Katrina Smith-Mannschott


Last Name

Smith-Mannschott

First Name

Katrina

ORCID

0000-0002-3400-2587

Organisational unit

Filters

2021 - 20245
Reset filters

Search Results

Publications 1 - 5 of 5
  • Universality of breath figures on two-dimensional surfaces: An experimental study
    Item type: Journal Article
    Stricker, Laura; Grillo, Fabio; Marquez, E.A.; et al. (2022)
    Physical Review Research
    Droplet condensation on surfaces produces patterns, called breath figures. Their evolution into self-similar structures is a classical example of self-organization. It is described by a scaling theory with scaling functions whose universality has recently been challenged by numerical work. Here, we provide thorough experimental testing, where we inspect substrates with vastly different chemical properties, stiffness, and condensation rates. We critically survey the size distributions and the related time-asymptotic scaling of droplet number and surface coverage. In the time-asymptotic regime, they admit a data collapse: the data for all substrates and condensation rates lie on universal scaling functions.
  • Dynamics of Wetting and Adhesion on Soft Substrates
    Item type: Doctoral Thesis
    Smith-Mannschott, Katrina (2024)
    The ubiquity of soft materials in our daily experiences, in addition to their growing importance in industrial applications, makes understanding their behavior of great interest. As research into contact between material interfaces shifted more towards compliant materials, it became clear that their behavior during contact differed from that of stiffer materials. The classical continuum mechanics model that had originally been developed for more rigid materials, needed to be augmented to include adhesive forces in order to explain the contact mechanics of these softer solids. However, as increasingly compliant solids came under study, it became evident that even this updated model was not quite able to accurately capture the geometry and force of contact. Further research showed that for very soft substrates, surface stress plays a vital role in determining contact behavior. Even with this progress, the area of contact mechanics of soft solids continues to be one rife with questions, in which we are still working to understand the deep fundamentals. This dissertation contributes to the field by exploring two aspects of contact mechanics of soft solids: (i) the effect of stretching a soft substrate on wetting at its surface and (ii) the dynamics of contact initiation. In the first part of this thesis, we use polydimethylsiloxane (PDMS) gels to establish that stretched, soft, smooth solids exhibit anisotropic wetting behaviors, contrary to expectations from our existing continuum mechanics model of contact behavior. We observe this anisotropy in static droplets of varying sizes, with smaller droplets exhibiting greater eccentricity than larger ones. Additionally, we show that the eccentricity of the droplet shape grows monotonically with the stretch applied to the substrate. We further demonstrate that this anisotropy extends to dynamic behavior as well, with droplets sliding more quickly in parallel, rather than perpendicular, to the stretch direction. By demonstrating that stretched, stiffer substrates do not reveal asymmetric wetting, we conclude that surface stresses contribute to this particular contact behavior. Subsequently in this thesis, the dynamics of how contact is established between a rigid glass spherical indenter and a soft PDMS substrate are explored. Here we confirmed that contact radius and tensile force during the initiation of zero-indentation contact both grow monotonically with substrate stiffness and indenter size. We determined that the growth curves over time could be collapsed onto universal curves showing overall logarithmic growth for each parameter set. Furthermore by combining the force and contact radius measurements, we were able to see hints of a weak power law dependence between the two. The final portion of this dissertation delves into some unexpected behavior we observed while exploring contact initiation. We found that electrostatic forces can have a significant influence on the adhesion dynamics between a PDMS substrate and a glass sphere. As the substrate was approached by the force probe, we measured an, in part, power law growth of force with distance from the surface. More surprisingly, we found that our soft PDMS substrate was able to jump multiple microns into contact with the indenter. This jump led to the establishment of a lasting adhesive contact for the softest substrate. Slightly stiffer substrates exhibited repeated attachment and detachment cycles over hundreds of seconds, with little to no change in the tensile force at attachment over that time. To our knowledge, this is the first time electrostatic forces have been observed to influence the contact behavior of soft solids. The investigations in this dissertation provide new experimental insights into the contact mechanics of compliant solids. We establish the existence of some previously unknown behaviors in both static and dynamics wetting and adhesion, making a significant contribution towards our further understanding of the contact behavior of soft substrates. Our work also lays important groundwork for future research into the interesting phenomena encountered herein.
  • Supramolecular gelation controlled by an iodine clock
    Item type: Journal Article
    Riedel, Solenn; Schweizer, Thomas; Smith-Mannschott, Katrina; et al. (2021)
    Soft Matter
    Programming supramolecular assembly in the time domain is a fundamental aspect of the design of biomimetic materials. We achieved the time-controlled sol–gel transition of a poly(vinyl alcohol)–iodine supramolecular complex by generating iodine in situ with a clock reaction. We demonstrate that both the gelation time and the mechanical properties of the resulting hydrogel can be tuned by properly selecting the clock parameters or through competitive iodine complexation.
  • Droplets Sit and Slide Anisotropically on Soft, Stretched Substrates
    Item type: Journal Article
    Smith-Mannschott, Katrina; Xu, Qin; Heyden, Stefanie; et al. (2021)
    Physical Review Letters
    Anisotropically wetting substrates enable useful control of droplet behavior across a range of applications. Usually, these involve chemically or physically patterning the substrate surface, or applying gradients in properties like temperature or electrical field. Here, we show that a flat, stretched, uniform soft substrate also exhibits asymmetric wetting, both in terms of how droplets slide and in their static shape. Droplet dynamics are strongly affected by stretch: Glycerol droplets on silicone substrates with a 23% stretch slide 67% faster in the direction parallel to the applied stretch than in the perpendicular direction. Contrary to classical wetting theory, static droplets in equilibrium appear elongated, oriented parallel to the stretch direction. Both effects arise from droplet-induced deformations of the substrate near the contact line.
  • Surface Tension and the Strain-Dependent Topography of Soft Solids
    Item type: Journal Article
    Bain, Nicolas; Jagota, Anand; Smith-Mannschott, Katrina; et al. (2021)
    Physical Review Letters
    When stretched in one direction, most solids shrink in the transverse directions. In soft silicone gels, however, we observe that small-scale topographical features grow upon stretching. A quantitative analysis of the topography shows that this counterintuitive response is nearly linear, allowing us to tackle it through a small-strain analysis. We find that the surprising increase of small-scale topography with stretch is due to a delicate interplay of the bulk and surface responses to strain. Specifically, we find that surface tension changes as the material is deformed. This response is expected on general grounds for solid materials, but challenges the standard description of gel and elastomer surfaces.
Publications 1 - 5 of 5