Changes In Molecular Mobility Research Articles

Change of network structure in agarose solution during gelation studied by multiple particle tracking and NMR measurements

The gelation mechanism of agarose solution on cooling has been successfully elucidated by measurements from macroscopic to microscopic scales using a dynamic rheometer, the multiple particle tracking with two different diameters and the pulsed-field-gradient stimulated echo (PGSTE) 1H NMR. The dynamic rheometer detected the gradual increase of G’ in the temperature range from 55 to 40 °C before the steep increase at the gelation temperature. The time-averaged mean square displacement (msd) obtained by multiple particle tracking for particles with diameter of 270 nm and 1000 nm revealed the generation of micro domains with the network structure obstructing particle diffusion. Further, the NMR measurements gave detailed information about the change of molecular mobility for agarose chains during the formation of the micro domains and the macroscopic overall network structure. These results suggest a gelation mechanism and gel network structure including the formation of micro domains in the temperature range from 55 to 40 °C and the connection among the micro domains by agarose aggregates to form the overall network structure at the gelation temperature.

Influence of Air Humidity Level on the Structure and Mechanical Properties of Thermoplastic Starch-Montmorillonite Nanocomposite during Storage.

Thermoplastic starch (TPS) consisting of corn starch and glycerol as a plasticizer, and TPS-montmorillonite (MMT) nanocomposite were stored at room temperature in the air with relative humidities (RH) of 11, 55 and 85% for seven weeks. Mechanical testing and dynamic mechanical thermal analysis (DMTA) were performed to detect changes in their mechanical properties. Solid-state NMR spectroscopy monitoring the changes in molecular mobility in the samples provided an insight into relations between mechanical properties and local structure. The results of mechanical testing indicated that the addition of MMT results in the increase in the tensile strength and Young's modulus while elongation at break decreased, indicating the reinforcing effect of MMT. DMTA experiments revealed a decrease in glass transition temperature of starch-rich phase below room temperature for samples stored at higher RH (55 and 85%). This indicates that absorbed water molecules had additional plasticizing effect on starch resulting in higher mobility of starch chain segments. Recrystallization in these samples was deduced from the shape of cross-polarization magic-angle spinning 13C NMR spectra. The shape of broad-line 1H NMR spectra reflected changes in molecular mobility in the studied samples during seven weeks of storage and revealed that a high amount of water molecules impacts the starch intermolecular hydrogen bond density.

Changes of molecular mobility of ascorbyl palmitate and α-tocopherol by phospholipid and their effects on antioxidant properties in bulk oil

Molecular mobility of ascorbyl palmitate and α-tocopherol in the presence of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) were determined by NMR relaxation technique. Synergistic effects of DOPC on the antioxidative capacities of ascorbyl palmitate were evaluated in DPPH radical scavenging assay and bulk oil matrix. NMR relaxation technique can provide information on the mobility of protons. Molecular mobility of two protons in hydroxyl group of ascorbyl palmitate decreased by 85 and 78% in the presence of DOPC compared to those without DOPC. However, proton mobility of α-tocopherol increased by 41% when DOPC was present. DOPC significantly enhanced the DPPH reactivity in medium chain triacylglycerol, while this effect was not observed in α-tocopherol. Mixture of ascorbyl palmitate with DOPC showed synergistic antioxidant properties in corn oil at 60 °C. DOPC may make protons of ascorbyl palmitate in more rigid state, which can enhance hydrogen donating ability and antioxidant properties of ascorbyl palmitate in bulk oils.

Changes in molecular mobility of sorbitol plasticized starch during aging

AbstractThermoplastic corn starch with 0.4 parts by weight of sorbitol plasticizer was studied using dynamic‐mechanical thermal analysis (DMTA) and hydrogen nuclear magnetic resonance (1H NMR) to assess the changes in molecular mobility during a period of 26 weeks of storage. Motional heterogeneity of this thermoplastic starch (TPS) was found even after a short aging time by means of DMTA. Besides the glass transition processes in starch‐rich and plasticizer‐rich domains, other relaxation processes appear in TPS samples aged for a longer time. Sorbitol release and/or some moisture uptake was observed in 1H NMR spectra of long‐aged samples. After the whole monitored aging period, sample surfaces were covered with white powder due to sorbitol leakage from the TPS structure.

Effect of moisture uptake on the texture of dried laver Porphyra. (Nori) studied by mechanical characterization and NMR measurements

Mechanical property measurements, 1H T2 measurement by low-field (LF) NMR and 13C T1 measurement by high-resolution cross polarization/magic angle spinning (CP/MAS) solid-state NMR were carried out to evaluate the structural changes of Nori upon moisture uptake. The texture of dry Nori changed to be tough and then soft upon moisture uptake. The increase of 1H T2 and decrease of 13C T1 were observed with an increase of moisture content indicating the increase of the molecular mobility of Nori components. The results of the LF-NMR suggested that the increase of mobility of the inert protons in rigid components is more dominated than that of the labile protons in soft components when Nori becomes the soggy state, whereas the mobility of the soft part increases more by moisture uptake when Nori becomes the wet state. The changes of molecular mobility of each main component (proteins and porphyran) were well depicted by the 13C T1 measurement, which represented the hydration of porphyran and proteins in the pulps and binder part. The change of mechanical properties of Nori was successfully elucidated with the NMR relaxation measurements.

A multilevel investigation supported by multivariate analysis for tomato product formulation

Industrial processing of tomato includes its cutting and mincing, thermal treatments, and the addition of ingredients, which might induce changes in physicochemical properties of the final products. In this frame, the impact of texturing/thickening [xanthan gum (X) or potato fiber (F)] on the macroscopic, mesoscopic and molecular properties of tomato double concentrate (TDC) was investigated to determine if F can efficiently substitute X, in association with small solutes (sugar and salt) and thermal treatment (cold and hot). At a macroscopic level, multivariate statistics (MANOVA) underlined that color change (ΔE) was increased by X and F addition contrary to heating and the addition of salt and sugar. MANOVA revealed that texture was greatly enhanced through the use of F over X. 1H NMR molecular mobility changes were more controlled by texturing agents (F and X) than thermal treatment and small solutes. Particularly F increased the more rigid population indicating stronger interaction with water molecules resulting in shear-thinning flow. However, adding X contributed into the increase of the dynamic and mobile populations. Therefore, F can be a valid “clean label” substitute of X in modulating tomato products properties.

Real time monitoring by time-domain NMR of ring opening metathesis copolymerization of norbornene-based red palm olein monomer with norbornene

Changes in molecular mobility throughout the metathesis copolymerization of a norbornene functionalized with a palm olein monomer and a pure norbornene were monitored in situ by time-domain 1H NMR, using a ruthenium catalyst. Reaction progress to produce branched palm oil-based copolymers was studied as a function of the amounts of monomers and catalyst. Transverse relaxation rates were determined from CPMG experiments and the results were in accordance with the reactivity ratios, which indicated production of gradient copolymers. Properties of the resulting material observed through TD-NMR measurements of the isolated copolymers corroborated the type of the used monomers. TD-NMR demonstrated to be a useful tool for learning copolymerization reactions, particularly in ROMP, for the first time.

Molecular mobility changes after high-temperature, short-time pasteurization: An extended time-domain nuclear magnetic resonance screening of ewe milk

This study presents an extensive investigation on the effect of pasteurization on raw whole ewe milk. Milk samples have been analyzed, throughout lactation (from February to July), by time-domain nuclear magnetic resonance (TD-NMR), collecting the characteristic TD-NMR relaxation parameters, proton longitudinal and transverse relaxation times (1H T1 and T2). Collected data aim at integrating previous NMR works, mainly focusing on dairy model systems (casein and whey proteins solutions and gels, reconstituted skim milk) and cheese, with specific reference to the effect of heat treatments. Whole ewe milk, from a single flock (Sarda sheep breed), was daily analyzed both as untreated (raw) and heat treated with a laboratory-scaled high-temperature, short-time treatment (72°C for 15 and 20 s). Moreover, molecular dynamics in milk were investigated by TD-NMR in different periods of lactation for the first time. As a consequence of high-temperature short-time treatment, 1H T1 and T2 consistently shifted to lower values with respect to raw counterparts. Statistical analysis indicated a significant decrease of T2 in treated samples, to an extent dependent on the heat treatment duration. A subset of dedicated experiments demonstrated that the observed T2 shift is largely ascribable to protein molecular rearrangements and, to a lesser extent, to the interaction of fat globules with proteins or other nonfat components (or both). In light of the crucial importance of detecting the application of a heat treatment to milk, the results reported here suggest TD-NMR relaxation parameters were able to describe heat-induced changes in molecular dynamics and interactions of milk components in a water-rich environment. The use of TD-NMR can be considered a potential suitable technique for quality control and assurance practices in the dairy industry. Upon statistical validation of methods, the application of TD-NMR in the dairy industry would take advantage of its low cost, reliability, and robustness.

Correlative analysis between solid-state NMR and morphology for blends of poly(lactic acid) and poly(butylene adipate-co-butylene terephthalate)

Morphological changes in polymer blending process were investigated using integrated analyses by solid-state NMR and magnetic relaxation. The study examined previous reported mechanical properties of polymer blends incorporating poly(lactic acid) (PLA) and poly(butylene adipate-co-butylene terephthalate) (PBAT) over a range of compositions, along with a crosslinking reagent. The X-ray diffraction (XRD) and the differential scanning calorimeter (DSC) results showed that the crystallinity of PLA decreased with increasing the PBAT content. According to the integrated analysis data and imaging by micro-focus X-ray computed tomography (CT), polymer tensile properties were dominated by interfacial affinity between the molecular mobilities of PLA and PBAT; depending on the blending ratio, the polymer morphology changed from a discontinuous “sea-island” form to a bicontinuous morphology. Addition of a crosslinking reagent was observed via X-ray CT to homogenize the PLA and PBAT blend at the micron length scale, even though both polymers were still heterogeneous at the nanoscale as elucidated by NMR analysis. As well as the morphological change in micro scale, the molecular mobility changes of the total polymer blend system, which could be evaluated by the integrated solid-state NMR analyses, brought about greater elongation at the break point in dynamic tensile testing.

The Use of Zinc Oxide Nanoparticles in Eva to Obtain Food Packing Films

The increasing demand for new packages with increased shelf life properties has stimulated the increase of research in the active packaging sector. The use of antimicrobial agents requires an in-depth study of their properties to avoid loss of efficiency of the polymer processing. In this context, the objective of this work was to evaluate the preparation of an 18% ethylene vinyl acetate copolymer (EVA) nanocomposite and zinc oxide (ZnO) as microbicidal nanoparticle, prepared in a monosulfon extruder. The nanoparticle was modified with octadecylamine and EVA 18 nanocomposite films were prepared and compared to the systems containing modified nanoparticle. These new materials were characterized by thermogravimetric analysis (TGA), Differential Scanning Calorimetry (DSC), X-Ray Diffraction (XRD), Dynamic Mechanical Analysis (DMA), Time Domain Nuclear Magnetic Resonance (NMR) to investigate the effect of zinc oxide nanoparticles on thermal properties, EVA crystallinity and antimicrobial effect. The TGA showed a tendency of increase of the thermal stability in different proportions of ZnO. DSC results did not show significant changes in thermal parameters. The XRD analysis showed an increase in the degree of crystallinity of the nanocomposites in relation to the EVA matrix and change in the crystallinity with the increase of ZnO percentages. DMA analysis indicates change in structural organization through the variation of storage modulus, loss, and tan delta. Time domain NMR data corroborate with XRD data through the change in molecular mobility.

Effect of annealing on microstructure and mechanical properties of polypropylene random copolymer

ABSTRACTIn this work, polypropylene random copolymer (PPR) was taken as an example to study the changes of mechanical properties related to its microstructure evolution. Firstly, the toughness and fracture morphology were analyzed by notched Izod impact test and scanning electron microscope. Annealing at relative lower temperatures (<100°C), mechanical properties are slightly enhanced, which should be pointed out that significant improvements have been observed when annealing at relative higher temperatures (>100°C). Secondly, the study was conducted from the conventional differential scanning calorimetry, wide angle X-ray diffraction, and small-angle X-ray scattering to analyses the changes in the crystalline and amorphous regions. Dynamic thermomechanical analysis was employed to explore the changes of molecular mobility in samples after annealing at different temperatures. Moreover, to find out the stress transfer between the crystalline regions and the amorphous regions, we did further analysis of the typical stress–strain curves and proposed the mechanism of microstructure evolution during annealing process. The results shown that amorphous rearranged and formed thinner lamellae when annealing at relative low temperature. While annealing at higher temperatures, the mobile and rigid amorphous regions rearranged into more perfect lamellae and the density of stress transmitters was increased significantly.

Characterisation of tack for uni-directional prepreg tape employing a continuous application-and-peel test method

Employing a test method with coupled application and peel phases, tack was characterised for a UD prepreg tape. Different aspects of tack were explored by varying test parameters and material condition. In addition, different surface combinations were studied. In general, the test parameters, feed rate and temperature, affect the balance between cohesion within the resin and adhesion between resin and substrate. Exploring a range of parameters is required to understand the effect of viscoelastic resin properties on tack. The application pressure determines the true contact area between prepreg and substrate and hence affects tack. Changes in molecular mobility in the resin related to specimen conditioning, i.e. ageing or moisture uptake, result in maximum tack to occur at lower or higher feed rates, respectively. Differences in tack for different material combinations can be attributed to different molecular interactions at the contact interfaces and different resin distributions on the prepreg surfaces.

Dielectric relaxation of fullerene C60-containing nanocomposites based on poly(phenylene oxide)

Molecular mobility of nanocomposites based on poly(phenylene oxide) (PPO) containing 1, 2, 4 and 8 wt% of C60 fullerenes was studied by dielectric spectroscopy. In all samples, two relaxation processes were present and caused by polarization of the single polar O group located between phenyl rings. This polarization includes two stages with the first stage (occurring in the glassy state) is caused by rotation of phenyl rings and the adjacent polar O groups by small angles that results in the local β process. The second stage (occurring at temperatures exceeding the glass transition temperature Tg) involves segmental mobility and leads to emergence of the α process. Molecular mobility in the region of the β process varies slightly with C60 concentration. In the case of the α process, molecular mobility changes non-monotonically with increasing fullerene concentration.

Effect of recycling agents in recycled asphalt binders observed with microstructural and rheological tests

In this study, the effect of recycling agents on recycled blends obtained from base and recycled asphalt binders and the performance of the rejuvenated binders with aging was investigated by means of Atomic Force Microscopy (AFM) and Dynamic Shear Rheometer (DSR). This study arises as the amount of recycled materials in asphalt pavements continues to increase. Recycled binders are significantly stiffer than base binders; however, the performance grade can be restored by inclusion of recycling agents. Nevertheless, intermediate temperature cracking performance evaluated by the Glover-Rowe (G-R) parameter indicated that the effect of the recycling agents is not sustained with subsequent aging, which could jeopardize its effectiveness in service. The AFM images provided microstructural information, which offer indications about changes in molecular mobility and degree of association with aging, presence of agglomerations, and the dispersive effect of recycling agents.

Sciatic nerve repair using poly(ε-caprolactone) tubular prosthesis associated with nanoparticles of carbon and graphene.

IntroductionInjuries to peripheral nerves generate disconnection between spinal neurons and the target organ. Due to retraction of the nerve stumps, end‐to‐end neurorrhaphy is usually unfeasible. In such cases, autologous grafts are widely used, nonetheless with some disadvantages, such as mismatching of donor nerve dimensions and formation of painful neuromas at the donor area. Tubulization, using bioresorbable polymers, can potentially replace nerve grafting, although improvements are still necessary. Among promising bioresorbable synthetic polymers, poly(l‐lactic acid) (PLLA) and poly(ε‐caprolactone) (PCL) are the most studied. Carbon nanotubes and graphene sheets have been proposed, however, as adjuvants to improve mechanical and regenerative properties of tubular prostheses. Thus, the present work evaluated nerve tubulization repair following association of PCL with nanoparticles of carbon (NPC) and graphene (NPG).MethodsFor that, adult Lewis rats were subjected to unilateral sciatic nerve tubulization and allowed to survive for up to 8 and 12 weeks postsurgery.ResultsNanocomposites mechanical/chemical evaluation showed that nanoparticles do not alter PCL crystallinity, yet providing reinforcement of polymer matrix. Thus, there was a decrease in the enthalpy of melting when the mixture of PCL + NPC + NPG was used. Nanocomposites displayed positive changes in molecular mobility in the amorphous phase of the polymer. Also, the loss modulus (E”) and the glass transition exhibited highest values for PCL + NPC + NPG. Scanning electron microscopy analysis revealed that PCL + NPC + NPG prostheses showed improved cell adhesion as compared to PCL alone. Surgical procedures with PCL + NPC + NPG were facilitated due to improved flexibility of the prosthesis, resulting in better stump positioning accuracy. In turn, a twofold increased number of myelinated axons was found in such repaired nerves. Consistent with that, target muscle atrophy protection has been observed.ConclusionOverall, the present data show that nanocomposite PCL tubes facilitate nerve repair and result in a better regenerative outcome, what may, in turn, represent a new alternative to pure PCL or PLLA prostheses.

Riboflavin as a Gras Luminescent Probe of Food and Pharmaceutical Quality

Riboflavin fluorescence has been characterized profusely, however little attention has been devoted to riboflavin phosphorescence. We have characterized steady state and time resolved phosphorescence of riboflavin from 77K to 333K in solvent mixtures (water:alcohol, water:glycerol) and amorphous solids (glucose, glucose oligomers, sucrose, dextran) to expand our knowledge on riboflavin photophysical properties and assess its potential use in quality monitoring.When excited at 440nm, the emission spectra of riboflavin exhibited maxima at 515nm (delayed fluorescence) and 620nm (phosphorescence). Deconvolution of the spectra to two individual bands characterized by asymmetric lognormal functions (I(ν)=I0∗exp{-ln(2)(ln[1+2b(ν-νp)/Δ2]/b)} ) facilitated the extraction of parameters and the analysis of their temperature dependence. Time resolved intensity decays were fitted using stretch, multi-exponential and distribution (by MEM) models.Riboflavin exhibited a lifetime of 184ms at 77K in glycerol-water. The lifetime decreased slowly below the solvent mixture's Tg (170K) and abruptly above Tg; e.g., an increase of 20K above Tg reduced the lifetime from 100ms to 10ms. This reduction was associated with molecular motions in the matrix.Molecular mobility was also modulated by changing the composition of the matrix, by using components of different molecular sizes or by adding plasticizers. Riboflavin phosphorescence also exhibited good sensitivity towards molecular mobility changes driven by composition. This suggests its use as a GRAS optical probe for molecular mobility and its potential application to optimize matrix composition in food and pharmaceutical products to enhance stability of micro and bioactive components. Continuous monitoring of riboflavin phosphorescence during heating and cooling cycles revealed differences in the delayed luminescence emission spectra, likely due to a higher rate of irreversible photodegradation of riboflavin at high temperatures. If properly characterized, the thermal dependence of riboflavin photodegradation can potentially be operationalized in sensors for temperature abuse.

The use of potato fibre to improve bread physico-chemical properties during storage

Bread staling reduction is a very important issue for the food industry. A fibre with high water holding capacity, extracted from potato peel, was studied for its ability to reduce bread staling even if employed at low level (0.4g fibre/100g flour). Physico-chemical properties (water activity, moisture content, frozen water content, amylopectin retrogradation) and 1H Nuclear Magnetic Resonance molecular mobility were characterised in potato fibre added bread over 7days of storage. Potato fibre addition in bread slightly affected water activity and moisture content, while increased frozen water content and resulted in a softer bread crumb, more importantly when the optimal amount of water was used in the formulation. Potato fibre also reduced 1H NMR molecular mobility changes in bread crumb during storage. Potato fibre addition in bread contributed to reduce bread staling.

A Comparative Study of Commercial Modified Celluloses as Bread Making Additives

The effect of commercial modified celluloses: microcrystalline cellulose, carboxymethyl cellulose, and hydroxypropylmethyl cellulose on bread quality attributes and their potential protective effect with respect to bread staling were analyzed. Two levels of gums were assayed (0.5 and 1.5 g/100 g flour). The best performance was obtained with carboxymethyl cellulose and hydroxypropylmethyl cellulose F 4 M at both levels; these gums led to higher specific volumes and a better crumb texture as measured by texture profile analysis. In general, crumbs were softer, more cohesive, and resilient and exhibited lower chewiness values. Other gums like microcrystalline cellulose and hydroxypropylmethyl cellulose F50 did not improve bread quality on the same extent. Mechanical spectra obtained by dynamic mechanical analysis assays indicated a marked change in molecular mobility when carboxymethyl cellulose was present. Bread staling was evaluated by texture profile analysis, moisture loss, and calorimetric assays. Gums did not avoid retrogradation and even exhibited an accelerating effect, probably due to changes in water retention and migration during storage. However, in most cases, final crumb hardness in samples with hydrocolloids was lower than that in the control sample.

Probing molecular dynamics of metal borohydrides on the surface of mesoporous scaffolds by multinuclear high resolution solid state NMR

Understanding of surface interactions between borohydride molecules and the surfaces of porous supports have gained growing attention for successful development of nano-confinement engineering. By use of in␣situ variable temperature (VT) magic angle spinning (MAS) NMR, molecular mobility changes of LiBH4 crystalline solid has been investigated in the presence of silica based and carbonaceous surfaces. Spin–spin J-coupling of 1H–11B in LiBH4 was monitored in series of VT NMR spectra to probe translational mobility of LiBH4 that appeared to be greatly enhanced upon surface contact. Such enhanced diffusivity was found to be effective in the formation of solid solution and co-confinement with other metal borohydrides. Co-confinement of LiBH4–Ca(BH4)2 mixture was demonstrated at temperature as low as 100°C, much lower than the reported bulk eutectic melting temperature. The discovery adds a novel property of LiBH4 that has been proven to be highly versatile in many energy related applications.

Solid‐state NMR study of spin finish of thermally treated PAN and PAN/CNT precursor fibers

ABSTRACTDry‐jet wet‐spun polyacrylonitrile (PAN) and PAN/carbon nanotubes (CNTs) precursor fibers coated by spin finishes were characterized using the solid‐state 1H nuclear magnetic resonance technique. Series of fiber samples were prepared upon thermal treatment at different temperatures (room temperature to 180°C). Using the Hahn echo sequence, relatively mobile components were identified and the effect of the heat treatment on those components was studied. It was observed that the mobile components are mainly the spin finishes. Heat treatment caused loss of one of the spin finishes (Type B) to a great extent (∼80%), whereas the other two spin finishes (Type A and Type C) were more stable. Additional information regarding the change in molecular mobility due to heat treatment was obtained by the spin‐lattice relaxation time (T1) analysis. It was found that the presence of CNT affects the T1 relaxation time of the polymer in the composite fiber, however, that of relatively mobile components remains unaffected. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40734.