Search results for "Architecture"
showing 10 items of 3706 documents
A Versatile Technique to Produce Porous Polymeric Scaffolds: The Thermally Induced Phase Separation (TIPS) Method
2017
Among the various scaffold fabrication techniques, thermally induced phase separation (TIPS) is one of the most versatile methods to produce porous polymeric scaffold and it has been largely used for its capability to produce highly porous and interconnected scaffolds. The scaffold architecture can be closely controlled by varying the process parameters, including polymer type and concentration, solvent/non-solvent ratio and thermal history. TIPS technique has been widely employed, also, to produce scaffolds with a hierarchical pore structure and composite polymeric matrix/inorganic filler foams.
The effect of free polymer on the interactions and the glass transition dynamics of microgel colloids.
2002
By studying the phase behaviour and the short range order of polystyrene microgel colloids in a good solvent we demonstrated that these particles can be considered as hard spheres or nearly hard spheres if the internal cross link density is made sufficiently high. A binary mixture of 1:50 crosslinked (1 crosslink per 50 monomers) particles with a size ratio R(small)/R(large) = 0.83 and a number ratio N(small)/N(large) = 2.7 was characterized with respect to the short range order and glass transition dynamics. We found that this mixture can be mapped onto a one-component hard sphere system with an effective polydispersity of 11%, even though for the particle interactions an inverse power pot…
Impact of Amino-Functionalization on the Response of Poly(ethylene glycol) (PEG) to External Stimuli
2022
It is shown that amino-functionalization of poly(ethylene glycol) (PEG) with the comonomer N,N-diethyl glycidyl amine (DEGA) triggers the emergence of extraordinary stimuli responsiveness and phase behavior of PEG. In dependence of the solution pH, tapered PEG-co-PDEGA exhibits a highly cooperative two-step inverse phase transition with respect to temperature. The polymer forms dispersed metastable nanoglobules in the medically relevant temperature range around human body temperature. Independently, cloud points can be adjusted between 40 and 90 °C via the pH of the solution. Changing the polymer architecture to a block structure, in pronounced contrast, the polymer exhibits a gradual growt…
Correlation between polymer architecture, mesoscale structure and photovoltaic performance in side-chain-modified poly(p-arylene-ethynylene)-alt-poly…
2011
Abstract Recent investigations have shown that an anthracene containing poly( p -arylene-ethynylene)-alt-poly( p -arylene-vinylene) statistical copolymer consisting of a well defined conjugated backbone, along which linear and branched alkoxy side chains are attached in a random manner, yields, compared to its counterparts with regular side chain substitution, an improved performance in polymer [6,6]:-phenyl-C 61 -butyric acid methyl ester (PCBM) bulk-heterojunction solar cells. The microscopic origin for the improved power conversion efficiency ( η ≈ 3.8%) of the statistical copolymer – which is the best in its material class – has not been resolved. We conducted grazing incidence wide-an…
Controlling supramolecular polymerization through multicomponent self-assembly
2016
The self-assembly into supramolecular polymers is a process driven by reversible non-covalent interactions between monomers, and gives access to materials applications incorporating mechanical, biological, optical or electronic functionalities. Compared to the achievements in precision polymer synthesis via living and controlled covalent polymerization processes, supramolecular chemists have only just learned how to developed strategies that allow similar control over polymer length, (co)monomer sequence and morphology (random, alternating or blocked ordering). This highlight article discusses the unique opportunities that arise when coassembling multicomponent supramolecular polymers, and …
Simulating Copolymeric Nanoparticle Assembly in the Co-solvent Method: How Mixing Rates Control Final Particle Sizes and Morphologies
2018
Abstract The self-assembly of copolymeric vesicles and micelles in micromixers is studied by External Potential Dynamics (EPD) simulations – a dynamic density functional approach that explicitly accounts for the polymer architecture both at the level of thermodynamics and dynamics. Specifically, we focus on the co-solvent method, where nanoparticle precipitation is triggered by mixing a poor co-solvent into a homogeneous copolymer solution in a micromixer. Experimentally, it has been reported that the flow rate in the micromixers influences the size of the resulting particles as well as their morphology: At small flow rates, vesicles dominate; with increasing flow rate, more and more micell…
Phase transitions in a single polymer chain: A micro-canonical analysis of Wang–Landau simulations
2008
Abstract We present simulation results for the phase behavior of a single chain for a flexible lattice polymer model using the Wang–Landau sampling idea. Using the micro-canonical density of states obtained with this method we will discuss the ability of an analysis in the micro-canonical ensemble to locate the coil-globule (continuous) and liquid–solid (first-order) transitions found for this problem using a canonical analysis.
Adsorption of Oligomers and Polymers into a Polymer Brush Formed from Grafted Ring Polymers
2013
The interaction of a ring polymer brush with a solution containing oligomers or free linear flexible macromolecules is studied by Monte Carlo simulation, varying the chain length of the free chains, and in selected cases also the lengths of the rings. Two grafting densities are studied, corresponding to semidilute and very concentrated conditions, and a comparison with the corresponding case of brushes formed from grafted linear chains is made. Although the ring polymer linear dimensions in the brushes show an anomalous scaling with ring length, similar to (noncatenated) ring polymer melts, the concentration profiles of oligomers and long macromolecules in ring polymer brushes differ only v…
Structure of Polymers
2014
The structure and thermodynamics of polymers are discussed both with an adapted version of Flory’s regular solution theory and the concept of scaling and random walks. The salient properties of polymers like segregation and elasticity are discussed in terms of these concept. The Flory-Stockmayer theory of gelation is introduced and related to the percolation concept.
Frictional drag between polymer bearing surfaces
2002
Some fundamental features of friction between two polymer bearing surfaces in relative sliding motion are investigated by molecular dynamics simulations. End-tethered and adsorbed polymers are considered under good and poor solvent conditions. The shear stress is measured while varying the solvent's viscosity, surface separation, degree of polymerization and grafting density. For all systems we observe shear thinning that is attributed to the orientation of the chains along the shear direction. This effect is particularly strong for brushes, for which the shear stress during the steady sliding state is mainly determined by the degree of overlap between the brushes.