Enterprise innovation and audit pricing: An evidence study from China's A-share listed companies.

Driven by innovation strategy, Chinese enterprises' innovation investment, and research and development capability have been continuously improved, and the audit risk caused by this has attracted widespread attention from the academic community. This study takes China's A-share listed companies from 2013 to 2021 as samples to empirically test the relationship between innovation input and audit pricing of Chinese enterprises. Research shows that the higher the innovation investment, the higher the audit cost. High-quality corporate governance, sufficient research and development personnel, research and development subsidies, and operating cash flow can all play a negative moderating role. A good innovation environment will weaken the positive influence between innovation input and audit fees. This study theoretically confirms the risk-oriented audit pricing mechanism, which is of great significance for optimizing enterprise innovation risk management and improving audit service levels.

Independent director compensation and stock price collapse: Inhibition or promotion-based on a financial background perspective.

This paper takes the financial independent directors' compensation of listed companies from 2014 to 2020 as the research object and uses empirical analysis to study whether the compensation of financial independent directors promotes or inhibits stock price collapse. The research results show that there is a significant positive correlation between the compensation of financial independent directors of listed companies and stock price collapse. In state-owned enterprises, the compensation of financial independent directors has an inhibitory effect on stock price collapse, but it is not significant. In non-state-owned enterprises, the compensation of financial independent directors has a significant promoting effect on stock price collapse. Further research finds that the improvement of internal control quality can weaken the promoting effect of financial independent directors' compensation on stock price collapse to a certain extent, and the weakening effect is particularly evident in non-state-owned enterprises. The attendance frequency of financial independent directors cannot effectively suppress stock price collapse, but instead has a promoting effect.

Silicone Nanofilament Coatings as Flexible Catalyst Supports for a Knoevenagel Condensation Reaction in Batch and Flow Systems.

In this work, silicone nanofilament (SNF) coatings were prepared via a droplet-assisted growth and shaping (DAGS) approach, where the preparation of the coatings is allowed under ambient conditions. The application of SNF coatings as catalyst supports for amino moieties from (3-aminopropyl)triethoxysilane (APTES) was investigated. With the optimized coating conditions identified, the Brunauer-Emmett-Teller surface areas of a bare glass filter substrate and bare glass beads after the coating have increased by 5-fold and 16-fold, respectively. The SNF-coated filters were readily functionalized with amino groups via a liquid-phase deposition process, and their catalytic activities for a Knoevenagel reaction were evaluated using a batch reactor and a packed bed reactor. In both reactors, the as-prepared filters demonstrated superior catalytic performance over the functionalized filters without SNF coatings. Notably, the unique flexibility of the SNF coatings allowed the facile preparation of a packed bed reactor and a scalable catalytic system. It is expected that the packed bed system established in this study will support the development and the use of various SNF-supported organocatalysts and catalytic materials.

Strengthening Interfacial Adhesion and Foamability of Immiscible Polymer Blends via Rationally Designed Reactive Macromolecular Compatibilizers.

Foams made of immiscible polymer blends have attracted great interest in both academia and industry, because of the integration of desirable properties of different polymers in a hybrid foam. However, the foamability and end-use properties are hampered because of the poor interfacial strength within the immiscible blends. Furthermore, few investigations have been carried out on the mechanisms by which interfacial strength and structure affect the foamability of polymer blends. In this work, two different reactive interfacial compatibilizers, i.e., poly(styrene-co-glycidyl methacrylate)-graft-poly(l-lactide) and poly(styrene-co-glycidyl methacry-late)-graft-poly(d-lactide), abbreviated as SG-g-PLLA and SG-g-PDLA, respectively, were designed and synthesized through reactive melt blending and subsequently applied to strengthen the interfacial strength and foamability of immiscible poly(butylene adipate-co-terephthalate) (PBAT)/poly(l-lactide) (PLLA) blends. Both compatibilizers could remarkably enhance the interfacial strength and foamability of the PBAT/PLLA blends, as evidenced by the significantly elongated dispersed phase in the resulting cocontinuous phase and more than 7000-fold increase in the cell density. Furthermore, the improved foamability was quantitively explained by the reduced gas diffusion and increased melt strength. Strikingly, the SG-g-PDLA introduced a stereocomplex crystal at the interface (i-SC), providing highly strengthened interfaces and nanoscale heterogeneous nucleation sites, which led to an energetically favorable cell nucleation. Moreover, foams with specifically laminated cell structures were fabricated by combining pressure-induced flow processing and i-SC strengthened interfaces. This work provides insight into the relationship between interfacial strength and formability of immiscible polymer blends and offers new possibilities for controlling cell morphologies and designing unique cell structures for polymer foams.

One-Step Synthesis of Dynamically Shaped Stiff Nanorods Using Soft Silicone Materials to Control Water Repulsion and Collection.

One-dimensional silicone nanostructures, such as filaments, wires, and tubes, have attracted significant attention, owing to their remarkable application capabilities in a large range of material and surface science. However, the soft mechanical properties of silicone cause vulnerability and irregularity in the synthesized structures, which limits their applications. Herein, a simple, solvent-free, and efficient dynamic Droplet Assisted Growth and Shaping (d-DAGS) strategy is proposed for the one-step synthesis and in situ control of the shape of silicone nanostructures. The special designed bamboo-shaped silicone nanorods (SNRs) that are produced by the repetitive dynamic regulation of growth conditions, concomitant with the periodic purging and injection of precursors, exhibit highly-regular and tunable structure with a specific number of segments, indicating that they can be tailor-made according to the requirements of various properties. The enhanced mechanical stiffness and chemical durability strongly support their excellent performances in water-resistance under both static and dynamic wetting conditions. The SNRs significantly promote buoyancy and self-cleaning properties; and exhibit very high water-harvesting efficiency compared with existing designs. Notably, the well-structured ultra-long rods with an ultrahigh aspect ratio (≈176) can also be fabricated by the d-DAGS method, and they can remain standing straight upwards and regular, even though they consist of flexible silicone.

Printable and Versatile Superhydrophobic Paper via Scalable Nonsolvent Armor Strategy.

Despite great scientific and industrial interest in waterproof cellulosic paper, its real world application is hindered by complicated and costly fabrication processes, limitations in scale-up production, and use of organic solvents. Furthermore, simultaneously achieving nonwetting properties and printability on paper surfaces still remains a technical and chemical challenge. Herein, we demonstrate a nonsolvent strategy for scalable and fast fabrication of waterproofing paper through in situ surface engineering with polysilsesquioxane nanorods (PSNRs). Excellent superhydrophobicity is attained on the functionalized paper surface with a water contact angle greater than 160°. Notably, the engineered paper features outstanding printability and writability, as well as greatly enhanced strength and integrity upon prolonged exposure to water (tensile strength ≈ 9.0 MPa). Additionally, the PSNRs concurrently armor paper-based printed items and artwork with waterproofing, self-cleaning, and antimicrobial functionalities without compromising their appearance, readability, and mechanical properties. We also demonstrate that the engineered paper holds the additional advantages of easy processing, low cost, and mechanochemical robustness, which makes it particularly promising for real world applications.

Photo-switchable supramolecular comb-like polymer brush based on host-guest recognition for use as antimicrobial smart surface.

Bacterial infections from biomedical devices pose a great threat to the health of humans and thus place a heavy burden on society. Therefore, developing efficient antibacterial surfaces has attracted much attention. However, it is a challenge to identify or develop a combination that efficiently integrates multiple functions via topological tailoring and on-demand function-switch via non-contact and noninvasive stimuli. To resolve this issue, a highly hydrophilic comb polymer brush was constructed here based on supramolecular host-guest recognition. Azobenzene (azo)-modified antifouling and antibacterial polymers were incorporated into cyclodextrin (CD)-modified antifouling polymer brushes grafted on the surface. The surface thus obtained possessed excellent antifouling performance with a low bacterial density of ∼6.25 × 105 cells per cm2 after 48 h and exhibited a high efficiency of ∼88.2% for killing bacteria. Besides, irradiation with UV light resulted in the desorption of the azo-polymers and a release of ∼85.1% attached bacteria. Irradiating visible light led to the re-adsorption of azo-polymers, which regenerated the fresh surface; the process could be repeated for at least three cycles, and the surface still maintained low bacterial attachments with a cell density of ∼7.10 × 105 cells per cm2, high sterilization efficiency of ∼93.8%, and a bacteria release rate of ∼83.1% in the 3rd cycle. The photo-switchable antibacterial surface presented in this research will provide new insights into the development of smart biomedical surfaces.

Versatile and Simple Strategy for Preparing Bilayer Hydrogels with Janus Characteristics.

Bilayer hydrogels are attracting tremendous attention for their capability to integrate several different functions on the two sides of the gel, that is, imparting the gel with Janus characteristics, which is highly desired in many engineering and biomedical applications including soft actuators, hydrogel patches, and wearable electronics. However, the preparation process of the bilayer materials usually involves several complicated steps and is time-consuming, while the interfacial bonding is another main concern. Here, a simple and versatile method is proposed to obtain bilayer hydrogels within just one step based on the method of introducing viscosity contrast of the precursors for different layers. The bilayer structure can be well maintained during the whole preparation process with a constrained interfacial molecular exchange to ensure the strong bonding strength. The key requirements for forming distinct bilayer structures in situ are studied and discussed in detail. Bilayer hydrogels with different chemical designs are prepared via this strategy to tailor the good distribution of desired functions for soft actuators, wound healing patches, and wearable electronics. We believe that the strategy illustrated here will provide new insights into the preparation and application of bilayer materials.

Designer Core-Shell Nanoparticles as Polymer Foam Cell Nucleating Agents: The Impact of Molecularly Engineered Interfaces.

The interface between nucleating agents and polymers plays a pivotal role in heterogeneous cell nucleation in polymer foaming. We describe how interfacial engineering of nucleating particles by polymer shells impacts cell nucleation efficiency in CO2 blown polymer foams. Core-shell nanoparticles (NPs) with a 80 nm silica core and various polymer shells including polystyrene (PS), poly(dimethylsiloxane) (PDMS), poly(methyl methacrylate) (PMMA), and poly(acrylonitrile) (PAN) are prepared and used as heterogeneous nucleation agents to obtain CO2 blown PMMA and PS micro- and nanocellular foams. Fourier transform infrared spectroscopy, thermogravimetric analysis, and transmission electron microscopy are employed to confirm the successful synthesis of core-shell NPs. The cell size and cell density are determined by scanning electron microscopy. Silica NPs grafted with a thin PDMS shell layer exhibit the highest nucleation efficiency values, followed by PAN. The nucleation efficiency of PS- and PMMA-grafted NPs are comparable with the untreated particles and are significantly lower when compared to PDMS and PAN shells. Molecular dynamics simulations (MDS) are employed to better understand CO2 absorption and nucleation, in particular to study the impact of interfacial properties and CO2-philicity. The MDS results show that the incompatibility between particle shell layers and the polymer matrix results in immiscibility at the interface area, which leads to a local accumulation of CO2 at the interfaces. Elevated CO2 concentrations at the interfaces combined with the high interfacial tension (caused by the immiscibility) induce an energetically favorable cell nucleation process. These findings emphasize the importance of interfacial effects on cell nucleation and provide guidance for designing new, highly efficient nucleation agents in nanocellular polymer foaming.

Cellulosic sponges with pH responsive wettability for efficient oil-water separation.

To obtain efficient oil-water separation materials with responsiveness, cellulosic porous materials with switchable wettability in response to pH changes were developed by reacting cellulose acetoacetate sponges with alkylamines of varying carbon chain length via dynamic covalent enamine bonds. The resulting sponges reversibly changed between being superhydrophilic (θwater = 0°) and highly hydrophobic (maximal θwater = 146°) under suitable pH conditions while maintained the favorable porous structures. Notably, the functionalized sponges exhibited high and selective oil absorption capacity (40-80 g/g) and satisfying desorption ability of 80%, and could efficiently separate oil-water mixtures and emulsions with extremely high efficiency (> 99%) in a controllable manner. With the three-dimensional micro/nano porous structure, switchable wettability and intrinsic environmentally friendliness, the pH responsive cellulosic sponges developed here hold great potential in controllable oil-water separation and oily wastewater purification.

Bubble Seeding Nanocavities: Multiple Polymer Foam Cell Nucleation by Polydimethylsiloxane-Grafted Designer Silica Nanoparticles.

We describe a successful strategy to substantially enhance cell nucleation efficiency in polymer foams by using designer nanoparticles as nucleating agents. Bare and poly(dimethylsilane) (PDMS)-grafted raspberry-like silica nanoparticles with diameters ranging from ∼80 nm to ∼200 nm were synthesized and utilized as highly efficient cell nucleators in CO2-blown nanocellular polymethyl methacrylate (PMMA) foams. The successful synthesis of core-shell nanoparticles was confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis, Brunauer-Emmett-Teller measurements, and transmission electron microscopy. The cell size and cell density of the obtained PMMA micro- and nanocellular foams were determined by scanning electron microscopy. The results show that increased surface roughness enhances the nucleation efficiency of the designer silica particles. This effect is ascribed to a decreased nucleation free energy for foam cell nucleation in the nanocavities at the melt-nucleator interface. For PDMS grafted raspberry-like silica nanoparticles with diameters of 155 and 200 nm, multiple cell nucleation events were observed. These hybrid particles had nucleation efficiencies of 3.7 and 6.2, respectively. The surprising increase in nucleation efficiency to above unity is ascribed to the significant increase in CO2 absorption and capillary condensation in the corresponding PMMA during saturation. This increase results in the presence of large amounts of the physical blowing agent close to energetically favorable nucleation points. Additionally, it is shown that as a consequence of cell coalescence, the increased number of foam cells is rapidly reduced during the first seconds of foaming. Hence, the design of highly efficient nucleating particles, as well as careful selection of foam matrix materials, seems to be of pivotal importance for obtaining polymer cellular materials with cell dimensions at the nanoscale. These findings contribute to the fabrication of polymer foams with high thermal insulation capacity and have relevance in general to the area of cellular materials.

Solvent-Free Fabrication of Flexible and Robust Superhydrophobic Composite Films with Hierarchical Micro/Nanostructures and Durable Self-Cleaning Functionality.

Superhydrophobic surfaces hold tremendous potential in a wide range of applications owing to their multifaced functionalities. However, the mechanochemical susceptibility of such materials hinders their widespread usage in practical applications. Here, we present a simple, solvent-free, and environmentally friendly approach to fabricate flexible and robust superhydrophobic composite films with durable self-cleaning functionality. The obtained composite film features unexpected but surprising hierarchical micro/nanoscopic structures as well as robust superhydrophobicity with a water contact angle of ∼170° and a sliding angle below 4°. Notably, the composite film exhibits mechanical robustness under cyclic abrasion, tape peeling, flexing, intensive finger wiping, and knife cutting; maintains excellent superhydrophobicity after long-time exposure to a high-humidity environment; and sustains exposure to highly corrosive species, such as strong acid/base solutions and organic solvents. The robust superhydrophobicity is ascribed to the induced micro/nanohierarchical surface structures, resulting in the trapped dual-scale air pockets, which could largely reduce the solid/liquid interface. In addition, even after oil contamination, the composite film maintains its water repellency and self-cleaning functionality. The robust superhydrophobic composite film developed here is expected to extend the application scope of superhydrophobic materials and should find potential usage in various industries and daily life.

Hierarchical Structured Multifunctional Self-Cleaning Material with Durable Superhydrophobicity and Photocatalytic Functionalities.

Self-cleaning materials, which are inspired and derived from natural phenomena, have gained significant scientific and commercial interest in the past decades as they are energy- and labor-saving and environmentally friendly. Several technologies are developed to obtain self-cleaning materials. The combination of superhydrophobic and photocatalytic properties enables the efficient removal of solid particles and organic contaminations, which could reduce or damage the superhydrophobicity. However, the fragility of the nanoscale roughness of the superhydrophobic surface limits its practical application. Here, a hierarchical structure approach combining micro- and nanoscale architectures is created to protect the nanoscale surface roughness from mechanical damage. Glass beads of 75 µm are partially embedded into a low-density polyethylene film. This composite surface is coated with silicone nanofilaments (SNFs) via the droplet-assisted growth and shaping approach, providing the nanoscale surface roughness as well as the support for the photocatalyst with enlarged surface area. TiO2 nanoparticles, which serve as the photocatalyst, are synthesized in situ on SNFs through a hydrothermal reaction. The self-cleaning effect is proved using wettability measurements for various liquids, degradation of organic contamination under UV light, and antibacterial tests. The enhanced mechanical durability of the hierarchical structure of the composite material is verified with an abrasion test.

Size-Dependent Submerging of Nanoparticles in Polymer Melts: Effect of Line Tension.

Adhesion of nanoparticles to polymer films plays a key role in various polymer technologies. Here we report experiments that reveal how silica nanoparticles adhere to a viscoelastic PMMA film above the glass transition temperature. The polymer was swollen with CO2, closely matching the conditions of nanoparticle-nucleated polymer foaming. It is found that the degree by which the particles sink into the viscoelastic substrate is strongly size dependent and can even lead to complete engulfment for particles of diameter below 12 nm. These findings are explained quantitatively by a thermodynamic analysis, combining elasticity, capillary adhesion, and line tension. We argue that line tension, here proposed for the first time in elastic media, is responsible for the nanoparticle engulfment.

Silica-Assisted Nucleation of Polymer Foam Cells with Nanoscopic Dimensions: Impact of Particle Size, Line Tension, and Surface Functionality.

Core-shell nanoparticles consisting of silica as core and surface-grafted poly(dimethylsiloxane) (PDMS) as shell with different diameters were prepared and used as heterogeneous nucleation agents to obtain CO2-blown poly(methyl methacrylate) (PMMA) nanocomposite foams. PDMS was selected as the shell material as it possesses a low surface energy and high CO2-philicity. The successful synthesis of core-shell nanoparticles was confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis, and transmission electron microscopy. The cell size and cell density of the PMMA micro- and nanocellular materials were determined by scanning electron microscopy. The cell nucleation efficiency using core-shell nanoparticles was significantly enhanced when compared to that of unmodified silica. The highest nucleation efficiency observed had a value of ∼0.5 for nanoparticles with a core diameter of 80 nm. The particle size dependence of cell nucleation efficiency is discussed taking into account line tension effects. Complete engulfment by the polymer matrix of particles with a core diameter below 40 nm at the cell wall interface was observed corresponding to line tension values of approximately 0.42 nN. This line tension significantly increases the energy barrier of heterogeneous nucleation and thus reduces the nucleation efficiency. The increase of the CO2 saturation pressure to 300 bar prior to batch foaming resulted in an increased line tension length. We observed a decrease of the heterogeneous nucleation efficiency for foaming after saturation with CO2 at 300 bar, which we attribute to homogenous nucleation becoming more favorable at the expense of heterogeneous nucleation in this case. Overall, it is shown that the contribution of line tension to the free energy barrier of heterogeneous foam cell nucleation must be considered to understand foaming of viscoelastic materials. This finding emphasizes the need for new strategies including the use of designer nucleating particles to enhance the foam cell nucleation efficiency.