A brief guide to polymer characterization: structure (IUPAC technical report)

To bolster the series of Brief Guides released by International Union of Pure and Applied Chemistry (IUPAC), here we introduce the first Brief Guide to Polymer Characterization. This article provides a concise overview of characterization methods for teachers, students, non-specialists, and newcomers to polymer science as well as being a useful manual for researchers and technicians. Unlike pure low molar mass chemical substances, polymers are not composed of identical molecules. The macromolecules which comprise a single polymer sample vary from one another, primarily in terms of size and shape, but often also in the arrangement or positioning of atoms within macromolecules (e.g., chain branching, isomerism, etc.). Polymer properties are often drastically different from those of other substances and their characterization relies on specialist equipment and/or common equipment used in a specialized way (e.g., particular sample preparation or data analysis). This Brief Guide focuses uniquely on the structural characterization (i.e., analyzing the molecular and multi-molecular aspects) of polymers. The complex nature of the structural variables possible in macromolecular materials often presents a challenge with regard to the detailed structural characterization of polymers. This Brief Guide provides a useful starting point to direct the reader to the most commonly used and useful techniques to characterize these structural variables

Hydration effects on spacing of primary-wall cellulose microfibrils: a small angle X-ray scattering study

Celery collenchyma cell walls are typical of primary plant cell walls in their composition but contain unusually well-oriented cellulose microfibrils that are packed with more regularity than normal, permitting small-angle X-ray scattering (SAXS) experiments that would not otherwise be possible. Small-angle scattering data were obtained for the cell walls in essentially their native state and for isolated cellulose, in a fibrous form that retained the physical shape and microfibril orientation of the native cell walls. The scattering patterns showed a distinct peak attributed to the interference contribution to the convolution of form and interference functions. The position of the peak attributed to the interference function implied a mean centre-to-centre microfibril spacing of approximately 3.2 nm in dry isolated cellulose and 3.8 nm in dry cell walls. Hydration increased the mean microfibril spacing in the cell walls to 5.4 nm but had only a small effect on the mean microfibril spacing of isolated cellulose. In the scattering profile from intact, hydrated cell walls it was just possible to discern the position of the first Bessel minimum, from which a microfibril diameter in the range 3.1-3.6 nm may be estimated. This estimate is likely to include attached hemicellulose chains. Porod plots of scattering intensity indicated a relatively sharp interface between microfibrils and their immediate surroundings. The SAXS data imply that cellulose microfibrils 2.6-3.0 nm in diameter are not quite in lateral contact with one another in the isolated cellulose and are augmented by hemicelluloses and separated by readily hydrated matrix polysaccharides in the native plant cell wall. © Springer Science+Business Media B.V. 2007

Additive Effects on Phase Transition and Interactions in Poly(vinyl methyl ether) Solutions

A comparative study of thermal response of poly(vinyl methyl ether) in the presence of different hydrophilic and hydrophobic additives was performed by Nuclear magnetic resonance (NMR) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and optical microscopy. The effect of polymer concentration and additive content on the appearance and extent of the phase transition was determined. A detailed study of interaction mechanism in solutions with two hydrophobic additives showed differences in the way in which polymer globules are formed. For solutions containing t-butyl methyl ketone and t-butanol, measurements of 1H spin-spin relaxations showed the presence of water and additive molecules bound in PVME globular structures. These originally-bound molecules are then slowly released from the globular-like structures. Incorporation of molecules into the globules disrupts the cooperativity of the transition and affects the size of globular structures

Structure of cellulose-deficient secondary cell walls from the irx3 mutant of Arabidopsis thaliana

In the Arabidopsis mutant irx3, truncation of the AtCesA7 gene encoding a xylem-speCific cellulose synthase results in reduced cellulose synthesis in the affected xylem cells and collapse of mature xylem vessels. Here we describe spectroscopic experiments to determine whether any cellulose, normal or abnormal, remained in the walls of these cells and whether there were consequent effects on other cell-wall polysaccharides. Xylem cell walls from irx3 and its wild-type were prepared by anatomically specific isolation and were examined by solid-state NMR spectroscopy and FTIR microscopy. The affected cell walls of irx3 contained low levels of crystalline cellulose, probably associated with primary cell walls. There was no evidence that crystalline cellulose was replaced by less ordered glucans. From the molecular mobility of xylans and lignin it was deduced that these non-cellulosic polymers were cross-linked together in both irx3 and the wild-type. The disorder previously observed in the spatial pattern of non-cellulosic polymer deposition in the secondary walls of irx3 xylem could not be explained by any alteration in the structure or cross-linking of these polymers and may be attributed directly to the absence of cellulose microfibrils which, in the wild-type, scaffold the organisation of the other polymers into a coherent secondary cell wall. © 2002 Elsevier Science Ltd. All rights reserved

CELL 156 Dimensions and structure of wood and primary cell wall cellulose microfibrils

No abstract available

Diversidade e estrutura genética espacial em duas populações de Myracrodruon urundeuva Fr. All. sob diferentes condições antrópicas Diversity and spatial genetic structure in two populations of Myracrodruon urundeuva Fr. All. under different antropic conditions

O objetivo deste trabalho foi estudar, por locos isoenzimáticos, a diversidade e a estrutura genética espacial de genótipos de Myracrodruon urundeuva em duas populações naturais, uma no Sudoeste (Selvíria-SEL) e outra no Sudeste (Paulo de Faria-PFA) do Brasil. Para isso, foram avaliados cinco sistemas isoenzimáticos, 25 e 30 indivíduos adultos das populações SEL e PFA, respectivamente. A estimativa da divergência genética entre populações foi baixa (=0,043). As heterozigosidades observada e esperada foram altas nas populações (0,317 e 0,511, respectivamente), e o excesso significativo de heterozigotos foi detectado na população PFA (= -0,252). A análise da distribuição genética espacial dos genótipos a partir do índice I de Moran revelou estruturação significativa até 5.224 m na população mais explorada (SEL, =0,09) e tendência à distribuição aleatória na população menos explorada (PFA, = -0,02). A provável causa da estruturação na população SEL foi a dispersão de sementes próxima às árvores-matriz, associada ao processo de recolonização a partir de sementes oriundas de poucos genótipos remanescentes. As implicações dos resultados são discutidas do ponto de vista da conservação e do melhoramento genético.<br>The diversity and spatial genetic distribution of Myracrodruon urundeuva genotypes were studied in two Brazilian populations in the Southwest (Selvíria-SEL) and Southeast Brazilian regions (Paulo de Faria-PFA). Twenty-five and thirty adult individuals were evaluated for five allozyme systems in SEL and PFA populations, respectively. Estimates of the genetic divergence between populations were low (=0.043). Observed and expected heterozygosities were high in both populations (0.317 to 0.511, respectively). Significant and excessive number of heterozygotes was detected in PFA population (=-0.252). The spatial distribution analysis through Moran's index I revealed a significant structuring up to 5,224 m in the more exploited population (SEL, =0.09) and a trend to randomness in the less exploited area (PFA, = -0,02). Seed dispersion near mother trees and the recolonization process through seeds from few genotypes are probable causes of the structuring in the SEL population. The implications of the results are discussed from the conservation and breeding point of views

Synapse-Mimicking Memristors Based on 3,6-Di(<i>tpy</i>)-9-Phenylcarbazole Unimer and Its Copolymer with Cobalt(II) Ions

The title compound, unimer U (tpy stands for 2,2′:6′,2″-terpyridin-4′-yl end-group), by itself shows the memristor effect with a retention time of 18 h and persistence of 11 h. Its coordination copolymer with Co(II) ions, [CoU]n, exhibits multimodal resistance changes similar to the synaptic responses observed in biological systems. More than 320 cycles of potentiation and depression measured in continuous sequence occurred without observing a significant current change, confirming the operational stability and reproducibility of the device based on the [CoU]n polymer. The synaptic effect of a device with an indium tin oxide (ITO)/[CoU]n/top-electrode (TE) configuration is more pronounced for the device with TE = Au compared to devices with TE = Al or Ga. However, the latter TEs provide a cost-effective approach without any significant compromise in device plasticity. The detected changes in the synaptic weight, about 12% for pair-pulse facilitation and 80% for its depression, together with a millisecond trigger and reading pulses that decay exponentially on the time scale typical of neurosynapses, justify the device’s ability to learn and memorize. These properties offer potential applications in neuromorphic computation and brain-inspired synaptic devices