## 3 Sample Environments
### Mechanical Deformation  
Uniaxial mechanical deformation studies on soft materials are relatively easy to implement and are extensively used by academics and in industrial materials testing laboratories. Several small-scale deformation stages are commercially available, but these are in general, only suited for qualitative tensile data involving local molecular conformations. To obtain quantitative tensile results simultaneously with the neutron scattering data, one has to make sure that the sample is uniform over its entire volume and not only at the point of intercept with the neutron beam. With the exception of ambient or near ambient temperatures, one encounters the issue of how to uniformly heat the sample. This obviously can be achieved by placing the entire deformation load frame in a temperature-controlled chamber, but in doing so, any temperature changes will be slow to equilibrate, thus limiting the technique's application with neutron scattering instrumentation. Since polymeric materials exhibit a wide variety of materials properties, the type of required load frame depends on the maximum tensile force and elongation required. Elastic rubber samples require little stress but a high strain, i.e., elongation [67], whilst the reverse is true for High Density Polyethylene (HDPE) [68]. For such samples, the required mechanical performance (i.e., stresses between 10 and 200 N) required of the load frames is easily covered by commercially available equipment from a variety of suppliers. Early on, mechanical deformation experiments were performed in a quasi-static fashion, i.e., deform-hold-collect data. This deformation protocol works well for some materials where the molecular relaxation times are long. Otherwise one has to revert to continuous stretch protocols where the data collection time can be problematic. This is often the situation when the materials are unclamped and allowed to molecularly relax [69]. Relaxation of isotopic blends of linear polyethylene and ethylene copolymers with butyl and hexyl was studied, but due to the relatively small amount of material in the neutron beam (intrinsic to this type of deformation experiments), data could only be obtained at 30 min time intervals. An extensive discussion on how the anisotropy manifests itself in scattering patterns, due to the molecular and domain orientation induced by applying the deformation, can be found in experiments of elastomeric polypropylene [70]. A method to increase the information content of on-line deformation experiments is the use of Digital Image Correlation (DIC) [71]. This optical method is easy to install on a neutron scattering instrument and allows one to probe the homogeneity of the deformation process over the entire sample and also provide macroscopic material parameters. See Figure 8. When combined with neutron scattering experiments, one obtains a more complete picture of the material's deformation behavior. Simultaneous DIC furthermore supplies additional validation of the reliability of the experimental results since mechanical problems, such as slippage at clamps, will be noticed earlier. Figure 7: A schematic of the fluidic Four Roll Mill device in which different flows can be generated. The flows can be created by applying a pressure flow in the channels marked with closed dots and opening the valves in the channels marked with the open dots. The neutron beam is directed along the white path between the flow channels with a diameter of 1 mm. The flow channels have dimensions of 2 \(\times\) 3 mm\({}^{2}\) (reproduced with permission from [66], [PERSON], Nature, 2018). Although homogeneous temperature control on samples that require large elongation is somewhat more complicated to achieve, other parameters like humidity can be relatively easy controlled. This requires the construction of a solid chamber around the moving parts. An example of this is the stress-induced long range ordering in spider silk [72].