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We report a systematic investigation on the structure–property relationships in glycerol‐plasticized poly(vinyl alcohol) (PVA)/cassava starch blends prepared via solution casting. In particular, PVA mixed with native, low‐oxidized, high‐oxidized, and pregelatinized cassava starches were characterized by means of SEM, XRD, FTIR, thermal analysis and mechanical testing and the immiscible systems were received. Burial tests over a period of several days suggested the preferential degradation of the starch and glycerol component (as indicated by the absence of FTIR signatures of those components) and the amorphous phase of PVA (as indicated by the enhanced crystallinity index of the degraded samples). The rheological properties of the blends seem to dictate their morphological characteristics that, in turn, have a profound impact on their mechanical properties. In that sense, the study highlights promising strategies for the development of a new family of polymeric materials that combine their biodegradable nature within superior mechanical properties. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48848.

A series of blend films comprised 88% hydrolyzed poly(vinyl alcohol) (PVA) with native cassava starch (NCS), high-oxidized cassava starch (HCS), and pre-gelatinized cassava starch (PCS) was prepared via solution casting. The blends were plasticized with glycerol or glycerol-sorbitol mixture. The structure of each blend film was characterized by Fourier-transform infrared spectroscopy and X-ray diffraction analysis. Cross-sections of the PVA/HCS and PVA/PCS blend films, imaged by scanning electron microscopy, indicated a PVA-rich/starch-rich bilayer structure, irrespective of the type of plasticizer in the blend. High degree of swelling of the blend films resulted to the fast degradation. All blend films were completely degraded in soil after 4 days. Significantly, we identified a number of blend films showed greater strength and elongation at break than low density polyethylene, suggesting that these environmentally benign blends could be ideal candidates for widespread applications currently dominated by petroleum-derived products.

The study focuses on structure-properties relationships in thermoplastic cassava starch (TPS) based biocomposites comprising 5-20 wt% of untreated and treated rice husk (RH). Alkaline treatment with 11% w/v NaOH removed the hemicellulose layer of RH as confirmed by Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA), and resulted in a larger population of -OH groups exposing on the fibril surface. Consequently, the filler-matrix interactions between treated RH and TPS were enhanced, although Brunauer-Emmett-Teller (BET) surface area analysis indicated that the surface area of treated RH was not increased. Interestingly, the biocomposites contained 20 wt% treated RH showed substantially improved tensile strength by a factor of 220% compared to the neat TPS. The biocomposite at 15 wt% treated RH showed high water absorption. TPS with all treated RH contents showed high biodegradation rate, while the thermal stability of the TPS/treated RH biocomposites was slightly decreased. These novel composites showed promising properties for applications as absorbents. [Abstract copyright: Copyright © 2020 Elsevier B.V. All rights reserved.]

Owing to their superior fluorescence performance, inexpensive synthesis and nontoxic nature, carbon dots (C-dots) are systematically explored in a variety of applications; in this review, we outline and critically discuss recent trends with respect to their potential exploitation in criminal investigation, forensic toxicology and anti-counterfeit interventions. Capitalising on their colour-tuneable behaviour (in the sense that they adopt different colours with respect to the incident radiation), C-dot-based compositions are ideal for the visual enhancement of latent fingerprints, affording improved contrast against multicoloured and patterned backgrounds. As highly sensitive and highly selective optical nanoprobes, C-dots show excellent analytical performance in detecting biological compounds, drugs, explosives, heavy metals and poisonous reactants. In addition, benefiting from their versatile structural and chemical composition, C-dots can be incorporated into ink and polymeric formulations capable of functioning as a new generation of cost-effective barcodes and security nanotags for object authentication and anti-counterfeit applications. Translating these encouraging research outcomes into real-life innovations with significant social and economic impact requires an open, multidisciplinary approach and a close synergy between materials scientists, biologists, forensic investigators and digital engineers.

We disclose a green, cost and time effective approach to impart photoluminescent properties to a range of polymeric materials, an otherwise solvent-intensive and tedious process. Our strategy relies on the thermal treatment of ethanolamine (a carbon and nitrogen-rich precursor) well dispersed within a polymer matrix and gives rise to fluorescent C-dot based nanocomposites, without compromising the physicochemical characteristics of the matrix. The strategy affords at least 20% conversion of the precursor towards fluorescent nanoparticles, eliminates the use of toxic chemicals and is thoroughly compatible with melt processing technologies routinely used in industry. While we focus here on polyethylene (PE), polypropylene (PP) and polyethylene glycol (PEG) nanocomposites, the approach is general and applicable to a variety of thermally stable polymers. The C-dots formed in situ within the PEG matrix have diameters in the range 1–40 nm (as revealed by TEM) and exhibit quantum yield 11% in water compared to 3% for the PE-derived nanoparticles.

Boron-doped multi-walled carbon nanotubes (B-MWCNTs) were synthesized, treated with hydrochloric acid, “piranha” solution, and decorated with gold nanoparticles (AuNPs). B-MWCNTs were characterized using Raman spectroscopy, scanning electron- and transmission electron microscopy, and electrochemical techniques. The results exhibit enhanced response and sensitivity of B-MWCNTs upon modification with AuNPs. Analysis of dopamine (DA) and epinephrine (EP) in presence of uric acid (UA) was investigated on B-MWCNTs/AuNPs in pig blood serum. Limits of detection of 0.20 and 0.30 μM were estimated for DA and EP, respectively. The findings demonstrate that B-MWCNTs/AuNPs is proper for analysis of DA and EP under coexistence of UA.

The carbon dots were investigated to reveal their light-emitting mechanism. The fluorescence spectra of carbon dots show typically two different types of photoluminescence: the excitation-independent component in the short wavelength, and the excitation-dependent component in the longer wavelength. The UV-Vis spectrum of carbon dots shows the absorption maximum of 340 nm which should be accredited to the n-π* transition of the carbonyl group in carbon dots. Absolute quantum yields of carbon dots dispersed in Polyvinyl alcohol is around 15% when the excitation wavelength is less than 425 nm, but decreases continuously when the excitation wavelength increases. The decay lifetimes of the carbon dots also show an abrupt change at excitation wavelength 425 nm. Time resolved photoluminescence was implemented from 31K to 291K to study the photoluminescence decay dynamics of carbon dots, resulting in the continuously decreasing of the lifetime as the temperature increases.

We present a novel family of biocompatible hydrogels containing Nafion and poly(ethylene oxide) based block copolymers. In aqueous environment, thermodynamically stable ionomer-copolymer complexes are formed, as evident by light scattering and quartz crystal microbalance experiments. Moreover, incorporation of Nafion dramatically modifies the phase behaviour and the rheological properties of copolymer hydrogels. The hybrid systems not only undergo sharp and thermally reversible sol-gel transitions below the body temperature, thus retaining their injectable nature, but they also generate mechanically robust hydrogels. Moreover, ibuprofen was continuously released over a period of 26 days for the Nafion/Pluronic hydrogel, compared to only 3 days for the Nafion-free system. The hybrid gels are promising candidates for 3D-bioprinting and controlled drug release applications.

The effects of cobalt acetate (CoAc), manganese acetate (MnAc), nickel acetate (NiAc) and zinc acetate (ZnAc) as fire retardant additive in intumescent polypropylene (PP) formulations containing PP/ammonium polyphosphate (APP)/pentaerythritol (PER) are reported. The limiting oxygen index (LOI) and vertical burning (UL94) tests and cone calorimetry were used to quantify the enhancement. Environmental chamber rheometry, thermal gravimetric analysis and the morphology of the residual char were used to investigate the mechanism of enhancement. The incorporation of small quantities of metal acetates had a significant influence on the fire behaviour. As an example, 0.7 wt% MnAc improved the UL 94 rating of PP/APP + PER (mass ratio 100/25, with APP/PER = 3/1) sample from V-2 to V-0, while 1 wt% MnAc reduced the peak heat release rate and the total heat release by 18% and 12% in the cone calorimeter. Rheological data, cone calorimetry, and photographs of the residual char showed how the fire retardancy of the systems were affected by the melt viscosity, which depended on the loading of metal acetate. During thermal decomposition, the metal acetates promote the crosslinking of the polymer and the fire retardant, reinforcing the protective intumescent layer. While, the effect is most potent at the optimal metal loadings. At higher MnAc loadings, the benefit of a stronger char is overwhelmed by the adverse effect of crosslinking on the transition char layer. Thus, this paper offers a new insight into the mechanism of the intumescent fire retarded PP system.

This work aims to employ fused deposition modelling 3D printing to fabricate immediate release pharmaceutical tablets with several model drugs. It investigates the addition of non-melting filler to methacrylic matrix to facilitate FDM 3D printing and explore the impact of (i) the nature of filler, (ii) compatibility with the gears of the 3D printer and iii) polymer: filler ratio on the 3D printing process. Amongst the investigated fillers in this work, directly compressible lactose, spray-dried lactose and microcrystalline cellulose showed a level of degradation at 135°C whilst talc and TCP allowed consistent flow of the filament and a successful 3D printing of the tablet. A specially developed universal filament based on pharmaceutically approved methacrylic polymer (Eudragit EPO) and thermally stable filler, TCP (tribasic calcium phosphate) was optimised. Four model drugs with different physicochemical properties were included into ready-to-use mechanically stable tablets with immediate release properties. Following the two thermal processes (hot melt extrusion (HME) and fused deposition modelling (FDM) 3D printing), drug contents were 94.22%, 88.53%, 96.51% and 93.04% for 5-ASA, captopril, theophylline and prednisolone respectively. XRPD indicated that a fraction of 5-ASA, theophylline and prednisolone remained crystalline whilst captopril was in amorphous form. By combining the advantages of thermally stable pharmaceutically approved polymers and fillers, this unique approach provides a low cost production method for on demand manufacturing of individualised dosage forms.

Heavy metal detection has become very important for the protection of water resource. In this work, a novel controllable probe is presented for the sensitive detection of Pb2+ in aqueous solutions. The probe was synthesized via the immobilization of surface functionalized carbon dots (named as CAEA-Hs) into the shell of the spherical polyelectrolyte brushes (SPB). The fluorescence of CAEA-H was firstly "turned off" via electrostatic interaction induced quenching. Based on the aggregation induced emission enhancement (AIEE), the fluorescence of the immobilized CAEA-H could be specifically turned on via the aggregation of the SPB particles. This fluorescence "turn on" sensor could selectively detect Pb2+ among five different metal ions with a relatively wide detecting range (0-1.67 mM) and good linear relationship (R 2 = 0.9958). Moreover, the aggregating behavior and nano-structure of CAEA-H loaded SPB have been systematically analyzed via small angle X-ray scattering, turbidity titration, and Zeta-potential measurement. Based on a series of control experiments, we finally gain an insight into the sensing mechanism of this novel sensing probe. This contributed a proof of concept demonstration that sensitive and selective chemical detection can be achieved via a C-dot/SPB synergistic platform.

This study focuses on the structural rearrangements and the photoluminescent behavior of pyrolytically derived carbon dots when subjected to a series of cyclic voltammetry sweeps. Although the electrical signals involved are not pronounced, multiple electrochemical cycling results in a progressive suppression of the photoluminescence, so that after 42 sweeps the intensity is reduced by one order of magnitude. At the same time, the fluorescence component stemming from the organic fluorophores is blue-shifted, while the contribution of the carbogenic cores is red-shifted. XPS and FTIR spectra reveal that the voltammetric field induces an extensive formation of C-O and C[double bond, length as m-dash]O at the expense of the C[double bond, length as m-dash]C bonds. Our findings indicate a close relationship between the electrochemical response and the structure of C-dots and, thus, have direct implications on the development of C-dot based electroluminescent materials, electrochemical sensors and solar cells.

Tough biodegradable films were prepared using a poly(vinyl alcohol) (PVA)/poly(vinyl pyrrolidone) (PVP) (1:1) blend with plasticizers of glycerol (GLY), sorbitol (SOR), and their (one to one) mixture. We studied the effect of plasticization on the structural, thermal, and mechanical properties of the PVA/PVP blend films. Fourier transform infrared spectra indicated good miscibility of the two components due to the H-bonding between the PVA and PVP molecules. The addition of plasticizers reduced the interaction between PVA and PVP, evidenced by an increase in the intensity of PVA diffraction peaks observed in the X-ray diffraction (XRD) characterization. Thermal degradation of the blends increased as a function of the plasticizer used. GLY affected thermal degradation more than SOR and the mixtures. The incorporation of the plasticizers promoted the growth of PVA crystals as evidenced by XRD patterns and the enthalpy of fusion (ΔHf) obtained by differential scanning calorimetry measurements. The introduction of SOR to the binary blend increased toughness seven times and imparted simultaneous and pronounced improvements to maximum tensile stress and elongation at break. This behavior holds out great promise for the development of a new generation of mechanically robust, yet thoroughly biodegradable materials that could effectively supplant conventional polymers in demanding applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46406.

The incorporation of a minor amount of carbogenic nanoparticles into powder compositions imparts remarkable colour-tuneability, without compromising the flowability. In a proof-of-concept demonstration we report the use of these hybrid nanopowders for the visual enhancement of latent fingerprints where they effectively resolve issues arising from poor contrast against multi-coloured or patterned backgrounds.

In recent years, nanosensor technology has experienced a rapid development because of the extensive scientific efforts in understanding of nanoscale phenomena and achieving innovative nanofabrication techniques. Carbon-based nanomaterials (CBNs), such as fullerenes, graphene, nanodiamonds, carbon nanotubes, and carbon nanodots, have recently gained considerable attention among scientific communities due to their unique chemical and physical properties. Thanks to intensive research efforts, the CBNs have found their place in a wide range of applications. These CBNs stand out as novel nanosensors due to their supreme performance in detecting heavy metal ions, gas molecules, food additives, antibodies, and toxic pesticides, as well as reporters for bioimaging. This special issue, to be published in 2017, addresses recent progress in the synthesis, characterization, structure-property relationships and applications of CBNs as novel nanosensors. We are confident that the accrual of these contributions will facilitate the applications of CBNs as innovative nanosensors in meeting the urgent needs for environmental monitoring, food safety control, healthcare, homeland security, and so forth. We have selected five papers, representing four different frontiers of this topic: graphene, silver nanoparticles, carbon nanotubes, and carbon nanodots.

The study focuses on the structure and viscoelasticity of poly(ethylene oxide)/carbon black fluids. The hybrids when subjected to extreme thermal annealing (at temperatures far above the melting point of the matrix) exhibit a 3–4 orders of magnitude increase in viscosity. Surprisingly, the effect is reversible and the viscosity reverts back to its initial value upon subsequent cooling. This rather unique sol–gel transition in terms of strength, steepness and thermal reversibility points to major structural rearrangements via extensive particle clustering, in agreement with microscopy observations. In related systems it was found that when matrix-particle electrostatic interactions are present the gelation is essentially diminished.

The incorporation of organically modified Lucentite nanoclay dramatically modifies the structure and morphology of the PVDF electrospun fibers. In a molecular level, the nanoclay preferentially stabilizes the all-trans conformation of the polymer chain, promoting anαtoβtransformation of the crystalline phase. The piezoelectric properties of theβ-phase carry great promise for energy harvest applications. At a larger scale, the nanoclay facilitates the formation of highly uniform, bead-free fibers. Such an effect can be attributed to the enhanced conductivity and viscoelasticity of the PVDF-clay suspension. The homogenous distribution of the directionally aligned nanoclays imparts advanced mechanical properties to the nanofibers.

Carbogenically coated silica nanoparticles (C-SiO2) exhibit color-tunability and carry great promise for two important forensic applications. First, the C-SiO2 nanopowders are ideal for fingerprint development, yielding strong contrast against multicoloured and patterned backgrounds. Second, spontaneous nanoparticle aggregation leads to non-duplicable, inexpensive nanotags that can support sustainable technologies to combat counterfeiting.

The incorporation of highly porous activated carbon (aC) to Nafion membranes confers unprecedented levels of water uptake (4 times higher for 10 wt% aC compared to neat Nafion) at a minimal dimensional swelling and results in dramatic enhancements in ionic conductivity at low relative humidity. This behavior reveals the development of a robust network of water nanochannels formed by the carbon pores and the polymeric ionic domains which are structurally stabilized by the rigid Nafion backbone and the non-deformable aC particles.

Motivated by the technological need for poly(ethylene terephthalate) materials with improved barrier properties together with the requirement for sustainability this study focuses on an eco-friendly sulfonated polyester as clay compatibilizer to facilitate polymer mixing during melt compounding. We demonstrate that the nanocomposites based on sulfonated polyester are a reliable alternative to their imidazolium counterparts, exhibiting enhanced properties (water vapor and UV transmission), without sacrificing the excellent transparency, clarity and mechanical strength of the matrix.

We report a systematic study of the crystallization and rheological behavior of poly(ethylene oxide) (PEO)–clay nanocomposites. To that end a series of nanocomposites based on PEOs of different molecular weight (103 < MW < 105 g/mol) and clay surface modifier was synthesized and characterized. Incorporation of organoclays with polar (MMT-OH) or aromatic groups (MMT-Ar) suppresses the crystallization of polymer chains in low MW PEO, but does not significantly affect the crystallization of high MW matrices. In addition, the relative complex viscosity of the nanocomposites based on low MW PEO increases significantly, but the effect is less pronounced at higher MWs. The viscosity increases in the series MMT-Alk < MMT-OH < MMT-Ar. In contrast to the neat PEO which exhibits a monotonic decrease of viscosity with temperature, all nanocomposites show an increase after a certain temperature. This is the first report of such dramatic enhancements in the viscoelasticity of nanocomposites, which are reversible, are based on a simple polymer matrix and are true in a wide temperature range.

We report the synthesis of multifunctional hybrids in both films and bulk form, combining electrical and ionic conductivity with porosity and catalytic activity. The hybrids are synthesized by a two-step process: (a) ice templation of an aqueous suspension comprised of Nafion, graphite oxide, and chloroplatinic acid to form a microcellular porous network and (b) mild reduction in hydrazine or monosodium citrate which leads to graphene-supported Pt nanoparticles on a Nafion scaffold.

Incorporation of Nafion to aqueous solutions of Pluronics adversely impacts micellization due to extensive Nafion/copolymer interactions. Light scattering and zeta potential measurements provide evidence for the formation of sizable and stable Nafion/copolymer complexes, in expense of the neat copolymer micelles. At high copolymer concentrations, the overall interaction diagram of Nafion/copolymer reflects the competitive action of the release of packing constraints due to micellar destabilization induced by Nafion on one hand and the gelator nature of the Nafion on the other. Measurements using a quartz crystal microbalance (QCM-D) show that aqueous solutions of Pluronics (even at very low concentration) can dissolve the Nafion coating on the crystal resonator, while typical low molecular weight ionic surfactants fail to induce similar effects. These studies demonstrate that complexation with this class of copolymers is a facile route to impart dispersibility to Nafion in aqueous environments that otherwise can be achieved through tedious and harsh treatments.

The bulk and surface characteristics of a series of coatings based on PDMS-polyurea segmented copolymers were correlated to their fouling release performance. Incorporation of polyurea segments to PDMS backbone gives rise to phase separation with the extensively hydrogen bonded hard domains creating an interconnected network that imparts mechanical rigidity. Increasing the compositional complexity of the system by including fluorinated or POSS-functionalized chain extenders or through nanoclay intercalation, confers further thermomechanical improvements. In analogy to the bulk morphology, the surface topography also reflects the compositional complexity of the materials, displaying a wide range of motifs. Investigations on settlement and subsequent removal of Ulva sporelings on those nanostructured surfaces indicate that the work required to remove the microorganisms is significantly lower compared to coatings based on standard PDMS homopolymer. All in all, the series of materials considered in this study demonstrate advanced fouling release properties, while exhibiting superior mechanical properties and, thus, long term durability.

Structure-properties relationships in poly(vinylidene fluoride-co-hexafluoropropylene), PVDF-HFP, clay nanocomposites are reported for the first time. Addition of organically modified clays to PVDF-HFP promotes an α to β transformation of the polymer crystals. The degree of transformation depends on the nature of the clay surface modifier and scales with the strength of the interactions between the clay and the polymer. The nanocomposites exhibit significant increases in elongation to failure compared to the neat copolymer. In addition, their dielectric permittivity is higher over a wide temperature range. Their mechanical and dielectric properties scale similar to the amount of the β phase present in the nanocomposites.

Nafion–clay hybrid membranes with a unique microstructure were synthesized using a fundamentally new approach. The new approach is based on depletion aggregation of suspended particles – a well-known phenomenon in colloids. For certain concentrations of clay and polymer, addition of Nafion solution to clay suspensions in water leads to a gel. Using Cryo-TEM we show that the clay particles in the hybrid gels form a network structure with an average cell size in the order of 500 nm. The hybrid gels are subsequently cast to produce hybrid Nafion–clay membranes. Compared to pure Nafion the swelling of the hybrid membranes in water and methanol is dramatically reduced while their selectivity (ratio of conductivity over permeability) increases. The small decrease of ionic conductivity for the hybrid membranes is more than compensated by the large decrease in methanol permeability. Lastly the hybrid membranes are much stiffer and can withstand higher temperatures compared to pure Nafion. Both of these characteristics are highly desirable for use in fuel cell applications, since a) they will allow the use of a thinner membrane circumventing problems associated with the membrane resistance and b) enable high temperature applications.

A series of Nafion–clay nanocomposite membranes were synthesized and characterized. To minimize any adverse effects on ionic conductivity the clay nanoparticles were H+ exchanged prior to mixing with Nafion. Well-dispersed, mechanically robust, free-standing nanocomposite membranes were prepared by casting from a water suspension at 180 °C under pressure. SAXS profiles reveal a preferential orientation of Nafion aggregates parallel to the membrane surface, or normal plane. This preferred orientation is induced by the platy nature of the clay nanoparticles, which tend to align parallel to the surface of the membrane. The nanocomposite membranes show dramatically reduced methanol permeability, while maintaining high levels of proton conductivity. The hybrid films are much stiffer and can withstand much higher temperatures compared to pure Nafion. The superior thermomechanical, electrochemical and barrier properties of the nanocomposite membranes are of significant interest for direct methanol fuel cell applications.

The effect of added nanoclays to the morphological characteristics and the macroscopic properties in a blend of isotactic polypropylene (iPP) and poly(ethylene oxide) (PEO) is examined in this study. It is shown that strong interactions between the surfactant used for clay modification and the binary matrix can effectively control the spatial organization of the suspended polymer droplets. It is also shown that the emulsifying efficiency of nanoclays to the polymer blend has a critical effect on the macroscopic properties of the nanocomposites. In this study, we present a unique case in which the incorporation of a small amount of organically modified nanoclay induces a dramatic transformation from an opaque to a transparent system.

The interactions of bovine serum albumin (BSA) with three ethylene oxide/butylene oxide (E/B) copolymers having different block lengths and varying molecular architectures is examined in this study in aqueous solutions. Dynamic light scattering (DLS) indicates the absence of BSA-polymer binding in micellar systems of copolymers with lengthy hydrophilic blocks. On the contrary, stable protein-polymer aggregates were observed in the case of E 18B 10 block copolymer. Results from DLS and SAXS suggest the dissociation of E/B copolymer micelles in the presence of protein and the absorption of polymer chains to BSA surface. At high protein loadings, bound BSA adopts a more compact conformation in solution. The secondary structure of the protein remains essentially unaffected even at high polymer concentrations. Raman spectroscopy was used to give insight to the configurations of the bound molecules in concentrated solutions. In the vicinity of the critical gel concentration of E 18B 10 introduction of BSA can dramatically modify the phase diagram, inducing a gel-sol-gel transition. The overall picture of the interaction diagram of the E 18B 10-BSA reflects the shrinkage of the suspended particles due to destabilization of micelles induced by BSA and the gelator nature of the globular protein. SAXS and rheology were used to further characterize the structure and flow behavior of the polymer-protein hybrid gels and sols.

Critical micelle concentrations (cmc) of aqueous solutions of poly(methyl methacrylate)-block-poly(N-isopropylacrylamide) were determined at several temperatures by surface tensiometry. Below the lower critical solution temperature (LCST), the low Delta mic H 0 determined can be assigned to the PMMA block being tightly coiled in the dispersed molecular state, so that the unfavorable interactions of hydrophobic entities with water are minimized. Above the LCST the cmc value was found to increase; an anomalous behavior that can be directly related to the micelle-globule transition of the hydrophilic block. Interestingly, above the LCST the surface tension of relatively concentrated solutions was found to depend weakly on temperature not following the usual strong decrease with temperature expected for aqueous solutions.

The self-assembly of a fragment of the amyloid beta peptide that has been shown to be critical in amyloid fibrillization has been studied in aqueous solution. There are conflicting reports in the literature on the fibrillization of Abeta (16-20), i.e., KLVFF, and our results shed light on this. In dilute solution, self-assembly of NH 2-KLVFF-COOH is strongly influenced by aromatic interactions between phenylalanine units, as revealed by UV spectroscopy and circular dichroism. Fourier transform infrared (FTIR) spectroscopy reveals beta-sheet features in spectra taken for more concentrated solutions and also dried films. X-ray diffraction and cryo-transmission electron microscopy (cryo-TEM) provide further support for beta-sheet amyloid fibril formation. A comparison of cryo-TEM images with those from conventional dried and negatively stained TEM specimens highlights the pronounced effects of sample preparation on the morphology. A comparison of FTIR data for samples in solution and dried samples also highlights the strong effect of drying on the self-assembled structure. In more concentrated phosphate-buffered saline (PBS) solution, gelation of NH 2-KLVFF-COOH is observed. This is believed to be caused by screening of the electrostatic charge on the peptide, which enables beta sheets to aggregate into a fibrillar gel network. The rheology of the hydrogel is probed, and the structure is investigated by light scattering and small-angle X-ray scattering.

The introduction of ionic single-tailed surfactants to aqueous solutions of EO(18)BO(10) [EO = poly(ethylene oxide), BO = poly(1,2-butylene oxide), subscripts denote the number of repeating units] leads to the formation of vesicles, as probed by laser scanning confocal microscopy. Dynamic light scattering showed that the dimensions of these aggregates at early stages of development do not depend on the sign of the surfactant head group charge. Small-angle X-ray scattering (SAXS) analysis indicated the coexistence of smaller micelles of different sizes and varying polymer content in solution. In strong contrast to the dramatic increase of size of dispersed particles induced by surfactants in dilute solution, the d-spacing of corresponding mesophases reduces monotonically upon increasing surfactant loading. This effect points to the suppression of vesicles as a consequence of increasing ionic strength in concentrated solutions. Maximum enhancements of storage modulus and thermal stability of hybrid gels take place at different compositions, indicating a delicate balance between the number and size of polymer-poor aggregates (population increases with surfactant loading) and the number and size of polymer-surfactant complexes (number and size decrease in high surfactant concentrations).

The relationships between the microscopic structure and the macroscopic properties in two sets of clay nanocomposites based on polymer blends comprised of poly(vinylidene fluoride) (PVDF) and ethylene–vinyl acetate copolymer (EVAc) were examined. In nanocomposites based on a polymer blend matrix with high content of polar groups (VAc) the dispersion of polar nanoclay leads to significant enhancement in toughness and a substantial increase in viscosity. However, in nanocomposite blends based on a less polar matrix (i.e. with fewer VAc groups) it is the hydrophobic organoclay that leads to higher modulus and stronger viscoelasticity. The dispersion of nanoparticles and the mechanical response are discussed in terms of emulsifying efficiency of the clay particles in the immiscible polymer blend, an effect that largely depends on the localized interactions between the polymer groups and the clay surface modifier. The potential of nanoclays to serve as matrix sensitive structure-directing agents in tailor-made materials is demonstrated.

The tensile and dynamic mechanical properties of a nanocomposite, containing modified carbon nanofibers (MCNFs) homogenously dispersed in an elastomeric ethylene/propylene (EP) copolymer semicrystalline matrix (84.3 wt% P), have been correlated with the structure development. These properties were characterized by in situ synchrotron X-ray diffraction during stretching, dynamic mechanical analysis and X-ray analysis techniques over a wide temperature range. Upon sequential drawing, the tensile strength of the nanocomposite film was notably higher than that of the unfilled polymer even though both samples exhibited a similar amount of crystal fraction and the same degree of crystal orientation, revealing the effect of nanofiller reinforcement in the semicrystalline matrix. The mechanical spectra of the 10 wt% MCNF filled samples in both stretched and non-stretched states showed broadening of the elastic modulus at high temperatures, where the corresponding crystallinity index also decreased. It is conceivable that a significant fraction of chain orientation is induced in the vicinity of the nanofillers during stretching, and these stretched chains with reduced mobility significantly enhance the thermal mechanical properties.

The isothermal crystallization kinetics and the melting behavior of block copolymers of poly(ethylene oxide) and poly(1,2-butylene oxide) were studied by means of differential scanning calorimetry and rheometry to test the validity of rheological methods. The copolymers had different block lengths (hence different melt structures) and different block architectures (diblock EB and triblock EBE and BEB). For crystallization from disordered and lamellar melts, half-times for crystallization from rheometry were much shorter, and Avrami exponents were higher, than those from calorimetry. For more-highly structured melts (gyroid, hexagonal and cubic spheres), the half-times were comparable but the Avrami exponents from rheometry were still high compared to DSC. The differences between the rates of crystallization from calorimetry and rheometry are an artifact of the rheological measurements, at low crystallite volume fractions the rheology is directly proportional to the degree of crystallinity but at high crystalline volume fractions the proportionality is lost due to the changing connectivity of the crystals. The rates of crystallization ranked in order: lamellar>disordered≈gyroid>hexagonal≫cubic spheres. Other things being equal, the effect of block architecture was insignificant.

The solubilization properties of P60E348 (P = oxypropylene, E = oxyethylene, subscripts = number of repeating units) diblock copolymer micelles containing liquid crystals have been studied by light scattering and UV spectroscopy for mainly dilute solutions from the following viewpoints: (i) the micellar solubilization rate J of a nematic liquid crystal (LC), predominantly pentylcyanobiphenyl, (ii) the amount of solubilized material at saturation, and (iii) the apparent size of the P60E348 micelles containing LC and their intermicellar interaction properties. It was shown, in experiments with solubilization temperature Ts = 50 °C, that the rate J is inversely proportional to the copolymer concentration cp in the range 2 g L-1 ≤ cp ≤ 10 g L-1 whereas J is constant at higher values of cp. It was also shown that J increases strongly with an increase in temperature. The micellar hydrodynamic radius Rh was independent of temperature in the range 30 °C ≤ T ≤ 60 °C, whereas there was a reduction in the hydrodynamic virial coefficient kD and in the thermodynamic second virial coefficient A2 as T was increased (for Ts = 40 °C). To probe the intermicellar interference, the excess scattered intensity was measured as a function of cp, showing an increasing deviation from linearity, reflecting the transition from a dilute to a concentrated system and the increasing predominance of intermicellar interactions.

Graphitic and amorphous C-dots share common characteristics in their photoluminescence behavior. However, the graphitic dots have a lead as electrocatalyst for fuel cells, sensitizers, and electron acceptors for solar cells. The emergence of carbogenic nanoparticles (C-dots) as a new class of photoluminescent (PL) nanoemitters is directly related to their economical preparation, nontoxic nature, versatility, and tunability. C-dots are typically prepared by pyrolytic or oxidative treatment of suitable precursors. While the surface functionalities critically affect the dispersibility and the emission intensity of C-dots in a given environment, it is the nature of the carbogenic core that actually imparts certain intrinsic properties. Depending on the synthetic approach and the starting materials, the structure of the carbogenic core can vary from highly graphitic all the way to completely amorphous. This critical review focuses on correlating the functions of C-dots with the graphitic or amorphous nature of their carbogenic cores. The systematic classification on that basis can provide insights on the origins of their intriguing photophysical behavior and can contribute in realizing their full potential in challenging applications.