Density Of Hydroxyl Groups Research Articles

Functionalization of a chemically treated Ti6Al4V-ELI alloy with nisin for antibacterial purposes

This research aims to define a protocol for nisin adsorption onto Ti6Al4V- Extra Low Interstitial content (ELI) alloy to reduce the risk of peri-implant infections. The substrate is, first, etched to get a nanotextured surface with a high density of acidic hydroxyl groups and then functionalized with the antimicrobial peptide nisin. Nisin adsorption is performed at different pH values, in the range of 5–7. The nisin release in inorganic solutions mimicking physiological or pro-inflammatory conditions is tested. The surfaces are characterized by profilometry, SEM/EDS, contact angle and surface free energy measurements, zeta potential titrations, DLS, XPS, and UV–visible spectroscopy. Effective surface adsorption was achieved and maximized at pH 6. The coated surface has high surface energy suitable for tissue integration and it releases nisin in a time longer than 1 day. As a confirmation of the antibacterial properties due to the nisin adsorption, specimens were incubated with Staphylococcus aureus, whose metabolic activity was reduced by ≈ 70% in comparison to the untreated control, and the number of viable adhered colonies was ≈ 6 times reduced. In conclusion, coupling of nisin to a chemically treated titanium surface is promising for a bioactive and antibacterial surface for tissue integration.

Empirical Hydrogen Bonding Donor (HBD) Parameters of Organic Solvents Using Solvatochromic Probes - A Critical Evaluation.

The solvatochromicity of established solvatochromic UV/Vis probes, which appear to be sensitive to the so-called hydrogen bond donor (HBD) property of the solvent, is analysed using the hydroxyl group density of alcoholic solvents DHBD as a physical parameter in comparison to the pKa, the chemical benchmark for acidity. Reichardt's dye B30, Kosowers Z-indicator 1-ethyl-4-(methoxycarbonyl) pyridinium iodide (K), Kamlet-Tafts α, Dragos S parameter, Catalans SA scale, the cis-dicyano-bis (1,10-phenanthroline) iron II complex (Schilt's Ferrocyphen dye, Fe) and Gutmann's acceptor number (AN) have been investigated. The observed dependencies of the empirical polarity parameters as a function of DHBD for several alcoholic solvent families requires a ompletely new physicochemical understanding of these established HBD parameters. Only the AN scale (or Fe) is able to bridge the gap between global polarity and acidity, provided the values are interpreted correctly and applied accordingly.

Poly(styrene-co-4-hydroxystyrene) nanofiber membrane for highly selective and efficient Rb+ capture from high salinity solution

Highly selective and efficient rubidium ion (Rb+) capture from high salinity aqueous solutions has always been an extremely challenging task. Herein, a novel Rb+ selective adsorption nanofiber membranes are fabricated via electrospun by using a linear polymer poly(styrene-co-4-hydroxylstyrene) (P(S-co-VPh)) containing phenolic hydroxyl groups, which hydrolyzed from the copolymer of styrene (St) and 4-acetoxystyrene (AS). GPC, 1H NMR and FTIR, results showing that the polymer chain structures can be effectively regulated via changing the monomers ratio. After electrospinning, the morphologies and specific surface areas of as-prepared membranes are evaluated by FESEM and BET. The adsorption experiment results show that Rb+ adsorption capacity gradually increase with phenolic hydroxyl group density of the membrane surfaces. The adsorption process agrees with the Langmuir model, and the maximum adsorption capacity (qm) is up to 53.15 mg/g, and the adsorption kinetics obeys preferentially the pseudo-second-order kinetics. Intraparticle diffusion model shows that the adsorption is a multi-step limiting process and breakthrough curve is best fitted by the Yan model. Surprising, over 80% of the maximum adsorption capacity can be achieved within 15 min, and adsorption equilibrium is reached within 1.0 h. Furthermore, the excellent selectivity coefficient K of Rb+/Mn+ in high salinity binary mixtures are 580.2, 426.4, 258.1 and 128.3 for Na+ (9.6 g/L), Mg2+ (1.28 g/L), Ca2+ (0.4 g/L), K+ (0.5 g/L) used as the interfering ions, respectively. Moreover, the recovery rate remains exceeding 85% after five adsorption–desorption cycles, indicating that nanofiber membranes prepared by P(S-co-VPh) have significant application potential for rubidium separation and purification in the future.

Surface Hydroxyl Chemistry of Titania- and Alumina-Based Supports: Quantitative Titration and Temperature Dependence of Surface Brønsted Acid-Base Parameters.

Surface hydroxyl groups on metal oxides play significant roles in catalyst synthesis and catalytic reactions. Despite the importance of surface hydroxyls in broader material applications, quantitative measurements of surface acid-base properties are not regularly reported. Here, we describe direct methods to quantify fundamental properties of surface hydroxyls on several titania- and alumina-based supports. Comparing commercially available anatase, rutile, P25, and P90 titania, thermogravimetric analysis (TGA) indicated that the total surface hydroxyl density varied by a factor of 2, and each surface hydroxyl is associated with approximately one weakly adsorbed water molecule. Proton-exchange site densities, determined at 25 °C with slurry acid-base titrations, led to several conclusions: (i) the intrinsic acidity/basicity of surface hydroxyls were similar regardless of the titania source; (ii) differences in the surface isoelectric point (IEP) were primarily attributable to differences in the surface concentration of acid and base sites; (iii) rutile has a higher surface concentration of basic hydroxyls, leading to a higher IEP; and (iv) P25 and P90 titania have slightly higher surface concentrationsof acidic hydroxyls relative to anatase or rutile. Temperature effects on surface acid-base properties are rarely reported yet are significant: from 5 to 65 °C, IEP values change by roughly one pH unit. The IEP changes were associated with large changes to the intrinsic acid-base equilibrium constants over this temperature range, rather than changes in the composition or concentration of the surface sites.

Asphaltene inhibitor performance as a function of the asphaltene molecular/aggregate characteristics: Evaluation by interfacial rheology measurement and bulk methods

Asphaltene precipitation/deposition in well tubing and porous media is categorized as asphaltene damage. Addressing this issue, this study offers an asphaltene inhibitor (namely BZSS-012) and highlights the mutual dependence of the inhibitor-asphaltene molecular structure/functional groups for a successful inhibition performance. Asphaltenes were extracted from two dead oil samples, designated as A- and F- oil, characterized well and dissolved in n-hexane/toluene mixture to prepare A- and F-model oil. Interfacial rheology measurements, in addition to conventional asphaltene dispersant test (ADT), was introduced as a new test approach to evaluate the inhibitor performance. The dynamic interfacial tension (IFT) and dilational elasticity of the model oils-water interface were measured. In addition, the standard deviation from the Young-Laplace drop shape (YL-STD) during a high-amplitude compression-expansion of the interface was calculated. Compared to the F-asphaltene, the A-asphaltene molecules have a larger aromatic sheet size, shorter peripheral chains, higher heteroatom content, and higher density of hydroxyl groups, leading to a higher self-association tendency. However, the aggregates size of the F-asphaltene is larger than that of the A-asphaltene in the model oil. Despite its larger aggregates, the F-asphaltene has an enough extent and strength of interactions with the inhibitor, leading to the efficiency of 99.2% in the ADT test, much higher than 66.7% efficiency for the A-model oil. In addition, compared to the A-model oil, the F-model oil exhibits lower IFT values with a slower dynamic in-line with the F-asphaltene larger aggregates and revealing their outward functional groups. The addition of the inhibitor accelerates the dynamic of the IFT and results in lower IFT values. No sharp peak in the YL-STD of the F-model oil dosed with 50 ppmv of the inhibitor is observed. This reflects the inhibitor efficiency for controlling the association and networking of the asphaltene aggregates to inhibit interfacial asphaltenic film evolution. Monitoring the YL-STD seems to be an appropriate method to screen asphaltene inhibitors.

Influence of conversion on dielectric constant of Dicyandiamide cured epoxy resin:a molecular dynamic simulation and experiment study

In this study, molecular dynamic simulation and experiment study are combined to explore the main control factors of dielectric constant of Dicyandiamide cured epoxy resin. The density and glass transition temperature obtained by experiment and simulation were compared to verify the rationality of simulation models. Then dielectric constant was calculated by dipole fluctuation formula, here motion mobility, polarity, and free volume were employed to interpret the influence mechanism of conversion on dielectric constant. Results indicate that before gelation the dielectric constant is controlled by the content of unreacted monomers especially dicyandiamide, and after gelation it is dominated by the segmental mobility, hydroxyl group density and free volume, where the influence of segmental mobility is more significant than that of free volume and hydroxyl group density.

Research on Dynamic Mechanical Properties of Different Silane Coupling Agent In-situ Modified SSBR/Silica Composites

Hydroxyl density of silica surface will reduce and the compatibility of silica with rubber matrix will be improved through the modification of silica by silane coupling agent (SCAs). The silica-silica and silica-rubber interaction of silica filled solution polymerized styrene butadiene rubber (SSBR) in-situ modified by silane coupling agent TESPT and Si747 are studied by Dynamic Mechanical Analyzer (DMA). The effect of different types and loading amounts of SCAs on the dynamic mechanical properties of silica filled SSBR is investigated. The results show that the novel silane coupling agent Si747 has a more apparent effect on lessening the silica network than that of silane coupling agent TESPT, Hysteresis factor (tanδ) measured by DMA reduces, and the heat-built improves. It could also be found that Si747 modified composites have the lowest apparent activation energy, which is used to characterize the filler-rubber interaction, indicating the lowest temperature dependence.

Amorphous zirconium oxide activates peroxymonosulfate for selective degradation of organic compounds: Performance, mechanisms and structure-activity relationship

Application of heterogeneous advanced oxidation processes (AOPs) for wastewater treatment suffers from the low oxidant utilization efficiency, slow catalytic cycling and severe matrix interference. Herein, we report that amorphous zirconium dioxide (aZrO2), a redox-inert metal oxide, can efficiently activate peroxymonosulfate (PMS) to degrade organic micropollutants under very low oxidant doses and complex coexisting matrices. Distinct from conventional AOPs where radicals are formed, the surface Zr(IV)-PMS* complex was identified as the principal reactive species, and primarily conducted oxygen-atom-transfer route with selected molecules. Quantitative structure-activity relationship analysis indicated that the formation of Zr(IV)-PMS* complex was governed by the density of the surface hydroxyl groups. The strong interaction between the Zr atom and PMS caused the deviation of the negative charge from Zr(IV) metal sites to the oxidant. As a result, the O-O bond of the adsorbed PMS was prolonged and its oxidation potential elevated, which enabled it to directly react with contaminants. This study indicates the potential of aZrO2 as a novel and eco-friendly catalyst that activates PMS to selectively tackle organic contaminants, and sheds light on the designing of Fenton-like catalysts using redox-inert metals.

Adsorption of Pb2+ and methylene blue by Al-incorporated magadiite

The coexistence of heavy metals and organics in industrial wastewater is prevalent, and the removal of these toxic pollutants concurrently is of one of the greatest concerns facing wastewater treatment. In this study, a series of Al-incorporated magadiite (AlMagx, x represents nominal Si/Al ratio) were synthesized hydrothermally and investigated for their removal of Pb2+ and methylene blue (MB) in single- and binary-component solutions. The AlMagx featured a higher density of surface hydroxyl groups (6.4–12.7 sites·nm−2) and a greater negative surface than did the Al-free Magadiite (Mag). For single-component adsorption, the adsorption of both pollutants was pH-dependent. Under an optimal pH (= 3.00), the adsorption isotherms for Pb2+ and MB were consistent with the Langmuir and Freundlich models, respectively. AlMag240, having the highest surface hydroxyl density, displayed a maximum adsorption capacity of 113.5 and 220.2 mg·g−1 for Pb2+ and MB, respectively, exceeding that of Mag or other clay minerals. For Pb2+–MB binary-component adsorption, the removal efficiencies of Pb2+ declined by ∼4%–34% with higher MB concentrations, while MB's adsorption was slightly promoted by co-occurring Pb2+. Examination of adsorption mechanisms revealed that MB was adsorbed onto the external surface of AlMagx mainly via hydrogen bonding and electrostatic attraction, while Pb2+ was removed by ion exchange and subsequent hydroxyl-facilitated precipitation. The declined adsorption of Pb2+ was due to the rapid occupation of negative sites and hydroxyl sites by MB, and the slight promotion of MB adsorption with coexisting Pb2+ is likely owing to the increased negative charge of the adsorbents due to the increase in the solution ionic strength. These results demonstrated that the solution component is crucial to the adsorption process and that the AlMagx was a new adsorbent for the simultaneous removal of Pb2+ and MB.

A large-nanosphere/small-nanosphere (cellulose/silver) antibacterial composite with prominent catalytic properties for the degradation of p-nitrophenol

A well-designed spherical-nanocellulose (SNC)/silver-nanoparticle (AgNP) composite (SNC-AgNP) with a novel structure, a conjugate of large nanospheres (SNC, mean particle size 41 ± 9.7 nm) and small nanospheres (AgNPs, mean particle size 12 ± 6.3 nm), was prepared by the reduction of silver nitrate on plant-derived cellulose. The large nanospheres not only acted as a reducing agent, but more importantly, as a unique nano-spherical surface support, resulting in good dispersion of the small nanospheres. Thanks to this novel structure, the SNC-AgNPs possessed high antibacterial activity against the model microbes E. coli and S. aureus, and excellent catalytic properties for the degradation of p-nitrophenol. Notably, the catalytic rate constant (kapp = 1.6024 ± 0.0265 min−1) and catalytic activity factor (k = 5287.8 ± 644 min−1 g−1) of the SNC-AgNPs surpassed those of all cellulose-based Ag catalysts and most non-cellulose-based Ag catalysts. Moreover, the preparation of the SNC-AgNPs was high efficient, due to the high surface hydroxyl density of the SNC contributed from the cellulose II crystal structure, nano-spherical morphology, and low polymerization degree. Additionally, the thermal stability of the SNC-AgNPs was higher than most cellulose/Ag composite.

Impact of explosion-generated acoustic waves on atmospheric layers

Explosive events, such as artificial or accidental explosions, and volcanic eruptions, among others, generate low-frequency acoustic waves that propagate through and perturb atmospheric and ionospheric layers (e.g., the hydroxyl and oxygen airglow layers, the sodium layer, and the ionospheric D-region). The subsequent disturbances (i.e., airglow emission intensity, sodium or other minor species density, or electron density fluctuations) are potentially detectable by optical or radio remote sensing methods. Understanding and quantifying the impact of acoustic waves on atmospheric layers are, therefore, crucial steps for establishing detectability thresholds (e.g., relative to source scales and effective yields). In this work, we investigate the propagation of upwardly-traveling acoustic perturbations induced by 1t to-1 kt of TNT-equivalent ground explosions and their signatures on different atmospheric layers. Specifically, we estimate the amplitudes and periods of the induced fluctuations of hydroxyl, sodium, and electron densities at mesospheric through lower-thermospheric altitudes. This work investigates the potential of such layers to serve as sensors for characterizing lower-atmospheric explosive events and the complementarity of such indirect measurements with direct sensing, e.g., of pressure fluctuations in situ.

The Global Polarity of Alcoholic Solvents and Water - Importance of the Collectively Acting Factors Density, Refractive Index and Hydrogen Bonding Forces.

The D HBD quantity represents the hydroxyl group density of alcoholic solvents or water. D HBD is purely physically defined by the product of molar concentration of the solvent (N) and the factor Σn=n×f which reflects the number n and position (f‐factor) of the alcoholic OH groups per molecule. Whether the hydroxyl group is either primary, secondary or tertiary is taken into account by f. Σn is clearly linearly correlated with the physical density or the refractive index of the alcohol derivative. Relationships of solvent‐dependent UV/Vis absorption energies as E T(30) values, 129Xe NMR shifts and kinetic data of 2‐chloro‐2‐methylpropane solvolysis with D HBD are demonstrated. It can be shown that the E T(30) solvent parameter reflects the global polarity of the hydrogen bond network rather than specific H‐bond acidity. Significant correlations of the log k 1 rate constants of the solvolysis reaction of 2‐chloro‐2‐methylpropane with D HBD show the physical reasoning of the approach.

The effect of surface functional groups on the wettability of graphene oxide coated alumina substrate: Molecular dynamics simulations

In this article, molecular dynamic simulation was used to simulate the wetting process of graphene oxide coated alumina substrate. By changing the density of hydroxyl and epoxy groups on the surface of graphene oxide, the influence mechanism of two functional groups on the wetting process of water molecules was explored. From the simulation results, the increase of hydroxyl density can enhance the wettability of the substrate and reduce the wettability angle from 64.32° to 54.20°. By calculating the formation of the hydrogen bond in the wetting process, it is found that hydroxyl can significantly raise the hydrogen bond lifetime in the system. This increasing effect is particularly prominent in the observation of the hydrogen bond between water molecules and graphene oxide. The hydrogen bond lifetime increases from 2.20 ps to 12.77 ps. The result also reflects the reason why hydroxyl increases the wettability of the substrate. In addition, the increase of hydroxyl density also brings changes in hydrogen bond behavior and the number of hydrogen bonds. Under the condition of high epoxy density, most of the hydrogen bonds between water molecules and the substrate exist in the form of single hydrogen bonds, and the number is small. When the hydroxyl density increases, double-hydrogen bond, triple-hydrogen bond and single hydrogen bond appear in the model. In this process, the number of hydrogen bonds between the water droplet and the substrate is also increasing. Temperature is an important influence on the formation and lifetime of the hydrogen bond. High temperatures can promote the formation of the hydrogen bond between alumina and water molecules. In addition, it can also decrease the lifetime of all types of hydrogen bonds. Through the free energy perturbation theory, we get the free energy of different models in the wetting process. The results show that high hydroxyl density can improve the free energy of the wetting process, reduce the ability of spontaneous desorption and increase the stability of wetting. High temperatures can reduce the free energy and lead to the occurrence of desorption behavior. This article reveals the wetting mechanism of water molecules on graphene oxide coated alumina substrate, mainly reveals the influence of hydrogen bond and the change of free energy in the wetting process, which lays a theoretical foundation for the application of graphene oxide wetted coating on the aluminum alloy surface.

Tailoring the Hydroxyl Density of Glass Surface for Anionic Ring-Opening Polymerization of Polyamide 6 to Manufacture Thermoplastic Composites.

Reactive thermoplastics matrices offer ease of processing using well-known molding techniques (such as Resin Transfer Molding) due to their initially low viscosity. For Polyamide 6 (PA6)/glass composites, the hydroxyl groups on the glass surface slow down the anionic ring-opening polymerization (AROP) reaction, and can ultimately inhibit it. This work aims to thoroughly control the hydroxyl groups and the surface chemistry of glass particulates to facilitate in situ AROP-an aspect that has been barely explored until now. A model system composed of a PA6 matrix synthesized by AROP is reinforced with calcinated and silanized glass microparticles. We systematically quantify, by TGA and FTIR, the complete particle surface modification sequence, from the dehydration, dehydroxylation and rehydroxylation processes, to the silanization step. Finally, the impact of the particle surface chemistry on the polymerization and crystallization of the PA6/glass composites was quantified by DSC. The results confirm that a careful balance is required between the dehydroxylation process, the simultaneous rehydroxylation and silane grafting, and the residual hydroxyl groups, in order to maintain fast polymerization and crystallization kinetics and to prevent reaction inhibition. Specifically, a hydroxyl concentration above 0.2 mmol OH·g−1 leads to a slowdown of the PA6 polymerization reaction. This reaction can be completely inhibited when the hydroxyl concentration reaches 0.77 mmol OH·g−1 as in the case of fully rehydroxylated particles or pristine raw particles. Furthermore, both the rehydroxylation and silanization processes can be realized simultaneously without any negative impact on the polymerization. This can be achieved with a silanization time of 2 h under the treatment conditions of the study. In this case, the silane agent gradually replaces the regenerated hydroxyls. This work provides a roadmap for the preparation of reinforced reactive thermoplastic materials.

Research on controllable ozone oxidation on diamond surface

In recent years, there have been more and more researches on the surface modification of diamonds, however, the exact types and quantities of oxygen-related species on diamond surfaces and the method to control the condition parameters to obtain as many oxygen-containing groups as possible have been rarely studied so far. Therefore, in this work, we focused on these questions. And we find out that ozone oxidation would not affect the overall crystal structure and morphology of diamonds. Besides, changing oxidation time and ozone concentration would significantly influence the density of hydroxyl groups, which is manifested as a change of oxygen content. In order to make the hydroxyl density on diamond surface reach a high level (3.12 × 1014 units/cm2), so that diamonds can be better combined with the resin matrix, the ozone oxidation time should be 15 min, and the ozone concentration should be 115 g•m−3. And under these conditions, the thermal conductivity of diamond and polysiloxane composites can reach 8.02 W/mK.

Water-solid contact electrification causes hydrogen peroxide production from hydroxyl radical recombination in sprayed microdroplets.

Contact electrification between water and a solid surface is crucial for physicochemical processes at water-solid interfaces. However, the nature of the involved processes remains poorly understood, especially in the initial stage of the interface formation. Here we report that H2O2 is spontaneously produced from the hydroxyl groups on the solid surface when contact occurred. The density of hydroxyl groups affects the H2O2 yield. The participation of hydroxyl groups in H2O2 generation is confirmed by mass spectrometric detection of 18O in the product of the reaction between 4-carboxyphenylboronic acid and 18O-labeled H2O2 resulting from 18O2 plasma treatment of the surface. We propose a model for H2O2 generation based on recombination of the hydroxyl radicals produced from the surface hydroxyl groups in the water-solid contact process. Our observations show that the spontaneous generation of H2O2 is universal on the surfaces of soil and atmospheric fine particles in a humid environment.

Engineering network entanglement of functionalized graphene oxide/poly(acrylamide) nanocomposites for enhanced oil recovery

Hydroxyl-functionalized graphene oxide (OGO) was prepared from graphene oxide (GO) modified by diethanolamine (DEOA) to promote the interaction between nano sheets and polymer molecules. Three OGO samples with different GO to DEOA ratios, and an acrylamide-based polymer (PM) were synthesized. The nanoparticle and polymer hybrid systems were prepared using GO or OGO suspension into PM solution. The interaction strength investigation indicated that the hybrid system had two kinds of hydrogen bonds, one is between amide groups on polymer and the other is between amide groups on polymer and hydroxyl groups on nanosheets, and there was a competition for them. As a result, a proper surface hydroxyl density is critical to form a suitable molecular network for improving the hybrid property under harsh condition. The rheological properties of PM solution and these hybrid systems were studied, and the results showed that the introduction of OGO obviously improved the salt-resistance and temperature-tolerance of PM solution. The results from oil displacement experiments showed that the enhanced oil recovery ratio jumped to 20.9% for PM/OGO system, while it was only 13.8% for PM solution.

Synthesis of PPC-graft-poly(PEOMA) Brush and PPC Gels via Post-polymerization Modification of Hydroxyl-Functionalized Poly(propylene carbonate)

Post-polymerization modification offers a facile and effective tool for adapting polymer properties. However, it has not been applied to poly(propylene carbonate) (PPC) as traditional PPC lacks sufficient functional groups along the polymer chain. In the present work, for the first time, hydroxyl-functionalized PPC has been prepared and used to construct PPC-brush and cross-linked polymer gels through post-polymerization modification approach. PPC-brushes in the form of PPC-graft-poly(PEOMA) were obtained with controllable brush length and brush density via “grafting from” a PPC-macroinitiator which was synthesized from esterification reaction of PPC-OH with 2-bromoisobutyryl bromide. PPC permanent networks in the form of dioxane gels were prepared by cross-linking PPC-OH with 4,4′-diphenylmethane diisocyanate (MDI). Rheological measurement of the gels showed that the cross-linking density scales linearly with the hydroxyl group density in PPC-OH. This work not only offers a facile strategy to realize the post-modification of PPC but also spurs the devising of innovative biodegradable materials with tailored molecular architectures.

Characterization of kaolinite aqueous suspensions by acoustophoresis: Influence of crystallinity and of the ratio between basal and lateral surface of grains

The electrokinetic properties of aqueous suspensions of two kaolins were studied using the acoustophoretic method by measuring the ultrasonic attenuation spectrum in a wide frequency range (1–20 MHz). Then, the zeta potential is calculated according to the size distribution of grains. A high state of crystallinity of the kaolinite platelets strongly influences the amplitude and the variation of zeta potential versus the pH due to a high density of hydroxyl surface groups. It was also shown that specific adsorption occurs mainly with the hydroxyl surface groups of the platelet edges by using strong electrolytes (NaOH and HCl) and also organic molecules (Tiron and sodium salt of citrate). The variation of the surface chemical properties of platelets during the amorphous phase formation after temperature treatment of kaolin powder is also studied. The electrokinetic properties of kaolin suspensions treated between 200 and 800 °C successively show an increase in the positive contribution to the zeta potential up to 400 °C for the best-crystallized kaolinite and a decrease in the density of surface hydroxyl groups when the sheets delaminate from 400 °C for the less-crystallized kaolinite. This study shows that the characterization in aqueous suspension of surface properties of kaolinite complements other studies carried out on powder and therefore it makes it possible to choose kaolin as a raw material according to the intended application.

Antifreezing Hydroxyl Monolayer of Small Molecules on a Nanogold Surface.

The rational design of ice recrystallization inhibition (IRI) materials is challenging due to the poor understanding of the IRI mechanism at the molecular level. Here we report several new findings about IRI. (1) A dense hydroxyl monolayer of small molecules, e.g. 6-aza-2-thiothymine (ATT), adsorbed on a nanogold surface was demonstrated, for the first time, to have IRI activity. Five structural analogues adsorbed on groups nanogold with outward hydroxyl or methyl were created to evidence the origin of IRI activity. (2) Their IRI mechanism is closely related to the density of hydroxyls on a nanogold surface. However, the hydrophobic interaction in our model is not essential for macroscopic IRI activity. (3) A molecular dynamics simulation elucidates the hydroxyl density dependent IRI trajectories underlying the experimental observations, and the radial distribution function reveals that the methyl even slightly hinders the formation of hydrogen bonding due to a hydrophobic interaction. This work sheds more light on the IRI mechanism that should help in the customization of novel IRI materials.