Ice nucleation and growth is an important and widespread environmental process. Accordingly, nature has developed means to either promote or inhibit ice crystal formation, for example ice-nucleating ...proteins in bacteria or ice-binding antifreeze proteins in polar fish. Recently, it was found that birch pollen release ice-nucleating macromolecules when suspended in water. Here we show that birch pollen washing water exhibits also ice-binding properties such as ice shaping and ice recrystallization inhibition, similar to antifreeze proteins. We present spectroscopic evidence that both the ice-nucleating as well as the ice-binding molecules are polysaccharides bearing carboxylate groups. The spectra suggest that both polysaccharides consist of very similar chemical moieties, but centrifugal filtration indicates differences in molecular size: ice nucleation occurs only in the supernatant of a 100 kDa filter, while ice shaping is strongly enhanced in the filtrate. This finding may suggest that the larger ice-nucleating polysaccharides consist of clusters of the smaller ice-binding polysaccharides, or that the latter are fragments of the ice-nucleating polysaccharides. Finally, similar polysaccharides released from pine and alder pollen also display both ice-nucleating as well as ice-binding ability, suggesting a common mechanism of interaction with ice among several boreal pollen with implications for atmospheric processes and antifreeze protection.
The internal structure of nanometric microgels in water has been studied as a function of temperature, cross-linker content, and level of deuteration. Small-angle neutron scattering from ...poly(N-isopropylmethacrylamide) (volume phase transition ≈ 44 °C) microgel particles of radius well below 100 nm in D2O has been measured. The intensities have been analyzed with a combination of polymer chain scattering and form-free radial monomer volume fraction profiles defined over spherical shells, taking polydispersity in size of the particles determined by atomic force microscopy into account. A reverse Monte Carlo optimization using a limited number of parameters was developed to obtain smoothly decaying profiles in agreement with the experimentally scattered intensities. The results are compared to the swelling curve of microgel particles in the temperature range from 15 to 55 °C obtained from photon correlation spectroscopy (PCS). In addition to hydrodynamic radii measured by PCS, our analysis provides direct information about the internal water content and gradients, the strongly varying steepness of the density profile at the particle–water interface, the total spatial extension of the particles, and the visibility of chains. The model has also been applied to a variation of the cross-linker content, N,N′-methylenebisacrylamide, from 5 to 15 mol %, providing insight on the impact of chain architecture and cross-linking on water uptake and on the definition of the polymer–water interface. The model can easily be generalized to arbitrary monomer contents and types, in particular mixtures of hydrogenated and deuterated species, paving the way to detailed studies of monomer distributions inside more complex microgels, in particular core–shell particles.
In this work, we present a combination of a continuous flow reactor with in situ monitoring of the monomer conversion in a precipitation polymerization. The flow reactor is equipped with a preheating ...area for the synthesis of thermoresponsive microgels, based on
N
-isopropylacrylamide (NIPAM). The reaction progress is monitored with in situ FTIR spectroscopy. The monomer conversion at defined residence times is determined from absorbance spectra of the reaction solutions by linear combination with reference spectra of the stock solution and the purified microgel. The reconstruction of the spectra appears to be in good agreement with experimental data in the range of 1710 to 1530 cm
− 1
, in which prominent absorption bands are used as probes for the monomer and the polymer. With increasing residence time, we observed a decrease in intensity of the
ν
(C=C) vibration, originating from the monomer, while the
ν
(C=O) vibration is shifted to higher frequencies by polymerization. Differences between the determined
inline
conversion kinetics and
offline
growth kinetics, determined by photon correlation spectroscopy (PCS), are discussed in terms of diffusion and point to a crucial role of mixing in precipitation polymerizations.
Graphical Abstract
Continuous flow syntheses of acrylamide-based microgels in combination with in situ FTIR spectroscopy and offline particle characterization reveal information about the reaction progress.
The effect of deuteration on the volume phase transition (VPT) temperature of poly (
-isopropylmethacrylamide) (pNIPMAM) microgels in aqueous suspension is determined via IR spectroscopy and size ...measurements by photon correlation spectroscopy (PCS). We study the effect of a hydrogenated and a deuterated solvent (H₂O/D₂O), and of the hydrogenated and (partially) deuterated monomer. Deuteration of the monomer or copolymerization with deuterated monomers shifts the volume phase transition temperature (VPTT) by up to 8.4 K to higher temperatures, in good agreement with known results for pNIPAM microgels. Moreover, the shape of the swelling curve is found to depend on deuteration, with the highest deuteration leading to the sharpest VPT. Finally, the quantitative agreement between FTIR spectroscopy and PCS evidences the spatial homogeneity of the microgel particles. Our results are rationalized in terms of the effect of deuteration on hydrogen bonding. They shall be of primary importance for any experimental measurements close to the VPT involving isotopic substitution, and in particular contrast variation small angle neutron scattering.
The FlexiProb project is a joint effort of three soft matter groups at the Universities of Bielefeld, Darmstadt, and Munich with scientific support from the European Spallation Source (ESS), the ...small-K advanced diffractometer (SKADI) beamline development group of the Jülich Centre for Neutron Science (JCNS), and the Heinz Maier-Leibnitz Zentrum (MLZ). Within this framework, a flexible and quickly interchangeable sample carrier system for small-angle neutron scattering (SANS) at the ESS was developed. In the present contribution, the development of a sample environment for the investigation of soft matter thin films with grazing-incidence small-angle neutron scattering (GISANS) is introduced. Therefore, components were assembled on an optical breadboard for the measurement of thin film samples under controlled ambient conditions, with adjustable temperature and humidity, as well as the optional in situ recording of the film thickness via spectral reflectance. Samples were placed in a 3D-printed spherical humidity metal chamber, which enabled the accurate control of experimental conditions via water-heated channels within its walls. A separately heated gas flow stream supplied an adjustable flow of dry or saturated solvent vapor. First test experiments proved the concept of the setup and respective component functionality.
The European Spallation Source (ESS), which is under construction in Lund (Sweden), will be the leading and most brilliant neutron source and aims at starting user operation at the end of 2023. Among ...others, two small angle neutron scattering (SANS) machines will be operated. Due to the high brilliance of the source, it is important to minimize the downtime of the instruments. For this, a collaboration between three German universities and the ESS was initialized to develop and construct a unified sample environment (SE) system. The main focus was set on the use of a robust carrier system for the different SEs, which allows setting up experiments and first prealignment outside the SANS instruments. This article covers the development and construction of a SE for SANS experiments with foams, which allows measuring foams at different drainage states and the control of the rate of foam formation, temperature, and measurement position. The functionality under ESS conditions was tested and neutron test measurement were carried out.
As part of the development of the new European Spallation Source (ESS) in Lund (Sweden), which will provide the most brilliant neutron beams worldwide, it is necessary to provide different sample ...environments with which the potential of the new source can be exploited as soon as possible from the start of operation. The overarching goal of the project is to reduce the downtimes of the instruments related to changing the sample environment by developing plug and play sample environments for different soft matter samples using the same general carrier platform and also providing full software integration and control by just using unified connectors. In the present article, as a part of this endeavor, the sample environment for in situ SANS and dynamic light scattering measurements is introduced.
Smart Microgels from Unconventional Acrylamides Hannappel, Yvonne; Wiehemeier, Lars; Dirksen, Maxim ...
Macromolecular chemistry and physics,
July 2021, 2021-07-00, 20210701, Letnik:
222, Številka:
13
Journal Article
Recenzirano
Odprti dostop
In the present study, smart responsive microgels are synthesized from a series of alternative monomers, which are less common in micro‐ and nanogel research. Their swelling behavior is studied by ...means of photon correlation spectroscopy and Fourier transform infrared spectroscopy. In addition, these monomers are used to make copolymer microgels. In line with previous results for such copolymer particles the present work observes linear changes of the volume phase transition temperatures of the microgels as a function of the microgel composition. The presented systems allow to realize a broad range of transition temperatures, which is potentially interesting for applications in sensing, actuation, and drug delivery.
Homopolymer microgels based on unconventional acrylamides are synthesized and investigated with respect to their phase transition behavior, particle size, and shape by photon correlation spectroscopy, attenuated total reflection Fourier transform infrared spectroscopy, and atomic force microscopy. Mixtures of such alternative acrylamides yield copolymer microgels with, in most cases, a linear dependence of the volume phase transition temperature on the monomer composition.
In this study, we investigate the influence of the block copolymer architecture on the bending elasticity of polymer-rich lamellar phases. In detail, we study the polymer-rich system ...water/o-xylene/Pluronic triblock copolymer/C
TAB and change the polymer while keeping the mass ratios constant. We use neutron spin echo measurements (NSE) to determine κ. With the measurements we determine the relaxation rate
of the bilayer bending mode and subsequently calculate the bilayer bending modulus κ using the Zilman-Granek approach Zilman et al., Phys. Rev. Lett. 77, 4788-4791 (1996). Moreover, we have investigated the lamellar phases via small-angle X-ray scattering (SAXS) and have analysed the data with the modified Caillé theory to obtain the Caillé parameter η. Based on κ the bulk compression modulus
can be calculated. Increasing values of κ are found with increasing EO and PO block size in the range of 3.8 to 13.4
T. The computed values of
are in the range of 10
to 10
Pa.
The present study focuses on the swelling behavior of copolymer microgels of N-isopropylacrylamide (NIPAM) and acrylic acid (AAc) containing different concentrations of acrylic acid. The ...incorporation of the comonomer is investigated by Fourier transform infrared (FT-IR) spectroscopy and an incorporation threshold value for the comonomer is found, if the “classical” Pelton synthesis approach is used. The swelling of these microgels is analyzed by photon correlation spectroscopy (PCS) and fluorescence spectroscopy, using pyrene as a fluorescent probe. The deswelling of copolymer microgels with 10mol% and 15mol% nominal acrylic acid content can not be detected by PCS. However, in fluorescence measurements the PNIPAM phase transition is still observable. The reason for this difference is a non-uniform distribution of acrylic acid in the copolymer microgels, which makes them promising candidates for drug-delivery and -targeting applications.
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•Dynamic light scattering does not necessarily detect the collapse of a microgel if the collapse occurs on a local scale.•Fluorescence allows to access local changes inside the microgels.•FT-IR is a reliable method to determine the incorporation of a comonomer.
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