OCA series

# OCA – Optical contact angle measuring and contour analysis systems

The optical contact angle measuring and contour analysis systems of the OCA series are high precision optical measuring devices for the measurement of interfacial parameters and phenomena. In the following you will learn about the possibilities that the optical analysis of drop contours offers and about our OCA models with their extensive range of accessories and intuitive software control.

## Optical contact angle measurement and drop contour analysis

The optical analysis of drops that hang from a dosing needle or are placed on a solid surface facilitates the determination of different surface and interfacial parameters. The contact angle that a liquid drop establishes on a solid surface characterises the solid’s wetting behaviour with said liquid.

Having measured the contact angles of multiple test liquids the surface energy of the solid can be determined and the latter can be used to calculate the work of adhesion for different liquids.

The reliable and experimentally robust measurement of the contact angle aids on the development of surface coatings, composite materials, paints and varnishes or cleaning agents. In short: the measurement of contact angle helps in all situations where solids and liquids meet and advantage is to be gained by the control of wetting and adhesion properties.

Video: Water Roll-off

### Contact angle measurement

An equilibrium of vectorial forces dictates the contact angle ΘC at the three phase contact line of a deposited drop. The surface energy of the solid σS acts along the solid surface. The solid-liquid interfacial energy σSL acts in the opposite direction and the surface tension σL of the liquid acts tangential to the drop surface. This can be described by a simple scalar equation, the Young equation:

The drop is viewed in profile during the contact angle measurement. The image processing software recognises and records the drop contour, as well as the base line at the solid-liquid interface, and fits a mathematical function to the drop shape.

Contact angle at a solid-liquid-gas contact line

### Optical determination of surface and interfacial tension

When no other factor is in play a drop of liquid tends to form a sphere, due to its surface tension. The typical drop shape materialises because the drop is elongated due to gravity. The Young-Laplace evaluation of pendant drops recognises this fact: The characteristic shape of the drop profile yields the surface tension σL of a liquid.

In the case where a pendant drop is surrounded by a second liquid, rather than air, the interfacial tension between the two liquids can be deduced from the drop shape. For optical analysis the outer liquid has to be transparent. Depending on the relative densities, the inner liquid can be dosed either as a pendant drop or upwards, via a bent needle.

Pendant drop schematic and measurement of interfacial tension

### Surface energy of solids

To determine the surface energy of a solid one measures the contact angles of test liquids whose surface tensions including their dispersive and polar parts are known. These dispersive and polar parts are used to calculate the interfacial tension σSL between the solid and a liquid based on a suitable model.

An often applied model is the one of Owens, Wendt, Rabel and Kaelble (OWRK model) which considers the geometric mean of the dispersive and polar parts of the liquid’s surface tension σL and of the solid’s surface energy σS:

Substituting this expression in the Young equation, the polar and the dispersive part of the solid’s surface energy can be determined from the regression line in a suitable plot.

Regression line for determination of surface energy

The linear regression requires contact angle measurements with at least two different test liquids. However, as a regression line based on just two points contains no information on the accuracy of the result, contact angle measurements with at least three test liquids are recommended for the determination of the surface energy of solids.

Video: Automated Surface Energy Determination

### Lotus effect

A well quoted example of large contact angles can be found in nature: when water droplets come into contact with a lotus leaf they roll off without wetting the surface. During ‘roll off’ the drops take dirt particles with them, resulting in the self-cleaning of the leaf. Mimicking this “Lotus effect” is a popular research and product development topic in many technical fields. Self-cleaning facades, ceramics and other surfaces are regarded as highly desirable. In this context the ability to measure and record contact angles, of course, plays an essential role.

Water drops on a lotus leaf

## The OCA models

The optical contact angle measuring and contour analysis systems of the OCA series combine high resolution optics, exact liquid dosing and precise sample positioning into powerful and reliable measuring systems.

The modular approach to all hardware components allows for a multitude of configurations, ranging from manually operated basic devices to fully automated high-performance measuring systems. All OCA models are based on a common design philosophy and are built with a sturdy aluminium metal frame. Moreover, they all feature a LED lighting with manually and software-controlled intensity. Due to an automatic temperature drift compensation a stable and homogeneous illumination of the sample is guaranteed at all times.

For a compact overview of the OCA models download the product brochure or use our convenient online comparison of the different models.

### Measurements conforming to standards

Measurements that comply with various national and international standards are possible due to the high precision and extensive range of accessories of the OCA models. These standards are among others:

• ASTM C813
• ASTM D724
• ASTM D2578
• ASTM D5725
• ASTM D5946
• ASTM D7334
• ASTM D7490
• ASTM D7541
• DIN 55660
• DIN EN 15802
• ISO 8296
• ISO 15989
• ISO 27448

Schematic assembly of the OCA models

### OCA 15EC

The OCA 15EC is the entry level measuring device for professional contact angle measurements and drop shape analysis.

The sample table of the OCA 15EC can slide freely in X- and Y-direction and is locked into position with its switchable magnetic base. In Z-direction the sample table is adjustable using precision mechanics with a hand wheel.

The fast 6.5-fold zoom lens with manual focus and adjustable observation angle in combination with the USB 3 camera ensures pin-sharp drop images and facilitates the effortless analysis with the software.

With a single direct dosing system SD-DM or a double direct dosing system DD-DM liquids can be positioned and dosed with one or two electronic syringe modules ESr-N, respectively.

Direct tubeless dosing of the syringe content and the ability to use cost-saving disposable syringes and needles allow for short preparation times and minimal cleaning efforts.

Even though the OCA 15EC is a high precision measuring device designed for laboratory use, it is highly mobile and can effortlessly be taken apart with two star grip screws and be stored securely in a transport case.

#### Main features

• sample table horizontally movable (magnetic slide system) and adjustable vertically with precision mechanics
• high performance 6.5-fold zoom lens
• integrated continuous fine focus, and adjustable observation angle
• video measuring system with USB 3 camera
• LED-lighting with manual and software controlled intensity including automatic temperature drift compensation

OCA 15EC Package 2

#### Software

The software for the optical contact angle measuring and contour analysis systems of the OCA series is continuously being developed and enhanced with new features.

#### Accessories

Due to the modular product design the OCA 15EC can be combined with a multitude of options of the versatile OCA accessories range. Learn more about the available accessories.

OCA 15EC on tilting base unit TBU 100EC

### OCA 25

The OCA 25 is the all-purpose measuring device for contact angle measurements and drop shape analysis.

The sample table of the OCA 25 is adjustable along all three directions in space via precision axes with hand wheels. Hence, a fast and exact manual positioning of the sample is always guaranteed, even when using high-performance temperature chambers like the electrical temperature control unit TEC 700.

Analysis of even the fastest processes is possible recording up to 3250 frames/s using the 6.5-fold zoom lens and the high-performance camera with USB 3 interface. Hence, contact angles on adsorbing surfaces like tissues or powders can be measured reliably.

For dosing liquids the manual single and double direct dosing systems SD-DM and DD-DM can be used as well as the electronic multiple direct dosing systems DDE/x. The latter are able to electronically position one to four electronic syringe modules ESr-N.

Furthermore, a nanolitre dosing system can be used to generate extra small liquid drops. Even these are no challenge for the OCA 25 due to its high resolution optics.

#### Main features

• sample table adjustable in all three axis with precision mechanics
• high performance 6.5-fold zoom lens
• integrated continuous fine focus, and adjustable observation angle
• video measuring system with high-performance camera using USB 3 interface
• LED-lighting with manual and software controlled intensity including automatic temperature drift compensation

#### Software

The software for the optical contact angle measuring and contour analysis systems of the OCA series is continuously being developed and enhanced with new features.

#### Accessories

Due to the modular product design the OCA 25 can be combined with a multitude of options of the versatile OCA accessories range. Learn more about the available accessories.

OCA 25 with DDE/3

OCA 25 sample table with precision axes for exact manual positioning

### OCA 25 special models

The universal device platform opens the way to special models of the OCA 25, which satisfy even highest customer expectations and cope with the most challenging measuring environments.

#### OCA 25-HTV 1800

The high temperature measuring system OCA 25-HTV 1800 is capable of measuring contact angles at high temperatures of up to 1800 °C and under vacuum down to 10-5 mbar or under inert gas atmosphere, respectively.

##### Main features
• high temperature furnace up to 1800 °C
• vacuum tight flanges with connectors to an optional turbomolecular pump (flanges require a water counter cooling)
• inlets and gas supply system for Ar and N2
• high power supply and control electronics
• high performance 6.5-fold zoom lens with zoom extender
• integrated continuous fine focus, and adjustable observation angle
• video measuring system with high-performance camera using USB 3 interface
• LED-lighting with manual and software controlled intensity including automatic temperature drift compensation
##### Accessories

The application range and ease of use of the OCA 25-HTV 1800 can be further increased with optional accessories:

• dosing system for measurements at room temperature
• trolley cart for easy transport of the whole system
• turbomolecular pump for low pressures down to 10-5 mbar

OCA 25-HTV 1800 with optional trolley cart

#### OCA 25-PMC 750

The OCA 25-PMC 750 with its high pressure measuring chamber provides the opportunity to measure interfacial tensions and contact angles at pressures of up to 750 bar and under temperature conditions ranging from -30 °C to 200 °C.

##### Main features
• high pressure chamber with optical sapphire glass
• high pressure unit for generation and control of bulk liquid/gas pressure and drop liquid/gas pressure (manual or automatic)
• temperature controller for control of chamber temperature
• removable magnetic positioning system for solid samples
• a set of needles with different diameters for various interfacial tension ranges
• high performance 6.5-fold zoom lens
• integrated continuous fine focus, and adjustable observation angle
• video measuring system with high-performance camera using USB 3 interface
• LED-lighting with manual and software controlled intensity including automatic temperature drift compensation

OCA 25-PMC 750

### OCA 50 & OCA 50EC

The OCA 50 is the fully automatic measuring device for the time-saving analysis of the wettability of solid surfaces and the determination of the surface energy of solids.

The sample table of the OCA 50 can be positioned along all three directions in space via electronic high-performance axes, with both extraordinary speed and highest precision.

Combined with an electronic multiple direct dosing system DDE/x and up to four electronic syringe modules ESr-N the determination of surface parameters can be automated completely.

The automation of measurements succeeds easier than ever before thanks to the intuitive automation dialogue of the OCA software and its visual drop positioning system. Hence it is possible to determine, for example, the surface energy with four test liquids at different position of even large samples without any manual user intervention. This facilitates a complete and automated sample mapping.

In order to map silicon wafers, electronic turn tables with vacuum fixation are available. They allow to access any position for contact angle measurements, even on 12″ wafers.

In any case, the 6.5-fold zoom lens and the high-performance camera with USB 3 interface ensure optimal images of the deposited drops.

For a fast and intuitive device control, even during complex measurements, the TP 50 control panel with touch screen and precision control wheel is included with every OCA 50.

#### Main features

• sample table adjustable in all three directions in space with electronic high-performance axes
• high performance 6.5-fold zoom lens
• integrated continuous fine focus, and adjustable observation angle
• video measuring system with high-performance camera using USB 3 interface
• LED-lighting with manual and software controlled intensity including automatic temperature drift compensation
• included TP 50 control panel with touch screen and precision control wheel

#### Software

The software for the optical contact angle measuring and contour analysis systems of the OCA series is continuously being developed and enhanced with new features.

#### Accessories

Due to the modular product design the OCA 50 can be combined with a multitude of options of the versatile OCA accessories range. Learn more about the available accessories.

OCA 50 with DDE/4

OCA 50 electronic sample table with electronic turn table ETT/Vac

### OCA 200

The OCA 200 is the contact angle measuring and drop contour analysis system for microscopic and macroscopic structures.

The software-controlled, electrically driven optic alignment enables the OCA 200 to adjust the observation angle and to focus automatically.

With the trendsetting 10-fold zoom lens and the reliable auto focus system by DataPhysics Instruments, the OCA 200 is equipped to handle any kind of sample size from a macroscopic silicon wafer to the microscopic mesh structure of a coronary stent.

In combination with the high-performance camera with USB 3 interface even smallest drops of highly volatile liquids can be monitored.

The electrically driven sample table makes it possible to position micro-structured samples with highest precision and exceptional speed for fast automated measuring procedures.

With an electronic multiple direct dosing system DDE/x and up to four electronic syringe modules ESr-N liquids can be deposited on a macroscopic sample and its surface parameters can be determined automatically.

OCA 200 with DDE/4

For the analysis of micro-structured samples the nanolitre dosing system is available which can generate down to 10 nanolitre small droplets. These droplets are small enough to fit, for example, between the screw threads of a dental implant whose surface is to be analysed.

Even smaller structures can be analysed using the picolitre dosing system PDDS which can dose down to 30 picolitre small droplets. These allow contact angle measurement, for example, on the individual wires of the mesh structure of a coronary stent or on single fibres.

#### Main features

• sample table adjustable in all three directions in space with electronic high-performance axes
• trendsetting 10-fold zoom lens
• software-controlled, electrically driven optic alignment for autofocus and adjustment of the observation angle
• video measuring system with high-performance camera using USB 3 interface
• LED-lighting with manual and software controlled intensity including automatic temperature drift compensation
• included TP 50 control panel with touch screen and precision control wheel

Video: Picolitre dosing system PDDS

#### Software

The software for the optical contact angle measuring and contour analysis systems of the OCA series is continuously being developed and enhanced with new features.

#### Accessories

Due to the modular product design the OCA 200 can be combined with a multitude of options of the versatile OCA accessories range. With its extended zoom range and high resolution optics the OCA 200 is the device of choice when utilising smallest droplets like with the picolitre dosing system PDDS.

Nanolitre drop between the screw threads of a dental implant

## Portable and robot guided contact angle measurement

A continuous production control can prevent expensive product recalls. But often ready-made products are too large or too heavy for measuring systems designed for laboratory use like the DataPhysics Instruments OCA series. With the portable contact angle measuring system PCA 100M from DataPhysics Instruments the measuring device can be simply put on top of the sample.

The PCA 100M allows for a nondestructive material test even on large surfaces like whole windshields, car body parts, large-scale wafers or compound materials. Due to contact angle measurements and the determination of the surface energy, the quality of a coating or the sample cleanliness after a cleaning procedure can be evaluated directly during the production process.

The PCA 100M can be used almost anywhere, even in a clean room, thanks to the compact design and the easy connection to a laptop or an on-site PC. With the optional laboratory stand PCA-MS the PCA 100M can also be used as a laboratory device.

Contact angle measurement on an engine bonnet using the PCA 100M/4

In combination with single and multi axes robots the PCA 100R can be used to directly integrate an automated surface analysis into the production process. An appropriate robot cell is being designed according to customer needs and hence fits perfectly to the samples.

Individually adapted control software ensures a smooth transfer of the samples between the PCA 100R and other robot systems. Hence an automatic and reliable control of surface properties even inside a production line is guaranteed.

#### Main features

• Video measuring system with high-performance telecentric lens with integrated aperture and adjustable observation angle
• lighting with software-controlled intensity
• integrated multiple dosing system for two (PCA 100M/2) or four (PCA 100M/4) test liquids
• Integrated automatic refill system with flushing and cleaning functions for dosing up to 5000 drops per liquid receptacle
• optional adapter for measurements of the surface and interfacial tension based on the evaluation of pendant drops
• optional laboratory stand PCA-MS for laboratory use
• USB connection box for power supply and communication with the PCA 100M

#### Software

The software for the optical contact angle measuring and contour analysis systems of the OCA series is continuously being developed and enhanced with new features.