Multi-Scale Interfacial Structural Dynamics of Smart Polymers via Neutron Probes

Stimuli-responsive functional polymer thin films and their buried interfacial hierarchical structures determine actuation, self-repair and energy conversion performances, yet conventional characterization tools fail to statistically resolve nano-to-micrometer lateral assemblies buried beneath material surfaces. This work integrates systematic research on humidity-responsive self-healing PEDOT:PSS/cellulose supramolecular polymer films and the newly commissioned grazing-incidence very small-angle neutron scattering (GI-VSANS) platform at the China Spallation Neutron Source (CSNS) to elaborate the unique advantages of neutron grazing-incidence techniques for polymer interface structural dynamics. The supramolecular network crosslinked by hydrogen bonds endows composite films reversible hygroscopic swelling, autonomous crack recovery and fast humidity-triggered bending actuation. Via in-situ ultra-small-angle X-ray scattering (USAXS), multi-length-scale structural reconstruction from molecular hydrogen bond rearrangement to microcavity closure was quantitatively captured, revealing the multi-stage self-healing mechanism driven by water-mediated supramolecular reorganization. To further break the detection limit of conventional grazing-incidence scattering on micrometer-scale interfacial assemblies, a versatile GI-VSANS setup was established at CSNS VSANS beamline, equipped with multi-slit focusing collimation array and high-precision triaxial goniometer. This platform extends the accessible in-plane characteristic length from hundreds of nanometers to several micrometers, enabling non-destructive, depth-selective statistical characterization of buried polymer interfaces. Validation experiments on spin-cast and drop-cast colloidal polymer thin films prove GI-VSANS can precisely quantify particle size, interparticle spacing and long-range hexagonal hierarchical assemblies at solid-liquid and solid-air interfaces, which are inaccessible to traditional GISANS. Combined with the structural dynamic research of stimuli-responsive healable polymers, this work demonstrates that CSNS GI-VSANS provides an unprecedented analytical route to link interfacial micro/nanoscale structural evolution with macroscopic stimuli-responsive functions. The open-access GI-VSANS facility holds broad application prospects for soft robotics, flexible energy polymer films, biomacromolecular coatings and other advanced polymer systems requiring quantitative interfacial structural characterization under variable external stimuli.