Applications of freeze‐fracture replication to problems in materials and colloid science

Abstract

Understanding the relationship between the molecular structure and the macroscopic properties of polymer solutions and gels, oil-water-surfactant emulsions, lyotropic and thermotropic liquid crystals, colloidal dispersions, detergents, and other such "microstructured fluids" is essential to the optimal use of these commercially important materials. Modern rapid-freezing methods followed by freeze-fracture replication techniques are ideally suited to allow the direct visualization of the three-dimensional structure of the particles or units that make up the dispersion, while simultaneously revealing their orientation and distribution with molecular resolution. This paper reviews the necessary experimental conditions required to successfully exploit the freeze-fracture technique as it applies to microstructured fluid systems. The benefits and limitations of structural studies by freeze-fracture techniques as opposed to the more commonly used light, X-ray, and neutron-scattering methods are discussed. Freeze-fracture replicas can also be imaged by scanning tunneling microscopy to reveal directly three-dimensional fracture contours with improved resolution.

RETRACTED: Flexible bilayers with spontaneous curvature lead to lamellar gels and spontaneous vesicles

“…1 A shows a freeze-fracture TEM (FFTEM) image of 7:3 wt:wt CTAT:SDBS in 40% water. The image is typical of gently undulating but overall flat bilayers similar to other lipid and surfactant lamellar phases and thermotropic smectic phases (21,(29)(30)(31). The structure correlates well with the resolution-limited SAXS peaks, implying large lamellar domains.…”

Direct mapping of local director field of nematic liquid crystals at the nanoscale

“…We note that the polymer itself does not form fibers. Rather, the oriented structures observed in SEM are a consequence of the anisotropic mechanical properties of LCPs, in which the bulk elastic modulus is usually much smaller perpendicular to the director (21,42) and in which fractures occur along surfaces parallel to the director field (43,44). The same type of fracture pattern can be observed in a nematic polymer that has some similarity with our LCPs (42).…”

Thermoplastic elastomer gels. I. Effects of composition and processing on morphology and gel behavior

“…The quenched TPEGs displayed in Figures 3a, 4a, and 5a are rapidly cooled to a temperature below the styrene T g , thereby preserving the size, shape, and distribution of the S-rich micelles immediately following the pressing process. Since the quench conditions employed here are not expected to instantaneously immobilize the molecules comprising the TPEGs (as would a quench into, for example, a liquid cryogen 39 ), it remains questionable as to whether the micelles exhibit evidence of long-range order at 180°C or undergo microstructural refinement during quenching. Due to the extended period spent above the styrene T g (ca.…”