Scientific study on KRÜSS Stood-up Drop published

KRÜSS recently developed the Stood-up Drop®, a new method for measuring the receding contact angle. A recently published research paper proves that the Stood-up Drop meets scientific requirements for robustness and reproducibility.

Stood-up Drop: a fast, user-independent method

The receding angle describes the dewetting of a liquid from a sample. Until now, this angle could only be measured in a cumbersome manner by reducing a dispensed drop using a dosing needle. With the Stood-up Drop, the drop is instead dispensed at high speed onto the surface, where it spreads in a fraction of a second and immediately contracts back into a well-defined drop. The resulting recently receded contact angle (RRCA) is measured using video image analysis of the drop. The measured value is available much faster than with the classic method and is also far less dependent on user decisions, making it more reproducible.

Scientific relevance proven by new study 

From the outset, the development of the Stood-up Drop method was accompanied by scientific, collaborative research, the results of which have now been published. In addition to Thomas Willers from KRÜSS, the study involved renowned research teams led by Hans-Jürgen Butt and Doris Vollmer from the Max Planck Institute for Polymer Research (MPIP) and Detlef Lohse from the University of Twente. 

As part of the investigations, the Stood-up Drop was compared with the classic dynamic receding contact angle (DRCA) when reducing the dosed volume. The measured values showed good agreement for a large number of different materials, making the new method a reliable alternative.

Another focus was on fluid mechanics model calculations that simulated the formation of a Stood-up Drop. The numerical calculation of the contact angle showed excellent agreement with the experimental investigation of the drop using high-speed videos. Furthermore, the limits and validity ranges with regard to drop properties (volume, surface tension, density, viscosity) and wettability (contact angle θ below and above 90°) were calculated using fluid mechanics.

The results confirm the high reliability of the method when measuring with the standard test liquid water, especially on wettable surfaces. The method is also suitable for slightly hydrophobic samples (θ>90°), whereas with superhydrophobic materials (θ⨠90°) there tends to be no controlled dewetting, but rather the drop detaches from the sample. In this area, classic measurement methods should be used.

Versatile industrial and scientific applications

The Stood-up Drop correlates excellently with many empirical, manual methods such as the ink test for wettability or the crosshatch test for estimating the adhesion of a coating. The new method is already being used in industry to reduce the number of more complex tests or to replace them entirely. The recently published study proves that the Stood-up Drop also meets scientific criteria and complements and enriches the range of tools available for surface research.

Source

D. Diaz, A. Bhargava, F. Walz, A. Sharifi, S. Summaly, R. Berger, M. Kappl, H.-J. Butt, D. Lohse, T. Willers, V. Sanjay, D. Vollmer: Stood-up Drop to Determine Receding Contact Angles. In: Soft Matter, 2025. DOI: 10.1039/d5sm00985e.

▶  Read the freely accessible study

The title image was reproduced from the aforementioned reference with permission from the Royal Society of Chemistry.