Extracting the surface tension of soft gels from elastocapillary wave behavior

• Published in: Soft matter Vol. 14; no. 36; pp. 7347 - 7353
• Main Authors: Shao, X, Saylor, J. R, Bostwick, J. B
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 2018
• Subjects: Capillarity; Capillary waves; Crossovers; Elastic waves; Gels; Gravitational waves; Gravity; Gravity waves; Historical account; Rayleigh waves; Shear modulus; Surface energy; Surface properties; Surface tension; Tension; Transition zone; Weight
• ISSN: 1744-683X; 1744-6848
• DOI: 10.1039/c8sm01027g

Mechanically-excited waves appear as surface patterns on soft agarose gels. We experimentally quantify the dispersion relationship for these waves over a range of shear modulus in the transition zone where the surface energy (capillarity) is comparable to the elastic energy of the solid. Rayleigh waves and capillary-gravity waves are recovered as limiting cases. Gravitational forces appear as a pre-stress through the self-weight of the gel and are important. We show the experimental data fits well to a proposed dispersion relationship which differs from that typically used in studies of capillary to elastic wave crossover. We use this combined theoretical and experimental analysis to develop a new technique for measuring the surface tension of soft materials, which has been historically difficult to measure directly. Elastocapillary waves appear on the surface of soft gels and by measuring the dispersion of these waves we are able to extract the surface tension.