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Introduction to the Colloidal Glass Transition
| Content Provider | Semantic Scholar |
|---|---|
| Author | Weeks, Eric R. |
| Copyright Year | 2016 |
| Abstract | Colloids are suspensions of small solid particles in a liquid and exhibit glassy behavior when the particle concentration is high. In these samples, the particles are roughly analogous to individual molecules in a traditional glass. This model system has been used to study the glass transition since the 1980s. In this Viewpoint I summarize some of the intriguing behaviors of the glass transition in colloids and discuss open questions. G are an unusual state of matter in that they share some similarities to both liquids and solids. Molten glass is a liquid and can flow easily, but as it cools, its viscosity rises smoothly. In fact, upon cooling by several tens of degrees, the viscosity grows by 10 to 12 orders of magnitude. One rough definition of when a sample becomes a glass is when its viscosity is 10 times that of water, simply because viscosities that are any larger become problematic to measure. At this point the sample remains as disordered as a liquid on the molecular scale, but macroscopically appears solid. This is perhaps a dissatisfying situation, in that regular phase transitions are more obvious and well-defined as to the precise temperatures and pressures at which they occur. In contrast, the temperature required to form a glass depends on the cooling rate. Furthermore, one can note that if one waits decades flow can sometimes be observed, although this is not relevant for window glass. In the 1980s, colloidal suspensions were introduced as model systems which had a glass transition. Colloidal suspensions are composed of small (10 nm to 10 μm radius) solid particles in a liquid. Their glass transition is not as a function of temperature, but rather of concentration. At low concentration, particles undergo Brownian motion and diffuse through the sample freely. At higher concentrations, the particles pack together randomly (with a liquid-like structure), and macroscopically the sample viscosity grows dramatically as a function of concentration. Below the glass transition concentration, Brownian motion enables the sample to equilibrate, and the sample is still considered a liquid. Above the glass transition concentration, equilibration is no longer possible on experimental time scales, and macroscopically the sample has a yield stress like a regular elastic material. Colloidal glasses share many similarities to “regular” glasses. For example, they have a strong growth of their viscosity as the glass transition is approached; their structure is essentially unchanged at the glass transition; materials become dynamically heterogeneous as the transition is approached; confining colloidal samples modifies their glass transition. This Viewpoint cannot describe all of the interesting glassy phenomena that have been studied with colloidal glasses, although the reader is invited to consult longer review articles. Rather, a few representative experimental examples will be presented to demonstrate the advantages of colloids as a model system. A particular advantage is that their large size makes colloids directly observable with optical microscopy (see Figure 1) as well as indirectly observable with light scattering. Colloidal particles interact with one another with a variety of forces. This includes repulsive (such as electrostatic forces for charged particles) and attractive forces (such as the van der Waals force due to fluctuating electric dipole moments of the particles, which is quite strong at short-range). Discussing these Received: October 28, 2016 Accepted: December 16, 2016 Figure 1. Confocal microscopy image of a bidisperse colloidal sample with particle radii 1.18 and 1.55 μm. The scale bar represents 10 μm. Reproduced with permission from ref 20. Copyright Royal Society of Chemistry 2011. Viewpoint pubs.acs.org/macroletters © XXXX American Chemical Society 27 DOI: 10.1021/acsmacrolett.6b00826 ACS Macro Lett. 2017, 6, 27−34 This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.physics.emory.edu/faculty/weeks/lab/papers/weeksreview.pdf |
| Language | English |
| Access Restriction | Open |
| Subject Keyword | Adaptation American Cancer Society Behavior Brownian motion Charge (electrical) Colloids Computer cooling Cool - action Copyright Digital Object Identifier Eyeglasses Genetic Heterogeneity Glass Greater Ions Ising model License Linear scale Liquid substance Observable Particle Phase Transition Randomness Scientific Publication Smoothing Suspensions Transcutaneous Electric Nerve Stimulation Viewpoint Viscosity WAITS solid substance |
| Content Type | Text |
| Resource Type | Article |
