RESUMO
Supramolecular gels made from 2D building blocks are emerging as one of the novel multifunctional soft materials for various applications. This study reports on a class of supramolecular nanosheet gels formed through a reversible self-assembly process involving both intramolecular folding and intermolecular self-assembly of poly[oligo(ethylene glycol)-co-(phenyl-capped bithiophenes)]. Such hierarchical self-assembled structure allows the gels to switch between sol and gel states under either redox or thermostimulus. Moreover, the gels illustrate high Young's moduli, compared to their controls that are made from the same oligo(ethylene glycol) and phenyl-capped bithiophenes blocks but have highly covalent-crosslinked structures. The example might open a window for emerging supramolecular 2D materials to develop mechanically robust and stimuli-responsive soft materials without compromising their intrinsic functions.
Assuntos
Nanoestruturas/química , Polímeros/química , Temperatura , Módulo de Elasticidade , Géis/química , Substâncias Macromoleculares/síntese química , Substâncias Macromoleculares/química , Estrutura Molecular , Oxirredução , Tamanho da Partícula , Polímeros/síntese química , Propriedades de SuperfícieRESUMO
Dendrimeric macromolecules with defined shape and size are promising candidates for delivering drug or DNA molecules into cells. In this work we study the influence of an amphiphilic polyphenylene dendrimer on a model cell membrane consisting of a condensed 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid monolayer. A small surface pressure decrease is observed when the dendrimer solution is injected into the aqueous phase below the monolayer. X-ray reflectivity measurements show that the surface monolayer remains intact. The molecular-scale picture is obtained with sum-frequency generation spectroscopy. With this technique, we observe that the tails of the surfactant molecules become less ordered upon interaction with the amphiphilic polyphenylene dendrimer. In contrast, the water molecules below the DPPC layer become more ordered. Our observations suggest that electrostatic interactions between the negative charge of the dendrimer and the positively charged part of the DPPC headgroup keep the dendrimer located below the headgroup. No evidence of dendrimer insertion into the membrane has been observed. Apparently before entering the cell membrane the dendrimer can stick at the hydrophilic part of the lipids.
Assuntos
1,2-Dipalmitoilfosfatidilcolina/química , Dendrímeros/química , Interações Hidrofóbicas e Hidrofílicas , Polímeros/química , Eletricidade Estática , Ligação de Hidrogênio , Modelos Moleculares , Conformação Molecular , Tensão SuperficialRESUMO
A new straight forward approach to create nanoporous polymer membranes with well defined average pore diameters is presented. The method is based on fast mechanical deformation of highly entangled polymer films at high temperatures and a subsequent quench far below the glass transition temperature Tg . The process is first designed generally by simulation and then verified for the example of polystyrene films. The methodology does not need any chemical processing, supporting substrate, or self assembly process and is solely based on polymer inherent entanglement effects. Pore diameters are of the order of ten polymer reptation tube diameters. The resulting membranes are stable over months at ambient conditions and display remarkable elastic properties.
Assuntos
Nanoporos , Polímeros , Polímeros/química , Poliestirenos/química , Temperatura , Temperatura AltaRESUMO
Gecko-inspired arrays of micropillars made of a liquid crystalline elastomer display thermoswitchable adhesive behavior as a consequence of elongation changes caused by reorientation of the mesogens at the nematic-isotropic (N-I) phase transition.