Controlled processing of polymer nanoribbons: Enabling microhelix transformations

Flow‐coated, two‐dimensional polymer ribbon structures undergo a shape‐transformation into a three‐dimensional helix upon their release into a solution. Driven by surface forces and due to geometric asymmetry, the helix radius and spring constant depend upon the ribbon cross‐section dimensions, surface energy, and material elastic modulus. Such spring‐like microhelices offer multiple functionalities combined with mechanical stretching and shape recovery. Fabricating such microhelices requires a sequence of processing steps, beginning with flow‐coating of ribbons on a substrate, followed by etching of a “scum layer” to allow for an independent release into a solution, upon which shape‐transformation occurs. During the deposition‐etch‐release sequence, various control parameters influence the nanoribbon size and geometry, hence the helix properties. The experimental study presented here focuses on the influence of meniscus height, substrate velocity, substrate surface energy, and etch time on nanoribbon size (height and width), scum layer thickness, and helix radius. The results show that meniscus height and contact angle dictate flux toward the meniscus edge and volume available for spatial assembly, allowing control over the aspect ratio of ribbons. We vary the aspect ratio by two orders of magnitude, while maintaining geometric asymmetry needed for helix shape‐transformation. We provide robust scaling for the nanoribbon size and geometry and report the advantages and disadvantages of different parameters, in the control of polymer nanoribbon and helix fabrication. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1270–1278     

Modeling receding contact lines on superhydrophobic surfaces

We use mesoscale simulations to study the depinning of a receding contact line on a superhydrophobic surface patterned by a regular array of posts. For the simulations to be feasible, we introduce a novel geometry where a column of liquid dewets a capillary bounded by a superhydrophobic plane that faces a smooth hydrophilic wall of variable contact angle. We present results for the dependence of the depinning angle on the shape and spacing of the posts and discuss the form of the meniscus at depinning. We find, in agreement with ref 17 , that the local post concentration is a primary factor in controlling the depinning angle and show that the numerical results agree well with recent experiments. We also present two examples of metastable pinned configurations where the posts are partially wet.     

Double-networks based on interconnected amphiphilic “in–out” star first polymer conetworks prepared by RAFT polymerization

Double-network hydrogels were prepared using well-defined first networks comprising interconnected amphiphilic “in-out” star copolymers synthesized via sequential reversible addition-fragmentation chain transfer (RAFT) polymerization, and second networks based on a photopolymerized mixture of acrylamide and N,N′-methlyenebisacrylamide. All first and double-network hydrogels were characterized in terms of their aqueous degrees of swelling and mechanical properties in compression. The most hydrophobic first and double-network hydrogels exhibited the best mechanical properties, which may be attributed to their low aqueous swelling degrees and good mesoscale organization in water as revealed using small-angle neutron scattering (SANS) which showed that the size of the formed hydrophobic domains could be controlled by the polymer conetwork structure. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2161–2174     

Recent advances in covalent functionalization of carbon nanomaterials with polymers: Strategies and perspectives

Carbon nanomaterials (CNMs) have been proposed as promising nanofillers for polymer composites because of their high surface area, structural flexibility, good mechanical strength, and their unique thermal, optical, and electronic properties. However, the strong van der Waals interactions between individual nanoparticles have limited the manipulation of CNMs and restricted their use in many promising fields. The functionalization of CNMs has attracted great interest on synthesis of complex structures, and helped establish different facile, scalable, controllable and low-cost methods to graft well-defined polymers onto the surfaces of CNMs. This review highlights the advances made in recent years on the functionalization chemistry of carbon nanotubes and graphene with polymers by both the “grafting from” and “grafting to” techniques. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 622–631     

“Grafting through” polymerization involving surface-bound monomers

“Grafting through” polymerization represents copolymerization of free monomers in solution and polymerizable units bound to a substrate. Free polymer chains are formed initially in solution and can incorporate the surface-bound monomers, and thereby, get covalently bonded to the surface during the polymerization process. As more growing chains attach to the surface-bound monomers, an immobilized polymer layer is formed on the surface. We use a combination of computer simulation and experiments to comprehend this process for monomers bound to a flat impenetrable substrate. We concentrate specifically on addressing the effect of spatial density of the surface-bound monomers on the formation of the surface-attached polymers. We employ a lattice-based Monte Carlo model utilizing the bond fluctuation model scheme to provide molecular-level insight into the grafting process. For experimental validation, we create gradients of density of bound methacrylate units on flat silicon wafers using organosilane chemistry and carry out “grafting through” free radical polymerization initiated in bulk. We report that the proximity of the surface-bound polymerizable units promotes the “grafting through” process but prevents more free growing chains to “graft through'' the polymerizable units. The “grafting through” process is self-limiting in nature and does not affect the overall density of the surface-bound polymer layer, except in case of the highest theoretical packing density of surface-bound monomers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 263–274     

Formylated polystyrene for the fabrication of pore selective aldehyde group functionalized honeycomb patterned porous polystyrene films

Formylated polystyrene (PS‐CHO) was synthesized by chemical modification of polystyrene (PS) for the fabrication of honeycomb patterned (HCP) porous PS films with aldehyde group functionalized pores via breath figure method under humid conditions. The incorporation of hydrophilic aldehyde group affected the hydrophobicity of PS solution and assisted the self‐assembly of PS‐CHO toward pore. The presence of aldehyde groups in the films were proved by the post treatment with Tollens's reagent, which results in silver decoration at pores. The morphology of the films before and after silver decoration was studied by scanning electron microscopy analysis. The pore selectively self‐assembled aldehyde groups in the patterned porous films can have many applications as a reactive substrate in biomaterials and chemical moieties adhesion. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1181–1192     

Fabrication of well‐defined shape memory graft polymers derived from biomass: An insight into the effect of side chain architecture on shape memory properties

Fully sustainable shape memory polymers (SMPs) derived from ethyl cellulose (EC, derived from cellulose), tetrahydrofurfuryl methacrylate (THFMA, derived from furfural), and lauryl methacrylate (LMA, derived from fatty acids) were prepared via “grafting from” atom transfer radical polymer (ATRP). The “grafting from” ATRP strategy allows to fabricate SMPs with EC as a backbone, and LMA and THFMA copolymer as a side chain. By utilizing the one‐pot and sequential monomer addition approach, two types of SMPs with random/semi‐block side chain architectures were obtained, respectively. Random/semi‐block side chain architecture of SMPs was confirmed by DSC, DMA, SAXS, and TEM. The presence of microphase separation in the SMPs with semi‐block side chain architecture provided two distinct thermal transitions, which was needed for triple‐shape memory behavior. Shape memory study showed that SMPs with semi‐block side chain architecture exhibited excellent triple‐shape memory property, and also had higher shape recovery speed and shape recovery ratio than those with random side chain architecture. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1711–1720     

Differences in self‐assembly features of thermoresponsive anionic triblock copolymers synthesized via one‐pot or two‐pot by atom transfer radical polymerization

The self‐assembly process in aqueous solutions of the methoxyl‐poly(ethylene glycol)‐block‐poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic sodium)‐block‐poly(N‐isopropyl acrylamide) (PNIPAAM) triblock copolymer, synthesized via two different atomic transfer radical polymerization methods, namely “one‐pot” (P3‐sample) and “two‐pot” (P2‐sample), was studied by various experimental techniques. The “one‐pot” procedure leads to a copolymer (P3) where the PNIPAAM block is contaminated with a minor quantity of 2‐acrylamido‐2‐methyl‐1‐propane sulfonate (AMPS) residuals and this sample does not form micelles over the considered temperature region, but unimers and temperature‐induced aggregates coexist in the presence of a small amount of salt. The P2 polymer forms micelles and intermicellar structures, but the former moieties disappear at high temperatures, whereas the latter species contract with increasing temperature. Small‐angle neutron scattering results revealed correlation peaks, both for P3 and P2, and no micelle formation for P3, but a pronounced upturn of the scattered intensity at low wavevector values at elevated temperatures for the P2 copolymer. The findings from this study clearly show that the spurious AMPS residuals have a drastic influence on the self‐assembly and micelle formation of the triblock copolymer. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 524–534     

Rotation‐assisted formation of poly(3‐butylthiophene) nanowires: Morphology,microstructure, and electrical property

The phenomenon of “shear‐induced crystallization” is commonly observed for crystalline polymers. Herein, we demonstrate that this concept can be applied to promote the self‐assembly of the conductive nanowires (NWs) in dilute solution. It is found that, by a simple rotation‐assisted method, higher yield of poly(3‐butylthiophene) (P3BT) NWs in anisole solvent was obtained than the case under static condition. While the length as well as the crystal modification of the NWs is not changed. The structural analysis suggests that the P3BT NWs take the crystal modification of form I′ rather than the conventional form I, independent of the sampling condition. This conclusion is further confirmed by investigating the phase transition behavior of the NWs using synchrotron radiation wide‐angle X‐ray diffraction technique. Unexpectedly, the active layer in field‐effect transistor (FET) device fabricated by well‐shaped pure NWs network formed under the rotation field shows the comparable carrier mobility with that fabricated by the ambiguous NWs network obtained under the static condition, which implies that the amorphous part plays an important role in affecting the electrical property. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1027–1034     

Apparent relaxation‐time spectrum cutoff in dilute polymer solutions: An effect of solvent dynamics

The apparent short time cutoff of the relaxation‐time spectrum at surprisingly long times for polymers in solution is a well known but not yet understood observation. To elucidate its origins we revisit viscoelastic and oscillatory flow birefringence data for solutions and melts of two linear polymers (polystyrene and polyisoprene) and present new measurements of oscillatory flow birefringence of the latter. Previous measurements have suggested that the “flexibility” of both polymers in solution is smaller than in the melt on the basis of the breadth of the relaxation‐time spectrum of the solution as compared with that of the melt. Our new measurements have explored a higher effective frequency range than was previously possible. This has allowed us to observe the effect of the rotational relaxation time of the solvent on the dynamics of the solution at high frequencies. To obtain the polymer global motion contribution, one now needs to subtract from the solution properties a frequency‐dependent complex solvating environment contribution. We show that the decrease in apparent “flexibility” for solutions arises from the presence of a solvent that exhibits a rotational relaxation time and thus simple viscoelastic behavior somewhat near the frequency window of the experiment. Although recent predictions of a model for a chain in a solvent with a single relaxation time are in qualitative agreement with our results, our data suggest that the solution results may reflect the influence of solvent on the development of the “entropic spring” forces at short times. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2860–2873, 2001     

Looking inside the entanglement “tube” using molecular dynamics simulations

For 30 years, the dynamics of entangled polymers have been explained using the phenomenological “tube” model, where the “tube” represents the confining effects of surrounding chains, but the tube properties, such as its length and diameter, could only be inferred indirectly by fitting the tube model to rheological data. Now, however, molecular simulations are allowing these properties to be directly computed. The computational advances in molecular dynamics and related methods that have made this possible are here reviewed. In addition, it is discussed how new findings, such as an apparent time dependence of the tube diameter and direct observation of “hopping” of branch points along the tube, are helping to refine the tube model. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3240–3248, 2007     

Stability and disturbance of coating films

In the studies of two-roll metering and application systems, two types of disturbances were observed. These were termed “ring type” and “irregular” disturbances. This research established that the physical reason for the appearance of the ring type instability is the competition between surface tension and centrifugal forces at the liquid-air interface. The rings are generated at the surface of the dynamic liquid meniscus, in the gap between the rolls, because of the very large centrifugal forces there. Considering conditions of a constant interfacial pressure difference (pressure jump), one can reduce the problem to one with only one free parameter, viz., the radius of the meniscus, and calculate the wavelength of the disturbances. There is no single formula which will adequately describe the dynamic meniscus. Its curvature depends on the rheological properties of the fluid and on the kinematic conditions in the process. Dimensional analysis is combined with experimental findings to yield a formula for the radius of the meniscus for fluids having a high yield stress for the case of two counter-rotating rolls.The rheological behavior of a flowing starch adhesive in the dynamical meniscus is analyzed. The theoretical and experimental studies show that systems using two counter-rotating rolls practically always produced ring-type instabilities with all types of fluids.The picture is more complex for co-rotating roll systems. When non-Newtonian adhesives are used, ring type disturbances are observed in one zone of roll speed ratios, and irregular disturbances are observed in another zone. The two zones are separated by a speed ratio zone (a “speed window”) where a more or less perfectly stable fluid layer is observed. When Newtonian oils are used, there are two such speed windows. The first one corresponds to very low metering roll speeds and a minimum of liquid transfer to the applicator roll. The second stable zone occurs at high metering roll speeds and yields a maximum of liquid transfer. The physical reason for the high transfer rate in the high speed “window” is considered and shown to be the thin air layer following the surface of the metering roll. The air pumped into the metering gap returns along the applicator roll and accelerates the film on the applicator roll in the process. Under these conditions the fluid-air interface may become unstable, leading to the “irregular” type of disturbance.     

A New Approach for the Synthesis of Miktoarm Star Polymers Through a Combination of Thiol–Epoxy “Click” Chemistry and ATRP/Ring‐Opening Polymerization Techniques

A new approach was developed for synthesis of certain A₃B₃‐type of double hydrophilic or amphiphilic miktoarm star polymers using a combination of “grafting onto” and “grafting from” methods. To achieve the synthesis of desired miktoarm star polymers, acetyl protected poly(ethylene glycol) (PEG) thiols (M_n = 550 and 2000 g mol^?1) were utilized to generate A₃‐type of homoarm star polymers through an in situ protective group removal and a subsequent thiol–epoxy “click” reaction with a tris‐epoxide core viz. 1,1,1‐tris(4‐hydroxyphenyl)ethane triglycidyl ether. The secondary hydroxyl groups generated adjacent to the core upon the thiol–epoxy reaction were esterified with α‐bromoisobutyryl bromide to install atom transfer radical polymerization (ATRP) initiating sites. ATRP of N‐isopropylacrylamide (NIPAM) using the three‐arm star PEG polymer fitted with ATRP initiating sites adjacent to the core afforded A₃B₃‐type of double hydrophilic (PEG)₃[poly(N‐isopropylacrylamide)] (PNIPAM)₃ miktoarm star polymers. Furthermore, the generated hydroxyl groups were directly used as initiator for ring‐opening polymerization of ε‐caprolactone to prepare A₃B₃‐type of amphiphilic (PEG)₃[poly(ε‐caprolactone)]₃ miktoarm star polymers. The double hydrophilic (PEG)₃(PNIPAM)₃ miktoarm star polymers showed lower critical solution temperature around 34 °C. The preliminary transmission electron microscopy analysis indicated formation of self‐assembly of (PEG)₃(PNIPAM)₃ miktoarm star polymer in aqueous solution. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 146–156     

A Monte Carlo study of the coil-to-globule transition of model polymer chains near an attractive surface

When a polymer chain in solution interacts with an atomically smooth solid substrate, its conformational properties are strongly modified and deviate substantially from those of chains in bulk. In this work, the interplay of two competing transitions that affect the conformations of polymer chains near an energetically attractive surface is studied by means of Monte Carlo simulations on a cubic lattice. The transition from an extended to a compact conformation of a polymer chain near an attractive wall, as solubility deteriorates, exhibits characteristics akin to the “coil-to-globule” transition in bulk. An effective θ-temperature is determined. Its role as the transition point is confirmed in a variety of ways. The nature of the coil-to-compact transition is not qualitatively different from that in the bulk. Adsorbed polymer chains may assume “globular” or “pancake” configurations depending on the competition among adsorption strength, cohesive energy, and entropy. In a very relevant range of conditions, the dependence of the adsorbate thickness on chain-length is intermediate between that of 3-d (“semidroplets”) and 2-d (“pancake”) objects. The focus of this study is on rather long polymer chains. Several crucial features of the transitions of the adsorbed chains are N-dependent and various aspects of the adsorption and “dissolution” process are manifested clearly only at the “long chain” limit. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2462–2476, 2009     

Giant surfactants based on molecular nanoparticles: Precise synthesis and solution self‐assembly

Giant surfactants are polymer‐tethered molecular nanoparticles (MNPs) and can be considered as a subclass of giant molecules. The MNPs serve as functionalized heads with persistent shape and volume, which may vary in size, symmetry, and surface chemistry. The covalent conjugation of MNPs and polymer tails affords giant surfactants with diverse composition and architecture. Synthetic strategies such as “grafting‐from” and “grafting‐onto” have been successfully applied to the precise synthesis of giant surfactants, which is further facilitated by the emergence of “click” chemistry reactions. In many aspects, giant surfactants capture the essential features of small‐molecule surfactants, yet they have much larger sizes. They bridge the gap between small‐molecule surfactants and traditional amphiphilic macromolecules. Their self‐assembly behaviors in solution are summarized in this Review. Micelle formation is affected not only by their primary chemical structures, but also by the experimental conditions. This new class of materials is expected to deliver general implications on the design of novel functional materials based on MNP building blocks in the bottom‐up fabrication of well‐defined nanostructures. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1309–1325     

Laser emission in a 3D nanoporous polymer replica of amorphous blue phase III

Wide‐temperature polymer stabilized cubic blue phases (BPI and BPII) facilitated the emergence of practically feasible band‐edge BP lasers. However, the mysterious “blue fog” amorphous BPIII always remained elusive in terms of its applicability to photonic devices due to its random amorphous structure devoid of photonic bandgaps and due to the difficulty in effectively identifying and stabilizing it for practical applications. We present the first photonic device based on amorphous BPIII by demonstrating that a three‐dimensional BPIII polymer scaffold or template, when infiltrated with liquid crystal and laser dye, forms a system where random lasing action is generated due to multiple scattering events occurring in the nanoporous and disordered polymer replica of BPIII. This study represents a facile approach for the development of photonic devices which favorably exploit unique polymer network morphologies for laser emission. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 551–557     

Interfacial crosslinking of self‐assembled triblock copolymer nanoparticles via alkoxysilane hydrolysis and condensation

The use of amphiphilic triblock copolymers bearing a reactive alkoxysilane middle block as polymeric stabilizers is reported in this work. A series of poly(ethylene glycol) methyl ether methacrylate‐b‐(3‐trimethoxysilyl)propyl methacrylate‐b‐benzyl methacrylate (PEGMA‐b‐MPS‐b‐BzMA) triblock copolymers were prepared by RAFT solution polymerization and polymerization‐induced self‐assembly (PISA), respectively, where the various block lengths and overall composition were varied. The copolymers prepared by solution polymerization were employed as oil‐in‐water stabilizers where upon application of a catalyst, the 3‐(trimethoxysilyl)propyl methacrylate (MPS) block at the droplet interface was crosslinked to yield capsule‐like structures. The effectiveness of interfacial crosslinking was validated by dynamic light scattering and electron microscopy. In situ self‐assembly by the PISA method resulted in spherical nanoparticles of controllable size that were readily crosslinked by addition of base, with significant enhancement of colloidal stability. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1897–1907     

Monolayer and multilayer compact film formations on different substrates by physical deposition

Dissipative particle dynamics simulations are applied to investigate the monolayer and multilayer film formations on different solid substrates by physical deposition. The influences of the polymer concentration, the polymer chain length, the solvent quality, and the interactions between the polymer solution and the solid substrate surface on the film formation dynamics and the mechanism are studied in detail. The results are analyzed in terms of the thickness and the shape of the deposited film, the kinetics of phase separation in the polymer solution, and the contact angle formed between the polymer aggregations and the substrate surface. Moreover, we suggest two strategies, designing a deposition process analogous to “chemical titration” and physically blocking interlayer diffusion by a simple crosslinked network barrier, to deposit the compact monolayer and multilayer films with better quality, respectively. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 353–365, 2009     

“Smart” Catalysis with thermoresponsive ruthenium catalysts for miniemulsion ru‐mediated reversible deactivation radical polymerization cocatalyzed by smart iron cocatalysts

This work reports the use of cocatalysts in addition to “smart” ruthenium catalysts for Ru‐mediated reversible deactivation radical polymerization (RDRP) in miniemulsion, allowing for the synthesis of final products with significantly reduced residual metal. Using amine cocatalysts in miniemulsion allows for high conversions (> 90%) in under 10 h. Two forms of ferrocene cocatalysts are also used, including “smart” thermoresponsive PEGylated ferrocene derivatives (FcPEG) and ferrocene containing surfactants (FcTMA). Using “smart” thermoresponsive cocatalyst at low concentrations, rate enhancements in BMA and BzMA polymerizations are observed, with good catalyst removability. Using the FcTMA cocatalyst surfactant, increasing monomer hydrophobicity is shown to increase the polymerization rate and initiator efficiency. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 305–312     

Directed assembly of gold nanoparticles

As a complement to common “top–down” lithography techniques, “bottom–up” assembly techniques are emerging as promising tools to build nanoscale structures in a predictable way. Gold nanoparticles that are stable and relatively easy to synthesize are important building blocks in many such structures due to their useful optical and electronic properties. Programmed assembly of gold nanoparticles in one, two, and three dimensions is therefore of large interest. This review focuses on the progress from the last three years in the field of directed gold nanoparticle and nanorod assembly using, for example, DNA or specific chemical interactions as template.