Brownian motion studies of viscoelastic colloidal gels by rotational single particle tracking

Thermal and Modern, Non-Thermal Method Induction as a Factor of Modification of Inulin Hydrogel Properties

The aim of the study was to compare the properties of inulin hydrogels obtained with different methods, e.g., the traditional-thermal method and new, non-thermal methods, used in food production, like ultrasonic, high-pressure homogenization (HPH), and high hydrostatic pressures (HHPs). It was found that each of the compared induction methods allowed for obtaining inulin hydrogels. However, the use of non-thermal induction methods allows for obtaining a gel structure faster than in the case of thermal induction. In addition, hydrogels obtained with new, non-thermal methods differ from gels obtained with thermal treatment. They were characterized by higher stability (from 1.7 percent point-of-stability parameters for HHP 150 MPa to 18.8 for HPH II cycles) and in most cases, by improved microrheological properties-lower solid-liquid balance toward the solid phase, increased elasticity and viscosity indexes, and lowering the flow index. The gels obtained with the new, non-thermal method were also characterized by a more delicate structure, including lower firmness (the differences between thermal and non-thermal inductions were from 0.73 N for HHP at 500 MPa to 2.39 N for HHP at 150 MPa) and spreadability (the differences between thermal and non-thermal inductions were from 7.60 Ns for HHP at 500 MPa to 15.08 Ns for HHP at 150 MPa). The color of ultrasound-induced inulin gels, regarding the HPH and HHP technique, was darker (the differences in the L* parameter between thermal and non-thermal inductions were from 1.92 for HHP at 500 MPa to 4.37 for 10 min ultrasounds) and with a lower a* color parameter (the differences in the a* parameter between thermal and non-thermal inductions were from 0.16 for HHP at 500 MPa to 0.39 for HPH II cycles) and b* color parameter (the differences in the b* parameter between thermal and non-thermal inductions were from 1.69 for 5 min ultrasounds to 2.68 for HPH II cycles). It was also found that among the compared induction methods, the high-pressure technique has the greatest potential for modifying the properties of the created inulin hydrogels. Thanks to its application, depending on the amount of applied pressure, it was possible to obtain gels with very different characteristics, both delicate (i.e., soft and spreadable), using HHP at 150 MPa, and hard, using HHP at 500 MPa, the closest in characteristics to gels induced with the thermal method. This may allow the properties of hydrogels to be matched to the characteristics of the food matrix being created.

Diffracted X-ray Tracking for Observing the Internal Motions of Individual Protein Molecules and Its Extended Methodologies

In 1998, the diffracted X-ray tracking (DXT) method pioneered the attainment of molecular dynamics measurements within individual molecules. This breakthrough revolutionized the field by enabling unprecedented insights into the complex workings of molecular systems. Similar to the single-molecule fluorescence labeling technique used in the visible range, DXT uses a labeling method and a pink beam to closely track the diffraction pattern emitted from the labeled gold nanocrystals. Moreover, by utilizing X-rays with extremely short wavelengths, DXT has achieved unparalleled accuracy and sensitivity, exceeding initial expectations. As a result, this remarkable advance has facilitated the search for internal dynamics within many protein molecules. DXT has recently achieved remarkable success in elucidating the internal dynamics of membrane proteins in living cell membranes. This breakthrough has not only expanded our knowledge of these important biomolecules but also has immense potential to advance our understanding of cellular processes in their native environment.

Effects of varying casein and pectin concentrations on the rheology of high-protein cultured milk beverages stored at ambient temperature

Shelf-stable cultured milk beverages that have high protein levels can be difficult to successfully manufacture. With increasing protein level, rapid phase separation and gel formation occur in cultured beverages, which may not be prevented even with the inclusion of stabilizers such as high methoxy (HM) pectin. To limit protein aggregation in cultured milk beverages we investigated micellar casein as an interesting alternative to milk, due to the absence of whey proteins, which can contribute to increased gel strength in cultured products. In this study, micellar casein dispersed in ultrafiltered milk permeate was fermented to pH 4.1, blended with HM pectin, homogenized, thermally processed, and bottled for storage at ambient temperature for 6 mo. Utilizing response surface methodology with a central composite rotatable design, the protein and pectin contents were varied between 5 and 9% and 0.0 and 1.0%, respectively. The elastic modulus, loss tangent, and yield stress of these beverages were measured during storage to observe the extent of bond restructuring, whereas particle size and visual phase separation were measured to determine stability. Response variables were measured initially after thermally processing the beverages, and after 1 and 6 mo of storage at ambient temperature. All samples quickly formed gels after homogenizing, regardless of the pectin level. The stiffness (elastic modulus) of all samples increased throughout storage and was determined mainly by the protein content; however, the growth of elastic bonds over time was slowed with high levels of pectin. At 6 mo of storage, yield stress values were significantly lower for beverages with <7.5% protein when they were stabilized with ≥0.85% pectin. Prediction models for visual phase separation in beverages stored for 6 mo were significantly affected by the protein content, with increasing instability at lower protein levels. Models were used to identify optimal protein (<7.5%) and pectin (≥0.85%) concentrations to minimize the stiffness of gels during ambient storage. Samples in this optimized region were predicted to have low yield stress values and were easily fluidized by gentle shaking of the bottle at 6 mo.

Investigation of Micro-volume Viscosity with Janus Microbeads Based on Rotational Brownian Motion

Viscosity is an important property of liquids. A viscosity change of aqueous substances that deviates from their normal levels usually implies a compromise in quality due to degradation or microorganism proliferation. Monitoring of macro-scale viscosity can be simply realized by various conventional tools, such as rotational viscometers, capillary tubes, falling bodies, and so forth. Nevertheless, today, micro-volume viscosity measurement remains a challenging endeavor, resulting in rare, expensive, or difficult-to-obtain samples not very well studied. For this reason, a novel technique for micro-viscosity based on rotational Brownian motion is presented in this paper. Janus microbeads were made by coating fluorescent polystyrene beads with gold film. Taking advantage of the bead configuration of half gold/half fluorescence, the rotational Brownian signal was expressed in terms of blinking fluorescent intensity. The characteristic correlation time was derived from the blinking intensity of trace amounts of a selected medium over a certain time period, and results were correlated with viscosity. Given a volume of only 2 μL for each measurement, calibration of a series of glycerol–water mixtures (100%–1% (v/v) water content) yielded good agreement with the expected viscosity predictions over the range of 0.8–574.8 cP. Five common oil products, including lubricant oil, baby oil, food oil, olive oil, and motor oil, were further investigated to demonstrate the feasibility and practicability of the proposed technique. Data measured by the rotational Brownian motion-based diffusometer were comparable with those measured by a commercial rotational viscometer. The method also explicitly showed viscosity degradation after the oils were heated at a high temperature of over 100 °C for 10 min. Evaluation proved the proposed Janus microbead-enabled rotational diffusometric technique to be a promising approach for rapid and micro-scale viscosity measurement.

Investigation of Three-Dimensional Structure and Pigment Surrounding Environment of a TiO₂ Containing Waterborne Paint

Serial block-face scanning electron microscopy (SBFSEM) has been used to investigate the three-dimensional (3D) structure of a cured waterborne paint containing TiO₂ pigment particles, and the surrounding environment of the TiO₂ pigment particles in the cured paint film was also discussed. The 3D spatial distribution of the particles in the paint film and their degree of dispersion were clearly revealed. More than 55% of the measured TiO₂ particles have volumes between 1.0 × 10⁶ nm³ and 1.0 × 10⁷ nm³. From the obtained 3D images, we proposed that there are three different types of voids in the measured cured waterborne paint film: voids that exist in the cured paint themselves, voids produced by particle shedding, and voids produced by quasi-liquid phase evaporation during measurement. Among these, the latter two types of voids are artefacts caused during SBFSEM measurement which provide evidence to support that the pigment particles in the cured paint/coating films are surrounding by quasi-liquid environment rather than dry solid environment. The error caused by particle shedding to the statistical calculation of the TiO₂ particles was corrected in our analysis. The resulting 3D structure of the paint, especially the different voids are important for further systematic research, and are critical for understanding the real environment of the pigment particles in the cured paint films.

Radiation-driven rotational motion of nanoparticles

Focused synchrotron beams can influence a studied sample via heating, or radiation pressure effects due to intensity gradients. The high angular sensitivity of rotational X-ray tracking of crystalline particles via their Bragg reflections can detect extremely small forces such as those caused by field gradients. By tracking the rotational motion of single-crystal nanoparticles embedded in a viscous or viscoelastic medium, the effects of heating in a uniform gradient beam and radiation pressure in a Gaussian profile beam were observed. Changes in viscosity due to X-ray heating were measured for 42 µm crystals in glycerol, and angular velocities of 10-6 rad s-1 due to torques of 10-24 N m were measured for 340 nm crystals in a colloidal gel matrix. These results show the ability to quantify small forces using rotation motion of tracer particles.

Folding sticky elastica: dynamics and reversibility of folds in Langmuir monolayers

Lipid monolayers at the air/water interface are often subject to large mechanical stresses when compressed laterally. For large enough compression they fold in the out-of-plane direction to relax stress. The repetitive folding and unfolding of lung surfactant monolayers during breathing plays a critical role in conserving monolayer material at the air/water interface lining the lung. Although the mechanisms behind the folding have been explored recently, relatively little information exists regarding the implications of folding dynamics on the long-term stability of the monolayer. We address this question by investigating the dynamical effect of folding rate in a lipid monolayer containing nano-particles, using a combination of analytic theory, simulation and experiment. We find that the presence of adsorbed particles are essential for monolayer rupture during unfolding. These particles act as linkers pinning the folds shut. The rate of folding affects reversibility as well. We construct a reversibility phase diagram spanned by the compression period and the size of the adsorbed particles showing the complex interaction of fold morphology, particle diffusion, and linker unbinding that results in reversible or irreversible folding.

Novel silica stabilization method for the analysis of fine nanocrystals using coherent X-ray diffraction imaging

High-energy X-ray Bragg coherent diffraction imaging (BCDI) is a well established synchrotron-based technique used to quantitatively reconstruct the three-dimensional morphology and strain distribution in nanocrystals. The BCDI technique has become a powerful analytical tool for quantitative investigations of nanocrystals, nanotubes, nanorods and more recently biological systems. BCDI has however typically failed for fine nanocrystals in sub-100 nm size regimes - a size routinely achievable by chemical synthesis - despite the spatial resolution of the BCDI technique being 20-30 nm. The limitations of this technique arise from the movement of nanocrystals under illumination by the highly coherent beam, which prevents full diffraction data sets from being acquired. A solution is provided here to overcome this problem and extend the size limit of the BCDI technique, through the design of a novel stabilization method by embedding the fine nanocrystals into a silica matrix. Chemically synthesized FePt nanocrystals of maximum dimension 20 nm and AuPd nanocrystals in the size range 60-65 nm were investigated with BCDI measurement at beamline 34-ID-C of the APS, Argonne National Laboratory. Novel experimental methodologies to elucidate the presence of strain in fine nanocrystals are a necessary pre-requisite in order to better understand strain profiles in engineered nanocrystals for novel device development.

Deformation Twinning of a Silver Nanocrystal under High Pressure

Within a high-pressure environment, crystal deformation is controlled by complex processes such as dislocation motion, twinning, and phase transitions, which change materials' microscopic morphology and alter their properties. Understanding a crystal's response to external stress provides a unique opportunity for rational tailoring of its functionalities. It is very challenging to track the strain evolution and physical deformation from a single nanoscale crystal under high-pressure stress. Here, we report an in situ three-dimensional mapping of morphology and strain evolutions in a single-crystal silver nanocube within a high-pressure environment using the Bragg Coherent Diffractive Imaging (CDI) method. We observed a continuous lattice distortion, followed by a deformation twining process at a constant pressure. The ability to visualize stress-introduced deformation of nanocrystals with high spatial resolution and prominent strain sensitivity provides an important route for interpreting and engineering novel properties of nanomaterials.

Crystallography is more than crystal structures

New developments in neutron and synchrotron science and technology are discussed.

Hidden motion made known - rotational X-ray tracking reveals spinning colloids

Rotational x-ray tracking (RXT) is demonstrated as a promising new tool for investigating previously unobservable motion in crystalline nanoscale colloids. Its potential utility is demonstrated by applying it to measurements of the local viscoelastic properties of a gel-colloid nanocomposite.