pubmed.ncbi.nlm.nih.gov

The capillary adhesion technique: a versatile method for determining the liquid adhesion force and sample stiffness - PubMed

  • ️Thu Jan 01 2015

The capillary adhesion technique: a versatile method for determining the liquid adhesion force and sample stiffness

Daniel Gandyra et al. Beilstein J Nanotechnol. 2015.

Abstract

We report a novel, practical technique for the concerted, simultaneous determination of both the adhesion force of a small structure or structural unit (e.g., an individual filament, hair, micromechanical component or microsensor) to a liquid and its elastic properties. The method involves the creation and development of a liquid meniscus upon touching a liquid surface with the structure, and the subsequent disruption of this liquid meniscus upon removal. The evaluation of the meniscus shape immediately before snap-off of the meniscus allows the quantitative determination of the liquid adhesion force. Concurrently, by measuring and evaluating the deformation of the structure under investigation, its elastic properties can be determined. The sensitivity of the method is remarkably high, practically limited by the resolution of the camera capturing the process. Adhesion forces down to 10 µN and spring constants up to 2 N/m were measured. Three exemplary applications of this method are demonstrated: (1) determination of the water adhesion force and the elasticity of individual hairs (trichomes) of the floating fern Salvinia molesta. (2) The investigation of human head hairs both with and without functional surface coatings (a topic of high relevance in the field of hair cosmetics) was performed. The method also resulted in the measurement of an elastic modulus (Young's modulus) for individual hairs of 3.0 × 10(5) N/cm(2), which is within the typical range known for human hair. (3) Finally, the accuracy and validity of the capillary adhesion technique was proven by examining calibrated atomic force microscopy cantilevers, reproducing the spring constants calibrated using other methods.

Keywords: AFM cantilever; Salvinia effect; Salvinia molesta; adhesion; air layer; capillary forces; hairs; measurement; micromechanical systems; microstructures; sensors; stiffness; superhydrophobic surfaces.

PubMed Disclaimer

Figures

Figure 1
Figure 1

Description of the experimental method. (a) The experimental setup: A small elastic entity, in this case a hair (trichome) of Salvinia molesta, is placed between a luminescent screen and a CCD camera above a container filled with liquid. Using reverse action tweezers fixed on a stepper motor, the trichome is vertically descended onto the surface of the liquid (water). (b) After touching the liquid, the subsequent removal of the hair results in the formation of a meniscus. As the tip is pulled upwards, the meniscus eventually snaps off. The geometry of the mensicus immediately before snap-off (i.e., rupture of the meniscus) and the deformation of the trichome are recorded and evaluated.

Figure 2
Figure 2

Meniscus immediately before snap-off. The profile can be fit by an elliptical function (Equation 1, y(x)) with fitting parameters a, b, c as shown above. From Equation 2, the surface area of the meniscus is derived, enabling calculation of the energy required to build the meniscus (Equation 3) and the maximum pulling force on the trichome (Equation 4) equivalent to the water adhesion force of the trichome tip. By evaluating the elongation of the trichome, Δy, the elastic properties are determined.

Figure 3
Figure 3

Force–elongation curve of a Salvinia molesta trichome. CAT allows force–elongation curves of small elastic structures to be measured based on the evaluation of the meniscus at different stages of the experiment. The linear fit to the data illustrates that the deformation follows Hooke’s law quite well: before snap-off, the elongation of the trichome shows a linear force dependence. The systematic error of the force F corresponds to half of the height of each measuring point, whereas the systematic error of Δy was 3 µm in each case.

Figure 4
Figure 4

Examination of a human head hair. In this variation of the CAT, the hair is used as a bending spring. It is horizontally placed above the surface of the liquid in the tweezers and the bending before snap-off is measured with hair surfaces of different conditions (a) no coating (natural hair surface), (b) hair coated with teflon and (c) hair coated with silicone. Whereas the adhesion force depends on the coating, the elastic properties, such as the spring constant or Young’s modulus of the hair, remain unchanged by the coating.

Figure 5
Figure 5

Proof of concept and accuracy of CAT, using specially calibrated AFM cantilevers. Determining the spring constant of the calibrated cantilever using the same settings as used for the individual hairs (see above, Figure 4) yields a spring constant in agreement with that given by the manufacturer.

Similar articles

Cited by

References

    1. Barthlott W, Schimmel T, Wiersch S, Koch K, Brede M, Barczewski M, Walheim S, Weis A, Kaltenmaier A, Leder A, et al. Adv Mater. 2010;22:2325–2328. doi: 10.1002/adma.200904411. - DOI - PubMed
    1. Solga A, Cerman Z, Striffler B F, Spaeth M, Barthlott W. Bioinspiration Biomimetics. 2007;2:126. doi: 10.1088/1748-3182/2/4/S02. - DOI - PubMed
    1. Koch K, Barthlott W. Philos Trans R Soc London, Ser A. 2009;367:1487–1509. doi: 10.1098/rsta.2009.0022. - DOI - PubMed
    1. Koch K, Bhushan B, Barthlott W. Prog Mater Sci. 2009;54:137–178. doi: 10.1016/j.pmatsci.2008.07.003. - DOI
    1. Bhushan B, Jung Y C. Prog Mater Sci. 2011;56:1–108. doi: 10.1016/j.pmatsci.2010.04.003. - DOI

LinkOut - more resources