H. Henning Winter’s group measures, analyzes, and models the rheology of soft matter. This includes materials with dynamically evolving properties, such as physically and chemically crosslinking systems, crystallizing polymers, colloidal glasses, microphase-separating block copolymers, drying paints, aging bitumen, and structuring nanocomposites. It also includes complex materials, such as molten polymers, coacervates, adhesives, and hydrogels with molecular sensors. We place particular focus on the development of advanced experimental methods and models, as needed.
Access to publications of Winter group: http://rheology.tripod.com/HHWpublications.html
In a series of groundbreaking papers, Winter’s group pioneered a new general framework for gelation of amorphous materials. This has greatly impacted theoretical approaches to gelation and furthered the industrial development and use of novel complex materials, from adhesives, sealants, toners, and food materials to various materials for biomedical applications.
Figure: Rheological material functions of a polymer near its gel point. Frequency-invariant data at the gel point are the consequence of the powerlaw modulus at the gel point. (Winter HH* (2017) The Solidification rheology of amorphous polymers - vitrification as compared to gelation. Macromolecular Symposia 374:177–180)
In addition to contributions in gelation, Winter and his collaborators discovered the rheological scaling laws that govern the glass transition (colloidal and molecular). This led to a new criterion that can distinguish gels from soft glasses.
Figure: Colloidal glass transition, data on the left and relaxation time spectra on the right (Siebenbürger M, Hajnal D, Henrich O, Fuchs M*, Winter HH*, Ballauff M* (2009) Viscoelasticity and shear flow of concentrated, non-crystallizing colloidal suspensions: comparison with mode-coupling theory. J Rheology 53:707-720)
Figure: Relaxation modulus near the transition from liquid to solid behavior, shown for three distinct classes of internal connectivity. (Winter HH* (2013) Glass transition as the rheological inverse of gelation. Macromolecules 46:2425-2432)
Winter and his collaborators also pioneered a novel method of extracting relevant material properties from rheological data and theory. This became possible through a PC-based cyber infrastructure platform, which acts as virtual space for 15 of the world's leading rheology groups to share their expert rheology codes with researchers, students, and practitioners. The rheological software is used extensively in laboratories worldwide, both for academic research and businesses, including several Fortune 100 companies.
Figure: Bundling of global rheology expertise onto PC platform (IRIS Rheo-Hub) for research, teaching, and material development (Winter HH*, Mours M (2006) The cyber infrastructure initiative for rheology. Rheologica Acta 45:331-338)
Another research problem central to Winter’s group, is the efficient decomposition of solid particles of layered structure into their thin leaves (“exfoliation”). Clay, graphite, zeolite, and black phosphorus have been exfoliated in groundbreaking high-yield processes. The group’s work has resulted in the possibility to develop novel nanocomposites with synergistic properties (mechanical, electrical, filtration, and barrier).
Figure: Graphene chips from a novel exfoliation method of crystalline graphene providing high yield and easy processing. Properties of graphene chips (left) and yield comparison for sonication of graphite suspensions (right) (Liu W, Tanna VA, Yavitt BY, Dimitrakopoulos C, Winter HH* (2015) Fast production of high-quality graphene via sequential liquid exfoliation, ACS Appl Mater Interfaces 7: 27027−27030)
Recently, Winter and coworkers discovered a new relaxation mechanism which allows for rapid ordering of specific block co-polymers: Relaxation due to internal slip layers (ISL) in layered diblock co-polymers with alternating domains of polymer A and polymer B. Slipping in the middle of each of the domains is facilitated by a high concentration of free chain ends, which liquify the structure locally. While the ordering in conventional block co-polymers is known to be notoriously slow, ISL overcomes this problem for tailormade block co-polymers and makes them viable for industrial application.
Figure: Internal slip layers (ISL) in the middle of microphase separated di-block domains (marked by dotted arrows) of a bottlebrush co-polymer. The side chains themselves avoid overlap due to steric crowding and repulsive forces. The domain interface (dashed lines) is set at junction point between PEO and PS blocks, further constraining side chains. (Yavitt BM, Fei HF, Kopanati GN, Winter HH*, Watkins JJ* (2019) Power law relaxations in lamellae forming brush block copolymers with asymmetric molecular shape, Macromolecules, to appear)
Quark & quince, and growing tea (oregano and mint)
http://rheology.tripod.com/QuarkMakingOfHenning.htm - A recipe for homemade quark without rennet
http://rheology.tripod.com/Quittenmus.pdf - The homemade quince sauce