56 research outputs found
Self-consistent field theory for diblock copolymers grafted to a sphere
An efficient numerical self-consistent field theory (SCFT) algorithm is developed for treating structured polymers on spherical surfaces. The method solves the diffusion equations of SCFT with a pseudospectral approach that combines a spherical-harmonics expansion for the angular coordinates with a modified real-space CrankâNicolson method for the radial direction. The self-consistent field equations are solved with Anderson-mixing iterations using dynamical parameters and an alignment procedure to prevent angular drift of the solution. A demonstration of the algorithm is provided for thin films of diblock copolymer grafted to the surface of a spherical core, in which the sequence of equilibrium morphologies is predicted as a function of diblock composition. The study reveals an array of interesting behaviors as the block copolymer pattern is forced to adapt to the finite surface area of the sphere
The effect of polymer chain length on the mechanical properties of triblock copolymer gels
Tough and Self-Recoverable Thin Hydrogel Membranes for Biological Applications
Tough and selfârecoverable hydrogel membranes with micrometerâscale thickness are promising for biomedical applications, which, however, rarely be realized due to the intrinsic brittleness of hydrogels. In this work, for the first time, by combing noncovalent DN strategy and spinâcoating method, we successfully fabricated thin (thickness: 5â100 ”m), yet tough (work of extension at fracture: 105â107 J mâ3) and 100% selfârecoverable hydrogel membranes with high water content (62â97 wt%) in large size (â100 cm2). Amphiphilic triblock copolymers, which form physical gels by selfâassembly, were used for the first network. Linear polymers that physically associate with the hydrophilic midblocks of the first network, were chosen for the second network. The interânetwork associations serve as reversible sacrificial bonds that impart toughness and selfârecovery properties on the hydrogel membranes. The excellent mechanical properties of these obtained tough and thin gel membranes are comparable, or even superior to many biological membranes. The in vitro and in vivo tests show that these hydrogel membranes are biocompatible, and postoperative nonadhesive to neighboring organs. The excellent mechanical and biocompatible properties make these thin hydrogel membranes potentially suitable for use as biological or postoperative antiadhesive membranes
Surface Orientation of Polystyrene Based Polymers: Steric Effects from Pendant Groups on the Phenyl Ring
Near edge X-ray absorption fine structure (NEXAFS) coupled with
molecular dynamics simulations were utilized to probe the orientation
at the exposed surface of the polymer film for polystyrene type polymers
with various pendant functional groups off the phenyl ring. For all
the polymers, the surface was oriented so that the rings are nominally
normal to the film surface and pointing outward from the surface.
The magnitude of this orientation was small and dependent on the size
of the pendant functional group. Bulky functional groups hindered
the surface orientation, leading to nearly unoriented surfaces. Depth
dependent NEXAFS measurements demonstrated that the surface orientation
was localized near the interface. Molecular dynamics simulations showed
that the phenyl rings were not oriented strongly around a particular
âaverage tilt angleâ. In contrast, simulations demonstrate
that the phenyl rings exhibit a broad distribution of tilt angles,
and that changes in the tilt angle distribution with pendant functionality
give rise to the observed NEXAFS response. The more oriented samples
exhibit a higher probability of phenyl ring orientation at angles
greater than 60 degrees relative to the plane of the films surface
Implementation of CrankâNicolson scheme in cell dynamics simulation for diblock copolymers
Cellulose Nanofibrils and Diblock Copolymer Complex: Micelle Formation and Enhanced Dispersibility
A great
challenge to the utilization of bioderived cellulose nanofibrils
(CNFs) is related to dispersion, where the hydrophilic nature makes
them difficult to disperse in both organic solvents and hydrophobic
polymers. In this study, an amphiphilic diblock copolymer, polyÂ(methyl
methacrylate-<i>b</i>-acrylic acid) (PMMA-<i>b</i>-PAA), which contains a short interactive block of PAA and a long
hydrophobic block of PMMA, was utilized to modify the surface of CNFs
covered with carboxylic acid groups (CNF-COOH). The PAA block binds
to the surface carboxylic acid groups on the CNFs through the formation
of multiple hydrogen bonds, while the hydrophobic PMMA block enables
better dispersion of the CNFs as well as interfacial adhesion with
the matrix polymer. The attachment of PMMA-<i>b</i>-PAA
to the CNFs was confirmed through Fourier transform infrared spectroscopy.
Micelles were observed to form from a dispersion of CNF-COOH/PMMA-<i>b</i>-PAA complex in H<sub>2</sub>O. Good dispersion with individualized
nanofibrils has been achieved in dimethylformamide, dimethyl sulfoxide,
ethanol, and methanol even when a low amount of block copolymer was
functionalized on the CNF surface. The dispersion level of CNF-COOH/PMMA-<i>b</i>-PAA correlates well with the dielectric constant of the
solvents, where solvents with high dielectric constants are better
able to disperse the PMMA-<i>b</i>-PAA modified nanofibrils
Dissipative Particle Dynamics Study of SWCNT Reinforced Natural Rubber Composite System: An Important Role of Self-Avoiding Model on Mechanical Properties
Morphological Investigation of Midblock-Sulfonated Block Ionomers Prepared from Solvents Differing in Polarity
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