Three-dimensional (3D) microfabrication/nanofabrication technologies have revolutionized various fields by enabling the precise construction of complex microstructures/nanostructures1, 2, 3, 4, 5–6. However, existing methods face challenges in fabricating intricate 3D architectures from a diverse range of materials beyond conventional polymers. Here we introduce a universal 3D microfabrication/nanofabrication strategy compatible with a broad range of materials by precisely manipulating optofluidic interactions within a confined 3D space, enabling the creation of volumetric, free-form 3D microstructures/nanostructures. A femtosecond-laser-induced heating spot generates a localized thermal gradient, providing precise spatiotemporal control over optofluidic interactions of the nanoparticle-laden dispersions. This enables the rapid and highly localized assembly of nanoparticles with diverse shapes and compositions—including metals, metal oxides, carbon nanomaterials and quantum dots—into complex 3D microstructures. To demonstrate its versatility, we fabricate multifunctional microdevices, such as 3D microfluidic valves with size-selective sieving functionality, achieving fast separation of microparticles/nanoparticles with distinct dimensions, as well as microrobots integrated with four distinct functional materials, achieving multimodal locomotion powered by different external stimuli. This optofluidic 3D microfabrication/nanofabrication method unlocks new opportunities for advanced material innovation and miniaturized device development, paving the way for broad applications in colloidal robotics7, microphotonics/nanophotonics, catalysis and microfluidics.

Fracture network connectivity fundamentally controls subsurface fluid flow and rock mass behavior across spatial scales, yet determining the representative elementary volume (REV) remains a core challenge in geological system characterization. This study investigates scale-dependent connectivity through systematic analysis of natural outcrop data and artificial discrete fracture networks (DFNs). We implement a novel connectivity metric, C<inf>t</inf>, integrating both intra-cluster connectivity and inter-cluster interactions, and propose the Standard Deviation Stability Criterion (SDSC) for objective REV determination using second-order statistical measures. Analysis of 63 natural outcrop maps and various artificial DFN configurations reveals several key findings. First, fracture network connectivity exhibits pronounced scale-dependence with REV values approaching the same order of magnitude as the investigated systems, with mean REV values of 0.586 for natural outcrops and exceeding 0.2 for artificial networks. Second, preferential orientations increase REV requirements, particularly under stress conditions where only critically stressed fractures remain permeable, with fracture clustering further amplifying this effect. Third, in-situ stress conditions substantially increase REV requirements, with values nearly doubling when only critically stressed fractures remain active. Complete sealing creates the most challenging REV determination due to orientation selectivity, while partial sealing provides intermediate behavior by preserving orientation diversity. These findings demonstrate that obtaining representative volumes through conventional sampling presents fundamental limitations and provide critical insights for enhancing predictive models in subsurface engineering and environmental applications.

Controlling multiphase flow in disordered media is central to diverse practical contexts. Although nanoparticles have been widely utilised to modify surface wettability, factors governing their effects on dynamic displacement patterns remain unclear. Here, we identify the criterion for nanoparticle-induced wettability alteration during displacement by combining interfacial-scale wetting models, pore-scale microfluidic experiments and simulations. Motivated by striking contrasts in static wettability, we find that nanoparticle adsorption on solid surfaces affects displacement interfaces only when spreading of wetting films is pre-established, corresponding to corner-flow conditions. Displacement experiments under varying intrinsic wettability show that wetting-film development and non-aqueous droplet detachment are strengthened exclusively on moderately water-wet surfaces satisfying the corner-flow criterion. Investigations across designed porous structures with varying degrees of structural hierarchy validate the generality of the wettability criterion, while improvement in displacement efficiency diminishes with reduced hierarchy. The structural effect arises from variations in flow heterogeneity, with stronger heterogeneity simultaneously promoting film flow and ganglion mobilisation. The coupled impacts of wettability and structural conditions are summarised in an illustrative phase diagram delineating nanoparticle-tuned multiphase displacement. Our findings offer mechanistic insights into complex fluid flow in porous media and suggest optimised strategies for displacement control via nanoparticle suspensions.

Previous studies claimed that the non-monotonic effects of wettability came mainly from the heterogeneity of geometries or flow conditions on multiphase displacements in porous media. For macroscopic homogeneous porous media, without permeability contrast or obvious preferential flow pathways, most pore-scale evidence showed a monotonic trend of the wettability effect. However, this work reports transitions from monotonic to non-monotonic wettability effects when the dimension of the model system rises from two-dimensional (2-D) to three-dimensional (3-D), validated by both the network modelling and the microfluidic experiments. The mechanisms linking the pore-scale events to macroscopic displacement patterns have been analysed through direct simulations. For 2-D porous media, the monotonic effect of wettability comes from the consistent transition pattern for the full range of capillary numbers $Ca$ , where the capillary fingering mode transitions to the compact displacement mode as the contact angle $\theta$ decreases. Yet, it is indicated that the 3-D porous geometries, even though homogeneous without permeability contrast or obvious preferential flow pathways, introduce a different $Ca$ - $\theta$ phase diagram with new pore-scale events, such as the coupling of capillary fingering with snap-off during strong drainage, and frequent snap-off events during strong imbibition. These events depend strongly on geometric confinements and capillary numbers, leading to the non-monotonicity of wettability effects. Our findings provide new insights into the multiphase displacement dependent on wettability in various natural porous media and offer design principles for engineering artificial porous media to achieve desired immiscible displacement behaviours.

The pore-scale interfacial dynamics including main-meniscus flow and corner flow usually occurs in heterogeneous porous media and significantly affects the macroscopic multiphase flow process. Numerical research on the competition between main-meniscus flow and corner flow remains challenging due to the ambiguity in pore-scale interfacial dynamics and the complexity of upscaling these processes to porous media, given the substantial spatial and temporal scale differences. In this study, we proposed a critical capillary number (Cac $C{a}_{c}$) by considering the interplay of local capillary and viscous forces, which predicts transition from main-meniscus flow-dominated processes into corner flow-dominated processes during the strong imbibition. The Cac $C{a}_{c}$ criterion was integrated into a dynamic network model to translate pore-scale interfacial dynamics into multiphase flow patterns in porous media. The forced imbibition in heterogenous porous media under different Ca were simulated and compared to microfluidic experimental data. The comparison indicates that the dynamic competition between main-meniscus flow and corner flow has a vital impact on displacement behaviors predicted by pore-scale modeling, and our dynamic network model accurately captures the interfacial dynamics observed in microfluidic experiments. Moreover, the impact of interfacial dynamics on macroscopic multiphase flow pattern and displacement efficiency in heterogeneous porous media were addressed during strong imbibition under various viscosity ratios and capillary numbers. The phase diagram manifests a monotonic effect of viscosity ratio on displacement efficiency at high Ca due to the dominance of viscous fingering. A non-monotonic effect of viscosity ratio is revealed at low Ca, which is ascribed into competition between corner flow and main-meniscus flow. This study highlights the gap in the existing models of interfacial dynamics at pore scale, and provide an effective upscaling approach to investigate the multiphase flow in porous media.

The transition to a sustainable, low-carbon energy future requires transformative advancements in energy and environmental technologies. Carbon capture and sequestration, underground hydrogen storage, and nuclear waste geological disposal will be central aspects of a sustainable energy future, which hinge on a hidden world: reactive multiphase flows in opaque, heterogeneous porous media. Despite their foundational importance, the pore-scale dynamics that govern these technologies remain elusive. Here, we argue that microfluidic porous media are emerging as transformative platforms for the direct visualization of multiphase reactive flow in porous media and eventually optimizing these multiple physicochemical and biological processes. This review highlights critical scientific challenges associated with these sustainable energy solutions and summarizes the state-of-the-art microfluidic techniques for studying the interplay between multiphase flow, reactive transport, and biological effects in porous media. We also propose promising microfluidic technologies to support sustainable energy applications further. By offering a comprehensive overview of how microfluidic approaches deepen our understanding of fundamental pore-scale dynamics and connect them to large-scale behavior, this review is expected to promote both experimental and theoretical understanding of multiphase reactive flow in porous media, thereby informing material design, process optimization, and predictive modeling for scalable implementation. By fostering interdisciplinary collaboration across microfluidics, fluid mechanics, geophysics, materials science, and subsurface engineering, we hope to accelerate innovation and advance sustainable energy solutions.

Understanding and controlling particle transport in porous media is of widespread interest across diverse practical applications. Here, we report geometry-mediated accumulation effect on particle transport under dilute conditions driven by the interplay between particle lagging and viscosity effect, offering an alternative perspective for preferential flow control in porous media. Pore-to-throat velocity variations can trigger strong local accumulation of microgel particles in the absence of clogging effects, which is anomalous given the low Stokes number. Based on volume-averaged equations for two-phase flow, we theoretically elucidate the competition between the drag force representing particle-fluid interactions and an additional resistance force representing interparticle interactions, which governs particle accumulation and becomes significant only with concentration-sensitive viscosity. Differing from shear-induced migration driven by multibody hydrodynamic or collision interactions at higher concentrations, such accumulation occurs only in the presence of geometry variations, highlighting its promising impact on suspension flow in porous media. A new dimensionless number is proposed and validated by numerical simulations in typical pore-throat geometries to generally describe the triggering criterion and accumulation intensity. Investigations in heterogeneous porous media reveal varying accumulation patterns under various injection conditions, which are predictable applying theoretical descriptions. Unexpected preferential flow control performances arise from lateral flow reallocation, controlled by the formation and distribution of localized intense accumulation zones. Our findings provide insights into particle transport mechanisms and flow control strategies in microchannels and porous media.

Shale oil reservoirs are characterized by extremely complex structures and highly distributed nanopores, where fluid transport behaviors deviate significantly from the conventional Darcy’s law. Understanding the transport mechanisms of fluids confined at the nanoscale is therefore of great importance for accurately predicting shale oil recovery. In this study, we investigate the fundamental mechanism of fluid migration in nanopores using two-dimensional nanoporous structures, with particular emphasis on the coupled effects of pore structure scale and wettability on the micro-/nano-scale flow dynamics of water and oil system. To overcome the limitations of conventional models in capturing nanoscale effects with two-dimensional porous structures, a revised planar model for liquid transport in nanochannels is derived. This analysis highlights the substantial deviations in traditional volume-averaging approaches, which fails to properly represent flow physics under nanoscale confinement. Building on the new theoretical framework, a lattice Boltzmann method (LBM) is developed that explicitly incorporates two critical nanoscale effects: viscosity variations in the adsorbed fluid layer and velocity slip at the solid boundaries. This model enables a comprehensive examination of how pore size and contact angle jointly regulate the transport dynamics of fluids in nanoporous media. The simulation results revealed that viscosity variations within the adsorbed layer and velocity slip at the walls give rise to pronounced nanoscale effects, which gradually diminish as the channel size increases. Moreover, notable differences are observed under varying wettability conditions, underscoring the critical role of contact angle in controlling water/oil displacement mechanisms. Specially, strong hydrophilic conditions favor preferential water occupation of narrow pores, whereas hydrophobic conditions enhance oil continuity. Finally, a nanoscale transport regime map is constructed based on structural size and contact angle, offering a systematic framework to evaluate the interplay between nanoscale effects and wettability. This study provides important theoretical insights into fluid transport in nanoporous shale reservoirs and establishes a reference for developing cross-scale transport models in complex geological formations, ultimately contributing to improved strategies for shale oil exploitation.

Particle transport in subsurface porous media under multiphase flow conditions is widely concerned in many practical applications. Previous studies have focused on retention behaviors and interfacial effects, ignoring the unique role of pronounced rheological effect under dilute conditions. Here, we investigate how accumulation effect reshapes microgel particle transport and immiscible displacement process driven by concentration-sensitive viscosity. As a foundation, a mixture-rheology two-fluid model is developed and combined with color-gradient lattice Boltzmann method for modeling complex particulate multiphase flow. The consistency between simulation results and microfluidic experiments confirms the validity of our model in capturing accumulation phenomena. Results in heterogeneous dual-permeability structures reveal the two-way coupling between particle accumulation and interfacial evolution. Particle accumulation can be enhanced at higher injection concentrations and larger particle sizes, leading to the formation of filter-cake-like structures despite the absence of clogging effects. Capillary resistance further weakens the driving force for particle migration, intensifying local accumulation compared to suspension flow. The non-uniform concentration distribution contributes to flow rate reallocation via diversion effects, producing variable displacement patterns under varying conditions. Results in disordered media exhibit a similar trend as in the dual-permeability model but with more significant accumulation. The dramatic reduction in nonaqueous phase saturation by sweeping efficiency improvement indicates the promising application potential of such accumulation. Our findings deepen the understandings of particle transport in porous media with implications for manipulation of immiscible displacement.

We report an anomalous capillary phenomenon that reverses typical capillary trapping via nanoparticle suspension and leads to a counterintuitive self-removal of non-aqueous fluid from dead-end structures under weakly hydrophilic conditions. Fluid interfacial energy drives the trapped liquid out by multiscale surfaces: the nanoscopic structure formed by nanoparticle adsorption transfers the molecular-level adsorption film to hydrodynamic film by capillary condensation, and maintains its robust connectivity, then the capillary pressure gradient in the dead-end structures drives trapped fluid motion out of the pore continuously. The developed mathematical models agree well with the measured evolution dynamics of the released fluid. This reversing capillary trapping phenomenon via nanoparticle suspension can be a general event in a random porous medium and could dramatically increase displacement efficiency. Our findings have implications for manipulating capillary pressure gradient direction via nanoparticle suspensions to trap or release the trapped fluid from complex geometries, especially for site-specific delivery, self-cleaning, or self-recover systems.