Side Chain Length Research Articles

Effect of ionomer dispersions on the performance of catalyst layers in proton exchange membrane fuel cells

In this study, various ionomer dispersions having different equivalent weights, length of side chains, and dispersing solvents have been extensively analyzed to investigate the effect of the microstructure of catalyst layers on the performance of membrane-electrode assembly in proton exchange membrane fuel cells. Five different commercially available perfluorinated sulfonic acid ionomer dispersions have been used to prepare laboratory-made propylene glycol-based ionomer dispersions. The thickness of self-assembled ultra-thin films on silicon wafer for all types of ionomer dispersions has been measured and correlated mainly with the type of dispersing solvents (i.e., water, 2-propanol, and propylene glycol), the length of ionomer side chain, and the wettability. As a result, the short side chain and the propylene glycol-based ionomer dispersions form thicker films due to the smaller average size of their ionomer aggregates. The thick-ionomer wrapped catalyst layers especially prepared by the propylene glycol-based ionomer dispersions result in no influence on activation loss but approximately 42% less Ohmic loss and 43% higher limiting current density in proton exchange membrane fuel cells. In addition, it is confirmed that the slightly higher performance is exhibited as the thickness of ultra-thin ionomer film increases due to the effect of the length of side chains. The catalyst layers with the ionomer film over 100 nm show the higher performance than those below 100 nm. The MEA using Nafion D2020 having hydrophobic surface shows the lower increasing ratio (2.26%) in HFR than the one using Aquivion D98-25BS having hydrophilic surface due to the difference of the water-retaining ability.

Synthesis and comparative studies on the surface-active and biological properties of linear poly(glycidol) esters

• Linear poly(glycidol) esters were synthesized as novel nonionic surfactants. • Physical and biological evaluations were conducted to establish a structure–property profile. • Length of alkyl side chains revealed significant impact on the functional performance. Herein, a series of linear poly(glycidol) esters were synthesized as novel nonionic surfactants. Their surface activities, emulsifying capacities, thermal stabilities as well as hemolytic activities were comprehensively investigated to establish a structure–property profile, which clearly revealed the impact of different lengths of alkyl side chains on the associated functional performance. Therefore, our study offered a valuable reference for their potential practical applications.

Solution properties of hydrophobic derivatives of poly(ethylene-alt-maleic acid)

A library of hydrophobically modified polyelectrolytes was prepared by reacting linear alkyl amines with poly(ethylene-alt-maleic anhydride), followed by hydrolysis of the residual anhydride groups. Every reacted anhydride gives a pendent alkylamide plus a carboxylic acid group, and the result is a comb architecture. The lengths of the alkyl side chains were 3, 6, 8, or 10 carbons. The density of alkyl side chains was expressed as the fraction of anhydride groups reacted with alkyl amines (25 %, 50 %, and 75 %). The dominant factor influencing the aqueous solution properties is the alkyl chain length. C3 polymers had no pyrene receptive hydrophobic domains. C6 and C8 polymers bound pyrene at pH less than 6 and do not give reliable dynamic light scattering (DLS) results. C10 polymers displayed pyrene binding across the pH range and, based on DLS and AFM data, possibly appear as unimolecular nanogel dispersions from pH 7–9. At pH values > 9, our DLS measurements gave low-quality data, whereas at pH less than 7 both DLS and AFM results indicated nanogel aggregation. The C10 polymer properties were surprisingly insensitive to the degree of hydrophobic substitution over the range of 25–75 %. The nanogels with low alkyl contents were slightly more swollen and had high NaCl critical coagulation concentrations compared to the high alkyl content nanogels. These polymers are of particular interest because the non-derivatized maleic moieties in the polymers can form ester linkages to cellulose in an aqueous, catalyst-free process.

Effect of Hydrophobic Side Chain Length on Poly(carbazolyl terphenyl piperidinium) Anion Exchange Membranes

Effect of Hydrophobic Side Chain Length on Poly(carbazolyl terphenyl piperidinium) Anion Exchange Membranes

IPP/PE Multiblock Copolymers for Plastic Blend Recycling Synthesized by Coordinative Chain Transfer Polymerization

Recycling of blends of widely used plastics is a key challenge of the envisioned circular economy, and thus, protocols permitting the efficient synthesis of effective compatibilizers are highly desirable. We report herein that coordinative chain transfer polymerization permits the efficient one-pot synthesis of multiblock architectures of strictly linear polyethylene or high-density polyethylene (HDPE) and isotactic polypropylene (iPP). Various block copolymers having an iPP backbone and HDPE side chains were synthesized and used to compatibilize HDPE/iPP plastic blends. The synthesized block copolymers differ in their overall molecular weights and have different HDPE side chain lengths and numbers. A block copolymer with a molecular weight of Mp = 33,700 g × mol–1 including 4.5 HDPE side chains with a molecular weight of Mn = 600 g × mol–1 showed the highest efficiency for compatibilizing 30/70 wt % blends of HDPE/iPP with a 5 wt % compatibilizer addition. This block copolymer is also superior to commercially available compatibilizers.

Poly(carbazole-co-1,4-dimethoxybenzene): Synthesis, Electrochemiluminescence Performance, and Application in Detection of Fe3+

In this study, four polycarbazole derivatives (PCMB-Ds) with different alkyl side chains were designed and synthesized via Wittig–Horner reaction. A novel solid-phase electrochemiluminescence (ECL) system was prepared by immobilizing PCMB-D on an indium tin oxide (ITO) electrode with polyvinylidene fluoride (PVDF) in the presence of tripropylamine (TPrA). It could be found that the increase in alkyl side chain length had little effect on the ECL signal of PCMB-D, while the increase in the degree of polymerization (DP) greatly enhanced the ECL signal. Furthermore, the P-3/ITO ECL sensor based on the polyoctylcarbazole derivative (P-3) with the best ECL performance was successfully constructed and detected Fe3+ under the optimal experimental conditions. The ECL signal steadily diminished with the increased concentration of Fe3+ because of the competition and complexation between Fe3+ and P-3 under the condition of pH 7.4. This P-3/ITO platform could realize a highly sensitive and selective detection of Fe3+ with a wide detection range (from 6 × 10−8 mol/L to 1 × 10−5 mol/L) and low detection limit of 2 × 10−8 mol/L, which could allow the detection of Fe3+ in multiple scenarios, and would have a great application prospect.

The synthesis of quaternary N-alkyl tropinium cationic surfactants and study on their properties: effect of temperature, hydrophobic chain length and anions

• A series of quaternary N-alkyl tropinium cationic surfactants (TILS) with different anion were synthesized and characterized. • By changing counter ions, the krafft point was significantly reduced (from 313.15 K to below 273.15 K) • By increasing the hydrophobicity of anions, the critical micelle concentration ( CMC ) value of TILS decreased about 4-5 times (being compared with bromide). • The effects of temperature, hydrophobic chain length, and anions on the micellar properties of TILS were investigated. A series of quaternary N-alkyl tropinium cationic surfactants (TILS) were synthesized and characterized. The effect of temperature, hydrophobic chain length and anions on their properties were studied. By changing the structure of anion, the krafft point was significantly reduced (from 313.15 K to below 273.15 K) and wide temperature window was obtained. The critical micelle concentration ( CMC ) value of TILS based on electrical conductivity method was found to be decreased about 4-5 times by increasing hydrophobicity of anions. At lower temperature and longer hydrophobic chain, TILS had lower CMC value and better surface activity. The thermodynamic properties of micellization Gibbs free energy Δ G mic , enthalpy Δ H mic and entropy T Δ S mic of micelles were obtained by Mass action model. The result indicates that the micellization process of the TILS was spontaneous and more stable with the increase of anionic hydrophobicity. In addition, with the increase of hydrophobic side chain length, the driving force of surfactant micellization may be enthalpy driven at higher temperature and entropy driven at lower temperature. The micro-environment of TILS solution with different concentrations was studied by UV spectrophotometry with curcumin as a probe and the change of micro-environment was used to determine the CMC of TILS. The CMC values were similar obtained by two methods.

Protonated amines mediated CO2 mineralization of coal fly ash and polymorph selection of CaCO3

The extensive consumption of acid and alkaline reagents is the most critical challenge hindering the development of the pH-swing process for CO2 mineralization. To deal with the problem, the present paper demonstrates the feasibility of using protonated amine as the reagent in coal fly ash (CFA) based leaching-mineralization process. The protonated amine could leach Ca2+ from CFA and be converted into free amine. The free amine was supposed to be in-situ regenerated into protonated amine by grab protons released from the CaCO3 precipitation reaction. 13 typical amines with varying amino types, pKa values, and side-chain length, were selected to systematically investigate the effects of amino groups on Ca2+ leaching performance from CFA, carbonation performance, CaCO3 nucleation, and crystal growth, as well as the process mechanism. Results indicated that effective Ca leaching, CaCO3 precipitation, and protonated amine regeneration were achieved. There was a linear relationship between the Ca utilization efficiency and pKa values of different amines. TEA obtained the highest CaCO3 yield and Ca utilization efficiency of 56.8 % and 16.8 %, respectively. In addition, amines provided excellent control of the size, polymorph, and morphology of the CaCO3 product. The primary amino group had a more pronounced effect on vaterite stabilization than secondary and tertiary ones. Introducing a side chain could promote the vaterite transforming to calcite and increasing chain length could decrease the vaterite particle size. Moreover, the maximal utilization efficiency in MEA was 15.9 % at conditions: 160 g/L solid to liquid ratio, 58 % degree of protonation, and 2.0 mol/L MEA concentration.

Effect of Alkyl Side Chain Length on the Lithium-Ion Conductivity for Polyether Electrolytes.

The design guidelines of polymer structure to effectively promote lithium-ion conduction within the polymer electrolytes (PEs) are crucial for its practical use. In this study, the electrolyte properties of a simple polyether having alkyl side chains with varied lengths (−(CH2)m−H, m = 1, 2, 4, 6, 8, and 12) were compared and established a valid design strategy based on the properties of the alkyl side chain. Various spectro-electrochemical measurements successfully connected the electrolyte properties and the alkyl side chain length. Steric hindrance of the alkyl side chain effectively suppressed the interaction between ether oxygen and lithium-ion (m ≥ 2), decreasing the glass transition temperature and the activation energy of lithium-ion transfer at the electrode-electrolyte interface. The strong hydrophobic interactions aligned and/or aggregated the extended alkyl group (m ≥ 8), creating a rapid lithium-ion transport pathway and enhancing lithium-ion conductivity. A clear trend was observed for the following three crucial factors determining bulk lithium-ion transport properties along with the extension of the alkyl side chain: 1) salt dissociability decreased due to the non-polarity of the alkyl side chain, 2) segmental mobility of polymer chains increased due to the internal plasticizing effect, and 3) lithium-ion transference number increased due to the inhibition of the bulky anion transport by its steric hindrance. The highest lithium-ion conductivity was confirmed for the PEs with an alkyl side chain of moderate length (m = 4) at 70°C, indicating the optimized balance between salt dissociability, polymer segmental mobility, and selective lithium-ion transfer. The length of an alkyl side chain can thus be a critical factor in improving the performance of PEs, including thermal stability and lithium-ion conductivity. Precise tuning of the alkyl side chain-related parameters such as steric hindrance, polarity, internal plasticizing effect, and self-alignment optimizes the polymer segmental mobility and salt dissociability, which is crucial for realizing high lithium-ion conductivity for PEs.

Anion Exchange Membranes for Fuel Cells Based on Quaternized Polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene Triblock Copolymers with Spacer-Sidechain Design.

This work studied the polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) triblock copolymers functionalized by butyl quaternary ammonium (C4Q) groups and alkyl side chains of different chain lengths (Cn, n = 0 to 24). The hydrated membrane morphology was modeled by dissipative particle dynamics simulation at hydration levels from 10 to 30. A hydroxide model was devised to characterize the diffusivity of anions under the coarse-grained framework. In general, the ionomers with alkyl side chains provided ion conductivity of a similar level at a lower ion exchange capacity. All hydrated SEBS–C4Q–Cn ionomers showed clear phase separation of the hydrophobic and hydrophilic domains, featuring 18.6 mS/cm to 36.8 mS/cm ion conductivity. The hydrophilic channels expanded as the water content increased, forming more effective ion conductive pathways. Introducing excess alkyl side chains enhanced the nano-segregation, leading to more ordered structures and longer correlation lengths of the aqueous phase. The membrane morphology was controlled by the length of alkyl side-chains as well as their tethering positions. Ionomers with functionalized side chains tethered on the same block resulted in well-connective water networks and higher conductivities. The detailed structural analysis provides synthesis guidelines to fabricate anion exchange membranes with improved performances.

Precise Tailoring of Polyester Bottlebrush Amphiphiles toward Eco‐Friendly Photonic Pigments via Interfacial Self‐Assembly

AbstractBiodegradable photonic microspheres with structural colors are promising substitutes to polluting microbeads and toxic dyes. Here, amphiphilic polyester‐block‐poly(ethylene glycol) bottlebrush block copolymers (BBCPs) with polylactic acid or poly(ϵ‐caprolactone) as the hydrophobic block are synthesized and used to fabricate eco‐friendly photonic pigments. Molecular parameters of BBCPs, including rigidity and symmetry, are precisely tailored by variation of side chain lengths, which enables effective manipulation of interfacial tension (γ). Organized spontaneous emulsion mechanism is enabled only whenγfalls in a suitable range (10.6–14.3 mN m−1), producing ordered water‐in‐oil‐in‐water multiple emulsions and ordered porous structures. Consequently, highly saturated and tunable structural colors are observed due to coherent light scattering from the porous structures. Such photonic materials are nontoxic as confirmed by careful safety tests using aquatic model organisms.

Precise Tailoring of Polyester Bottlebrush Amphiphiles toward Eco-Friendly Photonic Pigments via Interfacial Self-Assembly.

Biodegradable photonic microspheres with structural colors are promising substitutes to polluting microbeads and toxic dyes. Here, amphiphilic polyester-block-poly(ethylene glycol) bottlebrush block copolymers (BBCPs) with polylactic acid or poly(ϵ-caprolactone) as the hydrophobic block are synthesized and used to fabricate eco-friendly photonic pigments. Molecular parameters of BBCPs, including rigidity and symmetry, are precisely tailored by variation of side chain lengths, which enables effective manipulation of interfacial tension (γ). Organized spontaneous emulsion mechanism is enabled only when γ falls in a suitable range (10.6-14.3 mN m-1 ), producing ordered water-in-oil-in-water multiple emulsions and ordered porous structures. Consequently, highly saturated and tunable structural colors are observed due to coherent light scattering from the porous structures. Such photonic materials are nontoxic as confirmed by careful safety tests using aquatic model organisms.

Comprehensive assessment of estrogenic activities of parabens by in silico approach and in vitro assays

Parabens are ubiquitous pollutants in the environment and humans due to their wide applications in food, pharmaceuticals, and personal care products. Although the estrogenic activity of some parabens has been confirmed, the underlying mechanisms and the structure-estrogenic activity relationship are still largely unclear. Here, we systematically used in silico and in vitro approaches to investigate the estrogenic potency of typical parabens, including methyl-, ethyl-, propyl-, iso-propyl-, butyl-, iso-butyl- and benzyl-paraben. Molecular dynamics simulations and binding free energy calculations were combined to investigate the atomic-level mechanism of paraben binding to estrogen receptors (ERs). Computational analysis showed that ER were the targets of tested parabens and kept a stable agonist conformation. The calculated total binding free energies suggested that van der Waals interactions were the major driving forces for paraben-ER interaction and correlated with the structure of paraben side chains. In in vitro assays, paraben with an aromatic side chain, benzyl-paraben, showed the strongest estrogenic activity at 0.01 μM and the EC50 at 0.796 ± 0.307 μM, on par with levels commonly detected in human organs. Among tested parabens with an alkyl side chain, the estrogenicity increased as the side chain length increased from 1 to 4, but no significant difference appeared between parabens with isomeric alkyl side chains (propyl- vs isopropyl and butyl- vs iso-butylparaben). The estrogenic activity of parabens was significantly related to the calculated binding energies (R2 = 0.94, p = 0.0012), depending on the side chains of parabens. Our findings provide a significant mechanism for parabens to disrupt estrogenic function and considerations for structural optimization from the perspective of environmental protection.

Side-Chain Length and Dispersity in ROMP Polymers with Pore-Generating Side Chains for Gas Separations.

Bottlebrush polymers with flexible backbones and rigid side chains have shown ultrahigh CO2 permeability and plasticization resistance for membrane-based gas separations. To date, this class of polymers has only been studied with polydisperse side chains. Herein, we report gas transport properties of a methoxy (OMe) functionalized polymer synthesized via ring-opening metathesis polymerization (ROMP) with uniform side-chain lengths ranging from n = 2 to 5 repeat units to elucidate the role of both side-chain length and dispersity on gas transport properties and plasticization resistance. As side-chain length increased, both Brunauer–Emmett–Teller (BET) surface area and gas permeability increased with minimal losses in gas selectivity. Increased plasticization resistance was also observed with increasing side-chain length, which can be attributed to increased interchain rigidity from longer side chains. Controlling the side-chain length provides an effective strategy to rationally control and optimize the performance of ROMP polymers for CO2-based gas separations.

(Invited) Photoabsorption and Excitation Energy Transfer in Fluorinated Non-Fullerene Acceptors for Organic Solar Cells

Recently, it was reported that OSCs based on non-fullerene acceptors have shown high photovoltaic performance with over 18% efficiency, being more than the power conversion efficiencies (PCEs) of 13% in OSCs based on fullerene. We considered theoretically the effects of fluorine atoms on the conversion efficiency of organic thin-film solar cells from the electronic analysis of donor/acceptor (D/A) complex interactions for NTz-Teh-FA and FNTz-Teh-FA using DFT. It was confirmed that it differs depending on the side-chain length, and it is necessary to consider the side-chain length. Because the longer the side-chain length, the lighter absorption and increased charge transfer. In the fluorinated acceptor, the polarity around the O atoms at both ends of the main chain was weakened, the twist angle of the molecular structure was reduced, and the light absorption at 600–700 nm was increased in the absorption spectrum. Therefore, it is considered that the fluorinated nonfullerene-type acceptor FNTz-Teh-FA, which has a long side chain, has the best light absorption and charge transfer. Excitation Energy Transfer (EET) calculations show that the Coulomb coupling contributes significantly. In addition, it was confirmed that the fluorinated complex had a higher EET. Therefore, it is considered that the charge separation efficiency is improved. Thus, it is considered that the short-circuit current density (JSC) is improved by improving the internal quantum efficiency (IQE), including the element of the charge separation efficiency.

Aliphatic Polyesters with White-Light Clusteroluminescence.

Single-molecule white-light emission (SMWLE) has many advantages in practical applications; however, the fabrication of SMWLE from nonconjugated luminescent polymers, namely, clusteroluminogens (CLgens), is still a big challenge. Herein, the first example of linear nonconjugated polyesters with SMWLE is reported. Twenty-four kinds of nonconjugated aliphatic polyesters with tunable clusteroluminescence (CL) colors and efficiency were synthesized by the copolymerization of six epoxides and four anhydrides. Experimental and calculation results prove that, at the primary structure level, the balance of structural flexibility and rigidity via adjusting the side-chain length significantly enhances the efficiency of CL without wavelength change. However, altering the chemical structures of the monomer from succinic anhydride to trans-maleic anhydride (MA), cis-MA, and citraconic anhydride (CA), secondary structures of these polyesters change from helix to straight and folding sheet accompanied by gradually red-shifted CL from 460 to 570 nm due to the increase in through-space n-π* interactions, as demonstrated by the computational and experimental results. Then, pure SMWLE with CIE coordination (0.30, 0.32) based on overlapped short-wavelength and long-wavelength CL is achieved in CA-based polyesters. This work not only provides further insights into the emission mechanism of CL but also provides a new strategy to manipulate the properties of CL by regulating the hierarchical structures of CLgens.

Delineation of the diamine monomers effect on the desalination properties of polyamide thin film composite membranes: Experimental and molecular dynamics simulation

The success of membrane desalination technology hinges on the properties of thin film composite (TFC) membrane that is commonly fabricated by interfacial polymerization (IP) of diamine and acyl chloride. The current study aimed to investigate the impact of the length of the alkyl side chain of the diamine monomers on the desalination performance of the TFC membranes. Four diamines (piperazine (PIP), 1-(2-aminoethyl)piperazine (EAP), 1,4-Bis(3-aminoprpyl)piperazine (DAPP), and m-xylylenediamine (XLN)) were used to fabricate four different TFC membranes with trimesoyl chloride (TMC) as a crosslinker. The merits of the TFC membranes were thoroughly characterized and the PIP was found to be advantageous compared to other diamines with different aliphatic alkyl chain lengths. Molecular dynamics simulations showed that PIP TFC membrane has a tight pore diameter of 1.1 nm and polar carboxylic groups within its pores, which makes it strongly hydrophilic reporting a water contact angle of 28°. The salt rejection (%) of the PIP TFC membrane followed the order: MgSO4 (91%) > Na2SO4 (85%) > Na2CO3 (77%) > NaCl (32%). The increase in feed pressure, temperature or velocity had a positive impact on the permeate flux. However, salt rejection deteriorated as the temperature of the feed increased.

Highly Ordered Supramolecular Assembled Networks Tailored by Bioinspired H-Bonding Confinement for Recyclable Ion-Transport Materials

Highly Ordered Supramolecular Assembled Networks Tailored by Bioinspired H-Bonding Confinement for Recyclable Ion-Transport Materials

The Effects of Charged Amino Acid Side-Chain Length on Diagonal Cross-Strand Interactions between Carboxylate- and Ammonium-Containing Residues in a β-Hairpin.

The β-sheet is one of the common protein secondary structures, and the aberrant aggregation of β-sheets is implicated in various neurodegenerative diseases. Cross-strand interactions are an important determinant of β-sheet stability. Accordingly, both diagonal and lateral cross-strand interactions have been studied. Surprisingly, diagonal cross-strand ion-pairing interactions have yet to be investigated. Herein, we present a systematic study on the effects of charged amino acid side-chain length on a diagonal ion-pairing interaction between carboxylate- and ammonium-containing residues in a β-hairpin. To this end, 2D-NMR was used to investigate the conformation of the peptides. The fraction folded population and the folding free energy were derived from the chemical shift data. The fraction folded population for these peptides with potential diagonal ion pairs was mostly lower compared to the corresponding peptide with a potential lateral ion pair. The diagonal ion-pairing interaction energy was derived using double mutant cycle analysis. The Asp2-Dab9 (Asp: one methylene; Dab: two methylenes) interaction was the most stabilizing (−0.79 ± 0.14 kcal/mol), most likely representing an optimal balance between the entropic penalty to enable the ion-pairing interaction and the number of side-chain conformations that can accommodate the interaction. These results should be useful for designing β-sheet containing molecular entities for various applications.

Effect of Side Chain Length in Polystyrene POM–POMs on Melt Rheology and Solid Mechanical Fatigue

Effect of Side Chain Length in Polystyrene POM–POMs on Melt Rheology and Solid Mechanical Fatigue