Microphase Separation Of Diblock Copolymers Research Articles

Synthesis of Self-Assembled Metal-Oxide Nanostructures in a Diblock Copolymer Matrix and Integration onto Semiconductor Surfaces

ABSTRACTThe synthesis of self-assembled ZnO nanostructures at room temperature using a microphase separated diblock copolymer as a template is reported. Poly(norbornene) / poly(norbornene-dicarboxylic acid) diblock copolymers were synthesized using Ring Opening Metathesis Polymerization (ROMP). The polymers were dissolved and the solutions were doped with ZnCl2. Films were formed from this solution, and subsequently reacted with NH4OH. This converted the ZnCl2 into ZnO contained within the microphase-separated nanodomains of the block copolymer. Fourier Transform Infrared Spectroscopy verified the association of the metal to the second block of the polymer, and X-ray Photoelectron Spectroscopy verified the conversion of the salt to ZnO nanoclusters. The development of such ZnO - block copolymer nanocomposites is targeting the functionalization of nanostructures into device technologies.

Electroless Deposition of Nanoscale Copper Patterns via Microphase-Separated Diblock Copolymer Templated Self-Assembly

By use of an ultrathin film of microphase-separated poly(styrene-block-methyl methacrylate) as a template, nanometer-scale patterns of tetraalkylammonium passivated palladium colloids can be generated. This pattern serves, in turn, as the template for the electroless deposition of semicontinuous 20 nm wide copper nanostructures, which is approximately a factor of 2 smaller than feature sizes that can be generated by state-of-the-art lithographic processes.

Membrane catalysts for partial hydrogenation of 1,3-butadiene: catalytic properties of palladium nanoclusters synthesized within diblock copolymer films

Palladium nanoclusters were synthesized within microphase-separated diblock copolymer films of [MTD] 113[Pd(Cp N)PA] 50 (MTD=methyltetracyclododecene, Cp N= endo-2-(cyclopentadienylmethyl)norborn-5-ene, PA=η 3-1-phenylallyl). The organometallic repeat units were reduced by exposing the films to hydrogen at 100°C, leading to the formation of nearly monodisperse palladium nanoclusters. TEM was used to measure the cluster size. The nanocomposite films were active and selective catalysts for the gas phase hydrogenation of 1,3-butadiene. Selectivity for butenes was improved by lowering the hydrogen partial pressure, and lower temperature favored formation of 1-butene over 2-butenes.

Synthesis and microphase separation of diblock copolymers of styrene and p-chlorostyrene prepared by using N-oxyl capped macroinitiators

Diblock copolymers of styrene and p-chlorostyrene (PS-b-PpClS) were prepared via chain extension polymerization of N-oxyl-capped polystyrene macroinitiators with p-chlorostyrene. The kinetics plots of the copolymerizations are approximately first order with respect to monomer concentrations. The addition of p-chlorostyrene to the macroinitiators yields microphase separated polymers, which were studied by transmission electron microscopy and small-angle X-ray scattering. The results on the morphology of the block copolymers obtained by both methods are in excellent agreement. A variety of block copolymer structures ranging from highly ordered hexagonally packed cylinders or systems with the simultaneous occurrence of cylinders and lamellae to relatively disordered spheres is observed.

Synthesis and microphase separation of diblock copolymers of styrene andp-chlorostyrene prepared by usingN-oxyl capped macroinitiators

Diblock copolymers of styrene and p-chlorostyrene (PS-b-PpClS) were prepared via chain extension polymerization of N-oxyl-capped polystyrene macroinitiators with p-chlorostyrene. The kinetics plots of the copolymerizations are approximately first order with respect to monomer concentrations. The addition of p-chlorostyrene to the macroinitiators yields microphase separated polymers, which were studied by transmission electron microscopy and small-angle X-ray scattering. The results on the morphology of the block copolymers obtained by both methods are in excellent agreement. A variety of block copolymer structures ranging from highly ordered hexagonally packed cylinders or systems with the simultaneous occurrence of cylinders and lamellae to relatively disordered spheres is observed.

Domain patterns in copolymer-homopolymer mixtures

We introduce a dynamical model and carry out computer simulations for phase separation of diblock copolymer-homopolymer mixtures. The homopolymer chains are assumed to be compatible with one of the blocks of the diblock copolymers whereas the two blocks of the diblock copolymer chains are mutually incompatible. In this system, two kinds of phase separation, namely macrophase separation of diblock copolymers and homopolymers and microphase separation in diblock copolymers, take place simultaneously by decreasing temperature. Depending on the strength of the interactions, the domain pattern and its ordering process are changed. We can see both phenomena. One is macrophase separation, which dominates the time evolution of the system; the other is the formation of the mesoscale structure in the whole of the system. We show some typical phase-separated patterns and investigate the kinetics of phase ordering of these patterns by evaluating structure factors.

Synthesis of metal nanoclusters within microphase-separated diblock copolymers: sodium carboxylate vs carboxylic acid functionalization

Conversion of carboxylic acid groups, within the morphologies of [MTD] 400[NORCOOH] 50 diblock copolymers, to the sodium carboxylate form, [MTD] 400[NORCOONa] 50, results in large increases in both the rate and extent of transition metal and rare earth ion uptake from metal acetates, chlorides, nitrates, and sulfates. A[MTD] 400[NORCOONa] 50 film was subjected to four consecutive Ag + loading and reduction sequences, resulting in a cumulative loading of approximately 26 wt% Ag in the overall polymer/Ag composite. Mean crystal diameters of 37, 50, 64, and 65 Å were estimated following the first, second, third, and fourth, loading and reduction sequences, respectively. During a single loading and reduction sequence, cluster size (ca. 30 Å) within [MTD] 400[NORCOOH] 50 was found to be relatively insensitive to the extent of Ag + uptake, for loadings between 40 and 500 mg Ag +/g polyNORCOOH, consistent with a nucleation-controlled cluster formation process.

Catalytic properties of palladium nanoclusters synthesized within diblock copolymer films: hydrogenation of ethylene and propylene

Palladium nanoclusters were synthesized within microphase-separated diblock copolymer films of [MTD] 113[Pd(Cp N)PA] 50 (MTD=methyltetracyclododecene, Cp N= endo-2-(cyclopentadienylmethyl)norborn-5-ene, PA= η 3-1-phenylallyl). The organometallic repeat units were reduced by exposing the films to hydrogen at 100°C, leading to the formation of nearly monodisperse palladium nanoclusters. TEM, SAXS, and WAXS were used to characterized the polymer morphology and cluster size. The nanocomposites were active catalysts for hydrogenation of ethylene and propylene. The cluster size and voids within the polymer matrix were important factors in determining the catalyst activity, expressed as the moles of alkene hydrogenated per mole palladium per second. In contrast to permeation results that showed that the permeability of propylene in polyMTD is greater than that of ethylene, the catalyst activity for hydrogenation of ethylene was greater than that for propylene.

Switching supramolecular polymeric materials with multiple length scales

It was demonstrated that polymeric supramolecular nanostructures with several length scales allow straightforward tailoring of hierarchical order-disorder and order-order transitions and the concurrent switching of functional properties. Poly(4-vinyl pyridine) (P4VP) was stoichiometrically protonated with methane sulfonic acid (MSA) to form P4VP(MSA)1.0, which was then hydrogen-bonded to pentadecylphenol. Microphase separation, re-entrant closed-loop macrophase separation, and high-temperature macrophase separation were observed. When MSA and pentadecylphenol were complexed to the P4VP block of a microphase-separated diblock copolymer poly[styrene-block-(4-vinyl pyridine)], self-organized structures-in-structures were obtained whose hierarchical phase transitions can be controlled systematically. This microstructural control on two different length scales (in the present case, at 48 and 350 angstroms) was then used to introduce temperature-dependent transitions in electrical conductivity.

Lower and Upper Critical Ordering Temperatures in Compressible Diblock Copolymer Melts from a Perturbed Hard-Sphere-Chain Equation of State

The random-phase approximation is combined with the perturbed hard-sphere-chain (PHSC) equation of state for copolymer systems to represent the microphase separation transition in compressible diblock copolymer melts. The PHSC equation of state takes into account the equation-of-state effect that results from differences in compressibility between pairs of segments comprising a diblock copolymer; these differences favor demixing. Upon increasing the temperature of a microphase-separated diblock copolymer melt, theory first predicts an order-to-disorder transition that corresponds to the upper-critical-solution-temperature behavior in the binary blend of parent homopolymers. At conditions where the equation-of-state effect is significant, theory also predicts a disorder-to-order transition at further elevated temperature that follows closely the lower-critical-solution-temperature behavior in the binary blend containing the parent homopolymers. To compare theory with experiment, we obtain the binary intera...

Synthesis of Cu and CuO nanoclusters within microphase-separated diblock copolymers

A general methodology has been established for the synthesis of 40–120 A Cu nanoclusters within the morphologies of [MTD]400[NORCOOH]50 and [MTD]400[NORCOONa]50 diblock copolymer films. In this technique the films are soaked in aqueous copper(II) acetate solutions prior to reduction of the sequestered Cu2+ ions. A loading of 4.2 wt% Cu in the overall polymer–Cu composite was achieved in the case of [MTD]400[NORCOONa]50, during a single loading and reduction sequence. Upon exposure of the films to air, the polymer-imbedded Cu nanoclusters oxidize to form CuO. The transparent polymer–CuO composite films exhibit a broad absorption in the near-infrared region and may have potential applications as near-infrared filters.

Instabilities and Disorder of the Domain Patterns in Systems with Competing Interactions

The dynamics of the domains is studied in a two-dimensional model of the microphase separation of diblock copolymers in the vicinity of the transition. A criterion for the validity of the mean field theory is derived. It is shown that at certain temperatures the ordered hexagonal pattern becomes unstable with respect to the two types of instabilities: the radially-nonsymmetric distortions of the domains and the repumping of the order parameter between the neighbors. Both these instabilities may lead to the transformation of the regular hexagonal pattern into a disordered pattern.

The amplitude and phase-diffusion equations for lamellar patterns in block copolymers

The phase-diffusion equation which describes the behavior of lamellar patterns in microphase-separated diblock copolymers is derived. All the long-wavelength instability boundaries are identified. Also derived is the amplitude equation near the onset of microphase separation. The relation between various models of lamella-forming systems is explored.

Synthesis of metal nanoclusters within microphase-separated diblock copolymers: ICP-AES analysis of metal ion uptake

The rate and extent of aqueous metal ion transport (Ag +, Au +3, Cu +2, Eu +2, Eu +3, Fe +2, Fe +3, Gd +3, Ni +2, Pd +2, Pt +2, and Pt +4) into microphase-separated block copolymers of methyl-tetracyclododecene (MTD) and 2-norbornene-5,6,-dicar☐ylic acid (NORCOOH) was monitored using inductively coupled plasma atomic emission spectroscopy. Continuous interconnected polyNORCOOH domains were found to be necessary for metal ion uptake. The metal-bound car☐ylate ions in the polyNORCOOH domains can be re-protonated by hydrogen reduction, rendering them active for further participation in metal binding. Following reduction, metal nanocluster-containing films were characterized using wide-angle X-ray scattering, infrared spectroscopy, and ultraviolet-visible spectroscopy.

Microphase separation of diblock copolymer induced by directional quenching

Computer simulation is carried out for studying the microphase separation of a two-dimensional diblock copolymer (DBCP) system under directional quenching. By setting the quenching boundary between the stable and the unstable phase, and shifting the boundary with a constant velocity, the time evolution of the domain morphologies is examined numerically on the basis of the time-dependent Ginzburg–Landau type equation with the free-energy functional for the DBCP. Three different types of morphologies are found for the symmetric (i.e., f=0.5) DBCP system. One is the irregular lamellar morphology and is essentially equivalent to that produced by homogeneous quenching. The other two are regular and are characteristics of directional quenching process. One of the regular lamellar morphologies is perpendicular to the quench boundary on the average, whereas the other one is parallel to the quench boundary. For the asymmetric DBCP system with f=0.4, which forms the equilibrium morphology of triangular phase, the mode of regular lamellar morphology with the normal of lamellae perpendicular to the quench boundary appears first under the condition of directional quenching when the initial thermal fluctuation is very small. The growth rate of the triangular phase gets faster when the initial thermal fluctuation increases. Therefore, our results reveal that the thermal fluctuation promotes the appearance of the mode of triangular morphology for the case of f=0.4.

Synthesis of metal nanoclusters within microphase-separated diblock copolymers: a ‘universal’ approach

A general methodology has been established for the synthesis of transition metal nanoclusters within the carboxylic acid functionalized domains of microphase-separated block copolymer films. In this technique the films are soaked in aqueous metal salt solutions prior to reduction of the sequestered metal ions with hydrogen or aqueous NaBH 4. Transmission electron microscopy observation, scanning transmission electron microscopy observation, electron scattering analysis and wide-angle X-ray scattering analysis were used to characterize the size, composition and crystal structure of the resulting metal nanoclusters.

Some mathematical aspects of the micro-phase separation in diblock copolymers

Abstract A free energy functional of nonlocal type is considered that was originally introduced to describe the micro-phase separation of diblock copolymer. A mathematical framework is given to the issues of the scaling law for stationary states and the governing equation of morphology. The scaling law is equivalent to finding a nice rescaling in order to have a well-defined limiting interfacial problem which is free from the interfacial thickness and the total chain length of copolymer, and the associated stationary problem becomes a morphology equation that governs the configuration of final patterns. Although the steady patterns become finer and finer in our scaling limit due to the mesoscopic nature, a possible rigorous approach is presented to stability and morphological selection problems for them.

Synthesis of PbS Nanoclusters within Microphase-Separated Diblock Copolymer Films

Synthesis of PbS Nanoclusters within Microphase-Separated Diblock Copolymer Films

Crystallization behaviour of a microphase-separated diblock copolymer

The crystallization behaviour of a microphase-separated diblock copolymer, ϵ-caprolactone- block-butadiene (PCL- b-PB), was observed by small-angle X-ray scattering employing synchrotron radiation. The Avrami analysis at the early stage of crystallization did not show any significant difference between PCL- b-PB and a poly(ϵ-caprolactone) homopolymer (PCL), suggesting that the initially existing microphase structure does not affect the early stage of crystallization. In the late stage, the crystallization of PCL- b-PB was significantly retarded compared to the case of PCL, and the rate was dependent on the microphase structure and/or molecular characteristics of the copolymer.

Molecular-weight factors affecting formation of the OBBD morphology in block copolymer blends

Microphase-separated diblock copolymers have been known since 1970 to exhibit three principal morphologies. These morphologies depend on the composition of the copolymer and include dispersed spheres of the minor component on either a BCC or FCC lattice, dispersed cylinders of the minor component on a hexagonal lattice, or alternating lamellae. Recent microstructural studies of starblock and diblock copolymers have shown that an ordered bicontinuous morphology is observed between the lamellar and cylindrical regimes. This microstructure is currently referred to as the ordered bicontinuous double-diamond (OBDD) morphology and is an example of the Pn3m space group. In poly(styrene-b-isoprene) (SI) diblock copolymers, it exists at approximately 62-66 vol% polystyrene (PS). Efforts aimed at producing this morphology by blending a copolymer with various PS homopolymers have also been successful, when the blend composition is 65-67 vol% PS and the molecular weight of the hompolymer (Mhps) is less than that of the styrene block in the copolymer (Ms). In this work, we have used transmission electron microscopy to elucidate some additional factors responsible for development of the OBDD and other bicontinuous morphologies.