Polar End Groups Research Articles

Molecular Origin of Donor- and Acceptor-Rich Domain Formation in Bulk-Heterojunction Solar Cells with an Enhanced Charge Transport Efficiency

Understanding the origin of different morphologies in bulk-heterojunction solar cells can provide effective guidelines to rational control of the morphologies in the active layer. Here, we have uncovered the importance of molecular interactions on the morphologies for not only donor materials but also for fullerene acceptors in organic solar cells through the multiscale coarse-graining molecular dynamic simulations at the real device level (∼83 nm × 83 nm × 83 nm). It is found that oligothiophene donors with polar end groups could not only facilitate the formation of continuous donor network but also promote the aggregation and connection of fullerenes toward efficient hole and electron transport. On the contrary, fullerenes are well dispersed at the molecule levels in the less polar oligothiophene matrix and thus contribute to the poor electron transport mobility and device performance, which is consistent with the observed differences in both morphology and charge transport properties of these two systems. These results would provide effective guidelines for the rational molecule design and morphology control to further enhance the device performance of organic solar cells.

High-resolution Kendrick Mass Defect Analysis of Poly(ethylene oxide)-based Non-ionic Surfactants and Their Degradation Products.

Matrix assisted laser desorption ionization (MALDI) high-resolution mass spectrometry (HRMS) and the recently introduced high-resolution Kendrick mass defect (HRKMD) analysis are combined to thoroughly characterize non-ionic surfactants made of a poly(ethylene oxide) (PEO) core capped by esters of fatty acids. A PEO monostearate surfactant is first analyzed as a proof of principle of the HRKMD analysis conducted with a fraction of EO as the base unit (EO/X with X being an integer) in lieu of EO for a regular KMD analysis. Data visualization is greatly enhanced and the distributions detected in the MALDI mass spectrum are assigned to a pristine (H, OH)-PEO as well as mono- and di-esterified PEO chains with palmitate and stearate end-groups in HRKMD plots computed with EO/45. The MALDI-HRMS/HRKMD analysis is then successfully applied to the more complex case of ethoxylated hydrogenated castor oil (EHCO) found to contain a large number of hydrogenated ricinoleate moieties (up to 14) in its HRKMD plot computed with EO/43, departing from the expected triglyceride structure. The exhaustiveness of the MALDI-HRMS/HRKMD strategy is validated by comparing the so-obtained fingerprints with results from alternative techniques (electrospray ionization MS, size exclusion and liquid adsorption chromatography, ion mobility spectrometry). Finally, aged non-ionic surfactants formed upon hydrolytic degradation are analyzed by MALDI-HRMS/HRKMD to easily assign the degradation products and infer the associated degradation routes. In addition to the hydrolysis of the ester groups observed for EHCO, chain scissions and new polar end-groups are observed in the HRKMD plot of PEO monostearate arising from a competitive oxidative ageing.

Liquid crystal anchoring transitions and weak anchoring interface formation at surfaces created by uniquely designed acrylate copolymers

Weak anchoring of liquid crystals (LCs) can, in principle, have the potential to provide lower operating voltage systems with an improved electro-optic response. The creation of such a liquid crystal system is an important goal for next-generation displays, including polymer-stabilized blue phases. Herein, we report a new method of weak anchoring for LCs in contact with uniquely designed amorphous side-chain copolymers that feature both mesogenic and non-mesogenic units. The mesogenic pendant enhances the compatibility with the LC molecules, while the non-mesogenic part reduces the possible azimuthal anchoring energy of the mesogenic side-chain on LCs. The copolymers with mesogenic pendants bearing polar and non-polar end groups favor planar and homeotropic alignments, respectively. Interestingly, LCs in a glass plate cell coated with these side-chain non-liquid crystalline copolymers showed anchoring transitions and weak anchoring interface formation at precise temperatures. The weak anchoring nature of LCs on copolymer surfaces was confirmed by their easy response to an applied magnetic field. These results suggest that the copolymers perform an important function as weak anchoring surfaces for nematic LCs.

Efficiency of sugarcane bagasse-based sorbents for oil removal from engine washing wastewater.

This work evaluates the efficiency of sugarcane bagasse-based sorbents in the sorption of oil from engine washing wastewater. The sorbents were obtained from sugarcane bagasse in the natural form (SB-N) and modified with either acetic anhydride (SB-Acet) or 3-aminopropyltriethoxysilane (SB-APTS). The results showed that the sorption capacity of these materials decreased in the following order: SB-APTS > SB-N > SB-Acet. The superior oil sorption capacity observed for SB-APTS was attributed to the polar amino end groups in the silane structure, which acted to increase the hydrophilic character of the fibers. However, all the sorbents obtained in this study were able to clean a real sample of wastewater from engine washing, leading to significant reductions in suspended matter, sediment, anionic surfactants, and turbidity.

Non-symmetric ether-linked liquid crystalline dimers with a highly polar end group

ABSTRACTA new class of non-symmetric dimeric compounds derived from 4-cyano-4′-hydroxybiphenyl in which two rigid parts are connected via flexible spacers have been designed and synthesised. These materials possess trialkoxy chains attached at one end of the molecule, while the other end consists of a biphenyl moiety terminated with the highly polar cyano group. The molecular structures of these dimers have been confirmed by elemental analysis and spectroscopic data and their phase behaviour has been characterised by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Almost all of the synthesised materials exhibit liquid crystalline properties depending on the number of carbon atoms in the terminal chains, where all short chains derivatives form nematic phases and depending on the length of the internal spacer long terminal chains homologues display crystalline or unidentified smectic phase.

Fabricating Nanometer-Thick Simultaneously Oleophobic/Hydrophilic Polymer Coatings via a Photochemical Approach.

The simultaneously oleophobic/hydrophilic coatings are highly desirable in antifogging, oil-water separation, and detergent-free cleaning. However, such coatings require special chemical structure, i.e., perfluorinated backbone and polar end-groups, and are too expensive for real-life application. Here, we have developed an UV-based photochemical approach to make nanometer-thick perfluoropolyethers without polar end-groups, which are not intrinsically simultaneously oleophobic/hydrophilic but cost-effective, become simultaneously oleophobic/hydrophilic. The contact angle, ellipsometry, and X-ray photoelectron spectroscopy (XPS) results indicated that the UV irradiation results in the covalent bonding between the polymer and the substrate, which renders more ordered packing of polymer chains and thus the appropriately small interchain distance. As a result, the small water molecules penetrate the polymer network while large oil molecules do not. As a result, the oil contact angle is larger than the water contact angle and the coating shows the simultaneous oleophobicity/hydrophilicity. Moreover, we also demonstrated that this nanometer-thick simultaneously oleophobic/hydrophilic coating has improved long-term antifogging performance and detergent-free cleaning capability and is mechanically robust. The photochemical approach established here potentially can be applied on many other polymers and greatly accelerate the development and application of simultaneously oleophobic/hydrophilic coatings.

Performance of cementitious materials produced by incorporating surface treated multiwall carbon nanotubes and silica fume

The outstanding mechanical properties of carbon nanotubes (CNTs) highlight them as potential candidates for cementitious material reinforcement. However, their low surface friction and the Van der Waals forces of attraction between them, cause the CNTs to aggregate with each other rather than bind with the cement matrix. A number of methods have been investigated by researchers to reduce the aggregation, improve dispersion and activate the graphite surface to enhance its interfacial interaction. These methods involve surface functionalization and coating, optimal physical blending, use of surfactant and other admixtures. This research investigates the use of silica fumes (an admixture), surface functionalized CNTs and cement paste to overcome those obstacles. CNTs with polar impurities end groups OH and COOH were examined. Mortar samples with non-functionalized CNTs dispersed in water solution, another with non-dispersed, non-functionalized CNTs, and a third batch with no CNTs (as control) was used also studied. Silica fumes volume fraction was varied from 0 to 30% to determine its effect. Compressive and flexural strengths of the different mixes were measured and compared. Qualitative analysis using Scanning Electron Microscope (SEM) and Energy-Dispersive Spectroscopy (EDS) were carried out to study the morphology of each mix. Results reveal a much higher enhancement in strength both compressive and flexural strengths for the functionalized CNTs with 30% silica fumes over the other samples.

Self-Assembly of X-Shaped Bolapolyphiles in Lipid Membranes: Solid-State NMR Investigations.

A novel class of rigid-rod bolapolyphilic molecules with three philicities (rigid aromatic core, mobile aliphatic side chains, polar end groups) has recently been demonstrated to incorporate into and span lipid membranes, and to exhibit a rich variety of self-organization modes, including macroscopically ordered snowflake structures with 6-fold symmetry. In order to support a structural model and to better understand the self-organization on a molecular scale, we here report on proton and carbon-13 high-resolution magic-angle spinning solid-state NMR investigations of two different bolapolyphiles (BPs) in model membranes of two different phospholipids (DPPC, DOPC). We elucidate the changes in molecular dynamics associated with three new phase transitions detected by calorimetry in composite membranes of different composition, namely, a change in π-π-packing, the melting of lipid tails associated with the superstructure, and the dissolution and onset of free rotation of the BPs. We derive dynamic order parameters associated with different H-H and C-H bond directions of the BPs, demonstrating that the aromatic cores are well packed below the final phase transition, showing only 180° flips of the phenyl ring, and that they perform free rotations with additional oscillations of the long axis when dissolved in the fluid membrane. Our data suggests that BPs not only form ordered superstructures, but also rather homogeneously dispersed π-packed filaments within the lipid gel phase, thus reducing the corrugation of large vesicles.

Molecular dynamics simulations of diffusion of submonolayer polar liquid lubricant films on solid surfaces

A fundamental understanding of the diffusion phenomena of submonolayer polar liquid films is important for achieving reliable lubrication between moving mechanical parts separated by a nanometer-sized gap. To acquire this understanding, we conducted molecular dynamics (MD) simulations of diffusion phenomena of submonolayer polar perfluoropolyether (PFPE) Zdol films on solid surfaces. To improve the accuracy of these simulations, we developed an all-atom model that includes hydrogen-bond potential and refined atomic charges for Zdol molecules and tested it through MD simulations of spreading of step-shaped submonolayer PFPE films. Our MD simulations reproduced the experimentally observed effects of polar end groups on the diffusion speed and molecular conformation of Zdol. We then conducted MD simulations of self-diffusion of submonolayer Zdol films; these simulations demonstrated that as the thickness of the submonolayer Zdol films decreases, molecular conformation becomes flatter and the self-diffusion coefficient decreases. These changes in molecular conformation partially explain our experimental finding that the spreading of step-shaped submonolayer polar PFPE films slows down with decreasing initial thickness.

Experimental study on thermophoresis of colloids in aqueous surfactant solutions

Thermophoresis refers to the motion of particles under a temperature gradient and it is one of the particle manipulation techniques. Regarding the thermophoresis of particles in liquid media, however, many open questions still remain, especially the role of the interfacial effect. This work reports on a systematic experimental investigation of surfactant effects, especially the induced interfacial effect, on the thermophoresis of colloids in aqueous solutions via a microfluidic approach. Two kinds of commonly used surfactants, sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), are selected and the results show that from relatively large concentrations, the two surfactants can greatly enhance the thermophilic mobilities. Specifically, it is found that the colloid–water interfaces modified with more polar end groups can potentially lead to a stronger thermophilic tendency. Due to the complex effects of surfactants, further theoretical model development is needed to quantitatively describe the dependence of thermophoresis on the interface characteristics.

Microphase Separation and Crystallization in H-Bonding End-Functionalized Polyethylenes

Well-defined, crystalline, low molar mass polyethylene PEx (where x is the molar mass 1300 and 2200 g mol–1) bearing thymine (Thy) or 2,6-diaminotriazine (DAT) end groups have been synthesized from amino-terminated PE. Either double-layer or monolayer solid-state morphologies were attained depending on the nature of the end-group(s). PE1300-NH2, PE1300-DAT, and the equimolar blend PE1300-Thy/DAT-PE1300 all organized into double-layer structures composed of extended PE chains sandwiched between H-bonding chain-ends. The double-layered morphology arose from the microphase separation of the polar end-groups and the nonpolar PE chains and was frozen by the crystallization of the PE domains. The regularity of the PE lamellar stacking was higher for the stronger and more directional associated pair Thy/DAT compared with samples of either PE-NH2 or PE-DAT. For PE1300-Thy, the mesoscopic organization was driven by the crystallization of Thy domains prior to crystallization of the PE chains, forcing the small prop...

The Role of Functional End Groups of Perfluoropolyether (Z-dol and Z-03) Lubricants in Augmenting the Tribology of SU-8 Composites

In an earlier work, we demonstrated the development of SU-8 composites using perfluoropolyether (PFPE) as lubricant filler which reduced friction coefficient by ~7 times and enhanced wear life of SU-8 by more than four orders of magnitude. In this work, we have investigated the role of chemical bonding between SU-8 and PFPE molecules using two types of PFPE lubricants (i.e., Fomblin® Z-dol and Z-03) in improving the tribological properties of the composite. Z-dol has polar (–OH) end groups whereas Z-03 has non-polar (CF3) end groups. SU-8 with Z-dol (SU-8 + Z-dol) films yielded ~8 times greater wear life than SU-8 with Z-03 (SU-8 + Z-03) films and more by four orders of magnitude than pure SU-8. The nature of the films was analyzed in detail by chemical and physical characterization techniques like X-ray photoelectron spectroscopy, water contact angle and thermo-gravimetric analysis. The results validated the role of polar end functional group of Z-dol in covalent binding with SU-8 upon UV plasma treatment that resulted in improved tribological properties.

Polyborosiloxanes (PBSs), Synthetic Kinetics, and Characterization

We synthesized polyborosiloxanes (PBSs) from poly(dimethylsiloxane) (PDMS) and boric acid (BA) by heating a mixture of these compounds to 200 °C. During the reaction the PDMS chains are subject to random scission, upon which the new chain ends get modified by −Si–O–(BO)m(OH)n moieties. This insight is based on gel permeation chromatography (GPC) results on the evolution of the molecular-weight distribution during the modification process, in combination with Fourier transform infrared (FTIR) spectroscopy to identify chemical moieties. We invented a refinement procedure in which the ill-defined polydisperse polar end groups can be converted into predominately borono, −Si–O–B(OH)2, by hydrolysis of boroxane bonds, B–O–B, and subsequent removal of released BA. The resulting PBSs form supramolecular elastomers owing to hydrogen bonding among the end groups. The viscoelastic behavior of the supramolecular elastomers was investigated by dynamic rheometry, and we found that the dynamic moduli increases dramatica...

Sulfone-mediated syntheses of crocetin derivatives: regioselectivity of highly functionalized building blocks.

New C5 sulfone building blocks containing a masked polar end group have been devised for the efficient synthesis of carotenoids with polar termini. Chemoselectivity or the regiochemical issue of the highly functionalized units has been carefully addressed depending on the soft or hard nature of electrophiles. These building blocks have been successfully applied to the syntheses of crocetin derivatives, crocetin dial and the novel crocetin dinitrile.

Study of the Thermal Decomposition of PFPEs Lubricants on a Thin DLC Film Using Finitely Extensible Nonlinear Elastic Potential Based Molecular Dynamics Simulation

Perfluoropolyethers (PFPEs) are widely used as hard disk lubricants for protecting carbon overcoat reducing friction between the hard disk interface and the head during the movement of head during reading and writing data in the hard disk. Due to temperature rise of PFPE Zdol lubricant molecules on a DLC surface, how polar end groups are detached from lubricant molecules during coating is described considering the effect of temperatures on the bond/break density of PFPE Zdol using the coarse-grained bead spring model based on finitely extensible nonlinear elastic potential. As PFPE Z contains no polar end groups, effects of temperature on the bond/break density (number of broken bonds/total number of bonds) are not so significant like PFPE Zdol. Effects of temperature on the bond/break density of PFPE Z on DLC surface are also discussed with the help of graphical results. How bond/break phenomenonaffects the end bead density of PFPE Z and PFPE Zdol on DLC surface is discussed elaborately. How the overall bond length of PFPE Zdol increases with the increase of temperature which is responsible for its decomposition is discussed with the help of graphical results. At HAMR condition, as PFPE Z and PFPE Zdol are not suitable lubricant on a hard disk surface, it needs more investigations to obtain suitable lubricant. We study the effect of breaking of bonds of nonfunctional lubricant PFPE Z, functional lubricants such as PFPE Zdol and PFPE Ztetrao, and multidented functional lubricants such as ARJ-DS, ARJ-DD, and OHJ-DS on a DLC substrate with the increase of temperature when heating of all of the lubricants on a DLC substrate is carried out isothermally using the coarse-grained bead spring model by molecular dynamics simulations and suitable lubricant is selected which is suitable on a DLC substrate at high temperature.

Imine-linked chemosensors for the detection of Zn2+ in biological samples

A chemosensor 1 with a long hydrocarbon chain and polar end group is synthesized by the simple condensation reaction of a long chain amine with salicylaldehyde. A long chain hydrocarbon with a polar end group is used because of its solubility in an aqueous surfactant solution, which ensures that it can be used in a neutral water medium. The rationale for choosing an aryl aldehyde with –OH functionality is based upon the fact that a chelate ring consisting of an –OH group and an sp2 nitrogen donor is always better for the selective recognition of Zn2+. The sensor shows selective binding to Zn2+ in 1% Triton-X-100 solution. Binding of Zn2+ by sensor 3 leads to an approximately 300% enhancement in the fluorescence intensity of the sensor, due to the combined effects of excited state intramolecular proton transfer (ESIPT) and the inhibition of the photo-induced electron transfer (PET) process by the –OH group. The fluorescence emission profiles of sensor 1 show some changes in the low and high pH ranges, however the sensor remains stable in the pH range 4–9, which makes it appropriate for use in biological fluids.

Oligonorbornenes with Hammock‐Like Crown Ether Pendants as Artificial Transmembrane Ion Channel

Trimeric oligonorbornenes with hammock-like crown ether pendants 3b and 3c were selectively synthesized by cascade metathetical cyclopolymerization upon treatment with the first generation Grubbs catalyst. These crown-ether-containing oligonorbornenes are impregnated in egg yolk phosphatidylcholine (EYPC) liposome as an artificial ion channel. The efficiency of the sodium ion transport properties has been examined. Oligomer 3c having a polar hydroxy end group exhibits the highest transport efficiency, which is comparable with the best efficiencies reported in literature. The orientation of the crown ether moieties in these oligomers may be critical for the ion transport properties.

Study of the Spreading of Perfluoropolyether Lubricants on a Diamond-Like Carbon Film

Nonpolar perfluoropolyether (PFPE) Z and PFPE Zdol with polar end groups are widely used as hard disk lubricants for protecting carbon overcoats by reducing friction between the hard disk and head during movement of the head while reading and writing data on the hard disk. We investigate the spreading phenomenon of PFPE Z and PFPE Zdol on a thin diamond-like carbon (DLC) film adopting molecular dynamics (MD) simulations based on a coarse-grained bead-spring model to describe the thickness profiles and molecular movement, which evolve with time and temperature. In the present article, the hard disk surface was considered as a DLC and the position of its carbon atoms was obtained by heating and quenching the face-centered cubic (FCC) or body-centered cubic (BCC) diamond structures by MD simulation using the Tersoff potential. To simulate PFPE Z and PFPE Zdol on a thin DLC film using a coarse-grained bead-spring model based on finitely extensible nonlinear elastic potential and nonbonded potential, the original DLC thin film was compressed to half of its original configuration in all three spatial dimensions. How PFPE Z and PFPE Zdol on the DLC surface spread with time are briefly discussed. How the spreading profile of PFPE Z and PFPE Zdol on the DLC film spreads laterally and on the DLC film as a circular shape beyond its original position is also discussed. The effect of temperature on the film thickness and spreading area of PFPE Z and PFPE Zdol on the DLC film is also discussed. We show that the time dependence for the spreading of PFPE Z and PFPE Zdol droplets deviated from the expected proportionality to the square root of time in their spreading profiles with time. The model-calculated spreading rate of PFPE Z and PFPE Zdol on a thin DLC film increased inversely with absolute temperature as expected.

Specific Hydration on p-Nitroaniline Crystal Studied by Atomic Force Microscopy

The molecular-scale structure of water was studied over the (101) surface of p-nitroaniline crystals using advanced atomic force microscopy. p-Nitroaniline contains two polar groups on opposite ends of the nonpolar benzene ring and presents a surface of controlled heterogeneity. The cross-sectional distribution of force applied to the tip was precisely determined and was related to the local density of the structured water. Force modulations were present on the polar end-groups and absent on the benzene ring, suggesting water localization on the polar end-groups.

A new family of four-ring bent-core nematic liquid crystals with highly polar transverse and end groups.

Non-symmetrically substituted four-ring achiral bent-core compounds with polar substituents, i.e.., chloro in the bent or transverse direction in the central core and cyano in the lateral direction at one terminal end of the molecule, are designed and synthesized. These molecules possess an alkoxy chain attached at only one end of the bent-core molecule. The molecular structure characterization is consistent with data from elemental and spectroscopic analysis. The materials thermal behaviour and phase characterization have been investigated by differential scanning calorimetry and polarizing microscopy. All the compounds exhibit a wide-ranging monotropic nematic phase.