Optical Tensiometers

Here you can find information about the following standards:

ASTM D7334-08

Significance and Use

This standard is useful for characterizing the wettability of surfaces. A surface that is easy to wet is one over which a coating is more likely to give good adhesion and appearance and less likely to suffer surface tension related defects such as crawling, cratering, pin-holing and orange peel.

This standard also can be used to test pigment surfaces for wettability, particularly by potential surfactant- or resin-based dispersants or mill bases. Easily wetted pigments are more likely to be easy to disperse and dispersants/mill bases that wet pigments of interest are more likely to disperse those pigments well. Although the contact angle is governed by the surface tensions of the test liquid and test surface, the angle cannot provide a surface tension value directly.

A low advancing contact angle value (< 45°) is indicative of wetting and angles of 10 to 20º are indicative of excellent wetting. Water can be used as a test liquid to establish (via the advancing contact angle) whether a surface is hydrophilic (angle < 45º), hydrophobic (angle > 90º) or somewhere in-between (angle of 45 to 90º). Water contact angles have been used to estimate surface cleanliness before and after cleaning operations, ease of wettability of surfaces by waterborne coatings and the effectiveness of rinsing processes.

An organic liquid such as a solvent also can be used to characterize a substrate, coating or pigment. The resultant contact angle will depend on the surface tensions of the liquid and the test surface. A low surface tension (energy) test surface will not be wetted by a liquid with high surface tension. In addition to water and solvents, a surfactant dispersion or dispersant solution can be used to test a pigment surface. Any test liquid that is a potential dispersant for a test pigment must wet the pigment well or it will not work as a dispersant.

Contact angle measurements can be used to map surfaces in terms of hydrophilicity, presence of low surface tension components or contaminants, or variations in composition. Other analytical methods such as infrared microscopy would be needed to identify the chemical moieties that give the contact angle differences.

This test method can be used on nearly all coatings and substrates and may be extended to pigments by compressing the pigment powder into a solid disk.

  1. Scope

    1.1  This practice covers the measurement of the angle of contact when a drop of liquid is applied to a coated surface, substrate, or preformed disk of pigment.
    1.2  There are two types of contact angles, advancing and receding. This standard deals only with advancing contact angles. 
    1.3  This practice is intended to supplement the manufacturer’s instructions for the device being used to make the measurements, but is not intended to replace them.
    1.4  A common test liquid is water, but many other liquids such as solvents, surfactant and dispersant solutions and even liquid paints can be used.
    1.5  This practice is based on goniometry, which involves the observation of a sessile drop of test liquid on a solid substrate.
    1.6  Although contact angles are governed by surface tension, this standard cannot be used to measure surface tension directly.
    1.7  The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.


ASTM D7490-08

Significance and Use

The method described in this standard is based on the concept that the total free energy at a surface is the sum of contributions from different intermolecular forces, such as dispersion, polar and hydrogen bonding. There are other techniques that employ three components (dispersion, polar and hydrogen bonding). These methods are further complicated by needing three to five test liquids and are not practical for routine testing. This method uses contact angles of two liquids to provide data for the calculation of two components, dispersion, γsd, and polar, γsp.

Dispersion and polar component data, along with the total solid surface tension, are useful for explaining or predicting wetting or adhesion, or both, of coatings on pretreatments, substrates and other coatings. Low solid surface tension values often are a sign of contamination and portend potential wetting problems. High polar components may signal polar contamination. There is evidence in the literature that matching of polar components of topcoats and primers gives better adhesion.

Solid surface tensions of pigments, particularly the polar components, may be useful in understanding dispersion problems or to provide signals for the composition of dispersants and mill bases. However, comparison of pigments may be difficult if there are differences in the roughness or porosity, or both, of the disks prepared from them.

Although this technique is very useful in characterizing surfaces, evaluating surface-active additives and explaining problems, it is not designed to be a quality control or specification test.

  1. Scope

    1.1  This test method describes a procedure for the measurement of contact angles of two liquids, one polar and the other nonpolar, of known surface tension on a substrate, pigment (in the form of a disk), or cured or air dried coating in order to calculate the surface properties (surface tension and its dispersion and polar components) of the solid.
    1.2  The total solid surface tension range that can be determined using this method is approximately 20 to 60 dynes/cm.
    1.3  The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
    1.4  This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 


ASTM D5946-09

Significance and Use

The ability of polymer films to retain inks, coatings, adhesives, etc. is primarily dependent on the character of their surfaces and can be improved by one of several surface-treating techniques. The electrical discharge treatment, such as corona treatment, has been found to increase the wetting tension of a polymer film. The stronger the treatment, the more actively the surface reacts with different polar interfaces. It is therefore possible to relate the contact angle of a polymer film surface to its ability to accept and retain inks, coatings, adhesives, etc., if the ink, coating, or adhesive contains the polar functionalities. Contact angle in itself is not a completely acceptable measure of ink, coating, or adhesive adhesion.

The wetting tension of a polymer film belongs to a group of physical parameters for which no standard of accuracy exists. The wetting tension of a polymer cannot be measured directly because solids do not change shape measurably in reaction to surface energy. Many indirect methods have been proposed. Different test methods tend to produce different results on identical samples. Practical determination of a solid’s surface energy uses this interaction of the solid with test liquids.

Although the level of surface treatment of polymer films has been traditionally defined in the industry in terms of dynes/cm (mN/m), these values are derived from a subjective interpretation of the observed test liquid behavior.

The following ranges of water contact angle values can be used as a guide for defining the level of surface treatment of polyolefins and many other polymer films with initial low surface energies:

Level of treatment Water contact angle
Marginal or no treatment >90°
Low treatment 85-90°
Medium treatment 78-84°
High treatment 71-77°
Very high treatment <71°

The suitability of the test for specification acceptance, manufacturing control, and end use of polymer films will have to be established through capability studies for each particular film and treatment.

Almost all materials have variations in contact angle as one moves from point to point. Non-uniform treatment of film with corona treaters may also add variability to the results. Therefore, multiple measurements are necessary to reflect variation in treatment and surface roughness.

  1. Scope

    1.1  This test method covers measurement of the contact angle of water droplets on corona-treated polymer film surfaces.
    Note 1—This test method is identical to ISO 15989.
    1.2  The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
    1.3  This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 


ASTM C813-90 (2009)

Significance and Use

The contact angle test is nondestructive and may be used for control and evaluation of processes for the removal of hydrophobic contaminants. The test may also be used for the detection and control of hydrophobic contaminants in processing ambients. For this application, a surface free of hydrophobic films is exposed to the ambient conditions and is subsequently tested.

  1. Scope

    1.2  The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
    1.3  This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.


ASTM G205-10

Significance and Use

In the absence of water, the crude oil is noncorrosive. The presence of sediment and water makes crude oil corrosive. Test Methods and provide methods for the determination of the water and sediment content of crude oil.

The corrosivity of crude oil containing water can be determined by a combination of three properties (Fig. 1) (1) : the type of emulsion formed between oil and water, the wettability of the steel surface, and the corrosivity of water phase in the presence of oil.

Water and oil are immiscible but, under certain conditions, they can form emulsion. There are two kinds of emulsion: O/W and W/O. W/O emulsion (in which oil is the continuous phase) has low conductivity and is thus less corrosive; whereas O/W (in which water is the continuous phase) has high conductivity and, hence, is corrosive (see ISO 6614) (2). The conductivities of various liquids are provided in Table 1(3). The percentage of water at which W/O converts to O/W is known as the emulsion inversion point (EIP). EIP can be determined by measuring the conductivity of the emulsion. At and above the EIP, a continuous phase of water or free water is present. Therefore, there is a potential for corrosion.

Whether water phase can cause corrosion in the presence of oil depends on whether the surface is oil wet (hydrophobic) or water wet (hydrophilic) (4-8). Because of higher resistance, an oil-wet surface is not susceptible to corrosion, but a water-wet surface is. Wettability can be characterized by measuring the contact angle or the conductivity (spreading method).

In the contact angle method, the tendency of water to displace hydrocarbon from steel is measured directly by observing the behavior of the three-phase system. The contact angle is determined by the surface tensions (surface free energies) of the three phases. A hydrocarbon-steel interface will be replaced by a water-steel interface if this action will result in an energy decrease of the system. To determine whether the surface is oil wet, mixed wet, or water wet, the angle at the oil-water-solid intersection is observed and measured.

In the spreading method of determining wettability, the resistance between steel pins is measured. If a conducting phase (for example, water) covers (wets) the distance between the pins, conductivity between them will be high. On the other hand, if a non-conducting phase (for example, oil) covers (wets) the distance between the pins, the conductivity between them will be low.

Dissolution of ingredients from crude oils may alter the corrosiveness of the aqueous phase. Based on how the corrosivity of the aqueous phase changes in its presence, a crude oil can be classified as corrosive, neutral, inhibitory, or preventive crude. Corrosiveness of the aqueous phase in the presence of oil can be determined by methods described in Test Method, Guide, Practice, Test Method, and NACE TM0172.

  1. Scope

    1.2  This guide does not cover detailed calculations and methods, but rather a range of approaches that have found application in evaluating the corrosivity of crude oil.
    1.3  Only those methodologies that have found wide acceptance in crude oil corrosivity evaluation are considered in this guide.
    1.4  This guide does not address the change in oil/water ratio caused by accumulation of water at low points in a pipeline system.
    1.5  This guide is intended to assist in the selection of methodologies that can be used for determining the corrosivity of crude oil under conditions in which water is present in the liquid state (typically up to 100°C). These conditions normally occur during oil and gas production, storage, and transportation in the pipelines.
    1.6  This guide does not cover the evaluation of corrosivity of crude oil at higher temperatures (typically above 300°C) that occur during refining crude oil in refineries.
    1.7  This guide involves the use of electrical currents in the presence of flammable liquids. Awareness of fire safety is critical for the safe use of this guide.
    1.8  The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
    1.9  This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.


    IEC 62961

    Interfacial tension (IFT) of insulating oil against water has been used for a long time as a criterion for ageing evaluation. It is well known that the interfacial tension of insulating liquids depends on the interfacial concentration of the surface active amphiphilic aged products at the time of measuring.

    Unlike ASTM D971 which provides only a single value at quite a short time, IEC 62961 extends the measurement with the aim to be more accurate and to be able to distinguish especially the differences between differently aged ester oils.


    ISO 15989:2004

    ISO 15989:2004 specifies a method of measuring the contact angle of water droplets on corona-treated polymer film surfaces and subsequently determining the wetting tension of the film.

    The method is applicable to practically any polymer film. It is not applicable, however, if the surface of the film exhibits a chemical affinity for water.


    ISO 27448:2009

    ISO 27448:2009 deals with fine ceramics.

    ISO 27448:2009 specifies a test method for the determination of the self-cleaning performance of materials that contain a photocatalyst or have photocatalytic films on the surface, and which are usually made from semiconducting metal oxides such as titanium dioxide.

    This method is used to measure the water contact angle under illumination with ultraviolet light, which is one of the indices influencing the self-cleaning performance of photocatalytic materials.

    ISO 27448:2009 does not include water-permeable substrates, rough surfaces that do not have exposed water droplets, highly hydrophobic, powder or granular materials, or visible light-sensitive photocatalysts.


    ISO 19403

    ISO 19403 specifies optical test methods for the measurement of contact angle, surface tension, surface free energy and for the determination of polar and dispersive fractions. It is restricted for non-Newtonian fluids and can be applied for the characterization of substrates, coatings and coating materials. The ISO 19403 is divided into seven parts, each specifying a separate optical test method. Each part defines the measurement set up, procedure, test conditions, and evaluation criteria.

    ISO 19403-1
    Terminology and general principles

    Part one of ISO 19403 specifies the critical terms and defines the general principles for the determination of contact angle, surface tension and surface free energy with optical test methods. It summarizes pendant drop analysis principle and the most used surface free energy methods, the Owens-Wend-Rabel-Kaeble and Wu methods.

    ISO 19403-2
    Determination of the surface free energy of solid surfaces by measuring the contact angle

    Part two of ISO 19403 specifies contact angle measurement for the determination of surface free energy of a solid which can be applied to study substrates and coatings. In addition, the standard presents a list of recommended liquids with known surface tension values which are recommended to be used in the measurements. The standard also highlights that morphological and chemical homogeneity have an influence on the results.
    According to the standard, at least three measurements should be conducted with at minimum of two different liquids. When only two liquids are used, water and di-iodomethane are recommended. If a third liquid is added, ethylene glycol should be chosen. Contact angle is calculated as the arithmetic mean value of the measured values, and the standard deviation should not exceed more than 3°. For the evaluation of the surface free energy, the Owens-Wend-Rabel-Kaeble method is recommended for high-energy surfaces (˃20 mJ/m2) and the Wu method for low-energy surfaces.

    ISO 19403-3
    Determination of the surface tension of liquids using the pendant drop method

    Part three of ISO 19403 specifies a pendant drop method to determine the surface tension of liquids which can be applied for liquid coating materials.
    In this method, surface tension is calculated from the shape of the pendant drop by using Young-Laplace equation. To evaluate the sufficiency for Young-Laplace evaluation, the standard defines a shape parameter value B (specified in ISO 19403-1) that should be within range of 0.60 ± 0.06. Too small droplets and too thin needles will create too spherical shaped droplets with small B-values. Large enough drops will deviate from spherical shape due to its own mass. The suitable outside diameter of the needle depends on the surface tension of the liquid and the density difference between the liquid and the ambient phase.

    ISO 19403-4
    Determination of the polar and dispersive fractions of the surface tension of liquids from an interfacial tension

    Part four of ISO 19403 specifies a method to determine the polar and dispersive fractions of the surface tension of liquids. This method could be applied for liquid coating materials, especially when drying effects occur during the measurement.
    In this method, a drop of the measured liquid is made while submerged in a reference liquid. The interfacial tension is analyzed in accordance with the Young-Laplace equation and should be measured from at least three drops. The polar and dispersive components of the tested liquid can be determined from the interfacial tension when the surface tensions of the test and reference liquid are known. If unknown, they can be measured in accordance with ISO 19403-3. N-alkanes and perfluoroalkanes suite well to be used as reference liquids as they are immiscible and able to form meniscus. For the calculation of the polar and dispersive fractions, Owens-Wendt-Rabel-Kaeble or the Wu method should be used.

    ISO 19403-5
    Determination of the polar and dispersive fractions of the surface tension of liquids from contact angle measurements on a solid with only a dispersive contribution to its surface energy

    Part 5 of ISO 19403 specifies a method to determine the polar and dispersive fractions of the surface tension of liquids from contact angle measurements. This method can be applied for liquid coating materials.
    This method requires that the surface tension of the liquid and the surface free energy of a dispersive solid are known. The reference solid should have polar fractions less than 0.5 mJ/m2 and it should be chemically and topologically homogenous. For instance, solids made of paraffin or PTFE could be used as reference solids. The dispersive fraction of the test liquid can be calculated with either Owens-Wendt-Rabel-Kaeble or Wu method depending on the surface free energy of the solid. The standard deviation should not exceed more than 1° for the contact angle of the tested liquid on the reference solid.

    ISO 19403-6
    Measurement of dynamic contact angle

    Part 6 of ISO 19403 specifies a method to measure dynamic contact angle and defines the concepts of advancing and receding contact angle. This method allows the characterization of wetting and dewetting properties, and also the morphological and chemical homogeneity of a solid.
    The standard defines dynamic contact angle as the angle that is measured during advancing or receding the three-phase boundary point. Dynamic contact angle should be measured from at least three drops with an optical contact angle measuring device. The dosing speed should be as slow as possible so that the contact angle of the drop is close to its thermodynamic equilibrium. The fitting should be done with the polynomial method. Wettability of the surface can be characterized by the advancing contact angle and dewettability by the receding angle.

    ISO 19403-7
    Measurement of contact angle on a tilt stage (roll-off angle)

    Last part of ISO 19403 specifies a method to measure roll-off angle in a dynamic measurement on a tilt stage. The roll-off angle gives essential information about a surface when studying, for instance, anti-adherent and easy-to-clean surfaces. This method can also be used to determine advancing and receding contact angles.
    Roll-off angle is the angle where the drop will roll off the surface when it is tilted with constant speed. The roll-off angle has been reached when both three-phase points have moved at least 1mm. The drop size and inclination speed influence the roll-off angle. Faster inclination speeds result in higher roll-off angles due to inertia of the drop. Advancing and receding contact angles are determined right when the roll-off angle is reached. The receding contact angle is usually smaller than the advancing angle. At least three drops should be measured and previously wetted positions should not be used.

    T 458 cm-04

    In this method (1-3), the contact angle between air and liquid on a paper surface is taken as a measure of the resistance of the paper surface to wetting by the liquid.

    The initial angle of contact or initial wettability is considered to be a measure of the ruling quality of the paper. The rate of change in the wettability is considered to be a measure of the writing quality.

    There are other important purposes for which surface wettability of a paper by contact angle measurement may be of interest, for example, with regard to adhesives. However, considerable modification of the procedure might be required. Hence, this procedure is restricted to ruling and writing purposes.


    T 558 om-10

    T 558 describes the measurement of surface wettability and absorbency of sheeted materials like paper using an automated contact angle tester. Contact angle measurements can be used to study relative sorptive rates of uncoated sorbent papers or to study the relatively printing or writing characteristics of coated or sized printing and writing papers. Contact angle is a precise empirical tool for use in studying specific liquid/substrate combinations for product and process improvements. The complex interaction between a liquid and a surface can be looked upon as a combination of three different processes: wetting, absorption, and adsorption.

    This test method is an automated approach to contact angle measurement applicable to a wide range of sheeted materials and liquids where interfacial contact angles range from near zero to near 180°.


    Force Tensiometers

    Here you can find information about the following standards:

    ASTM D1331-11

    Abstract

    These test methods cover the determination of surface tension and interfacial tension of solutions of surface-active agents using a tensiometer. Method A covers aqueous solutions of surface-active agents, but is also applicable to non-aqueous solutions and mixed solvent solutions. Method B is applicable to two-phase solutions. More than one solute component may be present, including solute components that are not in themselves surface-active.

    1. Scope

      1.1  These test methods cover the determination of surface tension and interfacial tension of solutions of surface-active agents, as defined in Terminology D459. Two methods are covered as follows:

        • Method A: Surface Tension
        • Method B: Interfacial Tension

      1.2  Method A is written primarily to cover aqueous solutions of surface-active agents, but is also applicable to non-aqueous solutions and mixed solvent solutions.
      1.3  Method B is applicable to two-phase solutions. More than one solute component may be present, including solute components that are not in themselves surface-active.
      1.4  This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Material Safety Data Sheets are available for reagents and materials. Review them for hazards prior to usage.


    ASTM D971-12

    Significance and Use

    Interfacial tension measurements on electrical insulating oils provide a sensitive means of detecting small amounts of soluble polar contaminants and products of oxidation. A high value for new mineral insulating oil indicates the absence of most undesirable polar contaminants. The test is frequently applied to service-aged oils as an indication of the degree of deterioration.

    1. Scope

      1.1  This test method covers the measurement of the interfacial tension between mineral oil and water, under non-equilibrium conditions.
      1.2  This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.


    ISO 1409:2006

    ISO 1409:2006 specifies a ring method for the determination of the surface tension of polymer dispersions and rubber lattices (natural and synthetic).

    The method is valid for polymer dispersions and rubber lattices with a viscosity less than 200 mPa·s. To achieve this, the dispersion or latex is diluted with water to a mass fraction of total solids of 40 %. If necessary, the solids content is further reduced to ensure that the viscosity is under the specified limit.

    The method is also suitable for pre-vulcanized lattices and compounded materials.


    OECD 115

    Abstract

    This Test Guideline describes methods to determine the surface tension (in N/m) of aqueous solutions. The methods are based on the measurement of the force which it is necessary to exert vertically on a stirrup or ring, in contact with the surface of the liquid, in order to separate it from the surface, or on a plate, with an edge in contact with the surface, in order to draw up the film that has formed. There are four different methods: the plate method, the stirrup method, the ring method and the OECD harmonized ring method. They are described in detail in the ISO Standard 304-1985. The methods described are applicable to aqueous solutions of most substances regardless of their degree of purity. The concentration should be 90% of the saturation solubility, but must below 1g/l. This shall therefore be carried out under a protective cover to avoid interference at 20°C approximately. The ring is immersed below the surface of the solution. Then the tabletop, where the measurement vessel is placed, is lowered gradually and evenly at a rate of approximately 0.5 cm/min to detach the ring from the surface until the maximum force is reached. The force is read on the tensiometer. After completing the first measurement, measurements are repeated until a constant surface tension value is reached.


    EN 14210

    This document specifies test methods for the determination of interfacial tension in the range from 4 mN/m to 50 mN/m between two immiscible liquids that can also be free from surface-active agents. It is particularly suitable for determining the interfacial tension between water or aqueous solutions and organic liquids that are immiscible with water.


    EN 14370

    This standard specifies test methods for the determination of surface tension of liquids, particularly surface-active agent solutions. The methods are suitable for determining the static surface tension of liquids, for example inorganic and organic liquids and solutions.