In this thesis I present the conception, design and utilisation of the first neutron grating interferometers at higher Talbot orders to quantitatively study the microstructure of colloidal and powder samples. Quantitative analysis is achieved by varying the setup dependent autocorrelation length ξ. I refer to the experimental approach of varying ξ while recording a series of DFIs as sub-pixel correlation length imaging, or ξDFI. These methodical developments enabled unprecedented experiments that make the spatially resolved extraction of scattering functions possible. In order to utilise the newly developed setups to quantitatively study microstructures we present the theoretical foundation of ξDFI and two simulation frameworks, evaluating error sources and performance parameters. The insights gained from the theoretical and simulation work is then used to apply ξDFI to the study of macroscopically heterogeneous microstructures and presented as three different experiments.