X-ray Diffraction Laboratory


Small angle X-ray scattering (SAXS) is a technique to measure the size and shape of nanometer particles.  The technique is particularly useful for particles suspended in solvents, such as proteins that are still in buffered aqueous solutions, and for amorphous solids such as plastic.  By examining x-rays that are scattered at small angles to the primary X-ray beam, we can measure information that is directly proportional to the size and shape of nanometer-sized objects.  The characteristics of materials at larger size scales are fundamentally different than at atomic scales.  Atomic scale structures are characterized by high degrees of order (crystals), and relatively simple and uniform building blocks (atoms). On the nano-scale, the building blocks of matter are not well organized and are described by complex and non-uniform building blocks. 

SAXS is well suited to study of plastics.  The SAXS image of a common plastic wrap will relay information on the internal structure of the plastic.  In this case, the plastic wrap is composed of a long amorphous polymer chains that wrap back on themselves to form crystalline sheets known as Lamellar crystallites.  The SAXS image tells us that these crystallites are relatively large and are stacked along one direction of the plastic sheet.  For an excellent reference on the structure of polymers see :  M. Kakudo and N. Kasai, X-ray Diffraction by Polymers (Tokyo: Kodansha Ltd, and Elsevier Pub. Co., Netherlands, 1972).

Typical Lamellar Structure

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