Soft solids and complex fluids: Program 2017

The idea of this summer school is to create a friendly learning atmosphere, to enable close contact between students and lecturers, and create opportunities for students to make lasting contacts with peers at other universities.

Topics for 2017:

Eric Weeks, Emory University Colloidal glasses and jammed emulsions
Colloids are suspensions of small solid particles in a liquid, and emulsions of droplets of one liquid in an immiscible second liquid. These materials exhibit glassy behavior when the particle (or droplet) concentration is high. In these samples, the particles are roughly analogous to individual molecules in a traditional glass. These model systems have been used to study the glass transition since the 1980’s. I’ll discuss the general phenomenology of these materials and present several recent developments.
Xiaoming Mao, University  of Michigan Critical mechanical structures: Maxwell lattices, phonon Green’s functions, and disordered networks
Critical mechanical structures are systems close to mechanical instability and exhibit a small number of floppy modes (i.e., normal nodes of motion which cost no elastic energy).  Many fascinating experimental phenomena, including jamming, glass transition, colloidal glass transition, and structural phase transition of crystals, involve passing through mechanical instability and thus could be studied as critical mechanical structures.  In this short course, we will discuss fundamental concepts of mechanical stability, introduce Maxwell lattices as simple examples of critical mechanical structures, and discuss Green’s functions methods that can be used to characterize mechanical problems in both ordered and disordered systems.
Daniel Blair, Georgetown University Rheo-Optical methods for quantifying soft and biological matter
Rheology and microrheology are powerful tools for quantifying the mechanical properties of soft and biological materials. In many cases, these techniques have fundamental limitations. Bulk rheology is precisely that — bulk, meaning that the microscopic physics must be inferred from constitutive models rather than direct measurements. In spite of this limitation, bulk rheology provides a way to explore the highly nonlinear behavior often associated with flowing soft matter; this is not the case for passive microrheology which is predicated on thermal fluctuations and linear response. To close the gap, we have developed a system that couples bulk rheometry to microscopy, providing us a way to probe the nonlinearities while simultaneously quantifying the physics of the microscale constituents.
In my lectures I will explain our technique in the context of various soft matter systems. After describing the fundamentals of rheological measurements and the basics of confocal microscopy, I will discuss the microscale physics of soft and biological materials when subjected to shear stresses. In particular, I will describe the route to shear thickening in colloidal suspensions, how biopolymers can harden and stiffen, how the flow of compressed emulsions is related to soft glasses, and describe how complex 3-D micro-environments are being created to quantify cellular hapto- and duro- taxis.
Benny Davidovitch, University of Massachsusetts Amherst Elasto-capillarity
We will address the mechanics of liquid interfaces in contact with solids, which are deformable due to their structure (e.g. filaments, sheets, or shells), or intrinsic nature (low Young’s modulus).  We will start with a basic description of the continuum mechanics of liquid interfaces (capillarity) and solids (elasticity), and will spend some time to elucidate some elementary (but confusing) concepts: surface tension, stress, deformability and inextensibility. Special attention will be given to identifying the various dimensionless groups underlying elasto-capillary phenomena, and understanding their physical role.  After this introduction, we will focus on some recent developments in the field, often described as “extreme mechanics” problems: wet hair, partial wetting of ultra-thin solids and of ultra-small drops, and wrapping problems.

Format:

The school will be a 5-day residential program running from noon on Sunday, May 28 to Thursday Evening, June 1, 2017. Four lecturers will give mini-courses composed of four 90-min lectures. The lectures will be interspersed with student presentations, and some social activities. Typically, we will have four lectures a day, leaving time for discussions scientific and otherwise. The lecturers may set assignments. More details on the courses will appear here closer to the date of the school.

Location:

UMass Amherst, the flagship campus of the University of Massachusetts system, is located in the scenic Pioneer Valley of Western Massachusetts, a 2-hour drive from Boston and 3 hours from New York City. The area is home to UMass and to four other liberal arts colleges. The area has a rich cultural environment in a rural setting. There are also a number of outdoor activities to fill in your free time – hiking and biking trails criss-cross the area.

Logistics:

There will be a fee of $425 for attending the school. The fee will cover on-campus lodging at UMass, breakfast, lunch and refreshments, as well as two evening meals. On other evenings, we will leave you to explore the eateries, bars, coffee-shops of Amherst and neighboring Northampton. The town is a 15 minute walk from campus, and there is free public transportation connecting the university and the town.

Posters:

All participants are encouraged to bring a poster describing the research they are involved in or going on in their research groups.  These posters do not need to report new or finished research results, and can be less formal than posters you would present at a regular conference.  We will have one or more poster sessions, where you can find out about what is happening at other universities.

Northeastern Granular Workshop:

You may want to attend the one-day Northeastern Granular Workshop, which will be held at Northeastern University in Boston on Friday, June 2, 2016 (the day after the summer school).  Registration for the NEGW is separate from the summer school; information on the NEGW will be posted at http://gibbs.engr.ccny.cuny.edu/NEGW.php.