EDS analysis results for the coated micropillars: (a) Top region; and (b) Side region.
Figure 10.11
Comparison of CAs for the plain region and patterned-and-coated region.
Figure 10.12
Photographs and detailed view for the selectively irradiated sample. Regions D, E, and F denote plain, patterned-and-coated, and e-beam irradiated regions, respectively.
Figure 10.13
Analyses of the e-beam irradiated (F) regions: (a) CA measurement; and (b) XPS analysis.
Figure 10.14
Comparison of water collection shapes at different treatment stages: (a) Plain PC sample; (b) After selective micropatterning; (c) After e-beam irradiation; and (d) After hydrophobic silane coating.
Figure 10.15
Movements of water droplets at the superhydrophobic-hydrophilic interface points.
Figure 10.16
Development of a hybrid surface with a combination of three surface treatments: (a) Stepwise development of the three treatments; (b) CAs measured in the six different regions.
Chapter 11
Figure 11.1
Biofouling on different surfaces immersed in water: (a) analysis device, (b) ship, and (c) screw. Reprinted from [11–13].
Figure 11.2
Schematic representation of the time dependent processes of marine fouling organisms. Reprinted from [17].
Figure 11.3
Representation of two models for biofouling growth (a) Sequential stages of fouling development on a surface. (b) Biofouling growth based on the probability that a particular organism will first colonise the substratum.
Figure 11.4
Antifouling options: (a) coatings containing biocides, (b) foul release coating, (c) superhydrophobic coating.
Figure 11.5
Anti-fouling mechanism of a superhydrophobic surface.
Chapter 12
Figure 12.1
(a) Corrosion of metallic materials [5] and (b) formation of a localized electrode pair (i.e., anode and cathode) on metal surface for corrosion reaction.
Figure 12.2
Water droplet on the lotus leaf (a) real image and (b) scanning electron microscopy (SEM) images of micro-nanostructures of lotus leaf [43, 44]. White scale bar = 20 µm.
Figure 12.3
Schematics of (a) an electrochemical double layer on negatively charged metal surface and (b) a three-electrode system for electrochemical corrosion test. (c) A typical
i vs.
η plot for the Butler-Volmer equation and (d) the Tafel plot (log
i vs. η
) to obtain corrosion potential (E
corr
) and corrosion current density (i
corr
).
Figure 12.4
(a) Contact angle (CA) on a smooth solid surface (Young’s model [69]), Wetting states on a rough surface: (b) Wenzel model [70] and (c) Cassie-Baxter model [71].
Figure 12.5
Schematic cross sections of superhydrophobic surfaces on metallic materials: (a) textured metal surface with a coating of low surface energy material, (b) textured coating of low surface energy material on metal, and (c) textured porous structure on metal surface with a coating of low surface energy material.
Figure 12.6
SEM images of the superhydrophobic surfaces on aluminum alloy and lotus leaf: (a) and (b) are the surfaces fabricated by chemical etching in HCl solution, (c) and (d) are the SEM images of lotus leaf[102, 131].
Figure 12.7
Morphology of the as-prepared superhydrophobic surface on the aluminum alloy: (a) SEM image showing microscale structure by laser irradiation, (b) 3-D image by confocal laser scanning microscopy, and (c) SEM image showing nanoscale structure after chemical etching [130].
Figure 12.8
SEM images of the as-prepared superhydrophobic surfaces obtained in ethanol based solution (Cerium(III) nitrate hexahydrate (0.05 M) + myristic acid (0.2 M)) at different electrodeposition voltages: (a) 10 V, (b) 20 V, (c) 30 V, (d) 40 V, (e) 50 V, and (f) 60 V [108].
Figure 12.9
FE-SEM micrographs of an aluminum alloy surface after different treatments: (a) cleaning, (b) dipping in boiling water, and (c) stearic acid modification. (d) Photograph of a10 µL water droplet on the superhydrophobic aluminum alloy surface, and the insert shows a droplet with a water contact angle of 155° and a rolling angle of 5° [111].
Figure 12.10
SEM images of anodic alumina nanostructures fabricated by a hard anodization (HA) process at 130 V and 1 °C in 0.3 M oxalic acid with varying anodization intervals (0–60 s at every 10 s): (a) planar pore nanostructures; (b) single pillar-on-pore nanostructures of low aspect-ratio tips; (c–f) bundled pillar-on-pore nanostructures with increasing bundle size. Each row represents tilted, top, and side views, respectively. The last row shows higher magnification images of the sidewalls of the base pore structures [141]. Scale bars = 1 µm.
Figure 12.11
SEM images of aluminum surface prepared with silica sol-gel coating of tetraethylorthosilicate (TEOS)/ vinyltriethoxysilane (VTES) as co-precursors under different molar ratios between ammonium hydroxide (NH
4
OH) and ethanol, (a) 0.096; (b) 0.28; (c) 0.48 and (d) 0.86 [121]. Images of water droplet and its contact angle (WCA) are shown as inserts.
Chapter 13
Figure 13.1
ADSA data for selected liquids (see Kwok
et al.
[23]). First column formamide (FA), second glycerol(GLY) and third methylene iodide (aka diiodomethane) (MeI). Bottom row shows drop radius, r(cm) for spreading liquid versus time. The first row shows calculated surface tension (mN/m) and the second row contact angle (degrees). Only glycerol shows wetting characteristics consistent with Kwok and Neumann’s [4] requirements. MeI (diiodomethane or methylene iodide) shows stick-slip behavior while formamide shows decreasing contact angle with time of exposure. The graphs show representative behavior of selected liquids listed in Table 13.1. The problems shown here might go unnoticed if only goniometer data were collected.
Figure 13.2
Cos (
θ
) versus liquid surface tension for data listed in Table 13.1. Gray points are goniometer data and black points are ADSA data. Lines show fit of the data meeting the Kwok and Neumann assumptions in Table 13.1 to the Kwok-Neumann model. The fitted constants are listed in the text. Solid line is for the propyl polymer. The dashed line is for the hexyl polymer. ADSA data show a better fit to Kwok and Neumann’s equation than do goniometer data due to inclusion of data not fully meeting the assumptions required for application of Young’s equation. The data point near 50 nN/m is for methylene iodide (diiodomethane) which exhibits stick-slip spreading.
Figure 13.3
Cosine of calculated contact angle versus liquid surface tension for both propyl and hexyl polymers. Methylene iodide data have been excluded from the above plot. The predicted contact angles calculated from each of the three models discussed in this paper are comparable but the contact angles calculated from the van Oss, Chaudhury and Good model deviate the most when compared to the other models. C-C: Chen and Chang model. vOCG: van Oss, Chaudhury and Good model. K-N: Kwok and Neumann model.
Figure 13.4
Standard Error of the Residuals (Cos
θ
calc
– Cos
θ
expt
) for fits of Goniometer Data to either the van Oss, Chaudhury and Good model or the Chen and Chang model. Removal of methylene iodide from the data set improves the fit of both models. The Chen and Chang model generally has smaller residuals when compared to the van Oss, Chaudhury and Good model. The data from the Kwok and Neumann model show comparable errors. The ADSA data were used by Kwok and Neumann for the purposes of fitting their model. The goniometer data used are for all liquids that Kwok and Neumann studied except for those which showed stick-slip behavior (e.g. MeI)
Figure 13.5
Calculated values [20] of
γ
LW
and
γ
AB
(mJ/m
2
) for PMMA using the Owens and Wendt model. The figures suggest these parameters vary with the choice of liquid pairs. This variation is due to the experimental errors in the contact angle measurements. The liquids used are water (WT), bromonaphthalene (BN), methylene iodide (MI), tricresyl phosphate (TP), glycerol (GL) and formamide(FA).
Figure 13.6
W
a
vs. γ
LW
and γ
AB
of the probe liquids for PMMA. Points - the experimental data. Surface- fit to Owens and Wendt model. Units are mJ/m
2
.
Chapter 14
Figure 14.1
(a) Contact angle according to Young conditions, (b) Contact angle measured under real conditions.
Figure 14.2
(a) Image of the liquid contact angle, (b) Image of the liquid drop on the solid surface seen from the top.
Figure 14.3
Advancing, receding and equilibrium contact angles of water on the surfaces of ST-NP40, ST-MP4, ST-NP9, SN-NP40, SN-MP4 and SN-NP9 films.
Figure 14.4
Apparent surface free energy calculated from the CAH approach for the ST–NP40, ST–MP4, ST–NP9, SN–NP40, SN–MP4 and SN–NP9 films.
Figure 14.5
Optical microscopy images of surfaces of (a) ST–NP40, (b) ST–MP4, (c) ST–NP9, (d) SN–NP40, (e) SN–MP4 and (f) SN–NP9 films.
Figure 14.6
3D images from optical profilometry (0.9 × 1.3mm) for (a) ST–NP40, (b) ST–MP4, (c) ST–NP9, (d) SN–NP40, (e) SN–MP4 and (f) SN–NP9 films.
Figure 14.7
Side profiles from optical profilometry for (a) ST–NP40, (b) ST–MP4, (c) ST–NP9, (d) SN–NP40, (e) SN–MP4 and (f) SN–NP9 films.
Figure 14.8
SEM images with the layer magnification 20000×, 10000× and 5000× (a) ST–NP40, (b) ST–MP4, (c) ST–NP9, (d) SN–NP40, (e) SN–MP4 and (f) SN–NP9.
Figure 14.9
Model of wettability on an irregular rough surface.
Chapter 15
Figure 15.1
Pyrolytic carbon disc.
Figure 15.2
Fix-All adhesive used to glue the reference materials onto the aluminum block.
Figure 15.3
Aluminum block.
Figure 15.4
An unopened BioGlue syringe.
Figure 15.5
Attachment 1 of the BioGlue syringe.
Figure 15.6
Attachment 2 of the BioGlue syringe.
Figure 15.7
The push-off test device.
Figure 15.8
The attachment used for this experiment.
Figure 15.9
Hardened BioGlue droplet.
Figure 15.10
A graphical representation of data in Table 15.3.
Figure 15.11
A graphical representation of data in Table 15.4.
Figure 15.12
A graphical representation of average bond strength values from Table 15.3 and Table 15.4.
Figure 15.13
A graphical representation of the data in Table 15.5.
Figure 15.14
A graphical representation of the data in Table 15.6.
Figure 15.15
A graphical representation of average bond strength values from Tables 15.5 and 15.6.
Figure 15.16
Bond strength (BioGlue-to-Reference Materials) vs gamma c. Note: ‘gamma c’ refers to γ
c
and R-Sq refers to the R
2
value. The R
2
(adj) is a variant of the R
2
that has been adjusted for the number of predictors. S represents the average distance between the observed values and the regression line.
Figure 15.17
Bond strength (BioGlue-to-Reference Materials) vs gamma d. Note: ‘gamma d’ refers to γ
d
and R-Sq refers to the R
2
value. The R
2
(adj) is a variant of the R
2
that has been adjusted for the number of predictors. S represents the average distance between the observed values and the regression line.
Figure 15.18
Bond strength (BioGlue-to-Reference Materials) vs gamma p. Note: ‘gamma p’ refers to γ
p
and R-Sq refers to the R
2
value. The R
2
(adj) is a variant of the R
2
that has been adjusted for the number of predictors. S represents the average distance between the observed values and the regression line.
Figure 15.19
Bond strength (BioGlue-to-Reference Materials) vs gamma s. Note: ‘gamma s’ refers to γ
s
and R-Sq refers to the R
2
value. The R
2
(adj) is a variant of the R
2
that has been adjusted for the number of predictors. S represents the average distance between the observed values and the regression line.
Figure 15.20
Bond strength (BioGlue-to-Reference Materials) vs gamma c. Note: ‘gamma c’ refers to γ
c
and R-Sq refers to the R
2
value The R
2
(adj) is a variant of the R
2
that has been adjusted for the number of predictors. S represents the average distance between the observed values and the regression line.
Figure 15.21
Bond strength (BioGlue-to-Reference Materials) vs gamma d. Note: ‘gamma d’ refers to γ
d
and R-Sq refers to the R
2
value. The R
2
(adj) is a variant of the R
2
that has been adjusted for the number of predictors. S represents the average distance between the observed values and the regression line.
Figure 15.22
Bond strength (BioGlue-to-Reference Materials) vs gamma p. Note: ‘gamma p’ refers to γ
p
and R-Sq refers to the R
2
value. The R
2
(adj) is a variant of the R
2
that has been adjusted for the number of predictors. S represents the average distance between the observed values and the regression line.
Figure 15.23
Bond strength (BioGlue-to-Reference Materials) vs gamma s. Note: ‘gamma s’ refers to γ
s
and R-Sq refers to the R
2
value. The R
2
(adj) is a variant of the R
2
that has been adjusted for the number of predictors. S represents the average distance between the observed values and the regression line.
Figure 15.24
Plot showing comparison of the two titanium alloy specimens and 316 LSS.
Figure 15.25
Beilby layer formation. (Source: http://www.ewp.rpi.edu/)
Chapter 16
Figure 16.1
Typical 3-D profiles of (a) the as-received polyamide 6,6 and the CO
2
laser surface engineered polyamide 6,6; (b) NH50 and (c) NH100 samples.
Figure 16.2
Typical 3-D profiles of (a) the as-received PTFE sample (PAR) and the CO
2
laser surface engineered PTFE; (b) PT50 and (c) PH100.
Figure 16.3
A graph showing the viable cell count for each sample.
Figure 16.4
SEM micrograph of typical MSCs growth on Sample NH100 following 24 hours of incubation.
Figure 16.5
SEM micrographs of the stem cells adhering and growing on (a) laser welded NiTi alloy (WZ) and (b) the base material (BM) with white arrows identifying that some cells have kept their round morphology and (c) laser welded NiTi alloy showing the oriented cell growth with a dendritic pattern.
Figure 16.6
Graph showing the stem cell coverage for each sample following 24 hours of incubation.
Figure 16.7
Graph showing the viable cell count for the polyamide 6,6 samples, PTFE samples and the NiTi samples (WZ, HAZ and BM).
List of Tables
Chapter 1
Table 1.1
Summary of the most well-known models for contact angles on real surfaces.
Table 1.2
Example of colour gradients in BMP images. The 5-point regression is less sensitive to noise (no. 11 and 13) but is more nonspecific to positions (no. 3 and 6).
Table 1.3
Important definitions and logical conditions for automatic determination of specific statistical contact angle events relative to the threshold value (lv) in the range of 40 µm/°.
Table 1.4
Statistical overview of the independently computed statistical contact angle events (≡ “global values”) for all measurements of the specific contact angle events on a rinsed wafer [8].
Table 1.5
Statistical overview of the independently counted statistical contact angle events (≡ “global values”) for all measurements of the specific contact angle events on an RCA-cleaned wafer [8].
Table 1.6
Overview of the detailed, dependent statistical analysis of the contact angle relative to the ranges in the inclination angle
φ
a)
for the rinsed wafer; see publication [8].
Chapter 2
Table 2.1
Different types of contact angles defined in the literature.
Chapter 3
Table 3.1
Surface tension of test liquids.
Table 3.2
Results of ANOVA test. Different letters indicate significant differences at p < 0.05. ns: not significant.
Chapter 4
Table 4.1
Analysis of data on the wettability of two superhydrophobic surfaces on the basis of Eq. (4.8).
Chapter 7
Table 7.1
κ
B
values of nanorough Al
2
O
3
coatings.
Chapter 8
Table 8.1
Summary of nanofluid wetting behavior results reported in literature and our interpretations.
Chapter 10
Table 10.1
Comparison of wettability with different combinations of coating and micropatterning treatments
Table 10.2
Comparison of XPS surface analysis results in various regions with different treatments.
Chapter 12
Table 12.1
Summary of corrosion resistance of hydrophobic/superhydrophobic surfaces of aluminum and its alloys.
Chapter 13
Table 13.1
Measured contact angles (degrees) of various liquids on Poly(propene-alt-N-(n-propyl) maleamide and Poly(propene-alt-N-(n-hexyl) maleamide. Bold - ADSA confirms that proper assumptions are met. Gray - asssumptions not met and van Oss, Chaudhury and Good as well as Chen and Chang parameters are unknown. Normal type - asssumptions not met and van Oss, Chaudhury and Good as well as Chen and Chang parameters are known. ss - stick-slip behavior observed.
Table 13.2
Calculated values of the surface free energy and surface free energy components (mJ/m
2
) for both propyl and hexyl polymers.
Table 13.3
Surface tension components (mN/m) of liquids as reported by Dalal [20].
Table 13.4
Contact Angles (deg) of the Probe Liquids of Table 13.1 on the Tested Polymers [20].
Table 13.5
Fit of Dalal’s data to the Owens and Wendt Model.
Table 13.6
Fit of Dalal’s Data to the van Oss, Chaudhury and Good Model.
Table 13.7
Fit of Dalal’s Data to the Chen-Chang model.
Table 13.8
Corrected fit to Owens and Wendt Model.
Table 13.9
Corrected Fit to Chen and Chang model.
Table 13.10
Corrected Fit to van Oss, Chaudhury and good model.
Table 13.11
AICc* values for the model fits.
Table 13.12
AICc weights*.
Table 13.13
Comparison of fits to van Oss, Chaudhury and Good Model using Dalal’s original data (5 points) to a Simulated Data Set containing 20 points (4 replicates for each liquid)
Chapter 14
Table 14.1
List of silica powders used in the study.
Table 14.2
Roughness parameters for studied samples.
Chapter 15
Table 15.1
Table 15.2
List of tissues used in the study.
Table 15.3
Results from the first set of 7 reference materials.
Table 15.4
Results from the second set of 7 reference materials.
Table 15.5
Tissue-to-tissue bond strength (SuperGlue).
Table 15.6
Tissue-to-tissues bond strength (BioGlue).
APPENDIX: Table 15.1
(Compiled by: The Industry/University Center for BioSurfaces, University at Buffalo)
Chapter 16
Table 16.1
Common applications for polymers within the biomedical industry.
Table 16.2
Table showing roughness, contact angle and the corresponding surface free energy for each polymeric sample.
Table 16.3
Surface atomic composition and the surface roughness parameters for the various weldment regions.