28,077 research outputs found
Synthesis, thermal behavior, and aggregation in aqueous solution of poly(methyl methacrylate)-b-poly(2-hydroxyethyl methacrylate)
Indexación: ScieloABSTRACT
Amphiphilic block copolymers of poly(methyl methacrylate) PMMA and poly(2-hidroxyethyl methacrylate) PHEMA were synthesized by a two-step atom transfer radical polymerization (ATRP). Copolymers with various degrees of polymerization and different relative block sizes were obtained. The structure of the resulting polymers have been characterized and verified by FT-IR and 1H-NMR, molecular weight were determined by size exclusion chromatography analyses. The thermal properties of these polymers were investigated by differential scanning calorimetry DSC and thermogravimetric analysis TGA. The glass transition temperature of mono halogenated PMMA increases from 116 °C to 123 °C with increasing molecular weight, whereas the glass transition temperature of block copolymers depends slightly on polymer structure. The derivatives of TGA curves indicate that thermal degradation occurs in one stage. The self-assembly of PMMA-b-PHEMA in aqueous solution have been investigated by fluorescence probing methods. The critical micelle concentrations are in the range 10-6 - 10-7 M. The micropolarity sensed by pyrene is higher than in aggregates formed by block copolymers based on polystyrene.
Keywords: Block copolymers, glass transition temperature, thermogravimetric analysis, critical micelle concentration, fluorescence probing methods
Can ultrastrong coupling change ground state chemical reactions?
Recent advancements on the fabrication of organic micro- and nanostructures
have permitted the strong collective light-matter coupling regime to be reached
with molecular materials. Pioneering works in this direction have shown the
effects of this regime in the excited state reactivity of molecular systems and
at the same time has opened up the question of whether it is possible to
introduce any modifications in the electronic ground energy landscape which
could affect chemical thermodynamics and/or kinetics. In this work, we use a
model system of many molecules coupled to a surface-plasmon field to gain
insight on the key parameters which govern the modifications of the
ground-state Potential Energy Surface (PES). Our findings confirm that the
energetic changes per molecule are determined by single-molecule-light
couplings which are essentially local, in contrast with those of the
electronically excited states, for which energetic corrections are of a
collective nature. Still, we reveal some intriguing quantum-coherent effects
associated with pathways of concerted reactions, where two or more molecules
undergo reactions simultaneously, and which can be of relevance in low-barrier
reactions. Finally, we also explore modifications to nonadiabatic dynamics and
conclude that, for this particular model, the presence of a large number of
dark states yields negligible changes. Our study reveals new possibilities as
well as limitations for the emerging field of polariton chemistry
Faddeev fixed-center approximation to the system and the signature of a state
We perform a calculation for the three body scattering
amplitude by using the fixed center approximation to the Faddeev equations,
taking the interaction between and , and , and
and from the chiral unitary approach. The resonant structures show up in
the modulus squared of the three body scattering amplitude and suggest that a
hadron state can be formed. Our results are in agreement with
others obtained in previous theoretical works, which claim a new
resonance around 1920 MeV with spin-parity . The existence of these
previous works allows us to test the accuracy of the fixed center approximation
in the present problem and sets the grounds for possible application in similar
problems, as an explorative tool to determine bound or quasibound three hadron
systems.Comment: Published versio
Solution to Faddeev equations with two-body experimental amplitudes as input and application to J^P=1/2^+, S=0 baryon resonances
We solve the Faddeev equations for the two meson-one baryon system
and coupled channels using the experimental two-body -matrices for the interaction as input and unitary chiral dynamics to describe the interaction
between the rest of coupled channels. In addition to the obtained
before with the channel, we obtain, for and total
isospin of the three-body system , a resonance peak whose mass is around
2080 MeV and width of 54 MeV, while for we find a peak around 2126 MeV
and 42 MeV of width. These two resonances can be identified with the and the , respectively. We obtain another peak in the
isospin 1/2 configuration, around 1920 MeV which can be interpreted as a
resonance in the and systems.Comment: published versio
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