01953nas a2200181 4500008004100000022001400041245008300055210006900138260007100207300001400278490000800292520126200300100002501562700002701587700001701614700002801631856011201659 2009 eng d a1520-610600aSelf-assembly of silica particles in a nonionic surfactant hexagonal mesophase0 aSelfassembly of silica particles in a nonionic surfactant hexago a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcMAR a3423-34300 v1133 a

We investigate the process of self-assembly, and the resultant structures in composites of silica particles with a hexagonal mesophase of a nonionic surfactant and water. We report a systematic transition in behavior when the particle size is increased relative to the characteristic mesophase spacing. Water dispersible cage-like silsesquioxanes that are molecular analogues of silica particles and are smaller than the mesophase spacing swell the space between the surfactant cylinders. Silica particles comparable to the characteristic hexagonal spacing partition into the hexagonal phase and into strandlike particulate aggregates. Even larger particles phase separate from the hexagonal phase to form particulate strands that organize with a mesh size comparable to the wavelength of visible light. This self-assembly is reversible and the particles disperse by breaking up the aggregates on heating the composite into the isotropic phase. On cooling from the isotropic phase into the hexagonal, the particles are expelled from the growing hexagonal domains and finally impinge to form strandlike aggregates. Unusually, the isotropization temperature is increased in the composites as the particles nucleate the formation of the hexagonal phase.

1 aSharma, Kamendra, P.1 aKumaraswamy, Guruswamy1 aLy, Isabelle1 aMondain-Monval, Olivier uhttps://library.ncl.res.in/content/self-assembly-silica-particles-nonionic-surfactant-hexagonal-mesophase-001917nas a2200241 4500008004100000022001400041245014500055210006900200260007100269300001400340490000700354520100900361653001401370653001601384653001701400653001801417653001501435100002501450700002301475700002201498700002701520856012801547 2011 eng d a0897-475600aSelf-standing three-dimensional networks of nanoparticles with controllable morphology by dynamic templating of surfactant hexagonal domains0 aSelfstanding threedimensional networks of nanoparticles with con a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcAPR a1448-14550 v233 a

Assembly of nanoparticles into free-standing three-dimensional networks has implications for a wide range of applications. We show that dynamic templating of surfactant hexagonal domains is a facile technique to organize nanoparticles into a network of particulate strands. Dispersed particles (> 10 nm), independent of particle chemistry, assemble into networks, when the surfactant matrix cools into the hexagonal phase. We demonstrate assembly of inorganic, polymeric, and protein nanoparticles into networks. Where particle assembly is reversible, particles are coated with polymers that are subsequently cross-linked to stabilize the networks after surfactant removal. This technique involves near ambient temperatures and a benign water wash for template removal. The network mesh size can be varied from submicrometers to tens of micrometers by controlling the cooling rate. Particle networks can be flow-oriented prior to cross-linking, and interpenetrating networks can also be formed.

10ahexagonal10amacroporous10ananoparticle10aself assembly10asurfactant1 aSharma, Kamendra, P.1 aGanai, Anal, Kumar1 aGupta, Sayam, Sen1 aKumaraswamy, Guruswamy uhttps://library.ncl.res.in/content/self-standing-three-dimensional-networks-nanoparticles-controllable-morphology-dynamic-002219nas a2200193 4500008004100000022001400041245011400055210006900169260007100238300001600309490000700325520145100332100002001783700002001803700002101823700002701844700002201871856013201893 2011 eng d a0743-746300aSynthesis of poly-L-glutamic acid grafted silica nanoparticles and their assembly into macroporous structures0 aSynthesis of polyLglutamic acid grafted silica nanoparticles and a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcOCT a12124-121330 v273 a

Polypeptide-coated silica nanoparticles represent an interesting class of organic inorganic hybrids since the ordered secondary structure of the polypeptide grafts imparts functional properties to these nanoparticles. The synthesis of a poly-L-glutamic acid (PLGA) silica nanoparticle hybrid by employing N-carboxyanhydride (NCA) polymerization to synthesize the polypeptide chains and Cu catalyzed azide alkyne cycloaddition reaction to graft these chains onto the silica surface is reported. This methodology enables the synthesis of well-defined polypeptide chains that are attached onto the silica surface at high surface densities. The PLGA-silica conjugate particles are well dispersed in water, and have been thoroughly characterized using multinuclear (C-13, Si-29) solid state NMR, thermogravimetric analysis, Fourier transform infrared, dynamic light scattering, and transmission electron microscopy. The pH-dependent reversible aggregation of the PLGA-silica particles, driven by the change in PLGA structure, has also been studied. Preliminary results on the use of aqueous dispersions of silica-PLGA for the preparation of three-dimensional macroporous structures with oriented pores by ice templating methodology are also demonstrated. These macroporous materials, comprising a biocompatible polymer shell covalently attached to rigid inorganic cores, adopts an interesting lamellar structure with fishbone-type architecture.

1 aKar, Mrityunjoy1 aPauline, Minois1 aSharma, Kamendra1 aKumaraswamy, Guruswamy1 aGupta, Sayam, Sen uhttps://library.ncl.res.in/content/synthesis-poly-l-glutamic-acid-grafted-silica-nanoparticles-and-their-assembly-macroporous-001259nas a2200205 4500008004100000022001400041245011400055210006900169260011000238300001400348490000700362520041800369100002300787700001900810700002500829700002100854700002700875700002200902856012900924 2012 eng d a1359-734500aSynthesis of functional hybrid silica scaffolds with controllable hierarchical porosity by dynamic templating0 aSynthesis of functional hybrid silica scaffolds with controllabl aTHOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLANDbROYAL SOC CHEMISTRYcMAR a5292-52940 v483 a

We report a facile one-pot synthesis of hierarchically porous scaffolds, with independent control over nanoparticle mesoporosity and scaffold macroporosity. Our technique combines the chemistry of mesoporous silica nanoparticles with the control afforded by dynamic templating of surfactant mesophases. These materials are readily functionalizable and allow controllable spatial variation in macroporosity.

1 aGanai, Anal, Kumar1 aKumari, Sushma1 aSharma, Kamendra, P.1 aPanda, Chakadola1 aKumaraswamy, Guruswamy1 aGupta, Sayam, Sen uhttps://library.ncl.res.in/content/synthesis-functional-hybrid-silica-scaffolds-controllable-hierarchical-porosity-dynamic-002558nas a2200229 4500008004100000022001400041245008900055210006900144260007100213300001400284490000700298520173600305100002302041700001802064700001802082700001902100700002002119700001702139700002202156700002702178856012302205 2014 eng d a0897-475600aSoft colloidal scaffolds capable of elastic recovery after large compressive strains0 aSoft colloidal scaffolds capable of elastic recovery after large a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcSEP a5161-51680 v263 a

Assemblies of inorganic or glassy particles are typically brittle and cannot sustain even moderate deformations. This restricts the use of such materials to applications where they do not experience significant loading or deformation. Here, we demonstrate a general strategy to create centimeter-size macroporous monoliths, composed primarily (>90 wt %) of colloidal particles, that recover elastically after compression to about one-tenth their original size. We employ ice templating of an aqueous dispersion of particles, polymer, and cross-linker such that cross-linking happens in the frozen state. This method yields elastic composite scaffolds for starting materials ranging from nanoparticles to micron-sized dispersions of inorganics or glassy lattices. The mechanical response of the monoliths is also qualitatively independent of polymer type, molecular weight, and even cross-linking chemistry. Our results suggest that the monolith mechanical properties arise from the formation of a unique hybrid microstructure, generated by cross-linking the polymer during ice templating. Particles that comprise the scaffold walls are connected by a cross-linked polymeric mesh. This microstructure results in soft monoliths, with moduli similar to O (10(4) Pa), despite the very high particle content in their walls. A remarkable consequence of this microstructure is that the monolith mechanical response is entropic in origin: the modulus of these scaffolds increases with temperature over a range of 140 K. We show that interparticle connections formed by cross-linking during ice templating determine the monolith modulus and also allow relative motion between connected particles, resulting in entropic elasticity.

1 aRajamanickam, Raja1 aKumar, Sushma1 aKumar, Deepak1 aGhosh, Shankar1 aKim, Jong, Chul1 aTae, Giyoong1 aGupta, Sayam, Sen1 aKumaraswamy, Guruswamy uhttps://library.ncl.res.in/content/soft-colloidal-scaffolds-capable-elastic-recovery-after-large-compressive-strains-002769nas a2200217 4500008004100000022001200041245011000053210006900163260000800232300001600240490000700256520201100263100002102274700001902295700002102314700002602335700001602361700002302377700002702400856012402427 2018 eng d a743746300aSingle-particle tracking to probe the local environment in ice-templated crosslinked colloidal assemblies0 aSingleparticle tracking to probe the local environment in icetem cAPR a4603–46130 v343 a

We use single-particle tracking to investigate colloidal dynamics in hybrid assemblies comprising colloids enmeshed in a crosslinked polymer network. These assemblies are prepared using ice templating and are macroporous monolithic structures. We investigate microstructure-property relations in assemblies that appear chemically identical but show qualitatively different mechanical response. Specifically, we contrast elastic assemblies that can recover from large compressive deformations with plastic assemblies that fail on being compressed. Particle tracking provides insights into the microstructural differences that underlie the different mechanical response of elastic and plastic assemblies. Since colloidal motions in these assemblies are sluggish, particle tracking is especially sensitive to imaging artifacts such as stage drift. We demonstrate that the use of wavelet transforms applied to trajectories of probe particles from fluorescence microscopy eliminates stage drift, allowing a spatial resolution of about 2 nm. In elastic and plastic scaffolds, probe particles are surrounded by other particles—thus, their motion is caged. We present mean square displacement and van Hove distributions for particle motions and demonstrate that plastic assemblies are characterized by significantly larger spatial heterogeneity when compared with the elastic sponges. In elastic assemblies, particle diffusivities are peaked around a mean value, whereas in plastic assemblies, there is a wide distribution of diffusivities with no clear peak. Both elastic and plastic assemblies show a frequency independent solid modulus from particle tracking microrheology. Here too, there is a much wider distribution of modulus values for plastic scaffolds as compared to elastic, in contrast to bulk rheological measurements where both assemblies exhibit a similar response. We interpret our results in terms of the spatial distribution of crosslinks in the polymer mesh in the colloidal assemblies.

1 aSuresh, Karthika1 aSharma, D., K.1 aChulliyil, Ramya1 aSarode, Ketan, Dinkar1 aKumar, Ravi1 aChoudhary, Arindam1 aKumaraswamy, Guruswamy uhttps://library.ncl.res.in/content/single-particle-tracking-probe-local-environment-ice-templated-crosslinked-colloidal01239nas a2200181 4500008004100000022001400041245005900055210005200114260000900166300001200175490000700187520069100194100002100885700002100906700002700927700002200954856008100976 2019 eng d a1744-683X00aOn the sensitivity of alginate rheology to composition0 asensitivity of alginate rheology to composition cJAN  a159-1650 v153 a

The linear response of alginate-phenyl boronic acid (Alg-PBA) esters shows a universal, composition-independent viscoelastic fluid-like behaviour. Reversible association of alginates governs their rheology at all compositions (viz. at all alginate concentrations and solution pH). However, their high strain behaviour is very sensitive to composition. Tuning composition affords liquids that neck to form filaments capable of being drawn to large elongations without failure. We interpret our data by invoking strain-dependent association and dissociation rates for the alginates. High association rates at high strain result in materials with viscoelastic liquid like behaviour.

1 aSuresh, Karthika1 aHaering, Marleen1 aKumaraswamy, Guruswamy1 aDiaz, David, Diaz uhttps://library.ncl.res.in/content/sensitivity-alginate-rheology-composition02769nas a2200229 4500008004100000022001400041245013600055210006900191260000800260300001400268490000700282520195800289653002602247653001002273653002602283653001302309100001902322700002302341700002002364700002702384856012802411 2019 eng d a0969-023900aStructure-property relations in regenerated cellulose fibers: comparison of fibers manufactured using viscose and lyocell processes0 aStructureproperty relations in regenerated cellulose fibers comp cAPR a3655-36690 v263 a

Regenerated cellulose fibers are produced using two industrially dominant technologies: the viscose and lyocell processes. Here, we compare commercially available fibers, prepared using the viscose and lyocell processes. Single fibers are subjected to a variety of mechanical deformations to obtain stress-strain, stress relaxation and stress recovery data. These are fitted to a phenomenological model, whose parameters are interpreted in terms of the fiber semicrystalline microstructure. This simple model does not incorporate the complexities of semicrystalline microstructure. Rather, it represents structure in a semicrystalline polymer fiber in terms of an elastic crystalline phase that coexists with a viscoelastic Voigt-like glassy amorphous phase. Lyocell fibers are characterized by higher values of crystalline modulus relative to viscose. Lyocell fibers also have a higher amorphous phase modulus and a wider relaxation spectrum than viscose, suggesting that amorphous and crystalline phases are dispersed in close connectivity in lyocell. Viscose and lyocell fibers exhibit qualitative similarities in their mechanical response. On stretching, there is a transition in the stress-strain curve from a low strain elastic response at a critical value of strain. This critical strain has been incorrectly attributed to yielding of the fiber. We establish that this critical value corresponds to an apparent yield. When subjected to strains higher than this apparent yield point, the fibers develop a memory of the mechanical deformation. This memory decays slowly, logarithmically with time and is lost over about a day as the fiber structure transitions back to the original as spun fiber. Finally, we demonstrate that on wetting the fibers with water, there is an increase in the apparent yield strain for viscose fibers, but not for lyocell. We interpret these results in terms of the semicrystalline microstructure of the fibers.

10amechanical properties10aModel10aRegenerated cellulose10aYielding1 aSharma, Aakash1 aNagarkar, Shailesh1 aThakre, Shirish1 aKumaraswamy, Guruswamy uhttps://library.ncl.res.in/content/structure-property-relations-regenerated-cellulose-fibers-comparison-fibers-manufactured01642nas a2200145 4500008004100000245006900041210006900110260000800179490000700187520112800194100002501322700002101347700002701368856010101395 2021 eng d00aSlip behavior during pressure driven flow of Laponite suspension0 aSlip behavior during pressure driven flow of Laponite suspension cMAY0 v333 a

We investigate pressure driven pipe flow of Laponite suspension, as a model thixotropic fluid. The tendency of the suspension to age is controlled by addition of sodium chloride salt to vary the ionic strength. We use a syringe pump to prescribe the flow and observe that a steady state flow is obtained. Unusually, the steady state pressure drop required to maintain a constant flow rate decreases with an increase in the flow rate, in qualitative contrast to the expectation for Poiseuille flow. We demonstrate that experimental results obtained by varying the flow rate, salt concentration, and flow geometry (pipe diameter and length) can be collapsed onto a single universal curve that can be rationalized by invoking slip of the suspension at the tube walls. The Laponite suspension exhibits plug-like flow, yielding at the tube walls. Our results suggest that the slip length varies linearly with the flow rate and inversely with the tube diameter.

1 aKamdi, Prophesar, M.1 aOrpe, Ashish, V.1 aKumaraswamy, Guruswamy uhttps://library.ncl.res.in/content/slip-behavior-during-pressure-driven-flow-laponite-suspension