Effect Of Monomer Concentration Research Articles

Tröger’s base-derived thin film composite membrane for enhanced nanofiltration performance

Nanofiltration (NF) membrane technology serves as an efficient method for separation and purification, playing a vital role in various industrial fields such as water treatment, food processing, and pharmaceutical manufacturing. However, there are still drawbacks, such as limited flux due to densely crosslinked composite layer and poor stability in solvents. In this study, we report the fabrication of the thin-film composite (TFC) NF membrane using Tröger’s base-derived building block, aiming to manipulate intrinsic pore structures of the as-synthesized ultra-thin composite layer by introducing rigid dihedral units. The interfacial polymerization process is employed to enable the polycondensation of Tröger’s base-based diamine monomer and tri-aldehyde monomer via Schiff base reaction. The effects of monomer concentration, immersion time, interfacial polymerization reaction time, heat treatment time and temperature on the performance of NF membrane were studied. The optimized NF membrane presents a rejection of Methyl blue (MB) above 95.3 % and achieves a high water permeance of 43.4 L·m−2·h−1·bar−1. The water permeance is 2–3 times higher than the reported NF membranes with similar rejection ability. In addition, Tröger’s base-derived TFC NF membrane exhibits excellent long-term stability and good organic solvent tolerance. Considering the high water permeance and separation efficiency, the present membrane has significance in dye removal and separation processes.

A flexible, soft superabsorbent polyester-cotton blended fabric in-situ coated by poly(sodium acrylate-co-acrylic acid)

A novel pre-synthesized polymer is fabricated with sodium polyacrylate and acrylic acid through free radical polymerization. Interestingly, the pre-synthesized polymer is further polymerized on the polyester-cotton fabric in the presence of glycerol as a cross-linking agent forming superabsorbent fabric. The composite functional fabrics is prepared by two steps, namely synthesis and finishing process. Owing to the vital role of the viscosity of pre-polymer for the superabsorbent property, the effect of monomer concentration, temperature, time, dosage of initiator and degree of neutralization on the viscosity of pre-polymer is thoroughly investigated. Besides, the effects of the degree of neutralization and dosage of polymerization solution as well as cross-linking agent on the water absorption of the composite and unfinished polyester-cotton blended fabrics is compared, respectively. After treatment, the water absorption capacity increases from 1 to 323.52 g/g in 1 h, reaching a maximum value of 417.53 g/g after 3.5 h. Besides, the water transportation obeys a Fickian diffusion mechanism. Furthermore, the composite fabric exhibits an optimum water retention capacity of up to 4 h. This speedy and super-water-absorbing material exhibits great potential in practical applications, such as in sanitary articles, wound dressings, and soil moisture.

Deciphering the factors influencing electric field mediated polymerization and depolymerization at the solution–solid interface

Strong and oriented electric fields are known to influence structure as well as reactivity. The strong electric field (EF) between the tip of a scanning tunneling microscope (STM) and graphite has been used to modulate two-dimensional (2D) polymerization of aryl boronic acids where switching the polarity of the substrate bias enabled reversible transition between self-assembled molecular networks of monomers and crystalline 2D polymer (2DP) domains. Here, we untangle the different factors influencing the EF-mediated (de)polymerization of a boroxine-based 2DP on graphite. The influence of the solvent was systematically studied by varying the nature from polar protic to polar aprotic to non-polar. The effect of monomer concentration was also investigated in detail with a special focus on the time-dependence of the transition. Our experimental observations indicate that while the nucleation of 2DP domains is not initiated by the applied electric field, their depolymerization and subsequent desorption, are a consequence of the change in the polarity of the substrate bias within the area scanned by the STM tip. We conclude that the reversible transition is intimately linked to the bias-induced adsorption and desorption of the monomers, which, in turn, could drive changes in the local concentration of the monomers.

Insights on the chlorine resistance of polyester composite nanofiltration membranes

The use of chlorine as a pretreatment of water treatment and desalination processes causes a loss in performance and lifespan of the membranes usually employed in these processes. Polyester (PE) membranes have been proposed as an alternative due to the absence of amidic hydrogen; however, fabricating PE composite membranes with equivalent performance and high tolerance towards chlorine has proven challenging. In this work, we evaluate the effects of monomer concentration and blends, proton scavenger, surfactant concentration, reaction time and temperature on interfacial polymerization (IP) of trimesoyl chloride and resorcinol. Reaction temperature was the most crucial factor to achieve a PE coating film with high crosslinking degree (XD), high divalent rejection and excellent chlorine tolerance. The resorcinol membrane showed a Na2SO4 rejection of >90 % before and after 6000 ppmh-Cl2 at pH 7. XPS analysis showed that chlorination of PE membranes resulted in loss of CC bonds and increase in C–C and C–O bonds. At high crosslinking degrees, the changes caused by chlorine were minimal. Based on the characterization and the performance of the chlorinated membranes, ring chlorination followed by ring hydrolysis is the proposed mechanism for degradation of lower XD membranes.

Influence of monomer concentration on structures of fully condensed polyphenylsilsesquioxanes

Fully condensed polyphenylsilsesquioxanes have been prepared via the hydrolysis and condensation of the same phenyltrimethoxysilane (PTMS) monomer in different concentrations. The effect of monomer concentration on molecular structure of the final products has been thoroughly investigated. Cage structured polyphenylsilsesquioxane (OPS) and ladder-like structured polyphenylsilsesquioxane (L-PPSQ) can be selectively synthesized from the same starting materials at lower and higher initial monomer concentrations. Meanwhile, online infrared detector, React IR TM15 was used to monitor the real time variation of the concentration and characteristic absorption peaks of any intermediate products that may exist. Then, React IR TM15 coupled with 29Si nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC) and matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF-MS) were used to monitor and identify the intermediate species during the reaction. Mechanism studies indicated that the condensation reaction of OPS and L-PPSQ both proceed through a T1 structure dimer, which was formed by the quick hydrolysis of the PTMS monomer. As confirmed by 29Si-NMR, GPC and MALDI-TOF-MS, the synthesis mechanisms of OPS and L-PPSQ during the hydrolysis-condensation reactions were delineated.

Enhancing oil repellency of electron beam‐grafted polyethylene terephthalate fabric with 2‐(perfluorohexyl) ethyl acrylate monomer via pre‐irradiation

AbstractElectron beam (EB)‐induced graft polymerization is advantageous for the surface modification of fabrics. We investigated the effect of monomer concentration and the addition of alkyl groups on the oil repellency of polyethylene terephthalate (PET) fabrics treated with monomers containing fluoroalkyl groups through EB‐induced graft polymerization via pre‐irradiation. We use 2‐(perfluorohexyl) ethyl acrylate (FEA) and stearyl acrylate (SA(C18)) with long alkyl chains as vinyl monomers to induce reaction with radicals generated from EB irradiation. The weight gain and surface morphology of the PET fabrics change with the FEA monomer concentration. The uniformity of the EB‐grafted PET fabric surface is determined at low monomer solution concentrations. Results of X‐ray photoelectron spectroscopy analysis show that adding 0.1 mol/L of FEA monomer to the EB‐grafted PET fabric yields the highest dodecane contact angle of 93.4° and a surface fluorine concentration of 39.8%. The addition of SA(C18) monomer to the FEA monomer decreases the dodecane contact angle by 77.5° and yields a surface fluorine concentration of 19.1%. EB graft polymerization via pre‐irradiation results in a uniformly treated surface, and stable oil repellency is achieved when using solely the FEA monomer at a lower monomer concentration than that used in a similar irradiation method reportedly previously.

Thermal safety and overall kinetics for methyl methacrylate solution polymerization via on-line process analytical technology

Polymethyl methacrylate (PMMA) is widely used, but its polymerization process is highly hazardous and the relevant thermal hazards have not been adequately investigated. Herein, the thermal safety and kinetic mechanisms of methyl methacrylate (MMA) polymerization are explored. The effect of monomer concentration on the exothermic characteristics is first investigated using a reaction calorimeter. The results indicate that the exothermic behavior of this reaction is significantly influenced by the monomer concentration. Meanwhile, a quantitative relationship between the specific enthalpy and monomer concentration is determined. Moreover, overall rate expression is developed by a rapid quantitative method to further elucidate the quantitative dependence of reaction rate on the process conditions. Subsequently, adiabatic experiment is performed to reveal the thermal controllability of this reaction. Finally, risk level is ascertained to propose constructive countermeasures. This work provides guidance for the safe operation of MMA polymerization, and the methodology also furnishes universal solutions for analogous reactions.

Preparation and biotribological properties of PSBMA polyelectrolyte brush on PEEK surface

AbstractPEEK has been widely used in orthopedic implants for three decades. However, poor hydrophilicity and lower tribological properties are the weaknesses of PEEK that need to be optimized in artificial joint applications. Zwitterionic sulfobetaine methacrylate (SBMA) polyelectrolyte brushes are prepared on the PEEK surface by UV irradiation to improve the hydrophilicity and biotribological properties. The three‐factor and three‐level orthogonal experiments are designed to investigate the effects of monomer concentration, irradiation time, and temperature of the grafting quantity of SBMA on the PEEK surface. The composition of the grafted PEEK specimens is characterized by attenuated total reflection Fourier transform infrared spectroscopy (ATR‐FTIR) and X‐ray photoelectron spectroscopy (XPS). Hydrophilicity and biotribological properties are also characterized. Results show that SBMA is successfully grafted onto the PEEK surface by UV‐induced grafting polymerization, and the effects of the three process parameters on the grafting quantity are ranked as concentration > time > temperature. The hydrophilicity and biotribological properties are significantly improved due to the graft of the hydrophilic PSBMA polyelectrolyte brushes, and the improved biotribological can be attributed to the load‐bearing capacity of PSBMA polyelectrolyte brush and the boundary lubrication formed by the adsorption of water molecules.

Self-Repair of Cement Paste with Gas-Sensitive Graft Polymer

Summary To solve the problem of annular gas channeling in natural gas well cementing, isoprene rubber was used as graft matrix material, natural gas absorbing methyl methacrylate and octadecyl acrylate were used as functional monomers, a gas-inspired expansion graft polymer was prepared by graft copolymerization, and a natural gas-triggered self-repair cementing slurry was developed. The structure of gas-sensitive grafted polymer was characterized by Fourier transform infrared (FTIR) and 1H nuclear magnetic resonance (NMR), and the effects of monomer concentration and copolymer feed ratio on equilibrium swelling degree were investigated. For the cement stone (ring) samples with microcracks and microgaps, the gas-triggered repair performance of the system was evaluated by using a self-designed testing instrument. The results show that the gas-sensitive material can increase the gas channeling resistance of fractured cement paste by one to two orders of magnitude. The material system has been applied to 20 deep gas wells in Daqing Field, and the test results show that the system can guarantee the effective sealing of the cement sheath.

Recyclable Cholesteric Phase Liquid Crystal Device for Detecting Storage Temperature Failure.

The planar state of a cholesteric liquid crystal (CLC) often exhibits oily streak defects, which negatively impact the characteristics of precision optics, including transmission and selective reflection. In this paper, we introduced polymerizable monomers into liquid crystals and examined the effects of monomer concentration, polymerization light intensity, and chiral dopant concentration on oily streak defects in CLC. With the proposed method of heating cholesteric liquid crystals to the isotropic phase followed by rapid cooling, the oil streak defects presented in the liquid crystal can be successfully eliminated. Furthermore, a stable focal conic state can be obtained by a slow cooling process. Two stable states with different optical properties can be obtained based on the cholesteric liquid crystal at different cooling rates, which makes it possible to detect whether the stored procedure of temperature-sensitive material is qualified. These findings have widespread applications in devices that require a planar state without oily streak defects and temperature-sensitive detection devices.

Synthesis of nanofiltration membranes with enhanced monovalent and divalent selectivity using β-cyclodextrin, tannic acid and ZIF-8

β-cyclodextrin (β-CD) and tannic acid (TA) together as an organic phase and zeolitic imidazolate framework-8 (ZIF-8) as an additive can be used along with trimesoyl chloride (TMC) as a monomer to synthesize nanofiltration (NF) membranes. Those membranes have better separation performance and provide higher flux. In this study, a new NF membrane was synthesized using them to investigate the effects of monomer concentration, substrate morphology, and reaction temperature on membrane performance. The results showed that when the concentrations of both β-CD and TA were 1 wt%, the membranes had the highest selectivity (2.99) for monovalent and divalent salts. A 10-fold increase in TMC concentration (0.05 to 0.5 wt%) optimized membrane selectivity and flux. When both spongy and cavernous structures were present in the substrate, the membranes could achieve >85 % removal of monovalent and divalent salts. After the introduction of ZIF-8, the roughness of the membrane increased, and the removal rate of monovalent salts decreased significantly, resulting in a salt selectivity of 7.97 and a flux up to 27.81 ± 1.17 L/(m2 h). The growth of ZIF-8 on the membrane surface was assisted by an increase in the reaction temperature.

Kinetics of support-free interfacial polymerization polyamide films by in-situ absorbance spectroscopy

Understanding the kinetics of the interfacial polymerization (IP) reaction is one of the crucial factors in tailoring the characteristics and performance of reverse osmosis (RO) membranes. In this novel study, we report a kinetic investigation of polyamide (PA) film formation and growth by IP reaction between M-phenylenediamine (MPD) and trimesoyl chloride (TMC), in real-time, using the absorbance spectroscopy (AS) method. We investigated the effects of monomer concentrations, as well as that of IP reaction time for support free films, on kinetic behavior and film characteristics. The real-time results showed a significant effect of monomer concentration on the kinetics of reaction especially during the first few seconds of interfacial polymerization. We showed that the increase in thickness of film measured ex situ by transmission electron microscopy (TEM), follows similar trends to the in-situ absorbance with polymerization time, for this formulation. Furthermore, a quasi-linear trend between absorbance and film thickness, for formulations of TMC of 0.2 wt/wt% and MPD concentrations at or above 0.255 wt/wt%, was found, which was not apparent for lower MPD concentrations. This suggests that there may be a critical MPD concentration for a given TMC value that gives a ‘defect-free’ film; below this concentration a continuous (fully densified and defect free) film cannot form. This study confirms that the AS method, provides an opportunity to investigate the kinetics, predict the characteristics (structure) and optimize the IP conditions (monomer concentration ratio) to achieve RO and nanofiltration (NF) membranes with tailored performance.

A Novel Approach for the Development of Low-Cost Polymeric Thin-Film Nanocomposite Membranes for the Biomacromolecule Separation.

The separation of biomacromolecules, mainly proteins, plays a significant role in the pharmaceutical and food industries. Among the membranes' techniques, thin-film nanocomposite nanofiltration membranes are the best choice due to their high energy efficiency, excellent productivity, cost-effective and tuneable properties that have captured the attention of the efficient separation of biomacromolecules, especially from the industrial perspective. The present work directs the efficient separation study of proteins, namely, lysozyme, trypsin, pepsin, bovine serum albumin (BSA), and cephalexin, using a thin-film nanocomposite membrane integrated with Arg-MMT (arginine-montmorillonite) clay nanoparticles. The surface morphology and cross-section images of the TFN membranes were studied using a field emission scanning electron microscope (FE-SEM) and a high-resolution transmission electron microscope (HR-TEM). The thermal stability and hydrophilicity of the membranes were examined using thermogravimetric analysis (TGA) and contact angle, respectively. The surface chemistry of the selective layer has different functional groups that were analyzed using FTIR spectroscopy. The performance of the membranes was studied at different trans-membrane pressures and permeation times. The effect of monomer concentration on the separation performance of the membranes was also studied at different permeation times. The membranes' antibacterial activity was evaluated using the Muller-Hinton disk diffusion method using gram-negative Escherichia coli (E. coli) and gram-positive Staphylococcus aureus (S. aureus) bacteria. The highest rejection was achieved for BSA up to 98.92 ± 1%, and the highest permeation was obtained against lysozyme feed solution up to 26 L m-2 h-1 at 5 bar pressure. The membrane also illustrated excellent rejection of cephalexin antibiotics with a rejection of 98.17 ± 1.75% and a permeation flux of 26.14 L m-2 h-1. The antifouling study performed for the membranes exhibited a flux recovery ratio of 86.48%. The fabricated thin-film nanocomposite membrane demonstrated a good alternative for the separation of biomacromolecules and has the potential to be used in different sectors of industry, especially the pharmaceutical and food industry.

MPD and TMC supply as parameters to describe synthesis-morphology-performance relationships of polyamide thin film composite membranes

This study assesses the influence during interfacial polymerization on polyamide thin film composite (TFC) morphology and performance of varying monomer concentrations and organic phases with widely varying physico-chemical characteristics (interfacial tensions (IFT) with water, viscosity and monomer equilibrium partitioning). These physico-chemical characteristics were used to introduce two new descriptors of the synthesis-structure-performance relationship of polyamide TFC membranes: ‘MPD supply’ and ‘TMC supply’. Three non-ionic solvents (hexane, isopar G and hexyl acetate (HA)) are studied in parallel with three room temperature ILs (RTILs). It is found that well-performing membranes are prepared until one of the monomers is added in excess. The susceptibility of the system to excess of one of the monomers depends on the interplay of MPD and TMC supply, which determines the system-specific monomer concentration range for high salt rejecting membranes. By combining the results of the current study with literature data, qualitative synthesis-performance relationships are proposed. Overall, the tunability of the synthesis−structure−performance relationship of polyamide TFC membranes is shown by tying the effect of monomer concentration and organic phase on membrane performance and narrowing it down to MPD and TMC supply. The insights provided can assist in reducing the overall carbon footprint of RO membrane synthesis and operation.

Graft Polymerization of Stearyl Methacrylate on PET Track-Etched Membranes for Oil-Water Separation.

In this article, results of PET track-etched membranes (PET TeMs) hydrophobized by photo-induced graft polymerization of stearyl methacrylate (SM) inside the pores were presented. The effects of monomer concentration, time of irradiation and the nature of the solvent on the degree of grafting and membrane morphology were investigated. The PET TeMs with pore diameters ranging from 350 nm (pore density of 1 × 108 pore/cm2) to 3.05 µm (pore density of 1 × 106 pore/cm2) were hydrophobized and tested for oil–water separation by using hexadecane–water and chloroform–water emulsions. Studies have shown high separation performance for membranes (up to 1100 mL/m2·s) with large pore diameters while achieving a high degree of purification.

Sydnone-maleimide based cascading double 1,3-dipolar cycloaddition for synthesis of “A(A′) + B3” type hyperbranched polyimide

A new A(A′) + B3 approach to synthesizing hyperbranched polyimides (HBPIs) based on sydnone-maleimide double cycloaddition (SMDC) was investigated. N-phenylsydnone as the latent bifunctional monomer A(A′) exhibited the unique nonequal reactivity in SMDC reaction, and the irreversibly double cycloadduct was the only resultant of SMDC. Therefore, the gelation could be effectively avoided and the degree of branching (DB) was improved. The structures of HBPIs were well characterized by FT-IR, 1H NMR, 13C NMR and GPC. The effects of monomer concentration, feeding modes and molar ratios on the polymerization of HBPIs were investigated. The polymerization based on SMDC could be efficiently proceeded at relative high monomer concentration to afford HBPIs with moderate molecular weight and low polydispersity. Due to the characterics of SMDC, only the HBPIs terminated with maleimde groups could be obtained by the A(A′) + B3 approach, and they could be further modified easily. All the as-synthesized HBPIs exhibited the good solubility and thermal stability.

Influence of monomer concentration on the morphology, contact angle, water uptake, and antibacterial activity of grafted cellulose obtained from peel durian

The objective of the current study is to evaluate and determine the effect of monomer concentration of ClAETA on the grafting copolymerization of oxidized cellulose which isolated from peel durian. Four concentrations of ClAETA were used in this study, e.g., 40, 50, 60, and 70%. Several analyses were performed to determine the material characteristic, e.g., degree of grafting, FT-IR, surface morphology, contact angle, degree of swelling, and antibacterial activity. The result showed, monomer concetration plays a significant role to the physical and surface morphology of DAC-ClAETA. The degree of grafting of ClAETA was found in the range of 15-31%, and at the concentration of 50% the grafted oxidized cellulose has 30.4% of degree of grafting. SEM images showed the pore volume has linear correlation to the monomer concetration, it increased the surface roughness. Also, the contact angle confirmed the hydrophilicity and degree of swelling of grafted oxidized cellulose was increase that linear to ClAETA concentration. DAC-g- ClAETA was found antibacterial active against S. aureus, S. epidermis, and C. albicans than DAC.

Zwitterionic copolymer modified polyethersulphone/sulfonated polysulphone membranes for enhancing dye/salt selective separation

AbstractTwo monomers, positively charged N,N‐dimethylaminoethyl methacrylate (DMAEMA) and negatively charged monomer sodium vinylsulfonate (VSA), were employed to generate a zwitterionic copolymer layer on the surface of PES/SPSf blend membrane via UV‐light grafting. The effect of monomer concentration and irradiation time on the properties of the modified membranes was studied. Results showed that the degree of grafting (DG) accelerated with the increase in monomer concentration and irradiation time. The zeta potential of the zwitterionic membrane was tailored from negative (−21.4 mV) to positive charge (+30.8 mV) by varying the concentration DMAEMA monomer and irradiation time. Optimized membrane fabrication conditions were 15 g L−1 of DMAEMA and 10 min irradiation time (Mc15). The molecular weight cut‐off of Mc15 was calculated to be 40 kDa, while the zeta potential was found to be +8.56 mV (pH = 7). Mc15 showed excellent rejection rates for both positively and negatively charged dyes. In contrast Mc15 maintained low rejection rates for Na2SO4 (<10%) and high dye/salt selective separation performance (retention rates for basic blue 26 and Na2SO4 were 97 and 6.5%) over long continuous operation (50 h). In summary, our study provides tailoring implementation strategies to enhance dye/salt selective separation of tight ultrafiltration membranes.

Direct polycondensation of l-lactic acid in hydrophobic bis(trifluoromethanesulfonyl)imide-anionic ionic liquids: A kinetic study

Ionic liquids (ILs), instead of the classical organic solvents, have shown great improvements in chemical processes. Herein, Water-insoluble alkyl- and benzyl-substituted imidazolium bis(trifluoromethanesulfonyl)imides as non-volatile and thermostable solvents were employed in the direct polycondensation of l-lactic acid (LLA). The effects of monomer concentration, reaction temperature and miscibility between the ILs and poly(l-lactic acid) (PLLA) were comprehensively investigated. Biodegradable PLLA with weight-average molecular weight as high as 132 kDa was synthesized. Compared to melt-polycondensation of LLA, far higher molecular weight could be achieved via the solution polycondensation of LLA in ILs since the viscosity of the polymer melt could be significantly reduced based on the dilution effect of ILs. Polycondensation kinetics of LLA in bulk and in an IL demonstrated that the IL could accelerate the polycondensation of LLA. Influence of lactide, the main by-product, on the polycondensations of LLA was also studied kinetically.

Preparation and Characterization of Interfacially Polymerized Polyamide Membrane for Dye Removal

Interfacial polymerization of polyamide was conducted using hydrophobic and hydrophilic membrane support. The effects of monomer concentration were investigated, and the resulting thin-film composite membranes were tested for their performance in dye removal using different flow configurations. The results showed that a dense polyamide layer was successfully formed on the hydrophilic support, while a polyamide layer with a very loose structure was formed on the hydrophobic support. The polyamide layer became smoother and more hydrophilic as the concentration of trimesoyl chloride was increased, leading to increased permeate flux and reduced dye rejection. The highest sunset yellow rejection of 45.7% with a permeate flux of 4.9 L/m2.h was obtained when the polyamide layer was formed from trimesoyl chloride concentration of 0.05 w/v% (a high amine to acid chloride monomer ratio of 20) and the filtration was in cross-flow configuration.