###### Abstract  
Understanding soft and biological materials requires global knowledge of their microstructural features from elementary units at the nm scale up to larger complex aggregates in the micrometer range. Such a wide range of scale can be explored using the KWS-2 small-angle neutron (SANS) diffractometer. Additional information obtained by in situ complementary techniques sometimes supports the SANS analysis of systems undergoing structural modifications under external stimuli or which are stable only for short times. Observations at the local molecular level structure and conformation assists with an unambiguous interpretation of the SANS data using appropriate structural models, while monitoring of the sample condition during the SANS investigation ensures the sample stability and desired composition and chemical conditions. Thus, we equipped the KWS-2 with complementary light absorption and scattering capabilities: Fourier transform infrared (FTIR) spectroscopy can now be performed simultaneously with standard and time-resolved SANS, while in situ dynamic light scattering (DLS) became available for routine experiments, which enables the observation of either changes in the sample composition, due to sedimentation effects, or in size of morphologies, due to aggregation processes. The performance of each setup is demonstrated here using systems representative of those typically investigated on this beamline and benchmarked to studies performed offline. S 30 April 202129 May 202129 May 202130 April 202129 May 202130 April 202129 May 202130 May 202130 April 202129 May 2021  
matter systems. This is particularly crucial for dynamic systems, to ensure sample stability, purity, chemical conditions, to reduce ambiguities in data reduction, and for when it is not possible to perform further measurements or characterization on intermediate states ex situ. Given the high brilliance of synchrotron radiation, simultaneous analyses by X-ray and differential scanning calorimetry (DSC) or Raman spectroscopy were developed quite early at the Synchrotron Radiation Source in Daresbury, U.K. [2; 3], and used successfully since then [4; 5]. More recently, in situ size-exclusion chromatography (SEC) with SAXS [6] was developed for the first time at the Advanced Photon Source of Argonne National Laboratory (ANL, Lemont, IL, USA). This brought advantages in the field of protein scattering, in which samples very often typically show poor stability or aggregation tendency. As unique probes, neutrons interact differently with the \({}^{1}\)H and \({}^{2}\)H (deuterium, D) hydrogen isotopes: the large difference in the coherent scattering length density between H and D represents the basis of the contrast variation and contrast matching methods. As most of the soft matter and biological samples consist of hydrocarbon systems, the H/D substitution offers the possibility to vary the coherent scattering length density of a compound over a broad range. With this technique, selected constituents in a complex multi-component system can be labeled by isotope exchange. Depending on the created contrast--the squared difference between the scattering length density of one component and that of the other components or the environment medium--selected components or regions within a complex soft matter or biophysical morphology can be made visible or invisible in the scattering experiment without the chemical alteration of the system. Owing to technological developments in high-intensity specialized SANS instruments such as detectors and neutron guides [7; 8], exciting developments in the nature and number of characterization techniques that can be performed in situ on large-scale SANS instruments started to emerge. For example, the first implementation of an in situ SEC-SANS system was reported with a D22 instrument at the Institute Laue-Langevin (ILL, Grenoble, France) [9], while first results obtained with a simultaneous SANS and FTIR measuring system were collected with the KWS-2 instrument [10].