Abstract: Exposure to ionizing radiation has been found to induce changes in poly(vinylidene fluoride) (PVDF) homopolymers. The high dose gamma irradiation process induces the formation of C=C and C=O bonds in its [CH2-CF2]n main chain. The irradiation also provokes crosslinking and chain scission. All these radio-induced defects lead to changes in the PVDF crystalline structure. As a consequence, it is common to observe a decrease in the melting temperature (TM) and melting latent heat (LM) and some changes in its ferroelectric features. We have investigated the possibility of preparing nanocomposites of PVDF with graphene oxide (GO) through the radio-induction of molecular bonds. In this work, we discuss how the gamma radiation interacts with the nanocomposite crystalline structure.
Abstract: The combination of the properties of graphene oxide
(OG) and PVDF homopolymer makes their combined composite
materials as multifunctional systems with great potential. Knowledge
of the molecular structure is essential for better use. In this work, the
degradation of PVDF polymer exposed to gamma irradiation in
oxygen atmosphere in high dose rate has been studied and compared
to degradation of PVDF/OG composites. The samples were irradiated
with a Co-60 source at constant dose rate, with doses ranging from
100 kGy to 1,000 kGy. In FTIR data shown that the formation of
oxidation products was at the both samples with formation of
carbonyl and hydroxyl groups amongst the most prevalent products
in the pure PVDF samples. In the other hand, the composites samples
exhibit less presence of degradation products with predominant
formation of carbonyl groups, these results also seen in the UV-Vis
analysis. The results show that the samples of composites may have
greater resistance to the irradiation process, since they have less
degradation products than pure PVDF samples seen by spectroscopic
techniques.
Abstract: Paranoid ideation is a common thought process that
constitutes a defense against perceived social threats. The current
study aimed at the characterization of paranoid ideation in youths and
to explore the possible predictors involved in the development of
paranoid ideations. Paranoid ideation, shame, submission, early
childhood memories and current depressive, anxious and stress
symptomatology were assessed in a sample of 1516 Portuguese
youths. Higher frequencies of paranoid ideation were observed,
particularly in females and youths from lower socioeconomic status.
The main predictors identified relates to submissive behaviors and
adverse childhood experiences, and especially to shame feelings. The
current study emphasizes that the these predictors are similar to
findings in adults and clinical populations, and future implications to
research and clinical practice aiming at paranoid ideations are
discussed, as well as the pertinence of the study of mediating factors
that allow a wider understanding of this thought process in younger
populations and the prevention of psychopathology in adulthood.