Block copolymer self-assembly in non-conventional media such as ionic liquids and supercritical fluids has emerged as a promising avenue for creating nanostructured materials with tailored properties. Unlike traditional solvents like water or organic media, these alternative environments offer unique interactions that influence morphology, kinetics, and functionality. The distinct physicochemical properties of these solvents—such as low volatility, tunable polarity, and gas-like diffusivity—enable precise control over self-assembly processes, opening new pathways for advanced applications in energy storage, catalysis, and nanotechnology.

Ionic liquids, composed entirely of ions, exhibit negligible vapor pressure and high thermal stability, making them ideal for high-temperature processing. Their polar nature and ionic conductivity influence the segregation strength of block copolymers, altering microphase separation behavior. For example, poly(styrene)-block-poly(methyl methacrylate) (PS-b-PMMA) in imidazolium-based ionic liquids shows enhanced ordering due to selective solvation of the PMMA block. The high dielectric constant of ionic liquids screens electrostatic interactions, reducing defects in nanostructured morphologies. Studies indicate that lamellar spacing can increase by up to 30% compared to assemblies in conventional solvents, attributed to the extended conformation of polymer chains in ionic environments. The negligible volatility also allows for long annealing times without solvent loss, facilitating the formation of highly ordered structures.

Supercritical fluids, particularly supercritical carbon dioxide (scCO2), provide another unconventional medium with gas-like transport properties and liquid-like density. The solvent power of scCO2 is highly pressure-dependent, enabling reversible tuning of block copolymer solubility. Poly(ethylene oxide)-block-poly(1,1-dihydroperfluorooctyl acrylate) (PEO-b-PFOA) forms micelles in scCO2, with PFOA blocks preferentially solvated due to fluorophilicity. The low surface tension of scCO2 promotes the formation of mesoporous films upon depressurization, useful for membrane applications. Kinetic studies reveal that self-assembly in scCO2 occurs orders of magnitude faster than in organic solvents due to high diffusivity, with micelle formation completing within milliseconds under optimized conditions. The absence of residual solvent contamination is another advantage for biomedical and electronic applications.

Deep eutectic solvents, a subclass of ionic liquids, offer a cost-effective alternative with similar tunability. Composed of hydrogen bond donors and acceptors, they exhibit strong interactions with specific polymer blocks. For instance, choline chloride-urea mixtures selectively swell poly(ethylene glycol) domains in block copolymers, leading to well-defined gyroidal networks. The viscosity of these solvents can be adjusted by varying composition, impacting the self-assembly kinetics. Research shows that increasing the hydrogen bond donor ratio reduces aggregation rates by an order of magnitude, providing a handle for temporal control over nanostructure evolution.

Fluorous solvents, characterized by high fluorine content, are particularly effective for assembling fluorinated block copolymers. The low polarizability of these solvents creates a highly selective environment for fluorocarbon segments, driving strong microphase separation. Perfluoropolyether-block-poly(ethylene glycol) copolymers form reverse micelles in fluorinated media, with core sizes tunable by solvent fluorophilicity. These systems are relevant for drug delivery, where fluorophilic cores can encapsulate oxygen-sensitive therapeutics. Experimental data indicates loading efficiencies exceeding 80% for hydrophobic drugs, surpassing conventional aqueous micelles.

Liquid crystals as solvents introduce anisotropic interactions that template block copolymer alignment. Smectic phases, for example, guide the orientation of lamellar domains through cooperative ordering. Poly(styrene)-block-poly(butadiene) in nematic solvents exhibits a 15% increase in domain spacing compared to isotropic media, with alignment persisting after solvent removal. This approach is valuable for photonic materials requiring long-range order. The transition temperature of the liquid crystal can be used to trigger morphological changes, enabling stimuli-responsive nanostructures.

Applications of these systems are rapidly expanding. In energy storage, ionic liquid-templated block copolymers serve as solid electrolytes with ionic conductivities above 1 mS/cm at room temperature. The interconnected nanodomains facilitate ion transport while maintaining mechanical stability. Supercritical fluid-derived porous films are employed in gas separation membranes, demonstrating CO2/N2 selectivity ratios over 30. Fluorinated micelles in non-polar media are explored for oxygen delivery in biomedical contexts, with sustained release profiles spanning several days. Liquid crystal-templated assemblies enable tunable photonic crystals with reflectance peaks adjustable across the visible spectrum by varying copolymer composition.

The environmental benefits of these media are notable. Supercritical CO2 is non-toxic and recyclable, aligning with green chemistry principles. Ionic liquids can be reused multiple times without significant loss of performance, reducing waste generation. Deep eutectic solvents are often biodegradable, offering a sustainable alternative to traditional solvents.

Challenges remain in scaling up these processes, particularly regarding solvent recovery and cost. Ionic liquids, while reusable, require energy-intensive purification steps. Supercritical fluid processing demands high-pressure equipment, increasing capital expenditure. Ongoing research focuses on optimizing solvent-polymer interactions to minimize material usage while maximizing functionality. Advances in computational modeling aid in predicting self-assembly outcomes, reducing experimental trial and error.

The exploration of block copolymer self-assembly in non-conventional media represents a significant shift from traditional solvent systems. By leveraging the unique properties of ionic liquids, supercritical fluids, and related solvents, researchers achieve unprecedented control over nanostructure formation. These systems not only expand the toolkit for materials design but also address sustainability concerns associated with conventional solvents. As understanding of solvent-polymer interactions deepens, the scope of applications will continue to grow, spanning advanced materials, energy technologies, and biomedical engineering. The integration of experimental and theoretical approaches will be crucial for unlocking the full potential of these unconventional assembly platforms.