The design, development and performance of the time‐of‐flight (TOF) small‐angle diffractometer (SAD) at the Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory are described. Similar TOF‐SANS instruments are in operation at the pulsed neutron sources at Los Alamos National Laboratory, USA, at Rutherford Appleton Laboratory, England, and at KEK, Japan. These instruments have an advantage by comparison with their steady‐state counterparts in that a relatively wide range of momentum transfer (q) can be monitored in a single experiment without the need to alter the collimation or the sample‐to‐detector distance. This feature makes SANS experiments easy and very effective for studying systems such as those undergoing phase transitions under different conditions, samples that cannot be easily reproduced for repetitive experiments, and systems under high temperature, pressure or shear. Three standard samples are used to demonstrate that the quality of the SANS data from SAD is comparable with those from other established steady‐state SANS facilities. Two examples are given to illustrate that the wide q region accessible in a single measurement at SAD is very effective for following the time‐dependent phase transitions in paraffins and temperature‐ and pressure‐dependent phase transitions in model biomembranes.

Small-angle neutron scattering is a useful new approach to the study of zeolite crystallization from aluminosilicate gels and the action of template molecules. It has been applied to gels for synthesis of zeolite ZSM-5 using tetrapropylammoniurn ions as templates where the scattering length densities of the gel particles and their texture were determined using contrast variation methods. Gels formulated from soluble silicate incorporate template molecules promptly into an amorphous "embryonic" structure and crystallization ensues via a solid hydrogel transformation mechanism. Gels formulated from colloidal silica show different scattering behavior, and a liquid phase transport mechanism is inferred.

No abstract

No abstract

molecules, 12, 586 (1979).(52) Note that the use of "excluded volume" in this contextunswellable or inaccessible polymer regions due to cross-link density variations-should not be confused with the definition used in many theories in which "excluded volume" is defined as the fact that a given polymer molecule excludes others or itself from occupying its immediate place in space,47 although the concepts are similar. In this case "excluded volume" refers to supermolecular regions.