Summary: A modified random phase approximation method with a cumulant expansion for the semi‐flexible structure factor of diblock copolymers was exercised to describe the phase separation behavior of semi‐flexible and polydisperse diblock copolymers. Scattering curves and spinodal diagrams were calculated applying monomer specific input parameters. The influence of polydispersity was included applying basic concepts of mathematical statistics utilizing several probability density distributions in the case of the two single blocks. In contrast to semi‐flexibility, the main effect of polydispersity was found to shift the spinodal up, thus to enlarge the range of existence of the homogeneous phase.
Twofold Schultz‐Zimm distribution of diblock copolymers. 相似文献
Three‐dimensional mesoscopic morphologies and the thermodynamics of structural phase transitions of amphiphilic lipids at air‐water interfaces are studied using self‐consistent field theory. Changing the relative amount of lipids in the system led to a series of 3D morphologic phases with varying average interfacial area per molecule, mimicking a compression of the model membranes. Membranes of both saturated and unsaturated lipids undergo a transition from cylindrical micelle to lamella when the lipid content in the system increases from 2% to about 19–20%. With further increase in the lipid content, saturated lipids first develop non‐uniform quasi‐2D distributions in the lamella and then gradually transform into a hybrid morphology containing quasi‐planar lamellae. In contrast, unsaturated lipids develop reverse‐micellar morphologies.
A novel route towards the synthesis of well‐defined linear–dendronized diblock copolymers is reported. Precursor alkyne containing diblock copolymers were modified in a highly efficient cycloaddition reaction with dendritic azides of different generation. The dendronization has been shown to be selective and could be driven to completion under ambient conditions. The phase separation of such dendronized diblock copolymers was investigated in dependence of the generation size being attached. Compared to a linear–linear diblock copolymer as starting material the dendronization yielded in a pronounced phase separation. The nanoscaled features observed in thin films strongly depended on the dendron size and a variety of morphologies could be identified. Hence, the unique combination of controlled radical polymerization and click chemistry allows for the triggering of structured surfaces in the nanometer‐regime.
The phase behavior of graft copolymers in aqueous solution was investigated. The graft copolymers consist of poly(propylene glycol) (PPG) side chains and N,N‐dimethylacrylamide (dMA), N‐vinylimidazole (VIm), and N‐isopropylacrylamide (iPA), respectively, as backbones. Phase transition temperatures of the PPG copolymers increased with increasing the content of dMA and iPA as relatively more hydrophilic comonomers and with an increase in the degree of ionization of the incorporated VIm units.
Block copolymer nanopaticles were prepared from the mixture solutions containing good/poor solvents by a simple evaporation process. The block copolymers formed disorder, unidirectionally stacked lamellar, and onion‐like structures in nanoparticles depending on preparation temperatures. Thermal annealing induced the disorder‐order phase transition and order‐order phase transformation in the block copolymer nanoparticles, even though the annealing temperature is lower than the of one polymer segment. The unusual thermal behaviors suggest that the glass transition temperature of the block copolymer is decreased by the effect of nanoparticle, whose surface areas are larger than their volumes.
Summary: Self‐oscillating polymers and nano‐gel particles consisting of N‐isopropylacrylamide and the ruthenium catalyst of the Belousov‐Zhabotinsky reaction have been prepared. In order to clarify the crosslinking effect on the self‐oscillating behavior, the phase transition behaviors were investigated by measuring the transmittance and the fluorescence intensity of the polymer solution and the gel bead suspension. Cooperative effects due to crosslinking will play an important role for the design of nanoactuators.
Chemical structure of poly(NIPAAm‐co‐Ru(bpy)3). 相似文献
This study reports a continuous prepartion of spherical or hemispherical polymer particles simply utilizing the phase separation in polymer blend films during the coating process. We took an advantage of the strong phase separation between a water‐soluble crystalline polymer as a matrix and hydrophobic polymers as minor components. We demonstrated the prepartion of water‐soluble polystyrene (PS) particles, nitrilotriacetic acid (NTA)‐functionalized PS particles for protein separation, and semiconducting poly(3‐hexylthiophene) (P3HT) particles. The sizes of the particles could be controlled by adjusting the film thickness and weight fraction of the minor component polymers in the blend film. It provides a simple facile way to prepare polymer particles in a continous process.
Some new water‐soluble bis‐porphyrins, constituted of two porphyrin units spaced by means of aliphatic bridges of different lengths, were synthesized and characterized by MALDI‐TOF mass spectrometry, 1H NMR and UV‐vis spectroscopy. The hydrosolubility of these uncharged compounds was guaranteed from the presence of six long PEG chains bound on the peripheral positions of the two porphyrins. Cobalt and zinc derivatives were also prepared. In the case of Co‐bis‐porphyrin, the appearance of induced circular dichroism (ICD) signals in water solution confirmed the formation of stable complexes with some amino acids, in which the bis‐porphyrin behaves like molecular tweezers.
A novel self‐oscillating gel actuator with gradient structure, which generates a pendulum motion by fixing one edge of the gel without external stimuli was achieved. The gel was synthesized by copolymerizing the ruthenium catalyst for the Belousov‐Zhabotinsky reaction with N‐isopropylacrylamide and 2‐acrylamido‐2‐methylpropane sulfonic acid. Furthermore, we clarified that the period and amplitude for the self‐oscillating behavior of the gel actuator are controllable by changing the composition, temperature, and size of the gel. The maximum amplitude of the novel gel actuator is about a 100 times larger than that of the conventional self‐oscillating gel system.
Polymeric core–shell microstructures have been constructed through a new method, namely sequential precipitation, which is intrinsically a self‐assembly and phase separation process. High‐quality poly(vinyldene fluoride)–polycarbonate–lithium perchlorate composite films with spherical core–shell microstructures have been prepared and determined to consist of conducting cores and insulating shells. Because of the percolation effect, the resulting materials present a dielectric constant as high as 104–107 at the threshold.
Summary: Conjugated three‐ and four‐arm star polymers were successfully prepared by palladium catalyzed one‐pot Suzuki polycondensation of the multifunctional cores and an AB‐type monomer. The molecular weight of the star polymers could be controlled by the feed ratios of the monomers. The bromo end groups could be completely modified by fluorene mono boronic acid or triphenylamine mono boronic ester. The investigation of the optical, electrochemical, and thermal properties of the star polymers was also reported. All polymers exhibited good thermal stabilities and all the TPA‐capped polymers showed good hole‐transport abilities.
Preparation of three‐ and four‐arm star polyfluorences. 相似文献
A branched copolymer containing a degradable polyperoxide linkage at a branching point was synthesized by the radical copolymerization of dienyl‐functionalized polystyrene and polyisoprene macromonomers with molecular oxygen. The ternary mixture of the branched copolymer and the macromonomers showed phase‐separated structure after annealing at 45 and 90 °C. The adjacent spacing of the phase‐separated structure was in the order of submicron to micrometer, which is larger than that of general microphase separated structures, due to the presence of homopolymers (macromonomers). Annealing at 110 °C induced thermal decomposition of the polyperoxide followed by in‐situ collapse and a drastic morphology change in the phase‐separated structure.
A reverse‐barrier technique is used to enable the treatment of electrospun poly(vinylidene fluoride) nanofibrous membranes with supercritical carbon dioxide. The treatment induces the formation of nanopores and extended‐chain β crystallites of small lateral dimensions in the nanofibers. It also creates interfiber junctions, resulting in a remarkable improvement in mechanical properties of the membranes. The treated membranes are able to retain their shape very well after loading with an ionic liquid (IL). The ionic conductivity of the IL‐loaded membrane is very close to that of the neat IL.
Anisotropic porous polymeric materials fabricated from the phase separation method via spinodal decomposition are used in various practical engineering applications. We studied the formation of anisotropic porous polymeric materials numerically, by imposing an initial linear concentration gradient across a model polymer solution. The initial concentration gradient is placed at three different regions of the polymer sample for comparison purposes. All the simulation results are in good agreement with published experimental observations, which are reported from the applications of porous polymeric membranes. The structure development shows that an anisotropic porous morphology forms when an initial linear concentration gradient is applied to the model polymer solution.
This paper describes a poly(dimethylsiloxane) (PDMS)‐based microfluidic platform for constructing the phase diagram of poly(N‐isopropyl acrylamide) (PNIPAM) in aqueous solution. The PNIPAM solution was delivered into a nanoliter chamber through the main microchannel. An osmotic pressure difference was established between the chamber and the control microchannel by flowing a high‐concentration salt solution in the control microchannel. Controlled evaporation of water resulted in increasing concentration of PNIPAM. A phase diagram of PNIPAM was built by measuring the cloud points at different concentrations, with a minimum point at ≈40 wt.‐%. The microfluidic platform has the advantages of low sample consumption and rapid heat exchange rates, and allows studying viscous polymer solution.
For polymer systems of two crystalline phases of one polymer component, each phase being consisted of polymer crystals of a finite size, we derive the crystalline‐crystalline phase transition relationship, i.e., generalized Gibbs‐Thomson equation. Its application combined with the crystalline‐liquid transition relationship (usual Gibbs‐Thomson equation) to the phase behavior of PT phase diagram of polyethylene (PE) is investigated, where the orthorhombic‐hexagonal phase transition of PE crystal under high pressure being involved. Comparison with experimental data leads to the estimates of the structural characteristics such as the ratios of (the end surface free energy of polymer crystal/crystal length) for the respective crystalline phases.
The Ludwig‐Soret effect was investigated in the thermally induced phase separation process via SD in polymer solutions under an externally imposed spatial linear temperature gradient using mathematical modeling and computer simulation. The mathematical model incorporated non‐linear Cahn‐Hilliard theory for SD, Flory‐Huggins theory for thermodynamics, and the Ludwig‐Soret effect for thermal diffusion. 2D simulation results revealed that the Ludwig‐Soret effect had negligible impact on the phase separation mechanism in binary polymer solutions under a non‐uniform temperature field, as reflected by the time evolution of the dimensionless structure factor and the transition time from the early to the intermediate stages of SD.
