Nonpolar Groups Research Articles

Methyl-substitution affects dielectric, thermal, mechanical properties, and shrinkage of fluorinated epoxy

Fluorination reduces dielectric constant and dielectric loss of epoxy resins, expanding their applications in high-speed communication. The methyl group (-CH 3 ) is a non-polar and space-occupying group, and it can reduce dielectric constant ( D k ) in some situations. However, it is not well understood how the methyl groups affect dielectric properties, as well as thermal and mechanical properties of fluorinated epoxy resin. To address this question, we specifically select benzene and m-xylene as the reaction monomer for comparison. We synthesize two fluorinated epoxides, diglycidyl ether of 1,3-bis(1,1,1,3,3,3-hexafluoroisopropyl)-benzene (DGE-bHFIP-B) and diglycidyl ether of 4,6-bis(1,1,1,3,3,3-hexafluoroisopropyl)-m-xylene (DGE-bHFIP-MX). We then thermally cure these two epoxides catalyzed with boron trifluoride ethylamine (BF 3 ·MEA) to obtain EP-bHFIP-B and EP-bHFIP-MX. EP-bHFIP-MX with –CH 3 has D k of 2.49–2.51, slightly lower than EP-bHFIP-B with D k of 2.51–2.54 at a high frequency range of 8.2–12.4 GHz. Their D k is much lower than a commercial bisphenol A type epoxy resin (EP-51) with D k of 2.80–2.83. Additionally, EP-bHFIP-MX shrinks less than EP-bHFIP-B after curing, and exhibits higher glass transition temperature with T g − D M A of 181 °C, higher tensile strength of 39.76 ± 5.51 MPa, compared to 129 °C and 34.73 ± 5.10 MPa for EP-bHFIP-B. EP-bHFIP-B and EP-bHFIP-MX both have very low water absorption of 0.134% w/w and 0.147% w/w after being immersed in water for 24 h at 25 °C. Therefore, incorporating –CH 3 groups into phenylene rings of fluorinated epoxies, we can enhance thermal resistance, increase mechanical strength, and reduce shrinkage without compromising dielectric performance. • Two novel fluorinated epoxides with low dielectric constant are synthesized. • Methyl-substitution slightly decreases D k in fluroinated expoxies. • Methyl-substitution improves thermal, mechanical properties and reduces curing shrinkage.

Atomic mechanisms of separation failure at the asphalt–aggregate interface and its dependence on aging and rejuvenation: Insights from molecular dynamics simulations and DFT calculations

The microscopic interfacial properties between asphalt and aggregates determine the macroscopic cracking behaviors of asphalt mixtures. To provide guidance on durability enhancement for reclaimed asphalt pavement mixtures that are prone to cracking, the fracture resistance of asphalt–aggregate interface and its dependence on aging and rejuvenation was investigated by molecular dynamics simulations and density functional theory. The results revealed that although the separation resistance is influenced by the loading rate, temperature and aggregate composition, the separation of the virgin interface system usually occurs within the asphalt region. The aged interface also tends to separate inside the asphalt, but if the asphalt is severely aged, debonding occurs at the asphalt–aggregate interface because the cohesive strength within asphalt is stronger than the interfacial adhesion strength. The aged interface exhibits higher resistance to complete fracture than virgin interface under non-repetitive loading. However, the enhanced molecular polarity of aged asphalt reduces its molecular flowability, thus weakening the resistance of aged interface to fatigue failure. Rejuvenators containing both polar carboxyl groups and nonpolar alkyl groups function as intermediaries to promote the compatibility of aged asphalt molecules with virgin molecules, thus restoring the flowability and fatigue failure resistance of aged interface systems.

FORMULATION OF SOLID BATH SOAP PREPARATIONS OF PURPLE SWEET POTATO ETHANOL EXTRACT (IPOMEA BATATAS L) AS A SKIN MOISTURIZER

Soap is a surfatctant used to clean or wash something that is available in solid and liquid form. Soap can be useful as a cleaning tool, this is because soap molecules contain polar (bonded with water) and non-polar (bonded with oil) groups so that they can clean grease or dirt that is not lifted by water. Soap is made by applying a saphonification reaction using olive oil, NaOH, and purple sweet potato extract as the basic ingredients. The addition of NaOH concentration an affect the weight of the soap produced. Purple sweet potato is a sweet potato that has natural dyes a anthocyanins that function as antioxidant. The purpose of this study was to obtain a solid bath soap formulation with purple sweet potato extract. Furthermore, purple sweet potato extract was formulated based on formula with concentration difference of 3,5%, 4,5%, 5,5%. Furthermore, preparations have been made with organoleptic tests, pH tests, and foam stability tests. It can be concluded that purple sweet potato extract can be used as a solid soap preparation and there is a concentration effect on the organoleptic test soap quality, pH, foam stability and moisture content. The preparation of solid bath soap from purple sweet potato ethanol extract has the ability to moisturize the skin, and the highest concentration obtained at a concentration of 5,5% with 57,83% moisture can moisturize the skin and at concentration of 4,5% with 48,3% humidity as well. Can moisturize the skin but with a moderate level of humidity, and at a concentration of 3,3% with 43,00% humidity with a lower humidity level.

Roles of functional lipids in bacteriorhodopsin photocycle in various delipidated purple membranes

Purple membrane (PM) is composed of several native lipids and the transmembrane protein bacteriorhodopsin (bR) in trimeric configuration. The delipidated PM (dPM) samples can be prepared by treating PM with CHAPS (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate) to partially remove native lipids while maintaining bR in the trimeric configuration. By correlating the photocycle kinetics of bR and the exact lipid compositions of the various dPM samples, one can reveal the roles of native PM lipids. However, it is challenging to compare the lipid compositions of the various dPM samples quantitatively. Here, we utilize the absorbances of extracted retinal at 382 nm to normalize the concentrations of the remaining lipids in each dPM sample, which were then quantified by mass spectrometry, allowing us to compare the lipid compositions of different samples in a quantitative manner. The corresponding photocycle kinetics of bR were probed by transient difference absorption spectroscopy. We found that the removal rate of the polar lipids follows the order of BPG ≈ GlyC < S-TGD-1 ≈ PG < PGP-Me ≈ PGS. Since BPG and GlyC have more nonpolar phytanyl groups than other lipids at the hydrophobic tail, causing a higher affinity with the hydrophobic surface of bR, the corresponding removal rates are slowest. In addition, as the reaction period of PM and CHAPS increases, the residual amounts of PGS and PGP-Me significantly decrease, in concomitance with the decelerated rates of the recovery of ground state and the decay of intermediate M, and the reduced transient population of intermediate O. PGS and PGP-Me are the lipids with the highest correlation to the photocycle activity among the six polar lipids of PM. From a practical viewpoint, combining optical spectroscopy and mass spectrometry appears a promising approach to simultaneously track the functions and the concomitant active components in a given biological system.

Sugar-sugar interactions in oil suspensions containing surfactants and effects on macroscopic phenomena

Surfactants are used in confectionery production to control the viscosity and yield value of molten chocolate. To develop a deeper understanding of the structure–function relationship of surfactants in food-related particle suspensions, the apparent viscosity, yield value, sedimentation, and particle interactions of 10 wt% confectioner’s sugar-in-canola oil suspensions were investigated in the presence of up to 1 wt% commercial soy lecithin, polyglycerol polyricinoleate (PGPR), citric acid esters of monoacylglycerols (CITREM) or ammonium phosphatides (AMP). Atomic force microscopy (AFM) was used to measure attractive forces at the nano-Newton scale between a sugar substrate and a sugar crystal-functionalized AFM cantilever in an oil environment. For all but PGPR, addition of surfactant reduced the adhesion force between sugar surfaces up to a critical concentration above which the force increased, implying the presence of additional interactions. This critical concentration was assumed to be when monolayer coverage of the sugar surfaces by surfactant occurred (0.05 wt% for lecithin, 0.10 wt% for CITREM and AMP). No critical concentration was found for PGPR, with its greatest effect for each analysis occurring at the highest concentrations tested (0.60 and 1.00 wt%). The significance of these interactions on macroscopic phenomena such as apparent viscosity and sedimentation was also assessed. Like with the AFM data, there was an optimal concentration of added surfactant above which viscosity increased. Sedimentation rate greatly decreased with addition of PGPR while being only slightly affected by addition of lecithin, CITREM and AMP. An argument regarding their efficacy was made based on the relative sizes of the polar headgroup and nonpolar tail groups of the molecules, which contributed to how they adsorbed to the sugar surface. Overall, these results suggested that surfactant properties such as molecular weight and head group properties played an important role in modifying the interactions between sugar crystals in an oil-continuous environment.

Investigating agglomeration of kaolinite particles in the presence of dodecylamine by force testing and molecular dynamics simulation

Kaolinite, one of the main components of clay minerals, is detrimental to slime water sedimentation. Sedimentation, adsorption, surface tension, contact angle, and interaction force measurements were conducted to study the hydrophobic agglomeration mechanism in kaolinite particles in the presence of dodecylamine (DDA). The results showed that DDA could be adsorbed on the kaolinite surface, improving the surface hydrophobicity and promoting hydrophobic particle agglomeration. Kaolinite hydrophobic sedimentation was enhanced with increased DDA concentration. The settling velocity and the adsorption of DDA on slurry particles were optimal when the DDA concentration was 14 × 10-4 mol/L. The shape and size distribution significantly affected the particle-surface interaction. Reliable force data could not be obtained from colloidal probes made of actual clay particles. Therefore, silica-silica and silica-alumina systems were used to replace clay mineral particles for force testing. AFM results showed that electrostatic repulsion existed in silica-silica and silica-alumina particles in ultrapure water. With DDA addition, the electrostatic repulsive force in silica-silica and silica-alumina particles decreased, the hydration film was destroyed, and an adhesion force was generated. In addition, the silicon-oxygen (001) surface of kaolinite adsorbed DDA more easily than the aluminum-oxygen (001̅) surface. The adsorption behavior of DDA+ on the kaolinite (001) and (001̅) surfaces was calculated by molecular dynamics simulation to explore the adsorption mechanism of DDA on kaolinite surfaces. The results suggested that the DDA+ polar head groups were adsorbed on the kaolinite surface, whereas the non-polar groups faced the solution. DDA+ adsorbed more easily on the (001) surface than on the (001̅) surface.

Simultaneously Improving the Optical, Dielectric, and Solubility Properties of Fluorene-Based Polyimide with Silyl Ether Side Groups

Three fluorene-based polyimides with silyl ether groups (Si–PIs) were successfully synthesized by a simple and efficient silicon etherification reaction of hydroxyl-containing polyimides (OH–PIs) and tert-butylchlorodiphenylsilane (TBDPSCl), and their structures were confirmed by 1H NMR and IR spectra. The bulky nonpolar tert-butyldiphenylsilyl (TBDPS) side groups in the modified PI unit instead of the strong electron donor −OH group is conducive to decreasing electronic conjugation and charge transfer (CT) interaction along the PI chain. Accordingly, the optical, dielectric, and solubility properties of the modified Si–PI films are simultaneously improved compared with the precursor OH–PI films. The modified Si–PI films demonstrate a meaningful enhancement in the transmittances at a wavelength of 400 nm (T400) to 74–81% from 42 to 55% of OH–PI films and the regeneration of fluorescence characteristics. The dielectric constant and loss of Si–PI films are also obviously reduced to 2.63–2.75 and 0.0024–0.0091 at 1 kHz from 4.19 to 4.78 and 0.0173–0.0295 of OH–PI films, respectively, due to substituted with the bulky nonpolar TBDPS groups to increase the free volume and hydrophobicity of Si–PI films. The solubility of Si–PIs in low- or nonpolar solvents (such as CHCl3, CH2Cl2, acetone, and toluene) is significantly improved. Furthermore, Si–PI films still maintain relatively good thermal properties with the 5% weight loss temperature (T5%) in the range 470–491 °C under a nitrogen atmosphere and the glass transition temperature (Tg) in the range 245–308 °C.

Slurryability and Influencing Mechanism of Hydrophobic Structures in Additive-Coal-Water Ternary System.

This study investigates the effects of additive adsorption onto coal particles on surface properties, hydrophobic groups on the slurryability, and the moisture occurrence form on the performance of coal water slurry (CWS). Mechanisms related to the different hydrophobic structures of the additives are proposed. The adsorption method of sulfonated acetone formaldehyde enhances the adsorption capacity of coal surfaces but is not conducive to slurrying. Sodium lignin sulfonate has hydrophobic ends with nonpolar aromatic groups, three-dimensional macromolecular structures, and complex branched chains, which provide CWS with good stability and slurryability. Naphthalenesulfonate formaldehyde has a double benzene ring structure and provides the thick but nonuniform adsorption layers on coal surfaces. The many amorphous structures and low molecular weights of sodium humic sulfonate lead to nonuniform hydration films and poor slurryability. The results of this paper provide guidance for improving synergism in coal–water–additive systems and enhancing slurry performance.

Sequence Modulates Polypeptoid Hydration Water Structure and Dynamics.

We use molecular dynamics simulations to investigate the effect of polypeptoid sequence on the structure and dynamics of its hydration waters. Polypeptoids provide an excellent platform to study small-molecule hydration in disordered polymers, as they can be precisely synthesized with a variety of sidechain chemistries. We examine water behavior near a set of peptoid oligomers in which the number and placement of nonpolar versus polar sidechains are systematically varied. To do this, we leverage a new computational workflow enabling accurate sampling of polypeptoid conformations. We find that the hydration waters are less dense, are more tetrahedral, and have slower dynamics compared to bulk water. The magnitude of these shifts increases with the number of nonpolar groups. We also find that shifts in the water structure and dynamics are strongly correlated, suggesting that experimental insight into the dynamics of hydration water obtained by Overhauser dynamic nuclear polarization (ODNP) also contains information about water structural properties. We then demonstrate the ability of ODNP to probe site-specific dynamics of hydration water near these model peptoid systems.

Protein Electrostatics Investigated through Paramagnetic NMR for Nonpolar Groups.

Experimental validation of theoretical models for protein electrostatics remains rare. Recently, we have developed a paramagnetic NMR-based method for de novo determination of effective near-surface electrostatic potentials, which allows for straightforward examination of electrostatic models for biomolecules. In the current work, we expand this method and demonstrate that effective near-surface electrostatic potentials can readily be determined from 1H paramagnetic relaxation enhancement (PRE) data for protein CαH and CH3 groups. The experimental data were compared with those predicted from the Poisson-Boltzmann theory. The impact of structural dynamics on the effective near-surface electrostatic potentials was also assessed. The agreement between the experimental and theoretical data was particularly good for methyl 1H nuclei. Compared to the conventional pKa-based validation, our paramagnetic NMR-based approach can provide a far larger number of experimental data that can directly be used to examine the validity of theoretical electrostatic models for proteins.

Characteristics of peat functional group in Padang Island, Indonesia

Peat is composed of a diverse range of polar and nonpolar groups. Nonpolar groups, particularly those composed of aliphatic structures, tend to associate with one another and are therefore water-repellent (hydrophobic), a property that increases with the length of the chain of bonds. The drying process causes the nonpolar groups to interact with each other and form a long chain of bonds, reducing the ability of peatlands to bind water. As a result, it is vital to understand the chemical characteristics and functional groups associated with hydrophilicity and hydrophobicity. The chemical analysis comprises the following: ash content (500°C combustion method), C-org using the combustion method, N-total by Kjeldahl method, actual pH with soil water ratio of 1:5, and cation exchange capacity with NH4Oac pH 4.0. Additionally, the pelletized peat was examined for its constituent groups using an FTIR spectra and the Flaig et al., method (1975). Soil pH values on Padang Island ranged from 3.61 to 4.35 and the content of bases Ca, Mg, K, and Na in oligotrophic peat is very low, especially in thick peat (0-5 m). C-organic levels on Padang Island peat ranged from 4.42 to 53.32 percent, according to the results of the analysis. Peat with a thickness 0-5 m has functional groups dominated by C-O from ester, eter, fenol, while peat with a thickness 5-7 m, 7-9 m, >9 m is dominated with H OH group bonds, free OH.

Rheological Studies of Anionic Surfactants in Presence of Urea Derivatives and Monohydric Alcohols at Constant Temperature

Surfactants are adaptable amphiphilic compounds have an especially distinctive polar hydrophilic head and non-polar hydrophilic tail group. The surfactant is extensively used in each walk of life such as care products, domestic cleaners, pharmaceuticals, oil recovery, food handling, and nanotechnologies due to decreasing the interfacial tension,. The Micellization of anionic surfactants such as potassium dodecyl sulphate (KDS), sodium dodecyl sulphate (NaDS), sodium dodecyl benzene sulphonate (NaDBS) in presence of urea derivatives (2.0 M) in 2.5% alkanol-water systems at constant temperature (35ºC) are measured using the Agla micrometer syringe. The conclusion of this study gives the Critical Micelles Concentration (CMC) values of anionic surfactants decreased with the increase in methyl group of urea derivatives, monohydric alcohols (methanol, propanol butanol) and water systems at 35ºC.

Identifying nonadditive contributions to the hydrophobicity of chemically heterogeneous surfaces via dual-loop active learning.

Hydrophobic interactions drive numerous biological and synthetic processes. The materials used in these processes often possess chemically heterogeneous surfaces that are characterized by diverse chemical groups positioned in close proximity at the nanoscale; examples include functionalized nanomaterials and biomolecules, such as proteins and peptides. Nonadditive contributions to the hydrophobicity of such surfaces depend on the chemical identities and spatial patterns of polar and nonpolar groups in ways that remain poorly understood. Here, we develop a dual-loop active learning framework that combines a fast reduced-accuracy method (a convolutional neural network) with a slow higher-accuracy method (molecular dynamics simulations with enhanced sampling) to efficiently predict the hydration free energy, a thermodynamic descriptor of hydrophobicity, for nearly 200 000 chemically heterogeneous self-assembled monolayers (SAMs). Analysis of this dataset reveals that SAMs with distinct polar groups exhibit substantial variations in hydrophobicity as a function of their composition and patterning, but the clustering of nonpolar groups is a common signature of highly hydrophobic patterns. Further molecular dynamics analysis relates such clustering to the perturbation of interfacial water structure. These results provide new insight into the influence of chemical heterogeneity on hydrophobicity via quantitative analysis of a large set of surfaces, enabled by the active learning approach.

Оцінка полярності стабілізаторів емульсій на основі кам'яновугільної смоли.

Surface properties of emulsion stabilizers based on coal tar are determined by their polarity. Particles of coal matter and solid dispersed substances insoluble in quinoline are considered as stabilizers of emulsions of "water in tar" type. Polarity significantly affects the physicochemical properties of tars, to take into account the degree of hydrophobicity of coal tar, information about the dipole moment of the conditional molecules is necessary. In addition, the value of the dipole moment of coal particles that stabilize the emulsion "water in tar" is of interest. The existing methods for calculating the dipole moment of coal take into account the degree of carbonization of the substance, which does not allow to trace the contribution of the degree of metamorphism and the presence of heteroatoms separately. By regression processing of the data array of dipole moment values of individual aromatic compounds, the dependence on the elemental composition was obtained. The obtained dependence in character and absolute values well characterizes the correlation of the dipole moment of coal with the degree of carbonization. The obtained data make it possible to classify substances insoluble in quinoline as a dispersed component of coal tar with the highest polarity. The greatest surface activity is possessed by those substances that have polar and non-polar groups. Such substances have surface-active properties and act as stabilizers of emulsions "water in tar". Experimentally established a closer exponential relationship between the humidity of the tar and the content of substances insoluble in quinoline. An important role in the stabilization of water particles in the emulsion is played by the concentration of quinoline-insoluble substances in the tar. Its increase may be accompanied by aggregation of quinoline-insoluble particles. Together with the increased viscosity of the dispersion medium, coal tar with a high degree of pyrolysis is quite resistant to separation. Keywords: dipole moment, polarity, regression equation, quinoline insoluble substances, highly pyrolyzed tar. Corresponding author Bannikov Leonid P., e-mail: ukhinbannikov@gmail.com

Hydrophobic Modification Experiment and Characterization of FDU-15 with Different Pore Diameter

Three ordered mesoporous carbon materials FDU-15 with different pore diameter were used.The pore size of FDU-15 can be achieved by changing the temperature and calcination atmosphere during template removal calcination.There are more polar functional groups on the inner and outer surfaces of FDU-15 pores. As a highly hydrophilic group, hydroxyl will make FDU-15 adsorb more water molecules. In practical application, water molecules and PAHs (polycyclic aromatic hydrocarbons) will produce competitive adsorption. At the same time, PAHs are mainly non-polar compounds, so non-polar adsorbents are more conducive to the adsorption of PAHs.In conclusion, the nonpolar functional groups on the surface of FDU-15 will reduce the adsorption of PAHs, which is also caused by the poor thermal and hydrothermal stability of FDU-15 material, which limits the application of FDU-15.Therefore, hydrophobic modification of FDU-15 can reduce the number of hydroxyl functional groups on its surface, adjust the surface hydrophobicity, enhance the hydrothermal stability and improve the adsorption performance of FDU-15 for PAHs. The silylation hydrophobic modification of adsorbent is studied, and the FDU-15 with different pore diameter is hydrophobically modified. It is expected to obtain a modified FDU-15 with the best pore size by comparing its adsorption isotherm, which can be put into practical use. The hydrophobic modification in this study adopts post transplantation method, and the modified samples are characterized by FT-IR to test the modification effect.

EFEITO DO TRATAMENTO DE PLASMA DE BAIXA PRESSÃO NA ESTRUTURA DE SUPERFÍCIE DE SEMENTES DE Desmanthus virgatus L. WILLD.

ABSTRACT Low-pressure argon plasma at a controlled temperature of 40 ºC was used to overcome seed dormancy in Desmanthus virgatus (L.) Willd. Treatment times were 1, 3, and 5 minutes. Infrared analysis confirmed the presence of lipids, proteins, and carbohydrates without the formation of new functional groups. The low-pressure controlled environment and the inert gas plasma changed the intensity of polar and nonpolar groups present on the seed surface. These changes directly influenced the water absorption tests because all treated seeds germinated after 24, 36, and 312 hours in the treatments of one, three, and five minutes, respectively. Germination did not occur among untreated seeds, proving the effectiveness of plasma in overcoming dormancy. The pH and conductivity results showed that plasma treatment resulted in faster germination and lower nutrient release to the medium. In addition, the seeds treated for one and three minutes showed superior results for the germination potential, germination rate, and germination index, demonstrating the effectiveness of low-pressure plasma as a clean technique and an alternative tool for reducing environmental impacts in the surface modification of D. virgatus L. Willd seeds.

Traditional herbal compounds as candidates to inhibit the SARS-CoV-2 main protease: an in silico study

COVID-19, a disease caused by the SARS-CoV-2 virus, is responsible for a pandemic since March 2020 and it has no cure. Therefore, herein, different theoretical methods were used to obtain potential candidates from herbal compounds to inhibit the SARS-CoV-2 main protease (Mpro). Initially, the 16 best-scored compounds were selected from a library containing 4066 ligands using virtual screening by molecular docking. Among them, six molecules (physalin B 5,6-epoxide (PHY), methyl amentoflavone (MAM), withaphysalin C (WPC), daphnoline or trilobamine (TRI), cepharanoline (CEP) and tetrandrine (TET)) were selected based on Lipinski’s rule and ADMET analysis as criteria. These compounds complexed with the Mpro were submitted to triplicate 100 ns molecular dynamics simulations. RMSD, RMSF, and radius of gyration results show that the overall protein structure is preserved along the simulation time. The average ΔGbinding values, calculated by the MM/PBSA method, were −41.7, −55.8, −45.2, −38.7, −49.3, and −57.9 kcal/mol for the PHY-Mpro, MAM-Mpro, WPC-Mpro, CEP-Mpro, TRI-Mpro, and TET-Mpro complexes, respectively. Pairwise decomposition analyses revealed that the binding pocket is formed by His41-Val42, Met165-Glu166-Leu167, Asp187, and Gln189. The PLS regression model generated by QSPR analysis indicated that non-polar and polar groups with the presence of hydrogen bond acceptors play an important role in the herbal compounds-Mpro interactions. Overall, we found six potential candidates to inhibit the SARS-CoV-2 Mpro and highlighted key residues from the binding pocket that can be used for future drug design. Communicated by Ramaswamy H. Sarma

Structures of glass-forming liquids by x-ray scattering: Glycerol, xylitol, and D-sorbitol.

Synchrotron x-ray scattering has been used to investigate three liquid polyalcohols of different sizes (glycerol, xylitol, and D-sorbitol) from above the glass transition temperatures Tg to below. We focus on two structural orders: the association of the polar OH groups by hydrogen bonds (HBs) and the packing of the non-polar hydrocarbon groups. We find that the two structural orders evolve very differently, reflecting the different natures of bonding. Upon cooling from 400K, the O⋯O correlation at 2.8 Å increases significantly in all three systems, indicating more HBs, until kinetic arrests at Tg; the increase is well described by an equilibrium between bonded and non-bonded OH with ΔH = 9.1 kJ/moland ΔS = 13.4 J/mol/K. When heated above Tg, glycerol loses the fewest HBs per OH for a given temperature rise scaled by Tg, followed by xylitol and by D-sorbitol, in the same order the number of OH groups per molecule increases (3, 5, and 6). The pair correlation functions of all three liquids show exponentially damped density modulations of wavelength 4.5 Å, which are associated with the main scattering peak and with the intermolecular C⋯C correlation. In this respect, glycerol is the most ordered with the most persistent density ripples, followed by D-sorbitol and by xylitol. Heating above Tg causes faster damping of the density ripples with the rate of change being the slowest in xylitol, followed by glycerol and by D-sorbitol. Given the different dynamic fragility of the three liquids (glycerol being the strongest and D-sorbitol being the most fragile), we relate our results to the current theories of the structural origin for the difference. We find that the fragility difference is better understood on the basis of the thermal stability of HB clusters than that of the structure associated with the main scattering peak.

Facile fabrication of a fluorene-containing polyimide film-based fluorescent sensor for rapid and selective detection of fluoride ion

A fluorene-containing polyimide (PI) with tert-butyldimethylsiloxy (TBS) side groups (PI-TBS) was designed and readily prepared by a post-polymerization modification on hydroxyl-containing PI. When the electron-donating hydroxyl groups in PI chain are replaced with bulky non-polar TBS side groups, inter-chain charge transfer effect of the modified PI-TBS is effectively weakened, finally resulting in the fluorescent characteristic of PI-TBS. The as-obtained fluorescent PI-TBS film-based sensor for detection of fluoride ion (F−) displays the remarkable fluorescence quenching with a short response time and high selectivity over other coexistent anions, when PI-TBS film was immersed in the fluoride-containing solution. Moreover, after immersing in the fluoride-containing solution, the PI-TBS film shows a naked-eye visible color change to yellow-green from light yellow under daylight and an obvious fluorescence quenching under 365 nm UV light. The energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopic (XPS) analyses and density functional theory (DFT) calculation studies indicate that the selective fluoride-induced cleavage of the Si-O bond enhances the intramolecular charge transfer (ICT) in PI chains, leading to fluorescence quenching. This work provides a direct polymer film-based fluorescent sensor device for the fast, selective and naked-eye visible detection of F−.

Effect of the Surface Polarity, Through Employing Nonpolar Spacer Groups, on the Glass-Transition Dynamics of Poly(phenyl methylsiloxane) Confined in Alumina Nanopores

Broadband dielectric spectroscopy and differential scanning calorimetry were used to study the effect of changes in the surface conditions on the segmental dynamics of poly(phenylmethylsiloxane) confined in alumina nanopores. Functionalization was done using highly polar propyl phosphoric units separated by the assumed concentration of triethoxysilane groups (from N = 0 to N = 24). By adjusting the proportion between polar units and nonpolar spacers, it was possible to control the surface polarity. Modification of the surface conditions does not inhibit the formation of the adsorbed layer, as revealed by the presence of two Tg’s in calorimetric results. However, changes in the surface polarity will prevent the growth of the additional interlayer in between the core volume and the interfacial layer. Finally, we also found that the changes in the surface polarity affect the equilibration kinetics and can be used to control the time scale of the structural recovery toward the equilibrium state.