Tapestry of non-equilibrium phenomenon in colloidal domain: From directed assembly to emergent behavior

The multiscale self-assembly of atoms, molecules, and particles is the origin of all physical mesoscopic matter. The spatial organization, symmetry, and physical properties of the assembled structures are determined by thermodynamic characteristics of their building blocks. Colloidal particles are emerging as models for understanding governing principles of directed-assembly and non-equilibrium response of advanced materials. Here, I will present the concept of using internal and external field driven interactions to direct the assembly and spatial migration of colloids. First, I will present the principle of using magnetostatic interactions to direct surface patterning using sessile drop drying. In droplets of magnetite nanoparticles, magnetic establish a microconvection from droplet edge to center. This magnetostatic convection is used to assemble secondary nonmagnetic particles in droplets, allowing for the assembly of four distinct kinetically stable states, and enabling a new route for surface patterning. Second, I will introduce the concept of directing spatial motion and non-equilibrium behavior of metal-dielectric patchy colloids using external electric field. The electric field drives a local force imbalance around the particle, resulting into its direction motion. I will demonstrate that the particle’s velocity, chirality, and its 3D trajectory can be programed by engineering the patchy particle/cluster size and shape. I will show that the coupling of translation and rotational component of the energy enables programming helical motion in spherical colloids, and provides an alternative mode of navigating through complex cross-linked matrices. This approach introduces a new method of engineering the assembly and self-propulsion of microparticles, which could lead to the development of advanced micro-motors and miniature robots capable of navigating through complex biological environments

Surfactant adsorption and aggregate structure at silica nanoparticles: Effects of particle size and surface modification

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.The influence of particle size and a surface modifier on the self-assembly of the nonionic surfactant C12E5 at silica nanoparticles was studied by adsorption measurements and small-angle neutron scattering (SANS). Silica nanoparticles of diameter 13 to 43 nm were synthesized involving the basic amino acid lysine. A strong decrease of the limiting adsorption of C12E5 with decreasing particle diameter was found. To unveil the role of lysine as a surface modifier for the observed size dependence of surfactant adsorption, the morphology of the surfactant aggregates assembled on pure siliceous nanoparticles (Ludox-TMA, 27 nm) and their evolution with increasing lysine concentration at a fixed surfactant-to-silica ratio was studied by SANS. In the absence of lysine, the surfactant forms surface micelles at silica particles. As the concentration of lysine is increased, a gradual transition from the surface micelles to detached wormlike micelles in the bulk solution is observed. The changes in surfactant aggregate morphology cause pronounced changes of the system properties, as is demonstrated by turbidity measurements as a function of temperature. These findings are discussed in terms of particle surface curvature and surfactant binding strength, which present new insight into the delicate balance between the two properties.EC/FP7/226507/EU/Integrated Infrastructure Initiative for Neutron Scattering and Muon Spectroscopy/NMI3DFG, GRK 1524, Self-Assembled Soft-Matter Nanostructures at Interface

Bridging interactions of proteins with silica nanoparticles: The influence of pH, ionic strength and protein concentration

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Charge-driven bridging of nanoparticles by macromolecules represents a promising route for engineering functional structures, but the strong electrostatic interactions involved when using conventional polyelectrolytes impart irreversible complexation and ill-defined structures. Recently it was found that the electrostatic interaction of silica nanoparticles with small globular proteins leads to aggregate structures that can be controlled by pH. Here we study the combined influence of pH and electrolyte concentration on the bridging aggregation of silica nanoparticles with lysozyme in dilute aqueous dispersions. We find that protein binding to the silica particles is determined by pH irrespective of the ionic strength. The hetero-aggregate structures formed by the silica particles with the protein were studied by small-angle X-ray scattering (SAXS) and the structure factor data were analyzed on the basis of a short-range square-well attractive pair potential (close to the sticky-hard-sphere limit). It is found that the electrolyte concentration has a strong influence on the stickiness near pH 5, where the weakly charged silica particles are bridged by the strongly charged protein. An even stronger influence of the electrolyte is found in the vicinity of the isoelectric point of the protein (pI = 10.7) and is attributed to shielding of the repulsion between the highly charged silica particles and hydrophobic interactions between the bridging protein molecules.DFG, GRK 1524, Self-Assembled Soft-Matter Nanostructures at Interface

Synthesis and characterization of biodegradable lignin nanoparticles with tunable surface properties

Lignin nanoparticles can serve as biodegradable carriers of biocidal actives with minimal environmental footprint. Here we describe the colloidal synthesis and interfacial design of nanoparticles with tunable surface properties using two different lignin precursors, Kraft (Indulin AT) lignin and Organosolv (high-purity lignin). The green synthesis process is based on flash precipitation of dissolved lignin polymer, which enabled the formation of nanoparticles in the size range of 45–250 nm. The size evolution of the two types of lignin particles is fitted on the basis of modified diffusive growth kinetics and mass balance dependencies. The surface properties of the nanoparticles are fine-tuned by coating them with a cationic polyelectrolyte, poly(diallyldimethylammonium chloride). We analyze how the colloidal stability and dispersion properties of these two types of nanoparticles vary as a function of pH and salinities. The data show that the properties of the nanoparticles are governed by the type of lignin used and the presence of polyelectrolyte surface coating. The coating allows the control of the nanoparticles’ surface charge and the extension of their stability into strongly basic regimes, facilitating their potential application at extreme pH conditions

Multidirectional colloidal assembly in concurrent electric and magnetic fields

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Dipolar interactions between nano- and micron sized colloids lead to their assembly into domains with well-defined local order. The particles with a single dipole induced by an external field assemble into linear chains and clusters. However, to achieve the formation of multidirectionally organized nano-or microassemblies with tunable physical characteristics, more sophisticated interaction tools are needed. Here we demonstrate that such complex interactions can be introduced in the form of two independent, non-interacting dipoles (double-dipoles) within a microparticle. We show how this can be achieved by the simultaneous application of alternating current (AC)-electric field and uniform magnetic field to dispersions of superparamagnetic microspheres. Depending on their timing and intensity, concurrent electric and magnetic fields lead to the formation of bidirectional particle chains, colloidal networks, and discrete crystals. We investigate the mechanistic details of the assembly process, and identify and classify the non-equilibrium states formed. The morphologies of different experimental states are in excellent correlation with our theoretical predictions based on Brownian dynamics simulations combined with a structural analysis based on local energy parameters. This novel methodology of introducing and interpreting double-dipolar particle interactions may assist in the assembly of colloidal coatings, dynamically reconfigurable particle networks, and bidirectional active structures.DFG, GRK 1524, Self-Assembled Soft-Matter Nanostructures at Interface

Nanocapillarity-mediated magnetic assembly of nanoparticles into ultraflexible filaments and reconfigurable networks

The fabrication of multifunctional materials with tunable structure and properties requires programmed binding of their building blocks1,2. For example, particles organized in long-ranged structures by external fields3,4 can be bound permanently into stiff chains through electrostatic or van der Waals attraction4,5, or into flexible chains through soft molecular linkers such as surface-grafted DNA or polymers6–11. Here, we show that capillarity-mediated binding between magnetic nanoparticles coated with a liquid lipid shell can be used for the assembly of ultraflexible microfilaments and network structures. These filaments can be magnetically regenerated on mechanical damage, owing to the fluidity of the capillary bridges between nanoparticles and their reversible binding on contact. Nanocapillary forces offer opportunities for assembling dynamically reconfigurable multifunctional materials that could find applications as micromanipulators, microbots with ultrasoft joints, or magnetically self-repairing gels

Sol-gel chemistry mediated Zn/Al-based complex dispersant for SWCNT in water without foam formation

We report a bimetallic Zn/Al complex as an efficient inorganic dispersant for SWCNT, synthesized from Zn(CH3COO)(2) and Al(NO3)(3). The Zn/Al complex shows more than four times greater efficiency at dispersing SWCNT than widely used surfactants (CTAB and SDS). Besides remarkable dispersibility, the Zn/Al complex does not foam upon any shaking treatment and it can be used just after quick dissolution of the powdered form, which is a marked advantage over surfactants. The Zn/Al complex, containing amorphous Al(CH3COO)(3) and a complex of Zn2+ and NO3- ions, should have a unique dispersion mechanism, differing from the surfactants. Al(CH3COO)(3) has higher affinity for SWCNT than ions, adsorbing onto its surface in the first layer and attracting Zn2+ and NO3- ions. Charge transfer interactions between the Zn/Al complex and SWCNT, as evidenced by optical absorption spectroscopy, should induce a charge on SWCNT; the zeta potential of such coated SWCNT was +55 mV, indicating a high dispersion stability in aqueous media. Hence, the Zn/Al complex can widen the applications of SWCNT to various technologies such as the transparent and conductive films, as well as high performance composite polymers. (C) 2015 Elsevier Ltd. All rights reserved.ArticleCARBON. 94:518-523 (2015)journal articl

Development of Region Specific Hybrid Goat and their Performance Evaluation under High Altitude Condition

Goat meat (chevon) comprises an important source of protein to provide essential amino acids in addition to other meat and plant sources of proteins. Therefore, demands for chevon are huge from civil and defence sector in this region. However, there is limited availability of fresh tender chevon in Ladakh region round the year. Hence, there was a need of augmenting local availability of fresh goat meat by developing animal technology for fast growing region-specific crossbred goat for meat purpose that can efficiently perform under adverse climatic conditions prevailing in this region. The present crossbred goat was developed by using mixing genes of adaptive and meat traits through cross breeding between local goats (Changthangi and Gaddi breeds of goats) and Sirohi/Black Bengal goats. To develop this technology, we introduced Black Bengal and Sirohi from plain areas and native breed of goats viz. Gaddi and Changthangi goats for further adaptation and growth performance studies at Leh-Ladakh. After initial studies goats were divided into high altitude resistant/adapted and susceptible groups. High altitude resistant/adapted goats were taken for further cross breeding and pure breeding. All the kids produced out of this breeding were studied for physiological responses, growth performance, and blood biochemical parameters to know their adaptive and growth performance at high altitude. Crossbred kids of Sirohi ♂/Black Bengal ♂ X Changthangi ♀ had significantly (P<0.05) higher weight gain, adaptive physiological responses and blood biochemicals level as compared to exotic pure bred and other cross bred kids. These crossbred kids attained market weight faster than local as well as breeds from plain areas (Sirohi and Black Bengal goats). Average meat yield is 7-10 kg per adult crossbred goat if slaughtered at 9-12 month age. These cross bred (broiler goat) may be reared at Leh-Ladakh for meat purpose. Hence, this animal technology may help in increasing of fresh goat meat (chevon) supply to meet army’s and civil requirements in Leh-Ladakh

Evaluation of Physiological Parameters in Response to Endurance Exercise of Zanskar Ponies Adapted to High Altitude of Ladakh Region

Zanskar pony, a native horse breed of Ladakh mainly used for transportation in Trans-Himalayan region of India, is well adapted to high altitude hypobaric hypoxia environment. Due to extreme conditions of the Ladakh region, better endurance of these ponies under hypoxic and extreme cold conditions is of utmost concern for their recruitment in Indian Army. In the present study, 12 young trained Zanskar ponies were evaluated during endurance exercise at an altitude of 3292 meter above mean sea level. The animals were subjected to carriage transport with 65-70Kg load or riding on a track of 5-6 Km. Physiological parameters viz., pulse rate (PR), heart rate (HR), rectal temperature (RT), respiratory rate (RR) and oxygen saturation (SaO2) were recorded in Zanskar ponies during pre-exercise (T0), post- exercise (T1) and post recovery (T2, 2 hours post resting) stages. Results showed marked increase in PR, HR, RR and RT post exercise time points. The mean values of PR increased from 49.83±4.62 to 73.67±21.54 per minute, HR from 48±13.60 to 75±15.82 beats/min, RR from 37.83±9.70 to 57.67±13.48 per min and RT from 99.62±0.34 101.04±0.53 °F from pre stress to post endurance stress. The mean SaO2 level reduced significantly (88.58±6.75 at T0 versus 64.00±18.70 at T1 and 54.42±14.79 at T2) post exercise. This indicated limited availability of arterial oxygen for tissues which could be vital factor for adverse change in some of physio-biochemical parameters. Though the trend of physiological response was similar for all the 12 animals, still variation at individual animal level was observed during endurance stress. In future, some of these physiological parameters along with biochemical and molecular parameters could be evaluated as potential biomarkers in selecting ponies with superior endurance trait specifically under hypoxic conditions