Tuning the Viscoelastic Properties of Poly(<i>n</i>‑butyl acrylate) Ionomer Networks through the Use of Ion-Pair Comonomers

An organic ion-pair comonomer (IPC) based on anionic and cationic styrenic monomers was synthesized and copolymerized with <i>n</i>-butyl acrylate (BA) by reversible addition–fragmentation chain transfer (RAFT) polymerization to generate physically cross-linked polyampholyte ionomer networks. Evidence of microphase separation of the ion pairs to produce ion-rich domains was found by rheological and atomic force microscopy measurements. Comparison of these polymers to chemically similar cationic and anionic ionomers with only one type of ion covalently bound to the polymer backbone demonstrated that the connectivity of the ions to the polymer backbone had a strong effect on the viscoelastic properties. Characterization of the corresponding polyelectrolytes showed a ca. 125 °C increase in the glass transition temperature (<i>T</i>_g) from the cationic to the polyampholytic polyelectrolyte. In the ionomers, this elevated <i>T</i>_g allowed the vitrification of the ion-rich domains at ambient temperatures in the polyampholyte networks over a range of ion-pair concentrations. This produces long-lived physical cross-links at room temperature. The weak microphase separation of the neutral and ionic segments resulted in the increase of the effective volume fraction of the ion-rich domains, increasing the resulting modulus of the ionomers and plasticization of the ion-rich domains with the low <i>T</i>_g BA segments. This plasticization allowed ion hopping at accessible temperatures to enable thermoplastic processing at 150–200 °C. More generally, this work demonstrates that variation of the connectivity of the ion pairs is a facile method to tune the thermomechanical behavior of ionomers with nonmetal ion pairs

Facile Fabrication of a Shape Memory Polymer by Swelling Cross-Linked Natural Rubber with Stearic Acid

A facile method was developed for fabrication of a robust shape memory polymer by swelling cross-linked natural rubber with stearic acid. Commercial rubber bands were swollen in molten stearic acid at 75 °C (35 wt % stearic acid loading). When cooled the crystallization of the stearic acid formed a percolated network of crystalline platelets. The microscopic crystals and the cross-linked rubber produce a temporary network and a permanent network, respectively. These two networks allow thermal shape memory cycling with deformation and recovery above the melting point of stearic acid and fixation below that point. Under manual, strain-controlled, tensile deformation the shape memory rubber bands exhibited fixity and recovery of 100% ± 10%

Morphology Control in Mesoporous Carbon Films Using Solvent Vapor Annealing

Ordered mesoporous (2–50 nm) carbon films were fabricated using cooperative self-assembly of a phenolic resin oligomer with a novel block copolymer template (poly­(styrene-<i>block</i>-<i>N</i>,<i>N</i>-dimethyl-<i>n</i>-octadecylamine <i>p</i>-styrenesulfonate), (PS-<i>b</i>-PSS-DMODA)) synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. Due to the high <i>T</i>_g of the PS segment and the strong interactions between the phenolic resin and the PSS-DMODA, the segmental rearrangement is kinetically hindered relative to the cross-linking rate of the phenolic resin, which inhibits long-range ordering and yields a poorly ordered mesoporous carbon with a broad pore size distribution. However, relatively short exposure (2 h) to controlled vapor pressures of methyl ethyl ketone (MEK) yields significant improvements in the long-range ordering and narrows the pore size distribution. The average pore size increases as the solvent vapor pressure during annealing increases, but an upper limit of <i>p</i>/<i>p</i>₀ = 0.85 exists above which the films dewet rapidly during solvent vapor annealing. This approach can be extended using mesityl oxide, which has similar solvent qualities to MEK, but is not easily removed by ambient air drying after solvent annealing. This residual solvent can impact the morphology that develops during cross-linking of the films. These results illustrate the ability to fine-tune the mesostructure of ordered mesoporous carbon films through simple changes in the processing without any compositional changes in the initial cast film

Tailor-Made Fluorinated Copolymer/Clay Nanocomposite by Cationic RAFT Assisted Pickering Miniemulsion Polymerization

Fluorinated polymers in emulsion find enormous applications in hydrophobic surface coating. Currently, lots of efforts are being made to develop specialty polymer emulsions which are free from surfactants. This investigation reports the preparation of a fluorinated copolymer via Pickering miniemulsion polymerization. In this case, 2,2,3,3,3-pentafluoropropyl acrylate (PFPA), methyl methacrylate (MMA), and <i>n</i>-butyl acrylate (nBA) were copolymerized in miniemulsion using Laponite-RDS as the stabilizer. The copolymerization was carried out via reversible addition–fragmentation chain transfer (RAFT) process. Here, a cationic RAFT agent, <i>S</i>-1-dodecyl-<i>S</i>′-(methylbenzyltriethylammonium bromide) trithiocarbonate (DMTTC), was used to promote polymer-Laponite interaction by means of ionic attraction. The polymerization was much faster when Laponite content was 30 wt % or above with 1.2 wt % RAFT agent. The stability of the miniemulsion in terms of zeta potential was found to be dependent on the amount of both Laponite and RAFT agent. The miniemulsion had particle sizes in the range of 200–300 nm. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) analyses showed the formation of Laponite armored spherical copolymer particles. The fluorinated copolymer films had improved surface properties because of polymer–Laponite interaction

Solvent Dependence of the Morphology of Spin-Coated Thin Films of Polydimethylsiloxane-Rich Polystyrene-<i>block</i>-Polydimethylsiloxane Copolymers

The as-spun, thin film morphologies of a series polydimethylsiloxane-rich cylinder and lamellar-forming polystyrene-<i>block</i>-polydimethylsiloxane (PS<i>-<i>b</i>-</i>PDMS) copolymers with constant PDMS molecular weight and varying PS volume fraction were studied with a range of solvents of varying solubility parameter. It was found that PDMS occupies the surface of the thin films regardless of the choice of solvent used in spin-coating due to its extremely low surface tension. The morphology shifted from parallel cylinders to hexagonally perforated lamellar to parallel lamellar as the solvent was varied from PDMS to PS selective solvents (increasing solvent solubility parameter). The transition points between each morphology were also dependent on the volume fraction of the block copolymer where the transitions were observed at lower solubility parameter with increasing PS volume fraction of the polymer. The morphology variations are attributed to selective swelling effects of the individual blocks even under good solvent conditions. These results are discussed in the context of current theories of solvent evaporation induced ordering of block copolymer thin films

Thickness Limit for Alignment of Block Copolymer Films Using Solvent Vapor Annealing with Shear

The swelling and deswelling of a cross-linked polydimethylsiloxane (PDMS) pad adhered to a block copolymer (BCP) film during solvent vapor annealing (SVA) provides sufficient shear force to produce highly aligned domains over macroscopic dimensions in thin films. Here, we examine how far this alignment can propagate through the thickness of a BCP film to understand the limits for efficacy of the SVA-S (SVA with shear) process. Films of cylinder-forming polystyrene-<i>block</i>-polyisoprene-<i>block</i>-polystyrene (SIS) ranging from 100 nm to more than 100 μm are examined using the same processing conditions. The SIS surface in contact with the PDMS is always well-aligned, with Herman’s orientation parameter (<i>S</i>) exceeding 0.9 as determined from AFM micrographs, but the bottom surface in contact with the silicon wafer is not aligned for the thickest films. The average orientation through the film thickness was determined by transmission small-angle X-ray scattering (SAXS), with <i>S</i> decreasing gradually with increasing thickness for SIS films thinner than 24 μm, but <i>S</i> remains >0.8. <i>S</i> precipitously decreases for thicker films. A stop-etch-image approach allows the gradient in orientation through the thickness to be elucidated. The integration of this local orientation profile agrees with the average <i>S</i> obtained from SAXS. These results demonstrate the effective alignment of supported thick BCP films of order 10 μm, which could be useful for BCP coatings for optical applications

Three-Dimensional Printed Shape Memory Objects Based on an Olefin Ionomer of Zinc-Neutralized Poly(ethylene-<i>co</i>-methacrylic acid)

Three-dimensional printing enables the net shape manufacturing of objects with minimal material waste and low tooling costs, but the functionality is generally limited by available materials, especially for extrusion-based printing, such as fused deposition modeling (FDM). Here, we demonstrate shape memory behavior of 3D printed objects with FDM using a commercially available olefin ionomer, Surlyn 9520, which is zinc-neutralized poly­(ethylene-<i>co</i>-methacrylic acid). The initial fixity for 3D printed and compression-molded samples was similar, but the initial recovery was much lower for the 3D printed sample (<i>R</i> = 58%) than that for the compression-molded sample (<i>R</i> = 83%). The poor recovery in the first cycle is attributed to polyethylene crystals formed during programming that act to resist the permanent network recovery. This effect is magnified in the 3D printed part due to the higher strain (lower modulus in the 3D printed part) at a fixed programming stress. The fixity and recovery in subsequent shape memory cycles are greater for the 3D printed part than for the compression-molded part. Moreover, the programmed strain can be systematically modulated by inclusion of porosity in the printed part without adversely impacting the fixity or recovery. These characteristics enable the direct formation of complex shapes of thermoplastic shape memory polymers that can be recovered in three dimensions with the appropriate trigger, such as heat, through the use of FDM as a 3D printing technology

Three-Dimensional Printed Shape Memory Objects Based on an Olefin Ionomer of Zinc-Neutralized Poly(ethylene-<i>co</i>-methacrylic acid)

Three-dimensional printing enables the net shape manufacturing of objects with minimal material waste and low tooling costs, but the functionality is generally limited by available materials, especially for extrusion-based printing, such as fused deposition modeling (FDM). Here, we demonstrate shape memory behavior of 3D printed objects with FDM using a commercially available olefin ionomer, Surlyn 9520, which is zinc-neutralized poly­(ethylene-<i>co</i>-methacrylic acid). The initial fixity for 3D printed and compression-molded samples was similar, but the initial recovery was much lower for the 3D printed sample (<i>R</i> = 58%) than that for the compression-molded sample (<i>R</i> = 83%). The poor recovery in the first cycle is attributed to polyethylene crystals formed during programming that act to resist the permanent network recovery. This effect is magnified in the 3D printed part due to the higher strain (lower modulus in the 3D printed part) at a fixed programming stress. The fixity and recovery in subsequent shape memory cycles are greater for the 3D printed part than for the compression-molded part. Moreover, the programmed strain can be systematically modulated by inclusion of porosity in the printed part without adversely impacting the fixity or recovery. These characteristics enable the direct formation of complex shapes of thermoplastic shape memory polymers that can be recovered in three dimensions with the appropriate trigger, such as heat, through the use of FDM as a 3D printing technology

Bimodal Porous Carbon-Silica Nanocomposites for Li-Ion Batteries

Bimodal porous carbon-silica (BP-CS) nanocomposites exhibit advantageous properties from a design perspective for low-cost lithium-ion battery anodes. The BP-CS nanocomposites were fabricated using cooperative self-assembly of phenolic resin, tetraethylorthosilicate, and Pluronic F127 via a scalable roll-to-roll method. An etching reaction between molten KOH and silica at high temperature (∼700 °C) introduces micropores and increases the surface area from 446 m²/g to 1718 m²/g without the loss of the ordered mesostructure. This large surface area after etching is generally advantageous for electrochemical energy storage. The carbon framework not only provides electrical conductivity but also constrains the volumetric changes of SiO₂ during Li⁺ insertion and extraction to improve the capacity stability on charge–discharge cycling. The bimodal pores of BP-CS facilitate lithium-ion diffusion (mesopores) while maximizing the contact area between the electrolyte and electrode (micropores) as well as providing stress relief from Li⁺ insertion. These characteristics lead to a discharge capacity of 611 mAh g^–1 after 200 cycles at 200 mA g^–1 with over 99.5% Coulombic efficiency for all discharge cycles. Even when increasing the current rate to 3 A g^–1, a capacity of 313 mAh g^–1 is retained after 1500 cycles, corresponding to <0.005% fade in the capacity per cycle. The combination of a high rate performance, a good cycle stability at a high rate, and a scalable synthesis route with low-cost precursors makes BP-CS a promising inexpensive, carbon/SiO₂-based anode material for long lifetime batteries

Large-Scale Roll-to-Roll Fabrication of Ordered Mesoporous Materials using Resol-Assisted Cooperative Assembly

Roll-to-roll (R2R) processing enables the rapid fabrication of large-area sheets of cooperatively assembled materials for production of mesoporous materials. Evaporation induced self-assembly of a nonionic surfactant (Pluronic F127) with sol–gel precursors and phenolic resin oligomers (resol) produce highly ordered mesostructures for a variety of chemistries including silica, titania, and tin oxide. The cast thick (>200 μm) film can be easily delaminated from the carrier substrate (polyethylene terephthalate, PET) after cross-linking the resol to produce meter-long self-assembled sheets. The surface areas of these mesoporous materials range from 240 m²/g to >1650 m²/g with these areas for each material comparing favorably with prior reports in the literature. These R2R methods provide a facile route to the scalable production of kilograms of a wide variety of ordered mesoporous materials that have shown potential for a wide variety of applications with small-batch syntheses