ramé-hart Contact Angle Goniometers


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DROPimage Standard

DROPimage Standard ships with our Standard Goniometer (Model 200) and with our Advanced Goniometer (Model 300). It is also available as an upgrade for existing users of our previous-generation RHI software or for those who purchase our Model 120 or 190 tool and later wish to expand its capabilities.

Below is a video that illustrates how easy it is to calibrate the instrument and take contact angle measurements using our new version 2.1 of DROPimage Standard.

This second-generation application includes the following suite of surface energy tools:

Contact Angle Tool

The Contact Angle Tool characterizes the behavior of a liquid on a solid. When a liquid is placed in contact with a solid surface, the bare surface of the solid absorbs the vapor of the liquid until the volatility of the absorbed material is equal to that of the liquid. When equilibrium is established, there is a liquid-solid interface between the two phases. The tangent angle between solid and liquid is known as the contact angle.

Acid-Base Tool

The Acid-Base Tool evaluates the surface energy parameters of a given solid using the contact angles of three different test liquids. Van Oss et al have shown that the contribution due to acid-base interactions can be expressed in terms of the product of their electron donor and electron acceptor components by using three liquids, one apolar and two polar. Recommended test liquids are methylene iodide or bromonaphthalene for the apolar liquid and a polar liquid pair of either water and glycerol or water and formamide.

References:
C.J. van Oss, R.J. Good and M.K. Chaudhury; Adv. Colloid Interface Sci. 28, 35 (1987).
C.J. van Oss, R.J. Good and M.K. Chaudhury, J.; Chromatography 191, 53 (1987).
C.J. van Oss, R.J. Good and M.K. Chaudhury, J.; Langmuir 4, 884 (1988).

Surface Energy Tool

The Surface Energy Tool evaluates the surface energy of a given solid using the contact angles of different test liquids.

The geometric-mean method uses two pure liquids denoting their dispersive and non-dispersive values. Water and methylene iodide are a convenient choice for test liquids. Different liquid pairs tend to give different results. The surface energies and polarities of some low-energy solids obtained by this method are often much lower than those calculated by other methods.

Reference: D.K. Owens and R.C. Wendt, J Appl Polym. Sci. 13, 1741 (1969).

The harmonic-mean method also uses two liquids in its calculations. The results obtained with this method are regarded as accurate by Wu and agree remarkably well with other methods. However, some researchers consider that non-dispersive interactions across interfaces are mainly of acid-base nature and in that situation recommend using the acid/base tool.

Reference: S. Wu, J Polym. Sci C34, 19 (1971).

Work of Adhesion

The Work of Adhesion Tool determines an index of wetting ability of a liquid for a solid. The Adsorption Theory proposes that van der Waals interactions should be sufficient for good adhesion. The liquid/solid thermodynamic considerations give rise to this equation relating the reversible work of adhesion and surface free energies according to Young and Dupre, noting that the process of adhesion may be described in terms of opposites, namely the process of separation.

Reference: Buff, F.P. "The theory of capillarity", in Encyclopedia of Physics; Flugge, S., Ed: Springer-Verlag: Berlin, 1960; pp. 281-304.

Zisman's Plot Tool

The Zisman’s Plot Tool summarizes wetting behavior and allows predictions of an interpolative nature using a homologous series of liquids. Extensive series of measurements of contact angles of various liquids on low-energy polymer substrates were reported by W.A. Zisman, inventor of the Ramé-Hart Contact Angle Goniometer, and his coworkers at the Naval Research Laboratory. An empirical linear relation was found between the cosine of the contact angle and the surface tension of the liquid of the sessile drop. The extrapolation of the line to cosine (theta) = 1 gives the "critical surface tension" of the substrate.

The term "critical" is used because any liquid on the Zisman plot whose surface tension is greater than the "critical surface tension" makes a finite contact angle with the substrate. Critical surface tension values are useful empirical values that characterize relative degrees of surface energy of polymer substrates. Zisman’s empirical prediction fails for liquids that form hydrogen bonds or acid-base interactions with the substrate. These liquids would spread spontaneously on the substrate.

Reference: W.A. Zisman, ACS Adv. Chem. Ser. 43, 1 (1964).

Solid-Liquid-Liquid Surface Energy Tool

The Solid-Liquid-Liquid Surface Energy Tool evaluates the surface energy of a given solid using the contact angles of one test liquid on a solid submerged in a series of different liquids according to the method of Shultz et al.Water or formamide is usually used as the test liquid and a series of hydrocarbons as the continuos phase (hexane, cycohexane, octane, decane, hexadecane). At least 2 different continuous phase liquids must be used. The method is especially useful for high-energy solids as metals and oxides that are otherwise wetted by most liquids.

Reference:
J.Schultz, K.Tsutsumi and J.-B. Donnet, J.Colloid Interface Sci 59, 272 and 277 (1977)

Calibration Command

When the instrument is shipped, the system is fully calibrated. However, if the lens assembly is readjusted to any degree or any change is made to the magnification system, the instrument is no longer calibrated. The Calibration command uses a ball with a precise diameter to calibrate the magnification of the camera, resulting in 100% accurate readings. The calibration can then be verified at any time using a calibration check utility. All ramé-hart systems ship with a proprietary floating calibration ball.

	Syringe Tool
	The Automated Syringe Tool supports the ramé-hart automated dispenser option for the control of the drop volume. This tool can be programmed into a time table for automated advancing and receding and other types of studies. There is no limit to the number of different timed measurements that can be programmed.

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