Solid-state Morphology Research Articles

Not All Aggregates Are Made the Same: Distinct Structures of Solution Aggregates Drastically Modulate Assembly Pathways, Morphology, and Electronic Properties of Conjugated Polymers.

Tuning structures of solution-state aggregation and aggregation-mediated assembly pathways of conjugated polymers is crucial for optimizing their solid-state morphology and charge-transport property. However, it remains challenging to unravel and control the exact structures of solution aggregates, let alone to modulate assembly pathways in a controlled fashion. Herein, aggregate structures of an isoindigo-bithiophene-based polymer (PII-2T) are modulated by tuning selectivity of the solvent toward the side chain versus the backbone, which leads to three distinct assembly pathways: direct crystallization from side-chain-associated amorphous aggregates, chiral liquid crystal (LC)-mediated assembly from semicrystalline aggregates with side-chain and backbone stacking, and random agglomeration from backbone-stacked semicrystalline aggregates. Importantly, it is demonstrated that the amorphous solution aggregates, compared with semicrystalline ones, lead to significantly improved alignment and reduced paracrystalline disorder in the solid state due to direct crystallization during the meniscus-guided coating process. Alignment quantified by the dichroic ratio is enhanced by up to 14-fold, and the charge-carrier mobility increases by a maximum of 20-fold in films printed from amorphous aggregates compared to those from semicrystalline aggregates. This work shows that by tuning the precise structure of solution aggregates, the assembly pathways and the resulting thin-film morphology and device properties can be drastically tuned.

Polyethylene and Semiconducting Polymer Blends for the Fabrication of Organic Field-Effect Transistors: Balancing Charge Transport and Stretchability

Polyethylene is amongst the most used polymers, finding a plethora of applications in our lives owing to its high impact resistance, non-corrosive nature, light weight, cost effectiveness, and easy processing into various shapes from different sizes. Despite these outstanding features, the commodity polymer has been underexplored in the field of organic electronics. This work focuses on the development of new polymer blends based on a low molecular weight linear polyethylene (LPE) derivative with a high-performance diketopyrrolopyrrole-based semiconducting polymer. Physical blending of the polyethylene with semiconducting polymers was performed at ratios varying from 0 to 75 wt.%, and the resulting blends were carefully characterized to reveal their electronic and solid-state properties. The new polymer blends were also characterized to reveal the influence of polyethylene on the mechanical robustness and stretchability of the semiconducting polymer. Overall, the introduction of LPE was shown to have little to no effect on the solid-state properties of the materials, despite some influence on solid-state morphology through phase separation. Organic field-effect transistors prepared from the new blends showed good device characteristics, even at higher ratios of polyethylene, with an average mobility of 0.151 cm2 V−1 s−1 at a 25 wt.% blend ratio. The addition of polyethylene was shown to have a plasticizing effect on the semiconducting polymers, helping to reduce crack width upon strain and contributing to devices accommodating more strain without suffering from decreased performance. The new blends presented in this work provide a novel platform from which to access more mechanically robust organic electronics and show promising features for the utilization of polyethylene for the solution processing of advanced semiconducting materials toward novel soft electronics and sensors.

Side-Chain Density Driven Morphology Transition in Brush–Linear Diblock Copolymers

We report the synthesis and self-assembly of brush-linear diblock copolymers with variable side-chain length and density. Poly(pentafluorophenyl acrylate-g-ethylene glycol)-b-polystyrene ((PPFPA-g-PEG)-b-PS) brush-linear diblock copolymers are prepared by sequential reversible addition-fragmentation chain transfer (RAFT) polymerization of PPFPA and PS, followed by postpolymerization reaction between the precursor PPFPA-b-PS diblock copolymer and amine-functionalized PEG. By controlling the PEG chain length and the degree of substitution, we obtained brush-linear diblock copolymers with different side-chain lengths and densities. The solid-state morphologies of the diblocks are then examined by small-angle X-ray scattering (SAXS). At low PEG side-chain density, the segregation of PEG and PS away from PPFPA leads to the formation of PEG and PS lamellar domains with PPFPA in the interface. At high PEG side-chain density, the segregation is between the PPFPA-g-PEG brush block and the PS linear block, and the domain morphology is determined by the composition of the brush block. A partial experimental phase diagram is presented, and it illustrates the importance of both side-chain length and density on the microdomain morphology of brush-linear diblock copolymers.

Self-assembly of Li single-ion-conducting block copolymers for improved conductivity and viscoelastic properties

Single-ion conducting polyelectrolytes (SICPs) with mobile Li cation have recently gathered significant attention as an “ideal” electrolyte for safe solid-state rechargeable lithium batteries, because they eliminate salt concentration gradients and concentration overpotentials, allowing transference number (tLi+) values close to unity. In this work, a series of single ion conducting block copolymers, namely [(LiM)n-r-(PEGM)m]-b-(PhEtM)k (A-b-B), is synthesized via reversible addition-fragmentation chain transfer (RAFT) copolymerization of 1-[3-(methacryloyloxy)propylsulfonyl]-(trifluoromethanesulfonyl)imide (LiM), poly(ethylene glycol)methyl ether methacrylate (PEGM) and 2-phenylethyl methacrylate (PhEtM) with controlled PEGM:LiM ratio, molecular weights (Mn = 25.8 ÷ 85.9 kDa) and narrow polydispersity (Mw/Mn = 1.12 ÷ 1.21). The bulk ionic conductivity, solid-state morphology and thermal properties of block copolymers are studied as a function of their composition. Block copolymers having molecular weights in the range of 46 ÷ 63 kDa and any ratio of PEGM:LiM (from 3:1 to 7:1) tend to evolve in quasi-hexagonally-packed cylinders, while copolymers with higher molecular weights (Mn > 74 kDa) and the ratio of PEGM:LiM = 5:1 and MA/MB ≤ 2.0 show lamellar phase separation. The lamellar long-range ordering in poly[(LiM17-r-PEGM86)-b-PhEtM131] and poly[(LiM17-r-PEGM86)-b-PhEtM194] results not only in the improved viscoelastic (mechanical) performance compared to parent copolymer poly[LiM17-r-PEGM86] (complex viscosity = 2.5 × 108 mPa s and 8.7 × 104 mPa s at 25 °C, respectively), but also in the demonstration of sufficiently high ionic conductivity despite the decrease in Li+ amount (σ = 3.8 × 10−7 and 4.1 × 10−7 S/cm at 25 °C, correspondingly). The selected poly[(LiM17-r-PEGM86)-b-PhEtM131] further shows high tLi+ (0.96 at 70 °C) and wide electrochemical stability (4.4 V vs. Li+/Li at 70 °C), which results in reversible and stable cycling at high specific capacities (up to 150 and 118 mAh g−1 at C/20 and C/5 rates, respectively) when assembled in lab-scale truly-solid-state Li metal cells with Li/copolymer/LiFePO4 configuration.

Impact of charge generation and extraction on photovoltaic performances of spin- and blade-as well as spray-coated organic solar cells

The fullerene- and nonfullerene-based organic solar cells (OSCs), which are compatible with low-cost solution-coating technologies, have attracted widespread attention in recent years. However, compared to the OSCs by spin-coating, the underlying reasons behind photovoltaic degradation for the OSCs by blade- and spray-coating are rarely investigated, which severely limits the further progress of OSC industrialization. In this work, the JSC difference between fullerene/nonfullerene OSCs by different coating techniques is systematically studied by analyzing the internal quantum efficiency and reconstructing the external quantum efficiency. Moreover, for both the fullerene and nonfullerene systems, the ratio of charge recombination over charge extraction in the blade-coated OSCs is very close to that in the spin-coated devices, whereas there is a clearly larger discrepancy between the spray-coated and the spin-coated ones. In terms of the ultimately achieved power conversion efficiencies, which is mainly related to the solid-state morphologies of active films by different coating techniques, the fullerene system presents better tolerance to fab-scale coating methods than that of the nonfullerene system. The J-V curves calculated by the drift-diffusion equations fit well with the actual J-V curves, verifying the correctness of above analysis and the usefulness of our conclusions. This work demonstrates the causes of performance loss among the spin- and blade- and spray-coated fullerene/nonfullerene OSCs, which provides useful insights for future manufacturing of OSCs.

Selective and rapid water transportation across a self-assembled peptide-diol channel via the formation of a dual water array.

Achieving superfast water transport by using synthetically designed molecular artifacts, which exclude salts and protons, is a challenging task in separation science today, as it requires the concomitant presence of a proper water-binding site and necessary selectivity filter for transporting water. Here, we demonstrate the water channel behavior of two configurationally different peptide diol isomers that mimic the natural water channel system, i.e., aquaporins. The solid-state morphology studies showed the formation of a self-assembled aggregated structure, and X-ray crystal structure analysis confirmed the formation of a nanotubular assembly that comprises two distinct water channels. The water permeabilities of all six compounds were evaluated and are found to transport water by excluding salts and protons with a water permeability rate of 5.05 × 108 water molecules per s per channel, which is around one order of magnitude less than the water permeability rate of aquaporins. MD simulation studies showed that the system forms a stable water channel inside the bilayer membrane under ambient conditions, with a 2 × 8 layered assembly, and efficiently transports water molecules by forming two distinct water arrays within the channel.

Optimizing the Crystallization Behavior and Film Morphology of Donor–Acceptor Conjugated Semiconducting Polymers by Side-Chain–Solvent Interaction in Nonpolar Solvents

The solution state of a conjugated polymer plays a critical role in the film morphology and charge carrier mobility of the solution process organic field-effect transistors (OFETs). However, it remains challenging to establish the relationship between solution-state and solid-state morphologies. Herein, we report an effective strategy to control the film formation process and film morphology by regulating the solution state, specifically, through the interaction between the branched side chain of poly[4-(4,4-bis(2-octyldodecyl)-4H-cyclopenta[1,2-b:5,4-b′]dithiophen-2-yl)-alt-[1,2,5]-thiadiazolo[3,4-c]pyridine] (PCDTPT-ODD) and the nonpolar solvent. A precise adjustment of the solution state using the Hansen solubility parameter distance (Ra) has been achieved. Compared to the polar solvent, ordered aggregates were formed in the solution formed by nonpolar solvents. Interestingly, a highly ordered chain arrangement was observed in solutions with suitable Ra’s (8.2 and 9.4 MPa1/2 for hexane and isooctane, respectively). Importantly, solution-state aggregation was maintained in the drop-casting film due to the memory effect; the as-prepared films were composed of different fiber sizes and crystal regions. The fiber consisted of a face-on region, with the polymer chains in the fiber aligned perpendicular to the long axis of the fibers. The crystallization process of the edge-on region was independent of the face-on region. The face-on and edge-on regions were produced through the aggregated and disordered parts, respectively. As the Ra increased, the fiber size and the face-on region content increased. Finally, the OFET device mobility was optimized with a significant increase in μ (from 9.7 × 10–5 to 1.3 × 10–3 cm2 V–1 s–1). These results showed that the precise regulations of the solution state by the side-chain–solvent interaction play an important role in the film formation process, film morphology, crystallization behavior, and device properties.

Correction to: Influence of an Amide-Functionalized Monomeric Unit on the Morphology and Electronic Properties of Non-Fullerene Polymer Solar Cells

A straightforward competent strategy to attune the solid-state morphology, opto-electronic and photovoltaic properties of conjugated co-polymers has been studied by inserting different percentages of N,N-dimethylthiophene-3-carboxamide (TDM) monomeric units. The TDM percentage was varied from 20 to 100%, resulting in widening of the energy band gap. Fabrication of solar cells was performed with ITIC-4F as an electron acceptor to accomplish power conversion efficiencies (PCEs) of 7.8% for P4 (minimum TDM) and 0.85% for P1 (maximum TDM) under a thermal tempering process. A drastic drop in the PCE was noted with increasing percentage of TDM which agrees well with the optical, electronic, and morphological studies. Morphological analysis revealed high crystallinity for P4:ITIC-4F blend having minimum percentage of TDM units compared to its counterparts of higher TDM percentages. A sharp increase in π-π stacking is seen with reduced percentage of TDM units, leading to d spacing of 3.6 A. Detailed investigations regarding the charge carrier transport in relation to the π-π stacking of the polymeric film are well implemented in this work.

Double Crystallization and Phase Separation in Polyethylene-Syndiotactic Polypropylene Di-Block Copolymers.

Crystallization and phase separation in the melt in semicrystalline block copolymers (BCPs) compete in defining the final solid state structure and morphology. In crystalline–crystalline di-block copolymers the sequence of crystallization of the two blocks plays a definitive role. In this work we show that the use of epitaxial crystallization on selected crystalline substrates allows achieving of a control over the crystallization of the blocks by inducing crystal orientations of the different crystalline phases and a final control over the global morphology. A sample of polyethylene-block-syndiotactic polypropylene (PE-b-sPP) block copolymers has been synthesized with a stereoselective living organometallic catalyst and epitaxially crystallized onto crystals of two different crystalline substrates, p-terphenyl (3Ph) and benzoic acid (BA). The epitaxial crystallization on both substrates produces formation of highly ordered morphologies with crystalline lamellae of sPP and PE highly oriented along one direction. However, the epitaxial crystallization onto 3Ph should generate a single orientation of sPP crystalline lamellae highly aligned along one direction and a double orientation of PE lamellae, whereas BA crystals should induce high orientation of only PE crystalline lamellae. Thanks to the use of the two selective substrates, the final morphology reveals the sequence of crystallization events during cooling from the melt and what is the dominant event that drives the final morphology. The observed single orientation of both crystalline PE and sPP phases on both substrates, indeed, indicates that sPP crystallizes first onto 3Ph defining the overall morphology and PE crystallizes after sPP in the confined interlamellar sPP regions. Instead, PE crystallizes first onto BA defining the overall morphology and sPP crystallizes after PE in the confined interlamellar PE regions. This allows for discriminating between the different crystalline phases and defining the final morphology, which depends on which polymer block crystallizes first on the substrate. This work also shows that the use of epitaxial crystallization and the choice of suitable substrate offer a means to produce oriented nanostructures and morphologies of block copolymers depending on the composition and the substrates.

Controlling solid-state structure and film morphology in non-fullerene organic photovoltaic devices

Organic solar cells (OSCs) have long promised to provide renewable energy in a scalable, cost-effective way; however, for years, their relatively low efficiency has been a significant barrier to commercialization. Recent progress on cell efficiency means that OSCs are now much more competitive with other established technologies. These key advancements have come from better understanding and controlling the molecular structure, solid-state packing, and film morphology of the light absorbing layer. This focused review will explore the different ways that the solid-state structure and film morphology of the light absorbing layer can be controlled. It will examine the key features of an efficient light absorbing layer and present guiding principles for creating efficient OSCs. The future directions and remaining research questions of this field will be briefly discussed.

Rational primary structure design for boosting the thermoelectric properties of semiconducting carbon nanotube networks

The precise control of carbon nanotube structures plays a crucial role in understanding their intrinsic transport as well as in utilizing them for energy harvesting applications. In this paper, we elucidate that slight differences in the purity and diameter distribution of semiconducting single-walled carbon nanotubes (sc-SWCNTs) lead to the significant modulation of thermoelectric transport in their networks. Conducting polymers examined here enable the sorting of the sc-SWCNTs with desired purity and diameter distribution, as well as fixed solid state morphology. Particularly, the approximately tenfold enhancement of thermoelectric power factors is achieved by improving sc-SWCNT purity from 94% to 99% and increasing mean diameters from 1.0 to 1.2 nm. This work provides a rational design for boosting the thermoelectric properties of sc-SWCNT networks.

Alignment of linear polymeric grains for highly stable N-type thin-film transistors

Summary Temperature-insensitive properties are attractive for most electronics, including polymeric semiconducting devices. Especially, polymeric field-effect transistors (FETs) with high mobility have been important research targets due to their broad applications. However, polymeric FETs with stable charge transport operating at extremely cold or hot zones are faced with enormous challenges. In this study, the polyacrylonitrile was found to significantly tune the sizes of pre-aggregates of polymers in solutions and the crystallinity of the polymeric films. The orientation of 5–25 μm linear grains in the films were prepared through the bar-coating process with polyacrylonitrile as an additive, which stabilized the electron mobility over a wide range of temperatures. The linear-grain morphology of the film contributed to reducing the holes and grain boundaries in the transport paths of carriers. Typically, the top-gate FETs based on P(NDI2OD-T2) displayed a stable electron transporting behavior from 200 to 460 K, with mobility greater than 3.5 cm2V−1s−1.

Supercritical carbon dioxide assisted complexation of benznidazole: γ-cyclodextrin for improved dissolution

Benznidazole (BZ) and nifurtimox are first-line drugs for the treatment of Chagas disease, with BZ preferred due to its moderate side effects compared to nifurtimox. However, BZ has low aqueous solubility and a low dissolution rate which potentially limit its oral bioavailability. We now report for the first time efforts to improve the aqueous dissolution of BZ via processing and γ-cyclodextrin (γ-CD) complexation using supercritical carbon dioxide (scCO2). We first investigated the solubility of BZ in scCO2 and the effect of scCO2 processing on the solid-state, particle size characteristics and dissolution behaviour of processed BZ compared to un-processed BZ. Moreover, the efficacy of scCO2 in dissolving and complexing BZ with γ-CD was studied and compared with conventional freeze-drying (FD). The solubility of BZ in scCO2 was time-dependent (1.78 × 10-6 to 3.18 × 10-5 mol. mol−1) and reached the equilibrium after 10 h. Complexation efficiency and loading capacity were in the range of 4 ± 1.4% to 54 ± 10% and 1.8 ± 0.1% to 27 ± 5%, respectively, and they varied depend on the preparation method and conditions. XRD, DSC, and FTIR results revealed that although scCO2 was able to solubilise BZ, it did not change the solid-state morphology of BZ. Contrary, FD and γ-CD complexation were shown to affect the solid-state characteristics of BZ and γ-CD. The mean particle size of processed BZ was significantly reduced from 604 ± 61.50 nm (un-processed BZ) to 257 ± 41–385 ± 36.56 nm (processed BZ). Both the dissolution rate profiles and dissolution efficiency differed depending on preparation methods, process conditions, and BZ-to-γ-CD ratio, but they were significantly increased compared to un-processed BZ. Overall, this study demonstrated that the preparation methodology had substantial effects on the solid-state particle size/morphology characteristics and aqueous dissolution behaviour of BZ, both alone or in complexes with γ-CD, with potential to develop improved formulations.

How to reprogram the excitonic properties and solid-state morphologies of π-conjugated supramolecular polymers.

The development of supramolecular tools to modulate the excitonic properties of non-covalent assemblies paves the way to engineer new classes of semicondcuting materials relevant to flexible electronics. While controlling the assembly pathways of organic chromophores enables the formation of J-like and H-like aggregates, strategies to tailor the excitonic properties of pre-assembled aggregates through post-modification are scarce. In the present contribution, we combine supramolecular chemistry with redox chemistry to modulate the excitonic properties and solid-state morphologies of aggregates built from stacks of water-soluble perylene diimide building blocks. The n-doping of initially formed aggregates in an aqueous medium is shown to produce π-anion stacks for which spectroscopic properties unveil a non-negligible degree of electron-electron interactions. Oxidation of the n-doped intermediates produces metastable aggregates where free exciton bandwidths (ExBW) increase as a function of time. Kinetic data analysis reveals that the dynamic increase of free exciton bandwidth is associated with the formation of superstructures constructed by means of a nucleation-growth mechanism. By designing different redox-assisted assembly pathways, we highlight that the sacrificial electron donor plays a non-innocent role in regulating the structure-function properties of the final superstructures. Furthermore, supramolecular architectures formed via a nucleation-growth mechanism evolve into ribbon-like and fiber-like materials in the solid-state, as characterized by SEM and HRTEM. Through a combination of ground-state electronic absorption spectroscopy, electrochemistry, spectroelectrochemistry, microscopy, and modeling, we show that redox-assisted assembly provides a means to reprogram the structure-function properties of pre-assembled aggregates.

Processing and Properties of Melt Processable UHMW‐PE Based Fibers Using Low Molecular Weight Linear Polyethylene's

AbstractThe rheology, solid state drawability, morphology, and mechanical properties of polyethylene blends containing ultrahigh molecular weight polyethylene (UHMW‐PE) and linear‐low molecular weight polyethylene waxes (PEwax) are explored. Addition of PEwax enables melt processing of UHMW‐PE and improves solid state drawability, providing opportunities in recycling of UHMW‐PE waste. Small angle X‐ray scattering results show that both PEwax and UHMW‐PE align fully in the drawing direction, irrespective whether the PEwax has an Mn below or above the critical molecular weight at which entanglements can form (Mc). Tensile moduli of drawn specimen are in accordance to the Irvine–Smith model confirming that both UHMW‐PE and PEwax align in the drawing direction and no chain slip occurs toward zero strain and both UHMW‐PE and PEwax fractions, irrespective of their molecular weight, contribute fully to the modulus. Tensile strength of the blends scales according to the rule of mixtures where PEwax below Mc scale toward zero and those above Mc do contribute to the tensile strength. Modulus hence can be regarded as insensitive to the molecular weight of the PEwax used, whereas strength does show to be sensitive to the molecular weight of the PEwax.

Crack propagation and electronic properties of semiconducting polymer and siloxane-urea copolymer blends

A persistent challenge in the field of organic electronics is balancing the optoelectronic properties of π-conjugated semiconducting polymers with their thermomechanical properties. A popular and effective approach to resolve this dichotomy is to blend π-conjugated polymers with amorphous, stretchy elastomers. In this work, poly(diketopyrrolopyrrole-co-thienovinylthiophene) was blended with an easily-prepared poly(dimethylsiloxane)-based phenylurea copolymer (PDMS-PU) to further explore this approach. Interestingly, the differing surface energy and polarity of this soft amorphous copolymer in comparison to other common siloxane-based polymers blended with conjugated polymers showed little impact on the solid-state morphology. Various techniques were used to evaluate the properties of the polymer blends, including atomic force microscopy, UV–vis spectroscopy, and x-ray diffraction. An in-depth morphological evaluation was performed on the blend at varying strain, elucidating the formation of cracks at the nanoscale. The results show a significant decrease in crystallinity and increase in crack onset with increased PDMS-PU content. Fabrication of organic field-effect transistors (OFETs) utilizing the new polymer blends exhibited charge mobility up to 8.2 × 10−2 cm2 V−1 s−1, and charge transfer characteristics up to 75 wt.% PDMS-PU content. The study shows the promise of PDMS-PU/conjugated polymer blends for use in OFETs, and towards the large-scale preparation of mechanically robust and stretchable electronic devices.

Reversible thermo-driven solid-state morphological transformation of nanotextured spinel material

The present study, highlights essentially a phenomenon rarely encountered in NiFe2O4 nanoparticles self-assembled in the presence of organic azo dye (i.e. Methyl orange). To the best of our knowledge, NiFe2O4 nanoparticles with fibrous morphology is unprecedent. Unexpected features of solid-state morphology changes from zero-dimensional to quasi one-dimensional and back again were evaluated by applying a wide range of complementary physico-chemical characterization techniques to unequivocally assess the nature of the self-assembly process. Scanning electron microscopy reveals the reversibility of the above-mentioned process, under various applied conditions. Zero-dimensional nickel ferrite nanoparticles (as-synthesized) are assembled into quasi one-dimensional fibers, uniformly distributed in all three directions by adsorption of Methyl orange (MO) dye, with texture preserved after the photocatalytic process, and finally it returns to the initial appearance (zero dimensional) by applying a thermal treatment. The presented results may contribute to photocatalyst development by in/ex-situ tuning the morphology of the material, which allows active sites to spread over a wide internal surfaces and pores which, in turn, enhance the photodegradation ability of the catalyst.

Morphology evolution of functionalized styrene and methyl methacrylate copolymer latex nanoparticles by one-step emulsifier-free emulsion polymerization

Evolution of morphology in the latex nanoparticles synthesized by emulsion polymerization methods has been an interesting challenge. Herein, a fast and facile methodology was developed for the synthesis of functionalized latex nanoparticles based on polystyrene (PS) and poly(methyl methacrylate) (PMMA) by one-step emulsifier-free emulsion copolymerization with functional acrylic comonomers. These functional latex nanoparticles display different particle size in the range of 150–1400 nm and morphologies depending on the surface functional groups. Morphological investigation of the functionalized latex nanoparticles by scanning electron microscopy and transmission electron microscopy display that PMMA and PS latex nanoparticles with amide and hydroxyl functionalities have cauliflower like morphology with a non-smooth surface. The PS latex nanoparticles functionalized with epoxy groups have vesicular morphology in colloidal and red blood cell-like morphology in solid state. The PMMA latex nanoparticles containing epoxy and hydroxyl functionalities on the surface and also the PS latex nanoparticles functionalized with amide groups display highly monodispersed spherical morphologies. The porous surface was observed for the spherical PMMA and PS latex nanoparticles functionalized with carboxylic acid groups by using 4,4′-azobis(4-cyanovaleric acid) as the initiator. Different morphologies observed for the functional PS and PMMA latex nanoparticles prepared by one-step emulsifier-free emulsion polymerization are very interesting and have potential applications in drug-delivery, bioimaging, cell-labeling, and chemosensors.

Correlative analysis between solid-state NMR and morphology for blends of poly(lactic acid) and poly(butylene adipate-co-butylene terephthalate)

Morphological changes in polymer blending process were investigated using integrated analyses by solid-state NMR and magnetic relaxation. The study examined previous reported mechanical properties of polymer blends incorporating poly(lactic acid) (PLA) and poly(butylene adipate-co-butylene terephthalate) (PBAT) over a range of compositions, along with a crosslinking reagent. The X-ray diffraction (XRD) and the differential scanning calorimeter (DSC) results showed that the crystallinity of PLA decreased with increasing the PBAT content. According to the integrated analysis data and imaging by micro-focus X-ray computed tomography (CT), polymer tensile properties were dominated by interfacial affinity between the molecular mobilities of PLA and PBAT; depending on the blending ratio, the polymer morphology changed from a discontinuous “sea-island” form to a bicontinuous morphology. Addition of a crosslinking reagent was observed via X-ray CT to homogenize the PLA and PBAT blend at the micron length scale, even though both polymers were still heterogeneous at the nanoscale as elucidated by NMR analysis. As well as the morphological change in micro scale, the molecular mobility changes of the total polymer blend system, which could be evaluated by the integrated solid-state NMR analyses, brought about greater elongation at the break point in dynamic tensile testing.

Exploration of the Solid-State Sorption Properties of Shape-Persistent Macrocyclic Nanocarbons as Bulk Materials and Small Aggregates.

Porous molecular materials combine benefits such as convenient processability and the possibility for atom-precise structural fine-tuning which makes them remarkable candidates for specialty applications in the areas of gas separation, catalysis, and sensing. In order to realize the full potential of these materials and guide future molecular design, knowledge of the transition from molecular properties into materials behavior is essential. In this work, the class of compounds termed cycloparaphenylenes (CPPs)-shape-persistent macrocycles with built-in cavities and radially oriented π-systems-was selected as a conceptually simple class of intrinsically porous nanocarbons to serve as a platform for studying the transition from analyte sorption properties of small aggregates to those of bulk materials. In our detailed investigation, two series of CPPs were probed: previously reported hoop-shaped [n]CPPs and a novel family of all-phenylene figure-8 shaped (lemniscal) bismacrocycles, termed spiro[n,n]CPPs. A series of nanocarbons with different macrocycle sizes and heteroatom content have been prepared by atom-precise organic synthetic methods, and their structural, photophysical, and electronic attributes were disclosed. Detailed experimental studies (X-ray crystallography, gas sorption, and quartz-crystal microbalance measurements) and quantum chemical calculations provided ample evidence for the importance of the solid-state arrangement on the porosity and analyte uptake ability of intrinsically porous molecular nanocarbons. We demonstrate that this molecular design principle, i.e., incorporation of sterically demanding spiro junctions into the backbone of nanohoops, enables the manipulation of solid-state morphology without significantly changing the nature and size of the macrocyclic cavities. As a result, the novel spiro[n,n]CPPs showed a remarkable performance as high affinity material for vapor analyte sensing.