Intrinsic Viscosity Measurements Research Articles

Effect of Fucoidan on Conformation of Xanthan Gum and Its Tribo-Rheological Properties.

This study sought to explore the rheological and tribological properties of fucoidan-xanthan gum (XG) mixtures at different fucoidan concentrations. A conformational transition of XG from disordered to ordered forms was observed with an increasing fucoidan concentration, as determined by intrinsic viscosity measurements and Fourier transform infrared analysis. All mixtures exhibited non-Newtonian flow behavior with the yield stress. The mixture sample with 0.5% fucoidan displayed higher apparent viscosity at 100 s-1, yield stress, and viscoelastic moduli values than XG alone, suggesting viscoelastic synergism between the two biopolymers. However, these values exhibited a decreasing trend with higher fucoidan concentrations (0.5-2.0%), indicating a nullification of synergism. While XG alone exhibited antithixotropic behavior, fucoidan-XG mixtures showed thixotropic behavior, most pronounced at 1.0% fucoidan. A decreasing trend was observed in the maximum friction coefficient as the fucoidan concentration increased, indicating better lubricant properties. Collectively, our findings may enable widespread adoption and application of fucoidan in various industries.

Charge Mediated Changes to the Intrinsic Viscosity of Biopolymer Systems

A theoretical approach is presented to quantify the effect of ionic strength on the swelling and shrinkage of the hydrodynamic coil size of a generic biopolymer. This was conducted in view of extraction methods that often utilize acids and alkali combinations and, therefore, invariably impact the levels of salt found in commercially available biopolymers. This approach is supplemented by intrinsic viscosity measurements for the purpose of validation across a variety of biopolymer architectures, type of functionalization, as well as the quoted molar mass. By accurately capturing the magnitude of change in the coil size, it is discussed how a biopolymer coil size is far more sensitive to changes in the ionic strength than it is to the molar mass (or contour length) itself. In turn, it is highlighted why the current characterization strategies that make use of weight-averaged molar mass are prone to errors and cannot be used to establish structure—property relationships for biopolymers. As an alternative, the scope of developing an accurate understanding of coil sizes due to changes in the “soft” interactions is proposed, and it is recommended to use the coil size itself to highlight the underlying structure—property relationships.

Removal of acetyl-rich impurities from chitosan using liquefied dimethyl ether

Chitosan, recognized for its excellent biodegradability, biocompatibility, and antibacterial properties, has several potential applications, particularly in the biomedical field. However, its widespread use is hindered by inherent limitations such as low mechanical strength and safety concerns arising from a low degree of deacetylation and the presence of impurities. This study aimed to introduce an innovative purification method for chitosan via liquefied dimethyl ether (DME) extraction. The proposed technique effectively addresses the challenges associated with chitosan by facilitating deacetylation and impurity removal. Liquefied DME is emerging as the extraction solvent of choice owing to its advantages, such as low boiling point, safety, and environmental sustainability. The degree of deacetylation of chitosan was extensively evaluated using thermogravimetric–differential thermal analysis, Fourier transform infrared spectroscopy, X-ray diffraction, intrinsic viscosity measurements, solid-state nuclear magnetic resonance spectroscopy and X-ray photoelectron spectroscopy, and elemental analysis. The solubility of chitosan in liquefied DME was investigated using Hansen solubility parameters. This study contributes to the improvement of the safety profile of chitosan, thereby expanding its potential applications in various fields. The use of liquefied DME as an extraction solvent proved to be efficient in addressing the existing challenges and is consistent with the principles of safety and environmental sustainability.

Acrylamide Cross‐Linked Psyllium Polysaccharide with Improved Flocculation Performance for the Removal of Microplastics from Water

AbstractThis article presents a novel material of acrylamide (AM) cross‐linked psyllium polysaccharides (PLP) derivative, PLP‐AM, which can be used as an effective polymeric flocculant for the removal of microplastics (MP) from water. PLP‐AM was produced by radical polymerization of PLP and AM using microwave irradiation instead of conventional radical initiators. The characterization of PLP‐AM was carried out by FT‐IR spectroscopy, elemental analysis, intrinsic viscosity measurement and thermogravimetric analysis (TG). Polystyrene (PS), polyethylene terephthalate (PET) and polyvinyl chloride (PVC) were utilized to examine the flocculation performance of PLP‐AM. The optimum flocculation conditions were obtained by the comprehensive exploration of flocculant concentration, solution pH and temperature. In a solution with a pH 6 at 30 °C, the maximum removal percentages of PS and PVC by 60 mg/L of PLP‐AM were 92.55 % and 94.31 %, respectively, while 93.85 % of the maximum removal of PET percentage could be obtained by 80 mg/L of PLP‐AM. The results of zeta potential measurement revealed that there was adsorption electric neutralization between MP and PLP‐AM besides the adsorption bridging mechanism. These results suggest that PLP‐AM may bring an inspiration for the development of polymer flocculant to remove MP from water.

The effect of anionicity on mechanical degradation of polyacrylamide-type flocculants

The effect of ultrasonication, screening and shearing on five polyacrylamide-based flocculants of similar molecular weight but different degrees of anionicity (DA) was studied through measurement of intrinsic viscosity ([η]) and size exclusion chromatography (SEC) to investigate the influence of DA on the degradation of polymers. It was found that screening did not affect the [η] of the polymers while the effect of shearing was most noticeable in the cases of non-ionic and most anionic flocculants. Furthermore, ultrasonication caused a sharp decrease in the [η] which indicates a rapid degradation of the polymers. The results suggested that degradation of the polymers as a result of ultrasonication was irreversible since after a 24 hour resting period, the [η] did not recover to the values obtained for the untreated samples. Using a ratio of the [η] in distilled water to that in a dilute electrolyte as a measure of the relative flexibility of the flocculant chain, it was shown that the most flexible flocculants resisted ultrasonication and degradation better than those with rigid chains. Results from SEC confirmed that the degradation of polymers due to ultrasonication was a result of breakage of the polymer chains into sections of lower molecular weights.

Improved thermoelectric properties by copolymerization of conducting with insulating monomers on carbon nanotubes

In the present work, development of carbon nanotube (CNT)/poly(conducting-co-insulating monomer) structures was proposed to improve the thermoelectric (TE) performance in CNT/polyaniline (PANI) composites. To check the validity of this idea, we prepared multiwalled carbon nanotube (MWNT)/poly(aniline-co-acrylonitrile) composites by in-situ inverted emulsion copolymerization, and applied secondary doping with camphorsulfonic acid in m-cresol medium prior to the investigation of TE properties. The samples were characterized by FT-IR, UV–Vis, 1H NMR, DSC, GPC, CHNS elemental analysis, intrinsic viscosity, SEM, XRD, electrical resistance, Seebeck coefficient, thickness, and Hall measurements. We report that nitrile groups were hydrolyzed during the polymerization reactions to provide a polymer structure exhibiting aniline, acrylamide, acrylic acid, and glutarimide groups. Further, the poly(aniline-co-acrylonitrile) that prepared in the present work were random copolymers. Importantly, we found that 30 % MWNT/70 % poly(90ANI-co-10AN) composite exhibited a 63 % higher power factor (PF) of 5.48 μW/mK2 (σ: 225 S/cm, S: 15.6 μV/K) at 35 °C than that of 30 % MWNT/70 % PANI, which exhibited a PF of about 3.37 μW/mK2 (σ: 238 S/cm, S: 11.9 μV/K). This was ascribed to the decrease of carrier concentration together with the increase of carrier mobility in the 30 % MWNT/70 % poly(90ANI-co-10AN) composite as compared to the 30 % MWNT/70 % PANI.

Optimization and degradation studies of cellulose transesterification to palmitate esters in superbase ionic liquid

Cellulose palmitates (CPs) were synthesized with varying degrees of substitution (DS) via a catalyst-free, homogeneous transesterification of cellulose in a novel superbase ionic liquid (SB-IL) system, specifically 5-methyl-1,5,7-triaza-bicyclo[4.3.0]non-6-enium acetate [mTBNH][OAc], combined with dimethyl sulfoxide (DMSO) as a co-solvent, using vinyl palmitate as the acylating agent. We examined the influence of reaction temperature, reaction time, and the molar ratio of vinyl palmitate to anhydroglucose unit (AGU) on the DS, which ranged from 0.5 to 2.3 under the given conditions. Notably, the reaction order of the three hydroxy groups was C6–OH > C2–OH > C3–OH. To elucidate the chemical structure of CPs and confirm the transesterification process, various spectroscopic techniques including 1H nuclear magnetic resonance (NMR), 13C NMR, heteronuclear single quantum correlation (HSQC), and solid-state NMR were employed. Higher reaction temperatures and extended reaction times led to a decrease in the DS of CPs, potentially due to the degradation of some of the involved chemicals during the transesterification process. We also investigated the stability of the pure ionic liquid (IL) and the IL + DMSO solvent system at elevated temperatures by heating them at 100 °C for 5 h, confirming their chemical integrity through 1H NMR analysis. Additionally, we assessed the compatibility between the solvent system and cellulose by subjecting a mixture of cellulose and the solvent system to 100 °C for 5 h. To compare the structures of untreated cellulose and regenerated cellulose, Fourier transform infrared (FT-IR) spectroscopy was employed. Furthermore, we determined the molar mass of both untreated cellulose and regenerated cellulose, as well as CPs synthesized at higher reaction temperatures and longer durations, using intrinsic viscosity measurements. Lastly, we examined the solubility properties of CPs.

Synthesis of Poly(ethylene furanoate) Based Nanocomposites by In Situ Polymerization with Enhanced Antibacterial Properties for Food Packaging Applications.

Poly(ethylene 2,5-furandicarboxylate) (PEF)-based nanocomposites containing Ce-bioglass, ZnO, and ZrO2 nanoparticles were synthesized via in situ polymerization, targeting food packaging applications. The nanocomposites were thoroughly characterized, combining a range of techniques. The successful polymerization was confirmed using attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy, and the molecular weight values were determined indirectly by applying intrinsic viscosity measurements. The nanocomposites' structure was investigated by depth profiling using time-of-flight secondary ion mass spectrometry (ToF-SIMS), while color measurements showed a low-to-moderate increase in the color concentration of all the nanocomposites compared to neat PEF. The thermal properties and crystallinity behavior of the synthesized materials were also examined. The neat PEF and PEF-based nanocomposites show a crystalline fraction of 0-5%, and annealed samples of both PEF and PEF-based nanocomposites exhibit a crystallinity above 20%. Furthermore, scanning electron microscopy (SEM) micrographs revealed that active agent nanoparticles are well dispersed in the PEF matrix. Contact angle measurements showed that incorporating nanoparticles into the PEF matrix significantly reduces the wetting angle due to increased roughness and introduction of the polar -OH groups. Antimicrobial studies indicated a significant increase in inhibition of bacterial strains of about 9-22% for Gram-positive bacterial strains and 5-16% for Gram-negative bacterial strains in PEF nanocomposite films, respectively. Finally, nanoindentation tests showed that the ZnO-based nanocomposite exhibits improved hardness and elastic modulus values compared to neat PEF.

Novel method for the prediction of distribution and elution characteristic of several drugs in cellulose diacetate-water system: Interaction between mixed solvent and cellulose diacetate

Drug-loaded cellulose diacetate (CDA) membranes were prepared by dissolving cellulose diacetate in a mixed solvent of acetone and ethanol, adding the drug to it, pouring it on a glass plate and evaporating the solvent. In this study, it was prepared CDA membranes varying composition of the mixed solvent (the mass ratio of acetone (ACE) to ethanol (EtOH)) and investigated their microstructure and performance.The release properties of drugs in drug-loaded CDA membranes were examined in correlation with the composition of the mixed solvent and a method to be able to predict the release properties of drugs was proposed. Penicillin G potassium, streptomycin sulfate and ampicillin were used as drugs. The microstructure of the membranes was determined using SEM analysis and the release properties of drugs were measured using spectrofluorophotometer. It was shown that the composition of the mixed solvent can have a significant effect on the overall performance of CDA membrane. The intrinsic viscosity measurements and solubility parameter analysis proved that the intrinsic viscosity of CDA in polymer solutions with mixed solvents and the solubility parameter difference (Δδ) between mixed solvents and CDA were relative with the release properties of drugs. The release rates of drugs from the membrane related to △δ directly and the intrinsic viscosity inversely. Therefore, the release rates of drugs from CDA membrane can be controlled by changing the composition of the solvent used for the preparation of the polymer membrane.

Ring Expansion Alkyne Metathesis Polymerization.

The synthesis, characterization, and preliminary activity of an unprecedented tethered alkylidyne tungsten complex for ring expansion alkyne metathesis polymerization (REAMP) are reported. The tethered alkylidyne 7 is generated rapidly by combining alkylidyne W(CtBu)(CH2tBu)(O-2,6-i-Pr2C6H3)2 (6) with 1 equiv of an yne-ol proligand (5). Characterized by NMR studies and nuclear Overhauser effect spectroscopy, complex 7 is a dimer. Each metal center contains a tungsten-carbon triple bond tethered to the metal center via an alkoxide ligand. The polymerization of the strained cycloalkyne 3,8-didodecyloxy-5,6-dihydro-11,12-didehydrodibenzo[a,e]-[8]annulene, 8, to generate cyclic polymers was demonstrated. Size exclusion chromatography (SEC) and intrinsic viscosity (η) measurements confirm the polymer's cyclic topology.

Electrooxidation of Toxic Sulfite Material Using Ni-Ru-Based Heterometallo Supramolecular Polymer as Electrocatalyst: Synthesis and Kinetics Study

Considering the adverse effect of sulfite (SO3 2−), an effective Ni(II)- and Ru(II)-based heterometallic-supramolecular polymer (HMSMP) (polyNiRu) has been synthesized. PolyNiRu was characterized by Field-emission scanning electron microscopy (FE-SEM), and Fourier transmission infrared (FT-IR) spectroscopy. The formation of HMSMP was confirmed via UV–Vis spectroscopy. The molecular weight of polyNiRu (4.77 × 105 Da) was measured through intrinsic viscosity measurement following Mark-Houwink equation. The electrochemical behavior of polyNiRu modified glassy carbon electrode (polyNiRu_GCE) was investigated via CV and DPV. Furthermore, we have investigated the Tafel plot for this heterogeneous electrochemical system to calculate the number of transferred electrons during redox reactions. The limit of detection was found as 0.25 μM with a wide linear dynamic range of 10 to 600 μM. A probable surface mechanism has been studied toward SO3 2− oxidation at the interface of polyNiRu_GCE. Using the Butler-Volmer equation, the heterogeneous kinetic rate transfer constant and charge transfer coefficient were found as 1.02 × 10−6 cm2 s−1 and 0.68 respectively. These obtained parameters were further evaluated by simulated CV, which agreed with the experimental value. Excellent recovery with lower relative standard deviation (RSD) and high stability for 4000 s in analytic solution confirmed the reliability of using this polyNiRu_GCE in the practical assessment.

Synthesis, characterization, and swelling behavior of a poly(acrylamide‐co‐acrylic acid) copolymer: Application to water retention in two sandy agricultural soils in sub‐Saharan region

AbstractThe application of copolymer hydrogels based on acrylamide (AAm) and acrylic acid (AA) in sub‐Saharan soils can increase the quantity of water retained by the soil and improve plant establishment and growth. The aim of this work was to synthesize and characterize a copolymer based on acrylamide and acrylic acid and to evaluate its swelling capacity with different physicochemical parameters. This study also aimed to investigate the effect of metallic cations on the swelling capacity of the copolymer and to assess the improvement in water retention in sandy soils. The copolymer material was prepared by free‐radical polymerization in aqueous solution at a temperature of 60°C and characterized by Fourier transform infrared (FTIR) and x‐ray diffraction (XRD), and its average molecular weight was estimated from intrinsic viscosity measurements. The swelling capacity was evaluated with different physicochemical parameters, and the effect of metallic cations on the swelling capacity was investigated. Water retention in two sandy soils was also evaluated. The copolymer material containing 50% AAm and 50% AA can retain more than 8100% of water. The swelling ratio increased with increasing temperature, with a maximum swelling ratio at 65°C. The presence of metallic cations reduced the maximum swelling ratio of the copolymer material as the cation concentration increased. The copolymer material at 1% in a composition with the soil showed an improvement in the water retention of 12.2% and 7.9% for soil A and 7.9% for soil B. Soil air volume is improved by 19% for both soils. This study shows that the copolymer material has a high swelling ratio and can improve water retention in sandy soils. The copolymer can be used in agriculture to protect and improve plant growth and yield.Highlights Synthesis and characterization of a copolymer based on acrylamide and acrylic acid. Evaluating the swelling capacity with different physicochemical parameters. The application of this copolymer in sub‐Saharan soils increases the quantity of water retained. The copolymer is prepared by polymerization in aqueous solution and characterized by FTIR and XRD. This study shows that the copolymer has a high swelling ratio and improves water retention.

Electrochemical Detection of Sulfite Using Ni-Ru-Based Heterometallo-Supramolecular Polymer

We have fabricated a Ni (II)-Ru(II)-based heterometallo-supramolecular polymer (HMSMP)-modified glassy carbon electrode for the selective and sensitive electrochemical detection of sulfite (SO3 2-). The modified electrode (polyNiRu/GCE) was characterized by using scanning electron microscopy (SEM) and fourier transmission infrared (FT-IR) spectroscopy. Molecular weight of synthesized polymer (4.77 × 105 Da) was measured through intrinsic viscosity measurement following Mark-Houwink equation. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to investigate the electrochemical behavior of the modified electrode. The modified electrode showed high sensitivity of 0.06 µAµM-1cm-2 for SO3 2-. The detection limit (S/N = 3) for SO3 2- was 0.97 µM with a linear range of 10 to 1000 µM. The developed sensor was successfully examined for real sample analysis with tap water. Excellent recovery with lower relative standard deviation (RSD) and high stability for 4000s in analytic solution confirmed the reliability of using this polyNiRu/GCE in practical assessment.

Structure and Conformation of Hydroxypropylmethyl Cellulose with a Wide Range of Molar Masses in Aqueous Solution─Effects of Hydroxypropyl Group Addition.

The structure of hydroxypropylmethyl cellulose (HpMC) samples with a wide range of weight average molar masses (Mw) from 23 to 5000 kg mol-1, a controlled degree of substitution (DS) of 1.9 by methyl groups, and a molar substitution number (MS) of 0.25 by hydroxypropyl groups dissolved in aqueous solution was examined using static light scattering (SLS), dynamic light scattering (DLS), small-to-wide angle neutron scattering (S-WANS) techniques, and intrinsic viscosity ([η]) measurements. The determined Mw and the radius of gyration (Rg) showed the relationships Rg ∝ Mw1.0 and [η] ∝ Mw1.7 in a range of Mw < 100 kg mol-1, similar to rigid rod molecules in solution. However, exponents in the relationships decreased gradually with increasing Mw and reached ∼0.5 in a high Mw region, which is a typical value of flexible chain molecules for both Rg and [η]. These observations suggest that the HpMC samples behave as semiflexible rods with a certain persistence length (lp). The ratios of the hydrodynamic radius via DLS measurements to Rg also supported semiflexible rod behavior. Particle form factors and the average lengths (L) resulting from SLS and S-WANS experiments are well described with rigid rod particles in the range of Mw < 100 kg mol-1 and semiflexible rods with lp ∼ 100 nm in Mw > 100 kg mol-1. Because the average contour length (lc) calculated from Mw is approximately twice as long as L in the Mw range < 100 kg mol-1, the formed HpMC particles possess a folded hairpin-like elongated rigid rod structure. However, the lc/L value increases gradually in the range Mw > 200 kg mol-1, where the formed HpMC particles behave as semiflexible rods. The formed particle structure was substantially different from that found in methyl cellulose samples with a similar DS value, which showed rod-like behavior over a wide Mw range. The addition of hydroxypropyl groups only at MS = 0.25 effectively changed the formed particle structure.

Influence of the Type of Hydrolysis on the Intrinsic Viscosity of Lithraea Molleoides Fruit Gum

Lithraea Molleoides fruit Gum (LMFG) is obtained from the total hydrolysis of the fruit. The hydrolysis used are three, thermal (LMFG-T), basic (LMFG-B) and acid (LMFG-A). The aim of hydrolysis is bond breaking and de-esterification of polysaccharide, with the consequent increase in solubility and decrease in molecular weight. Intrinsic viscosity measurement is standard for polymers and biopolymers, as well as being inexpensive. Through intrinsic viscosity, in addition, the hydrodynamic radius, molecular weight, shape factor, etc. can be determined. The objective of this work is to be able to evaluate the different hydrolysis through intrinsic viscosity measurements and, in turn, to study the performance of each one of them.

Fabrication, Characterization and Toxicity Evaluation Chemically Cross Linked Polymeric Material: A Proof of Concept

Background: Natural mucilage is a highly beneficial biodegradable polymeric material. Natural mucilage is non-toxic, biodegradable and easily available.&#x0D; Aim: The current study is required to determine the properties of a basil seed mucilage-based polymeric network and its toxicity.&#x0D; Method: By using potassium persulfate (KPS) as an initiator, microwave-assisted synthesis, a green approach was used to produce a graft copolymer of a polymeric blend of Basil seed mucilage (BSM) and acrylamide (AM). Variable amounts of AM and KPS were used to optimize the best grade based on the highest percentage of grafting efficiency, and the results were investigated using intrinsic viscosity measurement, Fourier Transformation infrared spectroscopy (FTIR), DSC, H-NMR spectra, and X-ray diffraction. The degree of swelling is determined by the concentration of mucilage, monomer, and the density of crosslinking in the polymeric network. &#x0D; Result: The microwave irradiation process with potassium persulfate as the redox initiator is a visible, green, and cost-effective method. The BSM-4 batch showed 464% grafting and 107.23 % grafting efficiency. FTIR, DSC, H-NMR, and XRD analysis showed results about completing the grafting process and changes in functional groups. The BSM-4 batch proved that the basil seed mucilage polymeric network is safe for oral drug delivery of BCS class II and IV drugs. The findings of the toxicity study indicate that the developed polymeric network is safe and non-toxic, and it may eventually prove to be a superior option for many established and cutting-edge drug delivery methods when administering drugs orally.&#x0D; Conclusion: In conclusion, the Basil seed mucilage-based polymeric network will encourage long-term delivery of any BCS Class II or IV drug, and acute toxicity testing proved that the mucilage-based network is secure for oral drug delivery.

Liquid-gaseous phase pyrolysis polycondensation of oligosilanes to polycarbosilane: Influence of process variables on molecular and structural characteristics

Pyrolysis polycondensation of polysilane has been executed at different temperatures, pressures under catalyst/ no catalyst conditions in an autoclave reactor. Progress of polymerization was followed as a function of several process parameters such as temperature, pressure, intrinsic viscosity, average molecular weight and catalyst. Process analysis revealed that temperature and pressure had significant influence on the structure and properties of polycarbosilane. Gel permeation chromatographic data and intrinsic viscosity measurements confirmed the formation of polycarbosilane with average molecular weight up to 6300 Da. Average molecular weight, conversion and yield increased with use of catalyst. FT-IR and 29Si NMR established that structural formation and bonding network during the silane to carbosilane transformation as a function of process conditions.

Influence of Cross-Linking and Crystalline Morphology on the Shape-Memory Properties of PET/PEN/PCL Copolyesters Using Trimesic Acid and Glycerol.

PCL-based biodegradable shape-memory polymers (SMPs) are limited in strength, which restricts their practical applications. In this study, a series of novel SMPs, composed of poly(ethylene terephthalate) (PET), poly(ethylene naphthalate) (PEN), and poly(ε-caprolactone) (PCL), were synthesized and cross-linked using planar (benzene-1,3,5-tricarboxylic acid, BTC) or non-planar (glycerol, GC) cross-linkers via the one-pot method. The influence of different kinds of cross-linkers and hard segments of copolyesters on the thermal properties, crystallization behavior, mechanical properties, shape-memory performance, and degradability was investigated by FT-IR, 1H-NMR, DSC, DMA, TGA, XRD, tensile test, intrinsic viscosity measurement, and in vitro enzymatic degradation test. The results indicate that the tensile strength of the copolyester can be significantly improved from 27.8 to 53.2 MPa by partially replacing PET with PEN while maintaining its shape-memory characteristics. Moreover, a small amount of cross-linking modification leads to higher temperature sensitivity, improved shape recovery rate at third round (Rr(3) = 99.1%), and biodegradability in the cross-linked PET/PEN/PCL shape-memory polymers. By changing the crystallization morphology and cross-linking forms of the material, we have developed a shape-memory polymer with both high strength and a high shape recovery rate, which provides a new strategy for the development of shape-memory materials.

Challenging the Kauzmann paradox using an ultra-stable perfluoropolymer glass with a fictive temperature below the dynamic VFT temperature

Ultra-stable fluoropolymer glasses were created using vacuum pyrolysis deposition that show large fictive temperature Tf reductions relative to the glass transition temperature Tg of the rejuvenated material. Tf was also found to be 11.4 K below the dynamic VFT temperature TVFT. Glass films with various thickness (200–1150 nm) were deposited onto different temperature substrates. Glassy films were characterized using rapid-chip calorimetry, Fourier-transform infrared spectroscopy and intrinsic viscosity measurements. Large enthalpy overshoots were observed upon heating and a Tf reduction of 62.6 K relative to the Tg of 348 K was observed. This reduction exceeds values reported for a 20-million-year-old amber and another amorphous fluoropolymer and is below the putative Kauzmann temperature TK for the material as related to TVFT. These results challenge the importance of the Kauzmann paradox in glass-formation and illustrates a powerful method for the exploration of material dynamics deep in the glassy state (Tf < T < Tg).

Fe(II)-Based Metallo-Supramolecular Polymer Film for Electrochemical Detection of Nitrite: Studies of Kinetics and Reaction Mechanisms

Here, a monometallic supramolecular polymer (SMP) was synthesized for the fabrication of an electrochemical nitrite sensor, and a mechanism for nitrite detection was proposed based on the experimental findings. The SMP (polyFe) was synthesized using a symmetrical ligand containing terpyridine moieties [4′,4′′′′-(1,4- Phenylene) bis(2,2′:6′,2′′-terpyridine)] and ferrous acetate. Various analytical methods, such as ultraviolet/visible (UV/Vis) titration, field-emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and energy dispersive X-ray spectroscopy (EDS), were used to characterize polyFe. The molecular weight of polyFe was calculated from the intrinsic viscosity measurement using the Mark-Houwink-Sakurada equation. The electrochemical behavior of the fabricated sensor was investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The variation in scan rate from CV was used to investigate the kinetics of nitrite oxidation. A possible reaction mechanism was proposed based on the kinetic studies. The proposed sensor showed a good linear range of 2.49 μM to 1.23 mM and a limit of detection of 0.17 μM. Stability, interference, and reproducibility of the proposed sensor were also investigated. The CV technique was used to demonstrate the applicability of the nitrite sensor for real sample analysis. A satisfactory recovery with a low relative standard deviation was achieved.