Polymer Loading Research Articles

PEG-PE/clay composite carriers for doxorubicin: Effect of composite structure on release, cell interaction and cytotoxicity.

DOX PEG-PE/clay formulations were design as an efficient drug delivery system. The main aim was to develop PEG-PE/clay formulations of different structures based on various PEG-PE/clay ratios in order to achieve tunable release rates, to control the external surface characteristics and formulation stability. The formulations showed significantly higher toxicity in comparison to "free" DOX, explained by formulation internalization. For each cell line tested, sensitive and ADR resistant, a different formulation structure was found most efficient. The potential of PEG-PE/clay-DOX formulations to improve DOX administration efficacy was demonstrated and should be further explored and implemented for other cancer drugs and cells.

Fatigue damage assessment of unfilled polymers including self-heating effects

Cyclic plasticity and fatigue damage mechanisms dissipate part of the supplied strain energy to the system to induce either inelastic deformations and/or microflaws within the material system. Polymer material systems exhibit lower lifetimes when the self-heating phenomenon become significant that may lead to heat softening and thermal damage. Self-heating effect in cyclic loading of polymers can be correlated to the cyclic dissipative mechanisms. This work aims at developing a fully coupled elastic, plastic, thermal, and fatigue damage computational tool for unfilled polymers to investigate the role of self-heating in lifetime prognoses. The thermodynamics principles are incorporated to formulate the coupling between dissipative energies and thermomechanical constitutive laws. Continuum Damage Mechanics (CDM) is utilized to link microscale damage mechanisms to macroscale failures. The computational framework is implemented into a commercial FEA code (Abaqus) through user-defined coding. It is shown that the developed computational platform correlates well with the observed experimental data and it may constitute a powerful design tool for future developments.

Contemporary Drug-Eluting Stents and Vascular Response

Cardiovascular disease is a leading cause of death and disability worldwide. Current treatment strategies aimed at treating the consequences of coronary artery disease have embraced both optimal medical therapy and catheter based percutaneous coronary intervention with drug-eluting stents (DES). Current-generation DES elute predominantly mammalian target of rapamycin (mTOR) inhibitors, which act primarily as a cytostatic agent that retards vascular smooth muscle cell proliferation and migration; this occurs in response to injury and thus prevents restenosis. While DES have reduced restenosis, the use of first-generation DES was associated with an increased risk of late stent thrombosis and accelerated neointimal atherosclerosis (i.e. neoatherosclerosis), both major contributors to late stent failure. The underlying substrate of late DES failure is likely related to vascular endothelial dysfunction, which occurs after DES implantation. Initial concerns with first-generation DES have led to improvements in stent design, polymer load and biocompatibility, and pharmacologic agents, all of which have helped to improve healing responses, lessen late stent failure, and result in an overall improved safety profile. The armamentarium of DES has expanded from the current-generation durable polymer DES to bioresorbable polymer DES, polymer-free DES, and lastly totally bioresorbable vascular scaffolds with a goal of improving vascular responses and endothelial function while preserving anti-restenotic efficacy. We will review these contemporary DES in relation to their short and long-term effects on vascular biocompatibility and healing responses.

Effect of Clay Dispersion on the Nonisothermal and Isothermal Crystallization Behaviors of Polyethylene Composites

ABSTRACTThe presence of nanosized clay fillers can greatly influence the crystallization behaviors and crystalline morphologies of polymer composites. In this study, the modified montmorillonite polyethylene nanocomposites have been prepared by melt mixing, followed by injection molding. The morphology and microstructure of the composites were characterized by scanning electron microscopy and Fourier transform infrared spectrometry. The nanosized clay particles act as a nucleating agent in the solidification process of the matrix. The relative crystallinity ratio decreases with the decrement of polymer loading. Nonisothermal and isothermal crystallizations were conducted to characterize the crystallization kinetics of nanocomposites. The effects of clay dispersion on the crystallization of polymer were quantified by Avrami and Hoffman models. The addition of 1 wt% clay into polymer matrix has significantly increased the activation energy. The crystallization rate constants (G) have been determined which are higher for the composites than that for the polymer matrix.

Transverse crack initiation under combined thermal and mechanical loading of Fibre Metal Laminates and Glass Fibre Reinforced Polymers

The paper describes a temperature-dependent extension of the classical laminate theory (CLT) that may be used to predict the mechanical behaviour of Fibre Metal Laminates (FML) at cryogenic conditions, including crack initiation. FML are considered as a possible alternative class of structural materials for the transport and storage of liquified gasses such as LNG. Combining different constituents in a laminate opens up the possibility to enhance its functionality, e.g. offering lower specific weight and increased damage tolerance. To explore this possibility, a test programme is underway at the University of Twente to study transverse crack initiation in different material combinations under combined thermal and mechanical loading. Specifically, the samples are tested in a three-point bending experiment at temperatures ranging from 77 to 293 K. These tests will serve as a validation of the model presented in this paper which, by incorporating temperature-dependent mechanical properties and differential thermal expansion, will allow to select optimal material combinations and laminate layouts. By combining the temperature-dependent mechanical properties and the differential thermal contraction explicitly, the model allows for a more accurate estimate of the resulting thermal stresses which can then be compared to the strength of the constituent materials.

Nanoparticle-Enhanced Hydraulic-Fracturing Fluids: A Review

Summary Hydraulic-fracturing fluids are used to break down subterranean formations where oil and gas are trapped. Pad or prepad fluids are first pumped into the formation to generate the fracture geometry. Once the fracture geometry is created, additional fluid containing proppant is used to transport these solid particles into the fractures. Then, the hydraulic pressure is released and the fracture will tend to close. At that stage, the proppant prevents fracture closure and provides a conductive channel for hydrocarbons to flow into the wellbore. Biopolymers, synthetic polymers, foams, viscoelastic surfactant (VES) fluids, and slickwater are all used as fracturing fluids, each with properties that are beneficial under certain conditions. Today, their formulations are well-developed, and more recently, may incorporate small-sized particles in the nanometer size range. Such nanoparticles have addressed certain technological limitations of fracturing fluids. For example, VES fluids were reported to suffer high leakoff rates in moderate permeability reservoirs (200 md) and were limited in temperature (beyond approximately 220°F, viscosity was diminished significantly). Another challenge is the pressure-dependent behavior of borate-crosslinked gels, where the viscosity was found to drop significantly under high pressures. Also, in high-temperature reservoirs (>350°F), it is very challenging to design a fluid that can sustain enough viscosity for a required period of time. Synthetic polymers (mainly acrylamide-based polymers) are commonly used and have been reported to be used at high concentrations. These high-concentration requirements are imposed by the need for a stable viscosity under high-temperature conditions. High polymer loading increases the potential of formation damage caused by the fluid residue. These challenges, which can be addressed by nanotechnology, could have a major impact on hydraulic-fracturing applications. For instance, the working temperature limit of VES-based fluids was improved from 200 to 250°F (93 to 121°C) by adding zinc oxide (ZnO) and magnesium oxide (MgO) nanoparticles. The borate-crosslinked gels were found to maintain their viscosity at pressures up to 20,000 psi when using boronic acid-functionalized nanolatex silica particles as crosslinkers, while under such high pressures, conventional borate crosslinkers showed more than 80% reduction in viscosity. Moreover, the rheological properties of mixed VES/polymer fluids were enhanced when using nanoparticles. Use of foams can reduce the amount of water consumed in hydraulic fracturing. Alfa olefin sulfonate (AOS) surfactant can be foamed by use of carbon dioxide (CO2). Aluminum oxide nanoparticles were found to stabilize the foams created by AOS, VES, and CO2. This has a potential application in waterless fracturing. This review paper will capture all of these aspects and summarize the most recent experience of nanoparticle usage in hydraulic-fracturing fluids design.

Surface Modification of Wool Fabric with Chitosan and Gamma Radiation

Surface modification of wool was done with chitosan, gamma radiation and combined chitosan/gamma radiation to analyze how polymer loading%, k/s value, dye uptake% and wash fastness property vary of the dyed fabric. In this investigation scoured and bleached knitted wool fabric was treated with 0.1%, 0.3%, 0.5%, 0.7% and 1% chitosan and polymer loading was found as of 1.21%, 1.38%, 0.32%, 0.14% and 0.48% respectively. It was found that polymer loading % increase significantly with the decrease of chitosan concentration % up to a certain limit. Some samples were irradiated with 5kGy, 10kGy, 20kGy and 50kGy gamma radiation individually. Combined chitosan/gamma treatment was carried out by treating with 0.1% chitosan followed by treatment with 5kGy, 10kGy, 20kGy and 50kGy gamma radiation. The infrared spectrum of wool specimens were analyzed by Fourier Transform Infrared Spectrometer (FT-IR). It was found that the infrared spectrum of untreated and treated wool specimens were approximately same except the peak absorbs at 1340-1265 cm-1 which indicate the C-N stretch absorption of aromatic amines. After dyeing k/s value of untreated and treated wool specimens were measured using Data color 600®. There was a remarkable variation of k/s value on different treatment process. Dye uptake% of untreated and treated wool specimens were determined by using UV Visible Spectrophotometer in terms of absorbency. Color fastness to wash was measured using ISO standard. There was no significant change of wash fastness property of treated and untreated wool.

Thermal Property Analysis of Axle Load Sensors for Weighing Vehicles in Weigh-in-Motion System.

Systems which permit the weighing of vehicles in motion are called dynamic Weigh-in-Motion scales. In such systems, axle load sensors are embedded in the pavement. Among the influencing factors that negatively affect weighing accuracy is the pavement temperature. This paper presents a detailed analysis of this phenomenon and describes the properties of polymer, quartz and bending plate load sensors. The studies were conducted in two ways: at roadside Weigh-in-Motion sites and at a laboratory using a climate chamber. For accuracy assessment of roadside systems, the reference vehicle method was used. The pavement temperature influence on the weighing error was experimentally investigated as well as a non-uniform temperature distribution along and across the Weigh-in-Motion site. Tests carried out in the climatic chamber allowed the influence of temperature on the sensor intrinsic error to be determined. The results presented clearly show that all kinds of sensors are temperature sensitive. This is a new finding, as up to now the quartz and bending plate sensors were considered insensitive to this factor.

DESyne novolimus-eluting coronary stent is superior to Endeavor zotarolimus-eluting coronary stent at five-year follow-up: final results of the multicentre EXCELLA II randomised controlled trial.

Newer-generation drug-eluting stents (DES) have been shown to be superior to first-generation DES. Current-generation DES have zotarolimus, everolimus or biolimus as antiproliferative drugs. Novolimus, a metabolite of sirolimus, has been specifically developed to provide efficacy similar to currently available agents at a lower dose and thus requires a lower polymer load. We report the final five-year outcomes of the EXCELLA II trial comparing a zotarolimus-eluting stent (ZES) with a novolimus-eluting stent (NES). EXCELLA II is a prospective, multicentre, single-blind, non-inferiority clinical trial. Patients (n=210) with a maximum of two de novo lesions in two different epicardial vessels were randomised (2:1) to treatment with either NES (n=139) or ZES (n=71). At five-year follow-up, patients in the NES group had a significantly lower incidence of the patient-oriented (HR 0.53, 95% CI: 0.32-0.87, p=0.013) and device-oriented (HR 0.38, 95% CI: 0.17-0.83, p=0.011) composite endpoints. There was no difference in cardiac death and definite/probable stent thrombosis between the two groups; however, there was a trend towards reduction in myocardial infarction and repeat revascularisation in the NES group at five-year follow-up. At five-year follow-up, the incidence of device- and patient-oriented events was significantly lower in the NES group. Further studies, adequately powered for clinical outcomes, are warranted.

Use of waste plastic materials for road construction in Ghana

This paper forms part of research to solve two main problems in Ghana: firstly, the management of municipal solid waste (MSW), particularly with regards to used plastics which have overwhelmed major cities and towns; secondly, the formation of potholes onroads due to excessive traffic and axle weight. This study examines the effect of blending waste thermoplastic polymers, namely High density polyethylene (HDPE) and Polypropylene (PP) in Conventional AC-20 graded bitumen, at various plastic compositions. The plastics were shredded and blended with the bitumen ‘in-situ’, with a shear mixer at a temperature range of 160°C–170°C. Basic rheological parameters such as penetration, ring & ball softening point and viscosity tests were employed to determine the resulting changes from base bitumen.FTIR spectroscopy was also employed to study the chemical functionalities present in the bitumen composite. The properties of the unmodified bitumen were found to be enhanced with the changes recorded in the rheological properties of the polymer modified bitumen (PMB). It was observed that polypropylene polymer, showed profound effect on homogeneity and compatibility with slight linear increment in the viscosity, softening and penetration values as against relatively high changes for HDPE modified bitumen.The viscosity of unmodified bitumen was enhanced with the addition of the polymers and thixotropic effect was observed for both HDPE and PP at 60°C. For all modified binders prepared, the penetration values decrease as polymer-bitumen ratio increases whiles softening temperature generally increases as polymer ratio increases. The most compatible and incompatible blends for HDPE were respectively observed at 2% and 3% polymer loading. The most enhanced, homogenous blend is achieved with PP at 3% polymer loading. Three prominent peaks were identified in the spectrum of the unmodified bitumen, occurring at the 3000–2850cm−1 IR frequency range, typical of aliphatic CH symmetrical and asymmetrical stretches in alkanes. CH2 and CH3 bends were also observed at the characteristic frequencies of 1465cm−1 and 1375cm−1 respectively. A low intensity peak was observed within the 2400cm−1–2100cm−1 range, indicating the presence of a very weak −CC- or −CN group with an absorbance of precisely 0.12.The use of waste commodity plastics in binder modification carries the advantage of a cheap and effective means of enhancing conventional bitumen binder performance characteristics and is an alternative way to utilise plastic waste.

Development of Eudragit RS 100 Microparticles Loaded with Ropinirole: Optimization and In Vitro Evaluation Studies.

The current study aimed to develop novel pH independent microparticles loaded with ropinirole (ROP) for sustained drug release. Eudragit RS 100 was used as release retardant and microparticles were fabricated by oil-in-oil emulsion solvent evaporation method. A three-factor three-level Box-Behnken design using Design-Expert software was employed to optimize formulation variables. Ropinirole loaded microparticles were evaluated with respect to morphology, particle size, encapsulation efficiency, and in vitro release profile. Optical microscopy and SEM micrographs indicated spherical shape with smooth surface and well-defined boundary. The particle size was in the range of 98.86 to 236.29μm, being significantly increased with increasing polymer concentration. Higher polymer load also increased the thickness of internal polymer network, which led to reduced drug loss and higher entrapment efficiency (89%). The cumulative in vitro release was found to be in the range of 54.96 to 99.36% during the release studies (12h) following zero order release kinetics and non-Fickian diffusion pattern. The developed microparticles have the potential to sustain the release of ropinirole, which may lead to a reduction in its adverse effects and improved management of Parkinson's disease.

Reduced-Polymer-Loading, High-Temperature Fracturing Fluids by Use of Nanocrosslinkers

Summary In the quest to discover more natural-gas resources, considerable attention has been devoted to finding and extracting gas locked within tight formations with permeability in the nano- to microdarcy range. The main challenges associated with working in such formations are the intrinsically high-temperature and high-pressure bottom conditions. For formations with bottomhole temperatures at approximately 350–400°F, traditional hydraulic-fracturing fluids that use crosslinked polysaccharide gels, such as guar and its derivatives, are not suitable because of significant polymer breakdown in this temperature range. Fracturing fluids that can work at these temperatures require thermally stable synthetic polymers such as acrylamide-based polymers. However, such polymers have to be used at very-high concentrations to suspend proppants. The high-polymer concentrations make it very difficult to completely degrade at the end of a fracturing operation. As a consequence, formation damage by polymer residue can reduce formation conductivity to gas flow. This paper addresses the shortcomings of the current state-of-the-art high-temperature fracturing fluids and focuses on developing a less-damaging, high-temperature-stable fluid that can be used at temperatures up to 400°F. A laboratory study was conducted with this novel system, which comprises a synthetic acrylamide-based copolymer gelling agent and is capable of being crosslinked with an amine-containing polymer-coated nanosized particulate crosslinker (nanocrosslinker). The laboratory data have demonstrated that the temperature stability of the crosslinked fluid is much better than that of a similar fluid lacking the nanocrosslinker. The nanocrosslinker allows the novel fluid system to operate at significantly lower polymer concentrations (25–45 lbm/1,000 gal) compared with current commercial fluid systems (50–87 lbm/1,000 gal) designed for temperatures from 350 to 400°F. This paper presents results from rheological studies that demonstrate superior crosslinking performance and thermal stability in this temperature range. This fracturing-fluid system has sufficient proppant-carrying viscosity, and allows for efficient cleanup by use of an oxidizer-type breaker. Low polymer loading and little or no polymer residue are anticipated to facilitate efficient cleanup, reduced formation damage, better fluid conductivity, and enhanced production rates. Laboratory results from proppant-pack regained-conductivity tests are also presented.

Optimization of Apparent Peak Viscosity in Carboxymethyl Cellulose Fracturing Fluid: Interactions of High Total Dissolved Solids, pH Value, and Crosslinker Concentration

SummaryIt has been common practice to use a freshwater source (either ground water or surface water) as the base fluid for hydraulic fracturing with crosslinked-gel fluids. Currently, oil and gas operators are beginning to reuse and recycle the main byproduct of oil extraction, which is produced water. However, because of the high variability of produced-water quality (temporal and spatial), and the high content of total dissolved solids (TDS), the viscosity targets for the fluid can be difficult to achieve. The research described in this paper examines the sensitivity of higher-salinity waters to several variables related to the gel-formation process. The polymer used for the gel fluid was a carboxymethyl cellulose (CMC) derivative, and zirconium (Zr) was used as the crosslinking metal. Rheology experiments were conducted at different pH values, polymer loading, and crosslinker concentrations. The outcome of this research is presented in 3D contour-peak-viscosity maps that can be used by oil and gas operators and service companies to optimize the chemicals that are applied, thus reducing costs.

Cytocompatibility with osteogenic cells and enhanced in vivo anti-infection potential of quaternized chitosan-loaded titania nanotubes.

Infection is one of the major causes of failure of orthopedic implants. Our previous study demonstrated that nanotube modification of the implant surface, together with nanotubes loaded with quaternized chitosan (hydroxypropyltrimethyl ammonium chloride chitosan, HACC), could effectively inhibit bacterial adherence and biofilm formation in vitro. Therefore, the aim of this study was to further investigate the in vitro cytocompatibility with osteogenic cells and the in vivo anti-infection activity of titanium implants with HACC-loaded nanotubes (NT-H). The titanium implant (Ti), nanotubes without polymer loading (NT), and nanotubes loaded with chitosan (NT-C) were fabricated and served as controls. Firstly, we evaluated the cytocompatibility of these specimens with human bone marrow-derived mesenchymal stem cells in vitro. The observation of cell attachment, proliferation, spreading, and viability in vitro showed that NT-H has improved osteogenic activity compared with Ti and NT-C. A prophylaxis rat model with implantation in the femoral medullary cavity and inoculation with methicillin-resistant Staphylococcus aureus was established and evaluated by radiographical, microbiological, and histopathological assessments. Our in vivo study demonstrated that NT-H coatings exhibited significant anti-infection capability compared with the Ti and NT-C groups. In conclusion, HACC-loaded nanotubes fabricated on a titanium substrate show good compatibility with osteogenic cells and enhanced anti-infection ability in vivo, providing a good foundation for clinical application to combat orthopedic implant-associated infections.

Optimization of carboxylmethyl cellulose frac fluid in low TDS water sources based on pH and crosslinker concentrations

Hydraulic fracturing uses a large volume a water to extract the oil and gas deposited in shale gas and oil formations. Many oil and gas developments are located in semiarid to arid areas in the United States (US), where freshwater resources are scarce. Using lower quality waters, such as brackish water during hydraulic fracturing, could be a good alternative to freshwater resources, reducing the competition on these sources and easing the public concerns with water shortages. This article examines using brackish water with total dissolved solids (TDS) of 2500mg/L, optimization of carboxylmethyl cellulose (CMC) based fracturing fluid at different pH ranges and polymer concentrations. Five three dimensional (3D) contour maps were generated for peak viscosity at a polymer loading of 25–45 pounds per thousand gallons (ppt) of water. These viscosity maps are the first of their kind and help demonstrate that using poor quality water can be managed by optimizing the chemical composition of the fracturing fluid.

Reduced Crystallization Temperature Methodology for Polymer Selection in Amorphous Solid Dispersions: Stability Perspective.

API-polymer interactions, used to select the right polymeric matrix with an aim to stabilize an amorphous dispersion, are routinely studied using spectroscopic and/or calorimetric techniques (i.e., melting point depression). An alternate selection tool has been explored to rank order polymers for formation of stable amorphous dispersions as a pragmatic method for polymer selection. Reduced crystallization temperature of API, a parameter introduced by Zhou et al.,1 was utilized in this study for rank ordering interactions in API-polymeric systems. The trends in reduced crystallization temperature monitored over polymer concentration range of up to 20% polymer loading were utilized to calculate "crystallization parameter" or CP for two model systems (nifedipine and BI ABC). The rank order of CP, i.e., a measure of API-polymer interaction, for nifedipine followed the order PVP > PVP-VA > Soluplus > HPMCAS > PV Ac > PAA. This rank ordering was correlated to published results of molecular interactions and physical stability for nifedipine. A different rank ordering was observed for BI ABC: PAA > PVP > HPMCAS > Soluplus > PVPV-VA > PVAc. Interactions for BI ABC were not as differentiated when compared to nifedipine based on CP trends. BI ABC dispersions at drug loadings between 40 and 60% were physically stable for prolonged periods under ICH conditions as well as accelerated stress. We propose that large CP differences among polymers could be predictive of stability outcomes. Acceptable stability at pharmaceutically relevant drug loadings would suggest that the relative influence of downstream processes, such as polymer solubility in various solvents, process suitability and selection, and more importantly supersaturation potential, should be higher compared to stability considerations while developing compounds like BI ABC.

Hybrid Glucose/O2 Biobattery and Supercapacitor Utilizing a Pseudocapacitive Dimethylferrocene Redox Polymer at the Bioanode

Small implantable electronic devices require biologically compatible energy sources that are capable of delivering quick high-energy pulses. Combining batteries and supercapacitors allows for high power and energy density while providing both small size and biocompatibility. Here, we report a hybrid supercapacitor/biobattery whereby an oxygen-reducing cathode of bilirubin oxidase immobilized with anthracene-modified carbon nanotubes and tetrabutylammonium bromide-modified Nafion is coupled with a glucose bioanode of flavin adenine dinucleotide-dependent glucose dehydrogenase. The redox polymer, dimethylferrocene-modified linear poly(ethylenimine), used at the bioanode simultaneously immobilizes enzyme, mediates electron transfer, and acts as a pseudocapacitor where capacitance of the anode scales with increased polymer loading. Both multiwalled carbon nanotubes and carbon felt incorporated into the anode construction improve polymer conductivity, subsequently resulting in further improved anodic capacitan...

Silica-poly(styrenesulphonic acid) nanocomposites as promising acid catalysts

Silica-poly(styrene sulphonic acid) nanocomposites (SiO2-PSSA) were prepared using sol-gel methodologies. An amino functionalized organosilane (APTES) provides the anchoring sites for the retention of this acid polymer by the silica particles network. Aiming at optimizing the polymer loading and stability, different SiO2-PSSA nanocomposites were prepared by changing the type of solvent used in the synthesis, the aging protocol of the gel and the relative concentration of APTES. The effect of these modifications on the catalytic properties of the nanocomposites was explored in two different reactions driven by acid catalysts: xylose dehydration to furfural and esterification of oleic acid with methanol to yield biodiesel. Both reactions are of interest in the valorization of biomass and represent two illustrative cases to exploring the hydrothermal stability of the SiO2-PSSA nanocomposites under different conditions: aqueous phase at moderately high reaction temperatures (453K) and organic medium (methanol and oil) at low reaction temperature (333K), respectively. Polymer leaching was very intense in the case of furfural reaction because of the severe reaction conditions. On the contrary, for the case of the esterification of oleic acid, a reaction conducted under milder conditions, the deactivation by leaching is significantly prevented.

Loading and Delivery Characteristics of Binary Mixed Polymer Brush‐Grafted Silica Nanoparticles

Binary mixed poly(acrylic acid) (PAA)/polystyrene (PS) brush‐grafted silica nanoparticles are evaluated for loading and delivery of a hydrophobic fluorescent dye as a model drug. A previous cryo‐electron tomography study of mixed PAA/PS brush‐grafted silica nanoparticles shows that in N,N‐dimethylformamide (DMF) PAA and PS are microphase separated laterally, while in water PS collapses to form isolated domains within the PAA matrix. Thus, loading with hydrophobic small molecules can be performed in DMF, followed by slow transfer to an aqueous buffer. Loading and release experiments with the fluorescent dye Nile Blue indicate a release half‐life of ≈13 d. Comparison of the loading capability of mixed brush‐grafted nanoparticles with varying percentages of PS indicates that a high percentage of the hydrophobic PS polymer is required in the mixed‐brush layer for retention of Nile Blue. In vitro delivery experiments demonstrate that Nile Blue‐loaded mixed brush‐grafted nanoparticles can mediate delivery of dye to HeLa cells.image

Hydraulic Conductivity of Geosynthetic Clay Liners to Low-Level Radioactive Waste Leachate

AbstractHydraulic conductivity was evaluated for eight commercially available geosynthetic clay liners (GCLs) permeated with leachate characteristic of low-level radioactive waste (LLW) disposal facilities operated by the U.S. Department of Energy (DOE). Two of the GCLs (CS and GS) contained conventional sodium bentonite (Na-B). The others contained a bentonite–polymer mixture (CPL, CPH, GPL1, GPL2, and GPH) or bentonite–polymer composite (BPC). All GCLs (except GPL2 and GPH) were permeated directly with two synthetic LLW leachates that are essentially identical, except one has no radionuclides (nonradioactive synthetic leachate, or NSL) and the other has radionuclides (radioactive synthetic leachate, or RSL). Hydraulic conductivities to RSL and NSL were identical. For the CS and GS GCLs, the hydraulic conductivity gradually increased by a factor of 5–25 because divalent cations in the leachate replaced native sodium cations bound to the bentonite. The CPL, GPL1, and GPL2 GCLs with low polymer loading (1....