Attenuated Total Internal Reflectance Fourier Transform Infrared Spectroscopy Research Articles

Preparation and evaluation of chitosan/MCM-41-based spongy hydrogels loaded with tea tree oil

In this study, chitosan, polyvinyl alcohol, gelatin, MCM-41 and tea tree oil (TTO) were used as raw materials. MCM-41-based spongy hydrogels loaded with TTO were synthesized by physical cross-linking method. The TTO was first adsorbed into MCM-41 s. Then different contents of MCM-41 s were added to the hydrogel, which affected the properties of the hydrogel. The structure of hydrogels was analyzed by scanning electron microscopy (SEM) and attenuated total internal reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The mechanical properties of hydrogels were determined by swelling, degradation and ductility evaluation. The antibacterial effect and biocompatibility were determined by in vitro antibacterial and cytotoxicity examinations. In this study, the mechanical property of the hydrogels was enhanced with the increasing content of MCM-41 s. The hydrogels exhibited an excellent antibacterial effect attributed to the synergistic interaction between TTO and chitosan. Furthermore, the hydrogels showed superior biocompatibility property. In conclusion, the hydrogels prepared in this study have great potential for expanding their applications in the bacteriostatic field.

Corrosion inhibition of polyelectrolytes to the Al anode in Al-air battery: A comparative study of functional group effect

Al-air battery is a promising alternative to electrochemical storage systems because of their high energy density and low cost. However, the hydrogen evolution corrosion in alkaline electrolytes is a major obstacle before this technology can be commercially viable. In this paper, three polyelectrolytes as corrosion inhibitors for pure Al anodes in KOH electrolytes are investigated by electrochemical methods, hydrogen evolution rate (HER) tests, weight loss measurements, and surface characterization. The Attenuated Total internal Reflectance Fourier Transform Infrared spectroscopy (ATR-FTIR) and theoretical simulation results show that all the polyelectrolytes can be adsorbed on Al to form a protective barrier against the corrosive species. In particular, poly(allylamine) (PAH) exhibits the highest corrosion inhibition efficiency. Furthermore, galvanostatic discharge measurement reveals that the Al-air battery in PAH electrolyte exhibits the highest specific discharge capacity (1495.2 mA h g−1). Computational analysis shows that the inhibition performance depends on the frontier molecular orbital energy and adsorption energy.

In-situ micro-characteristics of fiber at the mortar transition zone in asphalt mixtures

Due to certain differences in physical and chemical properties of fibers used, there will be various defects in the internal structure of the resulted mixture from a microscopic perspective. The establishment of correlation between the microstructure characteristics and road performance of asphalt mixture has certain scientific research value. In this research, the proposed method of Resin Impregnated Mixture Slices was successfully used for the in-situ micromorphology, chemical heterogeneity and micro-mechanical properties investigation of lignin fiber, polypropylene (PP) fiber and polyester (PET) fiber at the mortar transition zone in asphalt mixtures. The box dimension presented by Fluorescence Microscope (FM) images indicates the most uniform distribution of polyester fibers. It is possible to trace methoxy group and ester group as an indicator on lignin fiber and polyester fiber in the thermodynamic distribution images of Attenuated Total internal Reflectance Fourier Transform Infrared spectroscopy (ATR-FTIR). And it was found that the fibers mainly concentrated in the inner region of asphalt mortar. In the testing mortar region of lignin, polypropylene and polyester fibers by Atomic Force Microscope-Quantitative Nano Mechanical (AFM-QNM), DMT-modulus in the areas containing fibers is 2.0 ∼ 18GPa, 1.0 ∼ 2.5GPa and 2.5 ∼ 5.0GPa, adhesion ranges from 50 ∼ 75nN, 20 ∼ 35nN, 30 ∼ 60nN, and the Dissipation values are 5.0 ∼ 15KeV, 0.5 ∼ 3.5KeV, 3.5 ∼ 7.0KeV, respectively. The mechanical properties of PP fiber modified asphalt mixture are considerably 0.5 ∼ 1.0 time lower than those of other samples due to the low-density and weak mechanical properties.

Flotation separation of acrylonitrile-butadienestyrene (ABS) and high impact polystyrene (HIPS) from waste electrical and electronic equipment (WEEE) by potassium permanganate surface modification

The wasted acrylonitrile–butadienestyrene (ABS) and high impact polystyrene (HIPS) have a great potential for recycling. However, it is difficult to recycle them due to the absence of an effective separation method. Permanganate oxidation is a kind of environmental protection process and plays an important role in green chemistry. In this study, the polymer surface modification by potassium permanganate was utilized to separate ABS and HIPS from waste electrical and electronic equipment (WEEE) by flotation. Attenuated total internal reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) results showed that potassium permanganate can oxidize butadiene and nitrile groups in ABS to form oxygen-containing hydrophilic groups. Butadiene in HIPS can also be oxidized to form oxygen-containing hydrophilic groups, but the increase is less than that of ABS. Scanning electron microscope (SEM) results show that the surface roughness of ABS is improved, but HIPS has no obvious change, which indicates that the surface wettability of ABS can be further improved with the improved surface roughness. The contact angle test results show that the contact angle decrease of ABS after surface modification is significantly higher than that of HIPS. The results showed that the optimum modification conditions are as follows: the concentration of potassium permanganate solution is 50 mM/L, modification temperature of 60 °C, and the modification time 30 min. The recovery and purity of ABS are 97.64% and 95.41%, respectively, and the recovery and purity of HIPS are 95.40% and 97.64%, respectively. This research provides a technical support for the high-value recycling of WEEE waste plastic.

Antifouling Properties of Dendritic Polyglycerols against Marine Macrofouling Organisms.

Dendritic polyglycerols (PGs) were synthesized and postmodified by grafting of poly(ethylene glycol) (PEG) and polypropylene glycol (PPG) diglycidyl ether groups, and their antifouling and fouling-release properties were tested. Coating characterization by spectroscopic ellipsometry, contact angle goniometry, attenuated total internal reflection-Fourier transform infrared spectroscopy (ATR-FTIR), and atomic force microscopy showed brushlike morphologies with a high degree of microscale roughness and the ability to absorb large amounts of water within seconds. PGs with three different thicknesses were tested in laboratory assays against settlement of larvae of the barnacle Balanus improvisus and against the settlement and removal of zoospores of the alga Ulva linza. Very low coating thicknesses, e.g., 11 nm, reduced the settlement of barnacles, under static conditions, to 2% compared with 55% for an octadecyltrichlorosilane reference surface. In contrast, zoospores of U. linza settled readily but the vast majority were removed by exposure to a shear force of 52 Pa. Both PEG and PPG modification increased the antifouling properties of the PG films, providing a direct comparison of the ultralow fouling properties of all three polymers. Both, the modified and the nonmodified PGs are promising components for incorporation into amphiphilic fouling-resistant coatings.

Bifunctional supported ionic liquid-based smart films for dyes adsorption and photodegradation

Herein, novel bifunctional smart films containing poly(styrene-butyl acrylate-ionic liquids) (P(S-BA-ILs)) and TiO2 were first prepared by a simple cast method and then used to demonstrate a superior bifunction of adsorption/desorption for dyes due to the property of reversible wettability switching and photodegradation under ultraviolet (UV) irradiation due to the addition of TiO2. The glass transition temperature (Tg) of P(S-BA-ILs) latex was characterized using a differential scanning calorimeter (DSC). The surface properties of films (P(S-BA-ILs)-TiO2) were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), attenuated total (internal) reflection Fourier transform infrared spectroscopy (ATR-FTIR), and water contact angle (WCA) measurements. The results showed that the films displayed reversible wettability switching of hydrophobicity (124.5 ± 2°)/hydrophilicity (10.5 ± 2°) and hydrophobicity (35.1 ± 2°)/hydrophilicity (93.1 ± 2°) triggered by pH and temperature, respectively. Additionally, the films exhibited large adsorption capacities for pollutants at different pH: brilliant red (BR) (6.6 mg cm−3) at pH 1, methylene blue (MB) (12.4 mg cm−3) and phenol (1.1 g cm−3) at pH 11, and metal ions As, Mo and Sb (1.11, 1.57, and 1.25 mg cm−3) at pH 1, as well as superior reusability and excellent in situ photodegradation performance. The convenient preparation of the smart films as well as the good bifunction of adsorption and photodegradation for dyes predicts potential for application to curb water pollution.

ATR-FTIR and Flow Microcalorimetry Studies on the Initial Binding Kinetics of Arsenicals at the Organic-Hematite Interface.

The environmental fate of arsenic compounds depends on their surface interactions with geosorbents that include clays, metal oxides, and natural organic matter (NOM). While a number of batch studies reported that NOM inhibits the uptake of arsenicals, it remains unclear how different classes of organic functional groups affect their binding mechanisms. We report herein the adsorption kinetics of arsenate and dimethylarsinic acid (DMA) with hematite nanoparticles pre-exposed to three types of low molecular weight organics: citrate, oxalate, and pyrocatechol as representatives to the majority of reactive organic functional groups in NOM. These studies were conducted using attenuated total internal reflection Fourier transform infrared spectroscopy (ATR-FTIR) and flow microcalorimetry at pH 7 with an emphasis on the role that electrolytes (KCl, NaCl, and KBr) play in the adsorption process. Results show that (1) negatively charged carboxylate versus hydrophobic phenyl groups influence amounts and initial rates of arsenicals adsorption on hematite nanoparticles to varying degrees depending on the type of complexes they form, (2) the type of electrolytes affects initial adsorption rate of DMA to a greater extent than arsenate when oxalate is present on the surface, and (3) the extent of organics retention by hematite nanoparticles is influenced by the type of the desorbing agent.

Adsorption behavior and mechanism of different arsenic species on mesoporous MnFe2O4 magnetic nanoparticles

Arsenic pollution poses severe threat to human health, therefore dealing with the problem of arsenic contamination in water bodies is extremely important. The adsorption behaviors of different arsenic species, such as arsenate (As(V)), p-arsanilic acid (p-ASA), roxarsone (ROX), dimethylarsenate (DMA) from water using mesoporous bimetal oxide magnetic manganese ferrite nanoparticles (MnFe2O4) have been detailedly investigated. The adsorbent was synthesized via a facile co-precipitation approach and recovered conveniently owing to its strong magnetic properties. The obtained MnFe2O4 with large surface area and abundant hydroxyly functional groups exhibited excellent adsorption performance for As(V) and p-ASA, in contrast to ROX and DMA with the maximum adsorption capacities of As(V), p-ASA, ROX and DMA of 68.25 mg g−1, 59.45 mg g−1, 51.49 mg g−1, and 35.77 mg g−1, respectively. The Langmuir model and the pseudo-second-order kinetic model correlated satisfactorily with the adsorption thermodynamics and kinetics, and thermodynamic parameters depicted the spontaneous endothermic nature for the adsorption of different arsenic species. The adsorption mechanism of different arsenic species onto MnFe2O4 nanoparticles at various pH values could be explained by surface complexation and molecular structural variations. Attenuated Total internal Reflectance Fourier Transform Infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) further proved that arsenic species were bonded to the surface of MnFe2O4 through the formation of an inner-sphere complex between the arsenic acid moiety and surface metal centers. The results would help to know the interaction of arsenic species with iron-manganese minerals and the mobility of arsenic species in natural environments.

Mapping of Biochemical Constituents in Platanus acerifolia Leaves By Analytical Techniques

Platanus acerifolia (Plataceae) is woody perennial tree, a native of Asia, Europe, and Eastern Mediterranean regions of the world. It is commonly cultivated and highly valued as an ornamental and medicinal tree. Its leaves as a natural waste is available in abudance, easy to obtain and cheap. In the present study, P. acerifolia leaves were obtained from Kocaeli region of Turkey at the autumn period. All of the specimens were dried in air before using analytical techniques. The leaves were analyzed by using X-ray diffraction (XRD), Attenuated Total internal Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electro Microscopy- Enegy-Dispersive X-ray Spectroscopy (SEM-EDX). All analysis were performed for providing an accurate detection of the leaf molecular structure, crystalline phase, chemical compositions (organic or inorganic constituent), elemental index, morphology and microstructure. From X-ray diffraction pattern, crystaline phase and chemical compositions of the leaf specimens were identified as whewellite (C2CaO4.H2O), schertelite (Mg(NH4)2H2(PO4)24H2O), silicon oxide (SiO2), amide (C13H17N7O3), ester (C37H68O8), benzene (C28H40O10). According to ATR-FTIR analysis results, characteristic peak values of the leaf specimens were detected functional groups as (P-O), (C=O), (ClO), (C-O), (P-O-H), (C-H), (N-H), (O-C=O), (K-NO), (Ca-CO), (NH), (C=H), (N=O), (O-H), (CH), (NN), (Si-O-Si). SEM-EDX analysis showed the present of carbon, nitrogen, oxygen, magnesium, silicon, phosphor, chloride, potassium, and calcium in the leaf specimens. Morphology and microstructure of opened or closed stomas, fiber of leaf specimens were monitored. The chemical compositions, the functional groups and the elements are responsible for various medicinal properties of P. acerifolia leaves. Nanoparticles obtained from the leaves by using developed plant extract process can be used as biomaterial, biosorbent and nanomedicine against various plant, human, and animal diseases or pathogens.

Unraveling the modified surface of the photographic paper “Japine”

Modification of the surface of a paper intended for coating with a photographic sensitizer will influence both its chemical and physical characteristics. A scientific examination was performed on the photographic paper, Japine, produced by the Platinotype Company from 1906 to 1937 for their platinum, silver, and palladium printing processes. Scanning electron microscopy (SEM) and non-invasive imaging by optical coherence tomography (OCT) reveal the presence of a very thin layer at the paper surface. Detailed investigation by attenuated total internal reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and gas chromatography-mass spectrometry (GCMS) analyses determined that this surface consists of a parchmentized layer created by chemical modification of the paper support rather than the presence of an applied coating. Reverse engineering studies suggest that the paper was prepared by treatment with sulfuric acid under select conditions to modify the structure of the cellulose only at the paper surface. SEM imaging demonstrates that the distribution of the platinum particles that make up the image is significantly altered on surface parchmentized papers compared to unmodified papers.

Heterogeneous Charge Transfer at the Amorphous Carbon/Solution Interface: Effect on the Spontaneous Attachment of Aryldiazonium Salts

The chemisorption of aryldiazonium salts is one of the most versatile reactions for the modification of carbon surfaces; in this work we investigated the spontaneous chemisorption of aryldiazonium salts at amorphous carbons of differing graphitic content in order to relate surface reactivity to the valence electronic properties of aryldiazonium cations and carbon surfaces. Two structural isomers that differ by their redox potential were chosen for our studies: 4-nitronaphthalenediazonium tetrafluoroborate (4NND) and 5-nitronaphthalenediazonium tetrafluoroborate (5NND). The adsorption of 4NND and 5NND was studied in situ via attenuated total internal reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and ex situ via electrochemistry on two types of graphitic amorphous carbons (a-C), containing 80% and 100% trigonally bonded carbon centers. These two forms of carbon were characterized via electrochemical impedance spectroscopy (EIS), and the more graphitic surface was found to display a heteroge...

A facile method for the fabrication of superhydrophobic films with multiresponsive and reversibly tunable wettability

This paper presents a facile method of fabricating smart film surfaces with multiresponsive, reversibly tunable wettability. In this method, when poly(styrene-n-butyl acrylate-acrylic acid) (P(S-BA-AA)) was mixed with TiO2 nanoparticles in tetrahydrofuran (THF) and then simply cast onto glass substrates, followed by drying at room temperature, intelligent films were formed. The as-obtained nanocomposite films not only exhibited very fast response to UV light, heat and pH, but also showed excellent reversibility. The formation mechanisms of the superhydrophobic films and their multiresponse were investigated in detail using scanning electron microscopy (SEM), attenuated total (internal) reflection Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS).

Spontaneous Grafting of Nitrophenyl Groups on Amorphous Carbon Thin Films: A Structure–Reactivity Investigation

Amorphous carbon materials find numerous applications in diverse areas ranging from implantable biodevices to electronics and catalysis. The spontaneous grafting of aryldiazonium salts is an important strategy for the modification of these materials, and it is widely used to display a range of functionalities or to provide anchoring groups for further functionalization. We have investigated the spontaneous attachment of 4-nitrobenzenediazonium salts from aqueous solutions onto amorphous carbon materials that differ in their sp2 content, with the aim of understanding to what extent bulk composition affects rates and yields of aryldiazonium adsorption at the carbon/solution interface. Amorphous carbons were deposited in the form of thin films via reactive magnetron sputtering and were characterized using a combination of Raman, infrared, UV–vis, and X-ray photoelectron spectroscopy to determine their sp2 content. Attenuated total internal reflection Fourier transform infrared spectroscopy (ATR-FTIR) was use...

Study of the spontaneous attachment of polycyclic aryldiazonium salts onto amorphous carbon substrates

Diazonium salts of two nitro-substituted polycyclic aromatic compounds were synthesized and their spontaneous covalent attachment onto amorphous carbon surfaces was studied via electrochemical and spectroscopic techniques. In situ spectroscopic monitoring of the grafting of these compounds at amorphous carbon surfaces via attenuated total internal reflection Fourier transform infrared spectroscopy (ATR-FTIR) highlighted a marked difference in adsorption rates, which was also evident via ex situ electrochemical analysis. We show that adsorption rate differences cannot be explained based on differences in the solvolysis rates of these two molecules. It was found instead that the relative position of the –N2+ groups with respect to the –NO2 groups affected the reduction potential of the diazonium cations and in turn their adsorption rate at amorphous carbon surfaces. We conclude that differences in the electron density at the carbon atom bound to the diazonium group are responsible for the differences observed in the spontaneous attachment at carbon.

Insights into the Surface Complexation of Dimethylarsinic Acid on Iron (Oxyhydr)oxides from ATR-FTIR Studies and Quantum Chemical Calculations

The surface chemistry of methylated arsenicals with ubiquitous geosorbents and industrial catalysts is poorly understood. These arsenic compounds pose both a health and an environmental risk in addition to being a challenge to the energy industry. We report herein a detailed spectroscopic analysis of the surface structure of dimethylarsinic acid (DMA) adsorbed on hematite and goethite using attenuated total internal reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Spectra of adsorbed DMA, DMA(ads), were collected in situ as a function of pH and ionic strength, using both H(2)O and D(2)O at 298 K in flow mode. Experimental data were complemented with DFT calculations of geometries and frequencies of hydrated DMA-iron oxide clusters. Results indicate the simultaneous formation of inner- and outer-sphere complexes with distinct spectral components. Desorption behavior of DMA due to chloride and phosphate was studied as a function of time from the decrease in the absorbance of apparent spectral features. The impact of our studies on the environmental fate of DMA in geochemical environments and the design of technologies to reduce arsenic content in fuels are discussed.

Investigation of Adsorption and Cross-Linking of a Mussel Adhesive Protein Using Attenuated Total Internal Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR)

Mytilus edulis foot protein 1 (Mefp-1) contains the redox-functional amino acid 3,4-dihydroxyphenylalanine (DOPA), which is a typical feature of most mefp proteins. We have previously shown, using combined optic (ellipsometry) and acoustic (QCM-D) measurements, that the oxidizing agent sodium periodate (NaIO4) and the transition metal ion Cu2+ promote cross-linking of Mefp-1. However, different chemical reaction mechanisms can not be distinguished using these methods. In the present study, we have complemented our previous investigations using Attenuated Total Internal Reflection Fourier Transform Infrared spectroscopy (ATR-FTIR), allowing a spectroscopic analysis of NaIO4 and Cu2+-induced cross-linking of Mefp-1 adsorbed on a ZnSe surface. In aqueous solution, adsorbed Mefp-1 displays absorption bands at 1570, 1472, 1260, and 973 cm−1. Upon addition of NaIO4 and Cu2+, the absorptions at 1570, 1472, and 973 cm−1 increase by approximately a factor of two. In contrast, the band at 1260 cm−1 disappears upon cross-linking using NaIO4, but remains unchanged upon addition of Cu2+. This demonstrates that the band at 1260 cm−1 is attributed to the C‒O stretching vibration of the side chain hydroxyl groups in DOPA and that Cu2+ forms complexes with DOPA rather than transform it into an o-quinone. Moreover, upon addition of NaIO4 after cross-linking using Cu2+, the band at 1260 cm−1 disappears, indicating that the complex formation between DOPA and Cu2+ is reversed when DOPA is transformed into the o-quinone. These results demonstrate that NaIO4, which initiates a similar reaction to the naturally occurring enzyme catechol oxidase, contributes to the formation of di-DOPA cross-links. In contrast, the dominating contribution to the cross-linking from Cu2+, which is accumulated at high concentrations in the byssus thread of the blue mussel, is via complex formation between the metal and DOPA residues.

Attenuated total internal reflection Fourier transform infrared spectroscopy: a quantitative approach for kidney stone analysis.

The impact of kidney stone disease is significant worldwide, yet methods for quantifying stone components remain limited. A new approach requiring minimal sample preparation for the quantitative analysis of kidney stone components has been investigated utilizing attenuated total internal reflection Fourier transform infrared spectroscopy (ATR-FT-IR). Calcium oxalate monohydrate (COM) and hydroxylapatite (HAP), two of the most common constituents of urinary stones, were used for quantitative analysis. Calibration curves were constructed using integrated band intensities of four infrared absorptions versus concentration (weight %). The correlation coefficients of the calibration curves range from 0.997 to 0.93. The limits of detection range from 0.07 +/- 0.02% COM/HAP where COM is the analyte and HAP is the matrix, to 0.26 +/- 0.07% HAP/COM where HAP is the analyte and COM is the matrix. This study shows that linear calibration curves can be generated for the quantitative analysis of stone mixtures provided the system is well understood especially with respect to particle size.

ATR-FTIR Studies on the Nature of Surface Complexes and Desorption Efficiency of p-Arsanilic Acid on Iron (Oxyhydr)oxides

The fate of organoarsenicals introduced to the environment through the application of arsenic-contaminated manure has attracted considerable attention after the recent implementation of the latest maximum contaminant level (MCL) of total arsenic in drinking water by the U.S. Environmental Protection Agency (EPA). We report herein detailed spectroscopic analysis of the surface structure of p-arsanilic acid (p-AsA) adsorbed on Fe-(oxyhydr)oxides using attenuated total internal reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Spectra of p-AsA(ads) were collected in situ as a function of pH and ionic strength and using D20 at 298 K in flow mode. Results indicate the formation of inner-sphere complexes, which are likely monodentate and become protonated under acidic pH(D). We also examined the desorption efficiency of p-AsA(ads) due to flowing electrolyte and phosphate solutions as low as 0.1 mol/m3 (3 ppm P) by collecting ATR-FTIR spectra as a function of time. Our results suggest that aqueous phosphate is an efficient desorbing anion of p-AsA(ads), which has implications on its bioavailability and mobility in geochemical environments.

Native E. coli inner membrane incorporation in solid-supported lipid bilayer membranes

Solid-supported bilayer lipid membranes (SBLMs) containing membrane protein have been generated through a simple lipid dilution technique. SBLM formation from mixtures of native Escherichia coli bacterial inner membrane (IM) vesicles diluted with egg phosphatidylcholine (egg PC) vesicles has been explored with dissipation enhanced quartz crystal microbalance (QCM-D), atomic force microscopy (AFM), attenuated total internal-reflection Fourier-transform infrared spectroscopy (ATR-FTIR), and fluorescence recovery after photobleaching (FRAP). QCM-D studies reveal that SBLM formation from vesicle mixtures ranging between 0% and 100% IM can be divided into two regimes. Samples with < or = 40% IM form SBLMs, while samples of greater IM fractions are dominated by vesicle adsorption. FRAP experiments showed that the bilayers formed from mixed vesicles with < or = 40% IM were fluid, and comprised a mixture of both egg PC and IM. ATR-FTIR measurements on SBLMs membranes formed with 30% IM confirm that protein is present. SBLM formation was also explored as a function of temperature by QCM-D and FRAP. For samples of 30% IM, QCM-D data show a decreased mass and viscoelasticity at elevated temperatures, and an increased fluidity is observed by FRAP measurements. These results suggest improved biomimetic characteristics can be obtained by forming and maintaining the system at, or close to, 37 degrees C.

ATR-FTIR Observations of Water Structure in Colloidal Silica: Implications for the Hydration Force Mechanism

Attenuated total internal reflection Fourier-transform infrared spectroscopy (ATR-FTIR) was used to probe the change in water structure in silica colloids as a function of particle density. The absorption index (k) spectra were calculated from the ATR spectra using the subtractive Kramers-Kronig transform in order to avoid the effects of the density-dependent refractive index on the raw spectra and allow direct comparison of the different chemical environments. Normalized difference spectra were obtained by subtracting the k spectrum of bulk water from those of the silica colloids. At low particle densities, these difference spectra reveal the presence of a strongly hydrogen-bonded hydration layer at the surface of the colloidal particles. At higher particle densities, the hydrogen-bonding network is increasingly disrupted. The results provide direct experimental evidence of hydrogen-bond breaking as the mechanism for the hydration force, which provides the extraordinary stability of colloidal silica.