Search results for "polymers"
showing 10 items of 3567 documents
Amphiphilic Poly(organosiloxane) Nanospheres as Nanoreactors for the Synthesis of Topologically Trapped Gold, Silver, and Palladium Colloids
2003
Amphiphilic poly(organosiloxane) nanospheres with different core−shell architectures are employed as passive nanoreactors for the synthesis of noble metal colloids. The amphiphilic poly(organosiloxane) nanospheres, which have diameters between 15 and 40 nm, possess a hydrophilic interior and a hydrophobic shell. Dispersed in organic solvents such as toluene, it has been achieved to transfer hydrophilic noble metal salts through the solvent into the nanospheres by either liquid−liquid or solid−liquid phase transfer. Subsequently, reduction of the noble metal salt with lithium triethylborohydride led to the formation of 2−5 nm sized noble metal colloids. If the network density of the shell of…
Using Janus Nanoparticles To Trap Polymer Blend Morphologies during Solvent-Evaporation-Induced Demixing
2015
Using ternary blends of polystyrene (PS), poly(methyl methacrylate) (PMMA), and Janus particles (JPs) with symmetric PS and PMMA hemispheres, we demonstrate the stabilization of dispersed and bicontinuous phase-separated morphologies by the interfacial adsorption of Janus particles during demixing upon solvent removal. The resulting blend morphology could be varied by changing the blend composition and JP loading. Increasing particle loading decreased the size of phase-separated domains, while altering the mixing ratio of the PS/PMMA homopolymers produced morphologies ranging from PMMA droplets in a PS matrix to PS droplets in a PMMA matrix. Notably, bicontinuous morphologies were obtained …
Tetrahydrofuran: More than a “Randomizer” in the Living Anionic Copolymerization of Styrene and Isoprene: Kinetics, Microstructures, Morphologies, an…
2020
The statistical anionic copolymerization of isoprene (I) and styrene (S) is commonly used to synthesize tapered block copolymers, enabling control of the phase behavior by adjusting the order–disor...
Adsorption of di-and triblock copolymers with functionalized butadiene-styrene blocks from dilute solution
1995
Abstract The adsorption behaviour of functionalized polystyrene-block-polybutadiene diblock copolymers, P(S-b-B), and polybutadiene-block-polystyrene-block-polybutadiene triblock copolymers, P(B-b-S-b-B), from dilute solutions in toluene onto silicon wafers was investigated by means of null-ellipsometry. Polar 4-(3,5-dioxo- 1,2,4-triazolidin-4-yl) benzoic acid groups (urazole groups) were attached randomly to the butadiene blocks. The PS blocks and the PB blocks adsorb not on the substrate surface, but only on the polar functional groups. It was verified that the adsorbed amount does not depend on the number of functional groups nor on the degree of polymerization of the polybutadiene block…
The glass transition of mixtures of polystyrene with alkyl-terminated oligostyrene — experimental evidence for microphase separation in a polymer ble…
1995
Mixtures of high molecular weight polystyrene (P n = 961.5 ; T g = 373 K) and sec-butyl-terminated oligostyrene (P n = 10.6 ; T g = 302 K) show a dependence of the glass transition on the composition (i.e., number-average molecular weight) which cannot be described by the classic equations of Fox & Flory or Kanig & Ueberreiter. Addition of small amounts of the oligostyrene strongly decreases the glass transition, and above an oligomer content of 40 wt.-% the glass transition remains constant within experimental error. This behavior can be attributed to the unfavorable interactions between the alkyl-terminated oligomer and the high molecular weight PS. As a result the oligomer is a bad solve…
Influence of the Copolymer Content on the Miscibility, Phase Behaviour and Morphology of a DGEBA/Polystyrene/Styrene-co-Maleic Anhydride Ternary Blend
2009
The miscibility, phase behaviour and morphology of ternary systems, formed by a DGEBA-based epoxy resin, polystyrene (PS) and styrene-co-maleic anhydride (SMA) copolymers have been investigated through phase diagrams. The analysis has been done in the absence and in the presence of 4,4'-methylene bis(2,6-diethyl aniline) (MDEA) as curing agent. In both cases, the influence of the copolymer content on blend compatibility, has been discussed. The results show that miscibility is enhanced by the presence of SMA copolymer in the blend and as the MA content in the copolymer is increased (from 7 to 14wt.-%), due to specific H-bonding interactions between the H-donor hydroxyl groups on the epoxy r…
Slow crack propagation in polyethylene: determination and prediction
1991
Abstract A model is developed connecting the stress intensity factor KI with the propagation rate d h d t of slow cracks. The model is based on the concept of the chain relaxation capability. Experimental KIversus d h d t data are reported for polyethylenes of varying molecular mass M, density ϱ, initial notch length h0 and at different stress levels σ. Predictions of the theory concerning the effect of each of these parameters on crack propagation are confirmed by the experimental results. In particular, the equation for KI as a function of d h d t does not contain h0 nor σ. Experimental plots of KIversus d h d t for common M but different h0 values coincide into a single curve. Also plots…
Linking structure and nanomechanical properties via instrumented nanoindentations on well-defined and fine-tuned morphology poly(ethylene)
2009
Several poly(ethylene) samples with a broad range of morphologies were studied in this work using nanoindentations. The samples had degrees of crystallinity ranging from 30 to 100% while their Young's modulus ranged from few tens of MPa up to several GPa. Experimental conditions for the correct evaluation of Young's modulus were at first identified, choosing a suitable loading rate in order to minimize viscoelastic effects on the unloading. The force curves, i.e., plots of applied load vs. penetration depth, were then analyzed following two common procedures available in the literature. None of these procedures leads to satisfying results when compared to other experimental techniques. Howe…
Conformational Properties of Semiflexible Chains at Nematic Ordering Transitions in Thin Films: A Monte Carlo Simulation
2014
Athermal solutions of semiflexible macromolecules with excluded volume interactions and with varying concentration (dilute, semidilute, and concentrated solutions) in a film of thickness D between ...
Monte Carlo modelling of the polymer glass transition
1993
We are proposing a lattice model with chemical input for the computer modelling of the polymer glass transition. The chemical input information is obtained by a coarse graining procedure applied to a microscopic model with full chemical detail. We use this information on Bisphenol-A-Polycarbonate to predict it's Vogel-Fulcher temperature out of a dynamic Monte Carlo Simulation. The microscopic structure of the lattice model is that of a genuine amorphous material, and the structural relaxation obeys the time temperature superposition.