Pree-Cha Kiatkirakajorn and Lucas Goehring:
"Formation of Shear Bands in Drying Colloidal Dispersions"
Phys. Rev. Lett. 115 (2015) 088302
[Journal URL], [BibTeX], [Abstract]

@article { kiatkirakajorn-prl-2015,
  title = {Formation of Shear Bands in Drying Colloidal Dispersions},
  author = {Kiatkirakajorn, Pree-Cha AND Goehring, Lucas},
  journal = {Physical Review Letters},
  volume = {115},
  issue = {8},
  year = {2015},
  pages = {088302-1--088302-5},
  doi = {10.1103/PhysRevLett.115.088302},
  publisher = {American Physical Society}

In directionally dried colloidal dispersions regular bands can appear behind the drying front, inclined at +/-45° to the drying line. Although these features have been noted to share visual similarities with shear bands in metal, no physical mechanism for their formation has ever been suggested, until very recently. Here, through microscopy of silica and polystyrene dispersions, dried in Hele-Shaw cells, we demonstrate that the bands are indeed associated with local shear strains.We further show how the bands form, that they scale with the thickness of the drying layer, and that they are eliminated by the addition of salt to the drying dispersions. Finally, we reveal the origins of these bands in the compressive forces associated with drying, and show how they affect the optical properties (birefringence) of colloidal films and coatings.

Lucas Goehring, Akio Nakahara, Tapati Dutta, So Kitsunezaki, and Sujata Tarafdar:
"Desiccation Cracks and their Patterns: Formation and Modelling in Science and Nature"
WILEY-VCH, Weinheim, Germany (2015)
ISBN: 978-3-527-41213-6
[Book URL], [BibTeX], [Description]

@book {geohring-2015,
  booktitle = {Desiccation Cracks and their Patterns: Formation and Modelling in Science and Nature},
  author = {Goehring, Lucas AND Nakahara, Akio AND Dutta, Tapati AND Kitsunezaki, So AND Tarafdar, Sujata},
  year = {2015},
  isbn = {978-3-527-41213-6},
  publisher = {WILEY-VCH, Weinheim, Germany},

Bringing together basic ideas, classical theories, recent experimental and theoretical aspects, this book explains desiccation cracks from simple, easily-comprehensible cases to more complex, applied situations.
The ideal team of authors, combining experimental and theoretical backgrounds, and with experience in both physical and earth sciences, discuss how the study of cracks can lead to the design of crack-resistant materials, as well as how cracks can be grown to generate patterned surfaces at the nano- and micro-scales. Important research and recent developments on tailoring desiccation cracks by different methods are covered, supported by straightforward, yet deep theoretical models. Intended for a broad readership spanning physics, materials science, and engineering to the geosciences, the book also includes additional reading especially for students engaged in pattern formation research.

Lucas Goehring and Stephen W. Morris:
"Cracking mud, freezing dirt, and breaking rocks"
Physics Today 67 (2014) 39
[Journal URL], [BibTeX]

@article {goehring-pt-2014,
  title = {Cracking mud, freezing dirt, and breaking rocks},
  author = {Goehring, Lucas AND W. Morris, Stephen},
  journal = {Physics Today},
  volume = {67},
  issue = {11},
  year = {2014},
  pages = {39--44},
  doi = {10.1063/PT.3.2584},
  publisher = {American Institute of Physics Publishing},

Stephan Herminghaus, Corinna C. Maass, Carsten Krüger, Shashi Thutupalli,
Lucas Goehring, and Christian Bahr:
"Interfacial mechanisms in active emulsions"
Soft Matter 10 (2014) 7008
[Journal URL], [BibTeX], [Abstract]

@article { herminghaus-sm-2014,
  title = {Interfacial mechanisms in active emulsions},
  author = {Herminghaus, Stephan AND Maass, Corinna C. AND Kr{\"u}ger, Carsten AND Thutupalli, Shashi AND Goehring, Lucas AND Bahr, Christian},
  journal = {Soft Matter},
  volume = {10},
  issue = {36},
  year = {2014},
  pages = {7008--7022},
  doi = { 10.1039/C4SM00550C},
  publisher = {The Royal Society of Chemistry},

Active emulsions, i.e., emulsions whose droplets perform self-propelled motion, are of tremendous interest for mimicking collective phenomena in biological populations such as phytoplankton and bacterial colonies, but also for experimentally studying rheology, pattern formation, and phase transitions in systems far from thermal equilibrium. For fuelling such systems, molecular processes involving the surfactants which stabilize the emulsions are a straightforward concept. We outline and compare two different types of reactions, one which chemically modifies the surfactant molecules, the other which transfers them into a different colloidal state. While in the first case symmetry breaking follows a standard linear instability, the second case turns out to be more complex. Depending on the dissolution pathway, there is either an intrinsically nonlinear instability, or no symmetry breaking at all (and hence no locomotion).

François Boulogne, Ludovic Pauchard, Frédérique Giorgiutti-Dauphiné, Robert Botet, Ralf Schweins, Michael Sztucki, Joaquim Li, Bernard Cabane and Lucas Goehring:
"Structural anisotropy of directionally dried colloids"
EPL 105 (2014) 38005
[Journal URL], [BibTeX], [Abstract]

@article { boulogne-epl-2014,
  title = {Structural anisotropy of directionally dried colloids},
  author = {Boulogne, Fran{\c{c}}ois AND Pauchard, Ludovic AND Giorgiutti-Dauphin{\'e}, Fr{\'e}d{\'e}rique AND Botet, Robert AND Schweins, Ralf AND Sztucki, Michael AND Li, Joaquim AND Cabane, Bernard AND Goehring, Lucas},
  journal = {EPL},
  volume = {105},
  year = {2014},
  pages = {38005p1--38005p6},
  doi = {10.1209/0295-5075/105/38005},
  publisher = {EPLA},

Aqueous colloidal dispersions of silica particles become anisotropic when they are dried through evaporation. This anisotropy is generated by a uniaxial strain of the liquid dispersions as they are compressed by the flow of water toward a solidification front. Part of the strain produced by the compression is relaxed, and part of it is stored and transferred to the solid. This stored elastic strain has consequences for the properties of the solid, where it may facilitate the growth of shear bands, and generate birefringence.

Lucas Goehring:
"Pattern formation in the geosciences"
Phil. Trans. A 371 (2013) 20120352
[Journal URL], [BibTeX], [Abstract]

@article { goehring-pt-2013,
  title = {Pattern formation in the geosciences},
  author = {Lucas Goehring},
  journal = {Philosophical Transactions of the Royal Society A},
  volume = {371},
  issue = {2004},
  year = {2013},
  pages = {20120352},
  doi = {10.1098/rsta.2012.0352},
  publisher = {Royal Society Publishing}

Pattern formation is a natural property of nonlinear and non-equilibrium dynamical systems. Geophysical examples of such systems span practically all observable length scales, from rhythmic banding of chemical species within a single mineral crystal, to the morphology of cusps and spits along hundreds of kilometres of coastlines. This article briefly introduces the general principles of pattern formation and argues how they can be applied to open problems in the Earth sciences. Particular examples are then discussed, which summarize the contents of the rest of this Theme Issue.

Lucas Goehring:
"Evolving fracture patterns: columnar joints, mud cracks and polygonal terrain"
Phil. Trans. A 371 (2013) 20120353
[Journal URL], [BibTeX], [Abstract]

@article { goehring-pt2-2013,
  title = {Evolving fracture patterns: columnar joints, mud cracks and polygonal terrain},
  author = {Lucas Goehring},
  journal = {Philosophical Transactions of the Royal Society A},
  volume = {371},
  issue = {2004},
  year = {2013},
  pages = {20120353},
  doi = {10.1098/rsta.2012.0353},
  publisher = {Royal Society Publishing}

When cracks form in a thin contracting layer, they sequentially break the layer into smaller and smaller pieces. A rectilinear crack pattern encodes information about the order of crack formation, as later cracks tend to intersect with earlier cracks at right angles. In a hexagonal pattern, in contrast, the angles between all cracks at a vertex are near 120°. Hexagonal crack patterns are typically seen when a crack network opens and heals repeatedly, in a thin layer, or advances by many intermittent steps into a thick layer. Here, it is shown how both types of pattern can arise from identical forces, and how a rectilinear crack pattern can evolve towards a hexagonal one. Such an evolution is expected when cracks undergo many opening cycles, where the cracks in any cycle are guided by the positions of cracks in the previous cycle but when they can slightly vary their position and order of opening. The general features of this evolution are outlined and compared with a review of the specific patterns of contraction cracks in dried mud, polygonal terrain, columnar joints and eroding gypsum–sand cements.

K. Thomas, Stephan Herminghaus, H. Porada, and Lucas Goehring:
"Formation of kinneyia via shear-induced instabilities in microbial mats"
Phil. Trans. A 371 (2013) 20120362
[Journal URL], [BibTeX], [Abstract]

@article { thomas-pt-2013,
  title = {Formation of kinneyia via shear-induced instabilities in microbial mats},
  author = {Thomas, K. AND Herminghaus, Stephan AND Porada, H. AND Goehring, Lucas},
  journal = {Philosophical Transactions of the Royal Society A},
  volume = {371},
  issue = {2004},
  year = {2013},
  pages = {20120362},
  doi = {10.1098/rsta.2012.0362},
  publisher = {Royal Society Publishing}

Kinneyia are a class of microbially mediated sedimentary fossils. Characterized by clearly defined ripple structures, Kinneyia are generally found in areas that were formally littoral habitats and covered by microbial mats. To date, there has been no conclusive explanation of the processes involved in the formation of these fossils. Microbial mats behave like viscoelastic fluids. We propose that the key mechanism involved in the formation of Kinneyia is a Kelvin-Helmholtz-type instability induced in a viscoelastic film under flowing water. A ripple corrugation is spontaneously induced in the film and grows in amplitude over time. Theoretical predictions show that the ripple instability has a wavelength proportional to the thickness of the film. Experiments carried out using viscoelastic films confirm this prediction. The ripple pattern that forms has a wavelength roughly three times the thickness of the film. This behaviour is independent of the viscosity of the film and the flow conditions. Laboratory-analogue Kinneyia were formed via the sedimentation of glass beads, which preferentially deposit in the troughs of the ripples. Well-ordered patterns form, with both honeycomb-like and parallel ridges being observed, depending on the flow speed. These patterns correspond well with those found in Kinneyia, with similar morphologies, wavelengths and amplitudes being observed.

Lucas Goehring, William J. Clegg, and Alexander F. Routh:
"Plasticity and fracture in drying colloidal films"
Phys. Rev. Lett. 110 (2013) 024301
[Journal URL], [BibTeX], [Abstract]

@article { goehring-PRL-2013,
  title = {Plasticity and fracture in drying colloidal films},
  author = {Goehring, Lucas, Clegg, William J. and Routh, Alexander F.},
  journal = {Physical Review Letters},
  volume = {110},
  issue = {2},
  year = {2013},
  pages = {024301},
  doi = {10.1103/PhysRevLett.110.024301},
  publisher = {American Physical Society}

Cracks in drying colloidal dispersions are typically modeled by elastic fracture mechanics, which assumes that all strains are linear, elastic, and reversible. We tested this assumption in films of a hard latex, by intermittently blocking evaporation over a drying film, thereby relieving the film stress. Here we show that although the deformation around a crack tip has some features of brittle fracture, only 20%–30% of the crack opening is relieved when it is unloaded. Atomic force micrographs of crack tips also show evidence of plastic deformation, such as microcracks and particle rearrangement. Finally, we present a simple scaling argument showing that the yield stress of a drying colloidal film is generally comparable to its maximum capillary pressure, and thus that the plastic strain around a crack will normally be significant. This also suggests that a film’s fracture toughness may be increased by decreasing the interparticle adhesion.

Tammy M. K. Cheng, Lucas Goehring, Linda Jeffery, Yu-En Lu, Jacqueline Hayles, Béla Novák, and Paul A. Bates:
"A Structural Systems Biology Approach for Quantifying the Systemic Consequences of Missense Mutations in Proteins"
PLoS Comput Biol 8 (2012) e1002738
[Journal URL], Open Access article, [BibTeX], [Abstract]

@article { cheng-PLOS-2012,
  title = {A Structural Systems Biology Approach for Quantifying the Systemic Consequences of Missense Mutations in Proteins},
  author = {Cheng, Tammy M. K. AND Goehring, Lucas AND Jeffery, Linda AND Lu, Yu-En AND Hayles, Jacqueline AND Nov{\'a}k, B{\'e}la AND Bates, Paul A.},
  journal = {PLOS Computational Biology},
  volume = {8},
  issue = {10},
  year = {2012},
  pages = {e1002738},
  doi = {10.1371/journal.pcbi.1002738},
  publisher = {Public Library of Science (United States)},

Gauging the systemic effects of non-synonymous single nucleotide polymorphisms (nsSNPs) is an important topic in the pursuit of personalized medicine. However, it is a non-trivial task to understand how a change at the protein structure level eventually affects a cell's behavior. This is because complex information at both the protein and pathway level has to be integrated. Given that the idea of integrating both protein and pathway dynamics to estimate the systemic impact of missense mutations in proteins remains predominantly unexplored, we investigate the practicality of such an approach by formulating mathematical models and comparing them with experimental data to study missense mutations. We present two case studies: (1) interpreting systemic perturbation for mutations within the cell cycle control mechanisms (G2 to mitosis transition) for yeast; (2) phenotypic classification of neuron-related human diseases associated with mutations within the mitogen-activated protein kinase (MAPK) pathway. We show that the application of simplified mathematical models is feasible for understanding the effects of small sequence changes on cellular behavior. Furthermore, we show that the systemic impact of missense mutations can be effectively quantified as a combination of protein stability change and pathway perturbation.