arXiv subjects

Gerald J. Schneider

Publications and source records attributed to Gerald J. Schneider.

12 recordsLinked to original sources

arXiv2024

Building a Simplistic Automatic Extruder: Instrument Development Opportunities for the Laboratory

A well-rounded introduction to work in a STEM laboratory is vital to scientific education. Besides the ability to use available instrumentation for sample characterization, students should also be imparted knowledge in the steps of instrument development and construction. These concepts can be taught using the example of lipid vesicle preparation via extrusion. Vesicle extrusion is a common technique that involves syringes pushing solutions through membrane filters and is used in fundamental studies on vesicles. Such research is important to better understand of biological phenomena and drug development. Well prepared samples are key to successful research. While the manual approach is very useful to acquire experience, automatic extrusion is more convenient, and automation often results in better reproducibility. These advantages can be combined in a simplistic automatic extruder, that does not require advanced technical skills to be assembled. It can therefore be used by various groups, ranging undergraduate to graduate students using equipment typically available. Using this approach, students can acquire different skillsets including coding, testing, and advanced use of building materials based on their properties. Finally, the quality of the automatic extruder is verified.

physics.ed-ph↗

arXiv2024

Ion-Mediated Structural Discontinuities in Phospholipid Vesicles

Despite intense research, methods for controlling soft matter's spontaneous self-assembly in-to well-defined layers remain a significant challenge. We observed ion-induced structural disconti-nuities of phospholipid vesicles that can be exploited for controlled self-assembly of soft materials. We used dynamic light scattering, zeta-potential measurement, cryo-electron microscopy, small-angle X-ray, and small-angle neutron scattering. All the experimental observations indicate that de-clining solvent quality and increasing osmotic pressure direct lipids to expel preferentially to the inner compartment. Upon reaching a critical concentration, excess lipids can form a new bilayer. This spontaneous self-assembly process causes simultaneous shrinkage of the aqueous core and expansion of the vesicle. This approach opens an intriguing path for controlling the self-assembly of bioinspired colloids, which can also serve as a vehicle to control the polymerization of multilayer polymeric systems.

cond-mat.soft↗

arXiv2024

Dynamics of nano-scale assemblies of amphiphilic PEG-PDMS-PEG copolymers

Micelles and vesicles are promising candidates in targeted drug/gene delivery, bioreactors, and templates for nanoparticle synthesis. We investigated the morphology and dynamics of PEG-PDMS-PEG triblock copolymer nano-scale assemblies regarding the membrane dynamics because the molecular dynamics of the membrane govern mechanical properties like the stability of a membrane. We studied the structure by cryogenic transmission electron microscopy, small-angle neutron scattering, and the dynamics by dynamic light scattering and neutron spin echo spectroscopy. We changed the length of the hydrophilic block to obtain micellar and vesicular systems. The vesicle has a membrane rigidity, $κ_η= 16 \pm 2 k_B T$, the same order of magnitude as the corresponding liposome value but one order of magnitude higher than polymeric interfaces in microemulsions. Hence, the height-height fluctuations of polymers in a polymersome seem much less than those measured for surfactants at an oil-water interface. Therefore, the polymersome is substantially more stable. The value is very close to liposomes, indicating a similar stability.

cond-mat.soft↗

arXiv2022

A Design Study of a Compact Small-Angle Neutron Scattering Instrument

Nanoscale structure determination belongs to one of the crucial tasks in materials science. Small-angle neutron scattering (SANS) is a highly valuable tool to investigate nanostructures. Here, we explore the possibility of a compact SANS instrument to be installed at an individual accelerator based pulsed low-flux source, and discuss applications in structural characterization, education, and training. Monte Carlo simulations of a realistic setup demonstrate the feasibility of such an instrument, with an ideal measurement taking about 7 hours. The anticipated length-scale measurement range is 0.5 nm to 50 nm. The minimalistic design results in an easy to operate, low maintenance instrument, independent of the schedules of large-scale facilities. Size, cost, and maintenance are comparable to laboratory small-angle X-ray scattering (SAXS) instruments, which makes SANS affordable for individual research teams at universities and provides unique chances for education and training. The proposed setup creates the opportunity to measure ultraslow structural changes, at a fraction of the cost of existing SANS instruments, hence enables weekly or monthly repetition rates. The concept can be expanded to an entire suite of instruments, including wide-angle neutron scattering (WANS) and diffraction, neutron reflectometry (NR), neutron radiography, grating interferometry (GI), and prompt gamma activation analysis (PGAA).

physics.ins-det↗

arXiv2021

Acetaminophen Interactions with Phospholipid Vesicles Induced Changes in Morphology and Lipid Dynamics

Acetaminophen (APAP) or Paracetamol, despite its wide and common use for pain and fever symptoms, shows a variety of side effects, toxic effects, and overdose effects. The most common form of toxic effects of APAP is in the liver where phosphatidylcholine is the major component of the cell membrane with additional associated functionalities. Although this is the case, the effects of APAP on pure phospholipid membranes have been largely ignored. Here, we used DOPC, a commonly found phospholipid in mammalian cell membranes to synthesize large unilamellar vesicles to investigate how the incorporation of APAP changes pure lipid vesicle structure, morphology, and fluidity at different concentrations. We used a combination of dynamic light scattering (DLS), small-angle neutron and X-ray scattering (SANS, SAXS), cryo TEM for structural characterization, and neutron spin-echo (NSE) spectroscopy to investigate dynamics. We showed that the incorporation of Acetaminophen in the lipid bilayer significantly impacts the spherical phospholipid self-assembly in terms of its morphology as well as influences the lipid content in the bilayer, causing a decrease in bending rigidity. We discussed how the overall impact of APAP molecules on the pure lipid membrane may play a significant role in the drug's mechanisms of action. Our results showed the incorporation of APAP reduces membrane rigidity as well as changes the spherical unilamellar vesicles into much more irregularly shaped vesicles. Although bilayer structure did not show much change when observed by SAXS, NSE and cryo-TEM results showed the lipid dynamics change with the addition of APAP in the bilayer which causes the overall decreased membrane rigidity. A strong effect on the lipid tail motion was also observed. rigidity. A strong effect on the lipid tail motion was also observed.

cond-mat.soft↗

arXiv2021

On the Determination of the Transition to Pure Reptation by Dielectric Spectroscopy

Polymer melts show a characteristic molecular weight dependent relaxation time that can be related to the unentangled and entangled regime. At high molecular weights, influence of contour length fluctuations and con-straint release cease and pure reptation prevails. With the broad frequency range dielectric spectroscopy can fol-low polymer dynamics over a very broad temperature range, with the additional advantage of recording the spec-tral shape which contains information on reptation. Here we investigate the apparent discrepancy in the molecular weight for the onset of pure reptation from the molecular weight dependence and the spectral shape. We examined the popular derivative method and compared it with a version that includes higher order terms. Higher order terms lead to a more accurate peak shape and position than those determined with the simpler version. This becomes important if experimental spectra contain conductivity and polarization contributions. Higher order terms require the introduction of an interpolating function to analyze experimental spectra, which lets the Havriliak-Negami function appear to be a more robust, yet reliable tool to determine the peak shapes. We reach the conclusion that molecular weight dependence and spectral shape can be both strongly affected by conductivity and polarization contributions. While this leaves uncertainties on the accurate value of the transition molecular weight, the peak shape points to the existence of reptation and contour length fluctuations in polyisoprene with a molecular weight greater than 1000 kg/mol, which would imply a ten times greater threshold molecular weight than expected from previous estimates using the molecular weight dependence.

cond-mat.soft↗

arXiv2020

Structure and dynamics of DOPC vesicles: A transformation from unilamellar to multilamellar vesicles by n-alkyl-PEO polymer

We investigate the influence of a non-ionic surfactant like polymer on phospholipid vesicles. Our results from cryogenic transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), small angle neutron and X-ray scattering (SANS/SAXS), identifies the existence of multilayer vesicles and an increase in size of the vesicles in presence of the polymers. We present a generalized model to obtain the bending rigidity from neutron spin echo spectroscopy (NSE) data for multilayer vesicles. We demonstrated that polymers are trapped in the lipid bilayer, causing a partial disruption in the vesicle, which is attributed to the reduction in bending rigidity per unit bilayer. We also observed substantial dampening of the trapped lipid tail motion in presence of the polymer. Our results highlighted the possibilities of using specialized polymers that can disrupt membrane and control their dynamics with possible application in topical drug or nutraceutical formulations.

cond-mat.soft↗

arXiv2020

Impact of Local Stiffness on Entropy Driven Microscopic Dynamics of Polythiophene

We exploited the high temporal and spatial resolution of neutron spin echo spectroscopy to investigate the large-scale dynamics of semiflexible conjugated polymer chains in solutions. We obtained the first experimental demonstration of earlier predicted single chain glassy state. We used a generalized approach of the well-established Zimm model of flexible polymers to describe the relaxation mode spectra of locally stiff polythiophene chains. The Zimm mode analysis confirms the existence of beads with a finite length that corresponds to a reduced number of segmental modes in semiflexible chains. Irrespective of the temperature and the molecular weight of the conjugated polymer, we witness a universal behavior of the local chain stiffness and invariability of the beads length. Our experimental findings indicate possibly minor role of the change in π-electron conjugation length (and therefore conjugated backbone planar to non-planar conformational transition) in the observed thermochromic behavior of polythiophene but instead point on the major role of chain dynamics in this phenomenon.

cond-mat.soft↗

arXiv2020

Influence of salt on membrane rigidity of neu-tral DOPC vesicles

Salt is a very common molecule in aqueous environments but the question of whether the interactions of monovalent ions Na^+ and Cl^- ,with the neutral heads of phospholipids are impactful enough to change the membrane rigidity is still a mystery. To provide a resolution to this long simmering debate, we investigated the dynamics of DOPC vesicles in the fluid phase with increasing external salt concentration. At higher salt concentrations, we observe an increase in bending rigidity from neutron spin echo spectroscopy (NSE) and an increase in bilayer thickness from small-angle X-ray scattering (SAXS). We compared different models to distinguish membrane undulations, lipid tail motions and the translational diffusion of the vesicles. All the models indicate an increase in bending rigidity by a factor of 1.3 to 3.6. We demonstrate that even for t > 10 ns, and for Q > 0.07 1/Å the observed NSE relaxation spectra is clearly influenced by the translational diffusion of the vesicles. For t < 5 ns, the lipid tail motions dominate the intermediate dynamic structure factor. As the salt concentration increases this contribution diminishes. We introduced a new time-dependent analysis for the bending rigidity that highlights only a limited Zilman-Granek time window where the rigidity is physically meaningful.

cond-mat.soft↗

arXiv2020

Modeling of Transient Trapping of Fatty Acid Tails in Phospholipids

We present the derivation of a new model to describe neutron spin echo spectroscopy and quasi-elastic neutron scattering data on liposomes. We compare the new model with existing approaches and benchmark it with experimental data. The analysis indicates the importance of including all major contributions into modeling of the intermediate scattering function. Simultaneous analysis of the experimental data on lipids with full contrast and tail contrast matched samples, reveals highly confined lipid tail motion. A comparison of their dynamics demonstrates the statistical independ-ence of tail-motion and height-height correlation of the membrane. A more detailed analysis indi-cates that lipid tails are subject to relaxations in a potential with cylindrical symmetry, in addition to the undulation and diffusive motion of the liposome. Despite substantial differences in the chemis-try of the fatty acid tails, the observation indicates a universal behavior. The analysis of partially deuterated systems confirms the strong contribution of the lipid tail to the intermediate scattering function. Within the time range from 5 to 100 ns, the intermediate scattering function can be de-scribed by the height-height correlation function. The existence of the fast-localized tail motion and the contribution of slow translational diffusion of liposomes determines the intermediate scattering function for t < 5 ns and t > 100 ns, respectively. Taking into account the limited time window lowers the bending moduli by a factor of 1.3 (DOPC) to 2 (DMPC) compared to the full range.

cond-mat.soft↗

arXiv2018

A New Ultrasonic Transducer Sample Cell for In Situ Scattering Experiments

Ultrasound irradiation is a commonly used technique for non-destructive diagnostics or targeted destruction. We report on a new versatile sonication device that fits in a variety of standard sample environments for neutron and X-ray scattering instruments. A piezoelectric transducer permits measuring of the time-dependent response of the sample in situ during or after sonication. We use small-angle neutron scattering (SANS) to demonstrate the effect of a time-dependent perturbation on the structure factor of micelles formed from sodium dodecyl sulfate (SDS) surfactant molecules. We observe a significant change during and after sonication and a time-dependent relaxation to the equilibrium values of the unperturbed system. The strength of the perturbation of the structure factor depends systematically on the duration of sonication. The relaxation behavior can be well reproduced after multiple times of sonication. Accumulation of the recorded intensities of the different sonication cycles improves the signal-to-noise ratio and permits reaching very short relaxation times. Due to the flexibility of our new in situ sonication device, different experiments can be performed, e.g. to explore molecular potentials in more detail by introducing a systematic time-dependent perturbation.

cond-mat.soft↗

arXiv2012

SPHERES, Jülich's High-Flux Neutron Backscattering Spectrometer at FRM II

SPHERES (SPectrometer with High Energy RESolution) is a third-generation neutron backscattering spectrometer, located at the 20 MW German neutron source FRM II and operated by the Juelich Centre for Neutron Science. It offers an energy resolution (fwhm) better than 0.65 micro-eV, a dynamic range of +-31 micro-eV, and a signal-to-noise ratio of up to 1750:1.

physics.ins-det↗