Characterization of the Core-Shell Nanoparticles Formed as Soluble Hydrogen-Bonding Interpolymer Complexes at low pH

The formation of soluble hydrogen-bonding interpolymer complexes between poly(acrylic acid) (PAA) and poly(acrylic acid-co-2-acrylamido-2-methyl-1-propane sulfonic acid)-graft-poly(N, N dimethylacrylamide) (P(AA-co-AMPSA)-g-PDMAM) at pH = 2.0 was studied. A viscometric study showed that in semidilute solution a physical gel is formed, due to the interconnection of the anionic P(AA-co-AMPSA) backbone of the graft copolymer, in a transient network, by means of the complexes formed between the PDMAM side chains of the graft copolymer and PAA. Dynamic and static light scattering measurements, in conjunction with small angle neutron scattering measurements, suggest the formation of core-shell colloidal nanoparticles in dilute solution, comprised by an insoluble PAA/PDMAM core surrounded by an anionic P(AA-co-AMPSA) corona. Even if larger clusters are formed in semidilute solution, the size of the insoluble core remains practically stable. Atomic force microscopy performed under ambient conditions, reveal that the particles collapse and flatten upon deposition on a substrate, with dimensions close to the ones of the dry hydrophobic core

Elektrokemijska detekcija mikročestica gela u morskoj vodi

We present the first atomic force microscopy (AFM) images of the native marine gel network and a new type of electrochemical signals of individual gel microparticles in seawater. Gel microparticles in seawater are selectively detected through specific amperometric signals using a dropping mercury electrode (DME) as a sensor. We have demonstrated that organic microparticles naturally present in Northern Adriatic seawater can be detected as single particles and sorted at the DME/seawater interface according to their hydrophobicity and supramolecular organization.Prvi puta prikazana je nanostruktura morskog gela oslikana mikroskopijom atomskih sila i nova vrsta elektrokemijskih signala mikročestica gela u morskoj vodi. Čestice gela u morskoj vodi selektivno se detektiraju kao specifični amperometrijski signali primjenom živine kapajuće elektrode kao senzora. Svaki signal je rezultat sudara mikročestice gela s rastućom površinom živine elektrode. Primjenom amperometrijske tehnike i živine kapajuće elektrode kao senzora organske mikročestice detektiraju se na dinamičkoj međupovršini živina elektroda/morska voda temeljem svojstava hidrofobnosti i supramolekulske organizacije kao površinski-aktivne i gel čestice

Investigations by AFM of Ageing Mechanisms in PLA-Flax Fibre Composites during Garden Composting.

PLA-flax non-woven composites are promising materials, coupling high performance and possible degradation at their end of life. To explore their ageing mechanisms during garden composting, microstructural investigations were carried out through scanning electron microscopy (SEM) and atomic force microscopy (AFM). We observe that flax fibres preferentially degrade 'inwards' from the edge to the core of the composite. In addition, progressive erosion of the cell walls occurs within the fibres themselves, 'outwards' from the central lumen to the periphery primary wall. This preferential degradation is reflected in the decrease in indentation modulus from around 23 GPa for fibres located in the preserved core of the composite to 3-4 GPa for the remaining outer-most cell wall crowns located at the edge of the sample that is in contact with the compost. Ageing of the PLA matrix is less drastic with a relatively stable indentation modulus. Nevertheless, a change in the PLA morphology, a significant decrease in its roughness and increase of porosity, can be observed towards the edge of the sample, in comparison to the core. This work highlights the important role of intrinsic fibre porosity, called lumen, which is suspected to be a major variable of the compost ageing process, providing pathways of entry for moisture and microorganisms that are involved in cell wall degradation

An AFM study of Poly(L-lactic acid) and Poly(D-lactic acid) macromolecules and their stereocomplexes at the solid-air interface

International audienceThe self assembly of PLA enantiomers have been studied at the nanometer scale using atomic force microscopy. At first, the conformation of D and L PLA macromolecules in dilute regime and the initial state of aggregation of both enantiomers were successively observed and compared with the aggregation of PLLA/PDLA blends. Our results points out differences in the aggregates structure between the homo-aggregates of each enantiomers and the 3 Dimensional stereocomplexes formed with racemic mixture of D and L entities. On the one hand, D or L PLA chains, which adopt a rigid conformation in dilute regime, form gradually aggregates that tend to grow from a nucleation center. On the other hand, stereocomplexes have a non-compact structure and are elongated with height variations within the fibrils that support the side by side aggregation of D and L helical structures to form thicker fibrils

Aggregation and pattering in thin films of PLA stereoisomers and stereocomplex: from conformation to glass transition

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