Synchrotron Small-angle X-ray Scattering Research Articles

Shish-kebab formation in the micro-injection molding of polyethylene: In-situ synchrotron small angle X-ray scattering study

The structural formation and evolution in high density polyethylene (HDPE) during the micro-injection molding process were investigated as a function of the mold temperature and injection speed utilizing an in situ synchrotron small angle X-ray scattering (SAXS) technique in conjunction with a portable micro-injection molding setup. It was found that shish-kebab structures were formed in all cases. The beginning of occurrence of shish is not much affected by the mold temperature, but the onset of the formation of kebab crystals is strongly dependent on the mold temperature. This mold temperature dependence of the kinetics of shish-kebab formation is attributed to the interplay between the crystallization rate in the outer layer and the formation rate of the shish-like structure, which was further evidenced by the multilayered structure of molded samples via ex situ microfocus scanning SAXS and wide angle X-ray diffraction (WAXD) measurements. On the other hand, the injection speed affects the long period of oriented lamellae and the dimension of the shish-like structure only slightly but influences the kinetics of structural formation evidently. The larger the injection speed, the earlier occurrence of oriented lamellae and shish formation is observed.

Nanoscale Structures of Tough Microparticle-Based Films Investigated by Synchrotron X-Ray Scattering and All-Atom Molecular-Dynamics Simulation.

In this study, the nanoscale structures of microparticle-based films are revealed by synchrotron small-angle X-ray scattering (SAXS) and all-atom molecular-dynamics (AA-MD) simulations. The microparticle-based films consisting of the simplest acrylate polymer microparticles are applied as a model because the films are formed without additives and organic solvents and exhibit high toughness properties. The characteristic interfacial thickness (tinter) obtained from the SAXS analysis reflects the mixing degree of polymer chains on the microparticle surface in the film. The cross-linking density of inner microparticles is found to be strongly correlated to not only several properties of individual microparticles, such as swelling ratio and radius of gyration, but also the tinter and toughness of the corresponding films. Therefore, the tinter and toughness values follow a linear relationship because the cross-linking restricts the mixing of polymer chains between their surfaces in the film, which is a unique feature of microparticle-based films. This characteristic also affects their deformation behavior observed by in situ SAXS during tensile testing and their density profiles calculated by AA-MD simulations. This work provides a general strategy for material design to control the physical properties and structures of their films for advanced applications, including volatile organic compound-free sustainable coatings and adhesives.

A structural investigation on the interactions of cotton fabric cellulose with olive oil and water

The cotton fabric consists of cellulose arranged in a complex structure with multiple levels of organization at different length scales. Understanding this structure and its interactions with water and oil is essential for developing efficient and environmentally friendly methods of cotton washing. In this study, the structure of raw cotton fabric cellulose and the effects of water and oil were examined across a broad range of length scales using spatially resolved synchrotron small-angle X-ray scattering (SAXS) and auxiliary techniques.Water was observed to penetrate the cotton fabric and interact across nearly all length scales. Although a certain amount of the material was not affected by water as seen by intact distance between microfibrils, fractal analysis of the scattering data indicated a loosening of the microfibril arrangement after contact with water. This process was hindered if the material had been pre-treated with oil and was not seen after subsequent washing with water or surfactant solution. Analyzing spatially resolved SAXS data using a bi-sinusoidal model and 2D maps of the oil-to-cotton ratio facilitates understanding the structure of the material and its interactions with oil on the molecular, nano and macrolevels.

PEGylation-Dependent Cell Uptake of Lipid Nanoparticles Revealed by Spatiotemporal Correlation Spectroscopy.

Polyethylene glycol (PEG) is a common surface modification for lipid nanoparticles (LNPs) to improve their stability and in vivo circulation time. However, the impact of PEGylation on LNP cellular uptake remains poorly understood. To tackle this issue, we systematically compared plain and PEGylated LNPs by combining dynamic light scattering, electrophoretic light scattering, and synchrotron small-angle X-ray scattering (SAXS) that unveils a striking similarity in size and core structure but a significant reduction in surface charge. Upon administration to human embryonic kidney (HEK 293) cells, plain and PEGylated LNPs were internalized through different endocytic routes, as revealed by spatiotemporal correlation spectroscopy. An imaging-derived mean square displacement (iMSD) analysis shows that PEGylated LNPs exhibit a significantly stronger preference for caveolae-mediated endocytosis (CAV) and clathrin-mediated endocytosis (CME) pathways compared to plain LNPs, with these latter being better tailored to MCR-dependent internalization and trafficking. This suggests that PEG plays a crucial role in directing LNPs toward specific cellular uptake routes. Further studies should explore how PEG-mediated endocytosis impacts intracellular trafficking and ultimately translates to therapeutic efficacy, guiding the design of next-generation LNP delivery systems.

Morphological analysis of polydisperse nanoplatelets using SAXS

Two-dimensional materials like graphene and boron nitride find applications in numerous innovations thanks to their high specific surface area and unusual electrical, thermal and optical properties. These materials are often produced via liquid-phase exfoliation, yielding nanoplatelets with a high degree of polydispersity. Unfortunately, methods for the characterization of both lateral dimension and thickness for dispersed polydisperse nanoplatelets are still lacking. In this work, a fast and quantitative method for the characterization of polydisperse nanoplatelets in dispersion is proposed using the example of graphene nanoplatelets (GNPs). The method is benchmarked using well-defined gibbsite nanoplatelets. Synchrotron small-angle X-ray scattering (SAXS) is used to probe the structure of the platelets over a wide range of length scales. The SAXS data are fitted with a polydisperse form factor for discs, which yields size distributions in both thickness and diameter. Benchmarking the procedure with the gibbsite model system shows excellent agreement between the SAXS results and previous transmission electron microscopy and atomic force microscopy data. The method is also successfully applied to GNPs from 1–60 layers in thickness and 20–2000 nm in diameter. We believe that this work brings reliable quantitative in situ characterization, for instance during preparation, of nanoplatelet dispersions within reach.

Destructuration of Canola Protein Gels during In Situ Gastrointestinal Digestion Studied by X-ray Scattering.

We are studying the destructuration of canola protein gels, as a solid food model, during in situ gastrointestinal digestion using synchrotron small-angle X-ray scattering (SAXS). Digestion of two gels, prepared by heating pH 8 and pH 11 solutions, was carried out by diffusion of enzymatic juices into the gel from the top of the capillary and monitored for several tens of hours. Very similar time evolutions of SAXS curves occur at different positions of the gel in the capillary, with a delay determined by the distance from the surface initially in contact with the digestive juice. The main phenomena observed are (i) at the scale of the protein conformation (1-5 nm). The scattering curve is a power law, the exponent of which measures the compactness (related to the degree of unfolding). It can be plotted as a function of the characteristic size of proteins/and interprotein distances and as a function of the scattering intensity. Such diagrams clearly show successive digestion processes. For the pH 11 gel, in which proteins are initially hardly unfolded, the digestive processes are unfolding (1st step), recompaction-aggregation phenomena (2nd step) due to gastrointestinal pH conditions and enzymatic cleavage, further unfolding-disaggregation (3rd step), and final protein cleavage (4th step) down to small peptides. For the pH 8 gel, proteins are initially unfolded, and only the last three steps are observed, showing the influence of easier access for the enzymes. (ii) At the scale of large aggregates (10-50 nm), we observe for both gels a decrease in the size and/or number of these aggregates during digestion and alteration of their interfaces. (iii) At the scale of the secondary protein structure, wide-angle X-ray scattering is very useful for detecting the degradation of the secondary protein structure at different steps of digestion.

Evaporation-induced self-assembly of Janus pyramid molecules from fractal network to core-shell nanoclusters evidenced by small-angle X-ray scattering

Self-assembly of nanoclusters (NCs) is an effective synthetic method for preparing functionalized nanomaterials. However, the assembly process and mechanisms in solutions still remain ambiguous owing to the limited strategies to monitor intermediate assembled states. Herein, the self-assembly process of amphiphilic molecule 4POSS-DL-POM (consisting of four polyhedral oligomeric silsesquioxanes, a dendritic linker, and one polyoxometalate) by evaporation of acetone in a mixed acetone/n-decane solution is monitored by time-resolved synchrotron small-angle X-ray scattering (SAXS). Scattering data assessments, including Kratky analysis, pair distance distribution function, and model fitting, track the self-assembly process of 4POSS-DL-POM from a fractal network to compact NCs, then to core–shell NCs, and finally to superlattice structure. The calculated average aggregation number of a core–shell NC is 11 according to the parameters obtained from core-shell model fitting, in agreement with electron microscopy. The fundamental understanding of the self-assembly dynamics from heterocluster into NCs provides principles to control building block shape and guide target aggregation, which can further promote the design and construction of highly ordered cluster-assembled functional nanomaterials.

Lyotropic Liquid Crystalline Phase Nanostructure and Cholesterol Enhance Lipid Nanoparticle Mediated mRNA Transfection in Macrophages

AbstractMacrophages are unique immune cells attracting growing attention as a potential candidate for cell‐based therapy for infectious diseases and cancer. Strategies that can reprogramme or gene‐edit macrophages hold potential across a spectrum of acute and chronic conditions. Herein, lipid nanoparticles (LNPs) are developed containing the ionizable lipid SM‐102, helper lipid monoolein which is known for self‐assembly in aqueous solutions into the inverse cubic lyotropic liquid crystalline mesophase, and cholesterol as an mRNA nanocarrier. The immortalized alveolar macrophage cell line (MH‐S cells) is utilized to investigate how cholesterol concentration impacts on mRNA delivery which is further validated using primary mouse alveolar macrophages isolated from the bronchoalveolar compartment and human monocyte derived macrophages. By using high‐throughput synchrotron small angle X‐ray scattering (SAXS), an acidification‐induced non‐ordered to ordered internal nanostructure transition of the formulated LNPs is observed, following the transition sequence of inverse micellar to hexagonal to cubic mesophase in the pH range from 7 to 4. Cholesterol is identified as another crucial component for superior mRNA transfection in macrophages, contributing to nanostructure transition and protein corona variation. Successful ex vivo mRNA transfection is also achieved in primary macrophages, highlighting the prospectivity of reprogramming macrophages as a cell therapy for lung diseases.

Correlating Substrate Reactivity at Electrified Interfaces with the Electrolyte Structure in Synthetically Relevant Organic Solvent/Water Mixtures.

Optimizing electrosynthetic reactions requires fine tuning of a vast chemical space, including charge transfer at electrocatalyst/electrode surfaces, engineering of mass transport limitations, and complex interactions of reactants and products with their environment. Hybrid electrolytes, in which supporting salt ions and substrates are dissolved in a binary mixture of organic solvent and water, represent a new piece of this complex puzzle as they offer a unique opportunity to harness water as the oxygen or proton source in electrosynthesis. In this work, we demonstrate that modulating water-organic solvent interactions drastically impacts the solvation properties of hybrid electrolytes. Combining various spectroscopies with synchrotron small-angle X-ray scattering (SAXS) and force field-based molecular dynamics (MD) simulations, we show that the size and composition of aqueous domains forming in hybrid electrolytes can be controlled. We demonstrate that water is more reactive for the hydrogen evolution reaction (HER) in aqueous domains than when strongly interacting with solvent molecules, which originates from a change in reaction kinetics rather than a thermodynamic effect. We exemplify novel opportunities arising from this new knowledge for optimizing electrosynthetic reactions in hybrid electrolytes. For reactions proceeding first via the activation of water, fine tuning of aqueous domains impacts the kinetics and potentially the selectivity of the reaction. Instead, for organic substrates reacting prior to water, aqueous domains have no impact on the reaction kinetics, while selectivity may be affected. We believe that such a fine comprehension of solvation properties of hybrid electrolytes can be transposed to numerous electrosynthetic reactions.

Highly Ordered Gyroid Nanostructured Polymers: Facile Fabrication by Polymerizable Pluronic Surfactants.

Highly ordered, network-nanostructured polymers offer compelling geometric features and application potential. However, their practical utilization is hampered by the restricted accessibility. Here, we address this challenge using commercial Pluronic surfactants with a straightforward modification of tethering polymerizable groups. By leveraging lyotropic self-assembly, we achieve facile production of double-gyroid mesophases, which are subsequently solidified via photoinduced cross-linking. The exceptionally ordered periodicities of Ia3d symmetry in the photocured polymers are unambiguously confirmed by synchrotron small-angle X-ray scattering (SAXS), which can capture single-crystal-like diffraction patterns. Electron density maps reconstructed from SAXS data complemented by transmission electron microscopy analysis further elucidate the real-space gyroid assemblies. Intriguingly, by tuning the cross-linking through thiol-acrylate chemistry, the mechanical properties of the polymer are modulated without compromising the integrity of Ia3d assemblies. The 3-D percolating gyroid nanochannels demonstrate an ionic conductivity that surpasses that of disordered structures, offering promising prospects for scalable fabrication.

Tooth acellular extrinsic fibre cementum incremental lines in humans are formed by parallel branched Sharpey’s fibres and not by its mineral phase

In humans, the growth pattern of the acellular extrinsic fibre cementum (AEFC) has been useful to estimate the age-at-death. However, the structural organization behind such a pattern remains poorly understood. In this study tooth cementum from seven individuals from a Mexican modern skeletal series were analyzed with the aim of unveiling the AEFC collagenous and mineral structure using multimodal imaging approaches. The organization of collagen fibres was first determined using: light microscopy, transmission electron microscopy (TEM), electron tomography, and plasma FIB scanning electron microscopy (PFIB-SEM) tomography. The mineral properties were then investigated using: synchrotron small-angle X-ray scattering (SAXS) for T-parameter (correlation length between mineral particles); synchrotron X-ray diffraction (XRD) for L-parameter (mineral crystalline domain size estimation), alignment parameter (crystals preferred orientation) and lattice parameters a and c; as well as synchrotron X-ray fluorescence for spatial distribution of calcium, phosphorus and zinc. Results show that Sharpey’s fibres branched out fibres that cover and uncover other collagen bundles forming aligned arched structures that are joined by these same fibres but in a parallel fashion. The parallel fibres are not set as a continuum on the same plane and when they are superimposed project the AEFC incremental lines due to the collagen birefringence. The orientation of the apatite crystallites is subject to the arrangement of the collagen fibres, and the obtained parameter values along with the elemental distribution maps, revealed this mineral tissue as relatively homogeneous. Therefore, no intrinsic characteristics of the mineral phase could be associated with the alternating AEFC incremental pattern.

Tailoring pore size of mesoporous silica and organosilica using biodegradable pentablock copolymer templates via EISA process

In this work, we have designed unique poly(lactic acid-co-glycolic acid)-b-poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)-b-poly(lactic acid-co-glycolic acid) pentablock copolymers using Pluronic F68 and F108 triblock copolymers as macroinitiators. The poly(lactic acid-co-glycolic acid) (PLGA) blocks were attached as glycolide and lactide monomers at the both ends of each F68 and F108 triblock copolymer. The molecular weights and the block fractions were confirmed by gel permeation chromatography (GPC) and proton nuclear magnetic resonance (1H NMR) for the four kinds of pentablock copolymers. Using these pentablock copolymers as templates, we synthesized mesoporous ethane-silicas as well as silicas by the evaporation-induced self-assembly (EISA) method. 1,2-bis(triethoxysily)ethane (BTEE) were used as an organosilica precursor. The mesoporous ethane-silica samples were characterized using synchrotron small angle X-ray scattering (SAXS), nitrogen sorption experiments, transmission electron microscopy (TEM), and solid-state 29Si CP-MAS NMR. Based on the experimental results, it was confirmed that the porosity and pore diameter can be varied with the PLGA weight fraction of the pentablock copolymer. It is due to the PLGA block in polymer forming the hydrophobic domain in micelles, which leads to the formation of increased pore size over 20 nm without any additive pore expander. In addition, it seems that as the organosilica precursor increases, the association number of block copolymers forming one micelle decreases, resulting in a decrease in pore size. In summary, the polymer template plays a vital part in tuning the structure of the mesoporous ethane-silica samples. Thus, the development of synthetic method of mesoporous organosilica materials using polymer templates with different topology is still challenging and can endow the unique structure and property for mesoporous organosilica for future applications.

Water Sorption and Structural Properties of Human Airway Mucus in Health and Muco-Obstructive Diseases.

Muco-obstructive diseases change airway mucus properties, impairing mucociliary transport and increasing the likelihood of infections. To investigate the sorption properties and nanostructures of mucus in health and disease, we investigated mucus samples from patients and cell cultures (cc) from healthy, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF) airways. Atomic force microscopy (AFM) revealed mucin monomers with typical barbell structures, where the globule to spacer volume ratio was the highest for CF mucin. Accordingly, synchrotron small-angle X-ray scattering (SAXS) revealed more pronounced scattering from CF mucin globules and suggested shorter carbohydrate side chains in CF mucin and longer side chains in COPD mucin. Quartz crystal microbalance with dissipation (QCM-D) analysis presented water sorption isotherms of the three types of human airway mucus, where, at high relative humidity, COPD mucus had the highest water content compared to cc-CF and healthy airway mucus (HAM). The higher hydration of the COPD mucus is consistent with the observation of longer side chains of the COPD mucins. At low humidity, no dehydration-induced glass transition was observed in healthy and diseased mucus, suggesting mucus remained in a rubbery state. However, in dialyzed cc-HAM, a sorption-desorption hysteresis (typically observed in the glassy state) appeared, suggesting that small molecules present in mucus suppress the glass transition.

In Operando Analysis of Milk-Based Oral Formulations during Digestion Using Synchrotron Small-Angle X-ray Scattering Coupled to Low-Frequency Raman Spectroscopy.

A low-frequency Raman (LFR) probe was coupled to an in-line small-angle X-ray scattering (SAXS) beamline to test the capabilities of a combinatory approach for the determination of lipid and drug behavior during the enzymatic lipolysis of milk-based oral formulations. Cinnarizine was used as the model drug, and its solubilization dynamics as well as its potential impact on the supramolecular structures formed by the digestion products of bovine milk were evaluated from the perspective of both techniques. The SAXS data were superior in distinguishing various liquid crystalline assemblies formed during the digestion process, with LFR providing complementary information regarding the formation of calcium soaps. On the other hand, studying changes in the LFR domain allowed the differentiation of drug solubilization and precipitation; processes that were less clear from the X-ray scattering data. Given the relative simplicity of the combined experimental setup, these results highlight the advantages that the combination of the two techniques can provide for understanding and developing new lipid-based formulations and will help to translate the results obtained at synchrotron facilities to routine analysis procedures in laboratory/industry-based environments.

SAXS unveils porous anodes for potassium-ion batteries: dynamic evolution of pore structures in Fe@Fe2O3/PCNFs composite nanofibers.

The porous structure of composite nanofibers plays a key role in improving their electrochemical performance. However, the dynamic evolution of pore structures and their action during ion intercalation/extraction processes for negative electrodes are not clear. Herein, porous carbon composite nanofibers (Fe@Fe2O3/PCNFs) were prepared as negative electrode materials for potassium-ion batteries. Electrochemical test findings revealed that the composites had good electrochemical characteristics, and the porous structure endowed composite electrodes with pseudo-capacitive behaviors. After 1500 discharge/charge cycles at a current density of 1000 mA g-1, the specific capacity of the potassium-ion batteries was 144.8 mAh g-1. We innovatively used synchrotron small-angle X-ray scattering (SAXS) technique to systematically investigate the kinetic process of potassium formation in composites and showed that the kinetic process of potassium reaction in composites can be divided into four stages, and the pores with smaller average diameter distribution are more sensitive to changes in the reaction process. This work paves a new way to study the deposition kinetics of potassium in porous materials, which facilitates the design of porous structures and realizes the development of alkali metal ion-anode materials with high energies.

Investigation of the Microstructure of PAN Precursor Fibers Obtained at Various Processing Stages

The production of high-performance carbon fibers relies heavily on the structural transformations of polyacrylonitrile (PAN) fiber during processing. In this article differential scanning calorimetry (DSC), synchrotron small-angle X-ray scattering (SAXS), and synchrotron wide-angle X-ray diffraction (WAXD) were used to study the changes of the thermal properties, voids and crystal structure of the PAN precursor fibers on industrial lines during the continuous processing stages, i.e., after the treatment in the coagulation bath, after stretching in boiling water and after stretching in high-temperature steam. The findings of this study suggest that after boiling water stretching the molecular chain motion of the PAN precursor fiber weaken, resulting in the expansion of the voids. After high-temperature steam stretching the voids became elliptical and oriented in the stretching direction. Although the boiling water stretching process partially damaged the (100) crystal planes of the PAN precursor fibers, it does not hinder their overall crystalline structure. The high stretching ratio primarily affected the orientation of the molecular chains. This orientation, even in the context of partial crystal plane disruption, further promoted the crystallization of the (100) crystal planes in the fibers. These experiments explored the correlation between the processing technology and fiber structure transformation of PAN-based carbon fibers, resulting in producing a guide for the preparation of high-performance carbon fibers with fewer defects.

Pore Characterization of Sandy Silty Soil in Metro Surrounding Rock: A Synchrotron Small-Angle X-ray Scattering Experiment

Pore Characterization of Sandy Silty Soil in Metro Surrounding Rock: A Synchrotron Small-Angle X-ray Scattering Experiment

The influence of mannose-based esters on the mesophase behaviour of lyotropic liquid crystalline nanosystems as drug delivery vectors

Lyotropic Liquid Crystalline (LLC) nanoparticles represent an emerging class of smart, biocompatible, and biodegradable systems for the delivery of drugs. Among these, structures with complex 3D architectures such as cubosomes are of particular interest. These are non- lamellar assemblies having hydrophobic and hydrophilic portions able to carry drugs of different nature. They can further be modulated including suitable additives to control the release of the active payload, and to promote an active targeting. Starting from monoolein (GMO) cubic phase, different concentrations of mannose-based esters were added, and the eventual structural modifications were monitored to ascertain the effects of the presence of glycolipids. Moreover, the structural properties of these nanosystems loaded with Dexamethasone (DEX), a very well-known anti-inflammatory steroid, were also studied. Experiments were carried out by synchrotron Small Angle X-ray Scattering (SAXS), Raman Microspectroscopy (RMS) and Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) measurements. The drug delivery potential (i.e. entrapment efficiency and release properties) of the obtained nanoparticles was evaluated. Finally, in vitro cytocompatibility and anti-inflammatory activity studies of the prepared formulations were carried out. Inclusion of mannose-based surfactants up to 10 mol% influenced the structural parameters of Im3m cubic phase and swollen cubic phases were obtained with the different glycolipids with lattice parameters significantly higher than GMO. A complete cytocompatibility and an increased DEX activity were observed, thus suggesting the possibility to use GMO/glycolipids nanoparticles to formulate innovative drug delivery systems.

Heating-Induced Switching to Hierarchical Liquid Crystallinity Combining Colloidal and Molecular Order in Zwitterionic Molecules.

Hierarchical self-assemblies of soft matter involving triggerable or switchable structures at different length scales have been pursued toward multifunctional behaviors and complexity inspired by biological matter. They require several and balanced competing attractive and repulsive interactions, which provide a grand challenge in particular in the "bulk" state, i.e., in the absence of plasticizing solvents. Here, we disclose that zwitterionic bis-n-tetradecylphosphobetaine, as a model compound, shows a complex thermally switchable hierarchical self-assembly in the solvent-free state. It shows polymorphism and heating-induced reversible switching from low-temperature molecular-level assemblies to high-temperature hierarchical self-assemblies, unexpectedly combining colloidal and molecular self-assemblies, as inferred by synchrotron small-angle X-ray scattering (SAXS). The high-temperature phase sustains birefringent flow, indicating a new type of hierarchical thermotropic liquid crystallinity. The high-temperature colloidal-level SAXS reflections suggest indexation as a 2D oblique pattern and their well-defined layer separation in the perpendicular direction. We suggest that the colloidal self-assembled motifs are 2D nanoplatelets formed by the lateral packing of the molecules, where the molecular packing frustration between the tightly packed zwitterionic moieties and the coiled alkyl chains demanding more space limits the lateral platelet growth controlled by the alkyl stretching entropy. An indirect proof is provided by the addition of plasticizing ionic liquids, which relieve the ionic dense packings of zwitterions, thus allowing purely smectic liquid crystallinity without the colloidal level order. Thus, molecules with a simple chemical structure can lead to structural hierarchy and tunable complexity in the solvent-free state by balancing the competing long-range electrostatics and short-range nanosegregations.

Research on Improving the Pre‐Oxidation Process of the Excellent Mechanical Strength Carbon Fiber

AbstractThis study uses synchrotron wide‐angle X‐ray diffraction (WAXD) and synchrotron small angle X‐ray scattering (SAXS) to carry out an in situ study of the pre‐oxidation process of polyacrylonitrile (PAN) fibers with two different preparation processes. Through analysis of 2D WAXD/SAXS data, this study divides the evolution of PAN fiber's crystal and microporous structures during pre‐oxidation into three and two stages, respectively. The evolution of PAN fiber's crystal structure during pre‐oxidation can be divided into three stages: 1) Initial stage: small‐sized crystals melt, crystal orientation decreases, and no cyclization reactions occur. 2) Intermediate stage: cyclization reactions happen in the amorphous region, leading to increased crystal size, crystal orientation, and crystallinity. 3) Final stage: cyclization reactions occur in the crystal region, resulting in reduced crystal size and orientation. The evolution of microporous structure can be divided into two stages: microporous shrinkage stage and microporous expansion stage. These features are analyzed using 2D WAXD/SAXS techniques. This study provides valuable references and guidance for the industrial production of PAN fibers by exploring the mechanism of the pre‐oxidation process in‐depth.