Nonpolar Groups Research Articles

Determination of surface free energy and acido-basicity of MXene materials measured by inverse gas chromatography at infinite dilution

Since the seminal report of Ti3C2Tx in 2011, MXene has emerged as a subject of considerable interest among researchers, finding diverse applications spanning energy storage, catalysis, and coatings. Despite extensive studies on the physicochemical properties of MXene, a comprehensive understanding of its surface energetics, free from environmental influences or external substitutes, remains lacking. This study aims to fill this gap by employing the inverse gas chromatography (IGC) technique at infinite dilution to delineate the London dispersive and specific components, alongside the Lewis acid-base characters, of surface free energy in MXene materials, including MAX phase and MXene. Our findings reveal that the London dispersive surface energy values of MAX phase and MXene range from 59.3 to 80.2 mJ m−2 and 107.8–119.9 mJ m−2, respectively, across temperature ranges of 303–333 K and 393–423 K. The observed augmentation in surface energy for MXene is attributed to a higher density of non-polar surface groups and an enlarged interlayer spacing. Additionally, our analysis indicates significantly higher acceptor (KA) and donor (KD) parameters for MXene (0.97 and 1.97, respectively) compared to MAX phase (0.41 and 0.63, respectively), suggesting a preference for the Lewis acid-base character in both materials, with MXene exhibiting a more pronounced tendency. These findings offer crucial insights into the fundamental surface energetic characteristics underlying multiple physicochemical properties of MXene. This understanding facilitates the informed design of interface engineering strategies, advancing the exploration and advancement of MXene-based technologies across a broad spectrum of applications.

Statistical analysis of the unique characteristics of secondary structures in proteins

Protein folding is a complex process influenced by the primary sequence of amino acids. Early studies focused on understanding whether the specificity or the conservation of properties of amino acids was crucial for folding into secondary structures such as α-helices, β-sheets, turns, and coils. However, with the advent of artificial intelligence (AI) and machine learning (ML), the emphasis has shifted towards the precise nature and occurrence of specific amino acids. In our study, we analyzed a large set of proteins from diverse organisms to identify unique features of secondary structures, particularly in terms of the distribution of polar, non-polar, and charged amino acid residues. We found that α-helices tend to have a higher proportion of charged and non-polar groups compared to other secondary structures and that the presence of oppositely charged amino acid residues in helices stabilizes them, facilitating the formation of longer helices. These characteristics are distinct to α-helices. This study offers valuable insights for researchers in the field of protein design, enabling the de-novo creation of short helical peptides for a range of applications. We have also developed a web server for extensive analysis of proteins from different databases. The web server is housed at https://proseqanalyser.iitgn.ac.in/

Highly-selective and temperature-compensated toluene sensor based on MOF-actuated optical WGM microresonator

This paper reports an optical fiber toluene sensor based on whispering gallery mode (WGM) microbottle resonator. The sensor includes a single-mode fiber (SMF)- no-core fiber (NCF)- SMF offset structure, which can be used as not only a coupler to couple light into the microbottle but also a multimode interferometer. The microbottle is formed by self-assembly of polydimethylsiloxane (PDMS) polymer doped with metal-organic framework (MOF) under the action of surface tension and gravity. The high specific surface area, suitable pore size, nitrogen-containing functional groups of MOF-Fe-PD and nonpolar groups on PDMS impart the high sensitivity and specific response of the sensor to toluene. When toluene is captured by the MOF and PDMS, the refractive index and volume of the cavity change, which affects the mode shift of WGM. According to test results, WGM of the sensor shows a linear sensitivity of 12.44pm/ppm with toluene concentration between 0 ppm and 337 ppm at room temperature, but it is affected by temperature crosstalk. While multimode interference dip is only sensitive to temperature, which can compensate for the mode shift of WGM caused by temperature change. Repeatability experiments show that the response and recovery time of the sensor are less than 70s. The method provides a toluene sensor with high selectivity, stable performance and simple preparation, which has potential environmental benefits and good industrial application prospects.

Structural designs and synthesis of co-polycarbonates with cyclohexyl and fluorene structures: Low-dielectric constant, high solubility, and superior mechanical properties

The rapid developments of high-speed communication and large-scale integrated circuits have accelerated the research for insulating dielectric materials with low dielectric constant, low dielectric loss, and good mechanical properties. In this study, a series of polycarbonate resins containing cyclohexyl and fluorene structures are synthesized by melt transesterification, which is low dielectric, highly thermally resistant, and soluble. The effects of fluorene structure contents on the properties of a co-polycarbonate resin were studied systematically. The results showed that the non-polar fluorene group could reduce the molecular polarization of co-polycarbonate, resulting in low permittivity of co-polycarbonate are 2.41-2.71@1MHz. In addition, the resin has excellent solubility and can be dissolved in NMP, CH2Cl2, THF, and other solvents at room temperature. Furthermore, the co-polycarbonate resins also exhibit superior heat resistance with glass transition temperature (Tg) of 160.6-173.1 °C as well as admirable mechanical properties with a tensile strength of 50.54-70.72 MPa. This makes it a promising candidate for high-speed communications and large-scale integrated circuits.

Switchable Photoelectric Response in High-Temperature Leadless Molecular Ferroelectric [C4N2H14][BiI5

Lead-free molecular ferroelectrics have garnered considerable attention for their promising potential, but such species with narrow band gap and sensitive photoelectric response are yet inadequate. Herein, we demonstrated the bulk ferroelectric photovoltaic effect in a novel lead-free molecular ferroelectric [C4N2H14][BiI5] with a Curie temperature (Tc) of 366 K and a narrow band gap (Eg) of 1.92 eV. The transformation of the crystal structure from the polar space group P21 to the nonpolar space group P21/m was elucidated using single-crystal X-ray diffraction. Room-temperature (RT) hysteresis loop reveals the intrinsic ferroelectricity of [C4N2H14][BiI5] with a relative small coercive field (Ec ∼ 0.27 kV/cm), saturation polarization (Ps ∼ 1.87 μC/cm2), and remanent polarization (Pr ∼ 1.61 μC/cm2). [C4N2H14][BiI5]-based solar device exhibits significant PV effects with a steady-state photocurrent (Jsc) of 3.54 μA/cm2 and a photovoltage (Voc) of 0.34 V under AM 1.5 G illumination, which can be significantly improved by adjusting the ferroelectric polarization, reaching a maximum Jsc of 140 μA/cm2 and Voc of 0.51 V. This work offers a promising avenue for lead-free molecular ferroelectric materials in the field of optoelectronic devices.

Simple and reversible method to control the surface energy of ITO branched nanowires for tuning wettability of micro/nanoscale droplets

Reversible control of hydrophobic and hydrophilic surfaces has gained attention due to their potential applications in microfluidic devices, membranes for electrochemical cells, and sensors. While external stimuli such as temperature and electric field can regulate surface properties, they cannot be selectively applied to specific regions, which limits the patterning of areas with different surface energies. Here, we present a simple and reversible method for converting hydrophobic and hydrophilic properties through surface treatments involving nonpolar (−CFx) or polar groups (–OH) on indium tin oxide branched nanowires (ITO BRs). The formation of nonpolar groups results in superhydrophobic surface. Subsequent ultraviolet ozone treatment, using a shadow mask, induces the exposed area to transition into a superhydrophilic state, while the unexposed area retains superhydrophobicity. This demonstrates the potential for selective-area surface energy patterning. Furthermore, we investigate the wetting behavior of nanoscale Ag nanoparticles (NPs) on surface-modified ITO BRs. It is observed that size and shape of Ag NPs depend on the surface energy of ITO BRs. Consequently, controlling the surface energy leads to the formation of unique geometric structure of Ag NPs, enhancing plasmonic light absorption and scattering at specific resonant wavelengths.

Wetting mechanism and alteration of nano-sized shale pores: Insights from contrast variation small angle neutron scattering

Wettability of tight shale is crucial for fluid flow and mass transport process in energy geosciences. However, understanding the interfacial chemistry and wetting mechanisms at sub-nano-pore scales remains a formidable challenge. In this study, the Contrast Variation technique of Small Angle Neutron Scattering (CV-SANS) is employed to investigate shale’s interfacial chemistry using reagents that possess a range of different polarities, including water, n-decane, toluene, and dimethyl methanamide. Through five different experimental strategies, we have demonstrated a successful modification of shale wettability, ranging from enhancement, weakening, to reversal. Delving into the mechanisms, we illustrated the crucial role of pre-existing liquid films in these changes, where the uniquely co-existing polar and non-polar functional groups in dimethyl methanamide acted as a conduit for interfacial chemistry adjustments. Furthermore, a solvent immersion led to matrix dilation as well as liberation of residual oil-occupied pores, resulting in altered pore size distributions, with hydrogen bonding playing a significant role in the polar groups. Interestingly, despite shale exhibiting a stronger affinity for oil over water, hydrophilic solvents induced more substantial dilation than lipophilic ones. Collectively, this work elucidates the dynamic change of interfacial chemistry via the configuration of polarity using chemical reagents, and the CV-SANS technique underscores its invaluable utilities in decoding the interfacial wettability traits in nanopore space of shale.

Fabrication of superhydrophobic titanium surfaces: impact of different micropatterns

ABSTRACT Offshore and nuclear power plants use titanium condensers to cool exhaust steam from turbines. Preparation of robust superhydrophobic Titanium surfaces is necessary to protect these condensers from fouling and pitting phenomena. This study investigates the impact of various laser-textured Titanium grade 2 surface configurations followed by silicone oil heat treatment on enhancing its wettability and tribological properties. Seven distinct micropatterns were fabricated using a fiber laser with a laser power of 7.5 W, a scanning speed of 300 mm/s, a scan loop of 10, and a pulse frequency of 20 kHz. Patterned surfaces were characterized using different techniques, namely, micro-hardness, surface morphology, wettability, elemental analysis and wear. Improvement in wetting property was observed in laser textured samples after heating with silicone oil due to the adsorption of nonpolar groups (C=O, –CH3) resulting in a low energy surface. The grid pattern surface exhibited the highest water contact angle (WCA) of 151.01° due to a dense microstructure.

Review of potentiometric determination of cationic surfactants

Abstract Cationic surfactants (CSs) are surface-active compounds containing a positively charged polar group and at least one alkyl chain as a nonpolar group. Due to their structure, they tend to adsorb on negatively charged surfaces and interact with biopolyanions. It leads to their wide use as disinfectants, cleaning agents, fabric softeners, hair care products, emulsifiers, corrosion inhibitors, etc. Considering their extensive use and also their toxicity, fast, simple, and accurate CSs determination is crucial in industrial process control, product quality assurance, and environmental monitoring. Potentiometric sensors meet all these requirements, so they stand as the primary method for CSs determination. In this review, numerous potentiometric methods for CSs determination have been described, with a particular focus on methods published in the period from 2000 to 2024. Due to their simplicity and good analytical performance, solid-state electrodes are the most commonly used type of sensor for CSs determination.

Quantitative analysis of intermolecular forces in cellulose microfibrils and hemicellulose with AFM nano-colloidal probes

It is an interesting research topic to study the interfacial interactions between hemicellulose and cellulose, specifically how hemicellulose's structure affects its binding to cellulose nanofibers. Our research proposes that dispersion interaction play an important role in this interfacial interaction, more so than electrostatic forces when considering the adherence of cellulose to xylan. To quantify these interactions, the Atomic Force Microscope (AFM) colloidal probe technique is applied to measure the intermolecular forces between cellulose nanofibers, which are attached to the probe and xylan. These measured forces are then analyzed in relation to the length, diameter and functional groups of the nanocellulose, as well as the molecular weight and side chains of the xylan. Moreover, the predominance of dispersion forces by contrasting the adhesive forces before and after the grafting of a large nonpolar group onto xylan. This modification significantly reduces contact between the cellulose and xylan backbone, thereby markedly diminishing the dispersion interactions. Parallel to the AFM experiments, molecular dynamics (MD) simulations corroborate the experimental results and support our hypotheses. Collectively, these findings contribute to a deeper understanding of polysaccharide interactions within lignocellulose.

Polar organic molecules assisting Mo-based cathode materials for enhanced zinc-ion transfer kinetics

The Mo-based oxides/sulfides are promising cathode materials for Zn-ion batteries (ZIBs). However, the volume expansion and poor intrinsic electronic conductivity limit their electrochemical performance. Herein, a strategy of introducing active organic small molecule (ethylenediamine) into the interlayer of the Mo-based oxides/sulfides (MoOS) is reported to solve these shortcomings. The experimental analysis reveals that ethylenediamine (EDA) can regulate the composition ratio of MoO3/MoS2 for its reduction ability, which can improve the electronic conductivity of the EDA-intercalated MoOS (MoOS-EDA). Besides, EDA can efficiently decrease the Zn2+ insertion energy for its strong coordinated ability with Zn2+, in combination with the enhanced interlayer spacing and the strong repulsion with Zn2+ from the non-polar group –CH2CH2 in EDA, leading to enhanced ionic transferring kinetics and Zn2+ storage ability. The theoretical and experimental analysis have confirmed the organic guest and inorganic skeleton all participate in the Zn2+ storage process. As a result, compared with the MoOS cathode, the MoOS-EDA exhibits improved specific capacity (203 vs. 88 mAh/g at 0.1 A/g) and prolonged cycle stability. Moreover, the soft-package cell based on MoOS-EDA cathode also delivers an impressive electrochemical performance. This work provides a strategy to improve the Zn2+ transfer kinetics in MoS2 cathode material towards high-performance ZIBs.

On the Moisture Absorption Capability of Ionic Liquids.

Due to their many attractive physicochemical properties, ionic liquids (ILs) have received extensive attention with numerous applications proposed in various fields of science and technology. Despite this, the molecular origins of many of their properties, such as the moisture absorption capability, are still not well understood. For insight into this, we systematically synthesized 24 types of ILs by the combination of the dimethyl phosphate anion with various types of alkyl group-substituted cyclic cations─imidazolium, pyrazolium, 1,2,3-triazolium, and 1,2,4-triazolium cations─and performed a detailed analysis of the dehumidification properties of these ILs and their aqueous solutions. It was found that these IL systems have a high dehumidification capability (DC). Among the monocationic ILs, the best performance was obtained with 1-cyclohexylmethyl-4-methyl-1,2,4-triazolium dimethyl phosphate, whose DC (per mol) value is 14 times higher than that of popular solid desiccants like CaCl2 and silica gel. Dicationic ILs, such as 1,1'-(propane-1,3-diyl)bis(4-methyl-1,2,4-triazolium) bis(dimethyl phosphate), showed an even better moisture absorption, with a DC (per mol) value about 20 times higher than that of CaCl2. Small- and wide-angle X-ray scattering measurements of eight types of 1,2,4-triazolium dimethyl phosphate ILs were performed and revealed that the majority of these ILs form nanostructures. Such nanostructures, which vary with the identity of the IL and the water content, fall into three main categories: bicontinuous microemulsions, hexagonal cylinders, and micelle-like structures. Water in the solutions exists primarily in polar regions in the nanostructures; these spaces function as water pockets at relatively low water concentrations. Since the structure and stability of the aggregated forms of the ILs are mainly governed by the interactions of nonpolar groups, the alkyl side chains of the cations play an important role in the DC and temperature-dependent equilibrium water vapor pressure of the IL solutions. Our experimental findings and molecular dynamics simulation results shed light on the moisture absorption mechanism of the IL aqueous solutions from a molecular perspective.

Structural Order in the Hydration Shell of Nonpolar Groups versus that in Bulk Water.

The poor solubility of nonpolar compounds in water around room temperature is governed by a large and negative entropy change, whose molecular cause is still debated. Since the Frank and Evans original proposal in 1945, the large and negative entropy change is usually attributed to the formation of ordered structures in the hydration shell of nonpolar groups. However, the existence of such ordered structures has never been proven. The present study is aimed at providing available structural results and thermodynamic arguments disproving the existence of ordered structures in the hydration shell of nonpolar groups.

Hydrophobic Aerogels from Vinyl Polymers Derived from Radical Polymerization: Proof-of-Concept.

Hydrophilicity is one important drawback of bio-based aerogels. To overcome this issue, a novel approach for the preparation of mesoporous, water repellent aerogels is introduced, which combines synthesis of cross-linked bio-based copolymers from methacrylate copolymerizations, followed by solvent exchange and supercritical drying steps. The influence of monomers with different nonpolar ester groups (methyl, vanillin, tetrahydrofurfuryl) on textural properties and water contact angles of the dry products is assessed. Final aerogels show generally high overall porosities (≈96%), low densities (0.07-0.11gcm-3) as well as fine, mainly mesoporous networks, and specific surface areas in the range of 120-240m2g-1. Hereby, choice of the methacrylate ester groups results in differences of the resulting pore-size distributions. Water repellency tests show stable static water contact angles in the hydrophobic range (≈100°) achieved for the substrate containing the vanillin ester group. On the contrary the other substrates absorb water quickly, which indicates a decisive role of the ester group. The presented approach opens up a new pathway to bio-based aerogels with intrinsic hydrophobicity. It is suggested that the properties are tailored by the choice of the monomer structure, hence enabling further adaption and optimization of the products.

The Influence of Functional Composite Coatings on the Properties of Polyester Films before and after Accelerated UV Aging.

The aim of this study was to cover biopolymeric packaging films based on PLA/PHBV blend with a functional composite coating (to retain their ecological character) and to investigate their antimicrobial properties before and after UV irradiation. As an active coating, the carrier hydroxypropyl methyl cellulose (HPMC), as well as its modified form with Achillea millefolium L., Hippophae rhamnoides L., and Hypericum L. extract (E) and a combined system based on the extracts and nano-ZnO (EZ), was used to obtain active formulations. Additionally, film surface morphology (SEM, FTIR-ATR) and color (CIELab scale) analysis of the pre- and post-UV-treatment samples were performed. The results confirmed that the E and EZ-modified films exhibited antibacterial properties, but they were not effective against phage phi6. Q-SUN irradiation led to a decrease in the activity of E coating against Staphylococcus aureus, Pseudomonas syringae, and Candida albicans. In this case, the effectiveness of EZ against C. albicans at 24 h and 72 h UV irradiation decreased. However, the irradiation boosted the antiviral effectiveness of the EZ layer. SEM micrographs of the film surface showed that UV treatment did not significantly influence the native film morphology, but it had an impact on the coated film. FTIR analysis results showed that the coatings based on HPMC altered the IR absorption of the nonpolar groups of the biopolyester material. The applied coatings only marginally affected film color changes and increased their yellowness after UV irradiation, whereas a composite layer of nano-ZnO limited these changes.

Miscibility prediction of polylactic acid/polyhydroxyalkanoate blends by molecular dynamics simulations

Blending polylactic acid (PLA) with polyhydroxyalkanoates (PHAs) represents a compelling approach to achieve fully bio-based blends with favorable properties. This work employed molecular dynamics (MD) simulations to study the miscibility of PLA and PHA with different side chain functional groups. The miscibility of the blends was assessed through analyzing snapshots of the blends, pair correlation function, radius of gyration, interaction energy, solubility parameter, and Flory−Huggins interaction parameter. Results revealed that the miscibility with PLA is predominantly affected by the polarity of the side chain functional group of PHA. To achieve effective blending with PLA, it is advisable to use PHAs with non-polar side chain groups. Examination of the glass transition temperature (Tg) for the miscible blends reveals that the rigidity of PLA can be reduced by blending with PHA bearing non-polar side chain functional groups.

The interaction of thiocyanate with peptides-A computational study.

According to the Hofmeister series, thiocyanate is the strongest "salting in" anion. In fact, it has a strong denaturant activity against the native state of globular proteins. A molecular level rationalization of the Hofmeister series is still missing, and therefore the denaturant activity of thiocyanate also awaits a robust explanation. In the last years, different types of experimental studies have shown that thiocyanate is capable to directly interact with both polar and nonpolar groups of polypeptide chains. This finding has been scrutinized via a careful computational procedure based on density functional theory approaches. The results indicate that thiocyanate is able to make H-bonds via both the nitrogen and sulfur atom, and to make strong van der Waals interactions with almost all the groups of polypeptide chains, regardless of their polarity.

Inside of the burst-phase intermediate of a protein folding. Hydration of hydrophobic groups

The thermal effect of the formation of the “burst-phase” folding intermediate has been studied using a titration calorimeter. It is shown that, unlike the total thermal effect of native structure formation, it can be both positive and negative depending on the temperature. The reasons for this paradoxical behavior are analyzed. A conclusion is drawn about the leading role of dehydration of non-polar groups in the first stage of folding.

Molecular mechanism of the degree of influence of ethoxy and alkyl structures on the wettability of low-rank coal

The mechanisms of the effects of decyl polyoxyethylene ether (DEO6), decyl polyoxyethylene ether (DEO8), and aliphatic alcohol polyoxyethylene ether (AEO6) on the wettability of coal dust from low-rank coal have been investigated in this study. The aim is to reveal the difference in the degree of influence of the structure of the alkyl and ethoxy groups. The surface tension test showed that AEO6, which can form a soft chain structure, could reach the critical micelle concentration (CMC) the fastest, followed by DEO6, and DEO8, which has the strongest polar effect, the slowest. The contact angle, settling time, and water retention experiments revealed that the AEO6-treated coal dust had the strongest wettability and water retention, which could effectively inhibit the coal dust and weaken the possibility of its secondary dust. Fourier transform infrared (FTIR) spectroscopy reveals that AEO6 with long alkyl chains can produce strong nonpolar effects, and in the process of adsorption with coal dust, it can produce strong hydrophobic bonding with nonpolar groups on the surface of low-rank coal, and finally form a directional adsorption conducive to the enhancement of wettability. Scanning electron microscope (SEM) showed a trend from DEO6-coal, DEO8-coal, and AEO6-coal appearing to have surfaces that sequentially become flatter and denser, with a gradual decrease in the number of loose particles and a weakening of the pore structure. Molecular dynamics (MD) simulations agree with the above experimental results. That is, the interaction between water molecules is stronger in the AEO6-modified coal system, followed by the DEO8 system and weakest in the DEO6 system. And the advantage of DEO8-coal is weaker than that of AEO6-coal but better than that of DEO6-coal. Based on the above experimental and simulation results, it can be concluded that the ability of the alkyl structure to influence the wettability of surfactant-modified coal dust is higher than the structure of the ethoxylate group, which will provide theoretical guidance for coal dust management and dust suppression.

Influence of non-polar groups in quaternary ammonium compounds on the growth of zinc dendrites

Dendritic growth is a common behavior during the electrodeposition of zinc, which degrades the compactness and thickness uniformity of the zinc film. In this work, a series of quaternary ammonium compounds (QAC) with different non-polar groups (based on the number of carbon atoms in non-polar groups represented as C1, C4, C8, C12 and C16, respectively) were introduced into the basic electrolyte to inhibit the zinc dendritic growth. The results showed that the deposition of zinc became smoother with the increase of non-polar group length, which was attributed to the fact that the non-polar groups of the additive limit the random diffusion of Zn2+ and changed the adsorption state of the surface, so that a uniform zinc film was obtained. Meanwhile, the Zn-Zn symmetric cells with the addition of C8 achieved a stable cycle time of over 600 h. But with the further increase of length (C12 and C16), the migration of Zn2+ to the electrode surface became extremely difficult for strong steric hindrance, resulting in a rough deposition morphology.