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The reinforcement of wood–polymer composite beams and other long structural components by means of strong continuous prestressed elements is considered, in theoretical and practical terms. The use of plunger extrusion to introduce such reinforcement during the shaping process is proposed.
The development of new polymer composites is highly dependent on the design of novel fillers that can bring more benefits in the design and control of structure–property–function than conventional solid particles. Here, inspired by the unique coupling structures of tough mussel byssus, we employ nanodroplets of high-boiling-point oligomers as the liquid filler to fabricate a new class of polymer–droplet composites (PDCs). The combination of nanodroplets and chain end/tail modifier in PDCs finally generates soft-coupling structures with chain ends coupled by the nanodroplets. With this strategy, brittle poly(lactic acid) is successfully transformed into a tough bioplastic with toughness improved by over 2000% via a minimal amount of the modifiers (1.5 wt %). Moreover, the composites show unexpected speed-enhanced energy absorption capability. A soft-coupling toughening mechanism is further proposed for the first time to understand the PDCs’ mechanical properties. This work also indicates the potential of nanodroplets as a new tool for tuning the mechanical properties and even functions of polymer composites.
Poly(lactide) (PLA) and poly(methyl methacrylate) (PMMA) are melt compounded with chopped glass fiber using laboratory scale twin-screw extrusion. Physical properties are examined using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), thermogravimetric analysis (TGA), tensile testing, impact testing, X-ray computed tomography (CT) scanning, and field emission scanning electron microscopy (FE-SEM). Molecular weight is determined using gel permeation chromatography (GPC). Miscibility of the blends is implied by the presence of a single glass transition temperature and homogeneous morphology. PLA/PMMA blends tend to show positive deviations from a simple linear mixing rule in their mechanical properties (e.g., tensile toughness, modulus, and stress at break). The addition of 40 wt % glass fiber to the system dramatically increases physical properties. Across all blend compositions, the tensile modulus increases from roughly 3 GPa to roughly 10 GPa. Estimated heat distortion temperatures (HDTs) are also greatly enhanced; the pure PLA sample HDT increases from 75 degrees C to 135 degrees C. Fiber filled polymer blends represent a sustainable class of earth abundant materials which should prove useful across a range of applications.
A key component of cooling devices is the transfer of entropy from the cold load to heat sink. An electrocaloric (EC) polymer capable of generating both large electrocaloric effect (ECE) and substantial electroactuation can enable EC cooling devices to pump heat without external mechanisms, resulting in compact designs and enhanced efficiency. However, achieving both high ECE and significant electroactuation remains challenging. Herein, it is demonstrated that poly(vinylidene fluoride‐trifluoroethylene‐chlorofluoroethylene‐double bond) [P(VDF‐TrFE‐CFE‐DB)] tetrapolymers can simultaneously generate high electrocaloric effects and electroactuations under low fields. These P(VDF‐TrFE‐CFE‐DB) tetrapolymers are synthesized through the dehydrochlorination of P(VDF‐TrFE‐CFE) terpolymer. By facile tuning the composition of the initial terpolymer to avoid pure relaxor state, tetrapolymers with optimal DB compositions are achieved, near the critical endpoint of normal ferroelectric phase with diffused phase transition. The nearly vanishing energy barriers between the nonpolar to polar phases result in a strong electrocaloric response and significant electroactuation. Specifically, the P(VDF‐TrFE‐CFE‐DB) tetrapolymer exhibits an EC entropy change Δ S of 100 J kg −1 K −1 under 100 MV m −1 : comparable to state‐of‐the‐art (SOA) EC polymers, while delivering nearly twice the electroactuation of the SOA EC polymers. This work presents a general strategy for developing EC materials that combine large electrocaloric effect and electroactuation at low electric fields.
We show that inorganic sulfides strongly influence transfer (migration) of nanoparticle mass out of polymer nanocomposites (PNCs) and into aqueous environments. We first manufactured two families of PNCs: one incorporating silver nanoparticles (AgNPs) and one incorporating CdSe quantum dots (QDs). Then, we assessed migration out of these PNCs and into aqueous media containing Na 2 S at concentrations ranging from 0 to 10 -4 M. Results show that Na 2 S strongly suppressed migration of Ag from AgNP-based PNCs: the migration into water spiked with 10 -6 M Na 2 S was 79% less than migration into water without Na 2 S, and no migration was detected (LOD ≈ 0.01 ng/cm 2 ) in water spiked with Na 2 S at 10 -5 M or 10 -4 M. With CdSe QD-based PNCs, Na 2 S suppressed Cd migration but enhanced Se migration, resulting in only a small net effect on the total QD migration but a large shift of the leachate composition (from favoring Cd by an average of 5.8 to 1 in pure water to favoring Se 9.4 to 1 when Na 2 S was present at 10 -4 M). These results show that common inorganic substances like sulfides may play a strong role in determining the environmental fate of polymer-dispersed nanoparticles and imply that migration tests conducted in purified water may not always accurately reflect migration into real environments.
Polyurea is of interest for blast mitigation of structures, which requires a good understanding of the dynamic properties including the shock Hugoniot and dynamic spall and shear strength. In this study, reverse impact experiments were used to determine the shock Hugoniot, direct impact experiments were used to determine the spall strength, and lateral manganin gauge experiments were used to determine the dynamic shear strength. Reverse impact experiments revealed that the Hugoniot has a linear fit at low pressures and appears to be undergoing a reaction at higher pressures. The spall strength experiments in this study in combination with the literature data showed that the spall strength increases as a function of pressure, which is unusual in polymers and may be attributed to polyurea transforming to a glassy phase. In the shear strength experiments, the shear stress was shown to increase with increasing longitudinal stress in polyurea, similar to estane, another elastomer.
The ability to characterize bulk and interfacial transport properties of polymer electrolytes is critical to realizing their potential applications in electrochemical energy storage devices. In this paper, we leverage custom microfabricated interdigitated electrode array (IDEs) as a platform to probe ion transport properties of polymer electrolytes films through electrochemical impedance spectroscopy (EIS) measurements. Using poly(ethylene oxide) (PEO) blended with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) as a model dry polymer electrolyte system, we investigate how geometric parameters of the IDEs influence the quality and analysis of EIS measurements. By focusing on films on the nanometer film thickness (ca. 50 nm), EIS measurements revealed diffusional processes near the electrode/polymer interface that may be difficult to observe with conventional thick films. Moreover, irreversible impedance spectra were observed at elevated temperatures when using IDEs with large electrode metal fractions. These irreversible processes were eliminated through passivation of the IDE with different oxides (SiO 2 , Al 2 O 3 , or TiO 2 ). Ultimately, the ionic conductivity of PEO-LiTFSI electrolytes is confidently determined when appropriate IDE geometries and equivalent circuits are used. Lastly, our work demonstrates the use of IDEs and nanothin polymer electrolytes films as a versatile platform for rapid and efficient interrogation of both bulk and interfacial electrochemical properties.
In this study, we focus on the influence of hydrophilic groups and metal-ion loading on adsorbent polymer conformation, which controls access to adsorption sites and may limit adsorption capacity. Gaining a better understanding of the factors that influence conformation may yield higher-capacity adsorbents. Polyamidoxime (PAO), deuterated-PAO polyacrylic acid diblock copolymers (d-PAO-b-PAA), and randomly configured copolymers (PAO-co-PAA) were synthesized and characterized by neutron reflectometry in air and D 2 O. For d-PAO-b-PAA, characterization was also performed after alkali conditioning and in simulated seawater. PAO and PAO-co-PAA, with similar molecular weight and grafting density, extended from 95-Å thickness in air to 180 and 280-Å in D 2 O, respectively. This result suggests that polymer swelling may cause the additional adsorption capacity observed when polymer hydrophilicity increases. Two d-PAO-b-PAA samples, A and B, with a d-PAO thickness of 55-Å swelled to 110-Å and 140-Å, respectively, with an overall thickness increase of ~160% in D 2 O. After alkali conditioning, molecular interactions increased the density of PAA near the PAO-PAA interface, while the d-PAO thickness only decreased by ~10 Å. The d-PAO thickness of both samples declined to ~90-Å after adsorption in simulated seawater due to polymer-chain crosslinking. In conclusion, these results are expected to aid in improving adsorbent synthesis to increase uranium capacity.
Organic–inorganic halide perovskites feature excellent optoelectronic properties but poor chemical stability. While passivating perovskite grain boundary (GB) by polymers shows prospects on long-term performance of perovskite solar cells (PSCs), its detailed impact on the ion migration phenomenon, which largely deteriorates the PSC stability, remains less probed. In this work, we introduce a new polar polymer, polycaprolactone (PCL), to passivate GBs of methylammonium lead triiodide (MAPbI 3 ) perovskite with only 1–2 polymer monolayers via direct backbone attachment. The PSCs with passivated MAPbI 3 , using a classic but less stable Spiro-OMeTAD (2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene) hole transport layer (HTL), exhibit improved power conversion efficiencies up to 20.1%, with 90% of the initial PCE being preserved after 400 h ambient storage, and 80% even after 100 h, 85 °C aging. The improved PSC stability indicates critical roles of PCL GB passivation in retarding moisture-induced decomposition and suppressing ion migration within the perovskite. Furthermore, time-of-flight secondary ion mass spectrometry reveals that I– ions can actively migrate into the electrode, HTL, and their interface in nonpassivated PSCs, even without an externally applied electric field, while such migration is significantly mitigated in PCL-passivated PSCs. This effective GB passivation by PCL suggests an important potential of polymer additives toward the development of stable high-performance PSCs.
We report the interfacial region formed in a polymer matrix around nanoparticles (NPs) controls many macroscopic properties of polymer nanocomposites (PNCs). However, understanding the factors controlling structure and properties of interfacial region remains a challenge. We demonstrated that the initial trapping of polymer chains at surfaces of NPs in solution strongly affects the macroscopic properties of PNCs. The most surprising result is that the differences in properties of PNCs persist even after an extremely long thermal annealing time. We ascribe the observed changes to the formation of interfacial layer that is trapped in a deep metastable state already in solution. Furthermore, presented analysis suggests that PNC equilibration time is defined by the chain desorption time that can be extremely long and, in some cases, even not accessible on a reasonable experimental time scale. These results highlight the importance of polymer solution concentrations on the formation of interfacial layer and the macroscopic properties of PNCs.
We demonstrate that the product of photoinduced electron transfer between a conjugated polymer host and a dilute molecular sensitizer is controlled by the structural state of the polymer. Ordered semicrystalline solids exhibit free charge generation, while disordered polymers in the melt phase do not. We use photoluminescence (PL) and time-resolved microwave conductivity (TRMC) measurements to sweep through polymer melt transitions in situ. Free charge generation measured by TRMC turns off upon melting, whereas PL quenching of the molecular sensitizers remains constant, implying unchanged electron transfer efficiency. The key difference is the intermolecular order of the polymer host in the solid state compared to the melt. We propose that this order-disorder transition modulates the localization length of the initial charge-transfer state, which controls the probability of free charge formation.
A bottom-up multi-scale modeling approach is used to develop an Integrated Computational Materials Engineering (ICME) framework for carbon fiber reinforced polymer (CFRP) composites, which has the potential to reduce development to deployment lead time for structural applications in lightweight vehicles. In this work, we develop and integrate computational models comprising of four size scales to fully describe and characterize three types of CFRP composites. In detail, the properties of the interphase region are determined by an analytical gradient model and molecular dynamics analysis at the nano-scale, which is then incorporated into micro-scale unidirectional (UD) representative volume element (RVE) models to characterize the failure strengths and envelopes of UD CFRP composites. Then, the results are leveraged to propose an elasto-plastic-damage constitutive law for UD composites to study the fiber tows of woven composites as well as the chips of sheet molding compound (SMC) composites. Subsequently, the failure mechanisms and failure strengths of woven and SMC composites are predicted by the meso-scale RVE models. Finally, building upon the models and results from lower scales, we show that a homogenized macro-scale model can capture the mechanical performance of a hat-section-shaped part under four-point bending. Along with the model integration, we will also demonstrate that the computational results are in good agreement with experiments conducted at different scales. The present work illustrates the potential and significance of integrated multi-scale computational modeling tools that can virtually evaluate the performance of CFRP composites and provide design guidance for CFRP composites used in structural applications.
This thesis makes significant advances to the understanding of bottlebrush polymers. While bottlebrushes have received much attention due to the recent discovery of their unprecedented properties, including supersoftness, ultra-low viscosity, and hyperelasticity, this thesis is the first fundamental investigation at the molecular level that comprises structure and dynamics. Neutron scattering experiments, detailed within, reveal spherical or cylindrical shapes, instead of a random coil conformation. Another highlight is the analysis of the fast dynamics at the sub nm-length scale. The combination of three neutron spectrometers and the development of a new analysis technique enabled the calculation of the mean-square displacement over seven orders of magnitude in time scale. This unprecedented result can be applied to a broad class of samples, including polymers and other materials. The thesis is accessible to scientists from other fields, provides the reader with easily understandable guidelines for applying this analysis to other materials, and has the potential to make a significant impact on the analysis of neutron scattering data.
Identifying membrane materials that have exceptional separation performance and stability to complex CO 2 -containing mixtures is a pressing topic in separation science. In this work, the membrane separation performance for a recently discovered class of contorted polymers synthesized via catalytic arene-norbornene annulation (CANAL) polymerization is presented. These CANAL polymers achieve high CO 2 /CH 4 selectivity of 68 after physical aging (up to ∼1 year), which significantly augments the size-sieving capabilities of the membranes. Binary CO 2 /CH 4 and ternary H 2 S/CO 2 /CH 4 testing result in a 41 % and 50 % enhancement in selectivities, respectively, for hyperaged (∼1 year) contorted CANAL polymers, highlighting their size-sieving capabilities. The remarkably high CO 2 /CH 4 mixed-gas and combined acid gas (CAG, (CO 2 +H 2 S)/CH 4 ) selectivities of 88 and 95, respectively, for CANAL-Me-S 5 F in particular surpass both the 2018 CO 2 /CH 4 mixed-gas and CAG upper bounds. Performance stability was also investigated for high concentrations of CO 2 , revealing a reduction in CO 2 /CH 4 mixed-gas selectivity without compromising CO 2 permeability, suggesting strong sorption of CO 2 but minimal plasticization effects for short testing periods. In addition, time-dependent plasticization shows negligible effects on CO 2 /CH 4 mixed-gas selectivity despite an increase in CO 2 permeability when exposed to high concentrations of plasticizing CO 2 over an extended period of 170 h. This study provides valuable insights into hyperaged CANAL polymers and their performance in practical industrial processes.
There is an increasing demand for nondestructive in situ techniques that measure chemical content, total thickness, and interface locations for multilayer polymer films, and SA Raman spectroscopy in combination with appropriate data models can provide this information. A scanning angle (SA) Raman spectroscopy method was developed to measure the chemical composition of multilayer polymer waveguide films and to extract the location of buried interfaces between polymer layers with 7–80-nm axial spatial resolution. The SA Raman method measures Raman spectra as the incident angle of light upon a prism-coupled thin film is scanned. Six multilayer films consisting of poly(methyl methacrylate)/polystyrene or poly(methyl methacrylate)/polystyrene/poly(methyl methacrylate) were prepared with total thicknesses ranging from 330-1260 nm. The interface locations were varied by altering the individual layer thicknesses between 140-680 nm. The Raman amplitude ratio of the 1605 cm -1 peak for PS and 812 cm -1 peak for PMMA was used in calculations of the electric field intensity within the polymer layers to model the SA Raman data and extract the total thickness and interface locations. There is an average 8% and 7% difference in the measured thickness between the SA Raman and profilometry measurements for bilayer and trilayer films, respectively.
Three series of low-bandgap polymers based on a novel quinoidal para -azaquinodimethane ( p -AQM) unit are devised and synthesized, enabling an in-depth study of the impact of structural factors such as polymer main chain, branching point of the side chain, and the length of the branch chains on the thin film morphologies and charge transport properties. Morphological studies reveal that the polymers composed of larger repeating units exhibit a stronger tendency to form edge-on lamella. In contrast, altering the side chain structures of polymers with the same main chain configuration indicates that the branching point position has a more deterministic impact than the branch chain length on the interchain interactions and the crystallite orientation. These results demonstrate a compound odd-even effect of the branching point on the chain packing and morphology, which correlates well with the corresponding field effect transistor performances. The polymer with the branching point at the fourth carbon displays the highest charge carrier mobility over 1.0 cm 2 V-Three series of low-bandgap polymers based on a novel quinoidal para -azaquinodimethane ( p -AQM) unit are devised and synthesized, enabling an in-depth study of the impact of structural factors such as polymer main chain, branching point of the side chain, and the length of the branch chains on the thin film morphologies and charge transport properties. Morphological studies reveal that the polymers composed of larger repeating units exhibit a stronger tendency to form edge-on lamella. On the other hand, altering the side chain structures of polymers with the same main chain configuration indicates that the branching point position has a more deterministic impact than the branch chain length on the interchain interactions and the crystallite orientation. These results reflect a compound odd-even effect of the branching point on the chain packing and morphology, which correlates well with the corresponding field effect transistor performances. The polymer with the branching point at the fourth carbon displays the highest charge carrier mobility over 1.0 cm 2 V -1 s -1 , concurrent with a bimodal texture. This study provides a comprehensive description of the correlations between polymer structures, thin film morphology, and device performances, providing a clear path to desirable bimodal thin film texture for charge transport.
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A series of amphiphilic ionic peptoid block copolymers where the total number (1 or 3) and position of ionic monomers along the polymer chain are precisely controlled have been synthesized by the submonomer method. Upon dissolution in water at pH = 9, the amphiphilic peptoids self-assemble into small spherical micelles having hydrodynamic radius in ~5–10 nm range and critical micellar concentration (CMC) in the 0.034–0.094 mg/mL range. Small-angle neutron scattering (SANS) analysis of the micellar solutions revealed unprecedented dependence of the micellar structure on the number and position of ionic monomers along the chain. It was found that the micellar aggregation number (N agg ) and the micellar radius (R m ) both increase as the ionic monomer is positioned progressively away from the junction of the hydrophilic and hydrophobic segments along the polymer chain. By defining an ionic monomer position number ( n ) as the number of monomers between the junction and the ionic monomer, N agg exhibited a power law dependence on n with an exponent of ~1/3 and ~3/10 for the respective singly and triply charged series. On the other hand, R m exhibited a weaker dependence on the ionic monomer position by a power law relationship with an exponent of ~1/10 and ~1/20 for the respective singly and triply charged series. Moreover, R m was found to scale with N agg in a power-law relationship with an exponent of 0.32 for the singly charged series, consistent with a weakly charged ionic star-like polymer model in the unscreened regime. This study demonstrated a unique method to precisely tailor the structure of small spherical micelles based on ionic block copolymers through controlling the sequence and position of the ionic monomer.