67 research outputs found
Evidence of a low-temperature dynamical transition in concentrated microgels
A low-temperature dynamical transition has been reported in several proteins.
We provide the first observation of a `protein-like' dynamical transition in
nonbiological aqueous environments. To this aim we exploit the popular
colloidal system of poly-N-isopropylacrylamide (PNIPAM) microgels, extending
their investigation to unprecedentedly high concentrations. Owing to the
heterogeneous architecture of the microgels, water crystallization is avoided
in concentrated samples, allowing us to monitor atomic dynamics at low
temperatures. By elastic incoherent neutron scattering and molecular dynamics
simulations, we find that a dynamical transition occurs at a temperature
~K, independently from PNIPAM mass fraction. However, the
transition is smeared out on approaching dry conditions. The quantitative
agreement between experiments and simulations provides evidence that the
transition occurs simultaneously for PNIPAM and water dynamics. The similarity
of these results with hydrated protein powders suggests that the dynamical
transition is a generic feature in complex macromolecular systems,
independently from their biological function
Study of network composition in interpenetrating polymer networks of poly(N isopropylacrylamide) microgels:the role of poly(acrylic acid)
Hypothesis: The peculiar swelling behaviour of poly(N-isopropylacrylamide)
(PNIPAM)-based responsive microgels provides the possibility to tune both
softness and volume fraction with temperature, making these systems of great
interest for technological applications and theoretical implications. Their
intriguing phase diagram can be even more complex if poly(acrylic acid) (PAAc)
is interpenetrated within PNIPAM network to form Interpenetrating Polymer
Network (IPN) microgels that exhibit an additional pH-sensitivity. The effect
of the PAAc/PNIPAM polymeric ratio on both swelling capability and dynamics is
still matter of investigation. Experiments: Here we investigate the role of
PAAc in the behaviour of IPN microgels across the volume phase transition
through dynamic light scattering (DLS), transmission electron microscopy (TEM)
and electrophoretic measurements as a function of microgel concentration and
pH. Findings: Our results highlight that aggregation is favored at increasing
weight concentration, PAAc content and pH and that a crossover PAAc content
C*_{PAAc} exists above which the ionic charges on the microgel become relevant.
Moreover we show that the softness of IPN microgels can be tuned ad hoc by
changing the PAAc/PNIPAM ratio. These findings provide new insights into the
possibility to control experimentally aggregation properties, charge and
softness of IPN microgels by varying PAAc content.Comment: preprint versio
Molecular mechanisms driving the microgels behaviour: a Raman spectroscopy and Dynamic Light Scattering study
Responsive microgels based on poly(N-isopropylacrylamide) (PNIPAM) exhibit
peculiar behaviours due to the competition between the hydrophilic and
hydrophobic interactions of the constituent networks. The interpenetration of
poly-acrilic acid (PAAc), a pH-sensitive polymer, within the PNIPAM network, to
form Interpenetrated Polymer Network (IPN) microgels, affects this delicate
balance and the typical Volume-Phase Transition (VPT) leading to complex
behaviours whose molecular nature is still completely unexplored. Here we
investigate the molecular mechanism driving the VPT and its influence on
particle aggregation for PNIPAM/PAAc IPN microgels by the joint use of Dynamic
Light Scattering and Raman Spectroscopy. Our results highlight that PNIPAM
hydrophobicity is enhanced by the interpenetration of PAAc promoting
interparticle interactions, a crossover concentration is found above which
aggregation phenomena become relevant. Moreover we find that, at variance with
PNIPAM, for IPN microgels a double-step molecular mechanisms occurs upon
crossing the VPT, the first involving the coil-to-globule transition typical of
PNIPAM and the latter associated to PAAc steric hindrance.Comment: preprint versio
Local structure of temperature and pH-sensitive colloidal microgels
The temperature dependence of the local intra-particle structure of colloidal microgel particles, composed of interpenetrated polymer networks, has been investigated by small-angle neutron scattering at different pH and concentrations, in the range (299÷315) K, where a volume phase transition from a swollen to a shrunken state takes place. Data are well described by a theoretical model that takes into account the presence of both interpenetrated polymer networks and cross-linkers. Two different behaviors are found across the volume phase transition. At neutral pH and T 307 K, a sharp change of the local structure from a water rich open inhomogeneous interpenetrated polymer network to a homogeneous porous solid-like structure after expelling water is observed. Differently, at acidic pH, the local structure changes almost continuously. These findings demonstrate that a fine control of the pH of the system allows to tune the sharpness of the volume-phase transition
Polymer Identification and Specific Analysis (PISA) of Microplastic Total Mass in Sediments of the Protected Marine Area of the Meloria Shoals
Microplastics (MPs) quantification in benthic marine sediments is typically performed by
time-consuming and moderately accurate mechanical separation and microscopy detection. In this
paper, we describe the results of our innovative Polymer Identification and Specific Analysis (PISA)
of microplastic total mass, previously tested on either less complex sandy beach sediment or less
demanding (because of the high MPs content) wastewater treatment plant sludges, applied to the
analysis of benthic sediments from a sublittoral area north-west of Leghorn (Tuscany, Italy). Samples
were collected from two shallow sites characterized by coarse debris in a mixed seabed of Posidonia
oceanica, and by a very fine silty-organogenic sediment, respectively. After sieving at <2 mm the
sediment was sequentially extracted with selective organic solvents and the two polymer classes
polystyrene (PS) and polyolefins (PE and PP) were quantified by pyrolysis-gas chromatography-mass
spectrometry (Pyr-GC/MS). A contamination in the 8–65 ppm range by PS could be accurately
detected. Acid hydrolysis on the extracted residue to achieve total depolymerization of all natural
and synthetic polyamides, tagging of all aminated species in the hydrolysate with a fluorophore,
and reversed-phase high performance liquid chromatography (HPLC) (RP-HPLC) analysis, allowed
the quantification within the 137–1523 ppm range of the individual mass of contaminating nylon 6
and nylon 6,6, based on the detected amounts of the respective monomeric amines 6-aminohexanoic
acid (AHA) and hexamethylenediamine (HMDA). Finally, alkaline hydrolysis of the residue from
acid hydrolysis followed by RP-HPLC analysis of the purified hydrolysate showed contamination by
polyethylene terephthalate (PET) in the 12.1–2.7 ppm range, based on the content of its comonomer,
terephthalic acid
Effects of a 4400 km ultra-cycling non-competitive race and related training on body composition and circulating progenitors differentiation
Background: NorthCape4000 (NC4000) is the most participated ultra-endurance cycling race. Eight healthy male Caucasian amateur cyclists were evaluated: (a) before starting the preparation period; (b) in the week preceding NC4000 (after the training period); (c) after NC4000 race, with the aim to identify the effects of ultra-cycling on body composition, aerobic capacity and biochemical parameters as well as on the differentiation of progenitor cells. Methods: Bioelectrical impedance analysis (BIA) and dual energy x-ray absorptiometry (DEXA) assessed body composition; cardiopulmonary exercise test (CPET) evaluated aerobic capacity. Differentiation of circulating progenitor cells was evaluated by analyzing the modulation in the expression of relevant transcription factors. In addition, in vitro experiments were performed to investigate the effects of sera of NC4000 participants on adipogenesis and myogenesis. The effects of NC4000 sera on Sestrins and Sirtuin modulation and the promotion of brown adipogenesis in progenitor cells was investigated as well. Two-tailed Student's paired-test was used to perform statistical analyses. Results: We observed fat mass decrease after training as well as after NC4000 performance; we also recorded that vitamin D and lipid profiles were affected by ultra-cycling. In addition, our findings demonstrated that post-NC4000 participant's pooled sera exerted a positive effect in stimulating myogenesis and in inducing brown adipogenesis in progenitor cells. Conclusions: The training program and Ultra-cycling lead to beneficial effects on body composition and biochemical lipid parameters, as well as changes in differentiation of progenitor cells, with significant increases in brown adipogenesis and in MYOD levels
Study of the compounding process parameters for morphology control of LDPE/layered silicate nanocomposites
AbstractA careful insight into melt compounding procedure is proposed in order to achieve a better understanding and control of the dispersion and orientation mechanisms of organo-clay platelets into LDPE nanocomposites. The method involved is the preparation of a maleic anhydride grafted polyethylene masterbatch containing 10 wt% organo-clay via twin-screw extrusion. A substantial nanodispersion and orientation of clay platelets was obtained as observed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. Moreover, the nanocomposites prepared by diluting the master-batch through the blend mixing with additional LDPE preserved or improved the exfoliation and lamellae orientation. Finally, the thermo-gravimetric analysis (TGA) showed a significant improvement of the thermal stability while both differential scanning calorimetry (DSC) and XRD evidenced a slight increase of the LDPE crystallinity degree with respect to neat polymer matrices thus suggesting the occurrence of orientation also for the polymer
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