Upgrade of JCNS SANS instrument KWS-2 for improved performance and beam-time efficiency

KWS-2 is a classical small angle neutron diffractometer where, following recent upgrades, the pinhole mode with different neutron-wavelengths and detector distances can be combined with focusing mode with MgF2 lenses to reach a wide Q-range between 2x10−4 and 1.0 Å−1. Further upgrades of the detection system and sample positioning system are currently in progress. A wide-angle detection prototype is currently being tested and optimized aiming at measurement conditions over an extended Q-range up to 2.0 Å−1, which will be beneficial for semi-crystalline materials and small biological morphologies. The high neutron flux provided by the FRMII reactor and transported by the optimized neutron guidance system requires an adjustment of the measurement routine for a more rational use of the beam time. A new versatile in-beam sample positioning system, which includes a multi-position carousel with temperature control, robotic elements, and a storage pool for sample cuvettes, has just been installed at the instrument’s sample position. This allows the instrument to be continuously supplied with samples and provides the ability to combine experiments on similar samples or topics into a common long experimental session. Here we report in detail on the expanded Q-range option of the KWS-2 from the perspective of current performance and planned upgrades, as well as the new sample positioning system with robotic elements

A molecular brush with thermoresponsive poly(2-ethyl-2-oxazoline) side chains: a structural investigation

The thermoresponsive behavior of a poly(2-oxazoline)-based molecular brush is investigated in aqueous solution. The molecular brush under study, PiPOx100-g-PEtOx17, has a poly(2-isopropenyl-2-oxazoline) (PiPOx) backbone grafted with thermoresponsive poly(2-ethyl-2-oxazoline) (PEtOx) side chains. Since the backbone degree of polymerization is only a factor of ~ 6 higher than the ones of the side chains, it features an architecture between a star-like polymer and a comb-like polymer. Its aqueous solution exhibits lower critical solution temperature (LCST) behavior with a cloud point temperature Tcp = 40.5 °C at 30 g L−1. The temperature-dependent structural evolution is disclosed using dynamic light scattering (DLS) and small-angle neutron scattering (SANS). An increase of the molecular brush size is found upon heating from room temperature to Tcp, which is attributed to the extension of the backbone resulting from the dehydration and collapse of the side chains. Above Tcp, the size decreases again, which indicates the collapse of the whole molecular brush. Large aggregates are found to be present in the solution in the temperature range 25–50 °C. These become more compact, as the temperature is increased across Tcp

Structural Properties of Micelles Formed by Telechelic Pentablock Quaterpolymers with pH-Responsive Midblocks and Thermoresponsive End Blocks in Aqueous Solution

We investigated the structural properties of dynamic micelles arising from the self-assembly of the multiresponsive pentablock quaterpolymer P(nBuMA8-co-TEGMA8)-b-PDMAEMA50-b-PEG46-b-PDMAEMA50-b-P(nBuMA8-co-TEGMA8) (nBuMA, TEGMA, DMAEMA, and EG are n-butyl methacrylate, tri(ethylene glycol) methyl ether methacrylate, 2-(dimethylamino)ethyl methacrylate, and ethylene glycol, respectively) in aqueous solution using a combination of scattering methods. In this multisegmented polymer, a pH-responsive BAB triblock copolymer from the weak cationic polyelectrolyte PDMAEMA and the hydrophilic PEG is end-capped by two blocks comprising random sequences of thermoresponsive TEGMA units and hydrophobic nBuMA units. Dynamic light scattering revealed the existence of single micelles and small clusters in dilute aqueous solution. The hydrodynamic radius of the micelles depends strongly on pH and temperature. The inner structure of the micelles was investigated by small-angle X-ray scattering, small-angle neutron scattering, and static light scattering, and micelles with a hydrophobic core containing a rather high fraction of water and a strongly swollen corona were found. The ratio of loops and dangling ends depends on temperature and pH

Thermoresponsive Molecular Brushes with Propylene Oxide/Ethylene Oxide Copolymer Side Chains in Aqueous Solution

The thermoresponsive behavior of two molecular brushes having poly(propylene oxide)–poly(ethylene oxide) copolymer side chains is investigated in aqueous solution, where the side chains have longer contour lengths than the backbone. The brushes differ in the side-chain architecture; they are either a diblock (PbE) or a random copolymer (PrE). For both types of brushes, an overall rodlike shape at room temperature is revealed by cryo-electron microscopy. A polymer-rich central part and a water-rich outer part are identified by small-angle neutron scattering (SANS). Upon heating up to the cloud point, the shell of PbE weakly dehydrates, while the one of PrE severely dehydrates along with a cylinder-to-disk transformation. Moreover, the aggregates formed above the cloud points feature significantly different inner structures: PbE aggregates are composed of strongly interpenetrating brushes, while PrE aggregates consist of loosely packed brushes. These differences indicate the important role of the side-chain architecture in the thermal dehydration behavior and the associated structural changes

Rigid-to-Flexible Transition in a Molecular Brush in a Good Solvent at a Semidilute Concentration

The structures of a molecular brush in a good solvent are investigated using synchrotron small-angle X-ray scattering in a wide range of concentrations. The brush under study, PiPOx$_{239}$-g-PnPrOx$_{14}$, features a relatively long poly(2-isopropenyl-2-oxazoline) (PiPOx) backbone and short poly(2-n-propyl-2-oxazoline) (PnPrOx) side chains. As a solvent, ethanol is used. By model fitting, the overall size and the persistence length as well as the interaction length and interaction strength are determined. At this, the interplay between form and structure factor is taken into account. The conformation of the molecular brush is traced upon increasing the solution concentration, and a rigid-to-flexible transition is found near the overlap concentration. Finally, the results of computer simulations of the molecular brush solutions confirm the experimental results

Temperature-Dependent Phase Behavior of the Thermoresponsive Polymer Poly( N -isopropylmethacrylamide) in an Aqueous Solution

Poly(N-isopropylmethacrylamide) (PNIPMAM) is a thermoresponsive polymer, exhibiting lower critical solution temperature (LCST) behavior in aqueous solution. We investigate the temperature-dependent phase behavior of PNIPMAM solutions in D2O using turbidimetry, differential scanning calorimetry (DSC), small-angle and very small-angle neutron scattering (SANS and VSANS), and Raman spectroscopy, covering a large concentration range and compare the results from PNIPMAM with the findings from its analogue poly(N-isopropylacrylamide) (PNIPAM). We find that the PNIPMAM chains only dehydrate 2-3 °C above the macroscopic cloud point temperature, TCP. Even in the one-phase state, loosely packed, large-scale inhomogeneities and physical crosslinks are observed, and the chain conformation of PNIPMAM is more compact than the one of PNIPAM. This is attributed to the attractive intermolecular interactions between the hydrophobic moieties. The phase transition of PNIPMAM is broader than the one of PNIPAM. Upon heating to the two-phase state, the PNIPMAM chains collapse and form mesoglobules. These are larger and more hydrated than for PNIPAM. This is attributed to the steric hindrance caused by the additional methyl groups, which weaken the intrapolymer interactions in the two-phase state. Thus, the methyl groups in the backbone of the PNIPMAM chains have a significant impact on the hydration and the structural behavior around the phase transition