Contact angle imagej

Contact angle imagej DEFAULT
This plug-in calculates the contact angle of a drop on a flat surface using the sphere approximation (theta=2atan(2h/l) and the ellipse approximation. This code has been written by Marco Brugnara and itos based on the plug-in "Pointpicker".

The necessity to have a self-developed software comes by considering that commercial softwares do not provide a sufficient enough description of the methods used in their contact angle calculation. In fact people often perform contact angle measurements, by applying the sphere approximation, neglecting in this way the gravity effect, or by calculating the tangent of the profile without limit the drop volume. In our experience, confirmed by the Literature as well, the maximum volume, whose profile as a sphere shape, is about 3-5 microlitres; it depends on the contact angle as well. For bigger drops the other possible approaches are 2: to use some "correction factors", present in Literature, or to apply another model called ADSA, which in fact calculates the angle applying on the profile the Laplace equation. This last model works really well on profiles strongly modified by the gravity, instead it has some trouble by solving the equation if the drop has an almost spherical profile. It is important to underline that in many commercial packages coming with the devices, it is often present another approach called in general "tangent line" which calculates the tangent of a fitting curve of the drop profile near the triphase line. This approach is a least debatable, if the best-fit function is polynomial equation, chosen only for its low chi square, but without any physical meaning. Then way to analyze images can furnish precise results, which are however meaningless if the drop volume is too large: in fact the contact angle is not the geometrical angle if this last one is modified by other forces than surface tension. In fact if the shape depends significantly on the gravity force, the resulting angle is not a value of contact angle as defined in Theory, but just an angle depending on the gravity. It is a pity that who develops these programs, most of the times does not know the Literature.

In our plug-in the image analysis works offline; it means that an image database is required. After a picture is loaded, the drop profile is detected. It is important to remind that the program was written supposing the drop is upside down. The reason is that our images are obtained by a camera connected to a microscope and the final picture is reversed up/down.

A manual detection of the base line is required, by choosing the FIRST 2 points. For this reason the plug-in could fail if the triphase line is not a straight line.

In the PlugIn Preferences menu the user finds the option "boundary conditions" where one can include or exclude one or both of these points in the drop profile.

Other 3 points are then requested along the drop profile in order to identify a ROI.

In order to calculate to contact angle, four different options are possible:

  • a Manual points selection
  • a measurement by using a circle best-fit
  • a measurement by using an ellipse best-fit
  • an analysis by applying both bestfits
When the manual points selection is chosen, the user need to detect the profile manually placing some points along the drop edge. The circle and the ellipse passing trough the points are reckoned.

The best-fit analysis automatically detects the drop profile; for this reason a very well defined picture is required. The user has the possibility to modify the threshold in order to exclude the main part of the background. After these points are automatically collected a best fit procedure of a circle or an ellipse or both can be applied.

It is important to point out that an ellipse best-fit analysis poses itself between the circle best fit (which has a physical meaning) and an absolute best-bit function. Some times can happen that the drop is not perfectly symmetric, or that there is a slight effect of the gravity. In this case an almost-circle analysis can provide useful results.

Our plug-in is completely open source and in a constant developing and there are still many things to improve. For instance many error controls are not implemented yet, so if points are chosen in the wrong sequence, the user just obtains meaningless results.

A sample image is available.


DropSnake Method for contact angle measurement of droplet


I am new to ImageJ, but would like to perform a contact angle measurement of droplets on several surfaces. I found that ImageJ with the plugin drop_analysis can do this with either the so-called LB-ADSA or the DropSnake method. As my samples are not completely leveled, I think the DropSnake method will work best. I have downloaded both ImageJ and the plugin from this page: and I am following this manual: I try to follow the steps in this manual but do not success completely. When I follow the steps as in “Typical Utilization” for DropSnake, as described on page 2, I am unable to attain the optimal red line/dots around the droplet (as they do in this video: It is like the buttons are unable to be pressed down. Does anyone know they reason for this? I would really appreciate any help!!

Best Regards,

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How do you measure contact angle in ImageJ?

  1. Measuring the Contact Angle in ImageJ (with the plug-in Contact Angle) Run ImageJ, open an image,
  2. and click Plug-In -> Contact Angle. To close the plug-in after.
  3. complete measurement for.
  4. Back to ImageJ, then Done.
  5. and right contact angles, 3 on the.
  6. Click the icon Point List, then.
  7. In the Result dialog:
  8. CIRCLE)

How do you measure contact angles?

Commercial contact angle goniometers employ a microscope objective to view the angle directly. In the static method a drop is deposited on a surface and the contact angle can be measured by looking at the drop through a goniometer (an instrument that measures contact angles).

How do you manually measure contact angles?

The sessile drop method is by far the most commonly used method to measure contact angle. It involves a syringe pump to produce the droplet of liquid (usually water), and a camera to observe the droplet on a substrate.

What is water contact angle?

Contact angle is a measure of wettability When a drop of water is placed on a solid, it will spread on the surface based on the intermolecular interactions between the solid and the liquid. Water contact angle will immediately give an indication of the wettability of the solid.

What is the unit of angle of contact?

The contact angle is the angle, conventionally measured through the liquid, where a liquid–vapor interface meets a solid surface. It quantifies the wettability of a solid surface by a liquid via the Young equation.

What is meant by angle of contact?

physics. : the angle between the meniscus and the containing walls of a column of liquid measured from the vertical wall below the surface of the liquid to the position of the tangent to the meniscus at its point of contact with the wall.

What is angle of contact give example?

Angle of contact is the angle at which a liquid interface meets a solid surface. It is denoted by θ. It is different at interfaces of different pairs of liquids and solids. For example: – Droplet of water on louts leaf. The droplet of water(Liquid) is in contact with the solid surface which is leaf.

What are the factors affecting angle of contact?

The angle of contact depends upon the liquid’s nature and the solid in contact and the medium which exists above the free surface of the liquid.

What is angle of contact in surface tension?

Contact angle is measured as the angle where a liquid or a vapor (but most often a liquid) interacts with a solid surface. Contact angle analysis is used to measure the quality of a solid surface. Surface tension analysis is used to measure the quality of a liquid.

What is the angle of contact in case of mercury?

When the adhesive forces are greater than the cohesive forces, a lower meniscus is formed and hence the angle of contact is an acute angle. Now, we can understand that when the liquid is mercury, the cohesive forces are greater than the adhesive forces. Therefore, the angle of contact is an obtuse angle.

What is the value of angle of contact for mercury?

It is about (8°). ✿ The angle of contact can have any value between 0 and 180 .

Why is the angle of contact obtuse in case of mercury?

The angle made by the mercury from the glass surface is always obtuse. The adhesive force between the molecules of glass and water is more than the cohesive force between the molecules of water. This results in the formation of a concave meniscus for the surface of water.

Why should detergents have small angle of contact?

Water with detergent dissolved in it has small angles of contact (θ). This is because for a small θ, there is a fast capillary rise of the detergent in the cloth. The capillary rise of a liquid is directly proportional to the cosine of the angle of contact (θ).

Why are drops and bubbles spherical?

The attractive force of surface tension causes the bubbles to take spherical shape. Because a sphere has the smallest surface area compared to other shapes with the same volume occupied, so it enables the particles to pack together close enough to achieve the tightest possible grouping than any other shape.

What is the cause of excess pressure inside a soap bubble?

Answer: Due to surface tension, the molecules on the surface film experience the net force in the inward direction normal to the surface. Therefore, there is more pressure inside than outside.

What is the excess pressure inside a soap bubble?

2×(2πRT). Hence the Excess pressure ΔP=8pa inside the bubble, So option D is correct.

How do you find excess pressure?

Let the external pressure be Po and the internal pressure P1. Both these formulae show that the excess pressure within a small bubble is greater than that within a larger bubble. Calculate the excess pressure within a bubble of air of radius 0.1 mm in water. Excess pressure = 2T/r = [2×72.

What is the pressure inside the drop of mercury?

Excess pressure inside a liquid drop =2Sr, where S is the surface tension of the liquid and r is the radius of drop. Hence the pressure inside the drop of the mercury is 1.0131×105Pa and the excess pressure inside the drop is 310 Pa.

Why excess pressure in a soap bubble is twice the excess pressure of a liquid drop of same radius?

Why excess pressure in a soap bubble is twice the excess pressure of a liquid drop of the same radius? Answer: A soap bubble has two free surfaces, one internal and another external; whereas liquid drop has only one outer free surface.

What is the phenomenon of surface tension?

Surface tension could be defined as the property of the surface of a liquid that allows it to resist an external force, due to the cohesive nature of the water molecules.

What is the excess pressure inside a bubble of soap solution of radius 5 mm?

Therefore, the excess pressure inside the soap bubble is 20 Pa.

What is the excess pressure inside a drop of mercury of radius 2 mm?

Excess pressure inside a drop is given as p = 2S/r.

On what factors the access pressure inside a drop of mercury depends?

The pressure inside a spherical drop is greater than the pressure outside. The way in which the excess pressure P depends on the radius a of the drop, and the surface tension γ and density ρ of the liquid is amenable to dimensional analysis.

Why is pressure inside a soap bubble greater than outside pressure?

There are two free surfaces of soap bubble. Due to surface tension, the molecules on the surface film experience the net force in the inward direction normal to the surface. Therefore, there is more pressure inside than outside.

Why is concave side pressure higher than convex side?

Answer. it depends on Surface tension. there is always an extra pressure of liquid drop if it’s on concave surface when it’s compared with convex side excess pressure would be less…

When a drop of liquid splits up into a number of drops?

When a liquid drop splits into a number of drops, area increase. As energy is required for increasing the surface area, hence energy is absorbed. So (d) is correct.

Which way is concave?

Convex and concave are two words that describe a line or shape, often in mathematics, science, or in relation to eyeglasses and mirrors. While convex means to bend or protrude outwards, concave is the opposite and means to bend inwards.

Why does salt increase surface tension of water?

Because of its charge, water molecules bind strongly to the ion. More strongly than they do to each other. So adding salt strengthens the network of intermolecular bonds in the water. So since surface tension is due to the intermolecular bonds, stronger intermolecular bonds will lead to higher surface tension.

ImageJ Contact Angle Measurement Tutorial

Drop Shape Analysis

Written by Aurélien Stadler and Daniel Sage

Contact angle is a simple and yet powerful tool for characterizing three-phase junctions. The technique of the sessile drop is today the most widely used method to measure this parameter. The commercial softwares available today are still very limited. They are often dependant of one measurement setup, and may fail under non-standard conditions.

We propose, here, two new methods to high-accuracy measure contact angles:

  • DropSnake is based on B-spline snakes (active contours) to shape the drop.
  • LBADSA is based on the fitting of the Young-Laplace equation to the image data
These methods have been implemented as a Java plug-in for the ImageJ software and we make it freely available. See the "free software" section to download.


[1] A.F. Stalder, T. Melchior, M. Müller, D. Sage, T. Blu, M. Unser, "Low-Bond Axisymmetric Drop Shape Analysis for Surface Tension and Contact Angle Measurements of Sessile Drops," Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2010.

[2] A.F. Stalder, G. Kulik, D. Sage, L. Barbieri, P. Hoffmann, "A Snake-Based Approach to Accurate Determination of Both Contact Points and Contact Angles," Colloids And Surfaces A: Physicochemical And Engineering Aspects, 2006.

Main Features

  • Interface detection: Considering that the interface position is a crucial parameter when measuring contact angle, the drop reflection has been integrated into the drop model, so that to detect the interface position.
  • Interpolated gradient-based energy: In order to provide high precision contact angle on a wide range of images, a drop detection method based on image gradient energy and cubic spline interpolation has been used. Based on this framework, two complementary drop models have been designed.
  • B-Spline Snake The B-snake approach provides a novel methodology suitable to drops that do not follow a global model. Its new model is based on B-spline snake which in reason of their elasticity unify the aspects of locality of the contact angle to the guidance provided by the global drop contour. With this approach, the whole drop shape is used to provide global information, nevertheless, the contact angle measurement remains local and similar to a polynomial fit.
  • Low Bond Axisymmetric Drop Shape Analysis This model is derived from a first order perturbation solution of the Laplace equation for axisymmetric drops. Using this global model of a drop, contact angles are obtained considering the whole drop profile. While offering a fair domain of application, this approximation is computationally much more efficient than a solution obtained from numerical integration (ADSA approach).

The software is based on a plugin for ImageJ, a general purpose free image-processing package. ImageJ has a public domain licence; it runs on several plateforms: Unix, Linux, Windows and Mac OS X.

Warning: Some users have encountered incompatibility with ImageJ versions higher than 1.47. In case of troubles, we recommend to use the ImageJ version 1.46 including Java. This version ij147-jdk6-64bit-setup.exe or ij147-jdk6-setup.exe is available at:

1. Installation

Get a copy of ImageJ. and download the plugin Extract in the "plugins" folder of ImageJ. All the files should extract in a new folder "drop_analysis". The whole process should not take more than a couple of minutes.

2. How of use

Open a drop image. Ensure that the image is grayscale. In the "plugin" menu, go under "drop_analysis" and choose one of the two methods: "LB_ADSA" or "DropSnake".

3. Contact

Daniel Sage

4. Conditions of use

You are free to use this software for research purposes, but you should not redistribute it without our consent. In addition, we expect you to include adequate citation whenever you present or publish results that are based on it.

5. Screenshot

Thanks to Laura Barbieri and to Marco Brugnara for the images.

  • the ImageJ's plugin
  • the manual
  • an image sample

Warning: Some of the unzip tools produce a drop_analysis folder inside of a drop_analysis folder. This hierarchical structure is not compatible for the image plugins. The correct structure is: ImageJ » plugins » drop_analysis » drop_analysis.jar

DropSnake Measurement

LB-ADSA Measurement


Angle imagej contact

Jonas M. Ribea, Nils R. Skovb, Ole-Andreas K. Kavlia, Armend G. Håtia, Henrik Bruusb and Bjørn T. Stokkea

a Department of Physics, Norwegian University of Science and Technology, NO–7491 Trondheim, Norway

b Department of Physics, Technical University of Denmark, DK–2800 Kongens Lyngby, Denmark

[email protected]

Why Is This Useful?

Contact angle measurements are important for characterizing the wettability of a liquid to a solid surface. In microfluidics they are of special interest as they provide insight into the intermolecular interactions between the sample liquid and the microchannel surface. Contact angle measurements are also important when assembling polydimethylsiloxane (PDMS) devices using oxygen plasma bonding. For optimal bond strength the water contact angle of plasma treated PDMS should be minimized as shown by Bhattacharya et al. [1] A current hurdle in measuring contact angles is the requirement of a setup that is expensive and non-portable. Here we show a method for measuring contact angles using materials and equipment found in a typical microfluidics lab.

What do I need?



  • Smartphone
  • Digital scale
  • Desiccator with vacuum pump
  • Oven
  • Syringe pump (optional)
  • Light source

For measurements:

  • Pipette (0.5–3μL)
  • Sample (e.g. deionized (DI) water or other liquid sample)

What do I do?

Prepare PDMS:

  1. Weigh 10:1 PDMS (Sylgard 184) in a plastic cup on the digital scale
  2. Mix the PDMS by hand using a plastic spoon
  3. Degas the PDMS in a desiccator to remove the bubbles

Make PDMS-lens:

  1. Use the tip of the plastic spoon handle (or a pipette) to place a small droplet of uncured PDMS in the center of a glass cover slip. Repeat with various amounts of PDMS to obtain lenses with varying magnification.
  2. Mount the cover slips upside down (e.g. between two glass slides) and cure the PDMS hanging at 70 °C for 15 min. Longer curing times might be necessary, if the drop is relatively large.
  3. Center the PDMS-lens over the camera of your smartphone and fixate it using tape.
  4. Test the focus of your camera. For our camera setup the best images were captured with lenses that focus around 2 cm.

Contact angle measurements:

Smartphone contact-angle setup: (A) Focus test of a PDMS lens. (B-C) The smartphone mounted on a syringe pump. The PDMS-lens is mounted on the front facing camera of an iPhone 6S and the sample is centered in front of the lens. The sample is mounted on the pusher block of a syringe pump which can be moved to adjust the focus.

  1. Make a sample stage preferably using a syringe pump or some other system that you can move. We mounted the smartphone on the syringe holder block with the camera pointing towards the pusher block. Make a sample holder on the pusher block using glass slides or other consumables found in the lab. Align the center of the stage with the center of the camera. Tip: aligning is easier if done using the sample that you want to measure. Put the sample on the block and move it into focus by releasing the pusher block and sliding it away/towards the camera. Increase the height of the stage until the top of the sample is centered in the camera.
  2. Place the light source behind the sample and illuminate the stage evenly. Tip: put the sample stage in front of a white wall and light up the wall for a homogenous background and optimal contrast.
  3. Place a small drop (0.5–3 μL) of DI water on top of the sample using a pipette. Place the drop near the sample edge closest to the camera.
  4. Move the sample edge into focus. Block out ambient light in the room.
  5. Measure the contact angle of the drop in the image e.g. using ImageJ [2] software with a plugin for contact angle measurements [3] or get a rough estimate using an app on your smartphone.[4]

Contact angle measurements of water on PDMS: (A) Raw image from iPhone 6S front-facing camera with PDMS-lens. (B) Direct measurement using app on smartphone (based on θ/2 calculation) (C-E) ImageJ measurements using DropSnake plugin. Unmodified PDMS (C) and PDMS treated with oxygen plasma with increasing intensity (D-E).

What else should I know?

The focal length of the PDMS-lens is determined by the volume of PDMS used as described by Lee et al. [5]. However, it is difficult to control the volume of PDMS using a pipette due to the high viscosity of PDMS. We recommend making a range of lens sizes and testing them on your smartphone camera to see which gives the right focal length. If your digital scale has milligram precision you can measure the amount of PDMS used for each lens. The mass of each PDMS-lens is typically less than 10 mg. You can decrease the focal length further by adding PDMS to an already cured lens. Modern smartphones have both a rear-facing and a front-facing camera and in our experience the drop focusing was easier when using the front facing camera. The images taken here were captured with an iPhone 6S from Apple using the front-facing camera with a 5MP sensor. The weight of the cured PDMS lens was 7 mg.

Tip: you can also remove the PDMS-lens from the cover slip and place it directly on your camera. Although, it might be more difficult to center.

Calculating contact angles from images of sessile drops can be done using a range of techniques.[6] If the drop volume is small and the contact angles are not extreme, we can generally neglect droplet distortion due to gravitational effects. Extrand and Moon [7] calculated that gravitational effects can be neglected for a water droplet sitting on a hydrophilic surface (θ=5°) if its volume is less than 5 μL and less than 2.7 μL on a hydrophobic surface (θ=160°). If we assume the drop to be spherical, the contact angle can be estimated by multiplying the angle between the base and the height of the droplet by 2. This is referred to as the θ/2-method and is implemented by e.g. the Contact Angle Measurement app [4] for iOS. Sessile drop measurements are generally limited by the experimental setup and operator error, but typically has a precision of ±3°.[8] Image-processing algorithms relying on curve fitting of the droplet outline can enhance reproducibility. ImageJ [2] with DropSnake-plugin [3] uses active contours (energy minimization) to track the outline of the drop and calculate contact angles. This increases precision, but is slower and currently requires analysis on a separate computer.


The Research Council of Norway is acknowledged for the support to the Norwegian Micro- and Nanofabrication Facility, NorFab (197411/V30).


  1. S. Bhattacharya, A. Datta, J. M. Berg and S. Gangopadhyay, J. Microelectromech. S., 2005 14, 590–597
  2. ImageJ software
  3. DropSnake ImageJ-plugin for contact angle measurements
  4. Contact Angle Measurement iOS app (Japanese)
  5. W. M. Lee, A. Upadhya, P. J. Reece, and T. G. Phan, Biomed. Opt. Express, 2014, 5, 1626–1635
  6. Y. Yuan and T. R. Lee, Surface Science Techniques, Springer, Berlin/Heidelberg, 2013, 51, 3–34.
  7. C. W. Extrand and S. I. Moon, Langmuir, 2010, 26, 11815–11822.
  8. A.F. Stalder, G. Kulik, D. Sage, L. Barbieri and P. Hoffmann, Colloids and Surfaces A: Physicochem. Eng. Aspects, 2006, 286, 92–103.
🔴 TUTORIAL IMAGE J (Drop Analysis)

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