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Purpose – The purpose of this paper is to continue studies previously reported with the primary focus of optimizing an inductor design. The potential benefits of hyperthermia for cancer therapy, particularly metastatic cancers of the prostate, may be realized by the use of targeted magnetic nanoparticles that are heated by alternating magnetic fields (AMFs). Design/methodology/approach – To further explore the potential of this technology, a high-throughput cell culture treatment system is needed. The AMF requirements for this research present challenges to the design and manufacture of an induction system because a high flux density field at high frequency must be created in a relatively large volume. Additional challenges are presented by the requirement that the inductor must maintain an operating temperature between 35 and 39°C with continuous duty operation for 1 h or longer. Results of simulation and design of two devices for culture samples and for in vitro tests of multiple samples in uniform field are described. Findings – The inductor design chosen provides a uniform distribution of relatively high magnetic field strength while providing an optimal reduction in the voltage and power requirement. Through development of design and selection of magnetic concentrator, the exposure of the cell cultures to the heat generated by the inductor is minimized. Originality/value – This method of generating uniform high AC magnetic fields in a large volume is beneficial for the study of hyperthermia in cells for a high throughput, necessary for cancer treatment research. [ABSTRACT FROM AUTHOR]

The adsorption of the strong polyelectrolyte sodium poly(styrenesulfonate) (NaPSS) to the air surface of water was investigated as a function of polymer concentration from the dilute regime to the beginning of the semidilute regime. Detailed segment profiles of the deuterated polymer were determined by neutron reflection (NR). Data were obtained for 0.67 and 2.50 M KCl. For two samples differing widely in molecular weight (1150 and 56.1 kg/mol), we find that with increasing polymer concentration the adsorbed amount first increases, reaches a maximum, and then decreases strongly. The PSS concentration at which the maximum is reached is dependent on both the molecular weight and the salt concentration in a manner that correlates with the chain overlap concentration. Regarding the segment profiles, at low polymer concentration the profiles are composed of a thin layer of high concentration at the air surface (trains), followed by a distinct second layer of much lower segment concentration that extends to larger depths into the liquid (loops and tails). Complementary X-ray reflection (XR) revealed a localization of ions about 10 Å below the surface for dilute PSS concentration. This layer becomes more diffuse at higher PSS concentration, in conjunction with the decrease in PSS adsorbed amount measured by NR. This surprising behavior of the adsorbed amount with polymer concentration is not explained by current SCF theory treating the adsorption of strong polyelectrolytes to neutral surfaces. We discuss a few possible explanations for this desorption transition. Finally, we observe that the surface tension decreases monotonically with increasing concentration of PSS in bulk solution but is not correlated with the adsorbed amount of PSS at the surface.

Specular neutron reflectivity has been used to investigate the structure of monolayers formed from linear−dendritic diblock copolymers at an air−water interface. The dendritic block copolymers consist of a linear poly(ethylene oxide) (PEO) block of 2000 molecular weight linked to a third or fourth generation polyamidoamine (PAMAM) dendron. The dendritic end groups were functionalized with deuterated stearic acid to make the dendritic block hydrophobic, resulting in a macroamphiphile. Results indicate that stable monolayers are formed with PEO resting on the subphase and stearate groups extending into the air. In general, at low surface concentrations the PEO block intermixes with the PAMAM dendron, whereas at high surface concentrations the PAMAM forms a distinct layer above the PEO. The ordering of the stearate groups functionalized on the dendrimer was dependent on generation. Stearate groups form a distinct ordered layer which is separate from the third generation PAMAM dendron, whereas the stearate groups are intermixed with fourth generation PAMAM segments due to the curvature of the higher generation dendron. The PEO block becomes intermixed with the water subphase if the monolayer is held at constant area for at least 10 h. These finding are consistent with earlier published studies of pressure−area isotherms of these systems on the Langmuir−Blodgett trough.

Chronocoulometry and the thermodynamic analysis of charge density data were employed to describe the energetics of sodium dodecyl sulfate (SDS) adsorption at the Au(111) electrode surface. Thermodynamic data such as the Gibbs excess, Gibbs energy of adsorption, and the film pressure of adsorbed SDS were determined for a broad range of electrode potentials, charge densities, and bulk SDS concentrations. The present results, combined with our previous scanning probe microscopy (SPM) studies, show that adsorption of SDS at the Au(111) electrode surface has a two-state character. At small or moderate absolute charge densities, the adsorbed SDS molecules aggregate into hemicylindrical stripelike micelles. This state is well-ordered. The unit cell of its two-dimensional lattice consists of two vectors that are 44 and 5.0 Å long and are oriented at an angle of 70°. The Gibbs excess data indicate that five SDS molecules are accommodated into the unit cell. At large positive charge densities, the hemimicellar aggregates melt to form a condensed film. The surface concentration of SDS doubles upon transition from the hemimicellar to the condensed state. We have performed neutron reflectivity experiments to determine the thickness of the hemimicellar and condensed films. The neutron reflectivity data indicate that the thickness of the condensed film is equal to 20.5 Å and is only 30% larger than the thickness of the hemimicellar state. The electrochemical and neutron reflectivity data indicate that the properties of the condensed state are best explained by a model of an interdigitated film in which half of the sulfate groups are turned toward the metal and half toward the solution.

We present here the results of neutron and X-ray reflectivity studies on the effects of solvent flow on the height and density profile of polymer chains chemically end-tethered to a surface. Our system consists of perdeuterated polystyrene chains, molar mass 80 000, that were chemically tethered to a silicon oxide surface via trichlorosilane (SiCl3) terminal groups. The brush was exposed to a range of flow rates in both toluene and cyclohexane to a maximum shear rate of 130 000 s^-1. We observe that both the polymer brush profile and height remain unchanged even at the highest flow rates and that no loss of polymer occurred. These results are discussed in the context of the various theoretical, simulation, and experimental results presented in the literature.

AbstractFor more than a decade, neutron reflectometry has been an active part of the research program at NIST and, over the years, a broad range of experiments have been performed on polymeric, magnetic, superconducting, and biomimetic thin film systems. Some examples include studies of diblock copolymer lamellar ordering [1], the magnetic coupling in “Giant Magneto-Resistance” and other multilayers [2,3], the structure of Langmuir-Blodgett films [4], the corrosion of electrode surfaces [5], the oxide layers of semiconductor surfaces, the absorption of macromolecules by biomimetic bilayers, and grazing angle diffraction experiments with polarized neutrons [6].

We have employed electrochemical and neutron reflectivity measurements to study the transfer of 4-pentadecyl-pyridine (C15−4Py), an insoluble amphiphilic surfactant, from the gas−solution (G−S) interface to the metal−solution (M−S) interface of a Au(111) electrode. Neutron reflectivity experiments have demonstrated that C15−4Py forms a bilayer at the Au(111) electrode surface. Electrochemical experiments demonstrated that this bilayer is formed spontaneously when the electrode surface is brought in contact with the film-covered G−S interface. The surfactant molecules can move from the G−S to the M−S interface across the triple-phase boundary formed where the metal, solution, and gas phases are in contact. Time-dependence experiments have shown that the spreading process is irreversible. Having formed a bilayer or monolayer at the M−S interface, the C15−4Py surfactant molecules do not move back to a film-free G−S interface. Three models were used to analyze the kinetics of spreading. Our results are best explained assuming that the spreading is a first-order surface reaction controlled by the activation barrier that the surfactant molecules have to overcome when crossing the triple-phase line.

The adsorption of the strong polyelectrolyte poly(styrenesulfonate) (PSS) to the air surface of dilute aqueous solutions was investigated as a function of molecular weight and salt concentration. Detailed segment profiles of the deuterated polymer were determined by neutron reflection. Surface activity was also examined through surface tension measurements. In general, the segment profiles are composed of a thin layer (10−20 Å thick) of high concentration at the air surface, followed by a distinct second layer of much lower segment concentration that extends to larger depths into the liquid. The high segment density at the air surface is due to a strong surface attraction, arising from the low surface energy of the PSS backbone relative to the surface tension of water. At low salt concentration, the profiles tend toward a single dense layer, suggesting that the chains lie nearly flat at the interface in that limit. The adsorbed amount increases with salt concentration, with a stronger dependence for higher molecular weight chains. The adsorbed amounts at the air/water interface are higher than reported previously for PSS adsorbed onto neutral solid surfaces, consistent with the fact that the air−liquid interface provides a stronger surface attraction. While the trends of adsorbed amount with salt concentration and molecular weight are in good agreement with numerical self-consistent-field lattice calculations, the measured bilayer profiles are rather different from the smoothly decaying theoretical profiles. The surface tensions of the PSS solutions are significantly lowered relative to those of pure salt solutions. Combining the reflectivity and surface tension measurements, an approximately linear relationship is established between the surface pressure and the PSS adsorbed amount.

To quantify the swelling response of polyelectrolyte dendrimers in aqueous solutions as affected by changes in solution conditions, we have studied eighth generation, G8, poly(amidoamine) (PAMAM) dendrimers in D2O using small-angle neutron scattering. The charge density is manipulated by varying the pH of the solution in order to protonate and deprotonate the primary and tertiary amines. The coherent scattered intensity at high q values yields size information from the form factor of individual dendrimers. The distance distribution functions of the dendrimers in a variety of experimental situations were determined by indirect Fourier transform. For all the conditions studied, we find that the size of G8 dendrimers is essentially insensitive to variations of the pH (4.7 < pH < 10.1) and of ionic strength (up to 3 M of NaCl). In all cases, the scattering curves yield density profiles that correspond well to a uniform sphere with a radius of gyration RG = 4.0 ± 0.15 nm. We conclude that the dendrimer size is essentially independent of the charge density or ionic strength of the solvent, contrary to the predictions of current models and simulations.

The adsorption of chicken egg white lysozyme at the functionalized silicon oxide−solution interface has been studied using the combined measurement of spectroscopic ellipsometry and neutron reflection. The solid oxide surface was modified by coating a self-assembled monolayer of pentadecyltrichlorosilane with terminal hydroxyl groups (abbreviated to C15OH). Neutron reflection measurement at the solid−D2O interface showed that the C15OH layer was 16 ± 2 Å thick and the volume fraction was 0.94 ± 0.05, suggesting the formation of a close-packed monolayer. The adsorption of lysozyme was made at pH 4 and 7 with lysozyme concentration ranging from 0.03 to 4 g dm^-3. The results were then compared with those from previous studies at the hydrophilic SiO2−water and the hydrophobed SiO2−water interfaces, with the latter formed by coating a monolayer of octadecyl trichlorosilane (abbreviated to OTS). At 0.03 g dm^-3 and pH 7 the surface excess was found to be 0.6 ± 0.3 mg m^-2 at the C15OH−water interface, as compared with 1.7 mg m^-2 at the SiO2−water interface and 1.9 mg m^-2 at the OTS−water interface. As lysozyme concentration is increased to 4 g dm^-3, the surface excess at the C15OH−water interface reaches 2.1 mg m^-2, as compared with 4.7 mg m^-2 at the hydrophilic SiO2−water interface and 5.1 mg m^-2 at the OTS−water interface. These values demonstrate the attainment of the minimum surface excess on the hydroxyl surface. Shifting solution pH from 7 to 4 reduces adsorption on all the surfaces studied, but the lowest level of adsorption is again obtained on the hydroxyl surface. The reversibility of the adsorption at the C15OH−water interface was examined by cycling the solution pH at different lysozyme concentrations. Adsorption was found to be completely reversible at the low lysozyme concentration of 1 g dm^-3, while at the high concentration of 4 g dm^-3 the adsorption was irreversible.

Structure within thin epoxy films is investigated by neutron reflectivity (NR) as a function of resin/cross-linker composition and cure temperature. Variation in the cross-link density normal to the substrate surface is examined by swelling the films with the good solvent d-nitrobenzene (d-NB). The principal observation is a large excess of d-NB near the air surface. This is not a wetting layer, but rather indicates a lower cross-link density in the near-surface region. This effect is due to preferential segregation of the cross-linker to the air surface, driven by the lower surface tension of the cross-linker relative to the epoxide oligomers. The magnitude of the effect is a function of composition and cure temperature. Exclusion of d-NB from the region immediately adjacent to the substrate surface is also observed, possibly indicating a tightly bound layer of epoxy. Regarding swelling in the bulk of the films, the behavior is nonsymmetric with departure from the stoichiometric ratio. The films deficient in curing agent show greater equilibrium swelling and faster swelling kinetics than the films with an excess of curing agent.

We present results of small-angle neutron scattering (SANS) investigations into the characteristics of charged poly(amidoamine) (PAMAM) dendrimer solutions in deuterium oxide. The study shows that ionic strength, surface charge density, and concentration are the crucial parameters controlling the degree of structural organization of the solution. Upon the addition of acid, HCl, we observe a peak in the scattering intensity. The results indicate that increasing ionization of terminal amines results in interparticle interactions giving rise to local, liquidlike ordering. These interactions can be screened by adding monovalent salt (NaCl) in large quantities. The short-range interactions were studied by systematically varying dendrimer and salt concentration (up to 2 M). Contrary to most weak polyelectrolyte systems, we did not observe a negative second virial coefficient, even for the highest salt concentrations.