scholarly journals Reconfigurable structure and tunable transport in synchronized active spinner materials

2020 ◽  
Vol 6 (12) ◽  
pp. eaaz8535 ◽  
Author(s):  
Koohee Han ◽  
Gašper Kokot ◽  
Shibananda Das ◽  
Roland G. Winkler ◽  
Gerhard Gompper ◽  
...  
Keyword(s):  
Rotating Magnetic Field ◽  
Model Systems ◽  
Self Healing ◽  
External Excitation ◽  
Excitation Field ◽  
Air Water Interface ◽  
Equilibrium Structures ◽  
Collective Interactions ◽  
Reconfigurable Structure ◽  
Dynamic Ensembles

Ensembles of actuated colloids are excellent model systems to explore emergent out-of-equilibrium structures, complex collective dynamics, and design rules for the next generation materials. Here, we demonstrate that ferromagnetic microparticles suspended at an air-water interface and energized by an external rotating magnetic field spontaneously form dynamic ensembles of synchronized spinners in a certain range of the excitation field parameters. Each spinner generates strong hydrodynamic flows, and collective interactions of the multiple spinners promote a formation of dynamic lattices. On the basis of experiments and simulations, we reveal structural transitions from liquid to nearly crystalline states in this novel active spinner material and demonstrate that dynamic spinner lattices are reconfigurable, capable of self-healing behavior and that the transport of embedded inert cargo particles can be remotely tuned by the parameters of the external excitation field. Our findings provide insights into the behavior of active spinner materials with reconfigurable structural order and tunable functionalities.

scholarly journals Internal and external catalysis in boronic ester networks

2021 ◽  
Author(s):  
Boyeong Kang ◽  
Julia Kalow
Keyword(s):  
Mechanical Properties ◽  
Binding Affinity ◽  
Polymer Networks ◽  
Model Systems ◽  
Self Healing ◽  
Dynamic Materials ◽  
Boronic Ester ◽  
Rate Acceleration ◽  
Exchange Spectroscopy ◽  
Kinetics Of

In dynamic materials, the reversible condensation between boronic acids and diols provides adaptability, self-healing ability, and responsiveness to small molecules and pH. Recent work has shown that the thermodynamics and kinetics of bond exchange determine the mechanical properties of dynamic polymer networks. However, prior studies have focused on how structural and environmental factors influence boronic acid–diol binding affinity, and design rules for tuning the kinetics of this dynamic bond are lacking. In this work, we investigate the effects of diol (or polyol) structure and salt additives on the rate of bond exchange, binding affinity, and the mechanical properties of the corresponding polymer networks. To better mimic the environment of polymer networks in our small-molecule model systems, we incorporated proximal amide groups, which are used to conjugate diols to polymers, and included salts commonly found in buffers. Using one-dimensional selective exchange spectroscopy (1D EXSY), we find that both proximal amides and buffering anions induce significant rate acceleration consistent with internal and external catalysis, respectively. This rate acceleration is reflected in the stress relaxation of gels formed using PEG modified with different alcohols, and in the presence of salts containing acetate or phosphate. These findings contribute to the fundamental understanding of the boronic ester dynamic bond and offer new molecular strategies to tune the macromolecular properties of dynamic materials.

Biological Fluid Interfaces and Membranes

2015 ◽  
Author(s):  
Aidan T. Brown ◽  
Pietro Cicuta
Keyword(s):  
Current Knowledge ◽  
Biological Fluid ◽  
Biological Fluids ◽  
Model Systems ◽  
Surface Films ◽  
Fluid Interfaces ◽  
Self Healing ◽  
Vitro Model ◽  
Air Interfaces

This article examines the properties of biological fluid interfaces and membranes, with particular emphasis on monolayers and bilayers. There are several examples of interfaces between biological fluids; the most relevant to human physiology are probably the liquid/air interfaces in the lungs and on the surface of the eyes. Both of these feature films with remarkable properties of compressibility and self-healing. After providing an overview of the constituent molecules of biological interfaces, this article reviews the current knowledge on surface films and membranes, giving context for their role in biology, but paying special attention to the basic physical ideas that underpin fundamental studies of in-vitro model systems. It also considers isolated membranes, characterized by tension, elasticity and viscous damping, as well as closed vesicles and cells where the membrane separates the cytoskeleton from the extracellular matrix.

scholarly journals Structure of DPPC Monolayers at the Air/Buffer Interface: A Neutron Reflectometry and Ellipsometry Study

Coatings ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 507
Author(s):  
Javier Carrascosa-Tejedor ◽  
Andreas Santamaria ◽  
Daniel Pereira ◽  
Armando Maestro
Keyword(s):  
Structural Information ◽  
Langmuir Monolayers ◽  
Neutron Reflectometry ◽  
Model Systems ◽  
Angle Of Incidence ◽  
Water Interface ◽  
Brewster Angle Microscopy ◽  
Degree Of Hydration ◽  
Novel Approach ◽  
Air Water Interface

Langmuir monolayers of 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine, known as DPPC, at the air/water interface are extensively used as model systems of biomembranes and pulmonary surfactant. The properties of these monolayers have been mainly investigated by surface pressure–area isotherms coupled with different complementary techniques such as Brewster angle microscopy, for example. Several attempts using neutron reflectometry (NR) or ellipsometry have also appeared in the literature. Here, we report structural information obtained by using NR and ellipsometry on DPPC monolayers in the liquid condensed phase. On one side, NR can resolve the thickness of the aliphatic tails and the degree of hydration of the polar headgroups. On the other side, ellipsometry gives information on the refractive index and, therefore, on the physical state of the monolayer. The thickness and surface excess obtained by multiple-angle-of-incidence ellipsometry (MAIE) is compared with the results from NR measurements yielding a good agreement. Besides, a novel approach is reported to calculate the optical anisotropy of the DPPC monolayer that depends on the orientation of the aliphatic chains. The results from both NR and ellipsometry are also discussed in the context of the existing results for DPPC monolayers at the air/water interface. The differences observed are rationalized by the presence of buffer molecules interacting with phospholipids.

Self-healing dynamic bond-based rubbers: understanding the mechanisms in ionomeric elastomer model systems

2015 ◽  
Vol 17 (32) ◽  
pp. 21005-21017 ◽  
Author(s):  
N. Hohlbein ◽  
A. Shaaban ◽  
A. R. Bras ◽  
W. Pyckhout-Hintzen ◽  
A. M. Schmidt
Keyword(s):  
Mechanical Properties ◽  
Tensile Tests ◽  
Model System ◽  
Model Systems ◽  
Time Dependent ◽  
Self Healing ◽  
Structure Property ◽  
Healing Efficiency ◽  
Oscillatory Rheology ◽  
Systematic Structure

Systematic structure-property investigations on the time-dependent mechanical properties of an ionomer model system with variation of the ionic fraction and the counter ion as obtained from SAXS, dynamic oscillatory rheology and tensile tests, deliver the prerequisites and tools for property adjustment and optimization of their self-healing efficiency.

3-D optical transfer in excitation field synthesis microscopes

1995 ◽  
Vol 53 ◽  
pp. 64-65
Author(s):  
Vijay Krishnamurthi ◽  
Brent Bailey ◽  
Frederick Lanni
Keyword(s):  
Standing Wave ◽  
Spatial Information ◽  
3D Structure ◽  
Complete Recovery ◽  
Weighting Factor ◽  
Optical Transfer Function ◽  
Excitation Field ◽  
Optical Transfer ◽  
Set Up ◽  
Focus Plane

Excitation field synthesis (EFS) refers to the use of an interference optical system in a direct-imaging microscope to improve 3D resolution by axially-selective excitation of fluorescence within a specimen. The excitation field can be thought of as a weighting factor for the point-spread function (PSF) of the microscope, so that the optical transfer function (OTF) gets expanded by convolution with the Fourier transform of the field intensity. The simplest EFS system is the standing-wave fluorescence microscope, in which an axially-periodic excitation field is set up through the specimen by interference of a pair of collimated, coherent, s-polarized beams that enter the specimen from opposite sides at matching angles. In this case, spatial information about the object is recovered in the central OTF passband, plus two symmetric, axially-shifted sidebands. Gaps between these bands represent "lost" information about the 3D structure of the object. Because the sideband shift is equal to the spatial frequency of the standing-wave (SW) field, more complete recovery of information is possible by superposition of fields having different periods. When all of the fields have an antinode at a common plane (set to be coincident with the in-focus plane), the "synthesized" field is peaked in a narrow infocus zone.

Nuclear coiled bodies and the nucleolus

1994 ◽  
Vol 52 ◽  
pp. 20-21
Author(s):  
K. Brasch ◽  
J. Williams ◽  
D. Gallo ◽  
T. Lee ◽  
R. L. Ochs
Keyword(s):  
Mouse Liver ◽  
Nuclear Body ◽  
Nuclear Bodies ◽  
Model Systems ◽  
Coiled Body ◽  
Rrna Processing ◽  
Malignant Cells ◽  
Sm Proteins ◽  
Coiled Bodies ◽  
Unique Protein

Though first described in 1903 by Ramon-y-Cajal as silver-staining “accessory bodies” to nucleoli, nuclear bodies were subsequently rediscovered by electron microscopy about 30 years ago. Nuclear bodies are ubiquitous, but seem most abundant in hyperactive and malignant cells. The best studied type of nuclear body is the coiled body (CB), so termed due to characteristic morphology and content of a unique protein, p80-coilin (Fig.1). While no specific functions have as yet been assigned to CBs, they contain spliceosome snRNAs and proteins, and also the nucleolar protein fibrillarin. In addition, there is mounting evidence that CBs arise from or are generated near the nucleolus and then migrate into the nucleoplasm. This suggests that as yet undefined links may exist, between nucleolar pre-rRNA processing events and the spliceosome-associated Sm proteins in CBs.We are examining CB and nucleolar changes in three diverse model systems: (1) estrogen stimulated chick liver, (2) normal and neoplastic cells, and (3) polyploid mouse liver.

Microtubule Dynamics and Organelle Transport in Reticulomyxa

1990 ◽  
Vol 48 (3) ◽  
pp. 194-195
Author(s):  
Yih-Tai Chen ◽  
Ursula Euteneuer ◽  
Ken B. Johnson ◽  
Michael P. Koonce ◽  
Manfred Schliwa
Keyword(s):  
Plasma Membrane ◽  
Light Microscopy ◽  
Cytoplasmic Dynein ◽  
Living Cells ◽  
Microtubule Dynamics ◽  
Model Systems ◽  
Organelle Transport ◽  
Biochemical Characteristics ◽  
Dependent Transport

The application of video techniques to light microscopy and the development of motility assays in reactivated or reconstituted model systems rapidly advanced our understanding of the mechanism of organelle transport and microtubule dynamics in living cells. Two microtubule-based motors have been identified that are good candidates for motors that drive organelle transport: kinesin, a plus end-directed motor, and cytoplasmic dynein, which is minus end-directed. However, the evidence that they do in fact function as organelle motors is still indirect.We are studying microtubule-dependent transport and dynamics in the giant amoeba, Reticulomyxa. This cell extends filamentous strands backed by an extensive array of microtubules along which organelles move bidirectionally at up to 20 μm/sec (Fig. 1). Following removal of the plasma membrane with a mild detergent, organelle transport can be reactivated by the addition of ATP (1). The physiological, pharmacological and biochemical characteristics show the motor to be a cytoplasmic form of dynein (2).

Sampling and analysis of the air-water interface with SEM and EDS of microlayers

1989 ◽  
Vol 47 ◽  
pp. 1004-1005
Author(s):  
Randall W. Smith ◽  
John Dash
Keyword(s):  
Heavy Metals ◽  
Surface Microlayer ◽  
Surface Films ◽  
Water Interface ◽  
Physical Processes ◽  
Infrared Spectroscopic Analysis ◽  
Eds Analysis ◽  
Air Water Interface ◽  
Significant Area ◽  
Bulk Chemical

The structure of the air-water interface forms a boundary layer that involves biological ,chemical geological and physical processes in its formation. Freshwater and sea surface microlayers form at the air-water interface and include a diverse assemblage of organic matter, detritus, microorganisms, plankton and heavy metals. The sampling of microlayers and the examination of components is presently a significant area of study because of the input of anthropogenic materials and their accumulation at the air-water interface. The neustonic organisms present in this environment may be sensitive to the toxic components of these inputs. Hardy reports that over 20 different methods have been developed for sampling of microlayers, primarily for bulk chemical analysis. We report here the examination of microlayer films for the documentation of structure and composition.Baier and Gucinski reported the use of Langmuir-Blogett films obtained on germanium prisms for infrared spectroscopic analysis (IR-ATR) of components. The sampling of microlayers has been done by collecting fi1ms on glass plates and teflon drums, We found that microlayers could be collected on 11 mm glass cover slips by pulling a Langmuir-Blogett film from a surface microlayer. Comparative collections were made on methylcel1ulose filter pads. The films could be air-dried or preserved in Lugol's Iodine Several slicks or surface films were sampled in September, 1987 in Chesapeake Bay, Maryland and in August, 1988 in Sequim Bay, Washington, For glass coverslips the films were air-dried, mounted on SEM pegs, ringed with colloidal silver, and sputter coated with Au-Pd, The Langmuir-Blogett film technique maintained the structure of the microlayer intact for examination, SEM observation and EDS analysis were then used to determine organisms and relative concentrations of heavy metals, using a Link AN 10000 EDS system with an ISI SS40 SEM unit. Typical heavy microlayer films are shown in Figure 3.

Microstructural observations of the “Wustite-Spinel” coexistence following quenching of cation-excess spinels, Ni2(1+x)Ti1-xO4

1990 ◽  
Vol 48 (4) ◽  
pp. 1058-1059
Author(s):  
Ian M. Anderson ◽  
Arnulf Muan ◽  
C. Barry Carter
Keyword(s):  
Film Growth ◽  
Spinel Phase ◽  
Model Systems ◽  
Ion Milling ◽  
Coexistence Of Phases ◽  
Nonequilibrium Conditions ◽  
Diffraction Patterns ◽  
Spinel Structures ◽  
Highly Porous ◽  
Standard Techniques

Oxide mixtures which feature a coexistence of phases with the wüstite and spinel structures are considered model systems for the study of solid-state reaction kinetics, phase boundaries, and thin-film growth, and such systems are especially suited to TEM studies. (In this paper, the terms “wüstite” and “spinel” will refer to phases of those structure types.) The study of wüstite-spinel coexistence has been limited mostly to systems near their equilibrium condition, where the assumptions of local thermodynamic equilibrium are valid. The cation-excess spinels of the type Ni2(1+x)Ti1-xO4, which reportedly exist only above 1375°C4, provide an excellent system for the study of wüstite-spinel coexistence under highly nonequilibrium conditions. The nature of these compounds has been debated in the literature. X-ray and neutron powder diffraction patterns have been used to advocate the existence of a single-phase, non- stoichiometric spinel. TEM studies of the microstructure have been used to suggest equilibrium coexistence of a stoichiometric spinel, Ni2TiO4, and a wüstite phase; this latter study has shown a coexistence of wüstite and spinel phases in specimens thought to have been composed of a single, non- stoichiometric spinel phase. The microstructure and nature of this phase coexistence is the focus of this study. Specimens were prepared by ball-milling a mixture of NiO and TiO2 powders with 10 wt.% TiO2. The mixture was fired in air at 1483°C for 5 days, and then quenched to room temperature. The aggregate thus produced was highly porous, and needed to be infiltrated prior to TEM sample preparation, which was performed using the standard techniques of lapping, dimpling, and ion milling.

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