Small variations in reaction conditions tune carbon dot fluorescence

The development of robust and reproducible synthetic strategies for the production of carbon dots with improved fluorescence quantum yields and distinct emission profiles is of great relevance given the vast range of applications of CDs. The fundamental understanding at a molecular level of their formation mechanism, chemical structure and how these parameters are correlated to their photoluminescence (PL) properties is thus essential. In this study, we describe the synthesis and structural characterization of a range of CDs with distinct physico-chemical properties. The materials were prepared under three minutes of microwave irradiation using the same common starting materials (GlcNH2·HCl 1 and EDA 2) but modifying the stoichiometry of the reagents. We show that small changes in reaction conditions leads to the tailoring of the fluorescent behaviour of the CDs from apparent blue to green emission. Structural analysis of the different CD samples suggested different reaction pathways during the CD formation and surface passivation, with the latter step being key to the observed differences. Moreover, we demonstrate that the different materials also respond reversibly to changes in pH, which we can attribute to different behaviour towards protonation/deprotonation events of distinct emission domains present within each nanomaterial. Our results highlight the importance of understanding the reaction pathways that lead to the formation of this carbon-based nanomaterials and how this can be exploited to develop tailored materials towards specific applications

Transparent and Hard Zirconia-Based Hybrid Coatings with Excellent Dynamic/Thermoresponsive Oleophobicity, Thermal Durability, and Hydrolytic Stability

Smooth, transparent, and extremely hard zirconia (ZrO₂)-based inorganic–organic hybrid films showing excellent dynamic oleophobicity, thermal durability, and hydrolytic stability were successfully prepared through a simple combination of zirconium tetrapropoxide (Zr­(O­(CH₂)₂CH₃)₄) with stearic acids. In this study, we have particularly focused on the effects of stearic acid molecular architecture (linear-stearic acid (LSA) and branched-stearic acid (BSA)) on surface physical/chemical properties. Although, in each case, the resulting hybrid (Zr:LSA and Zr:BSA) films achieved by a simple spin-coating method were highly smooth and transparent, the final surface properties were markedly dependent on their molecular architectures. Thanks to the thermal stability of BSA, our Zr:BSA hybrid films displayed a greatly improved thermal effective range (maximum of 200 °C), while for Zr:LSA hybrid films, serious thermal damage to surface dewetting behavior was observed at less than 150 °C. The hardness of the Zr:BSA hybrid films were markedly increased by curing at 200 °C for 1 h (from 1.95 GPa to 3.03 GPa), while maintaining their dynamic dewettability toward <i>n</i>-hexadecane, when compared with Zr:LSA hybrid films (0.95–1.19 GPa). Small volume <i>n</i>-hexadecane droplets (5 μL) were easily set in motion, sliding across and off our best Zr:BSA hybrid film surfaces at low substrate tilt angles (<10°) without pinning. Moreover, they also showed thermoresponsive dynamic dewetting behavior, reasonable resistance to hydrolysis in an aqueous environment, and antifingerprint properties

A Physical Approach To Specifically Improve the Mobility of Alkane Liquid Drops

Seamless control of resistance to liquid drop movement for polar (water) and nonpolar alkane (<i>n</i>-hexadecane, <i>n</i>-dodecane, and <i>n</i>-decane) probe liquids on substrate surfaces was successfully demonstrated using molten linear poly­(dimethylsiloxane) (PDMS) brush films with a range of different molecular weights (MWs). The ease of movement of liquid drops critically depended on polymer chain mobility as it relates to both polymer MW and solvent swelling on these chemically- and topographically identical surfaces. Our brush films therefore displayed lower resistances to liquid drop movement with decreasing polymer MW and surface tension of probe liquid as measured by contact angle (CA) hysteresis and tilt angle measurements. Subsequently, while mobility of water drops was inferior and became worse at higher MWs, <i>n</i>-decane drops were found to experience little resistance to movement on these polymer brush films. Calculating CA hysteresis as Δθ_cos = cos θ_R – cos θ_A (θ_A and θ_R are the advancing and receding CAs, respectively) rather than the standard Δθ = θ_A – θ_R was found to be advantageous for estimation of the actual dynamic dewetting behavior of various probe liquids on an inclined substrate

Novel Transparent Zirconium-Based Hybrid Material With Multilayered Nanostructures: Studies of Surface Dewettability Toward Alkane Liquids

We have successfully prepared unique inorganic–organic hybrid materials that demonstrate excellent transparency and dewettability toward various alkane liquids (<i>n</i>-hexadecane, <i>n</i>-dodecane and <i>n</i>-decane) without relying on conventional surface roughening and perfluorination. Such coatings were made using a novel family of hybrid materials generated by substituting carboxylic acids, with a range of alkyl chain lengths (CH₃(CH₂)_<i>x</i>−2COOH where <i>x</i> = total carbon number, i.e., 10, 12, 14, 16, 18, 22, or 24, into zirconium (Zr) tetra-propoxide complexes. This precursor was then mixed with acetic acid and spincast to produce transparent thin Zr-carboxylic acid (ZrCA_<i>x</i>) hybrid films using a nonhydrolytic sol–gel process. Fourier transform infrared spectroscopy provided proof of Zr–O–Zr network formation in the films upon casting and also followed changes to the physical nature (liquid-like or solid-like) of the alkyl chain assemblies depending upon alkyl chain length. X-ray diffractometry revealed that the hybrid films prepared using the longer chain carboxylic acids (ZrCA_{<i>x</i>≥18}) spontaneously self-assembled into lamella structures with <i>d</i>-spacings ranging from 29.5 to 32.7 Angstroms, depending on the length of the alkyl chain. On the other hand the remaining films (ZrCA_<i>x</i><18) showed no such ordering. Moreover, the dynamic dewetting behavior of our hybrid films with alkane liquids was also strongly affected by alkyl chain length. ZrCA<i>_x</i> films with x = 12, 14, and 16 showed the best dynamic oleophobicity among the seven hybrid films. In particular, small volume alkane droplets (5 μL) could be easily set in motion to move across and off ZrCA₁₄ film surfaces without pinning at low tilt angles (∼6°)

Passiflora quadrangularis

Alkylsilane-derived monolayer-covered surfaces generally display a reasonably good level of hydrophobicity but poor oleophobicity. Here, we demonstrate that the physical attributes of alkylsilane-derived surfaces (liquid-like or solid-like) are dependent on the alkyl chain length and density, and these factors subsequently have significant influence upon the dynamic dewetting behavior toward alkanes (C_<i>n</i>H_2<i>n</i>+2, where <i>n</i> = 7–16). In this study, we prepared and characterized hybrid films through a simple sol–gel process based on the cohydrolysis and co-condensation of a mixture of a range of alkyltriethoxysilanes (C_<i>n</i>H_2<i>n</i>+1Si­(OEt)₃, where <i>n</i> = 3, 6, 8, 10, 12, 14, 16, and 18) and tetramethoxysilane (TMOS). Surprisingly, when the carbon number (C_<i>n</i>) of alkyl chain was 10 and below, the produced hybrid films were all smooth, highly transparent, and showed negligible contact angle (CA) hysteresis. On these hybrid surfaces, 5 μL drops of alkanes (<i>n</i>-hexadecane, <i>n</i>-dodecane, and <i>n</i>-decane) could move easily at low tilt angles (<5°) without pinning. On the other hand, when the C_<i>n</i> exceeded 12, both transparency and mobility of probe liquids significantly worsened. In the former case, TMOS molecules played key roles in both forming continuous films (as a binder) and improving flexibility of alkyl chains (as a molecular spacer), resulting in the smooth liquid-like surfaces. Silylation of the hybrid film and subsequent dynamic CA measurements proved the presence of silanol groups on the outermost surfaces and demonstrated that the dynamic dewettability of hybrid films worsened as packing densities increased. Additionally, solvent effects (high affinity) between the alkyl chains and alkane liquids imparted a more liquid-like character to the surface. Thanks to these simple physical effects, the resistance to the alkane droplet motion across tilted surfaces was markedly reduced. With the longer carbon chains, the chain mobility was strictly inhibited by mutual interactions between neighboring alkyl chains even in the presence of TMOS molecules. The achieved surfaces displayed a solid-like nature along with surface defects, leading to inferior dynamic oleophobicity. Therefore, the critical C_<i>n</i> of alkyl chain used for determining final dynamic dewetting behavior against alkane liquids was 12. Furthermore, our hybrid surfaces exhibited excellent antifingerprint properties, particularly demonstrating low adhesion and easy removal from the surface

Novel Transparent Zirconium-Based Hybrid Material With Multilayered Nanostructures: Studies of Surface Dewettability Toward Alkane Liquids

We have successfully prepared unique inorganic–organic hybrid materials that demonstrate excellent transparency and dewettability toward various alkane liquids (<i>n</i>-hexadecane, <i>n</i>-dodecane and <i>n</i>-decane) without relying on conventional surface roughening and perfluorination. Such coatings were made using a novel family of hybrid materials generated by substituting carboxylic acids, with a range of alkyl chain lengths (CH₃(CH₂)_<i>x</i>−2COOH where <i>x</i> = total carbon number, i.e., 10, 12, 14, 16, 18, 22, or 24, into zirconium (Zr) tetra-propoxide complexes. This precursor was then mixed with acetic acid and spincast to produce transparent thin Zr-carboxylic acid (ZrCA_<i>x</i>) hybrid films using a nonhydrolytic sol–gel process. Fourier transform infrared spectroscopy provided proof of Zr–O–Zr network formation in the films upon casting and also followed changes to the physical nature (liquid-like or solid-like) of the alkyl chain assemblies depending upon alkyl chain length. X-ray diffractometry revealed that the hybrid films prepared using the longer chain carboxylic acids (ZrCA_{<i>x</i>≥18}) spontaneously self-assembled into lamella structures with <i>d</i>-spacings ranging from 29.5 to 32.7 Angstroms, depending on the length of the alkyl chain. On the other hand the remaining films (ZrCA_<i>x</i><18) showed no such ordering. Moreover, the dynamic dewetting behavior of our hybrid films with alkane liquids was also strongly affected by alkyl chain length. ZrCA<i>_x</i> films with x = 12, 14, and 16 showed the best dynamic oleophobicity among the seven hybrid films. In particular, small volume alkane droplets (5 μL) could be easily set in motion to move across and off ZrCA₁₄ film surfaces without pinning at low tilt angles (∼6°)

Unusual Dynamic Dewetting Behavior of Smooth Perfluorinated Hybrid Films: Potential Advantages over Conventional Textured and Liquid-Infused Perfluorinated Surfaces

From a viewpoint of reducing the burden on the environment and human health, an alternative method for preparing liquid-repellent surfaces without relying on the long perfluorocarbons (C_{((<i>X</i>–1)/2)}F_<i>X</i>, <i>X</i> ≥ 17) has been strongly demanded lately. In this study, we have successfully demonstrated that dynamic dewettability toward various probe liquids (polar and nonpolar liquids with high or low surface tension) can be tuned by not only controlling surface chemistries (surface energies) but also the physical (solid-like or liquid-like) nature of the surface. We prepared smooth and transparent organic–inorganic hybrid films exhibiting unusual dynamic dewetting behavior toward various probe liquids using a simple sol–gel reaction based on the co-hydrolysis and co-condensation of a mixture including a range of perfluoroalkylsilanes (FAS<i>X</i>, C_{((<i>X</i>–1)/2)}F_<i>X</i>CH₂CH₂Si­(OR)₃, where <i>X</i> = 3, 9, 13, and 17) and tetramethoxysilane (Si­(OCH₃)₄, TMOS). Dynamic contact angle (CA) and substrate tilt angle (TA) measurements confirmed that our FAS<i>X</i>-hybrid films exhibited excellent dynamic dewetting properties and were mostly independent of the length of perfluoroalkyl (R_f) groups. For example, 10 μL droplets of ultralow surface tension liquids (e.g., diethyl ether (γ = 16.26 dyn/cm) and <i>n</i>-pentane (γ = 15.51 dyn/cm)) could move easily on our FAS9-, FAS13-, and FAS17-hybrid film surfaces at low substrate TAs (<4°) without pinning. This is comparable or superior to the best perfluorinated textured and flat surfaces reported so far. This exceptional dynamic dewetting behavior appeared only when TMOS molecules were added to the precursor solutions; we assume this is due to co-condensed TMOS-derived silica species working as spacers between the neighboring R_f chains, enabling them to rotate freely and in doing so provide a surface with liquid-like properties. This led to the distinguished dynamic dewettability of our hybrid films, regardless of the small static CAs. Our FAS<i>X</i>-hybrid films also displayed excellent chemical and physical durability against thermal stress (∼250 °C), high-temperature (150 °C) oil vapor, and various other media (perfluoro liquid, boiling water, and weak acid) without degrading their dynamic dewettability. Such exceptional durability has been rarely seen on conventional perfluorinated surfaces reported so far

A Physical Approach To Specifically Improve the Mobility of Alkane Liquid Drops

Seamless control of resistance to liquid drop movement for polar (water) and nonpolar alkane (<i>n</i>-hexadecane, <i>n</i>-dodecane, and <i>n</i>-decane) probe liquids on substrate surfaces was successfully demonstrated using molten linear poly­(dimethylsiloxane) (PDMS) brush films with a range of different molecular weights (MWs). The ease of movement of liquid drops critically depended on polymer chain mobility as it relates to both polymer MW and solvent swelling on these chemically- and topographically identical surfaces. Our brush films therefore displayed lower resistances to liquid drop movement with decreasing polymer MW and surface tension of probe liquid as measured by contact angle (CA) hysteresis and tilt angle measurements. Subsequently, while mobility of water drops was inferior and became worse at higher MWs, <i>n</i>-decane drops were found to experience little resistance to movement on these polymer brush films. Calculating CA hysteresis as Δθ_cos = cos θ_R – cos θ_A (θ_A and θ_R are the advancing and receding CAs, respectively) rather than the standard Δθ = θ_A – θ_R was found to be advantageous for estimation of the actual dynamic dewetting behavior of various probe liquids on an inclined substrate

Unusual Dynamic Dewetting Behavior of Smooth Perfluorinated Hybrid Films: Potential Advantages over Conventional Textured and Liquid-Infused Perfluorinated Surfaces

From a viewpoint of reducing the burden on the environment and human health, an alternative method for preparing liquid-repellent surfaces without relying on the long perfluorocarbons (C_{((<i>X</i>–1)/2)}F_<i>X</i>, <i>X</i> ≥ 17) has been strongly demanded lately. In this study, we have successfully demonstrated that dynamic dewettability toward various probe liquids (polar and nonpolar liquids with high or low surface tension) can be tuned by not only controlling surface chemistries (surface energies) but also the physical (solid-like or liquid-like) nature of the surface. We prepared smooth and transparent organic–inorganic hybrid films exhibiting unusual dynamic dewetting behavior toward various probe liquids using a simple sol–gel reaction based on the co-hydrolysis and co-condensation of a mixture including a range of perfluoroalkylsilanes (FAS<i>X</i>, C_{((<i>X</i>–1)/2)}F_<i>X</i>CH₂CH₂Si­(OR)₃, where <i>X</i> = 3, 9, 13, and 17) and tetramethoxysilane (Si­(OCH₃)₄, TMOS). Dynamic contact angle (CA) and substrate tilt angle (TA) measurements confirmed that our FAS<i>X</i>-hybrid films exhibited excellent dynamic dewetting properties and were mostly independent of the length of perfluoroalkyl (R_f) groups. For example, 10 μL droplets of ultralow surface tension liquids (e.g., diethyl ether (γ = 16.26 dyn/cm) and <i>n</i>-pentane (γ = 15.51 dyn/cm)) could move easily on our FAS9-, FAS13-, and FAS17-hybrid film surfaces at low substrate TAs (<4°) without pinning. This is comparable or superior to the best perfluorinated textured and flat surfaces reported so far. This exceptional dynamic dewetting behavior appeared only when TMOS molecules were added to the precursor solutions; we assume this is due to co-condensed TMOS-derived silica species working as spacers between the neighboring R_f chains, enabling them to rotate freely and in doing so provide a surface with liquid-like properties. This led to the distinguished dynamic dewettability of our hybrid films, regardless of the small static CAs. Our FAS<i>X</i>-hybrid films also displayed excellent chemical and physical durability against thermal stress (∼250 °C), high-temperature (150 °C) oil vapor, and various other media (perfluoro liquid, boiling water, and weak acid) without degrading their dynamic dewettability. Such exceptional durability has been rarely seen on conventional perfluorinated surfaces reported so far

Why Can Organic Liquids Move Easily on Smooth Alkyl-Terminated Surfaces?

The dynamic dewettability of a smooth alkyl-terminated sol–gel hybrid film surface against 17 probe liquids (polar and nonpolar, with high and low surface tensions) was systematically investigated using contact angle (CA) hysteresis and substrate tilt angle (TA) measurements, in terms of their physicochemical properties such as surface tension, molecular weight/volume, dielectric constant, density, and viscosity. We found that the dynamic dewettability of the hybrid film markedly depended not on the surface tensions but on the dielectric constants of the probe liquids, displaying lower resistance to liquid drop movement with decreasing dielectric constant (ε < 30). Interfacial analysis using the sum-frequency generation (SFG) technique confirmed that the conformation of surface-tethered alkyl chains was markedly altered before and after contact with the different types of probe liquids. When probe liquids with low dielectric constants were in contact with our surface, CH₃ groups were preferentially exposed at the solid/liquid interface, leading to a reduction in surface energy. Because of such local changes in surface energy at the three-phase contact line of the probe liquid, the contact line can move continuously from low-surface-energy (solid/liquid) areas to surrounding high-surface-energy (solid/air) areas without pinning. Consequently, the organic probe liquids with low dielectric constants can move easily and roll off when tilted only slightly, independent of the magnitude of CAs, without relying on conventional surface roughening and perfluorination