Our labs are equipped with commercially available contact angle devices and with in-house developments. All measurements are carried out under constant climate (temperature: 23 °C, relative humidity: 50 %). The choice of a particular contact angle technique depends on the geometry of the system and the size and the shape of the solid sample. The accuracy of contact angle measurements can be affected by the quality of the solid surface (heterogeneity, roughness), the purity of the measuring liquids, the skill of the experimenter, but also by the methodology and procedure.

Many processes in polymer production, processing and application include wetting of solids by liquids. The contact angle θ is an important parameter to quantify the wettability of solid surfaces. It is defined as the angle θ formed between the liquid-fluid (vapor) and the solid-liquid interfaces, at the solid-liquid-fluid (vapor) three phase contact line.

Contact angles of sessile drops and captive (adhering) bubbles

Dr. Günter K. Auernhammer
Stefan Michel

Methods for dynamic wetting

• Rotating cylinder (in-house design)
• Drop slider (in-house design)
• Drop impact

Advancing and receding contact angles (low-rate)

Sessile, pendant drop and captive (adhering) bubble techniques

• DataPhysics OCA35L(DataPhysics, Germany)
• DataPhysics OCA40 micro(DataPhysics, Germany)
• Different experimental set-up for Axisymmetric Drop Shape Analysis -Profile (ADSA-P)(in-house development)

Tensiometers

Wilhelmy balance technique

• Tensiometer K12(Kruess GmbH, Germany)
• Tensiometer DCAT21 (DataPhysics, Germany)
• Tensiometer DCAT21SF (single fiber(DataPhysics, Germany)
• OBS2 (in-house development tensiometer)

Rotating drum

Our rotating drum consists of a stainless-steal cylinder that can realize contact line speeds from 100 µm/s up to 1 m/s in a controlled atmosphere. Through the optical observation, dynamic advancing and receding contact angles and flow profiles close to the contact line can be measured.

Drop slider

Built on an inverted microscope, the drop slider allows for controlled contact line velocities below 1 mm/s. With a astigmatic particle-tracking setup in the inverted microscope, we can measure the 3D fluid velocity in close vicinity to the contact line.

Drop impact

With high-speed cameras (Photron AX50, AX100, AX200), we follow fast processes with frame rates of up to 600 kHz.

Drop impact on a hydrophobic surface.

Sessile drop techniques

The sessile drop or, alternatively, the captive (adhering) bubble method are the most commonly used techniques for flat surfaces. In these cases, the contact angles are measured from the drop profile, either by the conventional goniometer-telescope or the more sophisticated and advanced Axisymmetric Drop Shape Analysis-Profile (ADSA-P). Using the goniometer technique, which is the most widely used procedure, the contact angle is determined simply by aligning a tangent with the sessile drop profile at the point of contact with the solid surface.

DataPhysics OCA35L

Captive bubble technique

In order to study highly hydrated polymer layers, captive bubble contact angle techniques have been applied. We use a captive bubble arrangement in conjunction with Axisymmetric Drop Shape Analysis-Profile (ADSA-P) to quantify the wettability of polymer materials in contact with pure water, electrolyte or aqueous protein solutions. Hydrophilic cellulose materials, adsorbed protein layers in their highly hydrated state or hydrogels can be studied in our lab. A temperature-controlled glass cell containing the measuring liquid permits measurements below and above the phase transition temperature Tcr of the hydrogel.

Wilhelmy balance technique

The Wilhelmy balance method is an excellent technique to measure contact angles indirectly on a flat plate of known perimeter of the plate cross-section or on thin fibers of known perimeter. In our labs, we use commercially available instruments and in-house developments consisting of a microbalance and a motor driven movable table, on which the liquid container is placed. The contact angle experiments can be performed under inert gas atmosphere and at elevated temperatures. In the classical Wilhelmy balance experiment the force F measured by a balance is the sum of gravitational, interfacial, buoyancy, and hydrodynamic forces. In the case of low-molecular liquids, shear forces can be neglected. For thin fibers (diameters less than 100 µm), the buoyancy force can also be ignored and the following simple equation results:

Scheme of wetting and wetting force

The perimeter p of the sample can be determined by using a liquid of known surface tension γlv for which the contact angle θ is zero. The contact angle θ of another liquid with known surface tension γlv can then be determined by measuring the force per unit length of the perimeter p. In the special case, when the contact angle is zero and the perimeter is known, the measured force is related directly to the liquid surface tension.

Surface tension of polymer melts

The Wilhelmy balance technique for polymer melts is a versatile technique to measure indirectly either the surface (wetting) tension of polymer melts or the contact angle at the solid-polymer melt interface. We use thin fibers (diameter < 100 µm) as solid probes. The advantage of this arrangement is that the density of the polymer melt is not needed to calculate its surface tension. Our instruments consist of supersensitive microbalances (accuracy: ± 2µg) and a motor driven movable table, on which a high-temperature cell containing the polymer sample is placed. The experiments can be performed under inert gas atmosphere and at elevated temperatures.

Technical Data:

Diameter of fibers: 8 to 100 µm
Net weight of solid polymer per gaging: ca. 50 mg
Measurement is carried out in an argon inert gas flow
Max. temperature: ca. 300°C

• Henrich, F., D. Fell, D. Truszkowska, M. Weirich, M. Anyfantakis, T.-H. Nguyen, M. Wagner, G. K. Auernhammer and H.-J. Butt (2016).
"Influence of surfactants in forced dynamic dewetting."
Soft Matter 12: 7782 - 7791. http://dx.doi.org/10.1039/C6SM00997B

• B. B. Straub, H. Schmidt, P. Rostami, F. Henrich, M. Rossi, C. J. Kähler, H.-J. Butt, G. K. Auernhammer (2021).
„Flow profiles near receding three-phase contact lines: influence of surfactants”
Soft Matter 17: 10090-10100. http://dx.doi.org/10.1039/D1SM01145F

• B. Zhao, Y. Jia, Y. Xu, E. Bonaccurso, X. Deng, G. K. Auernhammer, L. Chen (2021).
„What Can Probing Liquid--Air Menisci Inside Nanopores Teach Us About Macroscopic Wetting Phenomena?“
ACS Applied Materials & Interfaces 13, 6897—6905. https://doi.org/10.1021/acsami.0c21736

• Grundke, K. ; Azizi, M. ; Ziemer, A. ; Michel, S. ; Pleul, D. ; Simon, F. ; Voit, B. ; Kreitschmann, M. ; Kierkus, P.
"Hyperbranched polyesters as potential additives to control the surface tension of polymers"
Surface Coatings International / Part B: Coatings Transactions 88 (2005) 101-106

• Synytska, A. ; Michel, S. ; Pleul, D. ; Bellmann, C. ; Schinner, R. ; Eichhorn, K.-J. ; Grundke, K. ; Neumann, A.W. ; Stamm, M.
"Monitoring the Surface Tension of Reactive Epoxy-Amine Systems Under Different Environmental"
Conditions Journal of Adhesion 80 (2004) 667-683

• S. Schubotz, C. Honnigfort, S. Nazari, A. Fery, J.-U. Sommer, P. Uhlmann, B. Braunschweig, G. K. Auernhammer (2021).
„Memory effects in polymer brushes showing co-nonsolvency effects“
Advances in Colloid and Interface Science 294, 102442. https://doi.org/10.1016/j.cis.2021.102442

• Millican, J. ; Bittrich, E. ; Caspari, A. ; Pöschel, K. ; Drechsler, A. ; Freudenberg, U. ; Ryan, T. G. ; Thompson, R. L. ; Pospiech, D. ; Hutchings, L.
“Synthesis and characterisation of a mussel-inspired hydrogel film coating for biosensors”
European Polymer Journal 153 (2021) 110503

• Grundke, K. ; Pöschel, K. ; Synytska, A. ; Frenzel, R. ; Drechsler, A. ; Nitschke, M. ; Cordeiro, A. L. ; Uhlmann, P. ; Welzel, P.
“Experimental studies of contact angle hysteresis phenomena on polymer surfaces - Toward the understanding and control of wettability for different applications”
Advances in Colloid and Interfaces Science 222 (2015) 350-376

• Amornsudthiwat, P. ; Nitschke, M. ; Zimmermann, R. ; Friedrichs, J. ; Grundke, K. ; Pöschel, K. ; Damrongsakkul, S. ; Werner, C.
"Comprehensive characterization of well-defined silk fibroin surfaces: Toward multitechnique studies of surface modification effects"
Biointerphases 10 (2015) 029501

• Ziemer, A. ; Azizi, M. ; Pleul, D.Pleul ; Simon, F. ; Michel, S. ; Kreitschmann, M. ; Kierkus, P. ; Voit, B. ; Grundke, K.
„Influence of Hyperbranched Polyesters on the Surface Tension of Polyols“
Langmuir 20 (2004) 8096-8102

• Grundke, K., Michel, S.,Osterhold, M.
“Surface tension studies of additives in acrylic resin-based powder coatings using the Wilhelmy balance technique“
Progress in Organic Coatings 39, (2000), 101-106