AVS 71 Session BI2-MoM: Biomolecules and Biophysics at Interfaces

Soft materials are found in a host of applications, from adhesives and coatings to natural and synthetic biomaterials. Many of these materials comprise a lightly crosslinked polymer network, which can also be infused with a compatible liquid (i.e., swelling). Swelling offers additional functionality, like molecular transport, lubrication, and control over mechanical properties. However, understanding the behavior of soft and swollen interfaces is an ongoing challenge. For example, when crosslinked solids are sufficiently soft, or the characteristic size scale is small, they display liquid-like characteristics like capillarity, even without an infused liquid. When the networks are swollen, the swelling liquid itself provides true liquid behavior, creating multi-phase situations that are even more complex. Here we will leverage confocal microscopy to show how combinations of solid and liquid characteristics control the wetting on soft, swollen networks. In addition to network elasticity, we demonstrate that surface tension, liquid separation, and osmotic pressure are important considerations. We expand on our findings by developing a route to visualize dynamic contact lines of a dynamic, sliding drop. In addition to wetting, we exploit a combination of confocal microscopy and colloidal probe microscopy to study the effects of swelling on microscale friction. In this situation, creasing occurs, leading to solid-like stick-slip behavior. Creasing is mitigated by swelling, which appears to be a function of the swelling ratios.

Transparent semiconducting oxides play a critical role in fields ranging from corrosion, electrocatalysis and biocatalysis to the development of artificial leaf systems for solar fuel generation. However, their long-term stability remains a significant challenge, with photocorrosion being a major factor limiting performance. I will demonstrate how we employ an electrochemical flow cell coupled with inductively coupled plasma mass spectrometry (ICP-MS) to enable in situ, time-resolved monitoring of zinc release from zinc oxide (ZnO) single crystals under UV irradiation. This approach provides direct insights into the degradation pathways of ZnO, a key material in photoelectrochemical systems, including those inspired by natural photosynthesis.

We investigate the dissolution behavior of ZnO with (0001) and (101̅0) crystal orientations across a range of acidic and alkaline pH levels, examining potential-dependent dissolution under both oxygen and hydrogen evolution conditions. Our results highlight the significant influence of UV light and electrolyte pH on stability, closely linked to the intrinsic surface chemistry of ZnO. Notably, the polar ZnO(0001) orientation demonstrates superior stability at low potentials and under hydrogen evolution conditions. In contrast, non-polar ZnO(101̅0) exhibits higher dissolution rates, limiting its suitability for long-term water splitting and biocatalytic processes. It also highligths its role in corrosive processes where hydrogen can penetrate into materials leading to embrittlement.[1]

These findings underscore the critical role of surface structure and chemical stabilization in enhancing the durability of semiconducting oxides for materials stable against hydrogen permeation and next-generation energy conversion technologies. By optimizing surface design and understanding fundamental degradation mechanisms, it is possible to develop more resilient electroactive materials. I will discuss how the approach can be extended to other materials.

Reference.

[1] Dworschak et al. in ACS Appl Mater Interfaces, 2020 Nov 9;12(46):51530–51536. doi: 10.1021/acsami.0c15508 [https://doi.org/10.1021/acsami.0c15508]

[2] Ott et al. submitted

Knowledge about the free energy landscape of biomolecular reactions is necessary to understand how life works on the smallest scale. Unfortunately, obtaining experimental values of the free energy difference between two states like an unbound and a bound state of two molecules is rather difficult. [1] Jarzynski proposed an equality that connects the free energy difference between two states with the irreversible work that leads from one state to the other. Precisely, an average of all possible realizations of a process that moves the system from an equilibrium state to another state in equilibrium. Here, we test this hypothesis with experimental values. Using a simple model system, different nucleobase-pair interactions are measured using three different techniques that are able to measure the interactions force between two single molecules and up to 10⁷ interactions in a single experiment run. Using the Atomic Force Microscope (AFM), Optical Tweezers and the Surface Force Apparatus allows us to additionally investigate the scaling of biological single molecule interactions. Together with molecular dynamics simulations a strong foundation is laid to confirm Jarzynski’s equality and investigate the scaling of single-molecule interactions with a model system that is simplistic and biologically significant.

[1] 1. Gore J, Ritort F, Bustamante C. Bias and error in estimates of equilibrium free-energy differences from nonequilibrium measurements [Internet]. Vol. 100, Proceedings of the National Academy of Sciences. Proceedings of the National Academy of Sciences; 2003. p. 12564–9.

Corresponding/Presenting Author:Iago Peters, peters@iap.tuwien.ac.at