Recent Progress in Block Copolymer Self-Assembly for the Fabrication of Structural Color Pigments

The self-assembly of block copolymers (BCPs) into photonic materials has garnered increasing interest due to the versatility and ease of fabrication offered by the synthesized building blocks. BCPs are highly tunable, with their self-assembled structures' size being adjustable by modifying the block lengths, molecular weight(Mw), and polymer composition. This review provides a concise summary of the use of BCPs as photonic pigments, which generate color through structural manipulation rather than relying on chemical pigmentation. These photonic crystal pigments manipulate light behavior, including interference, diffraction, and diffusion, to generate specific colors. BCPs are categorized into two types: linear block copolymers (LBCPs) and brush block copolymers (BBCPs), each involving different monomers that form photonic crystals(PCs). The structural evolution and advancements of BCPs in various practical applications are also explored. It concludes by suggesting that structural color(SC) pigments based on eco-friendly PCs may replace traditional chemical ones in fields such as printing ink, biosensing, chemical sensing, and adaptive photonic materials.

Research progress on the conformational properties of comb-like polymers in dilute solutions

As a special type of branched polymers, comb-like polymers simultaneously possess the structural characteristics of a linear backbone profile and crowded sidechain branches/grafts, and such structural uniqueness leads to reduced interchain entanglement, enhanced molecular orientation, and unique stimulus-response behavior, which greatly expands the potential applications in the fields of super-soft elastomers, molecular sensors, lubricants, photonic crystals, etc. In principle, all these molecular features can be traced back to three structural parameters, i.e., the degree of polymerization of the backbone (Nb), the degree of polymerization of the graft sidechain (Ng), and the grafting density (σ). Consequently, it is of great importance to understand the correlation mechanism between the structural characteristics and physicochemical properties, among which, the conformational properties in dilute solution have received the most attention due to its central position in polymer science. In the past decades, the development of synthetic chemistry and characterization techniques has greatly stimulated the progress of this field, and a number of experiments have been executed to verify the conformational properties; however, due to the complexity of the structural parameters and the diversity of the chemical design, the achieved experimental progress displays significant controversies compared with the theoretical predictions. This review aims to provide a full picture of recent research progress on this topic, specifically, (1) first, a few classical theoretical models regarding the chain conformation are introduced, and the quasi-two-parameter (QTP) theory for the conformation analysis is highlighted; (2) second, the research progress of the static conformation of comb-like polymers in dilute solution is discussed; (3) third, the research progress of the dynamic conformation in dilute solution is further discussed. The key issues, existing controversies and future research directions are also highlighted. We hope that this review can provide insightful information for the understanding of the conformational properties of comb-like polymers, open a new door for the regulation of conformational behavior in related applications, and promote related theoretical and experimental research in the community.

Self-assembly of POSS-Polystyrene Bottlebrush Block Copolymers on an Angle-Robust Selective Absorber for Enhancing the Purity of Reflective Structural Color

A facile approach for improving color purity is explored by the introduction of an angle-robust selective absorber (ARSA) into bottlebrush block copolymer (BBCP)-based one-dimensional (1D) photonic crystals (PCs). The BBCPs of poly[(3-(12-(cis-5-norbornene-exo-2,3-dicarboximido)dodecanoylamino)propyl POSS)-block-(norbornene-graft-styrene)], P_x (x = 1-4), with ultrahigh molecular weights (M_n ∼ 2260 kDa) and low dispersities (D̵ ∼ 1.07) are synthesized by ring-opening metathesis polymerization. The 1D PCs of the lamellar structure are fabricated by self-assembly of the BBCP with different periodicities for full color-generation (blue, green, and red). The optically tailored substrate (i.e., ARSA) is used to modulate the spectral line shape with selective absorption in the near-infrared range. Optical simulation proposes the optimized 1D PC structures on the ARSA, and it provides the reproducibility of the predictable color. The simulated structures are well matched with the experimental results, verifying the enhancement of color saturation even at various incident angles (0-70°).

Self-Assembly of a C16M[Mn] Magnetic Surfactant in Water

A magnetic surfactant, which combines the properties of a surfactant with magnetic responsiveness, shows great potential in biotechnology, separation, adsorption, and catalysis, especially in non-invasive manipulation through a magnetic field. However, a molecularly magnetic surfactant is usually paramagnetic for the amorphous and less ordered structures. In this work, magnetic surfactant 1-methyl-3-hexadecane-imidazolium [MnCl₂Br] (C₁₆M[Mn]) is reported to self-assemble in water. The C₁₆M[Mn] magnetic surfactant self-assembles in water to form a lamellar hydrogel from 10 to 50 wt % at and below room temperature. The hydrogel changes from a gel to a sol at 30 °C, and the hexadecane chains in the hydrogel change from noncrystalline to crystalline at 0 °C. In the hydrogel state, the lamellar domain spacing is varied from 36 to 45 nm depending on the concentration and self-assembly temperature. After self-assembly, the magnetic susceptibility of the freeze-dried magnetic surfactant is increased. Most important is the fact that the freeze-dried sample at a high concentration (40-50 wt %) shows the highest magnetic susceptibility, which is related to the closer molecular packing and the more ordered structures. The self-assembly-induced increase in magnetic susceptibility provides a method for improving the magnetic properties of a magnetic surfactant.

Side-Chain Density Driven Morphology Transition in Brush-Linear Diblock Copolymers

We report the synthesis and self-assembly of brush-linear diblock copolymers with variable side-chain length and density. Poly(pentafluorophenyl acrylate-g-ethylene glycol)-b-polystyrene ((PPFPA-g-PEG)-b-PS) brush-linear diblock copolymers are prepared by sequential reversible addition-fragmentation chain transfer (RAFT) polymerization of PPFPA and PS, followed by postpolymerization reaction between the precursor PPFPA-b-PS diblock copolymer and amine-functionalized PEG. By controlling the PEG chain length and the degree of substitution, we obtained brush-linear diblock copolymers with different side-chain lengths and densities. The solid-state morphologies of the diblocks are then examined by small-angle X-ray scattering (SAXS). At low PEG side-chain density, the segregation of PEG and PS away from PPFPA leads to the formation of PEG and PS lamellar domains with PPFPA in the interface. At high PEG side-chain density, the segregation is between the PPFPA-g-PEG brush block and the PS linear block, and the domain morphology is determined by the composition of the brush block. A partial experimental phase diagram is presented, and it illustrates the importance of both side-chain length and density on the microdomain morphology of brush-linear diblock copolymers.

Temperature tunable flexible photo absorbers based on near-infrared 1D photonic crystal hybridized W-doped VO2nanostructures

Vanadium dioxide is a potential candidate for energy efficient smart windows and have crystalline phase transition temperature (T_c) at 68 °C. So far, literatures mainly emphasis on different synthetic strategies of tungsten doped VO₂which is a most effective dopant to reduceT_cof VO₂to near room temperatures. Until now, there is no report shows the incorporation of flexible 1D photonic crystals as spectrally selective, temperature tunable device to control the changes in optical transmission modulations of W-VO₂nanostrtcures, especially in the near IR region for smart window application. W-doped VO₂with various tungsten contents were synthesized with a facile hydrothermal route. We found that, with 1.1 at% of tungsten doping in intrinsic VO₂, the metal to insulator transition temperature is brought down to 37 °C from 68 °C. IR transmission of VO₂thin film can be reduced from 70% to 40% around room temperature, after doping. Significant absorption enhancement has been observed for both VO₂and W-doped VO₂films, deposited over tunable SiO₂/Ta₂O₅based distributed Bragg reflector (DBR) fabricated over flexible PET (poly-ethylene terephthalate) substrates. On depositing VO₂over ∼70% reflecting DBR, optical transmission is reduced to ∼15% from 35% while the temperature varies to 380 K from 300 K in IR regime. Number of stacks plays a crucial role for effective IR extinctions. A high quality DBR is fabricated by increasing no. of stacks from 4 to 7, with optical transmission of DBR reduced to nearly 5% in stop band. However, with 1.1 at% of W-VO₂over such 95% reflecting flexible DBR, optical transmission vanishes nearly, around room temperature itself in the stop bands of that DBR, which clearly indicates the significant absorption enhancement. W-VO₂/DBR hybrid can substantially modulate the solar heat flux and also imbuing DBR over flexible PET substrates offers retrofitting of the existing windows for energy economy. Thus these structures have promising potential applications for optical devices and practical design for smart windows.

Bioinspired structural color nanocomposites with healable capability

This minireview summarizes the recent development of healable structural color nanocomposites from the perspective of the construction strategies.

Evolution of Single Chain Conformation for Model Comb-Like Chains with Grafting Density Ranging from 0 to ∼100% in Dilute Solution

This work aims to experimentally clarify how the single chain conformation evolves as a function of grafting density for model comb-like chains in dilute solution in the whole density regime. Via a combination of rational design, precise synthesis and accurate characterization, we obtained four sets of PPA_Nb-g-PS₃₀-σ comb-like samples with well-defined architectures and accurately extracted their molecular parameters by triple detection size exclusion chromatography (TD-SEC). With these samples in hand, we quantified how the excluded volume interaction and chain conformation evolve with the grafting density (σ) in the whole density regime. Three main findings are reported: (i) the graft-graft excluded volume interaction is not ignorable even in the low σ-regime; (ii) contrary to theoretical predictions, both the excluded volume interaction and the chain conformation are found to be N_b-dependent; (iii) both R_g ∼ σ^1/3 and [η] ∼ σ⁰ are experimentally confirmed for comb-like chains from different σ and N_b, signifying a unique 3D mass-size growth pattern and a quasi-3D fractal feature. The obtained results help clarify some long-existed controversial issues in the field.