Developments in characterizing soft matter
- PDF / 761,433 Bytes
- 7 Pages / 585 x 783 pts Page_size
- 38 Downloads / 198 Views
tion Techniques for characterizing “hard” condensed matter are very familiar, including (conventional) electron microscopy, mechanical testing, and x-ray diffraction. This article will discuss corresponding approaches appropriate for soft matter. What is soft matter? An excellent short overview of topics encompassed by the phrase was given in the 1991 Nobel Lecture by the late Pierre-Gilles de Gennes, http://nobelprize.org/ nobel_prizes/physics/laureates/1991/gennes-lecture.html, one of the founding fathers of the field. (He notes that “Americans prefer to call it ‘complex fluids.’ ”) Soft matter covers many familiar everyday materials ranging from paints to cosmetics, beer foam and yogurt, to cement, and it increasingly intersects with biological systems such as human cells and their lipid membranes. At the more technological end of the spectrum, manufacturing of organic light-emitting diodes and photovoltaic devices relies on appropriate polymer processing (conveniently and cheaply from solution) derived from soft matter methodologies; nanotechnological solutions based on soft matter are elegantly discussed by Jones.1 What distinguishes soft condensed matter from hard is that the energy of deformations and fluctuations are comparable with thermal energy at room temperature, and the timescales
Athene M. Donald, Cavendish Laboratory at the University of Cambridge, UK, [email protected]
702
MRS BULLETIN • VOLUME 35 • SEPTEMBER 2010 • www.mrs.org/bulletin
over which these changes occur are typically of the order of seconds, so they are readily discernible. Think about applying paint; it works because the fluid flows readily on human timescales. Quantum mechanics is rarely needed to analyze these materials’ responses. In general, soft matter can be described as either a weak solid or a viscoelastic fluid and is normally electrically insulating (although aqueous solutions are obviously less so). These distinctions will indicate why traditional characterization techniques mentioned are unlikely to be particularly useful for soft matter without significant modifications. What follows is a discussion of two approaches specifically useful for this class of materials, namely environmental scanning electron microscopy (ESEM) and microrheology, with a brief discussion at the end of how dynamic scattering experiments (x-rays and, to a lesser extent, neutrons) can usefully be applied to follow real-time processes for such systems.
Environmental scanning electron microscopy How ESEM works The basic layout of ESEM is shown in Figure 1. Broadly speaking, the instrument is similar to a conventional SEM,
DEVELOPMENTS IN CHARACTERIZING SOFT MATTER
Pressure Range
Pressure Zone
10–7 torr
Gun Chamber
Gun Chamber Anode Aperture Column Lining Projection Apertures
10
–6
torr
10–4 torr 10
–1
torr
10 torr
Upper Column Environmental Chamber 2 Environmental Chamber 1 Specimen
Column Isolation Valve Upper Pressure–Limiting Aperture Vacuum Manifold Lower Pressure–Limiting Aperture and Integrated Detector Specimen Stage Figure 1. Schematic
Data Loading...
